Portable Surface-Enhanced Raman Scattering Sensor for Rapid Detection of Aniline and Phenol Derivatives by On-Site Electrostatic Preconcentration

SERS optrode as a “fishing rod” to direct pre-concentrate analytes from superhydrophobic surfaces

SERS optrodes were used to “fish” aqueous drops from superhydrophobic surfaces, which led to an improvement of 2–3 orders of magnitude in sensitivity. 20 pg of the pesticide triazophos was detected by this method.

Disposable screen printed electrochemical sensors: tools for environmental monitoring

Screen printing technology is a widely used technique for the fabrication of electrochemical sensors. This methodology is likely to underpin the progressive drive towards miniaturized, sensitive and portable devices, and has already established its route from "lab-to-market" for a plethora of sensors. The application of these sensors for analysis of environmental samples has been the major focus of research in this field. As a consequence, this work will focus on recent important advances in the design and fabrication of disposable screen printed sensors for the electrochemical detection of environmental contaminants. Special emphasis is given on sensor fabrication methodology, operating details and performance characteristics for environmental applications.

Disposable electrochemical aptasensor array by using in situ DNA hybridization inducing silver nanoparticles aggregate for signal amplification

Nanomaterials as tracing tags have been widely used in biosensors with high sensitivity and selectivity. In this work, a signal amplification electrochemical aptamer sensing strategy for the detection of protein was designed by combining the hybridization-inducing aggregate of DNA-functionalized silver nanoparticles (AgNPs) and differential pulse stripping voltammetry (DPSV) detection. The multiprobes containing hybridization DNA and aptamers were anchored onto the silver nanoparticles. The protein assay was prepared through the immobilization of capture aptamer that specifically recognizes platelet-derived growth factor (PDGF-BB) on gold nanoparticles modified screen-printed electrode (SPE) array. After a sandwich-type reaction, two kinds of DNA-modified AgNPs were simultaneously added on the electrode surface for specifically recognizing PDGF-BB and forming the AgNPs aggregate caused by in situ hybridization of DNA. Compared to the signal-labeled tag, the tracing aggregate tags showed a strong electroactivity for signal amplification through stripping detection of silver after preoxidation. By using the hybridization-inducing aggregate as electrochemical readouts, the sensor showed wide linear range and low detection limit. The hybridization-inducing AgNPs aggregate were further used as tracing tags in multiplied proteins assays for PDGF-BB and thrombin by using the SPE array chip as sensing platform. The cross-talk between different aptamer-modified electrodes on the same array was avoided because of the advantage of labeled AgNPs. The array detection was also applied in the logic gate operation. The proposed method described here is ideal for multianalytes determination in clinical diagnostics with good analytical performance.

Surface-imprinted core-shell Au nanoparticles for selective detection of bisphenol A based on surface-enhanced Raman scattering

Surface-imprinted core-shell Au nanoparticles (AuNPs) were explored for the highly selective detection of bisphenol A (BPA) by surface-enhanced Raman scattering (SERS). A triethoxysilane-template complex (BPA-Si) was synthesized and then utilized to fabricate a molecularly imprinted polymer (MIP) layer on the AuNPs via a sol-gel process. The imprinted BPA molecules were removed by a simple thermal treatment to generated the imprint-removed material, MIP-ir-AuNPs, with the desired recognition sites that could selectively rebind the BPA molecules. The morphological and polymeric characteristics of MIP-ir-AuNPs were investigated by transmission electron microscopy and Fourier-transform infrared spectroscopy. The results demonstrated that the MIP-ir-AuNPs were fabricated with a 2 nm MIP shell layer within which abundant amine groups were generated. The rebinding kinetics study showed that the MIP-ir-AuNPs could reach the equilibrium adsorption for BPA within 10 min owning to the advantage of ultrathin core-shell nanostructure. Moreover, a linear relationship between SERS intensity and the concentration of BPA on the MIP-ir-AuNPs was observed in the range of 0.5-22.8 mg L(-1), with a detection limit of 0.12 mg L(-1) (blank±3×s.d.). When applied to SERS detection, the developed surface-imprinted core-shell MIP-ir-AuNPs could recognize BPA and prevent interference from the structural analogues such as hexafluorobisphenol A (BPAF) and diethylstilbestrol (DES). These results revealed that the proposed method displayed significant potential utility in rapid and selective detection of BPA in real samples.

Rapid and sensitive in-situ detection of polar antibiotics in water using a disposable Ag-graphene sensor based on electrophoretic preconcentration and surface-enhanced Raman spectroscopy

A disposable Ag-graphene sensor was developed for rapid and sensitive in-situ detection of polar antibiotics in water using electrophoretic preconcentration (EP) and surface-enhanced Raman spectroscopy (SERS). The Ag-graphene sensor was fabricated by depositing Ag-graphene nanocomposites synthesized through a facile one-pot method on the disposable screen-printed electrodes (SPEs) and characterized by transmission electron microscopy (TEM) and atomic force microscopy (AFM). SERS properties and detection applicability of the developed sensor were systematically investigated. It is shown that the polar antibiotics can be selectively adsorbed on the oppositely charged sensors after applying different potentials during the EP procedure, and the SERS signals of antibiotics with an effective amplification can be achieved with proper time of preconcentration. Moreover, the Ag-graphene sensor could facilitate the molecule adsorption through weak π-π interactions between graphene and antibiotics, further improving the sensitivity of SERS detection. Under the optimum EP conditions, the representative SERS spectra of a mixed solution containing four different antibiotics can be obtained within 10 min, and each antibiotic is easily distinguished by its characteristic peaks with a sub-nM detection level. The results demonstrate that the proposed disposable Ag-graphene sensor based on EP-SERS can be used for rapid and sensitive in-situ detection of polar antibiotics in aqueous samples without a pre-separation step.

Critical issues in sensor science to aid food and water safety

The stability of food and water supplies is widely recognized as a global issue of fundamental importance. Sensor development for food and water safety by nonconventional assays continues to overcome technological challenges. The delicate balance between attaining adequate limits of detection, chemical fingerprinting of the target species, dealing with the complex food matrix, and operating in difficult environments are still the focus of current efforts. While the traditional pursuit of robust recognition methods remains important, emerging engineered nanomaterials and nanotechnology promise better sensor performance but also bring about new challenges. Both advanced receptor-based sensors and emerging non-receptor-based physical sensors are evaluated for their critical challenges toward out-of-laboratory applications.

Multiple depositions of Ag nanoparticles on chemically modified agarose films for surface-enhanced Raman spectroscopy

A facile and cost-effective approach for the preparation of a surface-enhanced Raman spectroscopy (SERS) substrate through constructing silver nanoparticle/3-aminopropyltriethoxysilane/agarose films (Ag NPs/APTES/Agar film) on various solid supports is described. The SERS performance of the substrate was systematically investigated, revealing a maximum SERS intensity with four layers of the Ag NP deposition. The enhancement factor of the developed substrate was calculated as 1.5 × 10(7) using rhodamine 6G (R6G) as the probe molecule, and the reproducibility of the SERS signals was established. A high throughput screening platform was designed, manufactured and implemented which utilised the ability to cast agarose to assemble arrays. Quantitative analysis of 4-aminobenzoic acid (4-ABA) and 4-aminothiophenol (4-ATP) was achieved over a ∼0.5 nM-0.1 μM range.

Single-molecule surface-enhanced Raman spectroscopy

A general overview of the field of single-molecule (SM) surface-enhanced Raman spectroscopy (SERS) as it stands today is provided. After years of debates on the basic aspects of SM-SERS, the technique is emerging as a well-established subfield of spectroscopy and SERS. SM-SERS is allowing the observation of subtle spectroscopic phenomena that were not hitherto accessible. Examples of the latter are natural isotopic substitutions in single molecules, observation of the true homogeneous broadening of Raman peaks, Raman excitation profiles of individual molecules, and SM electrochemistry. With background examples of the contributions produced by our group, properly interleaved with results by other practitioners in the field, we present some of the latest developments and promising new leads in this new field of spectroscopy.

Surface-enhanced Raman spectroscopy (SERS): progress and trends

Surface-enhanced Raman spectroscopy (SERS) combines molecular fingerprint specificity with potential single-molecule sensitivity. Therefore, the SERS technique is an attractive tool for sensing molecules in trace amounts within the field of chemical and biochemical analytics. Since SERS is an ongoing topic, which can be illustrated by the increased annual number of publications within the last few years, this review reflects the progress and trends in SERS research in approximately the last three years. The main reason why the SERS technique has not been established as a routine analytic technique, despite its high specificity and sensitivity, is due to the low reproducibility of the SERS signal. Thus, this review is dominated by the discussion of the various concepts for generating powerful, reproducible, SERS-active surfaces. Furthermore, the limit of sensitivity in SERS is introduced in the context of single-molecule spectroscopy and the calculation of the 'real' enhancement factor. In order to shed more light onto the underlying molecular processes of SERS, the theoretical description of SERS spectra is also a growing research field and will be summarized here. In addition, the recording of SERS spectra is affected by a number of parameters, such as laser power, integration time, and analyte concentration. To benefit from synergies, SERS is combined with other methods, such as scanning probe microscopy and microfluidics, which illustrates the broad applications of this powerful technique.

Localized surface plasmon resonance: nanostructures, bioassays and biosensing--a review

Localized surface plasmon resonance (LSPR) is an optical phenomena generated by light when it interacts with conductive nanoparticles (NPs) that are smaller than the incident wavelength. As in surface plasmon resonance, the electric field of incident light can be deposited to collectively excite electrons of a conduction band, with the result being coherent localized plasmon oscillations with a resonant frequency that strongly depends on the composition, size, geometry, dielectric environment and separation distance of NPs. This review serves to describe the physical theory of LSPR formation at the surface of nanostructures, and the potential for this optical technology to serve as a basis for the development bioassays and biosensing of high sensitivity. The benefits and challenges associated with various experimental designs of nanoparticles and detection systems, as well as creative approaches that have been developed to improve sensitivity and limits of detection are highlighted using examples from the literature.

Functionalizing metal nanostructured film with graphene oxide for ultrasensitive detection of aromatic molecules by surface-enhanced Raman spectroscopy

Surface-enhanced Raman spectroscopy (SERS) as a powerful analytical tool has gained extensive attention. Despite of many efforts in the design of SERS substrates, it remains a grand challenge for creating a general substrate that can detect diverse target analytes. Herein, we report our attempt to address this issue by constructing a novel metal-graphene oxide nanostructured film as SERS substrate. Taking advantages of the high affinity of graphene oxide (GO) toward aromatic molecules and the SERS property of nanostructured metal, this structure exhibits great potential for diverse aromatic molecules sensing, which is demonstrated by using crystal violet (CV) with positive charge, amaranth with negative charge, and neutral phosphorus triphenyl (PPh(3)) as model molecules.

Facile on-site detection of substituted aromatic pollutants in water using thin layer chromatography combined with surface-enhanced Raman spectroscopy

A novel facile method for on-site detection of substituted aromatic pollutants in water using thin layer chromatography (TLC) combined with surface-enhanced Raman spectroscopy (SERS) was explored. Various substituted aromatics in polluted water were separated by a convenient TLC protocol and then detected using a portable Raman spectrometer with the prepared silver colloids serving as SERS-active substrates. The effects of operating conditions on detection efficacy were evaluated, and the application of TLC-SERS to on-site detection of artificial and real-life samples of aromatics/polluted water was systematically investigated. It was shown that commercially available Si 60-F(254) TLC plates were suitable for separation and displayed low SERS background and good separation efficiency, 2 mM silver colloids, 20 mM NaCl (working as aggregating agent), 40 mW laser power, and 50 s intergration time were appropriate for the detection regime. Furthermore, qualitative and quantitative detection of most of substituted aromatic pollutants was found to be readily accomplished using the developed TLC-SERS technique, which compared well with GC-MS in terms of identification ability and detection accuracy, and a limit of detection (LOD) less than 0.2 ppm (even at ppb level for some analytes) could be achieved under optimal conditions. The results reveal that the presented convenient method could be used for the effective separation and detection of the substituted aromatic pollutants of water on site, thus reducing possible influences of sample transportation and contamination while shortening the overall analysis time for emergency and routine monitoring of the substituted aromatics/polluted water.