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In response to the growing demand for biomolecular diagnostics, metasurface (MS) platforms based on high-Q resonators have demonstrated their capability to detect analytes with smart data processing and image analysis technologies. However, high-Q resonator meta-atom arrays are highly sensitive to the fabrication process and chemical surface functionalization. Thus, spectrum scanning systems are required to monitor the resonant wavelength changes at every step, from fabrication to practical sensing. In this study, we propose an innovative dielectric resonator-independent MS platform that enables spectrometer-less biomolecule detection using artificial intelligence (AI) at a visible wavelength. Functionalizing the focused vortex MS to capture gold nanoparticle (AuNP)-based sandwich immunoassays causes the resulting vortex beam profiles to be significantly affected by the localized surface plasmon resonance (LSPR) occurring between AuNPs and meta-atoms. The convolutional neural network algorithm was carefully trained to accurately classify the AuNP concentration-dependent focused vortex beam, facilitating the determination of the concentration of the targeted diagnostic biomolecule. Successful in situ identification of various biomolecule concentrations was achieved with over 99 % accuracy, indicating the potential of combining an LSPR-susceptible MS platform and AI for continuously tracking various chemical and biological compounds. [Display omitted] • A dielectric resonator-independent and localized surface plasmon resonance-susceptible metasurface platform. • Diverse vortex beam patterns generation due to the localized surface plasmon resonance of gold nanoparticles on meta-atoms. • Determination of the concentration of targeted diagnostic molecules assisted by artificial intelligence. [ABSTRACT FROM AUTHOR]

Small extracellular vesicle-associated microRNAs (sEV-miRNAs) have emerged as critical biomarkers for cancer diagnosis, yet the rapid detection of these low-abundance molecules in clinical samples remains a formidable challenge. Herein, a simple turbo-like localized catalytic hairpin assembly (TL-CHA) was proposed for sEV-miR-1246 measurement. This electrochemical sensor achieves dual localization through the ingeniously use of AuNPs and DNA nanowires, which provides rich sites for CHA cascade amplification, significantly enhancing the effective reaction and amplify the detection response. Leveraging this innovative design, this biosensor demonstrated the ability to detect sEV-miRNA at concentrations as low as 5.24 aM in a time frame of 30 min. The precision of the measurements was validated through reverse transcription quantitative polymerase chain reaction. Furthermore, the sensor was used for analyzing plasma samples from gastric cancer patients yielded AUC values of 0.973 for all stages and 0.945 for early stages. This demonstrates the sensor's robust performance in both the staging diagnosis and early screening of gastric cancer. Therefore, this platform has great potential for the clinical cancer diagnosis. [Display omitted] • This work achieves dual localisation by using AuNPs and DNA nanotechnology, providing a simple tool for cancer screening. [ABSTRACT FROM AUTHOR]

We report a highly sensitive approach for detecting microRNA-21 (miR-21) in cancer cells and human serum by using Au@Si nanocomposite labeled lateral flow assay. The Au@Si nanocomposite was prepared by coating numerous 3–5 nm gold nanoparticles (GNP) on a silica nanoparticle (SiNP) with a diameter of 150 nm and used as colored label on the lateral flow assay for signal amplification. TEM results show there are around 1000 GNPs coated on the SiNP surface. The principle of miR-21 detection is based on on-strip DNA-microRNA hybridization reactions to form DNA-miR-21-DNA-Au@Si complexes, which are captured on the test zone of the lateral flow test strip and produce a visible red band. A thiol-modified detecting DNA probe (Det-DNA) and a biotin-modified capturing DNA probe (Cap-DNA), which are complementary to miR-21, were used to prepare the lateral flow test strips. After systematic optimization, the method can detect a minimum concentration of 1.0 pM miR-21, which is 60 times lower than that of the GNP-based lateral flow assay (Gao et al. Biosens & Bioelectro, 2014, 54, 578–584). The method was applied to detect miR-21 in cancer cells and spiked human serum with satisfactory results. Gold nanoparticles coated silica nanosphere as colored label for sensitive lateral flow microRNA-21 assay. Image 1 • Gold@Silica nanocomposite was prepared by loading around one thousand 3–5 nm gold nanoparticles on a silica nanosphere with a diameter of 150 nm. • Lateral flow microRNA-21 assay was developed by using the gold@Silica nanocomposite as colored tag for signal amplification. • A minimum concentration of 1.0 pM microRNA-21 can be detected visually within 20 min. • The detection limit is 60 folds lower than that of gold nanoparticle based lateral flow microRNA assay. • The assay was applied to detect microRNA-21 in cancer cells and human serum with satisfied results. [ABSTRACT FROM AUTHOR]

In the last few years, sildenafil and its analogues have emerged as an illegal ingredient in health food and products, causing illness and death. To address this problem, herein, a gold nanoparticle-based immunochromatographic assay for simultaneous detection sildenafil and its analogues was developed by using just one monoclonal antibody. This method can realize qualitative and quantitative analysis of sildenafil and its analogues with a detection range (IC 20 -IC 80) of 0.12–28.05 ng mL−1, the IC 50 was 0.31–8.45 ng mL−1 and the cut-off value was 5.0–80.0 ng mL−1. Meanwhile, this method could also accomplish semi-quantitative analysis of vardenafil with a cut-off value of 0.625 ng mL−1. The detection can be finished in 6 min and showed no cross-reactivity with avanafil and tadalafil. The recoveries of spiked samples ranged from 70.5 to 118.9% with a coefficient variation less than 15%, which confirmed the assay was sensitive, accurate and adapted to the rapid determination of sildenafil and its analogues. Sildenafil adulteration. Image 1 • A sensitive GNPs ICA for 10 sildenafil adulterants was developed based on one broad-spectrum mAb. • The comparison with reported antibodies were also made by molecular simulation to evaluate the better performance. • The test results of real samples have good correlation with UPLC-MS/MS. [ABSTRACT FROM AUTHOR]

The development of powerful techniques for sensitive detection of nucleic acids has attracted much attention for fabricating accurate biosensors in various fields, such as genomics, clinical diagnostics, and forensic sciences. Up to now, different systems have been introduced, the majority of which are expensive, time-consuming, and relatively low selectivity/limit of detection. These limitations caught our attention to fabricate a nucleic acid responsive system by combining three layers of signal amplification strategy, namely a split proximity circuit (SPC), a catalytic hairpin assembly (CHA), and a DNA hydrogel. Herein, by SPC operation, two initiators and a target strand were assembled and activated the CHA reaction in the presence of three 5′-cytosine (C)-rich hairpins. Then, produced C-rich embedded three-way junction structures could form i-motif structures under acidic environment followed by a transition from sol to gel state. To acquire a quantitative and colorimetric measurement, gold nanoparticles (GNPs) were used that encapsulated and sediment by the gel formation. The resulting platform detected the target with a limit of detection of 1 pM and considerable selectivity. Image 1 • DNA nanotechnology has sparked the construction of the many nanostructures in biosensing platform. • The present study enabled fabrication of a colorimetric nucleic acid responsive biosensor via LOD as low as 1 pM. • Three amplification strategies are implemented in this assay, namely SPC, CHA, and DNA hydrogel that provide high sensitivity and selectivity. • Monitoring of various targets, such as nucleic acid, metabolites, cancer cells, and sites of infection can be considered for this assay. [ABSTRACT FROM AUTHOR]

Rapid increasing outbreak of Hepatitis E virus (HEV) shows an urgent need of HEV detection. Instead of time consuming and expensive RT-qPCR, an efficient and quick monitoring system is in utmost demand which can be comparable with the RT-qPCR in term of reliability and detection limit. An advanced platform for immunoassay has been constructed in this study by a nanozyme that constitutes anti-HEV IgG antibody-conjugated gold nanoparticles (Ab-AuNPs) as core and in situ silver deposition on the surface of Ab-AuNPs as outer shell. The virus has been entrapped on the nanocomposites while the silver-shell has decomposed back to the silver ions (Ag+) by adding a tetramethylbenzidine (TMBZ) and hydrogen peroxide (H 2 O 2) which indirectly quantifies the target virus concentration. Counterpart to only applying nanozyme, by incorporation of the enhanced effect of Ag shell on the AuNP-based nanozyme, the advance deposition has been confirmed to prove the signal amplification mechanism in the proposed immunoassay. Most importantly, the sensor performances have examined on the HEV, collected from the HEV-infected monkey over a period of 45 days. It was successfully correlated with the standard RT-qPCR data, showing the applicability of this immunoassay as a real-time monitoring on the HEV infection. The in situ formation of AuNPs@Ag as nanozyme in this capture immunoassay leads to a promising advancement over the conventional methods and nanozyme-based immunoassay in real application which can be a good substitute of RT-qPCR in near future. Image 1 • In situ silver deposition on surface of gold nanoparticles was prepared. • An advanced platform for immunoassay has amplified signal significantly. • HEV was successfully detected from fecal sample from HEV-infected monkey. • Sensor performance was correlated with their standard RT-qPCR data. [ABSTRACT FROM AUTHOR]

Protein glycosylation is an important post-translational modification and glycoproteins are associated with many crucial metabolic progresses of life. In order to detect glycoproteins sensitively, we propose a gold nanoparticles (GNPs) enumeration method based on boronate affinity sandwich system, which is constructed between the boronic acid polymer functionalized magnetic nanoparticles (Fe 3 O 4 @MPS@VPBA NPs) and 4-mercaptophenylboronic acid modified GNPs (GNPs-MPBA) by the targeted glycoproteins as the linker. Therefore, the sandwich complex is formed, resulting in the decrease of GNPs-MPBA counts in the solution. Based on the dark-field microscope (DFM) imaging technique, the sensitive GNPs enumeration assay is developed for glycoproteins quantitation. Immunoglobulin (IgG), as one of the important glycoproteins, is introduced to evaluate the proposed method. A low detection limit of 1.22 ng mL−1 for IgG analysis is obtained. The result indicates that the proposed GNPs enumeration method offers a simple, effective, label-free and highly sensitive strategy without signal amplification. It also possesses great potential for various target molecules determination at the single-particle level in the future. Image 1 • A gold nanoparticles enumeration method is established for glycoprotein detection for the first time. • A specific boronate affinity sandwich system is constructed for glycoprotein assay. • A wider linear range of 10 ng mL−1 to 10 μg mL−1 and lower detection limit of 1.22 ng mL−1 are attained.. • The potential practicality is verified by analyzing IgG in complex serum samples. [ABSTRACT FROM AUTHOR]

In this study, a tunable biosensor using the localized surface plasmon resonance (LSPR), controlling the distance between fluorescent CdZnSeS/ZnSeS quantum dots (QDs) and gold nanoparticles (AuNPs) has been developed for the detection of virus. The distance between the AuNPs and QDs has been controlled by a linkage with a peptide chain of 18 amino acids. In the optimized condition, the fluorescent properties of the QDs have been enhanced due to the surface plasmon effect of the adjacent AuNPs. Successive virus binding on the peptide chain induces steric hindrance on the LSPR behavior and the fluorescence of QDs has been quenched. After analyzing all the possible aspect of the CdZnSeS/ZnSeS QD-peptide-AuNP nanocomposites, we have detected different concentration of influenza virus in a linear range of 10−14 to 10−9 g mL−1 with detection limit of 17.02 fg mL−1. On the basis of the obtained results, this proposed biosensor can be a good alternative for the detection of infectious viruses in the various range of sensing application. Image 1 • Tunable LSPR-based biosensor was developed by a fluorescent QDs and AuNPs, linked with a customized peptide. • Virus binding on the peptide chain induces restrictions on the LSPR transfer, resulting quenching. • Applying this sensor, influenza virus was detected in a wide linear range of 10−14 to 10−9 g mL−1. • This stable and covalently designed sensor shows excellent sensitivity with a detection limit of 17.02 fg mL−1. [ABSTRACT FROM AUTHOR]

Herein, we report a new probe for the determination of the concentration of NF-κB p50, one kind of DNA-binding transcription factors (TFs), by using Exonuclease III (Exo III)-aided amplification and gold nanoparticle mediated fluorescence intensity. Since TFs play critical roles in various biological processes, the detection of TFs can provide a lot of useful biological information for studding gene expression regulation related disease. In our system, in the presence of transcription factor, Exo III based amplification reaction was trigged. This enzymatic digestion results in the release of intermediate DNA and ultimately liberating the fluorophore (which, separated from the quencher of AuNP and BHQ2, now fluoresces). The released intermediate DNA then hybridizes with another strand3, whence the cycle starts anew. So, the fluorescence intensity reflects the NF-κB p50 concentration with a detection limit of 1.32 pM. Importantly, this method might be further extended to selectively detect various dsDNA-binding proteins by simply changing the binding-site sequences of strand1/strand2 duplex probes. Schematic presentation of the probe for ultrasensitive detection of NF-κB p50. In this probe, AuNP was employed as the frame and fluorophore Cy3 was used as the signal output element. Image 1 • We report a new strategy here for detecting NF-κB p50 concentration. • This strategy coupled DNA duplexes on AuNP surface with Exo III-aided amplification technique. • This strategy exhibits a good sensitivity with a limit of detection (LOD) of 1.32 pM. • This strategy has the potential for screening transcription factor inhibitors for drug research and development. [ABSTRACT FROM AUTHOR]

Gold nanoparticle-core spherical nucleic acids (AuNP core-SNAs), by virtue of the programmable nature of oligonucleotides, have yielded access to the innovative strategies for targeted biodiagnostics. Here, DNA-directed self-assembly of AuNP core-SNAs has been used to design a colorimetric method to sense HIV-1 viral nucleic acid. This strategy utilizes an oligonucleotide with sequence of 5′-untranslated region (5′ UTR) of the HIV-1 RNA genome anchored on the surface of AuNPs and a complementary linker strand with a palindromic sequence tail. In the absence of HIV-1 target nucleic acid the complementary linker induces self-assembly of SNAs based on sequence symmetry in the free palindromic tail which can bridge two DNA double helices. While in the presence of the target DNA, due to linker-target duplex formation, the colloidal stability and the red color of the SNAs solution are preserved. Picomole amounts of target DNA can easily be detected with the naked eyes. A 95-mer synthetic DNA strand with the same sequence of HIV-1 viral RNA was utilized for positive control of HIV-1 RNA. The selectivity of the selected linker was satisfactory up to 90% match. Image 1 • A simple colorimetric method to detect HIV-1 nucleic acid is developed. • Palindromic nature of the designed linker made a single component self-assembly system. • The detection is based on the inhibitory effect of the target HIV genome on AuNP core-SNAs assembly. • The method may be generalized to any nucleic acid targets with palindromic regions in their genome. [ABSTRACT FROM AUTHOR]

MicroRNAs (miRNAs) hold potential as useful biomarkers for early diagnosis and evaluation of diverse cancers, but their low abundance and short length make the detection of miRNAs face low sensitivity and accuracy. Herein, a photoluminescence (PL)-resonance light scattering (RLS) dual-mode method was developed for the sensitive and accurate detection of miRNA-141 using CdTe quantum dots (QDs) and Au nanoparticles. The presence of miRNA-141 induced PL quenching and RLS increasing. The limit of detection (LOD) was as low as 3.7 fM, and the miRNA-141 was detected linearly in a range from 10 fM to 10 nM. The dual signals generated no mutual interference and were detected using the same spectrophotometer, allowing for mutual validation to ensure the accuracy and reliability of the detection results. This study proposes valuable references for constructing dual-mode detection methods. [Display omitted] • A dual-mode strategy was developed for quantitative detection of miRNA-141. • Photoluminescence and resonance light scattering were combined as detection signals. • A detection limit of 3.7 fM was obtained, and serum miRNA detection was satisfactory. • The same apparatus, mutual validation and rare interference guaranteed the accuracy. [ABSTRACT FROM AUTHOR]

Salivary melatonin is a clinically used biomarker for diagnosing circadian rhythm sleep disorders. Current melatonin detection assays are complex, expensive, and in many cases do not adequately measure low levels of salivary melatonin. Precisely measuring melatonin levels at multiple time points is crucial for determining dim light melatonin onset to evaluate its circadian fluctuation as well as the extent of circadian disruption and consequently adapt treatment regimens. Moreover, melatonin low levels in saliva challenges the reliability of routine clinical testing. This paper presents the development of a novel, highly sensitive, yet cost-effective, colorimetric assay for the rapid detection of salivary melatonin utilizing aptamer-AuNPs. Among several types of the aptamer tested, the 36-mer MLT-A-2 aptamer-AuNP probe showed the highest sensitivity with a melatonin limit of detection of 0.0011 nM along with a limit of quantification of 0.0021 nM in saliva. Moreover, our assay showed preferential interaction with melatonin when tested in presence of other structurally similar counter-targets. Taken together, this study provides new parameters for a melatonin assay that meets adequate levels of sensitivity and selectivity. The developed colorimetric assay could be adapted in a point-of-care system for profiling salivary melatonin levels at multiple time points during 24 h, crucial for accurately diagnosing and monitoring circadian rhythm sleep disorders and beyond. [Display omitted] • The ultralow level of salivary melatonin detected using an aptamer-AuNP probe based assay. • Aptamers have a salt dependency for their structural change and melatonin binding. • Truncated 36-mer MLT-A-2 aptamer-AuNP showed high sensitivity with LOD = 0.0011 nM. • Assay showed high specificity and selectivity in the presence of counter-targets. [ABSTRACT FROM AUTHOR]

Campylobacter is the most common cause of infectious intestinal disease, with nearly all cases caused by two species: C. jejuni and C. coli . We recently reported a gold nanoparticle-based two-stage aptasensing platform, which was improved in the present study for the rapid and on-site detection of both C. jejuni and C. coli in food samples. Compared to the previous platform, the improved platform yielded a more obvious colour change from red to purple due to the aggregation of gold nanoparticles, and does not require additional time or a pH optimization step for the aptamers to be adsorbed onto the gold nanoparticles. Using a highly specific aptamer that binds to live C. jejuni and C. coli , the improved aptasensor was highly effective for testing pure culture samples. The accuracy of the newly developed platform was comparable ( p  = 0.688) to that of the gold-standard detection method of tazobactam-supplemented culture, whereas it was superior to the official agar-based detection method ( p  = 0.016) in a validation study with 50 naturally contaminated chicken carcass samples. This is the first study on a colorimetric sensor that targets both live C. coli and C. jejuni in naturally contaminated samples. In addition, we provide the first evidence that both morphological status and the amount of Campylobacter present play key roles in the effectiveness of colorimetric detection. Thus, suitable selection of an antibody or aptamer with consideration of the morphological status of pathogens in samples is essential for direct detection without enrichment. Our data suggest that the sensor developed in this study can provide an excellent screening method, with a reduction in the detection time from 48 h to 30 min after enrichment, thus saving time, labour, and cost. [ABSTRACT FROM AUTHOR]

We have developed a gold nanoparticle (AuNP)–based CTG repeat probing system displaying high quenching capability and combined it with isothermal amplification for the detection of miRNA 146a . This method of using a AuNP-based CTG repeat probing system with isothermal amplification allowed the highly sensitive (14 aM) and selective detection of miRNA 146a . A AuNP-based CTG repeat probing system having a hairpin structure and a dT F fluorophore exhibited highly efficient quenching because the CTG repeat–based stable hairpin structure imposed a close distance between the AuNP and the dT F residue. A small amount of miRNA 146a induced multiple copies of the CAG repeat sequence during rolling circle amplification; the AuNP-based CTG repeat probing system then bound to the complementary multiple-copy CAG repeat sequence, thereby inducing a structural change from a hairpin to a linear structure with amplified fluorescence. This AuNP-based CTG probing system combined with isothermal amplification could also discriminate target miRNA 146a from one- and two-base-mismatched miRNAs ( ORN 1 and ORN 2 , respectively). This simple AuNP-based CTG probing system, combined with isothermal amplification to induce a highly sensitive change in fluorescence, allows the detection of miRNA 146a with high sensitivity (14 aM) and selectivity. [ABSTRACT FROM AUTHOR]

Surface-modified gold nanoparticles (GNPs) were synthesized via layer-by-layer process with alternating cationic polyallylamine and anionic poly(acrylic acid) polyelectrolyte layers leading to a highly hydrophilic biocompatible shell supporting colloidal stability. Afterwards, papain was covalently immobilized on the modified GNPs via amide coupling between the amino groups on papain and the terminal carboxylic groups of the modified GNPs by using N -(3-dimethylaminopropyl)- N' -ethylcarbodiimide and N -hydroxysulfosuccinimide sodium as coupling agents. The resultant papain-functionalized gold nanoparticles were characterized by surface plasmon resonance, dynamic light scattering and zeta potential measurements. The new technology resonant mass measurement was applied for determining the average number of papain molecules immobilized per GNP by measurement of the single nanoparticle buoyant mass in the range of femtograms. The activity of the immobilized enzyme was estimated by determination of the kinetic parameters ( K m , V max and k cat ) with the standard chromogenic substrate N α -benzoyl- dl -arginine-4-nitroanilide hydrochloride. It was found that K m of immobilized and free enzyme are in the same order of magnitude. On contrary, turnover numbers k cat were significantly higher for GNP-conjugated papain. Further, the gold nanobiocatalyst was applied for digestion of polyclonal human immunoglobulin G to yield protein fragments. The resultant fragment mixture was further analyzed by high-performance liquid chromatography-microelectrospray ionization-quadrupole-time-of-flight mass spectrometry, which demonstrated the applicability of the bioreactor based on papain functionalized GNPs. The immobilized papain not only has higher catalytic activity and better stability, but also can be easily isolated from the reaction medium by straightforward centrifugation steps for reuse. [ABSTRACT FROM AUTHOR]

A paper-based chemiresistive sensor consisting of a single-walled carbon nanotubes network with electrodeposited gold nanoparticles (AuNPs-SWCNTs) was developed for the sensitive detection of As(III). A new sensing strategy was also proposed combined with a paper-based device for As(III) chemiresistive detection based on the electrochemical doping of As(0) on the AuNPs-SWCNTs channel. The proposed paper-based chemiresistive sensor was manufactured by wax printing and vacuum deposition using a water-based SWCNTs ink. The sensor sensitivity was enhanced by optimizing the volume of SWCNTs ink used in the formation of the sensing network in the paper and the sweep segment of cyclic voltammetry used for the electrochemical deposition of AuNPs. Additionally, the mechanism of the sensing strategy based on the electrochemical n-doping of As(0) to the AuNPs-SWCNTs sensing channel was investigated using a liquid-ion gated FET system. The As(III) concentration detected by the as-fabricated chemiresistive sensor is as low as 1.35 × 10−5 μM which is even lower than the maximum permissible concentration in drinking water defined by the WHO. In this paper, we provide a simple strategy for developing paper-based chemiresistive sensors with unique properties for practical As(III) determination. [Display omitted] • A paper-based chemiresistive sensor was developed for the detection of As(III). • The properties of the proposed semiconducting channel were characterized. • A sensing strategy was proposed without using any bio-recognition elements. • The key parameters for the sensor fabrication were optimized. • The concentration of As(III) can be detected as low as 0.001 ppb. [ABSTRACT FROM AUTHOR]

Excessive glucose present in the blood of diabetic patients binds with the hemoglobin of red blood cells resulting in the formation of glycated hemoglobin (HbA 1c ). Measurement of HbA 1c levels may help in identifying the efficacy of the ongoing treatment and hence provide a better control over the disease. In the present study, we have synthesized a sensitive and stable scaffold, which consists of Au nanoparticles (GNPs)-dotted tubular TiO 2 , for the construction of an electrochemical HbA 1c biosensor. 12-phosphotungstic acid has been used as a reducer after depositing well-dispersed GNPs on TiO 2 nanotubes (TiO 2 NTs) and an electron mediator by accelerating the electron transfer between the conductor and protein. The fabricated electrode was characterized using scanning electron microscopy (SEM), cyclic voltammetry (CV), Fourier transform infrared spectroscopy (FTIR) and electrochemical impedance spectroscopic analysis (EIS). Biosensor exhibited low detection limit (0.5 μM), fast response time (3 s) and wide linearity (from 0.5 to 2000 μM). The working electrode was used 100 times over 4 months, when stored at 4 °C. The HbA1c biosensor was then effectively used to measure the % of HbA 1c in the blood of apparently healthy persons and diabetic patients. [ABSTRACT FROM AUTHOR]

The detection of protein is vital to fundamental research as well as practical applications. However, most detection methods depend on antibody-based assays which are faced with many shortcomings. Herein, we propose a colorimetric method for protein assays based on target-triggered activation of aptazyme, which may offer simple, rapid and cost-effective detection of the target protein. In this method, the conformation change of aptazyme induced by target protein is designed to be associated with aptazyme activation. Consequently, in the presence of the target protein, the designed DNA linkers will be cleaved into two fragments that fail to cross-link gold nanoparticles (GNPs), thus the color of GNP solution remains red, while the color will be changed in the absence of the target. Because of the advantages of aptazyme such as economic synthesis, stable, easy modification and its ability to accomplish signal recognition and signal amplification simultaneously, the method is thermostable, simple and cost-efficient. In this work, we have taken the detection of vascular endothelial growth factor (VEGF) as an example, which can present an analytical performance with as low as 0.1 nM detection limit, spanning a detection range of 3 orders of magnitude. What is more, the principle of this proposed new method can be extended as a universal assay method not only for the detection of analytes which have an aptamer but also for those analytes that have ligands. [ABSTRACT FROM AUTHOR]

We synthesized a biothiol-sensitive nanoprobe by assembling gold nanoparticles with a novel redox-responsive silica (ReSi) matrix using dithiobis (succinimidyl propionate) and (3-aminopropyl) trimethoxysilane. Thin layer disulfide-bonded networks of the ReSi could differentially respond to extra- and intracellular glutathione in cancer cells within 30 min; furthermore, targeted cellular uptake could be monitored in situ by fluorescence recovery. Sigmoidal dose–response pattern of the nanoprobes presented in this study were attributed to the buried disulfide-linked 3D nanostructure of the ReSi nanoshell, optimized at an appropriate thickness, enabling not only buffering of small redox disturbances in the extracellular milieu but also the satisfied sensitivity for rapid redox sensing. Such a ReSi-functionalized gold nanoparticle-based nanoconjugate possesses the potential to serve as an effective intracellular drug carrier for future cancer theranostics. [ABSTRACT FROM AUTHOR]

Herein, a rapid and simple gold nanoparticle based colorimetric and dynamic light scattering (DLS) assay for the sensitive detection of cholera toxin has been developed. The developed assay is based on the distance dependent properties of gold nanoparticles which cause aggregation of antibody-conjugated gold nanoparticles in the presence of cholera toxin resulting discernible color change. This aggregation induced color change caused a red shift in the plasmon band of nanoparticles which was measured by UV–Vis spectroscopy. In addition, we employed DLS assay to monitor the extent of aggregation in the presence of different concentration of cholera toxin. Our assay can visually detect as low as 10 nM of cholera toxin which is lower than the previously reported colorimetric methods. The reported assay is very fast and showed an excellent specificity against other diarrhetic toxins. Moreover, we have demonstrated the feasibility of our method for cholera toxin detection in local lake water. [ABSTRACT FROM AUTHOR]

Developments of sensitive, rapid, and cheap systems for identification of a wide range of biomolecules have been recognized as a critical need in the biology field. Here, we introduce a simple colorimetric sensor array for detection of biological thiols, based on aggregation of three types of surface engineered gold nanoparticles (AuNPs). The low-molecular-weight biological thiols show high affinity to the surface of AuNPs; this causes replacement of AuNPs’ shells with thiol containing target molecules leading to the aggregation of the AuNPs through intermolecular electrostatic interaction or hydrogen-bonding. As a result of the predetermined aggregation, color and UV–vis spectra of AuNPs are changed. We employed the digital mapping approach to analyze the spectral variations with statistical and chemometric methods, including hierarchical cluster analysis (HCA) and principal component analysis (PCA). The proposed array could successfully differentiate biological molecules ( e.g. , cysteine, glutathione and glutathione disulfide) from other potential interferences such as amino acids in the concentration range of 10–800 μmol L −1 . [ABSTRACT FROM AUTHOR]

A colorimetric sensor has been developed in this work to sensitively detect α-glucosidase activity and screen α-glucosidase inhibitors (AGIs) utilizing unmodified gold nanoparticles (AuNPs). The sensing strategy is based on triple-catalytic reaction triggered by α-glucosidase. In the presence of α-glucosidase, aggregation of AuNPs is prohibited due to the oxidation of cysteine to cystine in the system. However, with addition of AGIs, cysteine induced aggregation of AuNPs occurs. Thus, a new method for α-glucosidase activity detection and AGIs screening is developed by measuring the UV–vis absorption or visually distinguishing. A well linear relation is presented in a range of 0.0025–0.05 U mL −1 . The detection limit is found to be 0.001 U mL −1 for α-glucosidase assay, which is one order of magnitude lower than other reports. The IC 50 values of four kinds of inhibitors observed with this method are in accordance with other reports. The using of unmodified AuNPs in this work avoids the complicated and time-consuming modification procedure. This simple and efficient colorimetric method can also be extended to other enzymes assays. [ABSTRACT FROM AUTHOR]

Polydimethylsiloxane (PDMS) is widely used for microfabrication and bioanalysis; however, its surface functionalization is limited due to the lack of active functional groups and incompatibility with many solvents. We presented a novel approach for in situ fabrication of cleavable peptide arrays on polydimethylsiloxane (PDMS) via tert -butyloxycarbonyl ( t -Boc)/trifluoroacetic acid (TFA) chemistry using gold nanoparticles (AuNPs) as the anchor and a disulfide/amine terminated hetero-polyethylene glycol as the cleavable linker. The method was fine tuned to use reagents compatible with the PDMS. Using 5-mer pentapeptide, Trp 5 , as a model, step-by-step covalent coupling during the reaction cycles was monitored by Attenuated total reflectance-Fourier transform infrared spectrometer (ATR-FTIR), X-ray photoelectron spectroscopy (XPS), or atomic force microscopy (AFM), and further confirmed by mass spectrometry (MS) detection of the cleaved peptides. Using such a method, heptapeptides of the PKA substrate, LRRASLG (Kemptide), and its point mutated analogs were fabricated in an array format for comparative studies of cAMP-dependent protein kinase (PKA) activity. Based on on-chip detection, Kemptide sequence exhibited the highest phosphorylation activity, which was detected to a 1.5-time lesser extent for the point mutated sequence (LRRGSLG) containing the recognition motif (RRXS), and was nearly undetectable for another point mutated sequence (LRLASLG) that lacked the recognition motif. These results indicate that the reported fabrication method is able to yield highly specific peptide sequences on PDMS, leading to a highly motif-sensitive enzyme activity assay. [ABSTRACT FROM AUTHOR]

Oxidized low-density lipoproteins (OxLDLs) like malondialdehyde-modified low-density lipoprotein (MDA-LDL) play a major role in atherosclerosis and have been proposed as useful biomarkers for oxidative stress. In this study, gold-nanoparticles (GNPs) were functionalized via distinct chemistries with anti-MDA-LDL antibodies (Abs) for selective recognition and capture of MDA-LDL from biological matrices. The study focused on optimization of binding affinities and saturation capacities of the antiMDA-LDL-Ab-GNP bioconjugate by exploring distinct random and oriented immobilization approaches, such as (i) direct adsorptive attachment of Abs on the GNP surface, (ii) covalent bonding by amide coupling of Abs to carboxy-terminated-pegylated GNPs, (iii) oriented immobilization via oxidized carbohydrate moiety of the Ab on hydrazide-derivatized GNPs and (iv) cysteine-tagged protein A (cProtA)-bonded GNPs. Depending on immobilization chemistry, up to 3 antibodies per GNP could be immobilized as determined by ELISA. The highest binding capacity was achieved with the GNP-cProtA-Ab bioconjugate which yielded a saturation capacity of 2.24 ± 0.04 μg mL −1 GNP suspension for MDA-LDL with an affinity K d of 5.25 ± 0.11 × 10 −10 M. The GNP-cProtA-antiMDA-LDL bioconjugate revealed high specificity for MDA-LDL over copper(II)-oxidized LDL as well as native human LDL. This clearly demonstrates the usefulness of the new GNP-Ab bioconjugates for specific extraction of MDA-LDL from plasma samples as biomarkers of oxidative stress. Their combination as specific immunoextraction nanomaterials with analysis by LC–MS/MS allows sensitive and selective detection of MDA-LDL in complex samples. [ABSTRACT FROM AUTHOR]

Monodispersed and highly stable gold nanoparticles with a diameter between 8 and 9 nm were synthesized in a weakly alkaline medium by chemical reduction of AuCl 4 − using 5-hydroxyl-1,4-naphthoquinone, and stabilized by the simultaneously formed poly(hydroxyl-1,4-naphthoquinone). The electrochemical properties of the resultant poly(hydroxyl-1,4-naphthoquinone) stabilized gold nanoparticles (AuNQ NPs) and its electrocatalytic activity for glucose oxidation in alkaline media were then investigated using a range of techniques, including dc cyclic, rotating disk electrode and Fourier transformed large amplitude ac voltammetry. The results demonstrate that these AuNQ NP modified electrodes exhibit excellent catalytic activity toward glucose oxidation in the potential region where the premonolayer oxidation process occurs. The overall catalytic glucose oxidation process was found to be mass transport controlled under the experimental conditions employed, allowing measurements to be conducted with a high reproducibility. The AuNQ NP modified electrodes showed a high sensitivity of 183 μA mM −1 cm −2 with a wide linear dynamic range of 0.5–50 mM and a detection limit of 61 μM. However, despite its excellent tolerance toward ascorbic acid, significant interference from uric acid was found with this AuNQ NP modified electrode. [ABSTRACT FROM AUTHOR]

A chemically modified electrode consisting of Langmuir–Blodgett (LB) films of n -dodecanethiol functionalized gold nanoparticles (S DOD AuNP-LB), was investigated as a voltammetric sensor of organic and phenolic acids of interest in the wine industry. The nanostructured films demonstrated interfacial properties being able to detect the main organic acids present in grapes and wines (tartaric, malic, lactic and citric). Compared to a bare ITO electrode, the modified electrodes exhibited a shift of the reduction potential in the less positive direction and a marked enhancement in the current response. Moreover, the increased electrocatalytic properties made it possible to distinguish between the different dissociable protons of polyprotic acids. The S DOD AuNP-LB sensor was also able to provide enhanced responses toward aqueous solutions of phenolic acids commonly found in wines (caffeic and gallic acids). The presence of nanoparticles increased drastically the sensitivity toward organic acids and phenolic compounds. Limits of detection as low as 10 −6 mol L −1 were achieved. Efficient catalytic activity was also observed in mixtures of phenolic acid/tartaric in the range of pHs typically found in wines. In such mixtures, the electrode was able to provide simultaneous information about the acid and the phenol concentrations with a complete absence of interferences. The excellent sensing properties shown by these sensors could be attributed to the electrocatalytic properties of the nanoparticles combined with the high surface to volume ratio and homogeneity provided by the LB technique used for the immobilization. Moreover, the LB technique also provided an accurate method to immobilize the gold nanoparticles giving rise to stable and reproducible sensors showing repeatability lower than 2% and reproducibility lower than 4% for all the compounds analyzed. [ABSTRACT FROM AUTHOR]

In this work, we develop a simple and rapid sensing method for the visual and fluorescent detection of acetamiprid (AC) based on the inner-filter effect (IFE) of gold nanoparticles (AuNPs) on ratiometric fluorescent quantum dots (RF-QDs). The RF-QDs based dual-emission nanosensor was fabricated by assembling green emissive QDs (QDs 539 nm , λ em = 539 nm) on the surface of red emissive QDs (QDs 661 nm , λ em = 661 nm)-doped silica microspheres. The photoluminescence (PL) intensity of RF-QDs could be quenched by AuNPs based on IFE. Acetamiprid can adsorb on the surface of AuNPs due to its cyano group that has good affinity with gold, which could induce the aggregation of AuNPs accompanying color change from red to blue. Thus, the IFE of AuNPs on RF-QDs was weakened and the PL intensity of RF-QDs was recovered accordingly. Under the optimized conditions, the PL intensity of the RF-QDs/AuNPs system was proportional to the concentration of AC in the range of 0.025–5.0 μg mL −1 , with a detection limit of 16.8 μg L −1 . The established method had been used for AC detection in environmental and agricultural samples with satisfactory results. [ABSTRACT FROM AUTHOR]

A synergistic electrocatalytic effect was observed in sensors where two electrocatalytic materials (functionalized gold nanoparticles and lutetium bisphthalocyanine) were co-deposited using the Langmuir–Blodgett technique. Films were prepared using a novel method where water soluble functionalised gold nanoparticles [(11-mercaptoundecyl)tetra(ethylene glycol)] (SAuNPs) were inserted in floating films of lutetium bisphthalocyanine (LuPc 2 ) and dimethyldioctadecylammonium bromide (DODAB) as the amphiphilic matrix. The formation of stable and homogeneous mixed films was confirmed by π-A isotherms, BAM, UV–vis and Raman spectroscopy, as well as by SEM and TEM microscopy. The synergistic effect towards hydroquinone of the electrodes modified with LuPc 2 :DODAB/SAuNP was characterised by an increase in the intensity of the redox peaks and a reduction of the overpotential. This synergistic electrocatalytic effect arose from the interaction between the SAuNPs and the phthalocyanines that occur in the Langmuir–Blodgett films and from the high surface area provided by the nanostructured films. The sensitivity increased with the amount of LuPc 2 and SAuNPs inserted in the films and limits of detection in the range of 10 −7 mol L −1 were attained. [ABSTRACT FROM AUTHOR]

Highlights: [•] Aligned MWCNT/Au nanoparticles electrode was fabricated to use as a new DNA biosensor. [•] EIS was proposed for DNA detection of the TP53 gene mutation for the first time. [•] A low detection limit (1.0×10−17 M) was obtained without any amplification. [•] The biosensor exhibited high sensitivity, selectivity and reproducibility(RSD=2.1%). [•] This biosensor can be used for fast mutation screening related to human cancer types. [ABSTRACT FROM AUTHOR]

Highlights: [•] A novel colorimetric strategy for lead ion detection has been established. [•] The detection relies on DNAzyme functionalized gold nanoparticles. [•] Target-induced cleavage can mediate assembly of graphene oxide. [•] The method displays excellent performance for the detection of lead ion. [ABSTRACT FROM AUTHOR]

Highlights: [•] Immunosensor for simultaneous detection of four biomarkers on identical interface. [•] Aq, Thi, Fc and Co(bpy)3 3+ were adopted as signal tags. [•] Preparing Au/PDDA/PTCA/CNTs/redox-probe@D-Ab as signal tracer. [•] The immunosensor exhibited excellent sensitivity and selectivity. [ABSTRACT FROM AUTHOR]

Highlights: [•] A novel method for ultrasensitive detection of glycoproteins was described. [•] Gold-nanoparticle is chosen as a signal tag for glycoprotein detection in LDI-MS. [•] Gold-nanoparticle is the ideal signal reporter in LDI-MS. [•] A fM level detection of glycoproteins was achieved. [Copyright &y& Elsevier]

Highlights: [•] A simple and novel colorimetric method for detection of K+ was developed. [•] The aptasensor exhibited low detection limit and wide linear range to K+. [•] This method was able to detect K+ with high selectivity. [•] This colorimetric method exhibited excellent applicability. [ABSTRACT FROM AUTHOR]

Abstract: A novel homogeneous immunoassay based on Förster resonance energy transfer for sensitive detection of tumor, e.g., marker with carcinoembryonic antigen (CEA), was proposed. The assay was consisted of polyclonal goat anti-CEA antibody labeled luminescent CdTe quantum dots (QDs) as donor and monoclonal goat anti-CEA antibody labeled gold nanoparticles (AuNPs) as acceptor. In presence of CEA, the bio-affinity between antigen and antibody made the QDs and AuNPs close enough, thus the photoluminescence (PL) quenching of CdTe QDs occurred. The PL properties could be transformed into the fluorometric variation, corresponding to the target antigen concentration, and could be easily monitored and analyzed with the home-made image analysis software. The fluorometric results indicated a linear detection range of 1–110ngmL−1 for CEA, with a detection limit of 0.3ngmL−1. The proposed assay configuration was attractive for carcinoma screening or single sample in point-of-care testing, and even field use. In spite of the limit of available model analyte, this approach could be easily extended to detection of a wide range of biomarkers. [Copyright &y& Elsevier]

Abstract: An immunochromatographic assay (ICA) using gold nanoparticles coated with monoclonal antibody (McAb) for the detection of chromium ions (Cr) in water and serum samples was developed, optimized and validated. Gold nanoparticles coated with affinity-purified monoclonal antibodies against isothiocyanobenzyl-EDTA (iEDTA)-chelated Cr3+ were used as the detecting reagent in this completive immunoassay-based one-step test strip. The ICA was investigated to measure chromium speciation (Cr3+ and Cr6+ ions) in water samples. Chromium standard samples of 0–80ngmL−1 in water were determined by the test strips. The results showed that the visual lowest detection limit (LDL) of the test strip was 50.0ngmL−1. A portable colorimetric lateral flow reader was used for the quantification of Cr. The results indicated that the linear range of the ICA with colorimetric detection was 5–80ngmL−1. The ICA was also validated for the detection of chromium ions in serum samples. The test trips showed high stability in that they could be stored at 37°C for at least 12 weeks without significant loss of activity. The test strip also showed good selectivity for Cr detection with negligible interference from other heavy metals. Because of its low cost and short testing time (within 5min), the test strip is especially suitable for on-site large-scale screening of Cr-polluted water samples, biomonitoring of Cr exposure, and many other field applications. [Copyright &y& Elsevier]

Abstract: Because of their unique characteristics, DNAs have been widely studied for uses in biosensors. In this work, we utilize single-stranded homopolymeric deoxyadenosines (abbreviated as poly (dA)) as recognition elements and gold nanoparticles (abbreviated as AuNPs) as reporter parts for the construction of pH alarms, which are able to produce sharp colorimetric responses upon specific pH thresholds within the range from pH 2 to 4. These biosensors are convenient to prepare and easy to operate. Their pH thresholds for colorimetric response can be easily tuned by changes of DNA strand length, concentration and DNA sequence. With an increase in the number of nucleotide bases per DNA chain while keeping the overall number of nucleotide base in the system constant, the pH threshold can be raised. Increasing the concentration of the single-stranded poly (dA) DNA lowers the pH response threshold. Moreover, as they can sense a range as narrow as a 0.4 pH unit which equals to 2.5 fold [H+] change, they can be used as a potential pH alarm for specific pH range. [Copyright &y& Elsevier]

Abstract: An ultrasensitive aptamer-based bio bar code immunomagnetic separation and electrochemiluminescence (IM-ECL) method for the detection of protein is developed. The target protein is captured by biotin-labeled aptamer (biotin probe) and [Ru(bpy)3]2+ (TBR)-Au bio bar code-labeled aptamer (ECL nanoprobe), to form a double aptamer–protein sandwich complex. The complex is then immobilized on the streptavidin microbeads through biotin–streptavidin linkage and detected by ECL assay. The ECL signal of the target protein is amplified by the TBR-bio bar code DNAs. As an example, platelet-derived growth factor B-chain homodimer (PDGF-BB) was detected by the method. Experimental results show that the detection limit of the assay is 1pM of PDGF-BB. A calibration curve with a linearity range from 1pM to 10nM is established, thus, make quantitative analysis possible. The method has been used to detect PDGF-BB in fetal calf serum with minimum background interference. Due to the wide availability of aptamer for numerous proteins, this aptamer-based bio bar code IM-ECL method holds great promise in protein detection. [Copyright &y& Elsevier]

Abstract: A multiplexed electrochemical immunoassay method was developed for simultaneous ultrasensitive measurement of tumor markers based on electrochemical stripping analysis of silver nanoparticles (Ag NPs). The Ag NPs were deposited on a disposable immunosensor array with a reduction reaction catalyzed by nanogold labels. The immunosensor array was prepared by covalently immobilizing capture antibodies on chitosan modified screen-printed carbon electrodes. Through a sandwich-type immunoreaction, antibody-functionalized Au NPs were captured onto immunosensor surface to induce the silver deposition from a silver enhancer solution. The deposited Ag NPs could be directly measured by anodic stripping analysis in KCl solution. The catalytic deposition enhanced the analytical sensitivity for detection of protein markers. The interference of dissolved oxygen could be avoided as the detection was performed with positive stripping potential range. Using carcinoembryonic antigen and α-fetoprotein as model analytes, the proposed multiplexed immunoassay method showed wide linear ranges of three orders of magnitude with the detection limits down to 3.5 and 3.9pgmL−1, respectively. The localized silver deposition, as well as the stripping detection process, eliminated completely the electrochemical cross talk between adjacent immunosensors. The immunosensor array exhibited acceptable reproducibility, stability and accuracy, showing a promising potential in multianalyte determination for clinical application. [Copyright &y& Elsevier]

Abstract: An electrochemical DNA biosensor was fabricated by self-assembling probe single-stranded DNA (ssDNA) with a nanogold decorated on ionic liquid modified carbon paste electrode (IL-CPE). IL-CPE was fabricated using 1-butylpyridinium hexafluorophosphate as the binder and the gold nanoparticles were electrodeposited on the surface of IL-CPE (Au/IL-CPE). Then mercaptoacetic acid was self-assembled on the Au/IL-CPE to obtain a layer of modified film, and the ssDNA probe was further covalently-linked with mercaptoacetic acid by the formation of carboxylate ester with the help of N-(3-dimethylamino-propyl)-N′-ethylcarbodiimide hydrochloride and N-hydroxysuccinimide. The hybridization reaction with the target ssDNA was monitored with methylene blue (MB) as the electrochemical indicator. Under the optimal conditions, differential pulse voltammetric responses of MB was proportional to the specific ssDNA arachis sequences in the concentration range from 1.0×10−11 to 1.0×10−6 molL−1 with the detection limit as 1.5×10−12 molL−1 (3σ). This electrochemical DNA sensor exhibited good stability and selectivity with the discrimination ability of the one-base and three-base mismatched ssDNA sequences. The polymerase chain reaction product of arachis Arabinose operon D gene was successfully detected by the proposed method, which indicated that the electrochemical DNA sensor designed in this paper could be further used for the detection of specific ssDNA sequence. [Copyright &y& Elsevier]

Abstract: This article reports the integration of the fiber optic-particle plasmon resonance (FO-PPR) biosensor with a microfluidic chip to reduce response time and improve detection limit. The microfluidic chip made of poly(methyl methacrylate) had a flow-channel of dimensions 4.0cm×900μm×900μm. A partially unclad optical fiber with gold or silver nanoparticles on the core surface was placed within the flow-channel, where the volume of the flow space was about 14μL. Results using sucrose solutions of various refractive indexes show that the refractive index resolution improves by 2.4-fold in the microfluidic system. The microfluidic chip is capable of delivering a precise amount of biological samples to the detection area without sample dilution. Several receptor/analyte pairs were chosen to examine the biosensing capability of the integrated platform: biotin/streptavidin, biotin/anti-biotin, DNP/anti-DNP, OVA/anti-OVA, and anti-MMP-3/MMP-3. Results show that the response time to achieve equilibrium can be shortened from several thousand seconds in a conventional liquid cell to several hundred seconds in a microfluidic flow-cell. In addition, the detection limit also improves by about one order of magnitude. Furthermore, the normalization by using the relative change of transmission response as the sensor output alleviate the demand on precise optical alignment, resulting in reasonably good chip-to-chip measurement reproducibility. [Copyright &y& Elsevier]

Abstract: Fluorescent contrast agents with high specificity and sensitivity are valuable for accurate disease detection and diagnosis. Spherical gold nanoparticles (GNPs) can be smartly utilized for developing highly effective agents. The strong electromagnetic (plasmon) field on their surface can be very effective in influencing the electrons of fluorophores and, thus, manipulating the fluorescence output (i.e., either quenching or enhancement). Fluorescence quenching can be used for negative sensing, or for conditional de-quenching to increase the specificity. Fluorescence enhancement allows sensing to be more sensitive. The level of fluorescence alteration depends on the GNP size, the excitation and emission wavelengths and quantum yield of the fluorophore, and the distance between the GNP and the fluorophore. To understand the mechanisms of the fluorescence change by GNP, we have theoretically analyzed the parameters involved in the fluorescence alteration for commonly used fluorophores, with an emphasis on quenching. The results showed that the fluorescence of fluorophores with the excitation (Ex) and emission (Ex) wavelengths close to the GNP resonance peak tended to be significantly quenched by GNPs. For those fluorophores emitting fluorescence in red or near infrared, to achieve quenching, the distance between GNP and the fluorophore was required to be very short. In general, a shorter distance resulted in more quenching. Bigger GNPs require a shorter distance to achieve the same level of quenching. The fluorescence of a fluorophore with a lower quantum yield (especially the one with emission in far-red or near-infrared) is more difficult to be quenched by GNPs (requires very short distance). Instead, it can be enhanced. Based on the theoretical study, we have developed a near-infrared contrast agent, i.e., Cypate conjugated GNP via a short peptide spacer. Normally the fluorescence of Cypate was quenched. The spacer has a motif of a substrate for urokinase type plasminogen activator (uPA; cancer-secreting enzyme). This contrast agent emits fluorescence only in the presence of uPA, where the uPA cleaves the spacer. This design can be used in characterization of the cancer type and also in diagnosing other diseases with signature enzymes. [Copyright &y& Elsevier]

Abstract: The use of single gold nanoparticle plasmon-based spectroscopy for the sensitive, anion-selective detection of arsenate is described. The method is based on the selective formation of electrostatic complexes between arsenate and poly(allylamine hydrochloride) (PAH) and changes in the single particle plasmon in Rayleigh scattering profiles. PAH, when modified with gold nanoparticles, binds arsenate via its amine-functionalities. The scattering properties of the resulting selectively formed complexes are altered, leading to significant changes in the surface plasmon resonance wavelength. The limit of detection of the method was determined to be 10nM, which is ca. 13 times more sensitive than U.S. EPA regulation levels. The response is essentially linear in the concentration range of 50–300nM. The method also shows good selectivity for arsenate in the presence of other environmentally relevant anions, including H2PO4 −, SO4 2−, NO3 −, and Cl−. [Copyright &y& Elsevier]

Abstract: The potentiometric response of a carbon paste electrode modified with silica sol–gel and mercaptosuccinic acid (MSA) in the presence and absence of gold nano-particles was studied. The results showed that the electrode with gold nano-particles was responded to Al3+ ions as a hard metal ion. On the other hand, the electrode without gold nano-particles was responded to copper ions as a soft metal ion. The electrodes without and with gold nano-particles exhibits a Nernstian slope of 29.1 and 19.2mVdecade−1 for copper and aluminum ions over a wide concentration range of 4.3×10−7–1.0×10−2 and 4.5×10−7–1.6×10−3 molL−1, respectively. The detection limits of electrodes were 4.0×10−7 and 1.6×10−7 molL−1 for copper and aluminum ions, respectively. [Copyright &y& Elsevier]

Abstract: In order to develop a highly sensitive and selective piezoelectric transducer for the detection of DNA, the bio-recognizing probe is for the first time designed by introducing a hairpin structure and a recognition site for EcoRI into an oligonucleotide sequence and signal amplifiers are prepared by modifying gold nanoparticles (GNPs) with biomolecules, deepening the application and understanding of biomaterials. The piezoelectric transducer is prepared by immobilizing designed hairpin recognition probe onto the quartz-crystal-microbalance (QCM). In the absence of target DNA, the hairpin probe is removed from the QCM surface after exposure to endonuclease, inhibiting the subsequent signaling reaction. In contrast, introduction of target DNA can open the hairpin probe due to the probe/target hybridization, dissociating the cleavable double-stranded portion. In this case, even if being treated with endonuclease, the integrated hairpin probe is maintained. Subsequent introduction of GNPs modified with detection probes that can hybridize to the terminal sequence of hairpin probe results in a many-folds increase of the frequency response. Utilizing the proposed transduction scheme, the reliable target DNA detection can be accomplished. The detection limit of 2pM and dynamic response range for target DNA from 2 to 300pM are obtained. Furthermore, single-base mismatched DNAs can be easily identified. The developed proof-of-principle of a novel piezoelectric transduction scheme is expected to establish a potential platform for the disease-associated mutation analysis and DNA hybridization detection in biotechnology and medical diagnostics. [Copyright &y& Elsevier]

Abstract: This work proposed a simple, sensitive and low-cost multiplexed immunoassay by combining a disposable chip with gold nanoparticle (AuNP) as an electrochemical label. The immunosensors array as the disposable chip was firstly prepared by immobilizing capture antibodies on different screen printed carbon working electrodes by passive adsorption. With a sandwich mode, the analytes were then bound to the corresponding capture antibodies for further capture of the gold nanoparticle labeled antibodies. Gold nanoparticles were finally electrooxidized in 0.1M HCl to produce AuCl4 − for differential pulse voltammetric detection. Using human IgG and goat IgG as model targets, under optimal conditions this method achieved linear ranges from 5.0 to 500 and 5.0 to 400ngmL−1 with limits of detection of 1.1 and 1.6ngmL−1, respectively. This method eliminated completely electrochemical crosstalk between adjacent immunosensors due to the strong adsorption of the AuCl4 − on the printed carbon surfaces. The immunosensors array showed acceptable precision, reproducibility and stability, and could be readily applied to multianalyte determination for clinical diagnostics. [Copyright &y& Elsevier]

Abstract: Comparative studies of the potentiometric behavior of three mercapto compounds [2-((5-mercapto-1,3,4-thiadiazol-2-ylimino)methyl)phenol] (MTMP), [5-(2-methoxy benzylidene amino)-1,3,4-thiadiazole-2-thiol] (MBYT) and [5-(pyridin-2-ylmethyleneamino)-1,3,4-thiadiazole-2-thiol] (PYTT) self-assembled on gold nanoparticles (GNPs) as ionophores in carbon paste electrodes (CPEs) have been made. These mercapto thiadiazole compounds were self-assembled onto gold nanoparticles and then incorporated within carbon paste electrode. The self-assembled ionophores exhibit a high selectivity for copper ion (Cu2+), in which the sulfur and nitrogen atoms in their structure play a role as the effective coordination donor site for the copper ion. These carbon paste electrodes were applied as indicator electrodes for potentiometric determination of copper ions. The sensor based on PYTT exhibits the working concentration range of 4.0×10−9 to 7.0×10−2 M and a Nernstian slope of 28.7±0.3mVdecade−1 of copper activity. The detection limit of electrode was 1.0×10−9 M and potential response was pH independent across the range of 3.0–6.5. It exhibited a quick response time of <5s and could be used for a period of 45 days. The ion selectivity of this electrode for Cu2+ was over 104 times that for other metal cations. The application of prepared sensors has been demonstrated for the determination of copper ions in spiked water and natural water samples. [Copyright &y& Elsevier]

Abstract: A quick and reproducible electrochemical-based immunosensor technique, using magnetic core/shell particles that are coated with self-assembled multilayer of nanogold, has been developed. Magnetic particles that are structured from Au/Fe3O4 core–shells were prepared and aminated after a reaction between gold and thiourea, and additional multilayered coatings of gold nanoparticles were assembled on the surface of the core/shell particles. The carcinoembryonic antibody (anti-CEA) was immobilized on the modified magnetic particles, which were then attached on the surface of solid paraffin carbon paste electrode (SPCE) by an external magnetic field. This is an assembly of a novel immuno biosensor for carcinoembryonic antigen (CEA). The sensitivity and response features of this immunoassay are significantly affected by the surface area and the biological compatibility of the multilayered nanogold. The linear range for the detection of CEA was from 0.005 to 50ngmL−1 and the limit of detection (LOD) was 0.001ngmL−1. The LOD is approximately 500 times more sensitive than that of the traditional enzyme-linked immunosorbent assay for CEA detection. [Copyright &y& Elsevier]

Abstract: We report on a competitive, homogeneous immunoassay for the detection of the hapten digoxigenin. The assay is based on competitive fluorescence quenching by gold nanoparticles. Digoxigenin is indirectly labeled with the fluorophore Cy3B through bovine serum albumin and used as a marker. Gold nanoparticles functionalized with anti-digoxigenin antibodies serve as fluorescence quenchers. Free digoxigenin molecules in the analyte solution compete with the labeled markers for antibodies on the gold nanoparticles. The fluorescence signal depends linearly on the free digoxigenin concentration within a range of concentration from 0.5 to 3ngmL−1. The limit of detection is estimated as 0.2ngmL−1 and the limit of quantitation is estimated as 0.6ngmL−1. The method can be used to detect digoxin, a drug used to cure cardiac arrhythmia. [Copyright &y& Elsevier]