Optical fiber for side emission with surface modification

Abstract

A modified optical fiber for side emission includes a core comprising an optical fiber and a UV-C transparent polymer coating on the core. An average surface roughness of the UV-C transparent polymer coating is in a range of about 0.3 [mu] m to about 0.7 [mu] m, as measured by a root mean square of a distance difference measurement of a surface of the UV-C transparent polymer coating. Fabricating a modified optical fiber for side emission includes contacting a coated optical fiber with a solvent, where the coated optical fiber comprises a UV-C transparent polymer coating, and dissolving at least a portion of the UV-C transparent polymer coating in the solvent to produce a modified optical fiber for side emission, wherein the average surface roughness of the UV-C transparent polymer coating is in the range of about 0.3 [mu] m to about 0.7 [mu] m.

Description

[0001] Cross - Reference to Related Applications

[0002] This application claims the benefit of U.S. Patent Application No. 63 / 424,195, filed on November 10, 2022, the entire content of which is incorporated herein by reference.

[0003] Statement of Government Support

[0004] This invention was made with government support under Grant Nos. 1449500 awarded by the National Science Foundation and 80NSSC21C0034 awarded by the National Aeronautics and Space Administration. The government has certain rights in the invention. Technical Field

[0005] The present invention relates to laterally - emitting optical fibers having modified surfaces for germicidal UV - C disinfection. Background Art

[0006] Germicidal ultraviolet - C (UV - C) disinfection is a widely used technique, which is typically achieved using mercury lamps that have several drawbacks. Light - emitting diodes (LEDs) are mercury - free, and advancements over the past decade have improved their efficiency in the UV - C range. The current limitation of LEDs is the relatively small and limited illumination area of each of their chips, which limits the area or region where LEDs can disinfect microorganisms in water or surface biofilms. Summary of the Invention

[0007] A low - cost and tunable manufacturing method is described to enable germicidal light to be laterally emitted from a flexible glass optical fiber having a core diameter in the range of about 125 μm to about 1500 μm with an ultraviolet - C (UV - C) transparent polymer coating along the length of the optical fiber into air or water. An optical fiber that emits light along the length of the optical fiber is manufactured by partially dissolving the UV - C transparent polymer coating that covers the optical fiber core. The partial dissolution of the polymer coating produces a textured or roughened surface, which facilitates the lateral emission of light from the core of the optical fiber. The optical fiber design facilitates the use of UV - LED - based light for disinfection, oxidation, or other purposes. The size and flexibility of the laterally - emitting optical fiber (SEOF) allow for germicidal UV - C irradiation in hard - to - reach areas where microbial proliferation often occurs.

[0008] Although the disclosed inventive concept includes those defined in the appended claims, it should be understood that the inventive concept may also be defined in accordance with the following embodiments.

[0009] Embodiment 1 is a modified laterally - emitting optical fiber comprising:

[0010] A core, the core including an optical fiber; and

[0011] A UV-C transparent polymer coating on the core,

[0012] wherein the average surface roughness of the UV-C transparent polymer coating is in the range of about 0.3 μm to about 0.7 μm, as measured by the root mean square of the distance difference measurements of the surface of the UV-C transparent polymer coating.

[0013] Embodiment 2 is the modified side-emitting optical fiber according to Embodiment 1, wherein the optical fiber comprises glass or quartz.

[0014] Embodiment 3 is the modified side-emitting optical fiber according to Embodiment 1 or 2, wherein the core has a diameter in the range of about 125 μm to about 1500 μm.

[0015] Embodiment 4 is the modified side-emitting optical fiber according to any one of Embodiments 1 to 3, wherein the optical fiber has a refractive index in the range of about 1.4 to about 1.6.

[0016] Embodiment 5 is the modified side-emitting optical fiber according to any one of Embodiments 1 to 4, wherein the optical fiber has a numerical aperture in the range of about 0.1 to about 0.5.

[0017] Embodiment 6 is the modified side-emitting optical fiber according to any one of Embodiments 1-5, wherein the thickness of the UV-C transparent polymer coating is in the range of about 5 μm to about 50 μm before modification.

[0018] Embodiment 7 is the modified side-emitting optical fiber according to any one of Embodiments 1-6, wherein the UV-C transparent polymer coating comprises a fluorinated polymer.

[0019] Embodiment 8 is the modified side-emitting optical fiber according to any one of Embodiments 1-7, wherein the UV-C transparent polymer coating comprises nanoparticles having a diameter in the range of about 100 nm to about 500 nm.

[0020] Embodiment 9 is the modified side-emitting optical fiber according to Embodiment 8, wherein the nanoparticles comprise silicon, silicon dioxide oxide, gold, silver, other metals or other metal oxides.

[0021] Embodiment 10 is the modified side-emitting optical fiber according to Embodiment 9, wherein the nanoparticles are functionalized with an aminated organic compound, a carboxylated organic compound or a neutral organic ligand.

[0022] Embodiment 11 is a method of manufacturing a modified side-emitting optical fiber, the method comprising:

[0023] Contact a coated optical fiber with a solvent, wherein the coated optical fiber comprises a UV-C transparent polymer coating; and

[0024] Dissolve at least a portion of the UV-C transparent polymer coating in the solvent to produce a modified side-emitting optical fiber, wherein the average surface roughness of the UV-C transparent polymer coating is in the range of about 0.3 μm to about 0.7 μm.

[0025] Embodiment 12 is the method according to Embodiment 11, wherein the average surface roughness corresponds to the root mean square of the distance difference measurements of the surface of the UV-C transparent polymer coating.

[0026] Embodiment 13 is the method according to Embodiment 11 or 12, wherein the solvent comprises an organic solvent.

[0027] Embodiment 14 is the method according to Embodiment 13, wherein the organic solvent comprises a fluorinated organic solvent.

[0028] Embodiment 15 is the method according to Embodiment 14, wherein the fluorinated organic solvent comprises perfluorotributylamine.

[0029] Details of one or more embodiments of the subject matter of the present disclosure are set forth in the accompanying drawings and the specification. Other features, aspects, and advantages of the subject matter will become apparent from the specification, the drawings, and the claims. Description of the Drawings

[0030] Figure 1 Depicts a portion of a side-emitting optical fiber (SEOF) optically coupled to a light-emitting diode (LED).

[0031] Figure 2 Shows the surface roughness of a glass optical fiber coated with a UV-C transparent polymer, along with varying the treatment duration with perfluorotributylamine.

[0032] Figure 3 Shows the integrated light intensity along a glass optical fiber, along with varying the treatment duration of perfluorotributylamine.

[0033] Figure 4 Shows the load test results of mechanical failures of control optical fibers and optical fibers with low, medium, and high roughness.

[0034] Figure 5 Shows the minimum tolerance of the diameter of fibers with low, medium, and high surface roughness by bending.

[0035] Figure 6Shows the inhibition zones of Pseudomonas aeruginosa around the control and modified SEOF.

[0036] Figure 7 Shows the daily feed water concentration in the biofilm inhibition experiment in the pipe system. Detailed Description

[0037] The present disclosure relates to optical fibers for side-emitting ultraviolet-C (UV-C) (SEOF) for controlling biofilms and inactivating microorganisms in water or air. The outer surface of the UV-C transparent polymer coating on the optical glass fiber can be chemically and / or mechanically modified (altered, e.g., etched, textured, or roughened) to cause light scattering along the length of the fiber. The manufacturing method for making the modified side-emitting optical fiber can be tuned to cause different levels of side-emission of UV-C light. In some cases, such surface modification can be achieved during manufacturing. In other cases, such surface modification is achieved by partially removing the polymer uniformly coated on the optical fiber.

[0038] The light transmission and reflection between two different media (e.g., the optical fiber and the outer polymer layer) are affected by the refractive index (RI) of the environment and the incident angle at the interface. The UV-C transparent polymer CYTOP® used on the fiber has a refractive index (RI) of 1.34, which corresponds to a critical angle (θ c ) of 48° for total internal reflection (TIR) according to Snell's law. Thus, when the incident angle (θ) is between 0° (perpendicular to the surface) and 48°, all the light rays within the CYTOP® layer from the optical fiber can be side-emitted. When the polymer layer is uniform, only a part of the light can be side-emitted.

[0039] Modifying the surface of the outer polymer layer changes the refraction angle of the light in the polymer coating and causes side-emission of UV-C light along the length of the optical fiber. The light rays that nominally would undergo total internal reflection (TIR) can interact with a part of the boundary where the surface roughness changes and have θ < θc, thus causing transmission out of the fiber and causing a change in the direction of the reflected light rays, which can lead to further transmission through the boundary. Figure 1 Depicts a portion of a side-emitting optical fiber 100 having a core 102 and a UV-C transparent polymer coating 104 above the core. The degree of surface modification of the polymer is an adjustable parameter that can be changed to regulate the amount of UV-C light side-emitted from the fiber.

[0040] As described herein, an optical fiber core (e.g., glass or quartz) is typically coated with a flexible UV-C transparent polymer. Suitable examples of these polymeric materials include fluorinated polymers (e.g., CYTOP®). The core diameter of the optical fiber is typically in the range of about 125 μm to about 1500 μm, the refractive index of the optical fiber is typically in the range of about 1.4 to about 1.6, and its numerical aperture is typically in the range of about 0.1 to about 0.5. In some examples, the thickness of the polymer coating before modification is in the range of about 5 μm to about 50 μm. The polymer protection is used to protect the side-emitting optical fiber from physical damage and to achieve its bendability (i.e., maintain strength).

[0041] The polymer-coated optical fiber can be contacted with a solvent to partially dissolve the polymer coating to produce a modified (e.g., roughened) surface layer. In some examples, suitable solvents for partially dissolving the polymer include organic solvents (e.g., perfluorotributylamine, perfluoro-N-isopropylmorpholine, perfluoro-1,2-dimethylcyclohexane, or perfluorodecalin). In some examples, perfluorotributylamine is used to partially dissolve the polymer. The contact time of the polymer-coated optical fiber with the solvent is typically up to about 5 hours. Figure 2 The surface roughness of a 500 μm optical fiber is shown, along with varying the treatment duration with perfluorotributylamine. The solvent contact time can vary at different positions along the optical fiber to produce an optical fiber having varying roughness along its length.

[0042] The surface-modified side-emitting UV-C optical fiber can be fabricated to include nanoparticles in the polymer coating to promote light scattering along the length of the fiber. Suitable nanoparticle materials include silicon, silicon dioxide, gold, silver, or other metals or metal oxides. These materials can be functionalized with an aminated organic compound to produce a cationic surface charge, with a carboxylated organic compound to produce an anionic surface charge, or with a neutral organic compound. The nanoparticles can have a diameter in the range of about 100 nm to about 500 nm.

[0043] Mechanical testing confirmed the ability of roughened optical fibers to maintain the desired flexibility and mechanical strength of UV-C polymer-coated optical fibers with roughening. Using spatially sub-nanometer resolution pixelated data collected by an optical profiler, surface roughness was calculated by taking the root mean square of distance difference measurements of hundreds of data points collected at multiple locations on the fiber surface of a modified UV-C transparent polymer coating and a control (unmodified polymer-coated fiber). In some instances, the optical fibers for side emission had an average surface roughness in the range of about 0.3 μm to about 0.7 μm after contact with a solvent. Concomitant data collected by scanning electron microscopy (SEM) confirmed the optical profiler data, i.e., the surface modification changed the surface roughness. The solvent contact time can vary at different locations along the optical fiber to produce an optical fiber having varying roughness along its length.

[0044] Disclosed herein is a “subtractive engineering” method in which surface roughness on the outer CYTOP® polymer layer of SEOF is created by partially removing the outer CYTOP® polymer coating. This is achieved by exposing the SEOF to a solvent that dissolves the CYTOP® polymer (see Experiment 1), which creates surface roughness. The degree of surface roughness is controlled by exposing the SEOF to a solvent (e.g., perfluorotributylamine) for various treatment times. Longer treatment times in the solvent result in more “patches” or “roughness” on the outer polymer layer, with the surface roughness value increasing from 0.3 μm to over 0.6 μm. SEM and optical profiler measurements were used to monitor the resulting surface changes and quantify them as surface roughness parameter (SR, see Example 5).

[0045] The original coating had a very low SR value of 0.3 ± 0.02 μm, which was consistent with the on-line optical measurements performed in the draw tower. Treating the SEOF in the solvent for different durations produced a rougher surface, with the SR value increasing up to 0.65 ± 0.03 μm ( Figure 2 ).

[0046] The control SEOF side emitted 124 ± 6 μW / cm at the proximal end 2 , and decreased exponentially to 8 ± 2 μW / cm at the distal end 2 . For as-received unmodified (control) fibers (SR = 0.3 ± 0.02 μm) to fibers exposed to the solvent for the longest duration (SR ~ 0.6 μm), the light irradiance increased from 147 ± 6 μW / cm at the proximal end 2 to 610 ± 120 μW / cm 2 , and from 11 ± 0.8 μW / cm at the distal end 2 to 57 ± 11 μW / cm 2Therefore, surface roughness has a positive effect on the UV-C light emitted from the side of the SEOF. When the SR exceeds 0.5 μm, the side emission reaches a steady state, and further increases in roughness do not significantly enhance the side emission( Figure 3 ). To enable variable (i.e., adjustable) side-light illumination for SEOFs of different subtractive processes, based on the increase in side emission observed at each SR value, "low SR" is defined herein as approximately 0.3 to approximately 0.4 μm, "medium SR" is defined herein as approximately 0.4 to approximately 0.5 μm, and "high SR" is defined herein as a roughness greater than approximately 0.5 μm. Overall, it was found that after solvent treatment, the side emission increased by at least a factor of 5 at any position along the fiber.

[0047] Although a uniform CYTOP® layer with a thickness of 15 μm was observed before solvent treatment, various dissolution times resulted in less polymer remaining on the fiber. After 5 hours of treatment, the polymer layer completely dissolved in perfluorotributylamine.

[0048] Based on the increased light intensity of the side emission, a higher SR is desired. However, the modified SEOF with a higher SR is physically more brittle and less flexible. Tensile tests were performed on each fiber to determine the effect of surface roughness on the tensile strength. Figure 4 The tensile load-elongation response of the fiber up to the failure load is shown. The axial force that breaks the fiber by axially pulling both ends of the fiber was used to calculate the nominal tensile strength, using a diameter of 500 μm. The as-received fiber with a uniform polymer coating had a tensile strength of 750 MPa. The SEOFs with an SR range of 0.35 μm to 0.5 μm showed strength reductions to 540 MPa and 650 MPa, respectively. For the two most brittle samples, no statistically significant difference in tensile strength was observed between the high-roughness and bare glass fiber without polymer. To correlate the tensile strength with the allowable compliance of the fiber bent in a tube, flexibility measurements were performed by bending the fiber, where the SEOFs with different SR values were sequentially bent around circular mandrels of various sizes. Higher bending ability was observed with higher curvature. The SEOFs with an SR range of 0.35 μm to 0.5 μm met the average curvature of 0.1 - 0.2 mm -1 standard, which has sufficient compliance to be placed into almost all water systems. Further increasing the roughness reduced the flexibility such that there was no statistical difference in the diameter tolerance of the bare glass fiber. Overall, introducing low SR or medium SR (SR < 0.5 μm) onto the fiber with a polymer cladding increased the side emission and maintained the flexibility. The flexibility of the modified SEOF (i.e., capable of bending around a 1 cm radius curve) is suitable for many water applications (i.e., bending within household pipes and POU reactors).

[0049] When bacteria are subjected to UV-C stress from SEOF, biofilm formation is inhibited, producing an "inhibitory zone" (see Example 6). Unmodified SEOF (control) was placed 0.5 cm above the biofilm on an agar plate inoculated with Pseudomonas aeruginosa for overnight (12 h) UV-C exposure, producing an inhibitory zone 0.5 cm wide. The same experiment was conducted using fibers of SEOF with different SR values (solvent treatment times). Two cases were compared: 1) the same UV-C exposure time and different polymer subtraction (solvent treatment) times; and 2) the same polymer subtraction (solvent treatment) time and different UV-C exposures. As Figure 6 shown, the inhibitory zone of Pseudomonas aeruginosa biofilm generated by the tunable side emission of SEOF was significantly increased relative to the control.

[0050] To demonstrate that the SR-modified fibers are flexible enough for use in water systems with narrow geometries and perform better than unmodified fibers in controlling biofilms, a recirculating tube loop experiment was conducted (see Example 7). Five parallel 1-m long pipes were installed on a perforated plate, each pipe having two 180° curves (bending diameter = 10 cm). SEOF was inserted into each pipe. When SEOF was bent inside the pipe, the light intensity of SEOF was measured. Light measurements were made through 3-cm holes located every 10 cm along the length of the pipe, enabling the radiometer to enter the interior of the pipe. There was no more side emission at the bends than along the straight sections of the SEOF. There were two dark controls, one without SEOF and the other without an LED. One reactor was equipped with as-received coated optical fibers (SR = 0.3 μm) that emitted >10 μW / cm 2 along the first 30-cm length and <3 μW / cm 2 between 30 and 100 cm. 2 Then there were two replicated systems equipped with SEOF having a medium SR that provided >10-fold higher and significantly more uniform side emission than the as-received fibers; the light emitted from the side was 55 ± 7.5 μW / cm 2 at the proximal end and 25 ± 2.5 μW / cm 2 at the distal end. The distance between the optical fiber and the inner surface of the pipe ranged from approximately 0 to approximately 0.5 cm.

[0051] Two separate experiments were conducted with initial feed water concentrations of 10 3.9 ±0.07 CFU / mL and 10 5.9 ±0.1 CFU / mL to grow biofilms at high and low bacterial densities, respectively. The feed water Pseudomonas aeruginosa concentrations during the six-day recirculation period for these two experiments are shown in Figure 7 . In the absence of UV-C exposure, a uniform ~800 cfu / cm was formed inside the tubes of the dark controls2 Biofilm (10 2.9 ±0.12 CFU / cm 2 ). In a reactor equipped with non-SR-modified fibers (SR = 0.3 - μm), the biofilm was below the EPA-recommended limit of 100 cfu / cm for the first 20 cm of the tube, 2 where the calculated wall irradiance was ~4.5 μW / cm 2 . However, between 20 and 100 cm of the tube in the same reactor, it was measured as 100 - 800 CFU / cm along the length 2 . There was no statistical difference between biofilm formation and the dark control at the end of the reactor equipped with non-SR-modified fibers. At all positions in the two replicate tube systems with surface-modified SEOF, the measured biofilm density was ~10 CFU / cm 2 (10 0.68 ±0.5 CFU / cm 2 ) and below the EPA-recommended level. Overall, when the 275 nm irradiance calculated at the wetted surface of the tube wall >4.5 μW / cm 2 , the viable bacteria in the biofilm decreased by approximately 2-log.

[0052] Biofilm formation and growth or accumulation rates can be related to the levels of planktonic bacteria in the water flowing through the pipe system. The UV-C inhibition rate is expected to be greater than the biofilm growth rate to control microbial growth on the surface. Therefore, a second set of tube loop tests was conducted using feed water containing a higher level of planktonic Pseudomonas aeruginosa (>10 5 CFU / mL) during recirculation. The same as-received and surface-modified fibers were used. With this feed water, the biofilm in the dark control (10 4.3 ±0.1 CFU / cm 2 ) was higher, which had a planktonic level of >105 CFU / mL. All three reactors with surface-modified SEOF had lower biofilm density than the control reactor and followed the same trend as observed at lower levels of planktonic Pseudomonas aeruginosa. When >4.5 μW / cm 2 was delivered to the wetted surface, a reduction in biofilm density of greater than 1-log was observed in any of the reactors, but lower inhibition was observed for <4.5 μW / cm 2 . However, the degree of inhibition of SEOF on biofilm was different from that in the experiment with lower levels of planktonic Pseudomonas aeruginosa (i.e., <100 cfu / cm 2 ).

[0053] To integrate data from two tube-loop studies, the log reduction of live biofilm density by UV-C (log reduction, compared to unirradiated controls) was combined across all experiments. The resulting trend indicated that delivery of more than 10 to 20 μW / cm from the SEOF to the tube wall 2 resulted in more than a 1-log reduction in biofilm growth. This finding is particularly relevant in continuous recirculation systems, suggesting that higher UV-C irradiance levels may be necessary to maintain sufficient inactivation rates relative to the net growth rate of the planktonic bacterial population capable of continuous surface deposition.

[0054] Example

[0055] Example 1. Preparation and Surface of SEOF Modification

[0056] Customized solarized quartz optical fibers with a core diameter of 500 μm were manufactured at Molex (AZ, USA) and had the following properties: a core refractive index of 1.51 and a numerical aperture of 0.39. A smooth 15-μm thick CYTOP® polymer layer (BELLEX International Crop, Wilmington, DE) was coated onto the fibers in a commercial optical fiber drawing tower (Polymicro / Molex), which resulted in an outer fiber diameter of 528 ± 0.63 μm. To modulate the surface roughness, the ability of 15 types of solvents to gradually dissolve the CYTOP® layer and create a rough surface was evaluated. Among them, perfluorotributylamine, a fluorinated organic solvent (ThermoFisher, A19126) was suitable. This solvent could be replaced by other perfluorinated chemicals (i.e., perfluoro-N-isopropylmorpholine, perfluoro-1,2-dimethylcyclohexane, perfluorodecalin). The SEOF was immersed in the solvent for 0 - 5 hours at 30-minute intervals. The fibers were cut into 30-cm or 1-m lengths using a fiber cleaver (Vytran Fiber Cleaver, Thorlabs, NJ) with a uniform and clean surface verified by an inspection microscope (FS201, 200X, Thorlabs, NJ). The SEOF was assembled into SMA905 connectors and connected to an 80-mW UV-C LED driver (PearlLab Beam, AquiSense Technologies, Kentucky, U.S.A.) at 1-mm spacing distances. The UV-C LED module included a small fan and a heat sink on the back of the LED for heat dissipation.

[0057] Example 2. Flexibility Measurement, Method A

[0058] Tensile tests were performed on the modified SEOF to quantify the flexibility of SEOF with different surface roughnesses. The 30 cm SEOF treated with solvents for different times was fixed to an MTS 810 Load Frame and an MTS Exceed 42.503 Load Frame (MTS Headquaters, MN, USA). The SEOF was designed to be mounted on a curved surface where light from any UV lamp or LED chip was difficult to reach. Tensile strength tests were carried out through two clamps on each side of the fiber at a constant strain rate. The stress (force, N) required to pull out the fiber and the diameter (cm) required to bend the fiber into a circle until the sample broke were collected and compared for different treatments. The force required to pull off until fracture was equal to the stress required for bending fracture.

[0059] Example 3. Flexibility Measurement, Method B

[0060] Tensile tests were performed on the modified SEOF to quantify the flexibility of SEOF with different surface roughnesses. The 15 cm SEOF treated with solvents for different times was fixed to an MTS 810 Load Frame and an MTS Exceed 42.503 Load Frame (MTS Headquaters, MN, USA). The tests were carried out through two clamps on each side of the fiber at a constant strain rate. The tensile strength (MPa) required to pull out the fiber and the curvature (mm -1 )( Figure 5 ) required to bend the fiber into a circle until the sample broke were collected and compared for different treatments. Higher bending ability was demonstrated by a higher curvature.

[0061] Example 4. Light Measurement and Attenuation Model

[0062] The irradiance (μW / cm2) of the light emitted from the LED, emitted into the optical fiber, emitted from the side surface of the SEOF, or exiting the end of the optical fiber was measured by an optical spectro - radiometer (AvaSpec - 2048L, Avantes, CO). The measurements of the distance along the fiber length or perpendicular to the fiber surface were recorded. The measurements were made on the originally manufactured fibers and the fibers with different surface roughness modifications reduced. The UV - C dose at the surface was calculated using Equation 1:

[0063] UV - C dose (mJ / cm 2 ) = light intensity (mW / cm 2 ) × time (sec) (1)

[0064] The light intensity perpendicular to and away from the SEOF is the actual light intensity illuminating the surface. The light attenuating in air follows the Beer-Lambert law, which shows an exponential decrease along the distance. The light intensity at 0.5 cm, 1 cm, 1.5 cm, and 2 cm for each fiber is measured by a radiometer. Based on these measurements, a mathematical model is created according to Equation 2:

[0065] I (μW / cm 2 ) = I0e -kd (2)

[0066] where I (μW / cm 2 ) is the light intensity at a distance d (cm) perpendicular to the SEOF; I0 (μW / cm 2 ) is the light intensity measured on the surface of the SEOF; k (cm -1 ) is the attenuation coefficient. The cumulative power output (mW) of the light emitted along the SEOF is calculated using Equation 3:

[0067] (3)

[0068] where L (cm) and D (cm) are the length and diameter of the optical fiber, respectively.

[0069] Example 5. Surface Topography Measurement

[0070] The cross-sections of the SEOFs with and without surface modification are imaged by a scanning electron microscope (SEM) (FEI Philips XL-30, Eindhoven, the Netherlands). The changes in the CYTOP® layer are observed. The samples are mounted with graphite adhesive and coated with carbon, and then examined at a voltage of 10 kV. The surface roughness is further quantified by an optical profiler (Zygo ZeScope). SEOFs treated with solvent for 0 h, 1 h, 2 h, 3 h, 4 h, and 5 h are selected. A 50X objective lens combined with a 1.25x magnification changer is used for the best visualization of the fiber surface. At least three measurements are made along the length of each fiber sample, and each measurement gives a 3D image of 100-μm × 50-μm. Then the root mean square roughness (R rms ) of the surface is reported to compare the surface roughness between the samples. Figure 2Shows the change in the surface roughness of a 500-μm optical fiber with the duration of treatment with perfluorotributylamine. An attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectrometer (IFS 66v / S, Bruker Instruments, Billerica, MA, USA) was used to determine the changes in the functional groups associated with the CYTOP® layer before and after surface roughness modification. The spectrometer was equipped with a diamond crystal at an angle of 45°, and the average of 64 scans was collected for each scan during the measurement process.

[0071] Example 6. UV-C Exposure and Inhibition Region Analysis

[0072] First, Pseudomonas aeruginosa (ATCC 15692) was cultured overnight in LB medium (see Table 1) at 37 °C. Then, a 1-mL suspension was transferred to 25 mL of fresh LB medium and cultured at 37 °C until the optical density reached 1 cm -1 , which represents a bacterial concentration of approximately 10 9 CFU / mL. The suspension was diluted 100-fold with phosphate-buffered saline (PBS) solution (see Table 1) to obtain a 10 7 CFU / mL culture, which was then spread onto a grid square LB agar plate. The aim was to produce a thick cell layer to represent a biofilm. The SEOF was placed in the middle of the Petri dish, and the distance between the SEOF and the surface was approximately 0.5 cm. The SEOF was placed in the middle of the Petri dish, and the distance between the SEOF and the surface was approximately 0.5 cm. Immediately after cell spreading, UV-C exposure for 1 hour, 2 hours, or 3 hours was applied using the surface-modified SEOF.

[0073] After UV-C irradiation, the fiber was removed, and the plate was cultured at 37 °C for 12 hours. The distance between the two boundary edges where biofilm did not grow, centered at the position where the SEOF was placed, was defined as the inhibition zone. The irradiance at the edge was calculated using Equation 2 and correlated with the inhibition zone (cm) to determine the UV-C dose required to control the biofilm on the nutrient-rich agar surface. Additionally, three controls were performed: 1) inoculated agar surface without SEOF; 2) inoculated agar surface with only an unmodified SEOF inserted, without UV-C exposure; 3) inoculated agar surface with an unmodified SEOF inserted, with UV-C exposure overnight. Triplicate data were obtained using three different optical fibers on three different agar plates.

[0074] Example 7. Biofilm Inhibition Experiment in Water Using a Flexible Plastic Tubular Reactor

[0075] Pseudomonas aeruginosa was incorporated into the feed water reservoir reactor (4 L) containing 0.1 X M9 culture medium (see Table 1). The initial feed water concentration was 10 3.9±0.07 CFU / mL and 10 5.9 ±0.1 CFU / mL in two separate experiments to grow biofilms at high and low bacterial densities, respectively. The influent water Pseudomonas aeruginosa concentrations during the six-day recycle period for these two experiments are shown in Figure 7 . Standard household POU pipes (i.e., water heaters, bathroom / kitchen sinks) range in size from 0.5 cm to 1.9 cm; thus, a 1 cm pipe size was chosen. A single pump continuously recirculated the influent water through five parallel tubular reactors (1 cm in diameter, 1 m in length, polypropylene). Polypropylene was chosen because it is commonly used in household POU pipes. A needle valve controlled the flow through each tubular reactor, which was set at 200 mL / min and could be monitored by an in-line flow meter. Each 1 m long polypropylene tubular reactor included two 180° elbows to simulate potential real-world POU applications where a flexible SEOF might be more appropriate than a single point light source. The SEOF was inserted into the tubular reactor.

[0076] There were five parallel tubular reactors: 1) a control without SEOF; 2) a control with SEOF that was not irradiated (i.e., no LED); 3) an unmodified SEOF connected to an LED to represent lower radiant UV-C dose conditions; 4) and 5) were identical replicates where two moderately roughened modified SEOFs were connected to an LED to represent higher radiant UV-C dose conditions. The experiments involved water flowing continuously through the tubular reactors for 1 to 7 days. At the end of each experiment, 1 m sections of tubing were removed from the quick-disconnect device and ten equal-length specimens (3 cm) were cut out every 10 cm using a sterile razor. Each specimen was sonicated separately for 15 minutes to dislodge the biofilm from the surface into a PBS solution. The dislodged bacteria were cultured and counted on LB agar plates, and the data were used to calculate the biofilm density (CFU / cm 2 ) on the 3 cm tubing sections.

[0077] Table 1. Characteristics of LB medium, M9 medium, and PBS solution

[0078]

[0079] Although this disclosure contains many specific implementation details, these should not be construed as limitations on the scope of the subject matter or the scope that may be claimed, but rather as descriptions of features that may be specific to particular embodiments. Certain features described in the context of separate embodiments in this disclosure may also be implemented in combination in a single embodiment. Conversely, the various features described in the context of a single embodiment may also be implemented separately or in any suitable sub-combination in multiple embodiments. Moreover, although the previously described features may be described as acting in certain combinations and even initially claimed as such, in some cases, one or more features from the claimed combination may be deleted from the combination, and the claimed combination may be directed to a sub-combination or a variation of the sub-combination.

[0080] Particular embodiments of the subject matter have been described. Other embodiments, modifications, and permutations of the described embodiments are within the scope of the appended claims and will be apparent to those skilled in the art. Although the operations are depicted in the drawings or the claims in a particular order, this should not be construed as requiring that the operations be performed in the particular order shown or in sequential order, or that all of the illustrated operations be performed (some operations may be considered optional) to achieve the desired result.

[0081] Accordingly, the previously described example embodiments do not define or constrain this disclosure. Other changes, substitutions, and alterations are possible without departing from the spirit and scope of this disclosure.

Claims

1. A modified side-emitting optical fiber comprising: a core comprising an optical fiber; and a UV-C transparent polymer coating on the core, wherein the average surface roughness of the UV-C transparent polymer coating is in the range of about 0.3 μm to about 0.7 μm, as measured by the root mean square of the distance difference measurements of the surface of the UV-C transparent polymer coating.

2. The modified side-emitting optical fiber according to claim 1, wherein the optical fiber comprises glass or quartz.

3. The modified side-emitting optical fiber according to claim 1, wherein the core has a diameter in the range of about 125 μm to about 1500 μm.

4. The modified side-emitting optical fiber according to claim 1, wherein the optical fiber has a refractive index in the range of about 1.4 to about 1.

6.

5. The modified side-emitting optical fiber according to claim 1, wherein the optical fiber has a numerical aperture in the range of about 0.1 to about 0.

5.

6. The modified side-emitting optical fiber according to claim 1, wherein the thickness of the UV-C transparent polymer coating before modification is in the range of about 5 μm to about 50 μm.

7. The modified side-emitting optical fiber according to claim 1, wherein the UV-C transparent polymer coating comprises a fluorinated polymer.

8. The modified side-emitting optical fiber according to claim 1, wherein the UV-C transparent polymer coating comprises nanoparticles having a diameter in the range of about 100 nm to about 500 nm.

9. The modified side-emitting optical fiber according to claim 8, wherein the nanoparticles comprise silicon, silicon dioxide, gold, silver, other metals, or other metal oxides.

10. The modified side-emitting optical fiber according to claim 9, wherein the nanoparticles are functionalized with an aminated organic compound, a carboxylated organic compound, or a neutral organic ligand.

11. A method of manufacturing a modified side-emitting optical fiber, the method comprising: contacting a coated optical fiber with a solvent, wherein the coated optical fiber comprises a UV-C transparent polymer coating; and dissolving at least a portion of the UV-C transparent polymer coating in the solvent to produce a modified side-emitting optical fiber, wherein the average surface roughness of the UV-C transparent polymer coating is in the range of about 0.3 μm to about 0.7 μm.

12. The method according to claim 11, wherein the average surface roughness corresponds to the root mean square of the distance difference measurements of the surface of the UV-C transparent polymer coating.

13. The method according to claim 11, wherein the solvent comprises an organic solvent.

14. The method according to claim 13, wherein the organic solvent comprises a fluorinated organic solvent.

15. The method according to claim 14, wherein the fluorinated organic solvent comprises perfluorotributylamine.

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