Simple Synthesis of Cellulose-Based Nanocomposites as SERS Substrates for In Situ Detection of Thiram.

There is a growing interest in the use of flexible substrates for label-free and in situ Surface-enhanced Raman Spectroscopy (SERS) applications. In this study, a flexible SERS substrate was prepared using self-assembled Au/Ti3C2 nanocomposites deposited on a cellulose (CS) paper. The Au/Ti3C2 nanocomposites uniformly wrapped around the cellulose fibers to provide a three-dimensional plasma SERS platform. The limit of detection (LOD) of CS/Au/Ti3C2 was as low as 10-9 M for 4-mercaptobenzoic acid(4-MBA) and crystal violet (CV), demonstrating good SERS sensitivity. CS/Au/Ti3C2 was used for in situ SERS detection of thiram on apple surfaces by simple swabbing, and a limit of detection of 0.05 ppm of thiram was achieved. The results showed that CS/Au/Ti3C2 is a flexible SERS substrate that can be used for the detection of thiram on apple surfaces. These results demonstrate that CS/Au/Ti3C2 can be used for the non-destructive, rapid and sensitive detection of pesticides on fruit surfaces.

Ti3C2T x -AuNP based paper substrates for label-free SERS detection of bacteria and multimodal antibacterials.

Bacterial infections have become a serious global health problem due to the misuse of antibiotics which causes the emergence of antibiotic-resistant strains. Photothermal therapy (PTT) has been widely studied in recent years as a method to combat the development of bacterial resistance. However, PPT may cause damage to the human body due to excessive laser power. Therefore, it is important and urgent to develop a multifunctional platform that can sensitively detect bacteria and effectively inhibit or kill bacteria at low laser power. Herein, a novel multifunctional paper substrate of Ti3C2T x -AuNP was successfully synthesized by a self-assembly and freeze-drying method for bacterial detection and photothermal sterilization at low laser power. The typical Gram-negative Escherichia coli (E. coli) and the Gram-positive Methicillin-resistant Staphylococcus aureus (MRSA) were used as models to perform label-free, rapid and sensitive detection of bacteria based on the surface-enhanced Raman spectroscopy (SERS) method with detection limits as low as 105 CFU mL-1 and 5 × 105 CFU mL-1, respectively, demonstrating the paper substrate's ability to detect bacteria with sensitivity and accuracy. The paper substrate of Ti3C2T x -AuNP exhibits significant antibacterial effects when irradiated with 808 nm light at a low laser power of only 300 mW cm-2 and a short irradiation time of 5 minutes, and the germicidal rates for E. coli and MRSA were 99.94% and 92.71%, respectively. At the same time, the paper substrate of Ti3C2T x -AuNP also produces a variety of reactive oxygen species under 808 nm laser irradiation, resulting in photodynamic therapy (PDT). Accordingly, this paper substrate of Ti3C2T x -AuNP can not only sensitively detect bacteria, but also has photothermal and photodynamic sterilization, providing a promising countermeasure for the clinical treatment of diseases caused by multidrug-resistant bacteria.

Plasma amplifiers: multiscale light-enhanced uniform SERS composite substrates for breaking through resonance limitations.

A phenomenon known as plasmon resonance constitutes a unique optical effect that can induce an enhancement in localized electromagnetic fields, resulting in a substantial increase in the electromagnetic field intensity surrounding metallic nanostructures. In this work, the coupling effect of excitation of surface plasmon polaritons and local surface plasmons in nanoparticles is deeply studied under the background of nanoparticles/one-dimension grating composite structures through grating matching. By employing finite-difference time-domain simulations as our methodological approach, we discern gratings with a periodicity of 1.5 µm support surface plasmon bound states between the gratings. Furthermore, the modulation of SPs along the vertical sidewalls of the grating due to standing wave effects exhibits oscillatory behavior with varying grating heights. Experimental results obtained from the nanoparticle/grating composite SERS substrate validate theoretical predictions, demonstrating higher enhanced Raman signals at 633 nm compared to 532 nm. Remarkably, this structure exhibits good performance, with R6G detection sensitivity down to concentrations as low as 10-10 M and mapping achieving a relative standard deviation of 7.79%, underscoring its uniformity and capability of electromagnetic field enhancement.

All-solid highly sensitive fiber-tip magnetic field sensor based on a Fabry-Perot interferometer with a breakpoint structure.

An all-solid fiber-tip Fabry-Perot interferometer (FPI) coated with a nickel film is proposed and experimentally verified for magnetic field sensing with high sensitivity. It is fabricated by splicing a segment of a thin-wall capillary tube to a standard single-mode fiber (SMF), then inserting a tiny segment of fiber with a smaller diameter into the capillary tube, and creating an ultra-narrow air-gap at the SMF end to form an FPI. When the device is exposed to magnetic field, the capillary tube is strained due to the magnetostrictive effect of the nickel film coated on its outer surface. In addition, owing to the unique breakpoint sensitivity-enhancement structure of the air-gap FPI, the elongation of the capillary tube whose length is over 100 times longer than the air-gap width is entirely transferred to the cavity length change of the FPI, and the sensor is extremely sensitive to the magnetic field as proved by our experiments, achieving a high sensitivity of up to 2.236 nm/mT for a linear magnetic field range from 40 to 60 mT, as well as a low-temperature cross-sensitivity of 56 µT/°C. The all-solid stable structure, compact size (total length of ∼3.0 mm), and reflective working mode with high magnetic field sensitivity indicate that this sensor has good application prospects.

Quantitative Analysis of Trace Analytes with Highly Sensitive SERS Tags on Hydrophobic Interface.

Surface-enhanced Raman scattering (SERS) presents a promising avenue for trace matter detection by using plasmonic nanostructures. To tackle the challenges of quantitatively analyzing trace substances in SERS, such as poor enrichment efficiency and signal reproducibility, this study proposes a novel approach using Au@internal standard@Au nanospheres (Au@IS@Au NSs) for realizing the high sensitivity and stability in SERS substrates. To verify the feasibility and stability of the SERS performances, the SERS substrates have exhibited exceptional sensitivity for detecting methyl blue molecules in aqueous solutions within the concentration range from 10-4 M to 10-13 M. Additionally, this strategy also provides a feasible way of quantitative detection of antibiotic in the range of 10-4 M to 10-10 M. Trace antibiotic residue on the surface of shrimp in aquaculture waters was successfully conducted, achieving a remarkably low detection limit of 10-9 M. The innovative approach has great potential for the rapid and quantitative detection of trace substances, which marks a noteworthy step forward in environmental detection and analytical methods by SERS.

Effective enhancement of the non-Hermitian corner skin effect in reciprocal photonic crystals.

With the rich physical phenomena arising from non-Hermitian systems, the non-Hermitian skin effect (NHSE) has become a current research hotspot. Nowadays, the corner skin effect based on non-reciprocal photonic crystals has been proposed. Considering the complexity of realizing non-reciprocity, the corner skin effect based on reciprocal photonic crystals is well worth investigating. In this Letter, a non-Hermitian reciprocal geometry-dependent corner skin effect based on two-dimensional photonic crystals is presented, which is manifested as the distribution of eigenstates on the corners of a particular geometry by applying open boundary conditions in both directions of photonic crystals. For the better application of the NHSE in the future, such as highly sensitive sensors and lasers, a new, to the best of our knowledge, method that can effectively enhance the performance of the NHSE in photonic crystals is proposed. The method introduces both gain and loss in an ideal photonic crystal to enhance the non-Hermitian specificity of the system, which improves the performance of the non-Hermitian corner skin effect of photonic crystals by 64.5%. Furthermore, this geometry-dependent corner skin effect is corroborated with the spectral topology.

Deep learning model for dynamic color design of all-dielectric metasurfaces.

Silicon nanostructure colors have rapidly developed in recent years, offering high resolution and a broad color gamut that traditional pigments cannot achieve. The reflected colors of metasurfaces are determined by the geometric structure of the unit cell and the refractive index matching layer parameters. It is evident that the design of specific colors involves numerous parameters, making it challenging to achieve through conventional calculations. Therefore, the tandem network instead of conventional electromagnetic simulation is natural. The forward part of the network incorporates feature cross terms to improve accuracy, enabling high-precision predictions of structural colors based on structural parameters. The average color difference between the predicted and actual color values in the L,a,b color space is 1.38. The network has been proven to accurately predict the refractive index and height of the refractive index matching layer during the dynamic tuning process. Additionally, the issue of the inverse network converging to incorrect solutions was addressed by leveraging the characteristics of the activation function. The results show that the color difference between the colors designed by the inverse network compared to the actual colors in the L,a,b color spaces is only 2.22, which meets the requirements for commercial applications.

SPRi/SERS dual-mode biosensor based on ployA-DNA/ miRNA/AuNPs-enhanced probe sandwich structure for the detection of multiple miRNA biomarkers.

MicroRNA (miRNA) has broad application prospects in the early detection of various cancers. In this work, a SPRi/SERS dual-mode biosensor was developed on the same gold chip by AuNPs as the reinforcing medium. High throughput and sensitivity detection of three typical cervical cancer markers miRNA21, miRNA124 and miRNA143 were achieved based on the sandwich structure of polyA blocks-DNA capture probe/target miRNA/AuNPs-assistant probe or SERS nanoprobes. AuNPs greatly improved the SPR response due to mass increase and more sensitive refractive index changes. Meanwhile, due to the LSPR effect of AuNPs, the signal of SERS nanoprobe can be amplified. The miRNAs were detected in serum to verify its practicality. SPRi achieved detection of three miRNAs simultaneously. LODs were 6.3 fM, 5.3 fM and 4.6 fM, respectively, and wide dynamic response range of 500 pM-10 nM. While SERS assay ensured high sensitivity with LODs as low as 1 fM, 0.8 fM and 1.2 fM, respectively, and with the recoveries in the range of 90.0 %-100.2 %. The redundant detection signals of the two modes can provide more reliable data to prevent false positive or false negative detection, and have great application prospects in detection of cancer-related nucleic acids in early stage of disease.

Partially coherent twisted vector vortex beam enabling manipulation of high-dimensional classical entanglement.

In this paper, we present a novel form of a partially coherent beam characterized by classical entanglement in higher dimensions. We coin the term "twisted vector vortex (TVV) beam" to describe this phenomenon. Similar to multi-partite quantum entangled states in higher dimensions, the partially coherent twisted vector vortex beam possesses distinct properties such as non-uniform polarization, vortex phase, and twist phase. Through experiments, we offer empirical evidence for these three degrees-of-freedom in the light field. The results demonstrate that the state of the light is inseparable in terms of polarization and orbital angular momentum (OAM) modes. Additionally, the twist phase introduces an additional dimension in controlling the vector vortex beam. This research reveals the possibility of new controlling dimensions in classical entanglement through the chirality of coherence within partially coherent light. Consequently, this opens up new avenues for the utilization of partially coherent light in both classical and quantum domains.

Highly sensitive and selective SERS substrates with 3D hot spot buildings for rapid mercury ion detection.

Heavy metal ions, which are over-emitted from industrial production, pose a major threat to the ecological environment and human beings. Among the present detection technologies, achieving rapid and on-site detection of contaminants remains a challenge. Herein, capillaries with three-dimensional (3D) hot spot constructures are fabricated to achieve repaid and ultrasensitive mercury ion (Hg2+) detection in water based on surface-enhanced Raman scattering (SERS). The 4-mercapto pyridine (4-Mpy) serves as the Raman reporter with high selectivity, enabling the detection of Hg2+ by changes in adsorption configuration at the trace level. Under optimized conditions, the SERS response of 4-Mpy for Hg2+ exhibits good linearity, ranging from 1 pM to 0.1 µM in a few minutes, and the detection limit of 0.2 pM is much lower than the maximum Hg2+ concentration of 10 nM allowed in drinking water, as defined by the US Environmental Protection Agency (EPA). Simultaneously, combined with the theoretical simulation and experimental results, the above results indicate that the SERS substrates possess outstanding performances in specificity, recovery rate and stability, which may hold great potential for achieving rapid and on-site environmental pollutant detection using a portable Raman spectrometer.

Raman Spectroscopy of Emulsions and Emulsion Chemistry.

Emulsions are dispersed systems widely used in various industries. In recent years, Raman spectroscopy (RS), as a spectroscopic technique, has gained much attention for measuring and monitoring emulsions. In this review, we explore the use of RS on emulsion structures and emulsification, important reactions that use emulsions such as emulsion polymerization, catalysis and cascading reactions, as well as various applications of emulsions. We explore how RS is used in emulsions, reactions and applications. RS is a powerful and versatile tool for studying emulsions, but there are also challenges in using RS to monitor emulsion processes, especially if they are rapid or volatile. We also explore these challenges and difficulties, as well as possible designs that can be used to overcome them.

Hough transform-based multi-object autofocusing compressive holography.

Reconstruction of multiple objects from one hologram can be affected by the focus metric judgment of autofocusing. Various segmentation algorithms are applied to obtain a single object in the hologram. Each object is unambiguously reconstructed to acquire its focal position, which produces complicated calculations. Herein, Hough transform (HT)-based multi-object autofocusing compressive holography is presented. The sharpness of each reconstructed image is computed by using a focus metric such as entropy or variance. According to the characteristics of the object, the standard HT is further used for calibration to remove redundant extreme points. The compressive holographic imaging framework with a filter layer can eliminate the inherent noise in in-line reconstruction including cross talk noise of different depth layers, two-order noise, and twin image noise. The proposed method can effectively obtain 3D information on multiple objects and achieve noise elimination by only reconstructing from one hologram.

High overall performance uni-traveling carrier photodiodes for sub-THz wave generation.

Modified near-ballistic uni-traveling-carrier photodiodes with improved overall performances were studied theoretically and experimentally. A bandwidth up to 0.2 THz with a 3 dB bandwidth of 136 GHz and large output power of 8.22 dBm (99 GHz) under the -2V bias voltage were obtained. The device exhibits good linearity in the photocurrent-optical power curve even at large input optical power, with a responsivity of 0.206 A/W. Physical explanations for the improved performances have been made in detail. The absorption layer and the collector layer were optimized to retain a high built-in electric field around the interface, which not only ensures the smoothness of the band structure but also facilitates the near-ballistic transmission of uni-traveling carriers. The obtained results may find potential applications in future high-speed optical communication chips and high-performance terahertz sources.

Phase-insensitive amplifier gain estimation at Cramér-Rao bound for two-mode squeezed state of light.

Phase-insensitive amplifiers (PIAs), as a class of important quantum devices, have found significant applications in the subtle manipulation of multiple quantum correlation and multipartite quantum entanglement. Gain is a very important parameter for quantifying the performance of a PIA. Its absolute value can be defined as the ratio of the output light beam power to the input light beam power, while its estimation precision has not been extensively investigated yet. Therefore, in this work, we theoretically study the estimation precision from the vacuum two-mode squeezed state (TMSS), the estimation precision of the coherent state, and the bright TMSS scenario, which has the following two advantages: it has more probe photons than the vacuum TMSS and higher estimation precision than the coherent state. The advantage in terms of estimation precision of the bright TMSS compared with the coherent state is researched. We first simulate the effect of noise from another PIA with gain M on the estimation precision of the bright TMSS, and we find that a scheme in which the PIA is placed in the auxiliary light beam path is more robust than two other schemes. Then, a fictitious beam splitter with transmission T is used to simulate the noise effects of propagation loss and imperfect detection, and the results show that a scheme in which the fictitious beam splitter is placed before the original PIA in the probe light beam path is the most robust. Finally, optimal intensity difference measurement is confirmed to be an accessible experimental technique to saturate estimation precision of the bright TMSS. Therefore, our present study opens a new avenue for quantum metrology based on PIAs.

Generating a hollow twisted correlated beam using correlated perturbations.

In this study, a twisted correlated optical beam with a dark hollow center in its average intensity is synthesized by correlated correlation perturbation and incoherent mode superposition. This new hollow beam has a topological charge (TC) mode with a zero value compared with a coherence vortex that has a TC mode with a nonzero value. We transform the twisted correlated beam from solid centered to dark hollow centered by constructing a correlation between the twist factor and the spot structure parameter. Theoretical and experimental results show that twist correlation makes the random optical beam an asymmetric orbital angular momentum spectral distribution and a tunable intensity center. Controlling the correlation parameters can make the focal spot of the twisted beam a dark core when the dominant mode of the TC is still zero. The new nontrivial beams and their proposed generation method provide important technical preparations for the optical particle manipulation with low coherence environment.

Ultrasensitive detection of SARS-CoV-2 S protein with aptamers biosensor based on surface-enhanced Raman scattering.

A rapid and accurate diagnostic modality is essential to prevent the spread of SARS-CoV-2. In this study, we proposed a SARS-CoV-2 detection sensor based on surface-enhanced Raman scattering (SERS) to achieve rapid and ultrasensitive detection. The sensor utilized spike protein deoxyribonucleic acid aptamers with strong affinity as the recognition entity to achieve high specificity. The spherical cocktail aptamers-gold nanoparticles (SCAP) SERS substrate was used as the base and Au nanoparticles modified with the Raman reporter molecule that resonates with the excitation light and spike protein aptamers were used as the SERS nanoprobe. The SCAP substrate and SERS nanoprobes were used to target and capture the SARS-CoV-2 S protein to form a sandwich structure on the Au film substrate, which can generate ultra-strong "hot spots" to achieve ultrasensitive detection. Analysis of SARS-CoV-2 S protein was performed by monitoring changes in SERS peak intensity on a SCAP SERS substrate-based detection platform. This assay detects S protein with a LOD of less than 0.7 fg mL-1 and pseudovirus as low as 0.8 TU mL-1 in about 12 min. The results of the simulated oropharyngeal swab system in this study indicated the possibility of it being used for clinical detection, providing a potential option for rapid and accurate diagnosis and more effective control of SARS-CoV-2 transmission.

Self-Assembled MXene-Au Multifunctional Nanomaterials with Various Shapes for Label-free SERS Detection of Pathogenic Bacteria and Photothermal Sterilization.

Early diagnosis of pathogenic bacteria and treatment are essential to prevent further infection. Photothermal therapy (PTT) is a promising sterilization method with advantages of minimal invasiveness and high efficiency. The effect of PTT depends on the performance of photothermal materials. Herein, Ti3C2-Au nanomaterials were prepared by the electrostatic self-assembly method, and the absorption characteristics were modulated by changing the morphology of Ti3C2-Au to achieve high photothermal conversion efficiency and sensitive label-free SERS bacterial detection. The results showed that the prepared Ti3C2-Au had better SERS performance than Au and achieved direct and sensitive detection of Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). Under 808 nm laser irradiation, the photothermal conversion efficiency of Ti3C2-Au nanobipyramids (NBPs) was increased to 50.41% compared with the other two composites. The bactericidal rates of Ti3C2-Au NBPs against E. coli and S. aureus were 95.11 and 99.80% in 8 min, respectively, and the killing rates of nine other bacteria were all above 95%, showing broad-spectrum antibacterial properties. Cell viability studies showed that the Ti3C2-Au NBP had significantly improved biocompatibility compared with the Au NBP and was suitable for biological applications. It can simultaneously realize sensitive bacterial detection and photothermal sterilization and is important for the detection and inhibition of pathogenic bacteria.

Raman spectral classification algorithm of cephalosporin based on VGGNeXt.

In recent years, deep learning has been widely used in the field of Raman spectral classification. However, the majority of the training and test sets are generated by the same device (generally a portable Raman spectrometer), with little difference between them, and the trained model may not be directly applicable to other devices. In this study, we established a database of six cephalosporin Raman spectra and proposed a classification algorithm VGGNeXt for cephalosporin Raman spectra. VGGNeXt takes inspiration from ConvNeXt, borrows some tricks from Swin-T, and re-improves VGG. Training data were high-resolution spectra from a benchtop Raman spectrometer, and test data were low-resolution spectra from a portable Raman spectrometer. The impact of preprocessing and dataset size on algorithm accuracy was explored. The results show that our network outperforms other comparative algorithms in all cases. After preprocessing, the VGGNeXt model achieves 100% accuracy on both full and halved data sets, and 99.9% accuracy when there are only 10 data for each cephalosporin class. The results show that the experimental ideas and processing methods in this paper solve the problems of model transfer and instrument standardization to a certain extent, and the model has good robustness.

Photonic Moiré lattice waveguide with a large slow light bandwidth and delay-bandwidth product.

We proposed an effective approach to enlarge the slow light bandwidth and normalized-delay-bandwidth product in an optimized moiré lattice-based photonic crystal waveguide that exhibits intrinsic mid-band characteristics. A flatband corresponding to a nearly constant group index of 34 over a wide bandwidth of 82 nm centered at 1550 nm with near-zero group velocity dispersion was achieved. A large normalized-delay-bandwidth product of 0.5712 with a relative dispersion of 0.114%/µm was obtained, which is a significant improvement if compared with previous results. Our results indicate that the photonic moiré lattice waveguide could advance slow light applications.

Ultra-Broadband, Omnidirectional, High-Efficiency Metamaterial Absorber for Capturing Solar Energy.

In this study, we investigated an absorber based on a center-aligned tandem nanopillar array for ultra-broadband solar energy harvesting theoretically. A high-efficiency, omnidirectional absorber was obtained by introducing the center-aligned tandem nanopillar array embedded in an Al2O3 dielectric layer. The multi-coupling modes at different wavelengths were interpreted. The strong absorption can be adjusted by changing the radii and heights of nanopillars. According to the simulation results, the average absorptance of the absorber exceeded 94% in the wavelength range from 300 nm to 2000 nm. In addition, the high-efficiency absorption was insensitive to the incident angle and polarization state. The research not only proposed an absorber which possesses a huge potential value for application areas, such as thermal photovoltaic systems, infrared detection, and isotropic absorption sensors, but also pointed out a new way to design an absorber with high efficiency in an ultrabroad wavelength range.