•SHINERS technology is extended to Au(111) surface in nonaqueous solutions.•SPR-induced “hot electrons” catalyze hydrogenation reaction on a roughened Au surface.•Shell-isolated nanoparticles isolate “hot electrons” from Au nanoparticles.•Aprotic acetonitrile has no hydrogen source for catalytic hydrogenation.Surface-enhanced Raman spectroscopy (SERS) studies of electrode/solution interfaces are important for understanding electrochemical processes. However, revealing the nature of reactions at well-defined single crystal electrode surfaces, which are SERS-inactive, remains challenging. In this work, shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) was used for the first time to study electrochemical adsorption and hydrogenation reactions at single crystal surfaces in nonaqueous solvents. A roughened Au surface was also studied for comparison. The experimental results show that the hydrogenation of adsorbed p-ethynylaniline (PEAN) on roughened Au electrode surfaces occurred at very negative potentials in methanol because of the catalytic effect of surface plasmon resonance (SPR). However, because “hot electrons” were blocked by the silica shell of Au@SiO2 nanoparticles and aprotic acetonitrile was an ineffective hydrogen source, surface reactions at Au(111) were inhibited in the systems studied. Density functional theory (DFT) calculations revealed that the PEAN triple bond opened, allowing adsorption in a flat configuration on the Au(111) surface via two carbon atoms. This work provides an advanced understanding of electrochemical interfacial processes at single crystal surfaces in nonaqueous systems.Download high-res image (358KB)Download full-size image

The performance of a surface enhanced Raman spectroscopy (SERS) based magnetic immunoassay is critically dependent upon the properties of the magnetic nanoparticles, in which the plasmon enhanced optics and magnetism are integrated together. Tuning SERS activity and magnetism together still remains a significant challenge. Herein, a facile approach for the fabrication of Ni@Au magnetic nanoparticles was developed as the immune substrate for a competitive magnetic immunoassay. Immune Ni@Au nanoparticles and 4-mercaptobenzoic acid (MBA)-labelled immune Au nanoparticles (immune Au-MBA) were employed for detection of aflatoxin B1 (AFB1) through a SERS based competitive magnetic immunoassay. In the immune system, competitive binding with immune Au nanoparticles appeared between the free AFB1 and coating antigen modified Ni@Au nanoparticles; the concentration of AFB1 was determined by comparing the extent of the decrease in the SERS intensity of MBA labels. Based on the relationship between SERS intensity and AFB1 concentrations, the inhibitory concentration 50 (IC50) was determined to be about 27.1 fg mL−1 (around 0.03 ppt) with a reasonable correlation coefficient of 0.997 and the limit of detection was about 0.05 fg mL−1. The observation of unobvious cross-reactions suggested the high specificity of this strategy. By comparing to the traditional determination techniques, the present approach based on Ni@Au nanoparticles exhibited the highest sensitivity. In the spiking experiments, the recoveries ranged from 87.4% to 111.7% after the addition of standard AFB1 at different concentrations in fresh maize samples. The results were also verified by the commonly accepted LC-MS technique. It was revealed that the competitive magnetic immunoassay exhibited the distinct advantage of high sensitivity. The proposed approach is expected to be developed into a promising tool for quasi-quantitative detection of the trace residues of AFB1 in food.

•Fe3O4@Au nanoparticles monolayer film was fabricated at hexane/water interface.•The interparticle spacing was dynamically tuned by external magnetic field.•The response of SERS effect to the magnetic field was completely reversible.•The magnetism responsive film was used as substrate with tunable optical properties.A large surface-enhanced Raman scattering (SERS) effect is critically dependent on the gap distance of adjacent nanostructures, i.e., “hot spots”. However, the fabrication of dynamically controllable hot spots still remains a remarkable challenge. In the present study, we employed an external magnetic field to dynamically control the interparticle spacing of a two-dimensional monolayer film of Fe3O4@Au nanoparticles at a hexane/water interface. SERS measurements were performed to monitor the expansion and shrinkage of the nanoparticles gaps, which produced an obvious effect on SERS activities. The balance between the electrostatic repulsive force, surface tension, and magnetic attractive force allowed observation of the magnetic-field-responsive SERS effect. Upon introduction of an external magnetic field, a very weak SERS signal appeared initially, indicating weak enhancement due to a monolayer film with large interparticle spacing. The SERS intensity reached maximum after 5 s and thereafter remained almost unchanged. The results indicated that the observed variations in SERS intensities were fully reversible after removal of the external magnetic field. The reduction of interparticle spacing in response to a magnetic field resulted in about one order of magnitude of SERS enhancement. The combined use of the monolayer film and external magnetic field could be developed as a strategy to construct hot spots both for practical application of SERS and theoretical simulation of enhancement mechanisms.

Rapid separation and detection of analytes have been the focus of a growing body of investigation for potential applications including food safety and environment science. However, the development of a robust analytical technique for simultaneous rapid separation and on-line detection remains a formidable challenge. Herein, we report a rational design based on the combination of high performance liquid chromatography (HPLC) and surface-enhanced Raman spectroscopy (SERS) for the rapid separation and on-line detection of multi-analytes. In particular, a plasmonic nanoparticle-modified capillary (NPMC) is fabricated through a self-assembly process and connected to a HPLC effluent-end port. After separation by HPLC, the analytes are adsorbed onto plasmonic nanoparticles in the capillary and then detected by SERS. The resulting HPLC-SERS coupled detection system can simultaneously achieve rapid separation and provide on-line molecular structural information of multi-analytes. In addition, we also demonstrate the on-line detection of a pesticide molecule (thiram) in an orange using this combined system. Importantly, the detection limit can be down to 10−7 mol L−1. These findings indicate that our coupled HPLC-SERS system offers a promising analytical technique in modern analytical science and technology.

Human epididymis protein 4 (HE4), as a serological marker, has been proposed to be the most promising tumor marker in ovarian cancer diagnosis. An approach based on surface enhanced Raman spectroscopy (SERS) and a magnetic immunoassay technique was developed successfully for rapid detection and separation of HE4 with high sensitivity and selectivity. The detection was involved in the construction of a unique sandwich structure using a bottom-up method, which consisted of HE4 antibody and SERS reporter coated Au nanoparticles (A) and target HE4 antigen and HE4 antibody-modified magnetic core–shell Fe3O4@Au nanoparticles (B). The sandwich structure was effectively enriched by using a magnet for SERS detection. This approach exhibited an extremely high specificity in the detection of HE4 due to the strong specific interaction between the antibody and the corresponding antigen. The results revealed that the limit of detection (LOD) of the present approach was as low as 100 fg mL−1 and demonstrated a linear relationship between SERS intensities and lgc in a concentration range of 1 pg mL−1 to 10 ng mL−1. Accompanied by the magnetic enrichment procedure after the assembling of the sandwich structure, almost all of the HE4 protein was removed. The immuno Fe3O4@Au nanoparticles were regenerated by releasing the HE4 from the sandwich structure into the acidified methanol solution, and it could be used for magnetic enrichment and SERS detection for at least five times. Moreover, two kinds of immuno nanoparticles (A and B) could be developed as reagent kits in the clinical diagnosis of ovarian cancer.

Human epididymis protein 4 (HE4), as a serological marker, has been proposed to be the most promising tumor marker in ovarian cancer diagnosis. An approach based on surface enhanced Raman spectroscopy (SERS) and a magnetic immunoassay technique was developed successfully for rapid detection and separation of HE4 with high sensitivity and selectivity. The detection was involved in the construction of a unique sandwich structure using a bottom-up method, which consisted of HE4 antibody and SERS reporter coated Au nanoparticles (A) and target HE4 antigen and HE4 antibody-modified magnetic core–shell Fe3O4@Au nanoparticles (B). The sandwich structure was effectively enriched by using a magnet for SERS detection. This approach exhibited an extremely high specificity in the detection of HE4 due to the strong specific interaction between the antibody and the corresponding antigen. The results revealed that the limit of detection (LOD) of the present approach was as low as 100 fg mL−1 and demonstrated a linear relationship between SERS intensities and lgc in a concentration range of 1 pg mL−1 to 10 ng mL−1. Accompanied by the magnetic enrichment procedure after the assembling of the sandwich structure, almost all of the HE4 protein was removed. The immuno Fe3O4@Au nanoparticles were regenerated by releasing the HE4 from the sandwich structure into the acidified methanol solution, and it could be used for magnetic enrichment and SERS detection for at least five times. Moreover, two kinds of immuno nanoparticles (A and B) could be developed as reagent kits in the clinical diagnosis of ovarian cancer.