Construction of optimized Au@Ag core-shell nanorods for ultralow SERS detection of antibiotic levofloxacin molecules

π-π conjugated PDI supramolecular regulating the photoluminescence of imine-COFs for sensitive smartphone visual detection of levofloxacin

As the contamination and enrichment in food chain of levofloxacin (LV) antibiotics have caused a significant threat to life safety, the instant detection of LV has become an urgent need. Here, a PDI-functionalized imine-based covalent organic framework (PDI-COF300) was prepared by the electrostatic self-assembly method as fluorescent probe for smartphone visual detection of LV, which exhibited excellent fluorescence quantum yield (82.68%), greater stability, high sensitivity with detection limit of 0.303 μM. Based on the results of molecular docking and Stern-Volmer equation, the LV detection by PDI-COF300 was mainly a static quenching process through π-π stacked hydrophobic interactions and fluorescence resonance energy transfer. Besides, PDI-COF300 was applied to LV detection in environmental medium and milk samples with recoveries from 85.56% to 108.34% and relative standard deviations <2.70%. This work also provided a new general strategy for using PDI-COF in smartphone devices and fluorescent papers for LV fluorescence detection and microanalysis.

An accuracy improved ratiometric SERS sensor for rhodamine 6G in chili powder using a metal-organic framework support

Internal standard molecule 4-mercaptobenzoic acid (4-MBA) embedded Au core-Ag shell nanorods (Au-MBA@Ag NRs) were prepared by a seed-mediated growth method, then loaded on octahedral MIL-88B-NH₂ to obtain a novel ratiometric SERS substrate of Au-MBA@Ag NRs/PSS/MIL-88B-NH₂ (AMAPM) for detecting rhodamine 6G (R6G) in chili powder. The porous structure and excellent adsorption ability of MIL-88B-NH₂, allowed for increased loading of Au-MBA@Ag NRs, thereby shortening the distance between adsorbed R6G and the "hot spot" resulting from local surface plasmon resonance (LSPR) of Au-MBA@Ag NRs. Based on the SERS characteristic peak ratio of R6G to 4-MBA, the ratiometric SERS substrate displayed improved accuracy and excellent performance for R6G detection, with a wide linear range of 5-320 nM and a low detection limit of 2.29 nM as well as fine stability, reproducibility and specificity. The proposed ratiometric SERS substrate offered a simple, fast and sensitive sensing strategy for R6G detection in chili powder, which demonstrated potential applications in food safety and the analysis of trace analytes in complex matrices.

Reliable and Rapid Detection and Quantification of Enrofloxacin Using a Ratiometric SERS Aptasensor

Reliable detection and quantification of antibiotic residues in food using surface-enhanced Raman spectroscopy remain challenging, since the intensities of SERS signals are vulnerable to matrix and experimental factors. In this work, a ratiometric SERS aptasensor using 6-Carboxyl-X-Rhodamine (ROX)-labeled aptamers and 4-mercaptobenzonitrile (4-MBN)-functionalized gold nanoparticles (Au NPs) as SERS probes was established for the reliable and rapid detection and quantification of enrofloxacin. In the presence of enrofloxacin, the conformational transform of aptamers took place, and the distance between ROX and Au NP increased, which resulted in a decrease in the SERS signal intensity of ROX. Meanwhile, the intensity of the SERS signal of 4-MBN was used as an internal standard. Reliable determination of enrofloxacin was realized using the ratio of the SERS signal intensities of ROX to 4-MBN. Under optimal conditions, the developed ratiometric SERS aptasensor provided a wide linear range from 5 nM to 1 µM, with a correlation coefficient (R²) of 0.98 and a limit of detection (LOD) of 0.12 nM (0.043 ppb). In addition, the developed ratiometric SERS aptasensor was successfully applied for the determination of enrofloxacin in fish and chicken meat, with recovery values of 93.6-112.0%. Therefore, the established ratiometric SERS aptasensor is sensitive, reliable, time-efficient, and has the potential to be applied in the on-site detection of enrofloxacin in complex matrices.

Recent Progress in Nanotechnology-Based Approaches for Food Monitoring

Throughout the food supply chain, including production, storage, and distribution, food can be contaminated by harmful chemicals and microorganisms, resulting in a severe threat to human health. In recent years, the rapid advancement and development of nanotechnology proposed revolutionary solutions to solve several problems in scientific and industrial areas, including food monitoring. Nanotechnology can be incorporated into chemical and biological sensors to improve analytical performance, such as response time, sensitivity, selectivity, reliability, and accuracy. Based on the characteristics of the contaminants and the detection methods, nanotechnology can be applied in different ways in order to improve conventional techniques. Nanomaterials such as nanoparticles, nanorods, nanosheets, nanocomposites, nanotubes, and nanowires provide various functions for the immobilization and labeling of contaminants in electrochemical and optical detection. This review summarizes the recent advances in nanotechnology for detecting chemical and biological contaminations in the food supply chain.

Sensitive detection of ferbam by coupling solid phase microextraction with surface enhanced Raman spectroscopy based on Au nano-glass capillary

In this study, we developed an innovative approach that combines solid phase microextraction (SPME) with surface-enhanced Raman spectroscopy (SERS) to detect pesticide ferbam rapidly. An Au nano-glass capillary was fabricated by coating template-freely synthesized three-dimensional network Au nanostructures (3D-NW AuNSs) on the roughened surface of glass capillary and used for SPME and SERS respectively. Significant Raman signals were obtained by the SPME-SERS method, followed by detection of ferbam in water and orange juice samples with only 1 min SPME process. Results showed that Au nano-glass capillaries could achieve the detection of ferbam with limit of detection of 0.05 μg/L, and coefficient of determination (R²) of 0.9913. The recovery of predicted results was in the range of 88.46-103.29% and the relative standard deviation (RSD) was 3.5-8.2%. This study demonstrated potential capability of the SPME-SERS method for rapid (within 1 min) and sensitive detection of organic compounds in complex matrices. The SERS-active Au nano-glass capillary is easy to carry and operate, and is expected to play a role in the detection of trace pollutants.

The Role of Surface Enhanced Raman Scattering for Therapeutic Drug Monitoring of Antimicrobial Agents

The rapid quantification of antimicrobial agents is important for therapeutic drug monitoring (TDM), enabling personalized dosing schemes in critically ill patients. Highly sophisticated TDM technology is becoming available, but its implementation in hospitals is still limited. Among the various proposed techniques, surface-enhanced Raman scattering (SERS) stands out as one of the more interesting due to its extremely high sensitivity, rapidity, and fingerprinting capabilities. Here, we present a comprehensive review of various SERS-based novel approaches applied for direct and indirect detection and quantification of antibiotic, antifungal, and antituberculosis drugs in different matrices, particularly focusing on the challenges for successful exploitation of this technique in the development of assays for point-of-care tests.

Shell thickness-controlled synthesis of Au@Ag core-shell nanorods structure for contaminants sensing by SERS

The accessibility of contaminants detection methods is urgently required for environmental and food safety control. In this report, we developed the Au@Ag core-shell nanorod structures for contaminants sensing by surface-enhanced Raman spectroscopy (SERS). The silver shell thickness and the corresponding plasmon wavelength of Au@Ag core-shell nanorods were tuned by changing the coating time and the silver precursor amount. Moreover, these structures exhibit ultra-sensitive detection ability for Nile blue A dye and Fenobucarb pesticide sensing by SERS. Interestingly, the highest Raman enhancement factor is obtained for the Au@Ag core-shell sample with a minimal silver shell thickness leaded by the optimal enhancement of the electromagnetic field of bimetallic structures. Hence, our report demonstrates that the combination of unique features of two plasmonic metals into core-shell structures promises potential applicability in SERS-based analysis.

A Review of Detection of Antibiotic Residues in Food by Surface-Enhanced Raman Spectroscopy

Antibiotics, as veterinary drugs, have made extremely important contributions to disease prevention and treatment in the animal breeding industry. However, the accumulation of antibiotics in animal food due to their overuse during animal feeding is a frequent occurrence, which in turn would cause serious harm to public health when they are consumed by humans. Antibiotic residues in food have become one of the central issues in global food safety. As a safety measure, rapid and effective analytical approaches for detecting these residues must be implemented to prevent contaminated products from reaching the consumers. Traditional analytical methods, such as liquid chromatography, liquid chromatography mass spectrometry, and capillary electrophoresis, involve time-consuming sample preparation and complicated operation and require expensive instrumentation. By comparison, surface-enhanced Raman spectroscopy (SERS) has excellent sensitivity and remarkably enhanced target recognition. Thus, SERS has become a promising alternative analytical method for detecting antibiotic residues, as it can provide an ultrasensitive fingerprint spectrum for the rapid and noninvasive detection of trace analytes. In this study, we comprehensively review the recent progress and advances that have been achieved in the use of SERS in antibiotic residue detection. We introduce and discuss the basic principles of SERS. We then present the prospects and challenges in the use of SERS in the detection of antibiotics in food. Finally, we summarize and discuss the current problems and future trends in the detection of antibiotics in food.

Assessment of the efficiency of synergistic photocatalysis on penicillin G biodegradation by whole cell Paracoccus sp

Background

The Paracoccus sp. strain isolated from sludge was identified and evaluated for catalytic activity in the degradation of penicillin G.

Results

High degradation efficiency and synergistic catalytic effects of the whole cell and visible light without additional catalysts were observed. The key factors influencing the degradation and kinetics of penicillin G were investigated. The results showed the phenylacetic acid, which was produced during penicillin G biodegradation, exhibited stronger inhibiting effects on KDSPL-02. However, this effect was reduced by visible light irradiation without any additional photocatalyst; furthermore, the rate of penicillin G biodegradation was accelerated, reaching a 100% rate in 12 h at a penicillin G concentration of 1.2 g/L. Four key intermediates produced during penicillin G degradation were isolated and identified by LC–MS, ¹H NMR, and ¹³C NMR. Enzymes involved in the PAA pathway were proposed from a genomic analysis of KDSPL-02.

Conclusions

These results provide a new method for bio-degrading of penicillin or other antibiotic pollutants using photoaccelerating biocatalysts with greater efficiency and more environmentally friendly conditions.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13036-021-00275-4.

Silk fibroin fibers decorated with urchin-like Au/Ag nanoalloys: a flexible hygroscopic SERS sensor for monitoring of folic acid in human sweat

Surface-enhanced Raman scattering (SERS) spectroscopy has become a powerful and sensitive analytical tool for the detection and assessment of chemical/biological molecules in special scenarios. Herein we propose a flexible hygroscopic SERS biocompatible sensor based on the silk fibroin fibers (SFF) decorated with urchin-like Au/Ag nanoalloys (NAs). The hybrid SFF-Au/Ag NAs with a stronger absorbance capacity (500∼1100 nm) and excellent hygroscopicity provide a remarkable higher near-infrared (NIR)-SERS activity than that of bare urchin-like Au/Ag NAs. The interesting NIR-SERS sensor enables the limit of detection (LOD) of folic acid (FA) to be achieved at nanomolar (nM, 10^-9 M) level, facilitating the ultrasensitive monitoring of FA in human sweat and offering reliable real-time personal health management in the near future.

Synthesis of Asymmetric One-Dimensional Pd on Au Bimetallic Nanostructures

Nanostructures composed of a gold nanorod (AuNR) core and a Pd/Pt shell are of great interest due to their potential application as plasmon resonance-enhanced catalysts. However, the synthesis of well-defined one-dimensional bimetallic nanostructures with precise control over shell thickness and length remains a challenge. In this study, we report a detailed and systematic study on the chemical synthesis of a uniform Pd shell on single crystalline and pentahedrally twinned (PHT) AuNRs of various lengths. AuNRs were used as a template, and the slow and controlled reduction of Pd(II) ions on preformed AuNRs was carried out for the formation of rectangular-shaped Au@Pd bimetallic nanorods. The Pd shell thickness around the AuNRs was controlled by the supply of Pd(II) ions in the growth solution. We were able to grow a ∼20 nm uniform Pd shell around the AuNR, keeping the rod-like morphology intact without local nucleation to form irregular shapes and randomly overgrown nanostructures. The formation of bimetallic nanorods was also extended beyond typical single crystalline nanorods to PHT high aspect ratio gold nanorods and nanowires, using them as templates. To our surprise, unusually curved asymmetric nanorods were formed when the Pd deposition was carried out on AuNRs longer than ∼800 nm which could be possibly due to a Pd and Au lattice mismatch at the interface and higher flexibility of the nanorods when they exceeded certain lengths.

Onsite/on-field analysis of pesticide and veterinary drug residues by a state-of-art technology: A review

Pesticides and veterinary drugs are generally employed to control pests and insects in crop and livestock farming. However, remaining residues are considered potentially hazardous to human health and the environment. Therefore, regular monitoring is required for assessing and legislation of pesticides and veterinary drugs. Various approaches to determining residues in various agricultural and animal food products have been reported. Most analytical methods involve sample extraction, purification (cleanup), and detection. Traditional sample preparation is time-consuming labor-intensive, expensive, and requires a large amount of toxic organic solvent, along with high probability for the decomposition of a compound before the analysis. Thus, modern sample preparation techniques, such as the quick, easy, cheap, effective, rugged, and safe method, have been widely accepted in the scientific community for its versatile application; however, it still requires a laboratory setup for the extraction and purification processes, which also involves the utilization of a toxic solvent. Therefore, it is crucial to elucidate recent technologies that are simple, portable, green, quick, and cost-effective for onsite and infield residue detections. Several technologies, such as surface-enhanced Raman spectroscopy, quantum dots, biosensing, and miniaturized gas chromatography, are now available. Further, several onsite techniques, such as ion mobility-mass spectrometry, are now being upgraded; some of them, although unable to analyze field sample directly, can analyze a large number of compounds within very short time (such as time-of-flight and Orbitrap mass spectrometry). Thus, to stay updated with scientific advances and analyze organic contaminants effectively and safely, it is necessary to study all of the state-of-art technology.

Graphene oxide-grafted plasmonic Au@Ag nanoalloys with improved synergistic effects for promoting hot carrier-driven photocatalysis under visible light irradiation

Plasmonic metallic nanostructure with unique hot carrier-driven photocatalysis has recently emerged as a promising photocatalyst. Herein, we show that the plasmonic photocatalysis can be significantly promoted by supporting bimetallic Au@Ag nanoalloys (NAs) on graphene oxide (GO). The obtained Au₃@Ag₁/GO (molar ratio of Au to Ag∼3:1) with improved synergistic effects provides a remarkable higher visible-light (>400 nm) photocatalytic activity for a complete degradation (99.36%) of tetracycline hydrochloride (TCH) molecules within 70 min, while about 61.74% or 62.38% via monometallic Au/GO or Ag/GO. The optimum photocatalytic performance is attributed to the production of high yield hot carriers on NAs with enhanced localized surface plasmon resonance property and the pronounced photoinduced electron-transfer ability of modified GO support by overgrowth of NAs. These findings enable the optimal Au₃@Ag₁/GO to become an appealing high-performance photocatalyst for promoting diverse photochemical reactions.

Atomistic description of plasmonic generation in alloys and core shell nanoparticles

Using the extended discrete interaction model we investigate the tunabilty of surface plasmon resonances in alloys and core-shell nanoparticles made from silver and gold in the small (1-15 nm) nanoscale regime where classical models based on the bulk dielectric constant may not apply. We show that the surface plasmon resonance of these alloys and core-shell particles to a large extent follow Vegard's law irrespective of the geometry of the nanoparticle. The evolution of the polarizability with size demonstrates a highly non-linear behaviour of the polarizability with the ratio of the constituents and geometry in alloys and core-shell nanoparticles, with the exception of the longitudinal surface plasmon resonance in nanorods and, partly, nanodisc alloys. We here show that the non-linear behaviour can be explained in terms of the difference in polarizability of the mixing constituents and local effects causing a quenching of the dipoles for geometries with a low aspect ratio. A thorough statistical investigation reveals that there is only a small dependence of the surface plasmon resonance on atomic arrangement and exact distribution in a nanoparticle and that the standard deviation decreases rapidly with the size of the nanoparticles. The physical ground for the random distribution algorithm for alloys in discrete interaction models is explained in detail and verified by a statistical analysis. For nanoparticles below 4 nm a sampling strategy is recommended.

Plasma-assisted electrochemical synthesis of monodisperse Au and Au@Ag core-shell nanoparticles

The synthesis of well defined nanoparticles with green chemistry has been an area of intense investigation, but still requires development. In this study, we propose a novel approach for controlling the particle size and distribution through diffusion-controlled growth of plasma-assisted electrochemical synthesis. The continuous, controlled addition of an Au precursor with syringe pump successfully controls the particle size in the range of 50-300 nm with a monodisperse size distribution. Moreover, gold nanoparticles can be formed successfully without any stabilizer and reducing agent. Through optimization of the reaction parameters, including the reaction temperature, discharge current of the microplasma, pH, and concentration of D-(-)-fructose, we verify two distinct feature of diffusion-controlled growth that the particle growth is good agreement of theoretical growth rate (r ∼ t ^1/3) and the formed gold nanoparticles exhibit polyhedral or near-spherical shapes. This method has been applied to synthesize Au@Ag core-shell nanoparticles and control the Ag shell thickness.