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[Display omitted] • An ultrasensitive electrochemical DNA biosensor coupled with dual amplification strategy was developed. • DNA-Au bio-bar codes improved the hybridization efficiency and reduced the cross reaction between the targets and reporter DNA. • AgNPs deposited on AuNPs exhibited a dramatic enhancement of DNA hybridization signal. • The DNA biosensor achieved sensitive detection of MDR1 gene with a detection limit of 33 fM (S/N = 3). Given the tumors might develop multidrug resistance (MDR) during chemotherapy that leading to treatment failure, rapid and sensitive determination of MDR1 gene is an effective tool to monitor the development of MDR. Herein, we established an electrochemical deoxyribonucleic acid (DNA) biosensor coupled with dual amplification strategy based on DNA-Au bio-bar codes and enhancement of silver for sensitive and selective determination of MDR1 gene. Specifically, DNA-Au bio-bar codes as signal probe were prepared by immobilizing complementary and non-complementary sequences on gold nanoparticles (AuNPs), so as to reduce the cross reaction between the target and reporter DNA. In addition, AuNPs-catalyzed reduction of silver ions greatly amplified the current signal. Under the optimal conditions, the current signal was proportional to the base-10 logarithm of target DNA concentration in a wide range from 100 fM to 1 nM with a detection limit as low as 33 fM (S/N = 3). Moreover, without the need for target amplification, the prepared biosensor exhibited superior selectivity and high sensitivity even in the presence of other sequences. Therefore, the developed electrochemical DNA biosensor is a facile and sensitive platform for MDR1 gene detection. [ABSTRACT FROM AUTHOR]

This paper addresses two key challenges toward an integrated forward error-correcting biosensor based on our previously reported self-assembled quick-response (QR) code. The first challenge involves the choice of the paper substrate for printing and self-assembling the QR code. We have compared four different substrates that includes regular printing paper, Whatman filter paper, nitrocellulose membrane and lab synthesized bacterial cellulose. We report that out of the four substrates bacterial cellulose outperforms the others in terms of probe (gold nanorods) and ink retention capability. The second challenge involves remote activation of the analyte sampling and the QR code self-assembly process. In this paper, we use light as a trigger signal and a graphite layer as a light-absorbing material. The resulting change in temperature due to infrared absorption leads to a temperature gradient that then exerts a diffusive force driving the analyte toward the regions of self-assembly. The working principle has been verified in this paper using assembled biosensor prototypes where we demonstrate higher sample flow rate due to light induced thermal gradients. [ABSTRACT FROM AUTHOR]

Electrochemical DNA sensors represent a simple, accurate and economical platform for DNA detection. Gold nanoparticles are known to be efficient labels in electrochemical sensors and to be viable materials to modify the surface of electrodes thereby to enhance the detection limit of the sensor. For surface modification, gold nanoparticles are used in combination with nanomaterials like graphene, graphene oxide, or carbon nanotubes to improve electrochemical performance in general. This review (with 116 refs.) mainly covers the advances made in recent years in the use of gold nanoparticles in DNA sensing. It is divided into the following main sections: (a) An introduction covers aspects of electrochemical sensing of DNA and of appropriate nanomaterials in general. (b) The use of gold nanoparticles in DNA is specifically addressed next, with subsections on AuNPs acting as electrochemical labels, electron transfer mediators, signal amplifiers, carriers of electroactive molecules, catalysts, immobilization platforms, on silver enhancement strategies, on AuNPs modified with carbonaceous materials (such as graphenes and nanotubes), and on multiple amplification schemes. The review concludes with a discussion of current challenges and trends in terms of highly sensitive DNA based sensing using AuNPs. [ABSTRACT FROM AUTHOR]

This paper extends our previous work on silver-enhancement based self-assembling structures for designing reliable, self-powered biosensors with forward error correcting (FEC) capability. At the core of the proposed approach is the integration of paper-based microfluidics with quick response (QR) codes that can be optically scanned using a smart-phone. The scanned information is first decoded to obtain the location of a web-server which further processes the self-assembled QR image to determine the concentration of target analytes. The integration substrate for the proposed FEC biosensor is polyethylene and the patterning of the QR code on the substrate has been achieved using a combination of low-cost ink-jet printing and a regular ballpoint dispensing pen. A paper-based microfluidics channel has been integrated underneath the substrate for acquiring, mixing and flowing the sample to areas on the substrate where different parts of the code can self-assemble in presence of immobilized gold nanorods. In this paper we demonstrate the proof-of-concept detection using prototypes of QR encoded FEC biosensors. [ABSTRACT FROM PUBLISHER]

This paper presents a wireless, self-powered, affinity-based biosensor based on the integration of paper-based microfluidics with our previously reported method for self-assembling radio-frequency (RF) antennas. At the core of the proposed approach is a silver-enhancement technique that grows portions of a RF antenna in regions where target antigens hybridize with target specific affinity probes. The hybridization regions are defined by a network of nitrocellulose based microfluidic channels which implement a self-powered approach to sample the reagent and control its flow and mixing. The integration substrate for the biosensor has been constructed using polyethylene and the patterning of the antenna on the substrate has been achieved using a low-cost ink-jet printing technique. The substrate has been integrated with passive radio-frequency identification (RFID) tags to demonstrate that the resulting sensor-tag can be used for continuous monitoring in a food supply-chain where direct measurement of analytes is typically considered to be impractical. We validate the proof-of-concept operation of the proposed sensor-tag using IgG as a model analyte and using a 915 MHz Ultra-high-frequency (UHF) RFID tagging technology. [ABSTRACT FROM PUBLISHER]

In this paper, we present a silver-enhancement technique for self-assembling radio frequency (RF) antennas and demonstrate its application for remote biosensing. When target analytes or pathogens are present in a sample the silver-enhancement process self-assembles a chain of micromonopole antennas. As the size of the silver-enhanced particles grows, the chain of microantenna segments bridge together to complete a macroantenna structure. The change in the electrical impedance across the bridge modulates the reflection properties of the antenna at a desired frequency. In this paper, we have used this principle to model, optimize and design a ratiometric mode 915-MHz RF identification-based biosensor which uses relative received signal strength indicator (RSSI) to measure and detect different concentration levels of target analytes. We have validated the proof-of-concept for detecting two types of analytes: 1) IgG in rabbit serum at concentration levels ranging from 20 to 60 ng and 2) moisture in a sample at volumes ranging from 5 to 40 \mu \textL . A significant advantage of the proposed biosensor is that the concentration level of target analytes or pathogens can be remotely interrogated in a concealed, packaged or in a biohazardous environment, where direct electrical or optical measurement is considered to be impractical. [ABSTRACT FROM PUBLISHER]

Abstract: An aptamer-based quartz crystal microbalance (QCM) biosensor was developed for the selective and sensitive detection of leukemia cells. In this strategy, aminophenylboronic acid-modified gold nanoparticles (APBA-AuNPs) which could bind to cell membrane were used for the labeling of cells followed by silver enhancement, through which significant signal amplification was achieved. Both the QCM and fluorescence microscopy results manifested the selectivity of the sensor designed. A good linear relationship between the frequency response and cell concentration over the range of 2×103–1×105 cells/mL was obtained, with a detection limit of 1160cells/mL. This approach provides a simple, rapid, and economical method for leukemia cell analysis which might have great potential for further use. [Copyright &y& Elsevier]

Abstract: Nucleic acids based detection has become increasingly important for biomedical diagnostics, environmental monitoring and food screening. In this paper, a nanoporous alumina membrane based impedance sensing platform with gold nanoparticle tags amplification was developed for DNA sensing. Single stranded DNA (ssDNA) probes were first covalently immobilized in nanopore walls via chemical linkers. DNA hybridization in the nanopores induced blockage in the nanopores, which could be detected by electrochemical impedance spectroscopy (EIS). The blockage signal could be further amplified by gold nanoparticles (AuNPs) conjugation and silver catalytic deposition method to reach a limit of detection (LOD) of 50pM. This platform is promising for simple, rapid and sensitive DNA detection. [Copyright &y& Elsevier]

The establishment and rapid progress in sensitive biosensing using immunogold silver enhancement has occurred in the past 30 years. Its high sensitivity and simplicity have made immunogold silver enhancement a revolutionary technique for signal amplification in biosensing. This review focuses on the major applications of immunogold silver enhancement, with special emphasis on quantitative biosensing. In this review, the combinations of immunogold silver enhancement with a series of quantitative techniques, such as colorimetry, electrical and electrochemical methods, gravimetry, chemiluminescence, Raman spectroscopy, and inductively coupled plasma–mass spectrometry (ICP-MS), are discussed in detail. Immunogold silver enhancement has become one of the most useful methods in highly sensitive quantitative bioanalysis. The recent development of ICP-MS detection shows great potential in combination with immunogold silver enhancement. [ABSTRACT FROM AUTHOR]

Abstract: A new electrochemical immunosensor for the detection of protein biomarker platelet-derived growth factor BB (PDGF-BB) was developed based on graphene oxide (GO) initiated silver enhancement. The immunosensor was fabricated based on the traditional sandwich protocol using secondary anti-PDGF-BB antibody (Ab2) modified GO as label. Gold electrode was first modified with self-assembled monolayer (SAM) to block the electron transfer between the electrode and K3Fe(CN)6 solution. After the immobilization of primary anti-PDGF-BB antibody (Ab1) onto electrode via aminidation to the carboxylic group of SAM and the formation of the sandwich immuno-structure onto electrode surface, the electrode was immersed into silver enhancement solution for silver deposition. The deposited metal silver onto GO then mediated electron transfer across the SAM, producing redox current. The resulting immunosensor displays a wide range of linear response, low detection limit, good reproducibility and stability. The immunosensor was used to the detection of PDGF-BB contents in serum samples with satisfactory results. [Copyright &y& Elsevier]

Abstract: A highly sensitive electrochemical lectin biosensor has been developed for the first time using carbohydrate-stabilized gold nanoparticles and silver-enhancement technique. A target lectin protein, Concanavalin A (Con A), was specifically bound to the self-assembled monolayer of thiolated mannose on a gold electrode. Mannose-stabilized gold nanoparticles were added to form a sandwich-type complex with the Con A and were followed by silver-enhancement process to coat the mannose-stabilized gold nanoparticles with silver metal. The coated metallic silver was dissolved in an acidic solution and the resulting silver ions were detected by anodic stripping voltammetry. The present lectin biosensor gave a linear response (R 2 =0.999) for Con A concentration from 0.084μg/mL to 50.0μg/mL with a remarkable detection limit (S/N=3) of 0.070μg/mL, which is much lower compared to those obtained with the reported microgravimetric and colorimetric detection methods. [ABSTRACT FROM AUTHOR]

Abstract: This paper described poly(dimethylsiloxane) (PDMS)-gold nanoparticles (AuNPs) composite film as basis with silver enhancement for colorimetric detection of cardiac troponin I (cTnI). Stable PDMS-AuNPs composite film was simply prepared with dropping HAuCl4 solution in PDMS microchip, gold nanoparticles were both used as nuclei for silver enhancement and as basis for adsorption of antibody, immunoassay was implemented after BSA blocking. Because of the inhibition ability difference for silver enhancement between BSA and antibody-antigen complex, darkness of silver deposition was relative to the amount of antigen. The proposed colorimetric method was applied for clinical sample cTnI detection, results were consistent with that from enzyme-linked immunosorbent assay (ELISA). The composite film could be coupled with digital transmission of images for remote monitoring system in diagnosis, food control, and environmental analysis. [Copyright &y& Elsevier]

Abstract: This paper reports on the synthesis and characterization of a novel electrochemical label for sensitive electrochemical stripping metalloimmunoassays based on silver dendrimer-encapsulated nanoparticles (NPs). Silver dendrimer nanocomposites (Ag-DNCs) were synthesized from a generation 5–7 (G5–7) hydroxyl-terminated ethylenediamine-core-type (2-carbon core) PAMAM dendrimer. Several fixed ratios of Ag+/dendrimer were prepared with the aim to obtain stable nanocomposites with maximal silver loading in the interior of a polymeric shell. Synthesized Ag-DNCs were characterized by UV–vis spectrophotometry, atomic force microscopy (AFM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The G7 Ag-DNC synthesized in 2000 molar excess of silver (1/4 ratio of tertiary amine/Ag+) turned out a more suitable candidate for the label development. By combination of the differential pulse voltammetry (DPV) and the anodic stripping analysis (ASV) on a carbon electrode, down to 1.35×10+10 of individual Ag-DNCs (LOD=0.9pM, 25ml volume) was detected after the dissolution of silver nanoparticles in a diluted nitric acid. The potential advantages of proposed electrochemical label are discussed. [Copyright &y& Elsevier]

Abstract: A label-free immunosensor for the sensitive detection of human immunoglobulin G (IgG) was prepared based on gold nanoparticle–silver enhancement detection with a simple charge-coupled device (CCD) detector. The gold nanoparticles, which were used as nuclei for the deposit of metallic silver and also for the adsorption of antibodies, were immobilized into wells of a 9-well chip. With the addition of silver enhancement buffer, metallic silver will deposit onto gold nanoparticles, causing darkness that can be optically measured by the CCD camera and quantified using ImageJ software. When antibody was immobilized onto the gold nanoparticles and antigen was captured, the formed immunocomplex resulted in a decrease of the darkness and the intensity of the darkness was in line with IgG concentrations from 0.05 to 10ng/ml. The CCD detector is simple and portable, and the reported method has many desirable merits such as sensitivity and accuracy, making it a promising technique for protein detection. [Copyright &y& Elsevier]

Abstract: A successively signal-amplified electrochemical immunoassay has been reported on the basis of the biocatalytic deposition of silver nanoparticles with their subsequent enlargement by nanoparticle-promoted catalytic precipitation of silver from the silver-enhancer solution. The immunoassay was carried out based on a heterogeneous sandwich procedure using polystyrene microwells to immobilize antibody. After all the processes comprising the formation of immunocomplex, biocatalytic deposition of silver nanoparticles and following silver enhancement were completed, the silver on polystyrene microwells was dissolved and quantified by anodic stripping voltammetry (ASV). The effect of relevant experimental conditions, including the concentration of ascorbic acid 2-phosphate (AA-p) substrate and Ag(I) ions, the biocatalytic deposition time, and of crucial importance, the silver enhancement time, were investigated and optimized. The anodic stripping peak current was proportional to the concentration of human IgG in a dynamic range of 0.1–10ngml−1 with a detection limit of 0.03ngml−1. Scanning electron microscope (SEM) was applied to characterize the silver nanoparticles before and after silver enhancement on the surface of polystyrene microplates. By coupling the highly catalytic effect of enzyme and nanoparticles to successively amplify the analytical signal, the sensitivity of immunoassay was enhanced so dramatically that this approach would be a promising strategy to achieve a lower detection limit for bioassays. [Copyright &y& Elsevier]

In this letter, we show that a silver-enhancement technique can be used to self-assemble a radio-frequency (RF) antenna, which then can be used for designing a radio-frequency identification (RFID)-based biosensor. Using the proposed biosensor, the concentration of target analytes or pathogens can be remotely interrogated in a concealed, packaged, or in a bio-hazardous environment, where direct measurement is considered to be impractical. In the presence of the target analytes or pathogens, a silver-enhancement process self-assembles a chain of micromonopole antennas. As the size of the silver-enhanced particles grow, the chain of microantenna segments bridges together to complete a dipole structure that reflects impinging RF signals at a desired frequency. We validate the proof-of-concept for IgG detection and demonstrate that different concentrations of rabbit IgG (ranging from 20 to 60 ng in this letter) can be detected based on the strength of the reflected RF signal received at a 915-MHz COTS RFID reader. [ABSTRACT FROM PUBLISHER]