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Silver nanoparticles (AgNPs) conjugated with polymers are well-known for their powerful and effective antimicrobial properties. In particular, the incorporation of AgNPs in biocompatible catecholamine-based polymers, such as polydopamine (PDA), has recently shown promising antimicrobial activity, due to the synergistic effects of the AgNPs, silver(I) ions released and PDA. In this study, we generated AgNPs-PDA-patterned surfaces by localised electrochemical depositions, using a double potentiostatic method via scanning electrochemical cell microscopy (SECCM). This technique enabled the assessment of a wide parameter space in a high-throughput manner. The optimised electrodeposition process resulted in stable and homogeneously distributed AgNP-microspots, and their antimicrobial activity against Escherichia coli was assessed using atomic force microscopy (AFM)-based force spectroscopy, in terms of bacterial adhesion and cell elasticity. We observed that the bacterial outer membrane underwent significant structural changes, when in close proximity to the AgNPs, namely increased hydrophilicity and stiffness loss. The spatially varied antimicrobial effect found experimentally was rationalised by numerical simulations of silver(I) concentration profiles. [ABSTRACT FROM AUTHOR]

Efficient and affordable nucleic acid detection methods play a pivotal role in various applications. Herein, we developed an immobilization-free and label-free strategy to construct a photoelectrochemical nucleic acid biosensing platform based on interactions between silver nanoparticles and DNA. First, CRISPR-Cas12a exhibited a trans-cleavage effect on adenine nucleotide sequences upon recognizing the target DNA. The resulting adenine nucleotide sequences of varying lengths then engaged in interactions with silver nanoparticles, leading to a solution characterized by distinct light transmittance. Subsequently, the solution was positioned between the light source and the photoelectrode, strategically impacting the photon absorption step within the photoelectrochemical process. Consequently, the detection of nucleic acid was accomplished through the analysis of the resultant photocurrent signal. The developed platform exhibits a detection limit of 0.06 nM (S/N = 3) with commendable selectivity. The innovative use of adenine nucleotide sequences as cost-effective probes interacting with silver nanoparticles eliminates the need for complex interfacial immobilization processes, significantly simplifying the fabrication of DNA sensors. The outcomes of our research present a promising pathway for advancing the development of economically feasible miniature DNA sensors. [ABSTRACT FROM AUTHOR]

Carbon dots@noble metal nanoparticle composites are formed by combining carbon dots and metal nanoparticles using various strategies. Carbon dots exhibit a reducing ability and function as stabilisers; consequently, metal-ion solutions can be directly reduced by them to synthesise gold, silver, and gold–silver alloy particles. Carbon dots@gold/silver/gold–silver particle composites have demonstrated the potential for several practical applications owing to their superior properties and simple preparation process. Until now, several review articles have been published to summarise fluorescent carbon dots or noble metal nanomaterials. Compared with metal-free carbon dots, carbon dots@noble metal nanoparticles have a unique morphology and structure, resulting in new physicochemical properties, which allow for sensing, bioimaging, and bacteriostasis applications. Therefore, to promote the effective development of carbon dots@noble metal nanoparticle composites, this paper primarily reviews carbon dots@gold/silver/gold–silver alloy nanoparticle composites for the first time in terms of the following aspects. (1) The synthesis strategies of carbon dots@noble metal nanoparticle composites are outlined. The principle and function of carbon dots in the synthesis strategies are examined. The advantages and disadvantages of these methods and composites are analysed. (2) The characteristics and properties of such composites are described. (3) The applications of these composite materials are summarised. Finally, the potentials and limitations of carbon dots@noble metal nanoparticle composites are discussed, thus laying the foundation for their further development. [ABSTRACT FROM AUTHOR]

Plasmonic nanoparticles are an emerging tool for developing label-free multicolorimetric sensors for biosensing and chemosensing applications. The color absorbed by nanoparticles from visible light is influenced by their size, shape, orientation, and interparticle distance. Differently sized and shaped gold and silver nanoparticles exhibit a wide range of colors, aiding in the development of label-free sensors. Etching is the process of oxidizing nanoparticles, which alters their aspect ratio, shape, plasmonic peak, and outward appearance. It is typically used to create sensitive sensing platforms. Through etching, analytes could be detected in a simple, sensitive, and selective manner. The multicolor readout of nanoparticle etching-based multicolorimetric sensors can overcome the limitations of conventional colorimetric assays and improve the accuracy of visual inspection. This review discusses different approaches for target sensing using nanoparticle etching strategies like direct etching, enzyme-mediated etching, chemical reaction-driven etching, and anti-etching-based sensors and their mechanisms. In the future, etching strategies could be modified into portable sensing devices to detect a variety of analytes, which will aid in the development of on-time, in situ, and point-of-care sensing systems. [ABSTRACT FROM AUTHOR]

Silver nanoparticles (AgNPs) exhibit very interesting properties that have been employed in several kinds of applications spanning from antibacterial activity to plasmon–polaritons generation. Nanoparticle size strongly influences these applications. However, the characterization of ultrasmall AgNPs (particle diameter < 10 nm) encompassing different aspects such as average size, polydispersion, shape (anisotropy), concentration, and density remains a challenging task. To address these challenges, we combined TEM measurements with a computational framework based on Mie–Gans theory. This allowed us to describe the aforementioned AgNP features accurately. The synthesis of AgNPs in an aqueous medium involved the use of silver nitrate as a chemical precursor and sodium borohydride as a reducing agent, with polyvinylpyrrolidone acting as a stabilizing agent. Our outcomes showed that increasing the concentration of the precursor and reducing agent with a fixed 1 : 2 molar ratio tends to yield ultrasmall AgNPs with low to moderate polydispersion, a nearly spherical shape (low anisotropy), concentration in the nanomolar range and density close to silver bulk. Also, we established an analytical expression that correlates the extinction molar absorptivity to AgNP size considering the nanoparticle shape. Notably, the computational framework proved to be highly effective in extracting crucial information about the AgNPs from UV-vis spectroscopy data. In conclusion, our study sheds light on the unique properties of ultrasmall AgNPs and presents a comprehensive approach for properly characterizing these nanoparticles, paving the way for further advancements in their applications. [ABSTRACT FROM AUTHOR]

An electrochemical glucose sensor based on flexible materials is significant for wearable devices used for real-time health monitoring and diagnosis. However, applying flexible electrodes involves complex fabrication processes and might reduce detection sensitivity. To overcome these obstacles, we herein report a novel strategy for preparing a highly flexible enzyme electrode based on an electrospun poly(vinyl alcohol) (PVA) mat decorated with in situ grown silver nanoparticles (nano-Ag) for electrochemical glucose sensing. Ferrocene (Fc) was selected as an electron acceptor for glucose oxidase (GOD) in order to minimize the influence of oxygen. Electron transfer between GOD and Fc was facilitated by confining them within a mixed self-assembled monolayer (SAM) formed on a thin layer of gold deposited on top of the PVA/nano-Ag film. Nano-Ag was found to significantly increase the surface area of the electrode and improve the stability of electrode conductivity during tensile deformation. Electrochemical glucose detection was performed by chronoamperometry in the electroactivity domain of ferrocene, and good linearity (R2 = 0.993) was obtained in the range of 0.2–7 mM with a detection limit of 0.038 mM and a relative standard deviation (RSD) of 1.45% (n = 6). After being stuck to a bendable PDMS slice and bent, respectively, at 30° and 60° 50 times, the electrode showed slight changes in detection results (<4.78%), which remained within 8% when the bending angle increased to 90°. With its high flexibility, good detection performance, and convenient fabrication process, the proposed enzyme electrode showed good potential as a flexible platform for wearable glucose sensing systems. [ABSTRACT FROM AUTHOR]

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 novel enhanced fluorescent sensor system for zearalenone (ZON) determination in flour samples is presented. The ZON-selective molecularly imprinted polymer (MIP) films were developed with a computational modelling method and synthesised with cyclododecyl-2,4-dihydroxybenzoate as a "dummy" template and ethylene glycol methacrylate phosphate as a functional monomer acted as the selective recognition elements for ZON fluorescence detection. Spherical silver nanoparticles (AgNPs) were embedded in the MIP films' structure to enhance the sensor sensitivity. The imprinted films showed a high ZON recognition ability compared to non-imprinted films. Various factors that affected the measurement of the analysed sample were investigated and optimised. Embedding the AgNPs in the MIP films' structure led to an enhanced sensitivity (up to a 200-fold decrease of LOD) compared to unmodified MIP films. This fluorescent sensor system provided ZON analysis with high sensitivity, specificity, and a wider linear dynamic range of 5 ng mL−1 to 25 μg mL−1. An enhanced fluorescent sensor system based on MIP chips with embedded AgNPs could detect trace amounts of ZON in foods and feedstuffs with high sensitivity and selectivity. [ABSTRACT FROM AUTHOR]

Urinary potassium is an important parameter in clinical health diagnosis. Rapid and convenient detection of potassium ions (K+) in urine is essential for personal healthcare and health management. Here, crown ether (4-aminodibenzo-18-crown-6, ADC) modified silver nanoparticles (ADC-Ag NPs) were successfully prepared for one-step rapid colorimetric detection of urinary potassium. The detection mechanism is as follows: due to the matching sizes of the diameter of K+ and the cavity in crown ether 6, K+ is encapsulated between the cavities of two crown ethers, resulting in the clumping of ADC-Ag NPs and the color of the solution being altered. The colorimetric detection method has a fast response and is completed within 20 minutes. It also shows good selectivity and interference immunity. The lowest detectable concentration is 20 μM with the naked eye and 2.16 μM for UV-vis absorption spectroscopy. A good linear relationship (R2 = 0.9931) between the absorption intensity ratio and K+ concentration (0–100 μM) indicates that this colorimetric probe can be used to detect K+. The method was also applied for quantitative analysis of K+ in real urine samples with recovery between 116 and 120%. [ABSTRACT FROM AUTHOR]

The flexible surface-enhanced Raman scattering (SERS) platform has ceaselessly propelled the development of point-of-care testing (POCT) in diverse fields. Herein, we report a facile strategy for the SERS-chemometric analysis of four β-blockers (bisoprolol, metoprolol, acebutolol and esmolol) based on a super-sticky mussel-inspired hydrogel SERS tape. The surface morphology and mechanical properties of the hydrogel tape can be easily controlled by adjusting the compositional ratio. The optimized tape with excellent toughness and adhesiveness allows efficient collection of analytes through a simple "paste and peel off" approach, further by spraying with silver nanoparticles using a household sprayer to instantly assemble a flexible SERS substrate, the analytes can then detected by a portable Raman spectrometer. This POCT strategy enables the identification and discrimination of four similar β-blockers with high sensitivity and accuracy in combination with the statistical algorithms. The developed SERS tape is finally utilized for the recognition of β-blockers in simulated urine solution, which realizes a limit of detection of 1.0 ng mL−1, revealing a promising potential of this SERS-based POCT for the clinical detection of doping abuse. [ABSTRACT FROM AUTHOR]

Highly sensitive surface-enhanced Raman spectroscopy (SERS) sensing not only depends on an active substrate with high density of hot spots, but also depends more on whether the molecules can effectively enter the hot spot region. In this paper, a new SERS detection method based on the nano nest model is developed to autonomously capture molecules into hot spots. The nano nest is composed of silver nanowires modified with gold nanoparticles (Ag NW@Au NPs), which not only form high density hot spots between particles or particles-wires, but also have a coupled electromagnetic field enhancement effect. The SERS detection method based nano nest actively traps molecules through the capillary stage, and makes the molecules move toward densely stacked small gaps (hot spots) by capillary action. The above method has been used to detect different kinds of molecules, such as pesticide residues, adenosine triphosphate in culture medium, and antibiotic residues in aquatic products. In addition, an in situ SERS monitoring of allergic reactions was also performed using nano nests with the feature of actively trapping molecules into the hot spots. This nano nest will be able to perform a direct monitoring of biochemical reactions, and more importantly, it can provide a new scheme for SERS detection. [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]

We demonstrate a novel sensor platform with enhanced sensitivity and selectivity for detecting aflatoxin B1 – a common food toxin in cereals. The approach is based on a molecularly imprinted polymer film that provides selective binding of the aflatoxin B1 and fluorescence signal from the analyte molecule enhanced by the local electric field induced in close proximity to the surface of a silver nanoparticle excited at the localized surface plasmon resonance (LSPR) wavelength. Molecularly imprinted polymers (MIPs) with supramolecular aflatoxin-selective receptor sites and embedded spherical silver nanoparticles (with diameters 30–70 nm, the LSPR band 407 nm) were prepared in the form of a thin polymer film on the surface of a glass slide using in situ polymerization. The detection limit of the sensor for aflatoxin B1 is 0.3 ng mL−1, which is significantly lower than for a fluorescent sensor without silver nanoparticles. The plasmon-enhanced fluorescence factor is 33, and the linear dynamic range of the sensor is 0.3–25 ng mL−1. [ABSTRACT FROM AUTHOR]

Surface-enhanced Raman scattering (SERS) spectroscopy is a rapid and non-destructive optical detection method that has been applied in various applications. Recently, three-dimensional (3D) substrate-based silicon nanostructures have been widely used as SERS substrates due to their high detection sensitivity, repeatability, and reusability. This paper uses a simple and low-cost electroless etching deposition process to generate silver nanoparticle-decorated porous silicon (Ag-PS) substrates. We propose a contact deposition process to generate localized Ag-PS (LocAg-PS) for SERS analysis. Due to the hydrophilic LocAg-PS pad on the hydrophobic PS background, the sample droplets self-aligned to the predefined LocAg-PS pads and condensed into a higher local concentration for high sensitivity SERS detection without extensive search for the hot spot. The effects of critical fabrication parameters and SERS analysis on the LocAg-PS surface were evaluated. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

To prevent the transmission of brucellosis, rapid vertical flow technology (RVFT) was developed to detect brucellosis antibodies. To improve the sensitivity of the technique, lipopolysaccharides (LPS) were purified and used to detect brucellosis antibodies. To improve the sensitivity of serum antibody detection, a single multifunctional buffer was established in whole blood and other biological samples, and the advantages of the lateral flow immunoassay were retained. Flower-like gold nanoparticles were applied to RVFT for the first time. In this study, silver ions were catalyzed by flower-like gold nanoparticles into metal silver deposited on the surface of gold nanoparticles for the first time, which not only increased the particle size of gold nanoparticles, but also showed a more distinguishable black color on the test zone, further improving the sensitivity of RVFT. Standard Brucella-positive serum (containing Brucella antibody at 4000 IU mL-1) could be detected in this system even for a dilution factor of 2 x 10-3. The detection limit was 2 IU mL-1. RVFT can effectively avoid the false negative phenomenon in lateral flow immunoassay. RVFT is simple to operate, with a short reaction time, 2-3 minutes visible to the naked eye, without any equipment. Because it is very important to control the brucellosis epidemic, this approach has great application prospects in basic medical units and for veterinarians. [ABSTRACT FROM AUTHOR]

The contact distance between mitochondria (Mito) and endoplasmic reticulum (ER) has received considerable attention owing to their crucial function in maintaining lipid and calcium homeostasis. Herein, cubic spline algorithm-based depth-dependent fluorescence-free three-dimensional light-sheet super-resolution microscopy (3D LSRM) with dual-wavelength illumination sources was investigated to study the distance of Mito–ER contacts in various live cells. To detect wavelength-dependent scattering, 12 nm gold nanoparticles (AuNPs) and 20 nm silver nanoparticles (AgNPs) as fluorescence-free nanoprobes were conjugated with Mito and ER. The cubic spline algorithm-based method showed improved localization precision in lateral and axial directions compared with that for previously used least squares and least cubic algorithms. The cubic spline-based depth-dependent localization was applied to the spatial localization of nanoprobes in super-resolution images, in which the average distance of Mito and ER was 22.4 nm in HeLa cells, 22.2 nm in RAW264.7 macrophage cells, 21.9 nm in AGS cells, 21.4 nm in HT29 cells, and 21.3 nm in HEK293 cells. The distances were ∼12% larger than those previously determined by electron microscopy, which demonstrated that this method was accessible and reliable for studying the intracellular structures of various live cells at the subdiffraction limit resolution. [ABSTRACT FROM AUTHOR]

Prostate-specific antigen (PSA), a glycoprotein that is most likely to cause prostate cancer, has attracted widespread attention in recent years due to its increasing threat to people's lives and health. Herein, we developed a new signal-amplified photoelectrochemical (PEC) immunosensing method for quantitative monitoring of the target PSA based on the ion-exchange reaction for the in situ formation of ZnO/CdS/Ag2S nanohybrids triggered by the as-released silver ions (Ag+) from silver nanolabels. Initially, the introduction of a target PSA caused the formation of a sandwich immunocomplex in an anti-PSA capture antibody (cAb)-coated microplate with the help of a silver nanoparticle-labeled detection antibody (AgNPs-dAb). Thereafter, the introduced AgNPs were dissolved with acid to release numerous silver ions. In this regard, an ion-exchange reaction occurred between the silver ions and ZnO/CdS nanorods on the photosensitive electrode, thus producing ZnO/CdS/Ag2S nanohybrids to generate a relatively strong photocurrent. Under optimal conditions, the ion-exchange reaction-based PEC immunoassay exhibited a good linear range of 0.05–50 ng mL−1 and allowed the detection of the target PSA at a concentration as low as 0.018 ng mL−1. In addition, the PEC immunoassay displayed satisfactory repeatability, high specificity, and acceptable method accuracy. Importantly, the ion-exchange reaction-based PEC immunoassay provides a new perspective for the detection of other disease-related biomarkers by controlling the corresponding antibodies. [ABSTRACT FROM AUTHOR]

In this work, a novel electrochemiluminescence (ECL) aptasensor based on the resonance energy transfer (RET) effect between Ag3PO4-Cu-MOF (II) and silver nanoparticles (Ag NPs) is proposed. The ECL emission spectra of Ag3PO4-Cu-MOF and the ultraviolet absorption spectra of Ag NPs showed a good spectral overlap. Based on this, we designed an "on–off–on" ECL sensing strategy for the sensitive and specific detection of diethylstilbestrol (DES). Under the optimal conditions, the linear range of the sensor for DES detection was 1.0 × 10−12–1.0 × 10−4 M, with a detection limit of 7.2 × 10−13 M (S/N = 3). The method showed simple and fast operation, high sensitivity and selectivity, a strong anti-interference ability and good stability. More importantly, the developed aptasensor exhibited excellent recognition towards residual DES in actual water samples. The sensor has superior measurement capability and potential application value in the field of environment water quality monitoring. [ABSTRACT FROM AUTHOR]

Bismuth sulfide quantum dots (Bi2S3 QDs), which have excellent optical and thermoelectric properties, represent a green and non-toxic semiconductor material that has been widely used in catalysis and photoelectric conversion devices. At present, research on this material has gradually expanded into the biological field. Herein, the biomineralization method mediated by bovine serum albumin (BSA) was utilized to synthesize Bi2S3 QDs with monodispersity, excellent colloidal stability, and good biocompatibility. This is the first study on the electrochemiluminescence (ECL) characteristics of Bi2S3 QDs and related ECL mechanisms in detail. In addition, on the basis of Bi2S3 QDs, an ECL immunosensor was used for the ultrasensitive measurement of cyclin D1 (CCND1). The composite material, namely Au@Cu-Bi2S3 QDs was used as a high-sensitivity ECL probe, in which AuNPs were connected with Bi2S3 QDs through a copper(II) ion bridge. PDA-AgNPs made of dopamine (DA) and silver nanoparticles (AgNPs) were utilized as a carrier for fixing the primary antibody (Ab1), ultimately presenting a relatively wide detection range of 10 fg mL−1–1 μg mL−1. Moreover, quite a low detection limit (6.34 fg mL−1) was also obtained for an assay of CCND1. Results indicated that the immunosensor can provide a potential platform with fine stability and creditable reproducibility for clinical diagnosis. [ABSTRACT FROM AUTHOR]

The medical application of nanomaterials is growing fast. Amongst the most widely used, silver nanoparticles are antimicrobial agents whose key application is the care of burns and chronic wounds. Still, their absorption, distribution, metabolism and excretion behaviour in vivo has not yet been systematically investigated. We collected full-profile specimens of skin from four hospital patients with mid-to-deep thickness burns or equivalent skin wounds, treated with dressings containing silver nanoparticles or silver sulfadiazine. Synchrotron radiation μXRF/μXANES and laser ablation-ICP-MS were used to provide the first semi-quantitative/high resolution direct information on the spatiotemporal distribution and speciation of silver in vivo. The metal was rapidly released onto the wound surface, followed by a significant structure-dependent penetration into the damaged tissues. This was accompanied by sequential processes of metallic silver dissolution, chloride complexation, change to metal–thiol protein complexes, and final mobilization into deeper skin layers towards the vascular networks. Complete local clearance of silver was observed after 12 days of treatment in the case of full healing. The results provide a complete insight into the dynamics of silver in real human wounds, and a new basis for the design of innovative silver nanomaterials with optimal antibacterial efficacy and minimized risk for the patient. [ABSTRACT FROM AUTHOR]

Ultrasensitive detection of monomeric β-amyloid peptides is of fundamental significance for studying the pathological progression of Alzheimer's disease (AD). In this article, by facilely engineering a gold microelectrode interface, we developed a novel electrochemical biosensor for sensitive and selective monitoring of β-amyloid peptide (Aβ) monomers in cerebrospinal fluid (CSF). Through specific Cu2+-Aβ-hemin coordination, Aβ directed the assembly of Cu2+-PEI/AuNPs-hemin nanoprobes into network aggregates on a microelectrode interface, which promoted the enrichment of Aβ monomers on the microelectrode. Furthermore, the AuNP aggregate promotes the deposition of silver nanoparticles, which were utilized for the electrochemical stripping analysis of the Aβ monomer. The proposed method displayed ultra-sensitivity for Aβ monomers with the detection limit down to 0.2 pM. Besides, high selectivity toward Aβ monomers was observed. These remarkable analytical performances render the electrochemical biosensor useful for evaluating the dynamic change of Aβ monomer level in CSF of live mice with AD, promoting the investigation of the role that Aβ monomers play in brain events. [ABSTRACT FROM AUTHOR]

Resistive pulse sensing with nanopores is expected to enable identification and analysis of nanoscale objects in ionic solutions. However, there is currently no remarkable method to characterize the three-dimensional shape of charged biomolecules or nanoparticles with low-cost and high-throughput. Here we demonstrate the sensing capability of solid-state nanopores for shape characterization of single nanoparticles by monitoring the ionic current blockades during their electrophoretic translocation through nanopores. By using nanopores that are a bit larger than the particles, shape characterization of both spherical and cubic silver nanoparticles is successfully realized due to their rapid rotation with respect to the pore axis, which is further validated by our all-atom molecular dynamics simulations. The single-molecule approach based on nanopores will allow people to measure the dimension and to characterize the shape of single nanoparticles or proteins simultaneously in real time, which is significant for its potential application in investigation of structural biology and proteomics in the near future. [ABSTRACT FROM AUTHOR]

A novel platform of microfluidic paper-based analytical devices (μPADs) for dual detection of bisphenol A (BPA), a model analyte, was fabricated using an electronic digital plotter to create the stacked layer of μPADs and generate the lateral-flow channel without using an external pump. Two detection techniques, including electrochemical detection and laser desorption ionization mass spectrometric detection (LDI-MS), were used complementarily to improve the precision in the detection of BPA. The fluid sample was delivered to both detection zones by the capillary action, automatically generated from the fabricated microfluidic device. For an electrochemical sensor, two ballpoint pens filled with silver nanoparticles (AgNPs) and multiwall carbon nanotube (MWCNT) ink were used to print onto the paper with a contact printing method using a digital plotter. To further improve the sensitivity, zinc oxide (ZnO) was used to modify both electrochemical and LDI-MS detection zones. For BPA detection, high electrocatalytic properties and strong UV absorption of ZnO promote the electron transfer in the electrochemical sensor and ionization efficiency in LDI-MS with low interferences compared with a conventional organic matrix. Under optimal conditions, this platform showed a dual detection capability for BPA with a detection limit of 0.35 μM for electrochemical detection and with an ultralow detection limit of 0.01 pM for LDI-MS. This novel platform might be very useful for trace analyses requiring high precision detection of various analytes. [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]

A simple enzyme-free method based on surface-enhanced Raman scattering (SERS) was developed for the first time to detect H2O2 in food by etching a self-assembled film of silver nanoparticles (Ag NPs) on a glass substrate. H2O2 is able to oxidize Ag NPs to yield Ag+ ions; this process reduces the size of the Ag NPs and ultimately leads to a decrease in the SERS signal of the Raman probe. The intensities of the SERS spectra were strongly correlated with H2O2 concentration, which indicated that the Ag NP self-assembled SERS sensor can be successfully used for the quantitative analysis of H2O2. The main advantage of this SERS sensor is that it can directly detect H2O2 without introducing complex enzymatic reactions. This easy-to-operate and fast-response detection technology has great potential for the sensitive detection of H2O2 in food. [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]

Very close structure and property similarities among biothiols, such as glutathione (GSH), cysteine (Cys), and homocysteine (Hcy), present a major challenge to achieve their discriminative detection. In this contribution, a nanomaterial surface energy transfer (NSET) system was established to discriminate GSH from Cys and Hcy with the photoluminescence (PL) "switch-on" response. The nanosensor was constructed using nitrogen and sulphur co-doped carbon dots (N,S-CDs) and silver nanoparticles (AgNPs) through assembling an energy transfer-based quenching system, featuring the pH-promoted distinct PL "switch-on" response. Under neutral conditions, only Cys and Hcy can encapsulate AgNPs, leaving little chance for N,S-CD binding on the surface of AgNPs, which can lead to PL signal recovery, and the total quantity of Cys and Hcy can be determined. However, at pH 3.0 all three kinds of biothiols can lead to the PL signal recovery and the total quantity of GSH, Cys, and Hcy can be determined, due to the similar slopes and intercepts of their calibration curves. Thus, the concentration of GSH could be further calculated and the strategy was successfully applied for the detection of GSH in human serum, demonstrating its potential in bioanalysis and significance in addressing biological and medicinal requirements. [ABSTRACT FROM AUTHOR]

In this study, we report a metallobioassay for ultrasensitive electrochemical detection of prostate-specific antigen (PSA) based on DNA hybridization chain reaction (HCR) for amplifying the signal, which is derived from silver nanoparticles (Ag NPs) on DNA concatemers. The assay mainly consists of primary antibody (Ab1), secondary antibody (Ab2) with primer, and a signal probe. In the presence of PSA, a sandwich structure with DNA concatemers was formed, and numerous Ag NPs were loaded on the DNA concatemers, resulting in a strong signal, which appeared within the applied potential (−0.2 V to 0.3 V) in the phosphate-buffered saline (PBS). Differential pulse voltammetry (DPV) was employed to evaluate the analytical performance. Under optimal conditions, the DPV peak current of Ag NPs at about +0.09 V (vs. SCE) increased linearly as the logarithm of PSA concentration increased from 0.1 pg mL−1 to 75 ng mL−1, and the detection limit of PSA was estimated to be 0.033 pg mL−1 at the signal to noise ratio of 3. In addition, the assay was evaluated with human serum samples, and satisfying results were obtained, indicating that the assay can achieve PSA detection in the serum sample. [ABSTRACT FROM AUTHOR]

A novel ultrasensitive photoelectrochemical sensor for benzoyl peroxide (BPO) was constructed under visible light irradiation. A novel nanostructured material made of molecularly imprinted polymer (MIP)-modified silver iodide nanoparticle–titanium dioxide nanotube arrays (AgINPs–TiO2 NTs) was designed as a photoactive electrode (denoted as MIP@AgINPs–TiO2 NTs). AgI-sensitized TiO2 nanotube arrays were prepared by a simple dissolution–precipitation–calcination process and then employed as a matrix to graft the MIP recognition element. Such a newly designed molecularly imprinted photoelectrochemical sensor exhibits high sensitivity and selectivity for the determination of BPO. The photoelectrochemical analysis is highly linear over the BPO concentration range from 1 × 10−12 mol L−1 to 5 × 10−10 mol L−1 with a detection limit of 2.53 × 10−13 mol L−1 (S/N = 3, n = 11). The sensor designed based on a low cost and highly sensitive assay was successfully applied in the determination of BPO in spiked samples. [ABSTRACT FROM AUTHOR]

Direct detection, or inferring the presence of illicit substances, is of great forensic and toxicological value. Surface-enhanced Raman spectroscopy (SERS) has been shown capable of detecting such molecules in a quick and sensitive manner. Herein we describe an analysis strategy for quantitation of low concentrations of three analytes (methamphetamine, cocaine, and papaverine) by SERS analysis using the citrate capping agent that initially saturates the silver nanoparticles’ surface as an in situ standard. The citrate is subsequently displaced by the analyte to an extent dependent on the analyte's concentration in the analyte solution. A general model for the competitive adsorption of citrate and a target analyte was developed and used to determine the relative concentrations of the two species coexisting on the surface of the silver nanoparticles. To apply this model, classical least squares (CLS) was used to extract the relative SERS contribution of each of the two species in a given SERS spectrum, thereby accurately determining the analyte concentration in the sample solution. This approach, in essence, transforms citrate into a local standard against which the concentration of an analyte can be reliably determined. [ABSTRACT FROM AUTHOR]

Based on the inner filter effect and charge transfer dual response mechanism, a dual response ratiometric fluorescent probe (D-RFP) with two reversible signal changes for sensing H2O2 and glucose was developed. The D-RFP was proposed by embedding glycine-derived carbon dots (CDs) (λem = 400 nm) into silica nanoparticles and covalently linking CdTe quantum dots (QDs) (λem = 600 nm) onto the surface of silica nanoparticles. When silver nanoparticles (Ag NPs) were mixed with D-RFP, the fluorescence intensity of CDs can be quenched by Ag NPs via the inner filter effect. With the addition of H2O2, Ag NPs were etched to silver ions, thus recovering the fluorescence of CDs. In the meantime, fluorescence of QDs was quenched by Ag+via charge transfer. Under optimal conditions, D-RFP displayed high sensitivity toward H2O2 with a detection limit of 0.28 μM. Based on the conversion of glucose into H2O2, D-RFP can also be exploited for glucose sensing with a detection limit of 0.59 μM. The approach developed can be applied to monitor glucose levels in human serum samples with satisfactory results, and the results of the heathy and diabetic patients can be distinguished by the naked eye. Moreover, this method provides a new idea for designing a high-sensitivity D-RFP. [ABSTRACT FROM AUTHOR]

Ascorbic acid (AA) and alkaline phosphatase (ALP) serve as an important coenzyme and enzyme in multiple biological metabolism reactions, respectively, and abnormal levels of these substrates have been associated with several diseases. Herein, a new and simple fluorescence strategy has been developed for AA and ALP sensing by exploiting CdTe quantum dots (QDs) as an effective signal indicator. This method is mainly based on the selective fluorescence-quenching reaction between Ag+ and CdTe QDs, as opposed to silver nanoparticles (Ag NPs); Ag+ can be reduced to Ag NPs by AA. Furthermore, by taking advantage of AA as a mediator, this strategy is further exploited for ALP assay given that ALP can cause the hydrolysis of l-ascorbic acid-2-phosphate (AAP), which yields AA. Under optimal conditions, controlled generation of Ag NPs and the selective recognition-based sensing system exhibit high sensitivity toward AA and ALP with limits of detection (LODs) of 3 μM and 0.25 U L−1 and linear ranges of detection from 0 to 800 μM and 1 to 1000 U L−1, respectively. Moreover, the sensor was successfully used for assaying AA in fruit juice and ALP in human serum. The results demonstrate that the proposed fluorescence strategy has significant advantages, such as its simplicity, cost-effectiveness, and rapid runtime, and the operational convenience of this label-free method further demonstrates its potential for constructing effective sensors with biochemical and clinical applications. [ABSTRACT FROM AUTHOR]

The present work aims to study the effects that acute exposure to low concentrations of silver nanoparticles (AgNPs) cause in digestive glands of terrestrial isopods (Porcellio scaber). The experiments were designed to integrate different analytical techniques, such as transmission electron microscopy, atomic absorption spectroscopy, proton induced X-ray emission, and Fourier transform IR imaging (FTIRI), in order to gain a comprehensive insight into the process from the AgNPs’ synthesis to their interaction with biological tissues in vivo. To this aim, terrestrial isopods were fed with AgNPs having different shapes, sizes, and concentrations. For all the tested conditions, no toxicity at the whole organism level was observed after 14 days of exposure. However, FTIRI showed that AgNPs caused detectable local changes in proteins, lipids, nucleic acids and carbohydrates at the tissue level, to an extent dependent on the interplay of the AgNPs’ properties: shape, size, concentration and dissolution of ions from them. [ABSTRACT FROM AUTHOR]

We report for the first time the development of a distance-based paper sensor for a simple, inexpensive, instrument-free, and portable determination of chloride ions. Our analysis reaction is based on the oxidative etching of silver nanoparticles (AgNPs) to form AgCl in the presence of Cl− and H2O2. H2O2 reacts with AgNPs in the channel of the paper device and Cl− in the sample forming a white precipitate (AgCl) where the white color band length is proportional to the Cl− concentration. Quantification of Cl− is achieved by measuring the length of the white color band using a ruler printed on the side of the channel. Under optimal conditions, the distance-based paper sensor was characterized by a working range of 25–1000 mg L−1 (R2 = 0.9954) and the naked eye detection limit (LOD) was 2 mg L−1 (0.08 μg). Our sensor was found to be reproducible with a relative standard deviation of less than 4.51% (n = 10). The levels of Cl− in real water samples measured using our proposed device were within the error of the values measured using traditional tests but without the need for any external instrumentation. Therefore, our proposed method presents acceptable accuracy, precision, and high selectivity for point of need monitoring of Cl− in real water samples. [ABSTRACT FROM AUTHOR]

Previous studies have shown that nanoparticles can induce autophagy, and the main approach for investigating autophagy induced by nanoparticles is via traditional methods such as TEM and biochemical assay. These methods measurements suffer from the disadvantages of complicated experimental processes, cell destruction, as well as lack of characterization of individual stages of the autophagy pathway. Surface-enhanced Raman scattering (SERS) has been extensively used in biological applications. With the combination of SERS and chemometric methods, such as principal component analysis-linear discriminant analysis (PCA-LDA), identification and distribution mapping of endosomes and lysosomes in the endocytosis of Au nanoparticles has been achieved by segregating the spectra from complex SERS data sets in the previous study. In this study, silver@gold core–shell nanoparticles (Ag@Au NPs) were synthesized by reduction of gold ions on the surface of the silver nanoparticles, and the autophagy induced by Ag@Au NPs was studied with Ag@Au NPs serving both as an autophagy inducer and as a high-performance SERS substrate. Pro-survival autophagy induced by Ag@Au NPs was proved by the western blot assay, flow cytometry and fluorescent staining. Furthermore, the autophagy pathway in Ag@Au NPs-treated cells was first elucidated by SERS combined with a modified reference-based PCA-LDA methodology. This study provides a feasible way of using SERS to elucidate the autophagy pathway induced by nanoparticles. [ABSTRACT FROM AUTHOR]

As an emerging category of fluorophores, nucleic acid-stabilized silver nanoclusters (DNA/AgNCs) have attracted a great deal of interest and have been widely applied for interdisciplinary research. In this work, we have constructed a novel DNA/AgNC probe for cell apoptosis detection and imaging based on an enzyme-polymerized polyadenylic acid (poly-dA) DNA chain and a toehold strand displacement reaction. This method can effectively “tag” intracellular genomic DNA fragments, a biochemical hallmark of apoptosis, with poly-dA DNA chains up to 400-bases produced by terminal deoxynucleotidyl transferase (TdT)-activated polymerization. The strand displacement initiated by the target poly-dA DNA chain releases the quencher labeled-DNA from the DNA/AgNC probe, leading to a significant fluorescence lighting-up of DNA/AgNCs for the sensitive detection of cell apoptosis, with a high signal-to-background ratio (S/B = 58). Using the DNA/AgNC-based assay, as few as 20 apoptotic cells can be detected in vitro. Furthermore, the feasibility of our approach was demonstrated by the in situ quantitative analysis of apoptosis in HepG2 cells without the need for tedious washing and separation steps. [ABSTRACT FROM AUTHOR]

In this work, an application of a design of experiments approach for the optimization of an isoniazid assay on a single-area inkjet-printed paper-based analytical device (PAD) is described. For this purpose, a central composite design was used for evaluation of the effect of device geometry and amount of assay reagents on the efficiency of the proposed device. The factors of interest were printed length, width, and sampling volume as factors related to device geometry, and amounts of the assay reagents polyvinyl alcohol (PVA), NH4OH, and AgNO3. Deposition of the assay reagents was performed by a thermal inkjet printer. The colorimetric assay mechanism of this device is based on the chemical interaction of isoniazid, ammonium hydroxide, and PVA with silver ions to induce the formation of yellow silver nanoparticles (AgNPs). The in situ-formed AgNPs can be easily detected by the naked eye or with a simple flat-bed scanner. Under optimal conditions, the calibration curve was linear in the isoniazid concentration range 0.03–10 mmol L−1 with a relative standard deviation of 3.4% (n = 5 for determination of 1.0 mmol L−1). Finally, the application of the proposed device for isoniazid determination in pharmaceutical preparations produced satisfactory results. [ABSTRACT FROM AUTHOR]

A flexible 3D hybrid PC/Ag surface-enhanced Raman scattering (SERS) substrate was fabricated through the combination of electrospinning and in situ chemical reduction. Due to the rough surface morphology and the intricate 3D structure, a high density of Raman “hotspots” was formed at the junctions of cross-linked nanofibers, resulting in excellent sensitivity to a probe molecule (4-aminothiophenol). The nanofibers were modified with l-cysteine to capture TNT molecules by the formation of a Meisenheimer complex, after which positively charged 4-ATP-labelled AgNPs were introduced to the system, which both generated more hotspots and led to a linear relationship between the TNT concentration and the SERS intensity of the labelled molecules. As a result, a good linear response ranging from 10−8 to 10−12 M was achieved, and the detection limit for TNT was as low as 2.05 × 10−13 M. This strategy demonstrates an ultra-sensitive approach for the detection of trace amounts of TNT, and a promising method for the detection of many other analogous explosives. [ABSTRACT FROM AUTHOR]

Herein, a facile solvent mediated silver nanoparticle (AgNP) mirror was introduced as a reproducible and sensitive surface-enhanced Raman scattering (SERS) substrate. The AgNP mirror was fabricated based on commercially available citrate coated AgNPs via a facile and unique water–solvent interface assembly method without using any electrical equipment. By adding 0.2 mg ml−1 citrate coated AgNPs dropwise into a mediating solvent, self-assembled AgNP mirrors were formed instantly and gradually settled down at the bottom. The mediating solvent is the key for this fabrication, which should contain a mixture of a non-polar (e.g. hexane, cyclohexane, and iso-octane) and a polar (e.g., acetonitrile, acetone, methanol, and ethanol) organic solvents that have a lower density than water. The fabricated AgNP mirror showed a uniform monolayer arrangement which produced highly reproducible and sensitive signals. The coefficient of variance (i.e., percentage relative standard deviation) for AgNP mirrors was 7.3% compared to 33.0% for AgNP aggregates. A lower limit of detection (0.008 ppm) and a higher coefficient of determination (0.9981) for the detection of the fonofos pesticide were also obtained from the AgNP mirror compared to that from the AgNP aggregates. The practical application of this nanoscale AgNP mirror sensing substrate was also confirmed by its accurate quantification of 0.5 ppm fonofos in apple juice and green tea (i.e., 105.06% and 106.16% recovery value, respectively). [ABSTRACT FROM AUTHOR]

Surface-enhanced hyper-Raman scattering (SEHRS) spectra were obtained at desired positions on yeast by focusing a continuous wave near-infrared laser beam while silver nanoparticles (AgNPs) were simultaneously optically trapped. However, the optically trapped colloidal AgNP suspension bubbled up at the focusing point, preventing spectral measurement. In the case of optically trapped AgNPs functionalized with 4-mercaptobenzoic acid (p-MBA), surface-enhanced hyper-Rayleigh scattering was considerably strong, indicating the suppression of the photothermal conversion to form the bubble. Interestingly, the SEHRS peaks that are attributed not only to p-MBA, but also to other species, were very occasionally observed. They may be partly assigned to the β1,3 glucan and protein amide II band. The SEHRS peak at 1366 cm−1 was barely visible in the measurements of conventional baker's yeast even in the suspension (pH 9) despite the effects of high pH on p-MBA. In contrast, the SEHRS peak in the measurements of yeast for biological applications was occasionally observed at 1366 cm−1. This suggests that acidity is correlated with fermentation efficiency. At different positions on single yeast cells, the intensity of the SEHRS peak at 1366 cm−1 varied. This result represents the pH distribution on yeast. [ABSTRACT FROM AUTHOR]

This work reports a surface acoustic wave (SAW) DNA sensor that synergizes the surface mass effect for signal-amplified and sequence-specific DNA detection in blood serum. By combining an enzyme-mediated DNA extension reaction (both viscoelastic and mass fractions) with the in situ synthesis of silver nanoparticles (mass fraction), a highly sensitive SAW biosensing interface with synergistic mass loading was tailor-engineered. As target DNA hybridized with the surface-confined capture probes, the exposed 3′-OH terminal of the target sequence could be triggered to elongate in the presence of terminal deoxynucleoside transferase (TdT) and deoxy-ribonucleoside triphosphate (dNTP), thereby producing an evident mass effect. Importantly, the extended domain can serve as a template to specifically hybridize with Ag+-binding sequences. In the presence of reducing agents, the accumulated silver ions would nucleate for the in situ synthesis of silver nanoparticles, further enhancing the mass loading. By using this approach, we observed a rapid growth event of silver nanoparticles for signal enhancement, which improved the detection limit (0.8 pM) of the SAW sensor by 3 orders of magnitude as compared to the strategy without signal amplification (at the nanomolar level). The sensor also achieved a high specificity in discriminating even a single-mismatched DNA sequence, and meanwhile could probe the low-abundance DNA molecules directly in human serum with minimal interference. These advantages make the SAW biosensor promising for practical applications, such as monitoring of molecular interactions and disease diagnostics. [ABSTRACT FROM AUTHOR]

In this study, hyperbranched polyethyleneimine-protected silver nanoclusters (hPEI-AgNCs) with excellent electrochemiluminescence (ECL) emission in the presence of coreactant K2S2O8 were prepared by chemical reduction of silver ions (silver nitrate) coordinated with dendrigraft polymer, and successfully used for the construction of an ECL immunosensor. Polyaniline (PANI)/polypyrrole (PPy)-silver (Ag) dendrites with good electrical conductivity and biocompatibility were electropolymerized on the surface of indium tin oxide (ITO) electrode as carriers. Porous ZnO sphere-loaded hPEI-AgNCs-induced signal amplification strategies were integrated exquisitely and applied sufficiently. Taking carcinoembryonic antigen (CEA) as an example, under optimal conditions, the CEA concentration was determined to be in the range of 10−3 ng mL−1–100 ng mL−1 and with a detection limit of 0.4 pg mL−1 using this method; it exhibited excellent selectivity, high stability, and acceptable fabrication reproducibility. It was anticipated that hPEI-AgNCs would have promising applications in green, selective, and sensitive detection of target analytes in the future. [ABSTRACT FROM AUTHOR]

Artificial enzymes have become an increasingly interesting area of research due to their many advantages over natural protein enzymes which are expensive, difficult to isolate and unable to stand harsh environments. An important area of this research involves using metal nanoparticles as artificial enzymes, known as nanozymes, which exhibit peroxidase-like activity enabling them to catalyse the oxidation of substrates such as 3,3′,5,5′-tetramethylbenzidine (TMB) in the presence of hydrogen peroxide (H2O2), giving a colorimetric response. Here we exploit the catalytic activity of silver nanoparticles (Ag NPs) in a surface based silver-linked immunosorbent assay (SLISA) to detect human C-reactive protein (CRP), an inflammatory marker. Ag NPs were conjugated to antibodies with specific recognition for the corresponding target antigenic molecule, CRP, and the Ag NPs were used to catalyse the oxidation of TMB by H2O2. The resulting coloured oxidation product was detected using SERRS. We demonstrate that Ag NPs can replace the enzymes used in a conventional ELISA and a detection limit of 1.09 ng mL−1 of CRP can be achieved. It indicates the promise for SLISAs for biomarker detection and opens the way for further assays of this nature to be created. This novel assay has the potential to be optimised to detect lower levels of CRP and can be further extended for the sensitive and specific detection of other relevant biomarkers. [ABSTRACT FROM AUTHOR]

We have developed a novel method for detecting nicotinamide adenine dinucleotide (NAD+) based on fluorescent silver nanoclusters (AgNCs) stabilized by a dumbbell-shaped DNA template containing two cytosine-loops joined in a dsDNA stem. The design involves two types of components: a dumbbell-shaped DNA template and three enzymes. In the presence of NAD+ as a cofactor, Escherichia coli DNA ligase (E.coli DNA ligase) catalyzes template ligation to generate a sealed (no terminal nucleotides) dumbbell-shaped structure, preventing digestion by exonuclease III (Exo III) and exonuclease I (Exo I). The loop regions of the intact template serve as sites for the deposition of highly fluorescent AgNCs. In the absence of NAD+, the ligation reaction does not occur, and the unsealed dumbbell-shaped template is digested into mononucleotides via cooperation of Exo III and Exo I. The destruction of the DNA template results in the agglomeration of AgNCs into silver nanoparticles with low fluorescence. The fluorescence enhancement depends on the ligation and digestion of the DNA template, allowing quantitative detection of NAD+ in the range of 0.5 nM–5000 nM with a detection limit of ∼0.25 nM. [ABSTRACT FROM AUTHOR]

A surface-enhanced Raman scattering (SERS) tapered fiber probe has been developed by using a chemically-etched tapered fiber tip and silanization of the surface of the fiber taper, followed by the hydrothermal growth of silver nanoparticles (AgNPs) on the silanized fiber taper. 4-Aminothiophenol (4-ATP) was selected as the target analyte to study the SERS responses of the prepared fiber SERS probe in an optrode remote detection mode. The experimental results show that the prepared fiber probe exhibited the ability to detect the 4-ATP molecule at a concentration as low as 10−9 M and good reproducibility with the relative standard deviation (RSD) values being less than 9.1% for the strongest Raman peak. This work gives a novel and reliable way to realize a fiber SERS probe with high sensitivity, long-term stability, good reproducibility, and superior recyclability, exhibiting potential in SERS-based in situ detection application. [ABSTRACT FROM AUTHOR]

A rapid, sensitive, and label-free SERS detection method for bacteria pathogens is reported for the first time. The method, which is based on the combination of polyethylenimine (PEI)-modified Au-coated magnetic microspheres (Fe3O4@Au@PEI) and concentrated Au@Ag nanoparticles (NPs), was named the capture–enrichment–enhancement (CEE) three-step method. A novel Fe3O4@Au microsphere with monodispersity and strong magnetic responsiveness was synthesized as a magnetic SERS substrate and amino functionalized by PEI self-assembly. The negatively charged bacteria were quickly captured and enriched by the positively charged Fe3O4@Au@PEI microspheres, and the bacteria SERS signal was synergistically enhanced by using Fe3O4@Au@PEI microspheres and Au@Ag NPs in conjunction. The CEE three-step method proved useful in tap water and milk samples, and the total assay time required was only 10 min. Results further demonstrated that the CEE three-step method could be a common approach for detecting a wide range of bacteria, as verified by its detection of the Gram-positive bacterium E. coli and Gram-positive bacterium S. aureus at a detection limit of as low as 103 cells per mL. Therefore, our CEE three-step method offered the significant advantages of short assay time, simple operating procedure, and higher sensitivity than previously reported methods of SERS-based bacteria detection. [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]