Room temperature strongly coupled quantum emitters based on dna self-assembly plasmonic nanocavity

Abstract

The application relates to the technical field of nanophotonics and quantum optics, and specifically discloses a room-temperature strong-coupling quantum emitter based on a DNA self-assembled plasmonic nanocavity, which comprises a quantum dot and a single-layer closed spherical shell formed by a plurality of gold nanostars through tip interlocking, and a plasmonic resonance nanocavity is formed inside the single-layer closed spherical shell; the gold nanostar surface has asymmetrically distributed sharp protrusions. The application utilizes the synergistic effect of the geometric anisotropy of the gold nanostar and the dynamic bonding of DNA to realize accurate tip interlocking and spontaneous induction of closed curvature, effectively suppress radiation loss, realize strong coupling between a quantum dot exciton and a plasmonic cavity mode at room temperature, present stable Rabi splitting, and reduce the single-photon emission saturation power by about 25 times compared with that of a bare quantum dot. The device can be used as a room-temperature single-photon emission source or applied to a quantum information processing device.

Description

Technical Field

[0001] This application relates to the fields of nanophotonics and quantum optics, and in particular to a room-temperature strongly coupled quantum emitter based on a DNA self-assembled plasma nanocavity. Background Technology

[0002] In the fields of nanophotonics and quantum information processing, achieving strong coupling between a single quantum emitter and an optical cavity mode is fundamental to constructing room-temperature quantum logic gates, quantum key distribution sources, and ultrasensitive single-molecule sensors. This requires the optical cavity to possess both an extremely small mode volume and a sufficiently high quality factor (Q value) to satisfy the strong coupling criterion. However, current technologies still have significant limitations in constructing practical nanocavities capable of stably achieving room-temperature strong coupling.

[0003] While traditional top-down electron beam lithography offers high processing precision, its planar fabrication process limits its ability to construct fully enclosed three-dimensional cavity structures capable of omnidirectionally confining electromagnetic fields. Furthermore, lattice defects at the metal interfaces introduced during processing result in generally low quality factors (typically below 10) for localized surface plasmon resonances. 2 ), which cannot effectively suppress radiation loss.

[0004] In bottom-up self-assembly technology, assembly systems based on DNA origami or isotropic gold spheres lack geometric curvature induction mechanisms, limiting them to two-dimensional planes or simple stacked structures and making it difficult to form low-loss dark modes. Even assembly strategies based on anisotropic units such as gold nanorods, which primarily employ static DNA pairing, cannot dynamically calibrate the spatial orientation of units in the liquid phase, resulting in poor tip interlocking precision, low curvature continuity, and highly discrete and uneven distribution of intracavity "hot spots." Summary of the Invention

[0005] To address the challenges of existing technologies, such as the lack of biomimetic sealing mechanisms, difficulty in controlling the orientation of anisotropic particles, and high radiation loss leading to difficulties in meeting strong coupling conditions, which make it difficult for quantum emitters to be precisely located at the center of a strong field and to obtain stable, high-yield strongly coupled quantum emission devices at room temperature, this application provides a room-temperature strongly coupled quantum emitter based on a DNA self-assembled plasma nanocavity.

[0006] This application provides a room-temperature strongly coupled quantum emitter based on a DNA self-assembled plasma nanocavity, employing the following technical solution: A room-temperature strongly coupled quantum emitter based on a DNA self-assembled plasma nanocavity includes: A single-layer closed spherical shell is formed by multiple gold nanostars interlocking at their tips, and a plasma resonance nanocavity is formed inside the single-layer closed spherical shell; the gold nanostars have an anisotropic structure and their surfaces have asymmetrically distributed sharp protrusions; Quantum dots are encapsulated within the single-layer closed spherical shell. The quantum dots serve as exciton emission sources and are coupled with the optical field of the plasma resonant nanocavity.

[0007] Furthermore, the radius of curvature of the protrusion tips on the surface of the gold nanostar is less than 5 nm.

[0008] Furthermore, the spacing between adjacent protrusions on the surface of the gold nanostar is less than 2 nm.

[0009] Furthermore, the size of the quantum dot is 10-20 nm.

[0010] Furthermore, the size of the gold nanostar is 50-80 nm.

[0011] Furthermore, the single-layer closed spherical shell is composed of 20-30 gold nanostars.

[0012] Furthermore, the surface of the gold nanostar is modified with a first DNA chain, and the surface of the quantum dot is modified with a second DNA chain. The first DNA chain and the second DNA chain achieve encapsulation of the quantum dot at the center of the monolayer closed spherical shell through base complementary pairing.

[0013] Furthermore, the outer surface of the single-layer closed spherical shell is covered with a silver shell layer.

[0014] Furthermore, the outer surface of the silver shell is covered with a silicon dioxide protective layer.

[0015] This application also provides the application of the above-mentioned room-temperature strongly coupled quantum emitter based on DNA self-assembled plasma nanocavity in the preparation of room-temperature single-photon emission sources or quantum information processing devices.

[0016] In summary, this application includes at least one of the following beneficial technical effects: 1. This application utilizes the geometric anisotropy of the asymmetric tips of gold nanostars, combined with DNA dynamic bonding technology, to achieve template-free, fully enclosed three-dimensional core-satellite structure self-assembly. The distance between adjacent gold nanostar tips is less than 2 nm, forming a seamless closed plasmonic shell, overcoming the problem of open or semi-closed cavities caused by the lack of curvature in traditional self-assembly techniques. Through hybridization of localized surface plasmonic resonance at the gold nanostar tips, the electromagnetic field is three-dimensionally localized inside the cavity, forming a highly uniform "hot spot" region with an electric field enhancement factor as high as 6.9 × 10⁻⁶. 10 This significantly reduced radiation loss and yielded a quality factor far exceeding that of traditional plasmon structures.

[0017] 2. This application achieves strong coupling at room temperature by encapsulating a single quantum dot at the center of a plasmonic resonant nanocavity with an extremely small mode volume. Experiments show that the fluorescence emission spectrum of the obtained nanodevice exhibits a spectral split of approximately 220 meV, which is a typical characteristic of strong coupling. Compared to existing technologies where strong coupling effects typically require liquid helium temperatures (<4 K) to be achieved, this application stably obtains a strongly coupled quantum emission device at room temperature, breaking through the temperature limitation and providing a practical light source foundation for room-temperature quantum information processing.

[0018] 3. Due to the all-dimensional photon pumping effect and enhanced local density of states within the enclosed cavity, the photon emission rate of the encapsulated quantum dot is significantly improved. Time-correlated single-photon counting measurements show that the photon saturation power of the bare quantum dot is 118 mW, while the saturation power of the MS-QD@Ag@SiO2 nanodevice fabricated in this application is reduced to 4.77 mW, a reduction of approximately 25 times. This means that at the same excitation power, the single-photon emission brightness of the device in this application is increased by approximately 25 times, while effectively suppressing photobleaching under high excitation power, significantly improving the working stability and lifespan of the single-photon source.

[0019] 4. Unlike traditional static DNA ligation or rigid template methods, this application employs a dynamic orientation calibration mechanism mediated by complementary DNA pendant strands. This allows gold nanostars to adjust their spatial orientation in real time during liquid-phase assembly, achieving "point-to-point" interlocking. This mechanism eliminates interfacial lattice misalignments, ensures the uniformity of the cavity's electromagnetic field distribution, and improves device manufacturing yield and structural consistency. Furthermore, the batch fabrication time of this application is reduced to 6 hours, offering significant cost and efficiency advantages compared to traditional photolithography techniques (3-5 days).

[0020] 5. The DNA modification layer and gold / silver nanoparticles used in this application both exhibit good biocompatibility, and the resulting nanodevices can be applied to single-molecule detection or live-cell imaging in biological systems. Furthermore, by further mineralizing a silica protective layer outside the silver shell, oxidation of the metal surface and environmental interference are effectively isolated, allowing the device to be stored and used for a long time under normal experimental conditions. Its structural stability is significantly better than that of uncoated plasma nanocavities. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the MS-QD@Ag@SiO2 preparation in the embodiments of this application; Figure 2 These are the absorption spectra of the 13 nm gold seeds and gold nanostars in the embodiments of this application; Figure 3This is a comparison diagram of the photon excitation rates of the nanocavities formed by gold nanostars in the embodiments of this application and those of traditional spherical nanocavities; Figure 4 These are the fluorescence emission spectra of quantum dots and the scattering spectra of nanocavities formed by gold nanostars; Figure 5 This is a scanning electron microscope image (scale bar is 100 nm) of MS-QD@Ag@SiO2 prepared in the embodiments of this application. Figure 6 This is the fluorescence emission spectrum of MS-QD@Ag@SiO2 prepared in the embodiments of this application; Figure 7 These are the photon saturation curves of quantum dots and MS-QD@Ag@SiO2 prepared in the embodiments of this application. Detailed Implementation

[0022] The following is in conjunction with the appendix Figure 1-7 This application will be described in further detail.

[0023] This embodiment provides a room-temperature strongly coupled quantum emitter based on a DNA self-assembled plasma nanocavity, the fabrication process of which is as follows: Figure 1 As shown, DNA-1 was modified on the surface of gold nanostars (GNS); a streptavidin layer was assembled on the surface of biotinylated quantum dots (QD-Biotin), followed by the introduction of biotinylated DNA-2. Utilizing the specific recognition effect of biotin-streptavidin, DNA-2 was modified on the surface of the quantum dots; through the complementary base pairing of DNA-1 and DNA-2, the gold nanostars formed a monolayer closed spherical shell to encapsulate the quantum dots; finally, a silver shell layer and a silica protective layer were sequentially coated on the monolayer closed spherical shell formed by the gold nanostars.

[0024] The preparation method includes the following steps: Step 1: Preparation of gold seed solution: Dilute 1 mL of 1% HAuCl4·3H2O aqueous solution to 90 mL of ultrapure water; quickly inject 2 mL of 1% sodium citrate solution and stir magnetically for 10 minutes; add 1 mL of freshly prepared 0.1 M NaBH4 solution dropwise (at a rate of 5 drops per second), and stir overnight at room temperature to obtain the gold seed solution.

[0025] The UV-Vis absorption spectrum of the gold seed solution is as follows: Figure 2 As shown, the absorption peak is located at 520 nm, confirming that the gold seed particle size is 13 nm; the concentration of gold seeds is calculated to be 4.52 nM based on the absorbance at 450 nm.

[0026] Step 2, Preparation and Functionalization of Gold Nanostars: Step 2.1, Preparation of growth solution: The following reagents were added to 10 mg / mL PDDA (polydiallyl dimethyl ammonium chloride): 0.5 mL 1% HAuCl4 solution, 0.1 mL 1 mM AgNO3 solution, and 0.1 mL 0.1 M ascorbic acid (AA) solution; the mixture was stirred vigorously with a magnet for 5 minutes to obtain the growth solution.

[0027] Step 2.2, Growth of Gold Nanostars (GNS): 100 μL of a gold seed solution diluted 10 times was slowly injected into the growth solution; the solution was stirred vigorously overnight at room temperature, and then centrifuged to concentrate it to 1 / 10 of its original volume. PDDA in the growth solution, acting as a capping agent, preferentially adsorbed onto specific crystal faces, promoting anisotropic growth and forming spiny or urchin-like nanoprotrusion structures, thus obtaining gold nanostars (GNS).

[0028] The UV-Vis absorption spectrum of gold nanostars is as follows: Figure 2 As shown, its characteristic absorption peak is located at 650 nm; the final concentration of gold nanostars is calculated to be 97.6 pM based on the absorbance at 450 nm.

[0029] Step 2.3, Reduction and Coupling of Thiolized DNA: a) DNA pretreatment: Mix 100 μM thiolized DNA-1 strand with 10 mM TCEP solution (molar ratio 1:200) and incubate at room temperature for 1 hour to reduce disulfide bonds.

[0030] b) DNA coupling: The reduced DNA-1 and gold nanostars were mixed in 0.5×TBE buffer at a molar ratio of 50000:1 and incubated with shaking at room temperature to obtain DNA-1-GNS.

[0031] c) Purification: Centrifuge, ultrafilter, and wash to remove free DNA; disperse the final product in 1×TAE buffer and store at 4°C.

[0032] Step 3, Quantum Dot (QD) Modification: Quantum dots (average particle size of about 15 nm) are surface carboxylated (e.g., treated with mixed acid), activated with EDC / NHS, and then reacted with amino-biotin (e.g., Biotin-PEG4-NH2) to obtain biotinylated quantum dots (QD-Biotin).

[0033] Take 500 μL of 1 mg / mL ND-Biotin suspension, add 50 μL of 1 mg / mL streptavidin solution, mix well, incubate at room temperature for 1 hour, centrifuge and wash, and resuspend in 500 μL of 1×PBS to obtain streptavidin-modified quantum dot (QD-SA) suspension.

[0034] Take 10 μL of 100 μM Biotin-DNA-2 stock solution, dilute it to 2 μM with 1×PBS, add 500 μL of 2 μM Biotin-DNA-2 solution to the above 500 μL QD-SA suspension, mix well, and incubate at room temperature for 2 hours. Biotinylated DNA-2 will specifically bind to the remaining active binding sites on SA, thereby modifying the surface of quantum dots with DNA-2 to obtain DNA-2-QD; centrifuge and wash to remove free DNA.

[0035] The DNA-1 sequence is: 5'-ATGATATAGACGTTGTGGCAAAAAAAA-Thiol 3'; The DNA-2 sequence is: 5'-GCCACAACGTCTATATCATAAAAAAAA-biotin 3'.

[0036] Step 4, Gold shell assembly: DNA-2-QD and DNA-1-GNS were mixed in 1×TAE buffer at a molar ratio of 1:10 and incubated with shaking at room temperature to obtain quantum dots (MS-QD) encapsulated in a monolayer closed spherical shell of gold nanostars.

[0037] Figure 3 This is a comparison of the photon excitation rates of the nanocavities formed by the gold nanostars in this embodiment (yellow lines) and those of traditional spherical nanocavities (blue lines). Figure 3 It can be seen that the photon excitation rate of the nanocavity formed by gold nanostars is higher than that of the traditional spherical nanocavity.

[0038] The fluorescence emission spectra of quantum dots (QDs) and the scattering spectra of gold nanostars forming nanocavities (MS) are as follows: Figure 4 As shown, the MS resonance peak (650 nm) overlaps with the QD fluorescence peak (650 nm).

[0039] Step 5: Preparation of surface protective layer Add 100 mM silver nitrate solution, 100 mM ascorbic acid solution, and 100 mM sodium hydroxide solution to MS-QD. Stir vigorously at room temperature for 30 minutes until the solution turns light brownish-yellow. Purify at 1500 rpm for 3 minutes to obtain MS-QD@Ag.

[0040] Slowly add 400 μL of TMAPS to 20 mL of 1×TAE solution and stir for 20 minutes. Then slowly add 400 μL of LTEOS and stir for 20 minutes to obtain a mineralization precursor solution. Mix the mineralization precursor solution with MS-QD@Ag and incubate for 1-7 days to grow a mineralization layer, obtaining the final quantum emitter MS-QD@Ag@SiO2.

[0041] Scanning electron microscope image of MS-QD@Ag@SiO2 quantum emitter as shown below Figure 5 As shown, its surface exhibits a protruding structure. The fluorescence emission spectrum of the MS-QD@Ag@SiO2 quantum emitter is as follows: Figure 6 As shown, its fluorescence emission spectrum exhibits a 220 meV split. The photon saturation curve was obtained using time-correlated single-photon counting (TCSPC), as shown below. Figure 7 As shown, the saturation power of the bare quantum dot is 118 mW, while the saturation power of MS-QD@Ag@SiO2 is reduced to 4.77 mW, a decrease of approximately 25 times. This means that under the same excitation power, the single-photon emission brightness of the device in this application is increased by approximately 25 times, while effectively suppressing photobleaching under high excitation power. This significantly improves the working stability and lifespan of the single-photon source, making it suitable for use as a room-temperature single-photon emission source or for application in quantum information processing devices.

[0042] The above are all preferred embodiments of this application, and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A room-temperature strongly coupled quantum emitter based on a DNA self-assembled plasma nanocavity, characterized in that: include: A single-layer closed spherical shell is formed by multiple gold nanostars interlocked at their tips, and a plasma resonance nanocavity is formed inside the single-layer closed spherical shell; The gold nanostars have an anisotropic structure with asymmetrically distributed sharp protrusions on their surface; Quantum dots are encapsulated within the single-layer closed spherical shell. The quantum dots serve as exciton emission sources and are coupled with the optical field of the plasma resonant nanocavity.

2. The room-temperature strongly coupled quantum emitter based on a DNA self-assembled plasma nanocavity according to claim 1, characterized in that: The radius of curvature of the protrusions on the surface of the gold nanostar is less than 5 nm.

3. A room-temperature strongly coupled quantum emitter based on a DNA self-assembled plasma nanocavity according to claim 1, characterized in that: The distance between adjacent protrusions on the surface of the gold nanostar is less than 2 nm.

4. A room-temperature strongly coupled quantum emitter based on a DNA self-assembled plasma nanocavity according to claim 1, characterized in that: The quantum dots have a size of 10-20 nm.

5. A room-temperature strongly coupled quantum emitter based on a DNA self-assembled plasma nanocavity according to claim 1, characterized in that: The gold nanostars have a size of 50-80 nm.

6. The room-temperature strongly coupled quantum emitter based on a DNA self-assembled plasma nanocavity according to claim 1, characterized in that: The single-layer closed spherical shell is composed of 20-30 gold nanostars.

7. The room-temperature strongly coupled quantum emitter based on a DNA self-assembled plasma nanocavity according to claim 1, characterized in that: The surface of the gold nanostar is modified with a first DNA chain, and the surface of the quantum dot is modified with a second DNA chain. The first DNA chain and the second DNA chain are encapsulated at the center of the single-layer closed spherical shell through complementary base pairing.

8. The room-temperature strongly coupled quantum emitter based on a DNA self-assembled plasma nanocavity according to claim 1, characterized in that: The outer surface of the single-layer closed spherical shell is covered with a silver shell layer.

9. A room-temperature strongly coupled quantum emitter based on a DNA self-assembled plasma nanocavity according to claim 8, characterized in that: The outer surface of the silver shell is covered with a silicon dioxide protective layer.

10. The application of the room-temperature strongly coupled quantum emitter based on a DNA self-assembled plasma nanocavity as described in any one of claims 1-9 in the preparation of a room-temperature single-photon emission source or a quantum information processing device.

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