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This paper presents a novel approach for the fabrication of low cost Electrochemical-Surface Enhanced Raman Scattering (EC-SERS) sensing platforms. Laser Induced Graphene (LIG) electrodes were readily fabricated by direct laser writing of polyimide tapes and functionalized with silver nanoparticles (Ag NPs) to obtain hybrid Ag NPs – LIG electrodes suitable for EC-SERS analysis. Detection was achieved by coupling a handheld potentiostat with a Raman spectrograph, enabling measurement of SERS spectra of target analytes generated during voltage sweeps in the 0.0 to −1.0 V interval range. The sensing capabilities of the fabricated system were first tested with model molecule 4-aminobenzenethiol (4-ABT). Following sensitive detection of 4-ABT, EC-SERS analysis of food contaminant melamine in milk and antibiotic difloxacin hydrochloride (DIF) in river water was demonstrated, achieving sensitive detection of both analytes without pre-treatment steps. The easiness of fabrication, versatility of design, rapid analysis time and potential miniaturization of the system make Ag NPs – LIG electrodes suitable for a large range of in situ applications in the field of food monitoring and for environmental analysis. [ABSTRACT FROM AUTHOR]

A facile strategy has been reported to anchor silver nanoparticles (Ag NPs) onto three-dimensional reduced graphene oxide (3D rGO) via a green and simple method. An accurate and reliable electrochemical sensing platform based on Ag NPs/3D rGO was designed for the ultrasensitive detection of rifampicin (RIF). The morphology and features of Ag NPs/3D rGO were characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), Raman spectroscopy and electrochemical measurements. The interface of the modified electrode presented effective electrical activity for the analysis of RIF due to the large electrochemically active surface area and excellent electron transport ability. The sensor exhibited a good linear relationship in the range of 0.01 nM–45 μM and a low detection limit of 0.810 nM (S/N = 3). Crucially, the fabricated Ag NPs/3D rGO sensor was successfully utilized to assess RIF in human blood, drug and aquatic product samples. This sensing platform exhibited outstanding electrochemical performance for RIF detection and showed great potential application in clinical diagnosis, pharmaceutical and food-related fields. [ABSTRACT FROM AUTHOR]

It is important to further improve the electrophysiology and electrochemistry techniques of neurotransmitter detection. Here, we report the development of multifunctional nanopipette-based integrated approaches for the detection of neurotransmitters. We successfully fabricated a nanopipette with two independent functional units at the apex, a nanopore and a gold nanoelectrode (GNE). The GNE shows good electrochemical response to dopamine (DA). Furthermore, both the nanopore and nanoelectrode can effectively enrich DA but not ascorbic acid by electrical means. The enriched DA is then detected and analysed with an obviously improved signal-to-noise ratio by electrochemical methods and surface-enhanced Raman spectroscopy (SERS). In addition, with the addition of silver nanoparticles during enrichment, up to 10 times increase of the Raman intensity of DA can be observed. [ABSTRACT FROM AUTHOR]

We introduce a technique called ambient electrospray deposition Raman spectroscopy (AESD RS) for rapid and sensitive surface-enhanced Raman scattering (SERS) based detection of analytes using a miniature Raman spectrometer. Using electrospray, soft landing of preformed silver nanoparticles (AgNPs) was performed for 30–40 seconds for different concentrations of analytes deposited on conducting glass slides. Using AESD RS, SERS signals were collected within 4–6 minutes, including sample preparation. Transmission electron microscopy (TEM) and dark-field microscopy (DFM) were used to characterize the preformed AgNPs before and after electrospray. We achieved the nanomolar and micromolar detection of p-mercaptobenzoic acid (p-MBA) and 2,4-dinitrotoluene (2,4-DNT), respectively. In this work, 0.3 μL of preformed AgNPs were used, which is ∼33 times less in volume than the quantity needed for conventional SERS. Quantitation of unknown concentration of analytes was also possible. A similar amount of electrosprayed AgNPs was utilized to characterize Escherichia coli (E. coli) bacteria of different concentrations. Viability of bacteria was tested using fluorescence microscopic imaging. Besides reduced analysis time and improved reproducibility of the data in every analysis, which is generally difficult in SERS, the amount of AgNPs required is an order of magnitude lower in this method. This method could also be used to probe the real-time changes in molecular and biological species under ambient conditions. [ABSTRACT FROM AUTHOR]

We presented the fabrication of a silver nanoparticle (Ag NP) functionalized glass fiber (Ag-GF) substrate for combined surface-enhanced Raman scattering spectroscopy (SERS)/surface-assisted laser desorption/ionization (SALDI) mass spectrometry. Ag NPs were immobilized onto the surface of glass fibers through a simple sputter deposition process. The SERS and SALDI activities strongly depended on the nanostructures of the deposited Ag NPs on the GFs. The closely-packed Ag NPs with a size of 20–50 nm and an inter-particle nanoscale gap of less than 10 nm were effective for the simultaneously enhanced SERS/SALDI substrate via plasmonic/thermal “hot spots”, while the interconnected continuous Ag film reduced both the SERS/SALDI activities. The SERS enhanced factor (EFSERS) and SALDI enhanced factor (EFSALDI) were newly proposed. Finally, the concentration-dependent signal intensities of SERS and SALD-MS of sulfur compounds using an identical Ag NP-GF substrate were examined, and the linear dependence relationship in the log–log plot was demonstrated for the combined quantitative SERS/SALDI-MS analysis. [ABSTRACT FROM AUTHOR]

We synthesized a carbon nanotube (CNT) loaded with silver nanoparticles (AgNPs) composite as an effective surface enhanced Raman scattering (SERS) substrate via a low-cost, simple citrate reduction method. The hybrid materials were confirmed by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), ultraviolet-visible (UV-vis) spectrophotometer and Raman spectroscopy. Rhodamine 6G (R6G) was used as the probe analyte. The experimental results indicated that the detection concentration level was down to 10−14 M. Additionally, we discussed the uniformity by conducting SERS position mapping within an area of 5 μm × 5 μm; meanwhile, we performed time-course SERS mapping experiments to study the evaporation process of probe molecules of the prepared samples. Finally, we simulated the electromagnetic field distribution based on SEM images (obtained the ratio of surface area to the area of silver particles) by the finite difference time domain (FDTD) method. [ABSTRACT FROM AUTHOR]

An innovative and ultra-sensitive surface-enhanced Raman spectroscopic (SERS) method that uses a triple-functional surfactant ligand for nanoparticle surface binding, phase transfer and SERS signal reporting was developed for silver nanoparticle (AgNP) detection. The method was able to detect 100 ng L−1 of AgNPs in aqueous samples and 2 μg g−1 AgNPs in wheat plants. [ABSTRACT FROM AUTHOR]

Silver nanoparticles (Ag NPs) are one of the top five engineered nanoparticles that have been used in various products. Current methods for the measurement of Ag NPs are time consuming and expensive. Therefore, it is of critical importance to develop novel strategies to detect the presence of Ag NPs at low concentrations in different matrices. This study aimed at detecting and measuring Ag NPs in consumer products using surface-enhanced Raman spectroscopy (SERS) coupled with aminothiophenol (PATP) as an indicator molecule that binds strongly with Ag NPs. Quantification and qualification of Ag NPs were achieved using this method of acquiring SERS signals from Ag NP–PATP complexes. Four dietary supplement products and one nasal spray were selected to evaluate the performance of SERS in the detection of Ag NPs. Inductively coupled plasma optical emission spectrometry (ICP-OES) and transmission electron microscopy (TEM) were utilized to measure the physical properties of Ag NPs in the samples. The results demonstrate that distinctive Raman peaks of PATP can be used to distinguish Ag NPs from silver bulk particles and silver nitrate. SERS is able to detect Ag NPs with different sizes ranging from 20 to 100 nm, with the highest intensity for ∼30 nm Ag NPs. A partial least squares method was used to develop quantitative models for the analysis of spectral data (R = 0.94). These results indicate that the conjugation of Ag NPs with PATP can be measured by SERS. These results demonstrate that SERS is a simple and rapid method and has great potential to detect Ag NPs in various products. [ABSTRACT FROM AUTHOR]

Perchlorate, which causes health concerns because of its effects on the thyroid function, is highly soluble and mobile in the environment. In this study, diethyldithiocarbamate (DDTC)-modified silver nanoplates were fabricated on a copper wire to perform the on-site microextraction and detection of perchlorate. This fiber could be inserted into water or soil to extract perchlorate through electrostatic interaction and then can be detected by a portable Raman spectrometer, owing to its surface-enhanced Raman (SERS) activity. A relatively stable vibrational mode (δ(HCH)(CH3), (CH2)) of DDTC at 1273 cm−1 was used as an internal standard, which was negligibly influenced by the absorption of ClO4−. The DDTC-modified Ag/Cu fiber showed high uniformity, good reusability and temporal stability under continuous laser radiation each with an RSD lower than 10%. The qualitative and quantitative detection of perchlorate were also realized. A log–log plot of the normalized SERS intensity against perchlorate concentration showed a good linear relationship. The fiber could be also directly inserted into the perchlorate-polluted soil, and the perchlorate could thereby be detected on site. The detection limit in soil reached 0.081 ppm, which was much lower than the EPA-published safety standard. The recovery of the detection was 105% and comparable with the ion chromatography. This hyphenated method of microextraction with direct SERS detection may find potential application for direct pollutant detection free from complex sample pretreatment. [ABSTRACT FROM AUTHOR]

The demand for methods and technologies capable of rapid, inexpensive and continuous monitoring of health status or exposure to environmental pollutants persists. In this work, the development of novel surface-enhanced Raman spectroscopy (SERS) substrates from metal-coated silk fabric, known as zari, presents the potential for SERS substrates to be incorporated into clothing and other textiles for the routine monitoring of important analytes, such as disease biomarkers or environmental pollutants. Characterization of the zari fabric was completed using scanning electron microscopy, energy dispersive X-ray analysis and Raman spectroscopy. Silver nanoparticles (AgNPs) were prepared, characterized by transmission electron microscopy and UV-vis spectroscopy, and used to treat fabric samples by incubation, drop-coating and in situ synthesis. The quality of the treated fabric was evaluated by collecting the SERS signal of 4,4′-bipyridine on these substrates. When AgNPs were drop-coated on the fabric, sensitive and reproducible substrates were obtained. Adenine was selected as a second probe molecule, because it dominates the SERS signal of DNA, which is an important class of disease biomarker, particularly for pathogens such as Plasmodium spp. and Mycobacterium tuberculosis. Excellent signal enhancement could be achieved on these affordable substrates, suggesting that the developed fabric chips have the potential for expanding the use of SERS as a diagnostic and environmental monitoring tool for application in wearable sensor technologies. [ABSTRACT FROM AUTHOR]

Based on blood plasma surface-enhanced Raman spectroscopy (SERS) analysis, a simple and label-free blood test for non-invasive cervical cancer detection is presented in this paper. SERS measurements were performed on blood plasma samples from 60 cervical cancer patients and 50 healthy volunteers. Both the empirical approach and multivariate statistical techniques, including principal component analysis (PCA) and linear discriminant analysis (LDA), were employed to analyze and differentiate the obtained blood plasma SERS spectra. The empirical diagnostic algorithm based on the integration area of the SERS spectral bands (1310–1430 and 1560–1700 cm−1) achieved a diagnostic sensitivity of 70% and 83.3%, and a specificity of 76% and 78%, respectively, whereas the diagnostic algorithms based on PCA-LDA yielded a better diagnostic sensitivity of 96.7% and a specificity of 92% for separating cancerous samples from normal samples. This exploratory work demonstrates that a silver nanoparticle based SERS plasma analysis technique in conjunction with PCA-LDA has potential for improving cervical cancer detection and screening. [ABSTRACT FROM AUTHOR]

Silver nanoparticles (AgNPs) decorated filter papers combining solid-phase extraction (SPE) with surface enhanced Raman spectroscopy (SERS) achieved rapid collection of analytes and in situ detection. The AgNPs were fabricated by cellulose self-sacrificing reduction. Aqueous Ag(NH3)2OH was reduced by hydroxyl groups in cellulose under alkaline conditions. The AgNPs were highly uniform and firmly adhered to the microfibers. Reaction conditions were optimized by the probe molecule p-aminothiophenol (PATP) to attain the best Raman enhancement. Methylene blue trihydrate (MB) and 6-thioguanine (6-TG) were detected by flow-through method. The results exhibited outstanding SERS effect and an obvious improvement in detection limit was observed compared to common immersion methods. SERS detection was quantitative as the log-log plot of Raman intensity against MB and 6-TG concentrations showed a linear relationship. The SERS-active paper is degradable because it could be burned after analyte detection. [ABSTRACT FROM AUTHOR]