Bioelectrocatalytic signaling from immunosensors with back-filling immobilization of glucose oxidase on biorecognition surfaces

Enhancement of Colorimetric Response of Enzymatic Reactions by Thermally Evaporated Plasmonic Thin Films: Application to Glial Fibrillary Acidic Protein

We report the enhancement of the colorimetric response of horseradish peroxidase (HRP) and alkaline phosphatase (AP) in bioassays by thermally evaporated silver, gold, copper and nickel thin films. In this regard, a model bioassay based on biotin-avidin interactions was employed. Biotin groups and enzymes were introduced to all surfaces using a biotinylated linker molecule and avidin, respectively. The colorimetric response of HRP in the model bioassay carried out on the plasmonic thin films were up to 4.4-fold larger as compared to control samples (i.e., no plasmonic thin films), where the largest enhancement of colorimetric response was observed on silver thin films. The colorimetric response of AP on plasmonic thin films was found to be similar to those observed on control samples, which was attributed to the loss of enzymes from the surface during the bioassay steps. The extent of enzymes immobilized on to plasmonic thin films was found to affect the colorimetric response of the model bioassay. These findings allowed us to demonstrate the use of silver thin films for the detection of glial fibrillary acidic protein (GFAP), where the colorimetric response of the standard bioassays for GFAP was enhanced up to 67% as compared to bioassays on glass slides.

Stable Flexible Electrodes With Enzyme Cluster Decorated Carbon Nanotubes for Glucose-Driven Power Source in Biosensing Applications

Over the years, implantable sensor technology has found many applications in healthcare. Research projects have aimed at improving power supply lifetime for longevity of an implanted sensor system. Miniature power sources, inspired from the biofuel cell principle, can utilize enzymes (proteins) as catalysts to produce energy from fuel(s) that are perennial in the human body. Bio-nanocatalytic hierarchical structures, clusters made of enzyme molecules, can be covalently linked to the electrode’s surface to provide better enzyme loading and sustained activity. Carbon nanotube base electrodes, with high surface area for direct electron transfer, and enzyme clusters can achieve efficient enzymatic redox reaction. A redox pair of such bioelectrodes can make up a power source with improved performance. In this study, we have investigated high throughput processes for coupling enzyme catalysts with power harvesting mechanisms via a screen printing process and solution processing. The process incorporates enzyme (glucosse oxidase and catalase) micro-/nanocluster immobilization on the surface of carboxylated (functionalized) carbon nanotubes with screen printed electrodes. The 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide and N-hydroxysulfosuccinimide amide linkage chemistries were used to bind the enzyme molecules to nanotube surface, and bis[sulfosuccinimidyl] suberate (BS3) was used as the cross-linker between enzymes. Optimized enzyme cross-linking was obtained after 25 min at room temperature with 0.07 mmol BS3/nmol of enzymes, with which 44% of enzymes were immobilized onto the surface of the bioelectrode with only 24% enzyme activity lost. A cell, redox pair of bioelectrodes, was tested under continuous operation. It was able to maintain most of the enzyme activity for 7 days before complete deactivation at 16 days. Thus, the power harvesting mechanism was able to produce power continuously for 7 days. The results were also analyzed to identify impeding factors such as competitive inhibition by reaction byproduct and cathode design, and methods to rectify them have been discussed. Coupling this new and improved nanobiopower cell with a product removal mechanism and enzyme mutagenesis should provide enzyme protection and longevity. This would bring the research one step closer to development of compatible implantable battery technology for medical applications.

Electrochemical immune-biosensor for immunoglobulin G based bioelectrocatalytic reaction on micro-comb electrodes

A new amplification strategy of electrochemical signaling from antigen-antibody interactions was proposed via back-filling immobilization of horseradish peroxidase (HRP), immunoglobulin G antibodies (anti-IgG) and gold nanoparticles onto a three-dimensional sol-gel (3DSG)-functionalized biorecognition interface. The 3DSG sol-gel network was employed not only as a building block for the surface modification but also as a matrix for ligand functionalization. The signal-amplification was based on the bioelectrocatalytic reaction of the back-filling immobilization of HRP to H(2)O(2). With the non-competitive format, the formation of the antigen-antibody complex by a simple one-step immunoreaction between the immobilized anti-IgG and IgG in sample solution inhibited partly the active center of HRP, and decreased the immobilized HRP towards H(2)O(2) reduction. Under optimal conditions, the proposed immunosensor exhibited a good electrochemical behavior to IgG in a dynamic range of 1.12-162 ng/mL with a detection limit of 0.56 ng/mL (at 3delta). Moreover, the precision, reproducibility and stability of the as-prepared immunosensor were acceptable. Importantly, the proposed methodology would be valuable for diagnosis and monitoring of biomarkers and its metastasis.

Assessment of the interaction between a synthetic epitope of troponin C and its specific antibody using a label-free faradaic impedimetric immunosensor and α-Keggin silicotungstic heteropolyacid as a redox probe

The development of an immunosensor for the direct probing of the interaction between a cysteine-modified synthetic peptide, which corresponds to the epitope cTnC-89-98 of troponin C, and its specific antibody is described. Following immobilization of the peptide onto gold electrodes through the formation of a self-assembled monolayer, the alteration of the interfacial properties of the electrodes upon peptide-antibody interaction was traced by faradaic electrochemical impedance spectroscopy (EIS) using a silicotungstic heteropolyacid, H(4)SiO(4).12WO(3), as a redox probe. The electrochemical behaviour of the redox probe was evaluated with cyclic voltammetry and EIS. The effect of milk protein or 4-mercaptophenol, which was used as post-blocking agents, on the performance of the immunosensor, was investigated. Treatment with 4-mercaptophenol resulted in immunoeffective electrodes that successfully tested in anti-serum samples. An optimum dilution ratio of the samples, where the effect of the matrix on the measuring signal is negligible, was also determined.

Enzyme-catalyzed signal amplification for electrochemical DNA detection with a PNA-modified electrode

The signal amplification technique of peptide nucleic acid (PNA)-based electrochemical DNA sensor was developed in a label-free and one-step method utilizing enzymatic catalysis. Electrochemical detection of DNA hybridization on a PNA-modified electrode is based on the change of surface charge caused by the hybridization of negatively charged DNA molecules. The negatively charged mediator, ferrocenedicarboxylic acid, cannot diffuse to the DNA hybridized electrode surface due to the charge repulsion with the hybridized DNA molecule while it can easily approach the neutral PNA-modified electrode surface without the hybridization. By employing glucose oxidase catalysis on this PNA-based electrochemical system, the oxidized mediator could be immediately reduced leading to greatly increased electrochemical signals. Using the enzymatic strategy, we successfully demonstrated its clinical utility by detecting one of the mutation sequences of the breast cancer susceptibility gene BRCA1 at a sample concentration lower than 10(-9) M. Furthermore, a single base-mismatched sample could be also discriminated from a perfectly matched sample.

Biochemical and immunochemical characterization of the antigen–antibody reaction on a non-toxic biomimetic interface immobilized red blood cells of crucian carp and gold nanoparticles

A special protein assay system based on a highly hydrophilic, non-toxic and conductive biominetic interface has been demonstrated. To fabricate such assay system, red blood cells of crucian carp (RBC) was initially grown on a glassy carbon electrode surface (GCE) deposited nano-sized gold particles (GPs), a second gold nanoparticle layer (NG) was then absorbed on the RBC surface, and finally mammary cancer 15-3 antibody (anti-CA15-3) was attached on the functional RBC surface. A competitive immunoassay format was employed to detect CA15-3 with horseradish peroxidase (HRP)-labeled CA15-3 as tracer and hydrogen peroxide as enzyme substrate. When the immunosensor was incubated into a mixture solution containing HRP-labeled CA15-3 and CA15-3 sample for 1h at 37 degrees C, the amperometric response decreased with the increment of CA15-3 sample concentration. AFM images of the modified layer revealed a uniform distribution of protein and nanogold. In situ QCM and electrochemical measurements demonstrated that the wanted antibody-antigen reactions should occur with high specificity and selectivity. The specific immunoassay system can be developed further to yield sophisticated structures for other proteins.

Flow-injection immuno-bioassay for interleukin-6 in humans based on gold nanoparticles modified screen-printed graphite electrodes

A flow-injection electrochemical immunoassay system based on a disposable immunosensor for the determination of interleukin-6 (IL-6) was proposed. The immunosensor was prepared by entrapping horseradish peroxidase (HRP)-labeled IL-6 antibody into gold nanoparticles-modified composite membrane at a screen-printed graphite electrode. With a non-competitive immunoassay format, the immunosensor was inserted in the flow system with an injection of sample, and the injected sample containing IL-6 antigen was produced transparent immunoaffinity reaction with the immobilized HRP-labeled IL-6 antibody. The formed antigen-antibody complex inhibited partly the active center of HRP, and decreased the immobilized HRP to H2O2 reduction. The performance and factors influencing the performance of the immunosensor were investigated. Under optimal conditions, the current change obtained from the labeled HRP relative to thionine-H2O2 system was proportional to the IL-6 concentration in the range of 5-100 ng L(-1) with a detection limit of 1.0 ng L(-1) (at 3delta). The flow-injection immunoassay system could automatically control the incubation, washing and measurement steps with acceptable reproducibility and good stability. Moreover, the proposed immunosensors were used to analyze IL-6 in human serum specimens. Analytical results of clinical samples show the developed immunoassay has a promising alternative approach for detecting IL-6 in the clinical diagnosis.

Direct Electrochemical Immunoassay Based on Immobilization of Protein-Magnetic Nanoparticle Composites on to Magnetic Electrode Surfaces by Sterically Enhanced Magnetic Field Force

A direct electrochemical immunoassay system based on the immobilization of alpha-1-fetoprotein antibody (anti-AFP), as a model system, on the surface of core-shell Fe(2)O(3)/Au magnetic nanoparticles (MNP) has been demonstrated. To fabricate such an assay system, anti-AFP was initially covalently immobilized on to the surface of core-shell Fe(2)O(3)/Au MNP. Anti-AFP-modified MNP (bio-nanoparticles) were then attached to the surface of carbon paste electrode with the aid of a permanent magnet. The performance and factors influencing the performance of the resulting immunosensor were studied. alpha-1-Fetoprotein antigen was directly determined by the change in current or potential before and after the antigen-antibody reaction versus saturated calomel electrode. The electrochemical immunoassay system reached 95% of steady-state potential within 2 min and had a sensitivity of 25.8 mV. The linear range for AFP determination was from 1 to 80 ng AFP ml(-1) with a detection limit of 0.5 ng AFP ml(-1). Moreover, the direct electrochemical immunoassay system, based on a functional MNP, can be developed further for DNA sensor and enzyme biosensor.