SOLUTION-PROCESSED SILK-ZrO 2 PHOTONIC MULTILAYERS FOR ENCRYPTED STRUCTURAL COLOR

Abstract

Achieving high-performance, nanoscale photonic functionalities from naturally-derived biomaterials remains extraordinarily challenging. The ability to manipulate ultra-thin films of structural proteins—combined with photolithographic control of their polymorphism—unlocks a compelling route toward engineering biopolymer-based photonic crystals with precisely defined photonic bandgaps and reconfigurable structural colors. Disclosed herein is a robust, water-based fabrication process for silk / inorganic hybrid one-dimensional (1D) photonic crystals that overcomes many of the conventional difficulties in ensuring reproducibility, uniformity, and reliability at the nanoscale. Through a carefully designed solution-processing strategy, sequentially stacked nanofilms with controlled, tunable thicknesses below 100 nm are achieved, yielding silk / ZrO2 photonic crystals across the visible-spectrum. Ultraviolet irradiation further modulates the structural conformation of the silk nanofilms within the multilayer, enabling both passive structural color tunability and dynamically reconfigurable patterns. Silk-based photonic crystals that embed encrypted, water-responsive structural color codes are disclosed.

Description

SOLUTION-PROCESSED SILK-ZrO2PHOTONIC MULTILAYERS FOR ENCRYPTED STRUCTURAL COLORCLAIM TO PRIORITY

[0001] This application claims priority to and the benefit of United States Provisional Application 63 / 619,908, filed in the U.S. Patent and Trademark Office on January 11, 2024. The foregoing patent application is incorporated herein by reference in its entirety for all purposes.BACKGROUND

[0002] Transparent multilayered nanocomposites with periodic modulation of refractive indices, also called one-dimensional (ID) photonic crystals or distributed Bragg reflectors (DBRs), can effectively control the reflection behavior of light, making them useful for photonic materials and devices such as structural colors, colorimetric sensors, optical communication, and optoelectronic devices. To date, inorganic multilayer structures designed with such optical functions have been successfully manufactured using vacuum deposition techniques and applied to rigid photonic or electronic devices. Recently, biopolymers with advantages different from most inorganic materials in terms of biocompatibility, flexibility, and stimuli responsiveness have been spotlighted as one of eco-friendly photonic materials, however, incompatibility with conventional vacuum deposition techniques make it challenging to construct high-resolution multilayer structures suitable for optical functions.SUMMARY

[0003] In some aspects, the techniques described herein relate to a method of making a photonic multilayer exhibiting structural color, the method including the following steps: a) optionally aqueously depositing a base aqueously-deposited amphiphilic biopolymer to form a base polymer layer, wherein the optional aqueously depositing the base aqueously-deposited amphiphilic biopolymer utilizes a base amphiphilic biopolymer solution including the base aqueously-deposited amphiphilic biopolymer at a concentration by weight of between 0.5% and 8.0%; b) aqueously depositing a base aqueously-deposited semiconductor material onto the base polymer layer, thereby forming a base bilayer including the base polymer layer and a base semiconductor layer, wherein the base polymer layer includes a base aqueously-deposited amphiphilic biopolymer, wherein the base polymer layer has a base polymer thickness of between 10 nm and 500 nm and a base polymer uniformity of between 1 .0% and 10.0% or between 2.0% and 9.0% or between 3.0% and 8.0% of the base polymer thickness root mean square, wherein the base semiconductor layer has a base semiconductor thickness of between 10 nm and 500 nm and a base semiconductor uniformity of between 1.0% and 10.0% or between 2.0% and 9.0% or between 3.0% and 8.0% of the base semiconductor thickness root mean square, wherein the aqueously depositing of step b) utilizes abase aqueous semiconductor material solution including the base aqueously-deposited semiconductor material and the base aqueously-deposited amphiphilic biopolymer at a base biopolymer depositing concentration of between 0.001% and 0.5% or between 0.001% and 0.1%; c) optionally aqueously depositing one or more alternating bilayers atop the base bilayer, each of the one or more alternating bilayers independently including an alternating polymer layer and an alternating semiconductor layer, wherein the alternating polymer layer of each of the one or more alternating bilayers is independently composed of the base aqueously-deposited amphiphilic biopolymer or an independently-selected alternating amphiphilic biopolymer that is different than the base aqueously- deposited amphiphilic biopolymer, wherein the alternating semiconductor layer of each of the one or more alternating bilayers is independently composed of the base aqueously-deposited semiconductor material or an independently-selected alternating semiconductor material that is different than the base aqueously-deposited semiconductor material, wherein the alternating polymer layer of each of the one or more alternating bilayers independently has an alternating polymer thickness of between 10 nm and 500 nm and an alternating polymer uniformity of between 1.0% and 10.0% or between 2.0% and 9.0% or between 3.0% and 8.0% of the terminal polymer thickness root mean square, and wherein the alternating semiconductor layer of each of the one or more alternating bilayers independently has an alternating semiconductor thickness of between 10 nm and 500 nm and an alternating semiconductor uniformity of between 1.0% and 10.0% or between 2.0% and 9.0% or between 3.0% and 8.0% of the terminal semiconductor thickness root mean square; d) aqueously depositing the base aqueously-deposited amphiphilic biopolymer or a terminal aqueously-deposited amphiphilic biopolymer that is different than the base aqueously-deposited amphiphilic biopolymer onto the base semiconductor layer or a topmost semiconductor layer of the one or more alternating bilayers, wherein the terminal polymer layer has a terminal polymer thickness of between 10 nm and 500 nm and a terminal polymer uniformity of between 1.0% and 10.0% or between 2.0% and 9.0% or between 3.0% and 8.0% of the terminal polymer thickness root mean square, and wherein the aqueously depositing of step d) utilizes a terminal aqueous semiconductor material solution including the terminal aqueously-deposited amphiphilic biopolymer at a terminal biopolymer depositing concentration of between 0.5% and 8.0%; and e) aqueously depositing the base aqueously-deposited semiconductor material or a terminal aqueously-deposited semiconductor material that is different than the base aqueously-deposited semiconductor material onto the terminal polymer layer, thereby forming a terminal bilayer including the terminal polymer layer and a terminal semiconductor layer, wherein the terminal semiconductor layer has a terminal semiconductor thickness of between 10 nm and 500 nm and a terminal semiconductor uniformity of between 1.0% and 10.0% or between 2.0% and 9.0% or between 3.0% and 8.0% of the terminal semiconductor thickness root mean square,wherein the aqueously depositing of step e) utilizes a terminal aqueous semiconductor material solution including the terminal aqueously-deposited semiconductor material and the terminal aqueously-deposited amphiphilic biopolymer at a terminal biopolymer depositing concentration of between 0.001% and 0.5% or between 0.001% and 0.1%, wherein uniformity is optionally calculated as a difference divided by two times the average value, wherein the differences is between the maximum value and the minimum value.

[0004] In some aspects, the techniques described herein relate to a photonic multilayer exhibiting structural color, the photonic multilayer including: a base bilayer including a base polymer layer and a base semiconductor layer, wherein the base polymer layer includes a base aqueously-deposited amphiphilic biopolymer, wherein the base semiconductor layer includes a base aqueously-deposited semiconductor material, wherein the base polymer layer has a base polymer thickness of between 10 nm and 500 nm and a base polymer uniformity (optionally calculated as a difference between the maximum value and the minimum value divided by 2x the average value) of between 1.0% and 10.0% or between 2.0% and 9.0% or between 3.0% and 8.0% of the base polymer thickness root mean square, and wherein the base semiconductor layer has a base semiconductor thickness of between 10 nm and 500 nm and a base semiconductor uniformity of between 1.0% and 10.0% or between 2.0% and 9.0% or between 3.0% and 8.0% of the base semiconductor thickness root mean square; optionally one or more alternating bilayers, each of the one or more alternating bilayers independently including an alternating polymer layer and an alternating semiconductor layer, wherein the alternating polymer layer of each of the one or more alternating bilayers is independently composed of the base aqueously-deposited amphiphilic biopolymer or an independently-selected alternating amphiphilic biopolymer that is different than the base aqueously- deposited amphiphilic biopolymer, wherein the alternating semiconductor layer of each of the one or more alternating bilayers is independently composed of the base aqueously-deposited semiconductor material or an independently- selected alternating semiconductor material that is different than the base aqueously-deposited semiconductor material, wherein the alternating polymer layer of each of the one or more alternating bilayers independently has an alternating polymer thickness of between 10 nm and 500 nm and an alternating polymer uniformity of between 1.0% and 10.0% or between 2.0% and 9.0% or between 3.0% and 8.0% of the terminal polymer thickness root mean square, and wherein the alternating semiconductor layer of each of the one or more alternating bilayers independently has an alternating semiconductor thickness of between 10 nm and 500 nm and an alternating semiconductor uniformity of between 1.0% and 10.0% or between 2.0% and 9.0% or between 3.0% and 8.0% of the terminal semiconductor thickness root mean square; and a terminal bilayer including a terminal polymer layer and a terminal semiconductor layer, wherein the terminalpolymer layer includes a terminal aqueously-deposited amphiphilic biopolymer that is the base aqueously-deposited amphiphilic biopolymer or is different than the base aqueously-deposited amphiphilic biopolymer, wherein the terminal semiconductor layer includes the base aqueously- deposited semiconductor material or a terminal aqueously-deposited semiconductor material that is different than the base aqueously-deposited amphiphilic biopolymer, wherein the terminal polymer layer has a terminal polymer thickness of between 10 nm and 500 nm and a terminal polymer uniformity of between 1.0% and 10.0% or between 2.0% and 9.0% or between 3.0% and 8.0% of the terminal polymer thickness root mean square, and wherein the terminal semiconductor layer has a terminal semiconductor thickness of between 10 nm and 500 nm and a terminal semiconductor uniformity of between 1.0% and 10.0% or between 2.0% and 9.0% or between 3.0% and 8.0% of the terminal semiconductor thickness root mean square, wherein the base bilayer, the optional plurality of alternating bilayers, and the terminal bilayer form the photonic multilayer without gaps between the bilayers, and wherein each bilayer of the base bilayer, the plurality of alternating bilayers, and the terminal bilayer has a difference in index of refraction between its respective polymer layer and semiconductor layer, wherein the difference in index of refraction at a wavelength between 400 nm and 700 nm is at least 0.20, at least 0.25, at least 0.30, or at least 0.35, wherein uniformity is optionally calculated as a difference divided by two times the average value, wherein the differences is between the maximum value and the minimum value.

[0005] All documents mentioned herein are hereby incorporated in their entirety by reference. References to items in the singular should be understood to include items in the plural, and vice versa, unless explicitly stated otherwise or clear from the text. Grammatical conjunctions are intended to express any and all disjunctive and conjunctive combinations of conjoined clauses, sentences, words, and the like, unless otherwise stated or clear from the context.BRIEF DESCRIPTION OF THE FIGURES

[0006] The disclosure and the following detailed description of certain embodiments thereof may be understood by reference to the following figures:

[0007] Fig. 1A depicts process design for biopolymer / inorganic hybrid ID photonic crystals and depicts a schematic diagram illustrating sequential stacking of silk and ZrO film.

[0008] Fig. IB depicts the identification of solvents that crystallize the silk fibroin (SF) film without dissolving the Zr precursor.

[0009] Fig. 1C depicts the crystallinity of SF films treated with acetic acid (A A) and isopropanol (IPA).

[0010] Fig. ID depicts a comparison of surface coverage with an without the addition of amphiphilic SF in the aqueous Zr precursor.

[0011] Fig. IE depicts the surface coverage improvement with gradual addition of amphiphilic SF in the aqueous Zr precursor.

[0012] Fig. IF depicts a scanning electron microscopy (SEM) micrograph of a silk / ZrO ID photonic crystal.

[0013] Fig. 1G depicts a transmission electron microscopy (TEM) micrograph (left) and energy- dispersive X-ray spectroscopy (EDS) (second from left to right) mapping of the fabricated silk / ZrCF ID photonic crystal.

[0014] Fig. 2A depicts the thickness of SF film as a function of solution concentration. Data shows the mean (solid line) ± standard deviation (S.D.) (shaded area) (n = 5).

[0015] Fig. 2B depicts the thickness of ZrCF film as a function of solution concentration. Data shows the mean (solid line) ± standard deviation (S.D.) (shaded area) (n = 5).

[0016] Fig. 2C depicts the refractive index dispersion curves of SF and ZrO film.

[0017] Fig. 2D depicts control of structural color through silk layer thickness adjustment in the silkbased photonic crystals (Scale bar = 100 pm).

[0018] Fig. 2E depicts the measured and calculated reflectance of the silk / ZrO photonic crystals with 8 bilayers. Data shows the mean (solid line) + standard deviation (S.D.) (shaded area) (n = 5).

[0019] Fig. 3A depicts conformational transition in silk film with increasing UV exposure time.

[0020] Fig. 3B depicts the thickness change rate (%) of UV-exposed silk film.

[0021] Fig. 3C depicts the transition in photonic band gaps (PBGs) of silk / ZrO2 photonic crystals with 5 bilayers. The scale bar is 100 pm.

[0022] Fig. 4A depicts schematics illustrating the encoding process for humidity-responsive structural color patterns in silk-based photonic crystals.

[0023] Fig. 4B depicts the thickness changes of crystalline silk films (CSF) and amorphous silk films (ASF) under humidity exposure (n = 15).

[0024] Fig. 4C depicts the refractive index changes of CSF and ASF under humidity exposure (n = 15).

[0025] Fig. 4D depicts the change in central wavelength of PBGs in silk / ZrO2 photonic crystals with increasing relative humidity.

[0026] Fig. 4E depicts the CIE color space showing structural color transition during relative humidity changes from 20% to 100% and vice versa.

[0027] Fig. 4F depicts the response time and repeatability of PBG changes in response to humidity variations.

[0028] Fig. 4G depicts encrypted stimuli-responsive structural color codes in silk-based photonic crystals.

[0029] Fig. 4H depicts PBG wavelength contrast under different humidity status. Colored bars and error bars show the mean and S.D. (n = 3).

[0030] Fig. 5A depicts the change in contact angles of Zr solution over crystalline silk film.

[0031] Fig. 5B depicts a schematic illustration of wetting enhancement by amphiphilic SF at the hydrophobic surface.

[0032] Fig. 6 depicts the XPS survey spectra of silk (6A) and ZrO? (6B-D) films.

[0033] Figs. 7A and 7B depicts the reflection spectra of (Silk / ZrChls distributed Bragg reflectors (DBRs) as a function of silk layer thickness variation.

[0034] Fig. 8 A depicts the experimental setup for measuring angular reflectance of silk DBRs.

[0035] Fig. 8B depicts digital images of the silk DBRs.

[0036] Fig. 8C depicts the transition of DBR reflection band as the incident angle changes.

[0037] Fig. 9 depicts a comparison of RI contrast in recently reported solution-processed DBRs. The constituent layers’ maximum and minimum RI values correspond to the top and bottom of each bar graph.

[0038] Fig. 10 depicts a comparison of reflectance performance of recently reported solution- processed DBRs.

[0039] Fig. 11 A depicts the thickness and RI changes of silk films after 10 hours of UV exposure. Data points and error bars show the mean ± standard deviation (S.D.) (n = 4). Statistical analysis was performed via one-way ANOVA.

[0040] Fig. 1 IB depicts the thickness and RI changes of ZrCF films after 10 hours of UV exposures. Data points and error bars show the mean + standard deviation (S.D.) (n = 4). Statistical analysis was performed via one-way ANOVA.DETAILED DESCRIPTION

[0041] Before the present disclosure is described in further detail, it is to be understood that the disclosure is not limited to the particular embodiments described. It is also understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting. The scope of the present disclosure will be limited only by the claims. As used herein, the singular forms "a", "an", and "the" include plural embodiments unless the context clearly dictates otherwise.

[0042] In this application, unless otherwise clear from context, (i) the term “a” may be understood to mean “at least one”; (ii) the term “or” may be understood to mean “and / or”; (iii) the terms “comprising” and “including” may be understood to encompass itemized components or steps whether presented by themselves or together with one or more additional components or steps; and (iv) the terms “about” and “approximately” are used as equivalents and may be understood to permitstandard variation as would be understood by those of ordinary skill in the art; and (v) where ranges are provided, endpoints are included.

[0043] Approximately: as used herein, the term “approximately” or “about,” as applied to one or more values of interest, refers to a value that is similar to a stated reference value. In certain embodiments, the term “approximately” or “about” refers to a range of values that fall within 25%, 20%, 19%, 18%, 17%, 16%, 15%, 14%, 13%, 12%, 11%, 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, or less in either direction (greater than or less than) of the stated reference value unless otherwise stated or otherwise evident from the context (except where such number would exceed 100% of a possible value).

[0044] Composition: as used herein, may be used to refer to a discrete physical entity that comprises one or more specified components. In general, unless otherwise specified, a composition may be of any form - e.g., gas, gel, liquid, solid, etc. In some embodiments, “composition” may refer to a combination of two or more entities for use in a single embodiment or as part of the same article. It is not required in all embodiments that the combination of entities result in physical admixture, that is, combination as separate co-entities of each of the components of the composition is possible; however many practitioners in the field may find it advantageous to prepare a composition that is an admixture of two or more of the ingredients in a pharmaceutically acceptable carrier, diluent, or excipient, making it possible to administer the component ingredients of the combination at the same time.

[0045] Improve, increase, or reduce: as used herein or grammatical equivalents thereof, indicate values that are relative to a baseline measurement, such as a measurement in a similar composition made according to previously known methods.

[0046] Substantially: as used herein, the term “substantially” refers to the qualitative condition of exhibiting total or near-total extent or degree of a characteristic or property of interest. One of ordinary skill in the biological arts will understand that biological and chemical phenomena rarely, if ever, go to completion and / or proceed to completeness or achieve or avoid an absolute result. The term “substantially” is therefore used herein to capture the potential lack of completeness inherent in many biological and chemical phenomena.

[0047] It should be apparent to those skilled in the art that many additional modifications beside those already described are possible without departing from the inventive concepts. In interpreting this disclosure, all terms should be interpreted in the broadest possible manner consistent with the context. Variations of the term "comprising" should be interpreted as referring to elements, components, or steps in a non-exclusive manner, so the referenced elements, components, or steps may be combined with other elements, components, or steps that are not expressly referenced.Embodiments referenced as "comprising" certain elements are also contemplated as "consisting essentially of" and "consisting of" those elements. When two or more ranges for a particular value are recited, this disclosure contemplates all combinations of the upper and lower bounds of those ranges that are not explicitly recited. For example, recitation of a value of between 1 and 10 or between 2 and 9 also contemplates a value of between 1 and 9 or between 2 and 10.

[0048] As used herein, "silk fibroin" refers to silk fibroin protein whether produced by silkworm, spider, or other insect, or otherwise generated (Lucas et al., Adv. Protein Chem., 13: 107-242 (1958)). Any type of silk fibroin can be used in different embodiments described herein. Silk fibroin produced by silkworms, such as Bombyx mori, is the most common and represents an earth-friendly, renewable resource. For instance, silk fibroin used in a silk film may be attained by extracting sericin from the cocoons of B. mori. Organic silkworm cocoons are also commercially available. There are many different silks, however, including spider silk (e.g., obtained from Nephila clavipes), transgenic silks, genetically engineered silks, such as silks from bacteria, yeast, mammalian cells, transgenic animals, or transgenic plants, and variants thereof, that can be used. See, e.g., WO 97 / 08315 and U.S. Pat. No. 5,245,012, each of which is incorporated herein by reference in their entireties.

[0049] The unique chemical versatility, low-energy fabrication processes, ability to interact with the biological environment, and sustainable / biocompatible sourcing make the exploration of biopolymerbased photonic systems an especially compelling area of research for new functional materials that operate at the interface between technology and biology. Designing sophisticated, high-performance, nanoscale optical devices from naturally derived biomaterials, however, is challenging because of the tight tolerances required for uniformity and reproducibility at the sub- 100 nm scale.

[0050] Reconfigurable structural colors, stemming from changes in the lengthwise refractive index (RI) periodicity of photonic crystal systems in response to changing conditions, play a significant role in the advance of dynamic photonic systems. These adaptable optical functions necessitate extensive research into materials and complex optical nanostructures capable of dynamic responses. As a simple and facile way to respond to these technical demands, biopolymers with intrinsic adaptive traits have been utilized in multiple photonic crystal formats, successfully realizing dynamic optical behaviors.

[0051] Recent efforts towards new functional materials that operate at the interface between technology and biology have focused on structurally simple ID photonic crystals, which reduces the technical challenges associated with nanostructure manufacturing. However, the use of biopolymers necessitates solution deposition methods for distributed Bragg reflector (DBR) fabrication due to their incompatibility with vacuum processing techniques. This solution processing approach presentssome technical challenges. One key challenge is preventing undesirable physical or chemical reactions at the interfaces between successive film depositions, which requires the use of carefully chosen orthogonal solvents to avoid film damage. This inherently limits the available solvent- solvent pairs and restricts the pool of processable materials, thereby reducing the number of material combinations that can achieve a practical RI contrast (An) in photonic crystal development. Moreover, it is crucial to maintain a high degree of wettability between the film and the solution, which necessitates the obligatory use of additional treatments to control wetting. However, conventional pre-surface treatment approaches, like plasma surface treatments, could damage or change the physical or surface properties of biopolymer films.

[0052] Highlighted herein is the potential of water-based SF suspensions, derived from Bombyx mori cocoons, to overcome the limitations of solution processing and facilitate the development of high-quality, dynamically reconfigurable optical systems. By controlling their structural conformation, spin-coated silk nanofilms become water-insoluble, allowing the subsequent layering of high-refractive-index aqueous inorganic salt solutions, such as zirconyl chloride hydrate. This method removes the requirement for orthogonal solvents in multilayer stacking, allowing for the creation of high An and enabling the production of biopolymer-based photonic crystals with desirable properties.

[0053] Moreover, the amphiphilic nature of silk chains promotes intermolecular interactions during sequential water processing steps, resulting in seamless biopolymer / inorganic interfaces without using undesirable surface treatments. The resulting all-water-processed silk DBRs, consisting of high-resolution ultrathin silk / ZrCh stacks with a large An (~0.42 at 500 nm), exhibit programmable and highly reflective structural colors within the visible spectrum. To enhance reconfigurable functionality, UV light exposure was employed to alter the secondary structures of the silk films within the multilayered nanofilm configuration. This UV treatment induces localized thickness reduction and increased water-swelling capability. The photolithographic manipulation of polymorphism enables the creation of dynamically reconfigurable structural color patterns within the biopolymer-based DBR system with traditional cleanroom approaches, demonstrating potential applications in colorimetric humidity sensors and anti-counterfeiting hydrochromic codes.

[0054] In one aspect, a method of making a photonic multilayer exhibiting structural color includes steps a), b), c), d), and e). Step a) is optional and may include aqueously depositing a base aqueously-deposited amphiphilic biopolymer to form a base polymer layer. The deposition may utilize a base amphiphilic biopolymer solution including the base aqueously-deposited amphiphilic biopolymer at a concentration by weight of between 0.5% and 8.0%.

[0055] Step b) may include aqueously depositing a base aqueously-deposited semiconductor material onto the base polymer layer, thereby forming a base bilayer including the base polymer layer and a base semiconductor layer. The base polymer layer may include a base aqueously- deposited amphiphilic biopolymer. The base polymer layer may have a base polymer thickness of between 10 nm and 500 nm and a base polymer uniformity of between 1.0% and 10.0% or between 2.0% and 9.0% or between 3.0 and 8.0% of the base polymer thickness root mean square. The base semiconductor layer may have a base semiconductor thickness of between 10 nm and 500 nm and a base semiconductor uniformity of between 1.0% and 10.0% or between 2.0% and 9.0% or between 3.0% and 8.0% of the base semiconductor thickness root mean square. The aqueously depositing of step b) may utilize a base aqueous semiconductor material solution including the base aqueously- deposited semiconductor material and the base aqueously-deposited amphiphilic biopolymer at a base biopolymer depositing concentration of between 0.001% and 0.5% or between 0.001% and 0.1%.

[0056] Step c) is optional and may include optionally aqueously depositing one or more alternating bilayers atop the base bilayer, each of the one or more alternating bilayers independently including an alternating polymer layer and an alternating semiconductor layer. The alternating polymer layer of each of the one or more alternating bilayers may be independently composed of the base aqueously- deposited amphiphilic biopolymer or an independently-selected alternating amphiphilic biopolymer that is different than the base aqueously-deposited amphiphilic biopolymer. The alternating semiconductor layer of each of the one or more alternating bilayers may be independently composed of the base aqueously-deposited semiconductor material or an independently-selected alternating semiconductor material that is different than the base aqueously-deposited semiconductor material. The alternating polymer layer of each of the one or more alternating bilayers may independently have an alternating polymer thickness of between 10 nm and 500 nm and an alternating polymer uniformity of between 1.0% and 10.0% or between 2.0% and 9.0% or between 3.0% and 8.0% of the terminal polymer thickness root mean square. The alternating semiconductor layer of each of the one or more alternating bilayers may independently have an alternating semiconductor thickness of between 10 nm and 500 nm and an alternating semiconductor uniformity of between 1.0% and 10.0% or between 2.0% and 9.0% or between 3.0% and 8.0% of the terminal semiconductor thickness root mean square.

[0057] Step d) may include aqueously depositing the base aqueously-deposited amphiphilic biopolymer or a terminal aqueously-deposited amphiphilic biopolymer that is different than the base aqueously-deposited amphiphilic biopolymer onto the base semiconductor layer or a topmost semiconductor layer of the one or more alternating bilayers. The terminal polymer layer may have aterminal polymer thickness of between 10 nm and 500 nm and a terminal polymer uniformity of between 1.0% and 10.0% or between 2.0% and 9.0% or between 3.0% and 8.0% of the terminal polymer thickness root mean square. The aqueously depositing of step d) may utilize a terminal aqueous semiconductor material solution including the terminal aqueously-deposited amphiphilic biopolymer at a terminal biopolymer depositing concentration of between 0.5% and 8.0%.

[0058] Step e) may include aqueously depositing the base aqueously-deposited semiconductor material or a terminal aqueously-deposited semiconductor material that is different than the base aqueously-deposited semiconductor material onto the terminal polymer layer, thereby forming a terminal bilayer including the terminal polymer layer and a terminal semiconductor layer. The terminal semiconductor layer may have a terminal semiconductor thickness of between 10 nm and 500 nm and a terminal semiconductor uniformity of between 1.0% and 10.0% or between 2.0% and 9.0% or between 3.0% and 8.0% of the terminal semiconductor thickness root mean square. The aqueously depositing of step e) may utilize utilizes a terminal aqueous semiconductor material solution including the terminal aqueously-deposited semiconductor material and the terminal aqueously-deposited amphiphilic biopolymer at a terminal biopolymer depositing concentration of between 0.001% and 0.5% or between 0.001% and 0.1%. Uniformity may be calculated as a difference divided by two times the average value, wherein the difference is between the maximum value and the minimum value.

[0059] The aqueously depositing of any one of steps a), b), c), d), or e) may be performed via spin casting. The aqueously depositing of step a) may be performed via spin casting. The aqueously depositing of step b) may be performed via spin casting. The aqueously depositing of step c) may be performed via spin casting. The aqueously depositing of step d) may be performed via spin casting. The aqueously depositing of step e) may be performed via spin casting.

[0060] In another aspect, a photonic multilayer exhibits structural color, the photonic multilayer including a base bilayer including a base polymer layer and a base semiconductor layer, optionally one or more alternating bilayers, each of the one or more alternating bilayers independently including an alternating polymer layer and an alternating semiconductor layer, and a terminal bilayer including a terminal polymer layer and a terminal semiconductor layer.

[0061] The base polymer layer may include a base aqueously-deposited amphiphilic biopolymer. The base semiconductor layer may include a base aqueously-deposited semiconductor material. The base polymer layer may have a a base polymer thickness of between 10 nm and 500 nm and a base polymer uniformity (optionally calculated as a difference between the maximum value and the minimum value divided by 2x the average value) of between 1.0% and 10.0% or between 2.0% and 9.0% or between 3.0% and 8.0% of the base polymer thickness root mean square. The basesemiconductor layer may have a base semiconductor thickness of between 10 nm and 500 nm and a base semiconductor uniformity of between 1.0% and 10.0% or between 2.0% and 9.0% or between 3.0% and 8.0% of the base semiconductor thickness root mean square.

[0062] The alternating polymer layer of each of the one or more alternating bilayers may be independently composed of the base aqueously-deposited amphiphilic biopolymer or an independently-selected alternating amphiphilic biopolymer that is different than the base aqueously- deposited amphiphilic biopolymer. The alternating semiconductor layer of each of the one or more alternating bilayers may independently be composed of the base aqueously-deposited semiconductor material or an independently-selected alternating semiconductor material that is different than the base aqueously-deposited semiconductor material. The alternating polymer layer of each of the one or more alternating bilayers may independently have an alternating polymer thickness of between 10 nm and 500 nm and an alternating polymer uniformity of between 1.0% and 10.0% or between 2.0% and 9.0% or between 3.0% and 8.0% of the terminal polymer thickness root mean square. The alternating semiconductor layer of each of the one or more alternating bilayers may independently have an alternating semiconductor thickness of between 10 nm and 500 nm and an alternating semiconductor uniformity of between 1.0% and 10.0% or between 2.0% and 9.0% or between 3.0% and 8.0% of the terminal semiconductor thickness root mean square.

[0063] The terminal polymer layer may include a terminal aqueously-deposited amphiphilic biopolymer that is the base aqueously-deposited amphiphilic biopolymer or is different than the base aqueously-deposited amphiphilic biopolymer. The terminal semiconductor layer may include the base aqueously-deposited semiconductor material or a terminal aqueously-deposited semiconductor material that is different than the base aqueously-deposited amphiphilic biopolymer. The terminal polymer layer may have a terminal polymer thickness of between 10 nm and 500 nm and a terminal polymer uniformity of between 1.0% and 10.0% or between 2.0% and 9.0% or between 3.0% and 8.0% of the terminal polymer thickness root mean square. The terminal semiconductor layer may have a terminal semiconductor thickness of between 10 nm and 500 nm and a terminal semiconductor uniformity of between 1.0% and 10.0% or between 2.0% and 9.0% or between 3.0% and 8.0% of the terminal semiconductor thickness root mean square.

[0064] The base bilayer, the optional plurality of alternating bilayers, and the terminal bilayer may have a difference in index of refraction between its respective polymer layer and semiconductor layer. The difference in index of refraction at a wavelength between 400 nm and 700 nm is at least 0.20, at least 0.25, at least 0.30, or at least 0.35. Uniformity may optionally be calculated as a difference divided by two times the average value, wherein the differences is between the maximum value and the minimum value.

[0065] In the photonic multilayer or the method of making the photonic multilayer, the base aqueously-deposited amphiphilic biopolymer may be an aqueously-deposited amphiphilic protein. The base aqueously-deposited amphiphilic biopolymer may include aqueously-deposited silk fibroin. The base aqueously-deposited amiphilic biopolymer may consist of the aqueously-deposited silk fibroin.

[0066] In the photonic multilayer or the method of making the photonic multilayer, the terminal polymer layer may include the terminal aqueously deposited amphiphilic biopolymer that is different than the base aqueously-deposited amphiphilic biopolymer. The terminal aqueously-deposited amphiphilic biopolymer may be an aqueously-deposited amphiphilic protein. The terminal aqueously-deposited amphiphilic biopolymer may be an aqueously-deposited silk fibroin. The terminal aqueously-deposited amphiphilic biopolymer may consist of the aqueously-deposited silk fibroin.

[0067] In the photonic multilayer or the method of making the photonic multilayer, the photonic multilayer or the method may include the plurality of alternating bilayers. At least one of the base polymer thickness or the base semiconductor thickness may be between 20 nm and 400 nm or between 40 nm and 240 nm. The base polymer uniformity may be between 0.1% and 2.5% or between 0. 1 and 1.0% of the base polymer thickness root mean square. The base semiconductor uniformity may be between 0.1% and 2.5% or between 0.1% and 1.0% of the base semiconductor thickness root mean square.

[0068] In the photonic multilayer or the method of making the photonic multilayer, the terminal polymer thickness may be between 20 nm and 400 nm, or between 40 nm and 250 nm. The terminal semiconductor thickness may be between 20 nm and 400 nm, or between 40 nm and 250 nm. The terminal polymer uniformity may be between 0.1% and 2.5% or between 0.1% and 1.0% of the terminal polymer thickness root mean square. The terminal semiconductor uniformity may be between 0.1% and 2.5% or between 0.1% and 1.0$ of the terminal semiconductor thickness root mean square.

[0069] In the photonic multilayer or the method of making the photonic multilayer, the alternating polymer thickness may be between 20 nm and 400 nm, or between 40 nm and 250 nm. The alternating semiconductor thickness may be between 20 nm and 400 nm, or between 40 nm and 250 nm. The alternating polymer uniformity may be between 0.1% and 2.5% or between 0.1 % and 1.0% of the alternating polymer thickness root mean square. The alternating semiconductor uniformity may be between 0.1% and 2.5% of the alternating semiconductor thickness root mean square.

[0070] In the photonic multilayer or the method of making the photonic multilayer, the base polymer thickness and the terminal polymer thickness may be different. The base polymer thicknessand the terminal polymer thickness may be the same. The base polymer thickness, the alternating polymer thickness, and the terminal polymer thickness may be the same. The base semiconductor thickness and the terminal semiconductor thickness may be different. The base semiconductor thickness and the terminal semiconductor thickness may be the same. The base semiconductor thickness, the alternating semiconductor thickness, and the alternating semiconductor thickness may be the same.

[0071] In the photonic multilayer or the method of making the photonic multilayer, the one or more alternating bilayers may be a plurality of alternating bilayers and the alternating polymer thickness may be the same for each of the plurality of alternating bilayers. The one or more alternating bilayers may be a plurality of alternating bilayers and the alternating polymer thickness may be different for at least two of the plurality of alternating bilayers. The one or more alternating bilayers may be a plurality of bilayers and the alternating polymer thickness may be different for each of the plurality of alternating bilayers.

[0072] In the photonic multilayer or the method of making the photonic multilayer, the base polymer layer may have an index of refraction of between 1.25 and 1.75. The base semiconductor layer may have an index of refraction of between 1.75 and 2.25. The terminal polymer layer may have an index of refraction of between 1.25 and 1.75. The terminal semiconductor layer may have an index of refraction of between 1.75 and 2.25.

[0073] In the photonic multilayer or the method of making the photonic multilayer, the base polymer layer and the terminal polymer layer may have the same index of refraction. The base semiconductor layer and the terminal semiconductor layer may have the same index of refraction. Each alternating polymer layer may independently have an index of refraction of between 1.25 and 1.75. Each alternating polymer layer may have the same index of refraction.

[0074] In the photonic multilayer or the method of making the photonic multilayer, each alternating semiconductor layer may independently have an index of refraction of between 1.25 and 1.75. Each alternating semiconductor layer may have the same index of refraction. The base polymer layer, the terminal polymer layer, and each alternating polymer layer may have the same index of refraction. The base semiconductor layer, the terminal semiconductor layer, and each alternating semiconductor layer may have the same index of refraction. The photonic multilayer may have an uninterrupted lateral area of between 1 cm2and 1 m2or between 10 cm2and 0.1 m2.

[0075] An optical effect article may include the photonic multilayer of or made by the method of making the photonic multilayer. The base bilayer, the optional plurality of alternating bilayers, and the terminal bilayer may be assembled in a vertical direction. The optical effect article may include laterally-defined regions having one or more differences in the polymer layers, thereby providingdifferent changes in structural color between the laterally -defined regions upon changing humidity environments. The laterally-defined regions may form an image. The image may be visible in certain humidity conditions and invisible in different humidity conditions.

[0076] A method of using a photonic multilayer may include changing hydration state in the amphiphilic biopolymer layers in the photonic multilayer of or made by the method described above to water vapor, thereby causing a change in distance between the semiconductor layers in the photonic multilayer, thereby changing one or more properties of the structural color exhibited by the photonic multilayer. Changing hydration state may reveal a previously invisible image within the photonic multilayer. The method may further include acquiring an image of the photonic multilayer after changing hydration state and performing image analysis on the image. The previously invisible image may include a code, such as a one- or two-dimensional barcode.

[0077] Unless otherwise specified or indicated by context, the terms “a”, “an”, and “the” mean “one or more.” For example, “a molecule” should be interpreted to mean “one or more molecules.”

[0078] As used herein, “about”, “approximately,” “substantially,” and “significantly” will be understood by persons of ordinary skill in the art and will vary to some extent on the context in which they are used. If there are uses of the term which are not clear to persons of ordinary skill in the art given the context in which it is used, “about” and “approximately” will mean plus or minus <10% of the particular term and “substantially” and “significantly” will mean plus or minus >10% of the particular term.

[0079] As used herein, the terms “include” and “including” have the same meaning as the terms “comprise” and “comprising.” The terms “comprise” and “comprising” should be interpreted as being “open” transitional terms that permit the inclusion of additional components further to those components recited in the claims. The terms “consist” and “consisting of’ should be interpreted as being “closed” transitional terms that do not permit the inclusion of additional components other than the components recited in the claims. The term “consisting essentially of’ should be interpreted to be partially closed and allowing the inclusion only of additional components that do not fundamentally alter the nature of the claimed subject matter.

[0080] All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.

[0081] All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein.

[0082] Preferred aspects of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those preferred aspects may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect a person having ordinary skill in the art to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the abovedescribed elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.

[0083] While the invention has been illustrated and described in detail in the foregoing drawings and description, the same is to be considered as illustrative and not restrictive in character, it being understood that only illustrative embodiments thereof have been shown and described and that all changes and modifications that come within the spirit of the invention are desired to be protected. For example, any of the features or functions of any of the embodiments disclosed herein may be incorporated into any of the other embodiments disclosed herein.

[0084] The following examples illustrate some embodiments and aspects of the invention. It will be apparent to those skilled in the relevant art that various modifications, additions, substitutions, and the like can be performed without altering the spirit or scope of the invention, and such modifications and variations are encompassed within the scope of the invention as defined in the claims which follow. The following examples do not in any way limit the invention.

[0085] EXAMPLES

[0086] Example 1

[0087] Fig. 1A-G depicts a process design for biopolymer / inorganic hybrid ID photonic crystals. Fig. 1A outlines the fabrication strategy for multilayer sequential stacking of heterogeneous biopolymer and inorganic thin films. Spin-coated silk films are water-soluble due to a high proportion of random coil / alpha helix structures. This is therefore necessary to induce a conformational change and beta-sheet formation (i.e. “crystallization”) to prevent dissolution when water-based solvents are used in subsequent coatings. Common laboratory solvents like alcohols are often employed for this scope to increase the beta-sheet content of the silk film. However, to minimize the impact on the counterpart film from the ZrOCh solution, solvents with low solubility for the precursor, such as isopropanol (IPA) and acetic acid (A A), were chosen (Fig IB).

[0088] Fourier transform infrared spectroscopy (FTIR) analysis demonstrated that both AA and IPA-treated SF films had a significantly higher beta-sheet content of 60% compared to neat SF films (Fig. 1C). AA was selected as the crystallization solvent due to its lower solubility for the Zr precursor than IPA. To prevent unwanted interactions between the precursor solution and silk film during subsequent coating, the crystallized silk film was thermally treated at 230°C for 5 minutes, removing excess water molecules from both the film and its surface.

[0089] Applying a pure aqueous Zr solution onto the crystallized silk film led to incomplete wetting, primarily because the metal precursor solution formed a high contact angle of around 85 degrees on the underlying silk surface. While surface pre-treatments like oxygen plasma can enhance substrate wettability and achieve high-quality film coating, such treatments may negatively impact the biopolymer films, potentially compromising their material properties. To overcome this challenge, a small quantity of amphiphilic SF was added into the aqueous Zr precursor, thus enhancing wetting without resorting to plasma surface treatments. This approach significantly improves surface coverage (Fig. ID). This enhancement can be attributed to the amphiphilic characteristics of the SF heavy chain, which forms an adsorption layer on the substrate, facilitating interaction between the solution and the substrate. The SF surfactant’s ability to control interfacial energy is highly effective, as even a minimal addition of 0.01 w / v% results in over 90% surface coverage (Fig. IE). Subsequently, the spin-coated Zr precursor layer underwent thermal hydrolysis at 230 °C on a hot plate to form a water-insoluble ZrCh film.

[0090] The regenerated silk fibroin (SF) extracted from Bombyx mori cocoon mainly consists of four amino acids: Glycine (Gly), Alanine (Ala), Tyrosine (Tyr), and Serine (Ser). Gly and Ala are non-polar amino acids, imparting hydrophobic properties to the fibroin chain. On the other hand, Tyr and Ser, which possess hydroxyl groups, confer hydrophilicity to the fibroin. Moreover, the primary sequence of the fibroin’ s heavy chain comprises two large hydrophilic blocks at the terminals with an internal hydrophobic domain. The amphipathic characteristic of SF can enhance the interfacial interaction between substrate and solution. The fibroin chain, exhibiting amphiphilic properties, adsorbs at the interface regardless of the substrate’s degree of hydrophilicity. In turn, it reduces the interfacial energy between the solution and the substrate and increases the work of adhesion between the two interfaces.

[0091] Fig. 5A-B depicts amphiphilic SF-assisted wetting. Fig. 5A shows the time-dependent contact angle of Zr precursor solution with or without silk over acetic acid-treated crystallized silk film. It demonstrates how silk is efficient in interfacial energy control. In addition, the schematic diagram, Fig. 5B, illustrates the phenomenon of SF adsorbing onto the substrate at the wetting interface, enhancing interfacial affinity.

[0092] In this fabrication process, the silk film undergoes acetic acid and thermal processing treatment to enhance its water resistance and ensure complete drying after the coating process. Additionally, the Zr film is formed by coating a Zr solution containing a small amount of SF, followed by thermal hydrolysis. X-ray photoelectron spectroscopy (XPS) analysis was conducted to examine the effects of these process conditions on the chemical composition of each film. It was revealed that SF films are composed of carbon, oxygen, and nitrogen with atomic percentages of 57.4%, 22.0%, and 20.6%, respectively. ZrCh films consist, instead, mainly of oxide, zirconium, and carbon, with atomic percentages of 60.5%, 20.4%, and 19.1%, respectively. The XPS survey (Fig. 6) spectrum of the silk film exhibited results consistent with a previous study, while the Zirconium film was found to consist of ZrCh with some carbon impurities (Fig. 7). In particular, the chemical composition of our ZrCh film is regarded as one of the reasons for the lower refractive index (RI) (n ~ 1.98 at 500 nm) compared to pure ZrCh (n ~ 2.2 at 500 nm).

[0093] With this rationally designed processing strategy, the film thickness and biopolymer / inorganic interface can be meticulously controlled at the sub- wavelength scale, resulting in the successful fabrication of high-resolution biopolymer / inorganic hybrid ID photonic crystals. Fig. IF demonstrates the uniform and alternating stacking of silk films and ZrCh films in the horizontal plane (XY plane) as well as in the thickness direction (Z-axis). Additionally, a cross- sectional scanning transmission electron microscopy (STEM) image and energy-dispersive X-ray spectroscopy (EDS) mapping clearly show a distinct boundary between the deposited biopolymer and inorganic layers (Fig. 1 G).

[0094] Fig. 2A-E depicts optical properties of silk / ZrCb ID photonic crystals. Fig. 2 shows the optical properties of the Silk / ZrCh multilayered structure. The photonic bandgaps (PBGs), also referred to as stop bands of ID photonic crystals, are influenced by thickness and RI, as indicated by the Bragg-Snell equation (Equation 1):where d is the thickness and n is RI of each film material. This implies that precise control over the thickness of each constituent layer and the RI of each film is essential for designing the structural color of ID photonic crystals. The thickness of silk and ZrCh film can be linearly controlled, ranging from 50 nm to 180 nm for silk and from 20 nm to 60 nm for ZrCh, respectively, by adjusting the solution concentration at constant rotation speed (Fig. 2A and Fig. 2B). Additionally, Fig. 2C shows the dispersion curve of silk and ZrCh film within the visible wavelength range. The combination of these two biopolymer / inorganic materials forms a significantly large An (0.42 at 500 nm), surpassing what is achievable with polymer / polymer combinations previously reported. The large An was achieved bynot being constrained by the use of non-orthogonal solvents, which allowed for the selection of materials with an RI of 2.0 or higher to pair with silk.

[0095] The ability to reproducibly and precisely control the film thickness at the nanoscale allows for the accurate design of PBGs within the visible spectrum, facilitating the creation of various structural colors. Fig. 2D demonstrates the diverse spectral selectivity achieved by nanometer control of the silk film thickness while maintaining the ZrO? layer at 50 nm. By increasing the silk film thickness in 10 nm increments, PBGs spanning from the UV to the entire visible spectrum were assembled.

[0096] Fig. 7A depicts the reflection spectra of (Silk / ZrOz)s distributed Bragg reflectors (DBRs) as a function of silk layer thickness variation. The increase in silk concentration acts as a variable that influences the final thickness of the coated silk film, thereby allowing control over the reflection band of the multilayered thin film structure. The bandwidth, i.e. full width at half maximum (FWHM), of each spectrum is reported in the table (Fig. 7B).

[0097] Additionally, the fabricated photonic crystals exhibit a strong angle-dependent optical behavior characteristic of highly ordered photonic crystals. The experimental setup is shown in Fig. 8A and digital images of the DBRs are shown in Fig. 8B (Fig. 8A-C depicts the angular dependence of (5.0% silk / 0.5M ZrOz)s DBRs). DBRs fabricated using a 5 w / v% SF solution exhibit primary PBG at approximately 680 nm. As a highly ordered photonic crystal, it shows a blue shift of the PBG for increasing incidence angles (Fig. 8C), indicating strong iridescence.

[0098] Moreover, the process developed in this study allows for the multiple stacking of a laterally uniform film at a sub- wavelength scale, as illustrated in Fig. IF and Fig. 1G. As a result, the optical profiles at different spatial points exhibit minimal variation (i.e., narrow error band in measured spectra) and closely align with the theoretically calculated reflectance result (Fig. 2E). Notably, the silk / ZrOz photonic crystals exhibit excellent reflectivity performance (-85%) with a relatively small number of layers (N = 16)..

[0099] Fig. 9, Fig. 10, and Table 1 provide a comparison of the reflection performance and dielectric contrast between solution-processed DBRs reported in the last decade. As shown in Fig. 9, the silk film and ZrOz film used in this work exhibit relatively high RI contrast. Notably, both materials are biocompatible and fabricated using aqueous solution processes. Therefore, the technique developed in this study is particularly noteworthy as it offers an environmentally friendly approach to producing fully biocompatible multilayer structures with the highest level of RI contrast. The information regarding the materials, solvents, and refractive indices used in these studies is summarized in Table 1. Furthermore, as demonstrated in Fig. 10, this high RI contrast made itpossible to achieve high reflection performance even with a relatively small number of constituent layers.

[0100] Table 1

[0101] As evident from this comparative evaluation, we have established a sustainable and effective all-aqueous processing method for the fabrication of biopolymer-based photonic crystals. This is non-trivial in additive multilayer fabrication processes, as it demands the convergence of material properties and the finesse of nanofabrication techniques.

[0102] While this processing method provides a facile and efficient strategy for producing high- performance silk photonic crystals, it does have the drawback of losing reconfigurability. This limitation arises from the crystallization of the silk film during the processing, which reduces its adaptability to water, i.e., its swelling capability. However, this issue can be sufficiently overcome through additional methods that control the polymorphism of structural proteins. Indeed, several studies have reported the control of the physicochemical properties of silk films by regulating their structural conformation. We propose using UV light to control the crystallinity (i.e., P-sheet content) of silk films within multilayered structures, thereby enabling dynamically humidity-responsive structural color patterns.

[0103] Fig. 3A-C depicts the effect of UV irradiation on the polymorphism of silk films and the resulting impact on the optical properties of silk photonic crystals. Fig. 3 illustrates the effects of UV exposure on the structural conformation of silk nanofilms and its subsequent impact on the optical properties of multilayered silk photonic crystals. As previously studied, this is because UV radiation (254 nm, average irradiance ~ 4.45 mW / cm2) induces peptide scission in the silk film matrix, disrupting hydrogen bonding and causing a conformational transition from P-sheet to random coil or a-helix. The relative comparison of P-sheet content within the silk film at different UV irradiation times (0, 4, and 10 hrs) was confirmed through FTIR analysis (Fig. 3 A). Prior to UV exposure, the AA-treated silk film exhibited a dominant P-sheet structure (1625 cm’1in FTIR). After 4 hours of UV exposure, the content of random coil or a-helix structures (1650 cm1in FTIR) became nearly equivalent to that of P-sheet structures. Following a maximum of 10 hours of exposure, a notable reduction in the relative content of crystalline domains within the silk film was observed.

[0104] UV-induced peptide scission causes nanoscale films to become thinner (Fig. 3B). When silk films were exposed to UV for 4 hours, their thickness decreased by approximately 5% compared to unexposed films. Films exposed for 10 hours experienced an even more substantial reduction in thickness, around 13%. Notably, silk films exposed for over 4 hours showed greater thickness reduction when subjected to a 5-minute heat treatment at 230°C following UV lithography, with the most extreme example being a 25% decrease in thickness in the 10-hour irradiated silk film. It is believed that when long-term UV exposed silk film is subjected to heat treatment above the glass transition temperature (TG ~ 180°C), the shortened silk chains undergo molecular rearrangement within the matrix, resulting in further thickness reduction.

[0105] UV exposure appears to cause thickness reduction only in the silk film within the multilayered silk / ZrCh configuration. No significant changes were observed in the thickness and RI of the single Z1O2 film exposed to UV for 10 hours. The thickness and RI changes of single silk and ZrCh films under UV exposure can be observed in Fig. 11. Fig. 11 A-B depicts the changes in thickness and RI of single silk and ZrO? films according to a fixed UV exposure dosage. The UV lamp used in this study has an average irradiance of approximately 4.45 mW / cm2at a distance of about 5 cm. After 10 hours of long-term UV exposure, the silk film (Fig. 11 A) experienced a significant decrease in thickness and a slight decrease in RI. This can be attributed to the protein chain scission, reducing both thickness and RI. In contrast, the ZrOz film (Fig. 1 IB) showed no significant changes in either thickness or RI. The UV-induced deterministic thickness reduction of the silk film shifts the PBGs of silk photonic crystals toward shorter wavelengths (i.e., blue-shift), as depicted in Fig. 3C. Additionally, the effect of PBGs shift remains nearly constant even as the number of silk / ZrO pairs increases up to 10 layers. This result implies that UV irradiation effectively impacts at least 10 layers (or 5 bilayers) of silk / ZrOz multilayered nanostructures, indicating that UV light maintains enough energy to alter the structural conformation even though some of it may be absorbed by each layer.

[0106] When subjected to UV irradiation, the structural conformation of silk fibroin transitions from crystalline to amorphous. Consequently, UV-exposed silk DBRs exhibit heightened water responsiveness, characterized by increased water permeability and uptake capability, thus displaying reconfigurable structural colors upon exposure to ambient humidity. Fig. 4A-H depicts stimuli- responsive structural color patterns in silk / ZrOz photonic crystals. Fig. 4A illustrates the method to create humidity-responsive structural color patterns in silk-based DBRs. Fig. 4B and Fig. 4C compare the extent of thickness and RI changes with respect to humidity exposure for silk films with different degrees of crystallinity. It was observed that AA-treated crystalline silk film (CSF) showed negligible changes in thickness or RI when exposed to relative humidity (RH) exceeding 90%.Consequently, CSF films exhibited minimal swelling and RI reduction even under high humidity conditions. In contrast, the 10-hour UV-exposed amorphous silk film (ASF) readily swelled as water molecules infiltrated between the shortened peptide chains. This increased swelling capacity and enhanced responsiveness to humidity, results in a thickness increase of approximately 6 nm and an RI decrease of around 0.02 compared to the dry state. Fig. 4D illustrates that within the typical indoor humidity range (30% to 60% RH), the PBG central wavelength of the 10-hour UV-exposed silk photonic crystals gradually shifts toward longer wavelengths. However, in a water-rich environment (over 70% RH), this transition accelerates abruptly. The reason for the varying degrees of PBG shift with different humidity levels could be the nonlinear thickness variation of the silk film in response to humidity. While sweeping the RH within the range of 30% to 80%, the changes in structural color can be represented in CIE color space as the path of RGB color coordinates, as depicted in Fig. 4E. The overlapping paths of color coordinate shifts with humidity changes, without hysteresis behavior, signify reversible reconfigurability. This reversibility is further demonstrated in Fig. 4F, highlighting the rapid response and repeatability of wavelength transitions with variations in humidity. The butterfly structural color pattern, when exposed to a humid environment created by a humidifier, displayed rapid color changes within seconds and maintained a consistent level of wavelength shift across multiple cycles. Patterns exposed to UV for 10 hours exhibit a significant reduction in silk thickness, leading to extreme structural color shifts. This results in approximately 80 nm contrast in the PBG wavelength, creating a code that is clearly visible in the dry state. When these patterns are exposed to water, the UV-exposed areas swell more than the non-exposed areas, reducing the color contrast to about 6.5 nm. Consequently, as seen in the left sample in Fig. 4G, the pattern visually disappears when exposed to water. In contrast, patterns exposed to UV for 4 hours experience a smaller reduction in thickness, making it difficult to distinguish the code based on color contrast in the dry state. However, when exposed to humidity, these patterns swell more compared to the surroundings, generating color contrast and revealing the previously concealed code, as shown in the right sample in Fig. 4G. Changes in the central wavelength of PBGs in response to different humidity conditions are depicted in Fig. 4H.

[0107] Conclusion

[0108] An efficient, water-based method was developed to fabricate silk-based ID photonic crystals and encode reconfigurable structural color patterns. Long-standing challenges of orthogonal solvent use and interfacial- wettability were addressed by independently leveraging the structural conformation and amphiphilic nature of SF. The issue of low refractive index contrast was overcome by incorporating zirconyl chloride hydrate, achieving a high An (-0.42 at 500 nm), and enabling silkphotonic crystals with 85% reflectance using only 16 layers. Photolithographic regulation of silkconformation enabled spatial tuning of the multilayer nanostructures as shown by colorimetric humidity sensors and anti-counterfeiting hydrochromic codes demonstrator devices.

[0109] By eliminating the need for organic solvents, this all-water-based method may reduce environmental impact and enhance the biocompatibility of the resulting photonic structures while opening the path to a new class of bioresponsive adaptive optical systems.

[0110] Preparation of regenerated SF and ZrC precursor solutions

[0111] The process of SF extraction was based on previously published methods (Rockwood, D. N. et al. Materials fabrication from Bombyx mori silk fibroin. Nat Protoc 6, 1612-1631 (2011)). Briefly, B. mori silk cocoons (Tagima Shogi, Japan) were cut and boiled in 0.02 M Na COg (Sigma- Aldrich) solution for 30 min to remove sericin. The dried and degummed silk was dissolved in 9.3 M LiBr (Sigma- Aldrich) solution at 60 °C for Ih. The dissolved SF solution was placed into a dialysis tube (Fisherbrand, MWCO 3.5 K), followed by dialysis against deionized (DI) water for 3 days with at least 5 water changes. After the completion of dialysis, the solution was purified through centrifugation at 10,200 rpm for 20 min. The resulting SF solution was diluted to 2.0 ~ 6.0 w / v% for the spin coating process. 0.25 ~ 0.75 M of Zirconium precursor solutions were prepared by dissolving Zirconyl chloride octahydrate (Sigma- Aldrich) in DI water at the designated molar concentration. After dissolving the precursors in water, the solutions were thoroughly stirred for at least 12 hours using a vortex mixer. The solution was filtered through a 0.22 pm polyvinylidene fluoride (PVDF) membrane filter before use.

[0112] Fabrication of silk / ZrO DBRs

[0113] Silicon wafers were used as the substrate in this work. All wafers were diced into 1 cm2or 2 cm2using an automated dicing saw (Disco, DAD-321). Diced wafers were cleaned sequentially using acetone, isopropyl alcohol (IP A), and DI water in an ultrasonic cleaner before use. DBR structures were fabricated using a spin-coater (Laurell, WS-400B) by alternatively coating silk and Zirconium precursor solutions on cleaned wafers. The rotating speed and solution concentrations controlled each layer’s thickness. In order to fulfill the orthogonal solubility condition, silk films were crystallized by dropping 50 pL of glacial acetic acid (AA) (Sigma-Aldrich) during a spin coating process. The spin-coated silk films were then annealed on a hot plate at 250 °C for 5 minutes. The pure zirconium precursor solution does not completely spread over the silk film and tends to dewet. The contact angle of the zirconium precursor solution over the crystallized silk layer was around 85 degrees. In order to improve the wettability of the zirconium precursor solution to the silk film, a diluted silk aqueous solution was added to the zirconium precursor solution with varying w / v% concentrations. The spin-coated Zirconium precursor films also underwent thermal hydrolysison a hot plate at the same temperature and time. This thermal annealing makes the ZrCh films insoluble in water.

[0114] Pattern encryption in silk / ZrO DBRs using UV lamp

[0115] A germicidal UV lamp (VL-215G, 254 nm) was used to encrypt patterns or letters in the silk / ZrO DBRs. Shadow masks with designed shapes were placed over the DBRs, and the UV irradiation was carried out for different exposure times. The measured irradiance using a thermal power head (S310C, Thorlabs) at a 5 cm distance from the lamp surface was around 4.5 mW / cm2.

[0116] Analysis of silk film’s crystallinity

[0117] The degree of crystallization of SF film was analyzed using FTIR (Invenio S, Bruker). All FTIR spectra were acquired in the 400 ~ 4000 cm1range at 4 cm1resolution with an average of 32 scans.

[0118] Contact angle measurements of aqueous ZrOCh solutions over the crystalline silk film

[0119] The time-dependent contact angle of ZrOCh solutions over the crystalline silk film was measured using a custom-made goniometer. Crystalline silk films coated over a flat silicon substrate were placed over a z-axis manual stage (Thorlabs), and 2 pL of aqueous zirconium solution was dispensed over the silk film. Contact angles of the solution were imaged using a digital single-lens reflex (DSLR) camera (Canon Rebel EOS-SL1) with a minute interval. Image J’s contact angle plugin was used to extract the values of contact angles.

[0120] Surface coverage (%) of spin-coated ZrC film over the crystalline silk film

[0121] The zirconium precursor solution was spin-cast over crystallized silk films, followed by DSLR camera imaging. Using Image J, the image types were converted to 8-bit grayscale, and then pixels were separated into two classes by threshold command. Due to the color contrast between film and substrate, the coated area can be selectively filtered, and the ratio of the coated area to the entire substrate area was automatically measured using the measure command.

[0122] Chemical composition analysis of silk and ZrCh films

[0123] An X-ray Photoelectron Spectrometer (XPS) system (Nexsa, Thermo Scientific) was used for surface chemistry analysis. The surface of silk and ZrC films were XPS analyzed with a 100 pm2scanning size.

[0124] SEM and TEM analysis of silk / ZrC DBRs

[0125] A focused ion beam (FIB)-SEM (Helios 660, Thermo Fisher Scientific) was used for TEM sample preparation. After milling the sample, the cross sections of the prepared samples were imaged using a high-resolution electron beam mode of the FIB-SEM with an in-column detector (ICD) at 3.0 kV and 4.0 mm as the working distance. A field emission TEM (JEOL F200, JEOL) was used to image cross sections of the milled sample at the acceleration voltage of 80 kV. False-color elementdistribution maps were acquired for zirconium, oxide, and carbon using a high-angle annular darkfield imaging (HAADF) mode and EDS detector.

[0126] Refractive index characterization

[0127] A spectroscopic Ellipsometer (RC2, Woollam) was used for the thickness and optical constants characterization of silk and ZrO films. With different incident angles varying from 60 to 70 degrees with 5 degrees of incremental steps, a total of 5 points (top, center, bottom, left, and right) of film area was analyzed from UV (250 nm) to NIR (2250 nm) to get Psi and Delta values. The acquired ellipsometer curves were fitted with the Cauchy model to derive thickness and optical constants.

[0128] Optical characterization of silk / ZrOz DBRs

[0129] The normal incidence reflectivity of the photonic crystal was evaluated in the range of 300 nm to 1600 nm using a commercial reflectometer (F50-UVX, Filmetrics). The angular dependent reflectance of silk / ZrO photonic crystals was characterized using a home-made goniometer equipped with a lamp (Halogen illuminator, EKE, Kramer Scientific Corporation) and a spectrometer (USB2000, 200-800 nm, Ocean Optics). The sample was mounted on a rotating stage and illuminated by a 200 pm core fiber (P200-2-VIS-NIR, Ocean Optics) coupled to the lamp at 0inincident angle with respect to the normal to the sample. The reflected light was collected by a 600 pm core fiber (P600-2-VIS-NIR, Ocean Optics) coupled into the spectrometer and mounted on a manual rotating detector arm, concentrically aligned to the sample stage. To measure the angular reflection spectrum, the sample stage was manually rotated by 0in, (with 0inbeing the angle that the incident ray makes with respect to the normal of the sample stage). The detector arm was then rotated by an angle 0Out= 0in with respect to the normal of the sample (20i„ with respect to the incident beam). The angular dependence of the reflection of the sample was measured at increments of 10°, ranging from 0in= 20° to 0in= 60°. The recorded light intensity was normalized with respect to a silver mirror (PF10-03-P01, Thorlabs). The beam spot size varied between 0.835 mm2(0in=20°) and 1.57 mm2(0in=6O°). The collected spectra were smoothed using the software OceanView (Ocean Optics, boxcar width = 5) and normalized using the software Origin Pro2019.

[0130] ADDITIONAL STATEMENTS OF THE DISCLOSURE

[0131] In some implementations, the disclosed methods, photonic multilayers, and optical effect articles may be described in the following numbered clauses or otherwise described herein and as illustrated in Figs. 1 - 11. The disclosure includes the following clauses:1. A method of making a photonic multilayer exhibiting structural color, the method comprising the following steps:a) optionally aqueously depositing a base aqueously -deposited amphiphilic biopolymer to form a base polymer layer, wherein the optional aqueously depositing the base aqueously- deposited amphiphilic biopolymer utilizes a base amphiphilic biopolymer solution comprising the base aqueously-deposited amphiphilic biopolymer at a concentration by weight of between 0.5% and 8.0%; b) aqueously depositing a base aqueously-deposited semiconductor material onto the base polymer layer, thereby forming a base bilayer comprising the base polymer layer and a base semiconductor layer, wherein the base polymer layer comprises a base aqueously-deposited amphiphilic biopolymer, wherein the base polymer layer has a base polymer thickness of between 10 nm and 500 nm and a base polymer uniformity of between 1.0% and 10.0% or between 2.0% and 9.0% or between 3.0% and 8.0% of the base polymer thickness root mean square, wherein the base semiconductor layer has a base semiconductor thickness of between 10 nm and 500 nm and a base semiconductor uniformity of between 1.0% and 10.0% or between 2.0% and 9.0% or between 3.0% and 8.0% of the base semiconductor thickness root mean square, wherein the aqueously depositing of step b) utilizes a base aqueous semiconductor material solution including the base aqueously-deposited semiconductor material and the base aqueously-deposited amphiphilic biopolymer at a base biopolymer depositing concentration of between 0.001 % and 0.5% or between 0.001 % and 0.1 %; c) optionally aqueously depositing one or more alternating bilayers atop the base bilayer, each of the one or more alternating bilayers independently comprising an alternating polymer layer and an alternating semiconductor layer, wherein the alternating polymer layer of each of the one or more alternating bilayers is independently composed of the base aqueously-deposited amphiphilic biopolymer or an independently- selected alternating amphiphilic biopolymer that is different than the base aqueously-deposited amphiphilic biopolymer, wherein the alternating semiconductor layer of each of the one or more alternating bilayers is independently composed of the base aqueously-deposited semiconductor material or an independently-selected alternating semiconductor material that is different than the base aqueously-deposited semiconductor material, wherein the alternating polymer layer of each of the one or more alternating bilayers independently has an alternating polymer thickness of between 10 nm and 500 nm and analternating polymer uniformity of between 1.0% and 10.0% or between 2.0% and 9.0% or between 3.0% and 8.0% of the terminal polymer thickness root mean square, and wherein the alternating semiconductor layer of each of the one or more alternating bilayers independently has an alternating semiconductor thickness of between 10 nm and 500 nm and an alternating semiconductor uniformity of between 1.0% and 10.0% or between 2.0% and 9.0% or between 3.0% and 8.0% of the terminal semiconductor thickness root mean square; d) aqueously depositing the base aqueously-deposited amphiphilic biopolymer or a terminal aqueously-deposited amphiphilic biopolymer that is different than the base aqueously- deposited amphiphilic biopolymer onto the base semiconductor layer or a topmost semiconductor layer of the one or more alternating bilayers, wherein the terminal polymer layer has a terminal polymer thickness of between 10 nm and 500 nm and a terminal polymer uniformity of between 1.0% and 10.0% or between 2.0% and 9.0% or between 3.0% and 8.0% of the terminal polymer thickness root mean square, and wherein the aqueously depositing of step d) utilizes a terminal aqueous semiconductor material solution including the terminal aqueously-deposited amphiphilic biopolymer at a terminal biopolymer depositing concentration of between 0.5% and 8.0%; and e) aqueously depositing the base aqueously-deposited semiconductor material or a terminal aqueously-deposited semiconductor material that is different than the base aqueously- deposited semiconductor material onto the terminal polymer layer, thereby forming a terminal bilayer comprising the terminal polymer layer and a terminal semiconductor layer, wherein the terminal semiconductor layer has a terminal semiconductor thickness of between 10 nm and 500 nm and a terminal semiconductor uniformity of between 1.0% and 10.0% or between 2.0% and 9.0% or between 3.0% and 8.0% of the terminal semiconductor thickness root mean square, wherein the aqueously depositing of step e) utilizes a terminal aqueous semiconductor material solution including the terminal aqueously-deposited semiconductor material and the terminal aqueously-deposited amphiphilic biopolymer at a terminal biopolymer depositing concentration of between 0.001% and 0.5% or between 0.001% and 0.1%, wherein uniformity is optionally calculated as a difference divided by two times the average value, wherein the differences is between the maximum value and the minimum value.2. The method of clause 1, wherein the aqueously depositing of any one of steps a), b), c), d), or e) is performed via spin casting.3. The method of any one of the preceding clauses, wherein the aqueously depositing of step a) is performed via spin casting.4. The method of any one of the preceding clauses, wherein the aqueously depositing of step b) is performed via spin casting.5. The method of any one of the preceding clauses, wherein the aqueously depositing of step c) is performed via spin casting.6. The method of any one of the preceding clauses, wherein the aqueously depositing of step d) is performed via spin casting.7. The method of any one of the preceding clauses, wherein the aqueously depositing of step e) is performed via spin casting.8. A photonic multilayer exhibiting structural color, the photonic multilayer comprising: a base bilayer comprising a base polymer layer and a base semiconductor layer, wherein the base polymer layer comprises a base aqueously-deposited amphiphilic biopolymer, wherein the base semiconductor layer comprises a base aqueously-deposited semiconductor material, wherein the base polymer layer has a base polymer thickness of between 10 nm and 500 nm and a base polymer uniformity (optionally calculated as a difference between the maximum value and the minimum value divided by 2x the average value) of between 1.0% and 10.0% or between 2.0% and 9.0% or between 3.0% and 8.0% of the base polymer thickness root mean square, and wherein the base semiconductor layer has a base semiconductor thickness of between 10 nm and 500 nm and a base semiconductor uniformity of between 1.0% and 10.0% or between 2.0% and 9.0% or between 3.0% and 8.0% of the base semiconductor thickness root mean square; optionally one or more alternating bilayers, each of the one or more alternating bilayers independently comprising an alternating polymer layer and an alternating semiconductor layer, wherein the alternating polymer layer of each of the one or more alternating bilayers is independently composed of the base aqueously-deposited amphiphilic biopolymer or an independently- selected alternating amphiphilic biopolymer that is different than the base aqueously-deposited amphiphilic biopolymer,wherein the alternating semiconductor layer of each of the one or more alternating bilayers is independently composed of the base aqueously-deposited semiconductor material or an independently-selected alternating semiconductor material that is different than the base aqueously-deposited semiconductor material, wherein the alternating polymer layer of each of the one or more alternating bilayers independently has an alternating polymer thickness of between 10 nm and 500 nm and an alternating polymer uniformity of between 1.0% and 10.0% or between 2.0% and 9.0% or between 3.0% and 8.0% of the terminal polymer thickness root mean square, and wherein the alternating semiconductor layer of each of the one or more alternating bilayers independently has an alternating semiconductor thickness of between 10 nm and 500 nm and an alternating semiconductor uniformity of between 1.0% and 10.0% or between 2.0% and 9.0% or between 3.0% and 8.0% of the terminal semiconductor thickness root mean square; and a terminal bilayer comprising a terminal polymer layer and a terminal semiconductor layer, wherein the terminal polymer layer comprises a terminal aqueously-deposited amphiphilic biopolymer that is the base aqueously-deposited amphiphilic biopolymer or is different than the base aqueously-deposited amphiphilic biopolymer, wherein the terminal semiconductor layer comprises the base aqueously-deposited semiconductor material or a terminal aqueously-deposited semiconductor material that is different than the base aqueously-deposited amphiphilic biopolymer, wherein the terminal polymer layer has a terminal polymer thickness of between 10 nm and 500 nm and a terminal polymer uniformity of between 1.0% and 10.0% or between 2.0% and 9.0% or between 3.0% and 8.0% of the terminal polymer thickness root mean square, and wherein the terminal semiconductor layer has a terminal semiconductor thickness of between 10 nm and 500 nm and a terminal semiconductor uniformity of between 1.0% and 10.0% or between 2.0% and 9.0% or between 3.0% and 8.0% of the terminal semiconductor thickness root mean square, wherein the base bilayer, the optional plurality of alternating bilayers, and the terminal bilayer form the photonic multilayer without gaps between the bilayers, and wherein each bilayer of the base bilayer, the plurality of alternating bilayers, and the terminal bilayer has a difference in index of refraction between its respective polymer layer and semiconductor layer, wherein the difference in index of refraction at a wavelength between 400 nm and 700 nm is at least 0.20, at least 0.25, at least 0.30, at least 0.35,wherein uniformity is optionally calculated as a difference divided by two times the average value, wherein the differences is between the maximum value and the minimum value.9. The photonic multilayer or the method of any one of the preceding clauses, wherein the base aqueously-deposited amphiphilic biopolymer is an aqueously-deposited amphiphilic protein.10. The photonic multilayer or the method of any one of the preceding clauses, wherein the base aqueously-deposited amphiphilic biopolymer comprises aqueously deposited silk fibroin.11. The photonic multilayer or the method of the immediately preceding clause, wherein the base aqueously-deposited amphiphilic biopolymer consists of the aqueously-deposited silk fibroin.12. The photonic multilayer or the method of any one of the preceding clauses,13. The photonic multilayer or the method of any one of the preceding clauses, wherein the terminal polymer layer comprises the terminal aqueously deposited amphiphilic biopolymer that is different than the base aqueously-deposited amphiphilic biopolymer.14. The photonic multilayer or the method of the immediately preceding clause, wherein the terminal aqueously-deposited amphiphilic biopolymer is an aqueously-deposited amphiphilic protein.15. The photonic multilayer or the method of the immediately preceding clause, wherein the terminal aqueously-deposited amphiphilic biopolymer comprises aqueously deposited silk fibroin.16. The photonic multilayer or the method of the immediately preceding clause, wherein the terminal aqueously-deposited amphiphilic biopolymer consists of the aqueously-deposited silk fibroin.17. The photonic multilayer or the method of any one of the preceding clauses, wherein The photonic multilayer or the method includes the plurality of alternating bilayers.18. The photonic multilayer or the method of any one of the preceding clauses, wherein the base polymer thickness is between 20 nm and 400 nm.19. The photonic multilayer or the method of any one of the preceding clauses, wherein the base polymer thickness is between 40 nm and 250 nm.20. The photonic multilayer or the method of any one of the preceding clauses, wherein the base semiconductor thickness is between 20 nm and 400 nm.21. The photonic multilayer or the method of any one of the preceding clauses, wherein the base semiconductor thickness is between 40 nm and 250 nm.22. The photonic multilayer or the method of any one of the preceding clauses, wherein the base polymer uniformity is between 0.1% and 2.5% of the base polymer thickness root mean square.23. The photonic multilayer or the method of any one of the preceding clauses, wherein the base polymer uniformity is between 0.1% and 1.0% of the base polymer thickness root mean square.24. The photonic multilayer or the method of any one of the preceding clauses, wherein the base semiconductor uniformity is between 0.1% and 2.5% of the base semiconductor thickness root mean square.25. The photonic multilayer or the method of any one of the preceding clauses, wherein the base semiconductor uniformity is between 0.1% and 1.0% of the base semiconductor thickness root mean square.26. The photonic multilayer or the method of any one of the preceding clauses, wherein the terminal polymer thickness is between 20 nm and 400 nm.27. The photonic multilayer or the method of any one of the preceding clauses, wherein the terminal polymer thickness is between 40 nm and 250 nm.28. The photonic multilayer or the method of any one of the preceding clauses, wherein the terminal semiconductor thickness is between 20 nm and 400 nm.29. The photonic multilayer or the method of any one of the preceding clauses, wherein the terminal semiconductor thickness is between 40 nm and 250 nm.30. The photonic multilayer or the method of any one of the preceding clauses, wherein the terminal polymer uniformity is between 0.1% and 2.5% of the terminal polymer thickness root mean square.31. The photonic multilayer or the method of any one of the preceding clauses, wherein the terminal polymer uniformity is between 0.1% and 1.0% of the terminal polymer thickness root mean square.32. The photonic multilayer or the method of any one of the preceding clauses, wherein the terminal semiconductor uniformity is between 0.1% and 2.5% of the terminal semiconductor thickness root mean square.33. The photonic multilayer or the method of any one of the preceding clauses, wherein the terminal semiconductor uniformity is between 0.1% and 1.0% of the terminal semiconductor thickness root mean square.34. The photonic multilayer or the method of any one of the preceding clauses, wherein the alternating polymer thickness is between 20 nm and 400 nm.35. The photonic multilayer or the method of any one of the preceding clauses, wherein the alternating polymer thickness is between 40 nm and 250 nm.36. The photonic multilayer or the method of any one of the preceding clauses, wherein the alternating semiconductor thickness is between 20 nm and 400 nm.37. The photonic multilayer or the method of any one of the preceding clauses, wherein the alternating semiconductor thickness is between 40 nm and 250 nm.38. The photonic multilayer or the method of any one of the preceding clauses, wherein the alternating polymer uniformity is between 0.1% and 2.5% of the alternating polymer thickness root mean square.39. The photonic multilayer or the method of any one of the preceding clauses, wherein the alternating polymer uniformity is between 0.1% and 1.0% of the alternating polymer thickness root mean square.40. The photonic multilayer or the method of any one of the preceding clauses, wherein the alternating semiconductor uniformity is between 0.1% and 2.5% of the alternating semiconductor thickness root mean square.41. The photonic multilayer or the method of any one of the preceding clauses, wherein the alternating semiconductor uniformity is between 0.1% and 1.0% of the alternating semiconductor thickness root mean square.42. The photonic multilayer or the method of any one of the preceding clauses, wherein the base polymer thickness and the terminal polymer thickness are the same.43. The photonic multilayer or the method of any one of clauses 1 to the clause immediately preceding the immediately preceding clause, wherein the base polymer thickness and the terminal polymer thickness are different.44. The photonic multilayer or the method of any one of the preceding clauses, wherein the base semiconductor thickness and the terminal semiconductor thickness are the same.45. The photonic multilayer or the method of any one of clauses 1 to the clause immediately preceding the immediately preceding clause, wherein the base semiconductor thickness and the terminal semiconductor thickness are different.46. The photonic multilayer or the method of any one of the preceding clauses, wherein the base polymer thickness, the alternating polymer thickness, and the terminal polymer thickness are the same.47. The photonic multilayer or the method of any one of the preceding clauses, wherein the base semiconductor thickness, the alternating semiconductor thickness, and the terminal semiconductor thickness are the same.48. The photonic multilayer or the method of any one of the preceding clauses, wherein the one or more alternating bilayers is a plurality of alternating bilayers and the alternating polymer thickness is the same for each of the plurality of alternating bilayers.49. The photonic multilayer or the method of any one of clauses 1 to the clause immediately preceding the immediately preceding clause, wherein the one or more alternating bilayers is aplurality of alternating bilayers and the alternating polymer thickness is different for at least two of the plurality of alternating bilayers.50. The photonic multilayer or the method of any one of the preceding clauses, wherein the one or more alternating bilayers is a plurality of alternating bilayers and the alternating polymer thickness is different for each of the plurality of alternating bilayers.51. The photonic multilayer or the method of any one of the preceding clauses, wherein the base polymer layer has an index of refraction of between 1.25 and 1.75.52. The photonic multilayer or the method of any one of the preceding clauses, wherein the base semiconductor layer has an index of refraction of between 1.75 and 2.25.53. The photonic multilayer or the method of any one of the preceding clauses, wherein the terminal polymer layer has an index of refraction of between 1.25 and 1.75.54. The photonic multilayer or the method of any one of the preceding clauses, wherein the terminal semiconductor layer has an index of refraction of between 1.75 and 2.25.55. The photonic multilayer or the method of any one of the preceding clauses, wherein the base polymer layer and the terminal polymer layer have the same index of refraction.56. The photonic multilayer or the method of any one of the preceding clauses, wherein the base semiconductor layer and the terminal semiconductor layer have the same index of refraction.57. The photonic multilayer or the method of any one of the preceding clauses, wherein each alternating polymer layer independently has an index of refraction of between 1.25 and 1.75.58. The photonic multilayer or the method of any one of the preceding clauses, wherein each alternating polymer layer has the same index of refraction.59. The photonic multilayer or the method of any one of the preceding clauses, wherein each alternating semiconductor layer independently has an index of refraction of between 1.75 and 2.25.60. The photonic multilayer or the method of any one of the preceding clauses, wherein each alternating semiconductor layer has the same index of refraction.61. The photonic multilayer or the method of any one of the preceding clauses, wherein the base polymer layer, the terminal polymer layer, and each alternating polymer layer have the same index of refraction.62. The photonic multilayer or the method of any one of the preceding clauses, wherein the base semiconductor layer, the terminal semiconductor layer, and each alternating semiconductor layer have the same index of refraction.63. The photonic multilayer or the method of any one of the preceding clauses, wherein the photonic multilayer has an uninterrupted lateral area of between 1 cm2and 1 m2between 10 cm2and 0.1 m2.64. An optical effect article comprising the photonic multilayer of or made by the method of any one of the preceding clauses, wherein the base bilayer, the optional plurality of alternating bilayers, and the terminal bilayer are assembled in a vertical direction, wherein the optical effect article comprises laterally-defined regions having one or more differences in the polymer layers, thereby providing different changes in structural color between the laterally-defined regions upon changing humidity environments.65. The optical effect article of the immediately preceding clause, wherein the laterally-defined regions form an image.66. The optical effect article of the immediately preceding clause, wherein the image is visible in certain humidity conditions and invisible in different humidity conditions.67. A method of using a photonic multilayer, the method comprising changing hydration state in the amphiphilic biopolymer layers in the photonic multilayer of or made by the method of any one of the preceding clauses to water vapor, thereby causing a change in distance between the semiconductor layers in the photonic multilayer, thereby changing one or more properties of the structural color exhibited by the photonic multilayer.68. The method of the immediately preceding clause, wherein changing hydration state reveals a previously-invisible image within the photonic multilayer.69. The method of either two of the immediately preceding clauses, the method further comprising acquiring an image of the photonic multilayer after changing hydration state and performing image analysis on the image.70. The method of either of the two immediately preceding clauses, wherein the previously- invisible image includes a code, such as a one- or two-dimensional barcode.

[0132] EQUIVALENTS AND SCOPE

[0133] The recitation of a listing of elements in any definition of a variable herein includes definitions of that variable as any single element or combinations (or sub-combinations) of listed elements. The recitation of an embodiment herein includes that embodiment as any single embodiment or in combination with any other embodiments or portions thereof. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments of the invention described herein. The scope of the present invention is not intended to be limited to the above Description, but rather is as set forth in the following claims:

Claims

CLAIMSWhat is claimed is:

1. A method of making a photonic multilayer exhibiting structural color, the method comprising the following steps: a) optionally aqueously depositing a base aqueously-deposited amphiphilic biopolymer to form a base polymer layer, wherein the optional aqueously depositing the base aqueously- deposited amphiphilic biopolymer utilizes a base amphiphilic biopolymer solution comprising the base aqueously-deposited amphiphilic biopolymer at a concentration by weight of between 0.5% and 8.0%; b) aqueously depositing a base aqueously-deposited semiconductor material onto the base polymer layer, thereby forming a base bilayer comprising the base polymer layer and a base semiconductor layer, wherein the base polymer layer comprises a base aqueously-deposited amphiphilic biopolymer, wherein the base polymer layer has a base polymer thickness of between 10 nm and 500 nm and a base polymer uniformity of between 1.0% and 10.0% or between 2.0% and 9.0% or between 3.0% and 8.0% of the base polymer thickness root mean square, wherein the base semiconductor layer has a base semiconductor thickness of between 10 nm and 500 nm and a base semiconductor uniformity of between 1.0% and 10.0% or between 2.0% and 9.0% or between 3.0% and 8.0% of the base semiconductor thickness root mean square, wherein the aqueously depositing of step b) utilizes a base aqueous semiconductor material solution including the base aqueously-deposited semiconductor material and the base aqueously-deposited amphiphilic biopolymer at a base biopolymer depositing concentration of between 0.001% and 0.5% or between 0.001% and 0.1%; c) optionally aqueously depositing one or more alternating bilayers atop the base bilayer, each of the one or more alternating bilayers independently comprising an alternating polymer layer and an alternating semiconductor layer, wherein the alternating polymer layer of each of the one or more alternating bilayers is independently composed of the base aqueously-deposited amphiphilic biopolymer or an independently- selected alternating amphiphilic biopolymer that is different than the base aqueously-deposited amphiphilic biopolymer,wherein the alternating semiconductor layer of each of the one or more alternating bilayers is independently composed of the base aqueously-deposited semiconductor material or an independently-selected alternating semiconductor material that is different than the base aqueously-deposited semiconductor material, wherein the alternating polymer layer of each of the one or more alternating bilayers independently has an alternating polymer thickness of between 10 nm and 500 nm and an alternating polymer uniformity of between 1.0% and 10.0% or between 2.0% and 9.0% or between 3.0% and 8.0% of the terminal polymer thickness root mean square, and wherein the alternating semiconductor layer of each of the one or more alternating bilayers independently has an alternating semiconductor thickness of between 10 nm and 500 nm and an alternating semiconductor uniformity of between 1.0% and 10.0% or between 2.0% and 9.0% or between 3.0% and 8.0% of the terminal semiconductor thickness root mean square; d) aqueously depositing the base aqueously-deposited amphiphilic biopolymer or a terminal aqueously-deposited amphiphilic biopolymer that is different than the base aqueously- deposited amphiphilic biopolymer onto the base semiconductor layer or a topmost semiconductor layer of the one or more alternating bilayers, wherein the terminal polymer layer has a terminal polymer thickness of between 10 nm and 500 nm and a terminal polymer uniformity of between 1.0% and 10.0% or between 2.0% and 9.0% or between 3.0% and 8.0% of the terminal polymer thickness root mean square, and wherein the aqueously depositing of step d) utilizes a terminal aqueous semiconductor material solution including the terminal aqueously-deposited amphiphilic biopolymer at a terminal biopolymer depositing concentration of between 0.5% and 8.0%; and e) aqueously depositing the base aqueously-deposited semiconductor material or a terminal aqueously-deposited semiconductor material that is different than the base aqueously- deposited semiconductor material onto the terminal polymer layer, thereby forming a terminal bilayer comprising the terminal polymer layer and a terminal semiconductor layer, wherein the terminal semiconductor layer has a terminal semiconductor thickness of between 10 nm and 500 nm and a terminal semiconductor uniformity of between 1.0% and 10.0% or between 2.0% and 9.0% or between 3.0% and 8.0% of the terminal semiconductor thickness root mean square, wherein the aqueously depositing of step e) utilizes a terminal aqueous semiconductor material solution including the terminal aqueously-deposited semiconductor material andthe terminal aqueously-deposited amphiphilic biopolymer at a terminal biopolymer depositing concentration of between 0.001% and 0.5% or between 0.001% and 0.1%, wherein uniformity is optionally calculated as a difference divided by two times the average value, wherein the differences is between the maximum value and the minimum value.

2. The method of claim 1 , wherein the aqueously depositing of any one of steps a), b), c), d), or e) is performed via spin casting.

3. The method of any one of the preceding claims, wherein the aqueously depositing of step a) is performed via spin casting.

4. The method of any one of the preceding claims, wherein the aqueously depositing of step b) is performed via spin casting.

5. The method of any one of the preceding claims, wherein the aqueously depositing of step c) is performed via spin casting.

6. The method of any one of the preceding claims, wherein the aqueously depositing of step d) is performed via spin casting.

7. The method of any one of the preceding claims, wherein the aqueously depositing of step e) is performed via spin casting.

8. A photonic multilayer exhibiting structural color, the photonic multilayer comprising: a base bilayer comprising a base polymer layer and a base semiconductor layer, wherein the base polymer layer comprises a base aqueously-deposited amphiphilic biopolymer, wherein the base semiconductor layer comprises a base aqueously-deposited semiconductor material, wherein the base polymer layer has a base polymer thickness of between 10 nm and 500 nm and a base polymer uniformity (optionally calculated as a difference between the maximum value and the minimum value divided by 2x the average value) of between 1.0% and 10.0% or between 2.0% and 9.0% or between 3.0% and 8.0% of the base polymer thickness root mean square, and wherein the base semiconductor layer has a base semiconductor thickness of between10 nm and 500 nm and a base semiconductor uniformity of between 1.0% and 10.0% or between 2.0% and 9.0% or between 3.0% and 8.0% of the base semiconductor thickness root mean square;optionally one or more alternating bilayers, each of the one or more alternating bilayers independently comprising an alternating polymer layer and an alternating semiconductor layer, wherein the alternating polymer layer of each of the one or more alternating bilayers is independently composed of the base aqueously-deposited amphiphilic biopolymer or an independently- selected alternating amphiphilic biopolymer that is different than the base aqueously-deposited amphiphilic biopolymer, wherein the alternating semiconductor layer of each of the one or more alternating bilayers is independently composed of the base aqueously-deposited semiconductor material or an independently-selected alternating semiconductor material that is different than the base aqueously-deposited semiconductor material, wherein the alternating polymer layer of each of the one or more alternating bilayers independently has an alternating polymer thickness of between 10 nm and 500 nm and an alternating polymer uniformity of between 1.0% and 10.0% or between 2.0% and 9.0% or between 3.0% and 8.0% of the terminal polymer thickness root mean square, and wherein the alternating semiconductor layer of each of the one or more alternating bilayers independently has an alternating semiconductor thickness of between 10 nm and 500 nm and an alternating semiconductor uniformity of between 1.0% and 10.0% or between 2.0% and 9.0% or between 3.0% and 8.0% of the terminal semiconductor thickness root mean square; and a terminal bilayer comprising a terminal polymer layer and a terminal semiconductor layer, wherein the terminal polymer layer comprises a terminal aqueously-deposited amphiphilic biopolymer that is the base aqueously-deposited amphiphilic biopolymer or is different than the base aqueously-deposited amphiphilic biopolymer, wherein the terminal semiconductor layer comprises the base aqueously-deposited semiconductor material or a terminal aqueously-deposited semiconductor material that is different than the base aqueously-deposited amphiphilic biopolymer, wherein the terminal polymer layer has a terminal polymer thickness of between 10 nm and 500 nm and a terminal polymer uniformity of between 1.0% and 10.0% or between 2.0% and 9.0% or between 3.0% and 8.0% of the terminal polymer thickness root mean square, and wherein the terminal semiconductor layer has a terminal semiconductor thickness of between 10 nm and 500 nm and a terminal semiconductor uniformity of between 1.0% and 10.0% or between 2.0% and 9.0% or between 3.0% and 8.0% of the terminal semiconductor thickness root mean square,wherein the base bilayer, the optional plurality of alternating bilayers, and the terminal bilayer form the photonic multilayer without gaps between the bilayers, and wherein each bilayer of the base bilayer, the plurality of alternating bilayers, and the terminal bilayer has a difference in index of refraction between its respective polymer layer and semiconductor layer, wherein the difference in index of refraction at a wavelength between 400 nm and 700 nm is at least 0.20, at least 0.25, at least 0.30, or at least 0.35, wherein uniformity is optionally calculated as a difference divided by two times the average value, wherein the differences is between the maximum value and the minimum value.

9. The photonic multilayer or the method of any one of the preceding claims, wherein at least one of the base aqueously-deposited amphiphilic biopolymer or the terminal aqueously-deposited amphiphilic biopolymer is an aqueously-deposited amphiphilic protein.

10. The photonic multilayer or the method of any one of the preceding claims, wherein at least one of the base aqueously-deposited amphiphilic biopolymer or the terminal aqueously-deposited amphiphilic biopolymer comprises aqueously deposited silk fibroin.

11. The photonic multilayer or the method of the immediately preceding claim, wherein at least one of the base aqueously-deposited amphiphilic biopolymer or the terminal aqueously-deposited amphiphilic biopolymer consists of the aqueously-deposited silk fibroin.

12. The photonic multilayer or the method of any one of the preceding claims, wherein the terminal polymer layer comprises the terminal aqueously deposited amphiphilic biopolymer that is different than the base aqueously-deposited amphiphilic biopolymer.

13. The photonic multilayer or the method of any one of the preceding claims, wherein the photonic multilayer or the method includes the plurality of alternating bilayers.

14. The photonic multilayer or the method of any one of the preceding claims, wherein at least one of the base polymer thickness, the base semiconductor thickness, the terminal polymer thickness, the terminal semiconductor thickness, the alternating polymer thickness, or the alternating semiconductor thickness is between 20 nm and 400 nm or between 40 nm and 250 nm.

15. The photonic multilayer or the method of any one of the preceding claims, wherein the base polymer uniformity is between 0.1% and 2.5% or between 0.1% and 1.0% of the base polymer thickness root mean square.

16. The photonic multilayer or the method of any one of the preceding claims, wherein the base semiconductor uniformity is between 0.1% and 2.5% or between 0.1% and 1.0% of the base semiconductor thickness root mean square.

17. The photonic multilayer or the method of any one of the preceding claims, wherein the terminal polymer uniformity is between 0.1 % and 2.5% or between 0.1 % and 1 .0% of the terminal polymer thickness root mean square.

18. The photonic multilayer or the method of any one of the preceding claims, wherein the terminal semiconductor uniformity is between 0.1% and 2.5% or between 0.1% and 1.0% of the terminal semiconductor thickness root mean square.

19. The photonic multilayer or the method of any one of the preceding claims, wherein the alternating polymer uniformity is between 0.1% and 2.5% of the alternating polymer thickness root mean square.

20. The photonic multilayer or the method of any one of the preceding claims, wherein the alternating semiconductor uniformity is between 0.1% and 2.5% of the alternating semiconductor thickness root mean square.

21. The photonic multilayer or the method of any one of the preceding claims, wherein the base polymer thickness and the terminal polymer thickness are the same.

22. The photonic multilayer or the method of any one of claims 1 to the claim immediately preceding the immediately preceding claim, wherein the base polymer thickness and the terminal polymer thickness are different.

23. The photonic multilayer or the method of any one of the preceding claims, wherein the base semiconductor thickness and the terminal semiconductor thickness are the same.

24. The photonic multilayer or the method of any one of claims 1 to the claim immediately preceding the immediately preceding claim, wherein the base semiconductor thickness and the terminal semiconductor thickness are different.

25. The photonic multilayer or the method of any one of the preceding claims, wherein the base polymer thickness, the alternating polymer thickness, and the terminal polymer thickness are the same.

26. The photonic multilayer or the method of any one of the preceding claims, wherein the base semiconductor thickness, the alternating semiconductor thickness, and the terminal semiconductor thickness are the same.

27. The photonic multilayer or the method of any one of the preceding claims, wherein the one or more alternating bilayers is a plurality of alternating bilayers and the alternating polymer thickness is the same for each of the plurality of alternating bilayers.

28. The photonic multilayer or the method of any one of claims 1 to the claim immediately preceding the immediately preceding claim, wherein the one or more alternating bilayers is a plurality of alternating bilayers and the alternating polymer thickness is different for at least two of the plurality of alternating bilayers.

29. The photonic multilayer or the method of any one of the preceding claims, wherein the one or more alternating bilayers is a plurality of alternating bilayers and the alternating polymer thickness is different for each of the plurality of alternating bilayers.

30. The photonic multilayer or the method of any one of the preceding claims, wherein at least one of the base polymer layer or the terminal polymer layer has an index of refraction of between 1.25 and 1.75.

31. The photonic multilayer or the method of any one of the preceding claims, wherein at least one of the base semiconductor layer or the terminal semiconductor layer has an index of refraction of between 1.75 and 2.25.

32. The photonic multilayer or the method of any one of the preceding claims, wherein the base polymer layer and the terminal polymer layer have the same index of refraction.

33. The photonic multilayer or the method of any one of the preceding claims, wherein the base semiconductor layer and the terminal semiconductor layer have the same index of refraction.

34. The photonic multilayer or the method of any one of the preceding claims, wherein each alternating polymer layer independently has an index of refraction of between 1.25 and 1.75.

35. The photonic multilayer or the method of any one of the preceding claims, wherein each alternating polymer layer has the same index of refraction.

36. The photonic multilayer or the method of any one of the preceding claims, wherein each alternating semiconductor layer independently has an index of refraction of between 1.75 and 2.25.

37. The photonic multilayer or the method of any one of the preceding claims, wherein each alternating semiconductor layer has the same index of refraction.

38. The photonic multilayer or the method of any one of the preceding claims, wherein the base polymer layer, the terminal polymer layer, and each alternating polymer layer have the same index of refraction.

39. The photonic multilayer or the method of any one of the preceding claims, wherein the base semiconductor layer, the terminal semiconductor layer, and each alternating semiconductor layer have the same index of refraction.

40. The photonic multilayer or the method of any one of the preceding claims, wherein the photonic multilayer has an uninterrupted lateral area of between 1 cm2and 1 m2or between 10 cm2and 0.1 m2.

41. An optical effect article comprising the photonic multilayer of or made by the method of any one of the preceding claims, wherein the base bilayer, the optional plurality of alternating bilayers, and the terminal bilayer are assembled in a vertical direction, wherein the optical effect article comprises laterally-defined regions having one or more differences in the polymer layers, thereby providing different changes in structural color between the laterally-defined regions upon changing humidity environments.

42. The optical effect article of the immediately preceding claim, wherein the laterally-defined regions form an image.

43. The optical effect article of the immediately preceding claim, wherein the image is visible in certain humidity conditions and invisible in different humidity conditions.

44. A method of using a photonic multilayer, the method comprising changing hydration state in the amphiphilic biopolymer layers in the photonic multilayer of or made by the method of any one of the preceding claims to water vapor, thereby causing a change in distance between the semiconductor layers in the photonic multilayer, thereby changing one or more properties of the structural color exhibited by the photonic multilayer.

45. The method of the immediately preceding claim, wherein changing hydration state reveals a previously-invisible image within the photonic multilayer.

46. The method of either two of the immediately preceding claims, the method further comprising acquiring an image of the photonic multilayer after changing hydration state and performing image analysis on the image.

47. The method of either of the two immediately preceding claims, wherein the previously- invisible image includes a code, such as a one- or two-dimensional barcode.

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