Horseradish peroxidase-functionalized gold nanoparticle label for amplified immunoanalysis based on gold nanoparticles/carbon nanotubes hybrids modified biosensor

Diagnostic tests for hepatitis C: Recent trends in electrochemical immunosensor and genosensor analysis

Hepatitis C is a liver disease that is transmitted through contact with the blood of an infected person. An estimated 150 million individuals worldwide have been chronically infected with the hepatitis C virus (HCV). Hepatitis C shows significant genetic variation in the global population, due to the high rate of viral RNA mutation. There are six variants of the virus (HCV genotypes 1, 2, 3, 4, 5, and 6), with 15 recorded subtypes that vary in prevalence across different regions of the world. A variety of devices are used to diagnose hepatitis C, including HCV antibody test, HCV viral load test, HCV genotype test and liver biopsy. Rapid, inexpensive, sensitive, and robust analytical devices are therefore essential for effective diagnosis and monitoring of disease treatment. This review provides an overview of current electrochemical immunosensor and genosensor technologies employed in HCV detection. There are a limited number of publications showing electrochemical biosensors being used for the detection of HCV. Due to their simplicity, specificity, and reliability, electrochemical biosensor devices have potential clinical applications in several viral infections.

Electrochemical aptasensor for mucin 1 based on dual signal amplification of poly(o-phenylenediamine) carrier and functionalized carbon nanotubes tracing tag

Mucin 1 (MUC 1), as a most studied mucin, has become a useful marker for identifying breast cancer in the early stages. In this work, a novel method for the determination of MUC 1 in serum was developed based on a sandwich-type electrochemical aptasensor, which combined a dual signal amplification strategy of poly(o-phenylenediamine)-Au nanoparticles (PoPD-AuNPs) hybrid film as carrier and AuNPs functionalized silica/multiwalled carbon nanotubes core-shell nanocomposites (AuNPs/SiO2@MWCNTs) as tracing tag. The PoPD-AuNPs film provides a suitable microenvironment for stabilizing the primary aptamer (Apt) assembly, and the AuNPs/SiO2@MWCNTs enhances the surface area for immobilizing abundant secondary Apts as well as load large amounts of electrochemical probe thionine (Thi). In the presence of MUC 1, the sandwich-type recognition reacted on the aptasensor surface, and the Thi-AuNPs/SiO2@MWCNTs nanoprobes were captured onto the electrode surface to form biocomplex. AuNPs and MWCNTs could facilitate the electron transfer from Thi to the electrode, thus amplifying the detection response. Under the optimized experimental conditions, the proposed sensing strategy provided a wider linear dynamic range over three orders of magnitude with the detection limit down to 1 pM. Moreover, the aptasensor demonstrated good precision, acceptable stability and reproducibility.

Macrocyclic imidazolium-based amphiphiles for the synthesis of gold nanoparticles and delivery of anionic drugs

In the present work, we have explored the use of amphiphilic bis-imidazolium based macrocycles and an open chain analog for the successful synthesis of gold nanoparticles (AuNPs). The macrocyclic ligands incorporate hydrophobic chains of different lengths, and the newly synthesized ligands were further used for the synthesis of AuNPs in a biphasic system. The successfully synthesized AuNPs were thoroughly characterized. The sizes of the AuNPs were ca. 8 nm, using macrocyclic ligands bearing two 10 carbon atoms alkyl chains, ca. 5 nm in the case of macrocyclic ligands with two 18 carbon atoms alkyl chains, and ca. 7 nm for the open chain ligand with two 18 carbon atoms alkyl chains. Their possible application as vehicles to load and release anionic drugs (such as sodium ibuprofenate) was also assessed and compared with previously described open chain analogs. In this case, it was observed that the AuNPs had high efficiency in extracting sodium ibuprofenate from an aqueous solution. The application as a drug delivery vehicle was confirmed by in vitro release experiments at different pH values.

Simple flow injection for determination of sulfite by amperometric detection using glassy carbon electrode modified with carbon nanotubes-PDDA-gold nanoparticles

A new approach is presented for sensitive and selective measurement of sulfite (SO3(2-)) in beverages based on a simple flow injection system with amperometric detection. In this work, the sulfite sensor was a glassy carbon electrode modified with multiwall carbon nanotubes-poly(diallyldimethylammonium chloride)-gold nanoparticles composites (CNTs-PDDA-AuNPs/GC). Electrochemical oxidation of sulfite with this electrode was first studied in 0.1M phosphate buffer (pH 7.0) using cyclic voltammetry. The results indicated that the CNTs-PDDA-AuNPs/GC electrode possesses electrocatalytic activity for the oxidation of sulfite with high sensitivity and selectivity. Sulfite was quantified using amperometric measurement with the new sensor at +0.4V vs Ag/AgCl in conjunction with flow injection. The linear working range for the quantitation of sulfite was 2-200 mg L(-1) (r(2)=0.998) with a detection limit of 0.03 mg L(-1) (3σ of blank) and an estimated precision of 1.5%.The proposed method was successfully applied to the determination of sulfite in fruit juices and wines with a sample throughput of 23 samples per hour.

Enhancement of enzymatic colorimetric response by silver island films on high throughput screening microplates

In this study, we report the use of an enzyme-based hybrid platform, which is comprised of silver island films, enzymes (HRP and AP) and high-throughput screening (HTS) microplates, to enhance the colorimetric response of enzymatic reactions. The hybrid platform was designed in a two-step process: (i) deposition of SIFs onto HTS microplates with low, medium, and high loading (refers to the extent of the surface plasmon resonance peak of SIFs at 460 nm) using Tollen's reaction scheme; and (ii) attachment of b-BSA or BEA as linkers for the immobilization of enzymes. The presence of SIFs within the wells of the HTS microplates was confirmed using an optical spectrophotometer and real-color photography. Control experiments, where SIFs were omitted from the surfaces were carried out to confirm the effect of SIFs on the enzymatic colorimetric response. Significant colorimetric signal enhancement was observed for HRP or AP on SIFs (high loading) deposited HTS microplates using b-BSA (up to ~3-fold for AP and ~6-fold HRP) or BEA (up to ~7-fold for both HRP and AP), as compared to our control samples. The observed increase in colorimetric response can be attributed to the nature of BEA, which exposes surface-bound enzymes to the substrate present in bulk more efficiently than b-BSA. This study proves that SIFs can serve as a valuable tool to improve the signal output of existing bioassays carried out in HTS microplates, which can be applicable to the field biosensors and plasmonics.

A competitive electrochemical immunosensor for the detection of human interleukin-6 based on the electrically heated carbon electrode and silver nanoparticles functionalized labels

A facile one-step electrochemical reduction method was developed to prepare electrochemically reduced graphene oxide (ERGO) and gold-palladium bimetallic nanoparticles (AuPdNPs) as the platform of immunosensor. A novel competitive electrochemical immunosensor was then proposed by combining the ERGO-AuPdNPs platform with silver nanoparticles (AgNPs) functionalized polystyrene bionanolabel for the sensitive detection of human interleukin-6 (IL-6). An electrically heated carbon electrode (HCPE) was introduced in the detection procedure of the immunosensor, and further improved the sensitivity. The immunosensor exhibited a wide linear response to IL-6 ranging from 0.1 to 100000 pg mL(-1) with a detection limit of 0.059 pg mL(-1). The proposed method showed good precision, broad linear range, acceptable stability and high reproducibility, and could be used for the detection of IL-6 in real samples, which possessed promising application in clinical research.

Ultrasensitive IL-6 electrochemical immunosensor based on Au nanoparticles-graphene-silica biointerface

An Interleukin-6 (IL-6) electrochemical immunosensor was fabricated based on the Au nanoparticles (AuNP)-graphene-silica sol-gel as immobilization biointerface and AuNP-polydopamine (PDA)@carbon nanotubes (CNT) as the label of HRP-bound antibodies. The AuNP-graphene-silica sol-gel film was prepared in situ and modified on the ITO electrode, providing a stable network for the immobilization of antibody and exhibiting a dynamic working range of 1-40 pg/mL with a low detection limit of 0.3 pg/mL IL-6 (at 3s). The results of serum samples with the sensor received an acceptable agreement with the ELISA method. Importantly, this method provided a promising ultrasensitive assay strategy for clinical applications.

Multilayer lectin-glyconanoparticles architectures for QCM enhanced detection of sugar-protein interaction

Multivalent biorecognition of lectin layers by glyconanoparticle sugar-clusters has been used to generate multilayer nanoplatform architectures in a QCM sensing setup.

Hybridization chain reaction engineered DNA nanopolylinker for amplified electrochemical sensing of biomarkers

A DNA nanopolylinker was designed as a three dimensional nanoprobe with high loading of signal molecules for amplifying the biosensing signal. The nanoprobe was prepared by hybridization chain reaction engineering dsDNA polymerization on initiator DNA modified Au nanoparticle with two kinds of small molecule, for example, FITC-labeled DNA hairpins. The core-shell conjugate that was formed contained approximately 320 FITC molecules for further binding of signal molecules. With a sandwich-type immunoreaction and a biotin-streptavidin affinity reaction, the biotinylated core-shell nanoprobe was immobilized on the immunosensor surface, and the FITC molecules then bound enzyme labeled anti-FITC antibody to catalyze a silver deposition process, leading to a novel cascade signal amplification strategy. By combining the proposed strategy with stripping analysis of the deposited silver, an ultrasensitive immunoassay method for biomarker detection was developed. Under optimal conditions, this method showed a linear detection range over 5 orders of magnitude for carcinoembryonic antigen with a detection limit of 1.2 fg mL(-1) (about 18 molecules in 5.0 μL sample). The preparation of DNA nanopolylinker was simple and economic, and it could be used as a universal and multifarious probe for different bioanalytical techniques and showed the promising potential of the signal amplification strategy in the future design of biosensing methodology.

Enzyme-free colorimetric bioassay based on gold nanoparticle-catalyzed dye decolorization

A novel, enzyme-free and aptamer-based colorimetric platform for protein detection has been developed, which takes advantage of aptamer-functionalized magnetic beads (MBs) for target capture, concentration and separation, and aptamer-conjugated gold nanoparticle (AuNP)-catalyzed color bleaching reaction of methyl orange (MO) to generate the colorimetric signals. It was demonstrated that the proposed colorimetric sensing strategy enables simple, cost-effective, sensitive and specific thrombin detection without the use of any enhancing solutions and enzymes. Herein, by naked eye observation, we can detect the human thrombin with a detection limit of approximately 320 pM, which can be further decreased to 30 pM with the help of a UV-vis instrument. In addition, this method also works for targets with two or more binding sites.

An aptamer-based biosensing platform for highly sensitive detection of platelet-derived growth factor via enzyme-mediated direct electrochemistry

In this work, a new label-free electrochemical aptamer-based sensor (aptasensor) was constructed for detection of platelet-derived growth factor (PDGF) based on the direct electrochemistry of glucose oxidase (GOD). For this proposed aptasensor, poly(diallyldimethylammonium chloride) (PDDA)-protected graphene-gold nanoparticles (P-Gra-GNPs) composite was firstly coated on electrode surface to form the interface with biocompatibility and huge surface area for the adsorption of GOD layer. Subsequently, gold nanoclusters (GNCs) were deposited on the surface of GOD to capture PDGF binding aptamer (PBA). Finally, GOD as a blocking reagent was employed to block the remaining active sites of the GNCs and avoid the nonspecific adsorption. With the direct electron transfer of double layer GOD membranes, the aptasensor showed excellent electrochemical response and the peak current decreased linearly with increasing logarithm of PDGF concentration from 0.005 nM to 60 nM with a relatively low limit of detection of 1.7 pM. The proposed aptasensor exhibited high specificity, good reproducibility and long-term stability, which provided a new promising technique for aptamer-based protein detection.

Microfluidic beads-based immunosensor for sensitive detection of cancer biomarker proteins using multienzyme-nanoparticle amplification and quantum dots labels

This study reports the development of a microfluidic beads-based immunosensor for sensitive detection of cancer biomarker α-fetoprotein (AFP) that uses multienzyme-nanoparticle amplification and quantum dots labels. This method utilizes microbeads functionalized with the capture antibodies (Ab₁) and modified electron rich proteins as sensing platform that was fabricated within a microfluidic channel, and uses gold nanoparticles (AuNPs) functionalized with the horseradish peroxidase (HRP) and the detection antibodies (Ab₂) as label. Greatly enhanced sensitivity for the cancer biomarker is based on a dual signal amplification strategy: first, the large surface area of Au nanoparticle carrier allows several binding events of HRP on each nanosphere. Enhanced sensitivity was achieved by introducing the multi-HRP-antibody functionalized AuNPs onto the surface of microbeads through "sandwich" immunoreactions and subsequently multiple biotin moieties could be deposited onto the surface of beads resulted from the oxidation of biotin-tyramine by hydrogen peroxide. Streptavidin-labeled quantum dots were then allowed to bind to the deposited biotin moieties and displayed the signal. Secondly, enhanced mass transport capability inherent from microfluidics leads to higher capture efficiency of targets because continuous flow within micro-channel delivers fresh analyte solution to the reaction site which maintains a high concentration gradient differential to enhance mass transport. Based on the dual signal amplification strategy, the developed microfluidic bead-based immunosensor could discriminate as low as 0.2 pg mL⁻¹ AFP in 10 μL of undiluted calf serum (0.2 fg/chip), and showed a 500-fold increase in detection limit compared to the off-chip test and 50-fold increase in detection limit compared to microfluidic beads-based immunoassay using single label HRP-Ab₂. The immunosensor showed acceptable repeatability and reproducibility. This microfluidic beads-based immunosensor is a promising platform for disease-related biomolecules at the lowest level at their earliest incidence.

Bio-mimetically synthesized Ag@BSA microspheres as a novel electrochemical biosensing interface for sensitive detection of tumor cells

The use of a novel cytosensor, comprised of bio-mimetically synthesized Ag@BSA composite microspheres, for the detection of KB cells (a model system) is described. The Ag@BSA composite microspheres were immobilized on Au electrodes via Au-thiol bonds. Scanning electron microscopy (SEM), atomic force microscopy (AFM) and transmission electron microscopy (TEM) images revealed that the Ag@BSA were well-dispersed microspheres with an average diameter of 500 nm, including the monolayer of BSA. The immobilization of Ag@BSA composite microspheres onto Au electrodes is thought to increase the electrode surface area and accelerate the electron transfer rate while providing a highly stable matrix for the convenient conjugation of target molecules (such as folic acid) and the prolonged incubation of cells. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) studies showed that the fabricated cytosensor was able to detect KB cells ranging from 6.0×10(1) to 1.2×10(8) cells mL(-1) with a lower detection limit of 20 cells mL(-1). Due to its facile synthesis, high stability and reproducibility and cytocompatibility, the novel cytosensor described here could find multifarious uses in applications, such as cancer diagnosis, drug screening and cell adhesion studies.

Electrochemical immunoassay for CD10 antigen using scanning electrochemical microscopy

In the present study, a scanning electrochemical microscopic (SECM) method for imaging of antigen/antibody binding was proposed using CD10 antigen as the model. On the basis of anti-CD10 modified electrode, an electrochemical immunosensor for sensitive detection of CD10 antigen at low potential was developed by a multiple signal amplification strategy. Gold nanoparticles (AuNPs) served as carriers to load more secondary antibodies (Ab(2)) and horseradish peroxidase (HRP). The tip ultramicroelectrode was used to monitor the reduction current, and the 3-D images were obtained simultaneously. Under optimized conditions, the approach provided a linear response range from 1.0 × l0(-11) to 6.0 × l0(-11) M with a detection limit of 4.38 × 10(-12)M. SECM is a versatile system that can be used not only for quantitative current analysis but also for topographic imaging of binding reaction. In addition, specific binding of antigen-antibody could also be continuously and successfully monitored by SECM. This immunoassay provides a sensitive approach for detecting tumor marker, and has potential application in clinical diagnostics.

Immunogold labeling-induced synergy effect for amplified photoelectrochemical immunoassay of prostate-specific antigen

A new photoelectrochemical immunoassay for prostate-specific antigen (PSA) was successfully developed with high sensitivity via immunogold labeling.

Functionalized gold nanoparticle supported sensory mechanisms applied in detection of chemical and biological threat agents: a review

There is a great necessity for development of novel sensory concepts supportive of smart sensing capabilities in defense and homeland security applications for detection of chemical and biological threat agents. A smart sensor is a detection device that can exhibit important features such as speed, sensitivity, selectivity, portability, and more importantly, simplicity in identifying a target analyte. Emerging nanomaterial based sensors, particularly those developed by utilizing functionalized gold nanoparticles (GNPs) as a sensing component potentially offer many desirable features needed for threat agent detection. The sensitiveness of physical properties expressed by GNPs, e.g. color, surface plasmon resonance, electrical conductivity and binding affinity are significantly enhanced when they are subjected to functionalization with an appropriate metal, organic or biomolecular functional groups. This sensitive nature of functionalized GNPs can be potentially exploited in the design of threat agent detection devices with smart sensing capabilities. In the presence of a target analyte (i.e., a chemical or biological threat agent) a change proportional to concentration of the analyte is observed, which can be measured either by colorimetric, fluorimetric, electrochemical or spectroscopic means. This article provides a review of how functionally modified gold colloids are applied in the detection of a broad range of threat agents, including radioactive substances, explosive compounds, chemical warfare agents, biotoxins, and biothreat pathogens through any of the four sensory means mentioned previously.

Fe₃O₄/Au magnetic nanoparticle amplification strategies for ultrasensitive electrochemical immunoassay of alfa-fetoprotein

BACKGROUND

The purpose of this study was to devise a novel electrochemical immunosensor for ultrasensitive detection of alfa-fetoprotein based on Fe(3)O(4)/Au nanoparticles as a carrier using a multienzyme amplification strategy.

METHODS AND RESULTS

Greatly enhanced sensitivity was achieved using bioconjugates containing horseradish peroxidase (HRP) and a secondary antibody (Ab(2)) linked to Fe(3)O(4)/Au nanoparticles (Fe(3)O(4)/Au-HRP-Ab(2)) at a high HRP/Ab(2) ratio. After a sandwich immunoreaction, the Fe(3)O(4)/Au-HRP-Ab(2) captured on the electrode surface produced an amplified electrocatalytic response by reduction of enzymatically oxidized hydroquinone in the presence of hydrogen peroxide. The high content of HRP in the Fe(3)O(4)/Au-HRP-Ab(2) could greatly amplify the electrochemical signal. Under optimal conditions, the reduction current increased with increasing alfa-fetoprotein concentration in the sample, and exhibited a dynamic range of 0.005-10 ng/mL with a detection limit of 3 pg/mL.

CONCLUSION

The amplified immunoassay developed in this work shows good precision, acceptable stability, and reproducibility, and can be used for detection of alfa-fetoprotein in real samples, so provides a potential alternative tool for detection of protein in the laboratory. Furthermore, this immunosensor could be regenerated by simply using an external magnetic field.