Surface-Plasmonic-Field-Induced Photoredox Catalysis and Mediated Electron Transfer for Washing-Free DNA Detection

Distance-dependent electromagnetic radiation and electron transfer have been commonly employed in washing-free fluorescence and electrochemical bioassays, respectively. In this study, we combined the two distance-dependent phenomena for sensitive washing-free DNA detection. A distance-dependent surface plasmonic field induces rapid photoredox catalysis of surface-bound catalytic labels, and distance-dependent mediated electron transfer allows for rapid electron transfer from the surface-bound labels to the electrode. An optimal system consists of a chemically reversible acceptor (Ru(NH₃)₆³⁺), a chemically reversible photoredox catalyst (eosin Y), and a chemically irreversible donor (triethanolamine). Side reactions with O₂ do not significantly decrease the efficiency of photoredox catalysis. Energy transfer quenching between the electrode and the label can be lowered by increasing the distance between them. Washing-free DNA detection had a detection limit of approximately 0.3 nm in buffer and 0.4 nm in serum without a washing step.     

Amphibious sensor of temperature and refractive index based on D-shaped photonic crystal fibre filled with liquid crystal

ABSTRACT

A D-shaped photonic crystal fibre filled with liquid crystal was demonstrated as an amphibious sensor for detection of both temperature and refractive index, when combined with plasma materials. Specifically, the optical component is implanted into a complete optical system ensuring modulation of the external electric field. When the refractive index of the external solution changes from 1.0 to 1.6, the y-polarised mode has a loss spectrum with a wavelength sensitivity of up to 2275 nm/RIU, and the corresponding amplitude sensitivity is ?88.2RIU^?1. When the perceived temperature changes from 15°C to 50°C, the temperature of the sensor is correspondingly expressed as the maximum wavelength sensitivity of 9.09 nm/°C and the amplitude sensitivity of ?0.311°C^?1. In addition, the actual micro-operation processes have been studied in detail, such as polishing depth, coating thickness and coating method. This provides practical ideas for real-time sensing analysis that requires harsh environments.     

A time-dependent density functional study on optical response in all-inorganic lead-halide perovskite nanostructures

Recently, all-inorganic perovskite nanostructures have become a hot research topic due to their unique optical response and novel properties. Here, we theoretically study the optical response in Cs₂PbX₄ and CsPb₂X₅ (X = Cl, Br, and I) nanostructures. First, to study the ground state, we calculate the band structures of the periodic system using the HSE06 method, which shows that all those periodic perovskites possess the direct band gaps, with distribution from 2.225 to 3.536 eV. Their valence band maximum are mainly contributed from both halogen and lead atoms, while the conduction band minimum are mainly contributed from lead atoms. Then, we study the excited state using the time-dependent density functional theory method and find that, with the increase of halogen atom radius, the photogenerated carrier concentrations in perovskite nanostructures become larger, while the surface plasmon resonance becomes localized rather than long-range. Moreover, through the analysis of photocurrent and local field enhancement, Cs₂PbX₄ and CsPb₂X₅ nanostructures exhibit nearly 40 μA photocurrent along the direction of optical polarization. Besides, by regulating the different anions, we predict that field enhancement in Cs₂PbI₄ and CsPb₂I₅ share a much stronger distribution at both the center and border parts of Pb-I planes due to localized plasmon resonance, while other perovskites are distributed at the edge parts of Pb-I planes, caused by long-range plasmon resonance. Our research shows that all-inorganic perovskite nanostructures are great candidate materials for developing optoelectronic devices working in high-frequency and high-energy regions and improving their application in sensitive detection and sensors.     

Single‐Molecule Study of a Plasmon‐Induced Reaction for a Strongly Chemisorbed Molecule

Chemical reactions induced by plasmons achieve effective solar‐to‐chemical energy conversion. However, the mechanism of these reactions, which generate a strong electric field, hot carriers, and heat through the excitation and decay processes, is still controversial. In addition, it is not fully understood which factor governs the mechanism. To obtain mechanistic knowledge, we investigated the plasmon‐induced dissociation of a single‐molecule strongly chemisorbed on a metal surface, two O₂ species chemisorbed on Ag(110) with different orientations and electronic structures, using a scanning tunneling microscope (STM) combined with light irradiation at 5 K. A combination of quantitative analysis by the STM and density functional theory calculations revealed that the hot carriers are transferred to the antibonding (π*) orbitals of O₂ strongly hybridized with the metal states and that the dominant pathway and reaction yield are determined by the electronic structures formed by the molecule–metal chemical interaction.     

Enhanced Photochromism of Diarylethene Induced by Excitation of Localized Surface Plasmon Resonance on Regular Arrays of Gold Nanoparticles

Localized surface plasmon resonance (LSPR) excitation on the photochromic reaction of a diarylethene derivative (DE) was studied by surface enhanced Raman scattering (SERS). UV and visible light irradiations transform reversibly DE between open-form (OF) and closed-form (CF) isomers, respectively. A mixture of PMMA and DE (either OF or CF isomer) was spin-coated onto gold nanorods (GNRs) arrays, designed by electron beam lithography, with two localized surface plasmon resonances (LSPR) at distinct wavelengths, due to their anisotropy. The photochromic reaction rates from CF to OF isomers, under LSPR excitation, were monitored from SERS spectral changes under different polarizations, on the same GNR substrate to compare the effect of LSPR field strength. It appears that the photoisomerization rate was faster when LSPR was excited with the polarization parallel to the GNR long axis. The present results highlight a potential genuine mechanism, from near field LSPR excitation, involved in the photochromic enhancement of diarylethene photochromes.     

Chromatographic separation simulation of metal‐chelating peptides from surface plasmon resonance binding parameters

Some metal‐chelating peptides have antioxidant properties, with potential nutrition, health, and cosmetics applications. This study aimed to simulate their separation on immobilized metal ion affinity chromatography from their affinity constant for immobilized metal ion determined in surface plasmon resonance, both technics are based on peptide‐metal ion interactions. In our approach, first, the affinity constant of synthetic peptides was determined by surface plasmon resonance and used as input data to numerically simulate the chromatographic separation with a transport‐dispersive model based on Langmuir adsorption isotherm. Then, chromatographic separation was applied on the same peptides to determine their retention time and compare this experimental t_R with the simulated t_R obtained from simulation from surface plasmon resonance data. For the investigated peptides, the relative values of t_R were comparable. Hence, our study demonstrated the pertinence of such numerical simulation correlating immobilized metal ion affinity chromatography and surface plasmon resonance.     

Asynchronous sampling for ultrafast experiments with low momentum compaction at the ANKA ring

A high‐repetition‐rate pump–probe experiment is presented, based on the asynchronous sampling approach. The low‐α mode at the synchrotron ANKA can be used for a time resolution down to the picosecond limit for the time‐domain sampling of the coherent THz emission as well as for hard X‐ray pump–probe experiments, which probe structural dynamics in the condensed phase. It is shown that a synchronization of better than 1 ps is achieved, and examples of phonon dynamics of semiconductors are presented.     

Crystal Structure and Mass-, Electronic-, Infrared Spectral Studies on Hexaaqua Ni(II) Bis(O-Tolylazo-Citrazinate) Hexahydrate Complex

A new crystalline octahedral hexaaqua Ni(II) bis(o-tolylazo-citrazinate)hexahydrate complex was synthesized. The analytical data proved the formation of 1:2 stoichiometry. An X-ray structure investigation has been carried out. The triclinic space group is p and the unit cell parameters are a = 585.5 pm, b = 993 pm, c = 1139.4 pm, α = 101.6°, β = 97.4°, γ = 102.4°. Evaluation of intensity data revealed the structure with an R-value of 0.03 (2316 observed independent reflections). The compound consists of hexaaqua nickel(2+) ions, univalent anions of the carboxylic acid and six additional water molecules per     

Beam focusing through a tapered subwavelength aperture surrounded by dielectric surface gratings

A novel plasmonic nanolens formed by a tapered subwavelength metal slit surrounded by surface dielectric gratings is proposed and demonstrated numerically. By patterning surface corrugations on the output surface, the beam can be focused, by regulating the aperture, the focal length can be controlled effectively. Numerical simulations using Finite-Difference Time-Domain (FDTD) method coupled with anisotropic perfectly matched layer (APML) boundary conditions verify that the proposed metallic lens can focus the radiation on the scale of a wavelength below the substrate and the method is effective for the design of nano-optical devices such as optical microprobes.     

Synthesis and photophysical study of silver nanoparticles stabilized by unsaturated dicarboxylates

Solution-phase synthesis of nanometer-sized silver particles is reported by sodium borohydride reduction of AgNO_3. Two isomeric dicarboxylates (sodium maleate and sodium fumarate) have been used as stabilizing agents. The dicarboxylate-stabilized silver nanoparticles are characterized by UV-vis spectroscopy, high-resolution transmission electron microscopy (HR-TEM) and fourier transform infrared (FT-IR) spectroscopy. A qualitative comparison is made between the UV-vis spectral characteristic of the SPR band and the simulated curve obtained from modified Mie's theory. Silver nanoparticles prepared using these two isomeric dicarboxylates show intense fluorescence in the visible region. DFT with hybrid functional (B3LYP)-based frequency (IR) calculation of both the dicarboxylates and the respective nanoparticles are in good agreement with the experimental IR frequency. On the basis of this calculation a model has been proposed for the stabilization of silver nanoparticles by these two isomeric dicarboxylate anions.