Facile fabrication of three-dimensional gold nanodendrites decorated by silver nanoparticles as hybrid SERS-active substrate for the detection of food contaminants

Laser-chemical composite manufacturing of biomimetic stepped armor functional metal surface with wear resistance and anti-icing characteristics

Superhydrophobic surfaces have been demonstrated to exhibit excellent anti-icing effects, but they are susceptible to the loss of ice repellency as a result of external impacts. This paper proposes a novel bionic armour structure that combines an armour structure with an arrowroot bionic structure. A composite method combining laser etching and chemical modification was employed to achieve superhydrophobicity on the surface of the aluminium alloy. Furthermore, superhydrophobic surfaces with distinctive microstructures were investigated. The findings demonstrated that the contact angles and rolling angles of the second-order armour structure following low surface energy modification reached 158.5° and 3.5°, respectively. Furthermore, the mechanical stability of the surface of the armour step structure was investigated through a sandpaper cyclic wear test. It was observed that conventional micro-cone arrays lost their superhydrophobicity after a single abrasion test, whereas structured superhydrophobic surfaces exhibited a loss of superhydrophobicity after eight abrasion cycle tests. Furthermore, the prepared surface was demonstrated to exhibit excellent anti-icing properties through the simulation and subsequent testing of the delayed icing time of liquid droplets on different surfaces. The icing time of the second-order armoured superhydrophobic surface was found to be 12 times longer than that of the polished aluminium alloy surface. The research presented in this thesis provides new insights into the fabrication of biomimetic superhydrophobic metal surfaces with both good mechanical stability and icing resistance.

Rapid detection of thiram on apple surfaces using a flexible and sticky SERS substrate coupled with chemometric methods

In this paper, we developed a simple, rapid and sensitive method for detection of thiram on apple surfaces by surface enhance Raman spectroscopy (SERS) combined with chemometric methods. Ag NCs (Ag nanocubes) were firstly prepared by a sulfide-mediated polyol method. Then the flexible and adhesive Ag NCs@PDMS substrates were obtained by combining Ag NCs self-assembled films with PDMS films. Thiram residues on apple surfaces were transferred to the substrate using adhesion properties of Ag NCs@PDMS. And the SERS spectra were obtained by Raman microscopy and analyzed with chemometric methods. The results were analyzed by principal component analysis (PCA), for the limit of detection (LOD) of thriam on apple surfaces was 0.01 ppm. Principal component regression (PCR) and partial least squares regression (PLSR) were explored to develop quantitative models. Both models represented higher correlation coefficients (close to 1), but PLSR models exhibited better predictive performance, with the correlation coefficient was 0.99282 with a low root mean squared error of calibration (RMSEC = 0.438) and root mean squared error of validation (RMSECV = 0.597). The developed SERS method based on Ag NCs@PDMS substrate provide a simpler and more sensitive way to monitor thiram on apple surfaces.

Recent Advances in Developing Optical and Electrochemical Sensors for Monitoring Thiram and Future Perspectives

Thiram, as one widely used dithiocarbamate pesticide, has been considered seriously detrimental to food safety and human health because of poor efficiency, nonstandard/superfluous usage, and lack of a targeting effect. Developing high-performance sensors for thirams is strongly needed. With the rapid development of chemistry, biology, and materials science, many sensors have been constructed for thiram with high sensitivity and selectivity. Regarding the energy form of the signal, recognition mode, and detection principle, recent advances in the design and construction of optical and electrochemical sensors for thiram are summarized in this review, including colorimetric, luminescent, chemiluminescent, and electrochemical sensors. The advantages and disadvantages of the sensors for thiram including sensitivity, ability to avoid interference, recognition mechanism, signal output mode, and practicability are clarified in detail. Furthermore, the challenges faced, effective restrictions, and next direction of development are proposed for achieving more sensitive and selective analysis of thiram with less interference. We desire that this review will supply a solid theoretical basis and inspiration to generate innovative thinking for achieving new progress on thiram assays and the commercialization of the developed sensors in the future.

Surface-enhanced Raman scattering based on noble metal nanoassemblies for detecting harmful substances in food

Residues of harmful substances in food can severely damage human health. The content of these substances in food is generally low, making detection difficult. Surface-enhanced Raman scattering (SERS), based on noble metal nanomaterials, mainly gold (Au) and silver (Ag), has exhibited excellent capabilities for trace detection of various substances. Noble metal nanoassemblies, in particular, have extraordinary flexibility and tunable optical properties, which cannot be offered by single nanoparticles (NPs). These nanoassemblies, with their various morphologies synthesized using NPs through artificially induced self-assembly or template-driven preparation, can significantly enhance the local electric field and create "hot spots" due to the gaps between adjacent NPs. Consequently, the SERS properties of NPs become more prominent, leading to improved performance in the trace detection of various substances and detection limits that are considerably lower than the current relevant standards. Noble metal nanoassemblies show promising potential in ensuring food safety. This review discusses the synthesis methods and SERS properties of noble metal nanoassemblies and then concentrates on their application in detecting biotoxins, drug residues, illegal additives, and heavy metals. The study provides valuable references for further research into the application of nanoassemblies in food safety detection.

Engineering the Hot-Spots in Au-Ag Alloy Nanoparticles through Meniscus-Confined 3D Printing for Microplastic Detection

The escalating concern surrounding microplastic (MP) pollution necessitates urgent attention and the development of rapid techniques for quantifying extremely low concentrations. Surface-enhanced Raman spectroscopy (SERS) has emerged as a promising method due to its simplicity, high sensitivity, and rapid quantification capabilities. Herein, the efficacy of gold-silver alloy nanoparticles (3DPAu-Ag) substrates for detecting poly(methyl methacrylate) (PMMA) and polystyrene (PS) MPs is investigated. The 3DPAu-Ag SERS substrates are fabricated using the meniscus-confined electrochemical 3D printing (MC-E3DP) process, employing a nozzle of 0.8 mm size with 2.5 V potential at a printing speed of 0.4 mm s-1. The proposed SERS substrates exhibit exceptional sensitivity and are capable of detecting PMMA concentrations as low as 0.2 μg mL-1 and PS concentrations of 1.2 μg mL-1 within the ranges of 1-103 μg mL-1 and 10-104 μg mL-1, respectively. Remarkable enhancement factors (EFs) of up to 3.2 × 104 for PMMA and 9.3 × 103 for PS are achieved, underscoring the substrates' effectiveness. Furthermore, the investigation demonstrates outstanding uniformity and reproducibility of the 3DPAu-Ag substrates, with relative standard deviation (RSD) values of only 4.1 and 6.4%, respectively, across 31 and 5 measurements. Additionally, a minimal 17% decrease in the initial SERS signal value after 5 weeks highlights the substrates' high stability. This not only highlights the superior quality of the substrates but also positions them ahead of previously reported works in the literature. Moreover, this study also comes up with a plausible mechanism for MPs SERS detection facilitated by the 3DPAu-Ag substrates, offering insights into the underlying processes. Overall, 3DPAu-Ag substrates show promise for sensitive, stable MP detection, which is crucial for environmental monitoring.

Ultrasensitive detection and photocatalytic degradation of polyketide drug tetracycline in environment and food samples using dual-functional Ag doped zinc ferrite embedded functionalized carbon nanofibers

The efficient degradation and accurate quantification of tetracycline in environment and food samples is pivotal for ensuring public health and safety by monitoring potential contamination and maintaining regulatory standards. Hence, in this study, photocatalytic degradation of tetracycline and its electrochemical detection in environment and food samples based on dual-functional silver-doped zinc ferrite nanoparticles embedded chitosan-functionalized carbon nanofibers fabricated on a screen-printed carbon electrode (AgZFO/CHIT-CNF/SPCE) is presented. A hydrothermal method was used in the synthesis of Ag-doped ZFO, and chitosan was functionalized on the CNF surface using a swift and cost-effective chemical modification process of carboxyl groups. Various techniques, such as XRD, HRTEM, elemental mapping, EIS, XPS, FTIR, VSM, BET, UV-Vis DRS, and Raman spectroscopy were used to analyze the characteristics of the prepared nanocomposite. Cyclic voltammetry and differential pulse voltammetry were used to evaluate the surface-controlled electrocatalytic properties of AgZFO/CHIT-CNF towards tetracycline. Electrochemical tests revealed that the proposed electrode exhibited excellent sensitivity for detecting tetracycline. The fabricated electrode had a low detection limit of 1 nM and a wide linear range (0.2-53.2 μM). The sensor also demonstrated exceptional selectivity, stability, and reusability. The practical feasibility evaluated with real samples, including chicken feed, shrimp, milk, soil, and wastewater, resulted in high recovery values.

Ultrasensitive detection of thiram based on surface-enhanced Raman scattering via Au@Ag@Ag core/shell/shell bimetallic nanorods

We developed a highly sensitive and stable SERS-active substrate of Au@Ag@Ag core/shell/shell nanorods, formed by encapsulating Au nanorods (Au NRs) into a bilayer silver shell with Raman reporter molecules (4-mercaptobenzoic acid (4-MBA) and thiram) in the shell-shell gap. The core/shell/shell nanostructures demonstrated a high SERS enhancement and easy assembly. The important role of the bilayer silver shell in boosting the SERS intensity and detection sensitivity was revealed by comparing the performances of the Au@Ag@4-MBA@Ag NRs, Au@Ag@4-MBA NRs, and Au@4-MBA NRs. The obtained Au@Ag@4-MBA@Ag NRs exhibited a significantly promoted SERS intensity, which could reach around 2.6 times and 240 times that of the Au@Ag@4-MBA NRs and Au@4-MBA NRs, where the enhancement factor was found to be strongly correlated with the shell thickness. The controllable plasma properties and SERS effect of the Au@Ag@4-MBA@Ag NRs could be optimized by adjusting the dose of silver nitrate. The SERS substrate comprising core/shell/shell nanorods was highly reproducible and stable (retaining 83% SERS intensity after one month). Moreover, the highly sensitive detection of the pesticide thiram with a detection limit as low as 1.74 × 10-9 M was achieved by taking advantage of the great SERS response of the core/shell/shell nanostructures, which was 1-2 orders of magnitude lower than for other SERS substrates. The developed SERS substrate could be readily extended to embed other target analytes into the core/shell/shell nanostructure for novel and sensitive detection. This study could enable fresh approaches toward next-generation ultrasensitive analyte detection.

Perspectives on Novel Technologies of Processing and Monitoring the Safety and Quality of Prepared Food Products

With the changes of lifestyles and rapid growth of prepared food industry, prepared fried rice that meets the consumption patterns of contemporary young people has become popular in China. Although prepared fried rice is convenient and nutritious, it has the following concerns in the supply chain: (1) susceptible to contamination by microorganisms; (2) rich in starch and prone to stall; and (3) vegetables in the ingredients have the issues of water loss and discoloration, and meat substances are vulnerable to oxidation and deterioration. As different ingredients are used in prepared fried rice, their food processing and quality monitoring techniques are also different. This paper reviews the key factors that cause changes in the quality of prepared fried rice, and the advantages and limitations of technologies in the processing and monitoring processes. The processing technologies for prepared fried rice include irradiation, high-voltage electric field, microwave, radio frequency, and ohmic heating, while the quality monitoring technologies include Raman spectral imaging, near-infrared spectral imaging, and low-field nuclear magnetic resonance technology. These technologies will serve as the foundation for enhancing the quality and safety of prepared fried rice and are essential to the further development of prepared fried rice in the emerging market.

Effect of neutralization treatment on properties of chitosan/bamboo leaf flavonoids/nano-metal oxide composite films and application of films in antioxidation of rapeseed oil

Neutralization treatment improved the slow-release antioxidant food packaging function of chitosan (CS)/bamboo leaf flavone (BLF)/nano-metal oxides composite films. The film cast from the CS composite solution neutralized by KOH solution had good thermal stability. The elongation at break of the neutralized CS/BLF film was increased by about 5 times, which provided the possibility for its packaging application. After 24 h of soaking in different pH solutions, the unneutralized films swelled severely and even dissolved, while the neutralized films maintained the basic structure with a small degree of swelling, and the release trend of BLF conformed to the logistic function (R² ≥ 0.9186). The films had a good ability to resist free radicals, which was related to the release amount of BLF and the pH of the solution. The antimicrobial neutralized CS/BLF/nano-ZnO film, like the nano-CuO and Fe₃O₄ films, were effective in inhibiting the increase in peroxide value and 2-thiobarbituric acid induced by thermal oxygen oxidation of rapeseed oil and had no toxicity to normal human gastric epithelial cells. Therefore, the neutralized CS/BLF/nano-ZnO film is likely to become an active food packaging material for oil-packed food, which can prolong the shelf life of packaged food.

A highly sensitive surface-enhanced Raman scattering sensor with MIL-100(Fe)/Au composites for detection of malachite green in fish pond water

Concerns about food safety have been arisen due to the improper use of chemicals in aquaculture. Malachite green (MG) has attracted attention because of its illegal usage and its potential negative impacts on the environment and public health. Surface-enhanced Raman scattering (SERS) platforms coupled with different SERS substrates have been employed for rapid analysis of MG residues in food. However, the most commonly used SERS substrates were non-reusable and showed limited detection sensitivity. In this study, a novel SERS substrate with a good recyclability and a high sensitivity was prepared by electrostatically assembling together a metal-organic framework material called materials of institute lavoisie-100(Fe) (MIL-100(Fe)) and Au NPs. The lowest detectable concentration of MG was 10^-13 M based on the optimal substrate. The SERS sensor was applied for the detection of the trace MG in fish pond water, which was accomplished with the correlation coefficients R² = 0.991-0.996 in a concentration range of 10^-6-10^-13 M. Moreover, MIL-100(Fe)/Au was recycled at least five times, realizing a "detection to degradation", showing great potential for food contamination monitoring due to its distinguished performance.

A surface-enhanced Raman scattering sensor for the detection of benzo[a]pyrene in foods based on a gold nanostars@reduced graphene oxide substrate

In this study, a simple and sensitive surface-enhanced Raman scattering (SERS) sensor based on gold nanostars@reduced graphene oxide (AuNS@rGO) was successfully developed for the detection of benzo[a]pyrene in foods. The detection strategy involved benzo[a]pyrene adsorption on reduced graphene oxide, followed SERS detection of adsorbed molecules. Owing to the large electric fields generated by the gold nanostars under laser irradiation, which greatly amplified the Raman signals of benzo[a]pyrene, very high sensitivity for the target analyte was achieved. Under optimized conditions, the SERS sensor exhibited a wide linear detection range for benzo[a]pyrene (from 0.1 μg L^-1 to 10000 μg L^-1), with a low limit of detection of 0.0028 μg L^-1. Chicken samples spiked with benzo[a]pyrene were assayed using the sensor, with recoveries ranging from 89.20% to 100.80%. The benzo[a]pyrene content in roasted mutton sample was quantified using the SERS sensor and a reversed-phase high-performance liquid chromatography method, with similar results being obtained.

Label-free DNA detection using silver nanoprism decorated silicon nanoparticles: Effect of silicon nanoparticle size and doping levels

In the present work, we have fabricated silver nanoprism (AgNPrs)/silicon nanoparticle (SiNPs) hybrid arrays for highly sensitive detection of biomolecules via surface-enhanced Raman spectroscopy (SERS) technique. SiNPs having 7 to 37 nm in size and with phosphorous doping varying from 1 × 10¹⁹ to 1 × 10²⁰ cm^-3 were synthesized in nonthermal plasma synthesis. SiNPs were further immobilized on glass substrates using spin-coating, followed by deposition of AgNPrs using the drop-casting method. SERS studies showed that AgNPrs/SiNPs hybrid arrays exhibit substantial amplification of fingerprint bands of rhodamine 6G (R6G) compared to bare silicon as the reference. Raman signal intensity was found to be dependent on the size of SiNPs, with the largest nanoparticles exhibiting the highest SERS enhancement. In addition, an increase in phosphorous doping concentration was found to reduce R6G peak intensities. AgNPrs/SiNPs hybrid arrays showed excellent stability over time and high spot-to-spot reproducibility as well. Moreover, hybrid arrays enabled DNA detection through intense vibrational modes of human genomic DNA, with a lower detection limit of 1.5 pg/µL; indicating that AgNPrs/SiNPs sensors can serve as a reliable and cost-effective biosensing platform for rapid and label-free analysis of biomolecules.

Surface-enhanced Raman scattering based determination on sulfamethazine using molecularly imprinted polymers decorated with silver nanoparticles

Molecularly imprinted polymers (MIPs) were combined with surface-enhanced Raman scattering (SERS) and AgNPs were prepared by in situ reduction within the MIP for selective and sensitive detection of sulfamethazine (SMZ). The MIP@AgNPs composites were characterized in detail by several analytical techniques, showing the generation of polymers and the formation of AgNPs hot spots. The specific affinity and rapid adsorption equilibrium rates of MIP@AgNPs composites were verified by static and kinetic adsorption studies. The MIP@AgNPs with high selectivity and excellent sensitivity were used as SERS substrates to detect SMZ. A good linear correlation (R² = 0.996) in rang of 10^-10-10^-6 mol L^-1 was observed between the Raman signal (1596 cm^-1) and the concentration of SMZ. The limit of detection (LOD) was as low as 8.10 × 10^-11 mol L^-1 with relative standard deviations (RSD) of 6.32%. The good stability and reproducibility are also fully reflected in the SERS detection based on MIP@AgNPs. The method was successfully applied to the analysis of lake water samples, with recoveries in the range 85.1% to 102.5%. In summary, SERS detection based on MIP@AgNPs can be developed for a wider and broader range of practical applications. Schematic illustration of MIP@AgNPs sensor for the SERS detection of sulfamethazine.

Silver-Based Surface Plasmon Sensors: Fabrication and Applications

A series of novel phenomena such as optical nonlinear enhancement effect, transmission enhancement, orientation effect, high sensitivity to refractive index, negative refraction and dynamic regulation of low threshold can be generated by the control of surface plasmon (SP) with metal micro-nano structure and metal/material composite structure. The application of SP in nano-photonics, super-resolution imaging, energy, sensor detection, life science, and other fields shows an important prospect. Silver nanoparticles are one of the commonly used metal materials for SP because of their high sensitivity to refractive index change, convenient synthesis, and high controllable degree of shape and size. In this review, the basic concept, fabrication, and applications of silver-based surface plasmon sensors are summarized.

Nano-Engineered Surface Comprising Metallic Dendrites for Biomolecular Analysis in Clinical Perspective

Metallic dendrites, a class of three-dimensional nanostructured materials, have drawn a lot of interests in the recent years because of their interesting hierarchical structures and distinctive features. They are a hierarchical self-assembled array of primary, secondary, and terminal branches with a plethora of pointed ends, ridges, and edges. These features provide them with larger active surface areas. Due to their enormous active areas, the catalytic activity and conductivity of these nanostructures are higher as compared to other nanomaterials; therefore, they are increasingly used in the fabrication of sensors. This review begins with the properties and various synthetic approaches of nanodendrites. The primary goal of this review is to summarize various nanodendrites-engineered biosensors for monitoring of small molecules, macromolecules, metal ions, and cells in a wide variety of real matrices. Finally, to enlighten future research, the limitations and future potential of these newly discovered materials are discussed.

Au nanoparticles decorated covalent organic framework composite for SERS analyses of malachite green and thiram residues in foods

A three-dimensional (3D) surface-enhanced Raman scattering (SERS) substrate composed of gold nanoparticles (AuNPs) self-assembled covalent organic frameworks (COFs) was fabricated via the electrostatic interaction between positively charged COFs and negatively charged AuNPs, which exhibited excellent SERS performance and were successfully applied for the analyses of malachite green (MG) residue in different seafood products as well as thiram residue in several kinds of fruit juice. The raspberry-like structure SERS substrate has a larger surface area that can provide more adsorption sites in testing and improve the efficiency of sample enrichment. By using this developed SERS substrate, the detection linearity ranges are 1.0 × 10^-9 mol·L^-1-1.0 × 10^-6 mol·L^-1 for MG and 5.0 × 10^-8 mol·L^-1-1.0 × 10^-5 mol·L^-1 for thiram (R² ≥ 0.995). The detection limits are 6.2 × 10^-10 mol·L^-1 for MG and 1.7 × 10^-8 mol·L^-1 for thiram, respectively. The COF-AuNPs substrate was actually applied for analysis of MG in seafood products and thiram in different fruit juice, with the recoveries in the ranges of 94.67-108.99 % for MG and 95.00-107.58 % for thiram, and both of the relative standard deviation (RSD) are no more than 5.88 %. This work indicates that the developed COF-AuNPs substrate is promising for SERS analyses and detections of residues in foods.

Surface-Enhanced Raman Spectroscopy Substrates for Food Safety and Quality Analysis

Surface-enhanced Raman spectroscopy (SERS) has been identified as a fundamental surface-sensitive technique that boosts Raman scattering by adsorbing target molecules on specific surfaces. The application of SERS highly relies on the development of smart SERS substrates, and thus the fabrication of SERS substrates has been constantly improved. Herein, we investigate the impacts of different substrates on SERS technology including plasmonic metal nanoparticles, semiconductors, and hybrid systems in quantitative food safety and quality analysis. We first discuss the fundamentals, substrate designs, and applications of SERS. We then provide a critical review of the recent progress of SERS in its usage for screening and detecting chemical and biological contaminants including fungicides, herbicides, insecticides, hazardous colorants, and biohazards in food samples to assess the analytical capabilities of this technology. Finally, we investigate the future trends and provide practical techniques that could be used to fulfill the requirements for rapid analysis of food at a low cost.

Robotic written silver ink on photographic paper for detection of thiram residues in fruits

With the widespread application of pesticide in agriculture, pesticide residues in food have posed serious health risks to human. There is an urgent requirement to detect pesticide residues in food. In this work, a sensitive and effective method was employed to measure thiram residues in fruit using surface-enhanced Raman scattering (SERS) technique. Silver ink was written on photographic paper (AgNPs-photographic paper) directly by robotic writing technique. The AgNPs-photographic paper substrates possessed good SERS activities and high stability among four months. A good linear response between the peaks intensities and the logarithmic concentrations of thiram was obtained with the limit of detection (LOD) of 0.024 ppb. The substrates also exhibited excellent reproducibility with relative standard deviation (RSD) value less than 10% from ten different substrates. SERS mapping was tested to characterize the uniformity of AgNPs-photographic paper, and the RSD value was calculated to be 14.34% at 1377 cm^-1 measured by 120 points. The LOD values of apple and peach juice adulterated with thiram were 0.0024 and 0.024 ppm, respectively. The LOD values of thiram residues on apple and peach peels were both 0.25 ng/cm². It was demonstrated that the substrates prepared by robotic writing technique had great potential for practical application in food safety inspection.

Ultrasensitive flower-like TiO2/Ag substrate for SERS detection of pigments and melamine

TiO₂ flower like nanomaterials (FLNMs) are fabricated via a hydrothermal method and Ag nanoparticles (NPs) are deposited via electron beam evaporation. Several biological pigments (CV, R6G and RhB) are selected as target molecules to investigate their surface enhanced Raman scattering (SERS) property. The results demonstrate ultrasensitivity and high reproducibility. They reveal that the limit of detection (LOD) is 4.17 × 10^-16 M and the enhancement factor (EF) is 2.87 × 10¹⁰ for CV, and the LOD is 5.01 × 10^-16 M and 7.94 × 10^-14 M for R6G and RhB, respectively. To assess the reproducibility on TiO₂/Ag FLNMs SERS substrates, they are tested with 1.0 × 10^-13 M of CV, 1.0 × 10^-13 M of R6G and 1.0 × 10^-11 M of RhB, respectively. The relative standard deviations (RSD) are less than 12.93%, 13.52% and 11.74% for CV, R6G and RhB, respectively. In addition, we carry out melamine detection and the LOD is up to 7.41 × 10^-10 M, which is over 1000 times lower than the severest standards in the world. Therefore, the obtained TiO₂ FLNMs have potential application in detecting illegal food additives.

Simple Design Concept for Dual-Channel Detection of Ochratoxin A Based on Bifunctional Metal-Organic Framework

A simple fluorescence and electrochemical dual-channel biosensor based on bifunctional Zr(IV)-based metal-organic framework (Zr-MOF) was proposed to detect Ochratoxin A (OTA). The bifunctional Zr-MOF, with photoluminescence properties and enormous electroactive ligands, was exploited to load OTA-specific aptamers for designing signal probes, greatly simplifying the probe-fabrication process and improving sensing reliability. Upon specific recognition of aptamer toward OTA, the anchored probe was released from the sensing interface into the reaction solution. In this circumstance, the increased amount of the signal probe in reaction solution led to an enhanced fluorescence response, while the decreased amount of the signal probe on the sensing interface resulted in a diminished electrochemical response. According to the dual-channel signal change with increasing OTA concentration, the visual fluorescence strategy was established for intuitive OTA detection, and meanwhile, sensitive electrochemical assay with a detection limit of 0.024 pg/mL was also achieved with the help of one-step electrodeposition as a sensing platform. Moreover, the proposed dual-channel assay has been successfully applied to determine OTA levels in corn samples with rapid response, superior accuracy, and high anti-interference capability, providing a promising method for food safety monitoring.

Oil-Free Gold Nanobipyramid@Ag Microgels as a Functional SERS Substrate for Direct Detection of Small Molecules in a Complex Sample Matrix

Surface-enhanced Raman scattering (SERS) is a super-sensitive analysis technology based on the target molecular fingerprint information. The enhancement of local electromagnetic field of the SERS substrate would increase the target molecules' Raman intensity which adsorb on the surface of nanoparticles. However, the existing adhesive macromolecules in the complex mixed sample would interfere with the adsorption of small target molecules, and it weakens the Raman intensity of target molecules. Microgels are one of the potential materials to suppress the interference of adhesive macromolecules and to avoid the complex pretreatments. However, most of the current microgel synthesis methods involve complex operations with precise instrumentation or the interference of oil and organic reagents. In this work, a simple and oil-free method was proposed to synthesize the gold nanobipyramid (Au NBP)@Ag@hyaluronic acid microgel via the condensation reaction of carboxyl and amino groups. As a proof-of-concept demonstration for small-molecule detection, the rhodamine 6G (R6G) molecules were allowed to enter inside the microgel through the meshes and adsorb on the surface of Au NBP@Ag nanoparticles within 30 min, while the macromolecule (bovine serum albumin in this case) was retained outside the microgel in the meantime. In addition, under the combined action of lightning rod effect of Au NBP and surface plasmon resonance effect of silver render the microgels with high SERS activity. The synthetic Au NBP@Ag@hyaluronic acid microgels were applied to detect 6-thioguanine in the human serum without any pretreatment process, and it showed a high signal enhancement and stable SERS signal, which can satisfy the requirement of clinical diagnosis. These results show that the proposed microgels have potential applications in the field of point-of-care testing.

Silicon Microchannel-Driven Raman Scattering Enhancement to Improve Gold Nanorod Functions as a SERS Substrate toward Single-Molecule Detection

The investigation of enhanced Raman signal effects and the preparation of high-quality, reliable surface-enhanced Raman scattering (SERS) substrates is still a hot topic in the SERS field. Herein, we report an effect based on the shape-induced enhanced Raman scattering (SIERS) to improve the action of gold nanorods (AuNRs) as a SERS substrate. Scattered electric field simulations reveal that bare V-shaped Si substrates exhibit spatially distributed interference patterns from the incident radiation used in the Raman experiment, resulting in constructive interference for an enhanced Raman signal. Experimental data show a 4.29 increase in Raman signal intensity for bare V-shaped Si microchannels when compared with flat Si substrates. The combination of V-shaped microchannels and uniform aggregates of AuNRs is the key feature to achieve detections in ultra-low concentrations, enabling reproducible SERS substrates having high performance and sensitivity. Besides SIERS effects, the geometric design of V-shaped microchannels also enables a "trap" to the molecule confinement and builds up an excellent electromagnetic field distribution by AuNR aggregates. The statistical projection of SERS spectra combined with the SIERS effect displayed a silhouette coefficient of 0.83, indicating attomolar (10^-18 mol L^-1) detection with the V-shaped Si microchannel.