Application of a thermo-sensitive imprinted SERS substrate to the rapid trace detection of ofloxacin

A zinc oxide-silver nanocomposite-based SERS nanoplatform for ultrasensitive ofloxacin determination in beef and an ophthalmic solution: effects of ZnO and ZnO content on electron transfer and SERS enhancements

Surface-Enhanced Raman Scattering (SERS) is a powerful analytical tool, which is usually based on the use of noble metal nanoparticles. To further improve the performance of SERS sensors, the substrates have been modified, leading to the design and development of metal-semiconductor nanocomposites. In this work, a series of zinc oxide-silver (ZnO/Ag) nanocomposites with different ZnO contents were prepared and employed for Raman measurements of ofloxacin (OFL) to evaluate their SERS performance. By comparing their SERS sensing performance, the effects of ZnO and ZnO content were clarified. With the most optimal ZnO content of 16 wt%, the ZnO/Ag-based SERS sensor could detect OFL at concentrations ranging from 10-3 M to 10-11 M in standard solutions, achieving an ultralow limit of detection (LOD) of 1.5 × 10-11 M. The SERS signal of OFL on ZnO/Ag substrate has been improved with the EF calculated to be 1.8 × 106, which is about 10 times higher than on pure AgNPs (1.7 × 105). This impressive enhancement was achieved by the effects of Ag (electromagnetic and chemical enhancement) and ZnO (adsorption), individually, as well as the combining effects of the two components (additional electromagnetic enhancement and charge transfer). Furthermore, the advanced SERS sensor based on ZnO/Ag nanocomposite substrate could determine OFL content in beef and a commercial OFL ophthalmic solution.

Quantitative monitoring ofloxacin in beef by TLC-SERS combined with machine learning analysis

Ofloxacin is one kind of quinolone antibiotic drugs, the abuse of ofloxacin in livestock and aquaculture may bring bacterial resistance and healthy problem of people. The illegally feeding cattle with ofloxacin will help it keep health, but the sedimentation of ofloxacin could bring problem in food safety. The accurate, simple and instant monitoring ofloxacin from beef by portable sensor was of vital issue in food quality. A simple and reliable method was proposed for instant and quantitative detecting ofloxacin in beef, in which the thin-layer chromatography (TLC) -surface-enhanced Raman scattering (SERS) spectroscopy was in tandem with machine learning analysis base one principal component analysis-back propagation neural network (PCA-BPNN). The TLC plate was composed with diatomite, that was function as the stationary phase to separate ofloxacin from beef. The real beef juice was directly casted onto the diatomite plate for separating and detecting. The directly monitor ofloxacin from beef was achieved and the sensitivity down to 0.01 ppm. The PCA-BPNN was used as reliable model for quantitative predict the concentration of ofloxacin, that shown superior accuracy compared with the traditional model. The results verify that the diatomite plate TLC-SERS combined with machine-learning analysis is an effective, simple and accurate technique for detecting and quantifying antibiotic drug in meat stuff to improve the food safety.

Self-assembly flexible SERS imprinted membrane based on Ag nanocubes for selective detection of microcystin-LR

Silver nanocubes monolayer-modified polydimethylsiloxane (Ag NC/PDMS) flexible SERS substrates have been prepared by a three-phase interface self-assembly procedure. The combination of this method with membrane technology brings nanoparticles in close proximity, densely, and regularly arranged in monolayers over a large area, leading to excellent SERS properties. Considering the complexity of practical detection, molecular imprinted polymers (MIPs) were anchored on the surface of SERS substrate and applied to selective detection of microcystin-LR (MC-LR). It is worth mentioning that the SERS imprinted membranes (AP-MIMs) were still clearly detected at a concentration of 0.1 µg·L-1 of MC-LR in drinking water, and the detection limit was as low as 0.0067 µg·L-1. The substrate exhibited excellent uniformity with a relative standard deviation (RSD) of 6.1%. In the presence of interference molecules, AP-MIMs exhibited excellent selectivity for MC-LR. Furthermore, in the spiking and recovery tests of practical lake water samples, the method showed excellent recoveries ranging from 96.47 to 105.31%. It has been demonstrated that the prepared AP-MIMs can be applied to sensitive and specific detection of trace amounts of MC-LR in drinking water.

Preparation of SiO2@Ag@molecular imprinted polymers hybrid for sensitive and selective detection of amoxicillin using surface-enhanced Raman scattering

In this work, we fabricated a 300 nm-sized silver-coated silica (SiO₂@Ag) SERS substrate. Based on SiO₂@Ag, we designed SiO₂@Ag@molecular imprinted polymers (SiO₂@Ag@MIPs) to realize selectively detection of amoxicillin by coating a molecular imprinted layer averagely thinner than 10 nm on SiO₂@Ag. The as-prepared SERS-active substrate demonstrates excellent enhancement for amoxicillin as well as the enhancement factors were 1.63 × 10⁶ of SiO₂@Ag@MIPs and 2.97 × 10⁵ of SiO₂@Ag, respectively. The SiO₂@Ag@MIPs core-shell hybrids as SERS substrates and the minimum detectable concentration of amoxicillin was as low as 2.7 × 10^-9 M, and the detection limit of SiO₂@Ag was 2.7 × 10^-7 M. The linear relationship between intensities of characteristic peaks and concentrations of amoxicillin was established. Both SiO₂@Ag and SiO₂@Ag@MIPs substrates were highly sensitive and could achieve qualitative and semi-quantitative analysis of amoxicillin in aqueous media with good linear correlations. Based on the above, SiO₂@Ag@MIPs will be conducive to detecting actual samples and expanding the practical application.

Fabrication of a honeycomb-like bimetallic SERS substrate for the detection of triphenyltin chloride

Triphenyltin chloride (TPhT) is an organotin compound that causes intensive toxicological risk to the environment and humans. A detection method with high sensitivity and stability is therefore desired to better detect TPhT. In this study, a novel SERS substrate was prepared by sputtering an ultra-thin Au layer on a honeycomb-like silver nanoarray fabricated via the nanosphere lithography method. The ultra-thin Au layer was formed by sputtering the intermittent Au nanoparticles on the silver nanoarray, resulting in bimetallic coupling with dramatically increased hotspots and extremely high SERS enhancement with an analytical enhancement factor (AEF) of 6.08 × 10⁹ using Rhodamine 6G (R6G) as the probe molecule. Based on density functional theory (DFT) simulations, the Raman characteristic peaks of TPhT at 999 cm^-1 and 655 cm^-1 were selected for TPhT detection. The AEF of the SERS substrate HC5-AgAu was calculated to be 3.38 × 10⁶ with the detection concentration of TPhT down to 10^-10 M. The as-prepared honeycomb-like silver-gold bimetallic SERS substrate demonstrated great stability and sensitivity for TPhT detection, which might also be applied in monitoring many other environmental pollutants.

Study on surface enhanced Raman scattering of Au and Au@Al2O3 spherical dimers based on 3D finite element method

In this paper, the surface enhanced Raman scattering (SERS) characteristics of Au and Au@Al₂O₃ nanoparticle dimers were calculated and analyzed by using finite element method (3D-FEM). Firstly, the electric field enhancement factors of Au nanoparticles at the dimer gap were optimized from three aspects: the incident angle of the incident light, the radius of nanoparticle and the distance of the dimer. Then, aluminum oxide is wrapped on the Au dimer. What is different from the previous simulation is that Al₂O₃ shell and Au core are regarded as a whole and the total radius of Au@Al₂O₃ dimer is controlled to remain unchanged. By comparing the distance of Au nucleus between Au and Au@Al₂O₃ dimer, it is found that the electric field enhancement factor of Au@Al₂O₃ dimer is much greater than that of Au dimer with the increase of Al₂O₃ thickness. The peak of electric field of Au@Al₂O₃ dimer moves towards the middle of the resonance peak of the two materials, and it is more concentrated than that of the Au dimer. The maximum electric field enhancement factor 583 is reached at the shell thickness of 1 nm. Our results provide a theoretical reference for the design of SERS substrate and the extension of the research scope.