Search

Nitrites (NO2− ions) in food and drink play an important role in human health but require complicated operations before detection. Herein, we present a rationally designed SERS-enabled micro-chamber that comprised a drawn glass capillary with a tiny orifice (∼50 μm) at the distal tip, wherein the gold nanoparticles (Au NPs) are compactly coated on the inner wall surface. In this chamber, nitrites specifically trigger a pH and laser irradiance-dependent diazotization starting from p-aminothiophenol (PATP) absorbed onto the surface of Au NPs to form p,p′-dimercaptoazobenzene (DMAB) molecules, in which the presence of NO2− ions above 30.7 μM (1.38 ppm) in the siphoned liquid sample can be identified relying on SERS peak (1141 cm−1) intensity of the emerging azo moiety. Except for pH conditions, laser irradiance is more important but easily neglected in previous studies, which is capable of preventing generation of errors when the detection sensitivity was pursued through increasing the laser power. In this case, several real samples (rather than simple water samples), including honey, pickled vegetable and fermented bean curd, had been successfully detected accurately through such a convenient sampling micro-chamber. The SERS-enabled device could potentially be facilely incorporated with portable Raman instruments for a special application of food inspection in rapid and field analysis of NO2− ions. [ABSTRACT FROM AUTHOR]

Herein, we presented a novel logic gate based on an INHIBITION gate that performs parallel readouts. Logic gates performing INHIBITION and YES/OR were constructed using surface-enhanced Raman scattering as optical outputs for the first time. The strategy allowed for simultaneous reading of outputs in one tube. The applicability of this strategy has been successfully exemplified in the construction of half-adder using the two-output logic gates as reporting gates. This reporting strategy provides additional design flexibility for dynamic DNA devices. [ABSTRACT FROM AUTHOR]

A new label-free fluorescent turn-on-off mode for the sensitive detection of cysteine(Cys) and the identification of Cys over glutathione (GSH) was firstly proposed, mainly on the basis of two different combination ways between Ag + ions and GSH-capped gold nanoclusters, or to say, two different contribution ways to the fluorescence enhancement, Ag + ions combining with Au core structure and coordinating with carboxylate groups on the surface of gold nanoclusters, respectively (turn-on mode). The Au core-binding Ag + ions could merely be captured by Cys for its relatively smaller steric hindrance than that of GSH, resulting in the identification of Cys over GSH. The carboxylate-binding Ag + ions could be removed both by Cys and GSH, which, hence, could be used for the qualification of Cys and GSH (turn-off mode). Good selectivity and sensitivity for Cys over other amino acids were achieved. This new turn-on-off sensing strategy for Cys also had obvious advantages of simplicity, rapidity, ease of operation and a low cost. Under the optimized conditions, the linear range was 0.00–2.71 μM with the limit of detection of 16.54 nM for Cys and 15.59 nM for GSH. The probe also had a good application in Cys containing health products. [ABSTRACT FROM AUTHOR]

In this article, we for the first time present an original and ultrasensitive assay to detect Ag + ions, with which the aggregation of the given peptide-modified gold nanoparticles (peptide-AuNPs) can be triggered by the interaction between peptides and Ag + . The approach has rarely been used in the colorimetric determination of Ag + , because the mechanism of the above-mentioned interaction has not been studied through. In our assay, the principle of this interaction was investigated. Moreover, we applied it in the design of an extremely sensitive sensor for Ag + detection with great selectivity. It is the Ag + -induced folding structure of the peptides that leads to the aggregation of peptide-AuNPs. The aggregation involves the formation of 4-coordinated complexes between Ag + and peptides via bonding with the carbonyl oxygen and the nitrogen of the α-amino group in the peptides. The result shows that Ag + ions can be selectively detected as low as 7.4 nM with a linear range of 10–1000 nM. Compared with other approaches, the proposed approach demonstrates superior simplicity, sensitivity, stability and time-saving. Furthermore, the biosensor excels in the practical application in water samples (e.g., lake, tap and drinking water) owing to its non-interference and on-site rapid determination. [ABSTRACT FROM AUTHOR]

In this work, we propose for the first time a simple and novel approach based on SERS and As (III) -aptamer for detection of As (III) with excellent selectivity and sensitivity. To maintain the wonderful SERS substrate, Au@Ag shell–core nanoparticle has been successfully synthesized by seeds growth method. As-prepared Au@Ag not only has well-dispersed but also obtains high SERS efficiency. The novel As (III) biosensor has an excellent linear correlation with the concentration of As (III) ranging from 0.5 to 10 ppb. The detection limit of this assay for As (III) is 0.1 ppb (3 times standard deviation rules) which is lower than the maximum limitation guided by the United States Environmental Protection Agency (EPA) and the World Health Organization (WHO). Importantly, the results were demonstrated that no other ions interfered with the detection of As (III) in water. Further, this As (III) biosensor was demonstrated in monitoring As (III) in lake water samples with satisfactory results. [ABSTRACT FROM AUTHOR]

We describe herein a novel' “turn-on” SERS-based strategy for protease detection based on surface enhanced Raman scattering (SERS) and the mediation of spacing between 4-mercaptobenzoic acid (4-MBA) labeled gold nanoparticles (AuNPs) through enzyme assays. The method employed non-cross-linking aggregation of 4-MBA-modified AuNPs by peptides after treatment with target protease. Thus, SERS signals of 4-MBA are sharply increased because of the decreased electrostatic stability of AuNPs that initiated gold nanoaggregates incorporating Raman reporter molecules due to the formation of “Hot Spots”. Through this strategy, a novel and facile “turn-on” SERS biosensor for trypsin and thrombin based on enzymatic cleavage activity is established with sensitivity, selectivity and simplicity as AuNPs and peptides are easily accessible. Compared with other methods, this newly proposed method has improved sensitivity. The limit of detection was 85 fM (at the ratio of signal to noise, S/N=3:1) for trypsin. Controlled experiments showed that the method exhibited good selectivity over other proteases. We also proved that this principle could be easily adapted to detection of other proteases such as thrombin. The method demonstrated the capability for application in complex matrix samples. The results also presented the potential and superiority of SERS biosensor as a general approach for proteases based on enzyme activity. [ABSTRACT FROM AUTHOR]

Abstract: Stable SERS response originating from gold nanoparticles (Au NPs) is demonstrated for the first time to be suitable for detection of heparin with high selectivity. Herein we report a novel “turn-off” SERS assay for heparin based on Raman labelled Au NPs and competitive bonding between heparin and two specialized peptides, such as RKGSGRRLVKC (11-peptide) and CALNN (5-peptide). By means of coordination interactions and other non-electrostatic forces, these 5-peptide capped Au NPs are induced to undergo controllable aggregation upon the additive of 11-peptide and heparin with a concentration range (0–2.4U/mL), which correspondingly cause quantitative changes of SERS intensity of 4-MBA conjugated on Au NPs. The decreased Raman intensity obtained by subtracting two cases of additives which contain only 11-peptide and the mixture of 11-peptide and heparin, is proportional to the concentration of heparin over a range of 0.2–2.4U/mL (R 2=0.99157), with a limit of detection (LOD) of 0.042U/mL (S/N=3:1). Moreover, the proposed highly selective method has potential application for rapid, separation-free detection of heparin in human blood serum samples. [Copyright &y& Elsevier]

Abstract: Herein we describe a novel “turn-off” biosensing strategy for thrombin detection based on Surface Enhanced Raman scattering (SERS) and the mediation of spacing between 4-mercaptobenzoic acid (4-MBA) labeled gold nanoparticles (AuNPs). The multiple arginine peptides that initiated gold nano-aggregates incorporating Raman reporter molecules due to the formation of “Hot Spots”, are induced to disband by the addition of thrombin in which the peptides are catalytically cleaved into fragments and thus SERS signals of 4-MBA are sharply declined because of the weakened ability of fragments to induce aggregation. Through this strategy, a novel “turn-off” SERS biosensor for thrombin based on enzymatic amplification is established with sensitivity, selectivity and simplicity as AuNPs and peptides are easily accessible. Compared with non-enzymatic amplification based methods, this newly proposed method has improved sensitivity. The limit of detection was 160fM (at the ratio of signal to noise, S/N=3:1). Further, controlled experiments showed that the method exhibited good selectivity over other proteases. The method demonstrated the capability and the potential for application in complex matrix and future biomarker development. The results also presented the potential and superiority of SERS biosensor based on signal amplification. [Copyright &y& Elsevier]

Abstract: Enzyme immobilization is one of the key factors in constructing high-performance enzyme biosensors and biofuel cells (BFCs). Herein, we propose a new protocol for efficient immobilization of a glycoprotein enzyme based on the interaction of the 1, 2- or 1, 3-diols in the glycoprotein with a boronic acid functionalized monomer. Briefly, casting a mixture of glucose oxidase (GOx) and anilineboronic acid (ABA) followed by a NaAuCl4 solution to an Au-plated Au electrode surface yielded a GOx–poly(ABA) (PABA)–gold nanoparticle (Aunano) bionanocomposite, and chitosan (CS) was then cast and air-dried. In the present protocol, the small-sized Aunano or Au subnanostructures can form near/on the enzyme molecule, which greatly promotes the electron transfer of enzymatic reaction and enhances the amperometric responses. The thus-prepared CS/GOx–PABA–Aunano/Au-plated Au electrode worked well in the first-/second generation biosensing modes and as a bioanode in a monopolar biofuel cell, with analytical or cell-power performance superior to those of most analogues hitherto reported. [Copyright &y& Elsevier]