Prussian blue nanoparticle-labeled aptasensing platform on graphene oxide for voltammetric detection of α-fetoprotein in hepatocellular carcinoma with target recycling

An enzyme-free electrochemical aptasensing platform based on a graphene oxide nanosheet-modified gold-disk electrode was developed for the voltammetric detection of alpha-fetoprotein (AFP) in hepatocellular carcinoma by using a Prussian blue nanoparticle (PBNP)-labeled aptamer. The electroactive PBNP, a typical signal-generation tag, was utilized for the labeling of the aminated AFP aptamer by using covalent conjugation. The electrochemical sensing platform was prepared in a simple manner on the basis of a π-π stacking reaction between the immobilized graphene oxide and the PBNP-labeled AFP aptamer. Upon target AFP introduction, the analyte reacted with the aptamer, thus resulting in the dissociation of the PBNP from the nanosheets. In the presence of DNase I, the newly formed AFP/aptamer-PBNP complex was cleaved to release target AFP, which could react again with the aptamer on the nanosheets, thereby causing target recycling. During this process, the cleaved PBNP-aptamer was far away from the electrode to decrease the voltammetric signal. Under optimum conditions, the voltammetric peak current of the modified electrode decreased with the increment of the target AFP concentration within the linear range of 0.01-300 ng mL^-1 at a low detection limit of 6.3 pg mL^-1. The precision and reproducibility of the aptasensing protocol were acceptable (CV: <15% for intra-assay and inter-assay). Other possible nontarget biomarkers did not interfere significantly with the voltammetric signal of this system. Human serum samples containing target AFP were assayed with electrochemical aptasensing and a commercial human AFP ELISA kit, and gave well-matched results from these two methods. Importantly, our strategy provides a new horizon for the determination of disease-related proteins.

Chemiluminescence of luminol catalyzed by electrochemically oxidized ferrocenes

Ferrocenes oxidized at an indium tin oxide-coated glass electrode catalyze the chemiluminescent reaction of luminol with hydrogen peroxide. The catalytic reaction has been studied with ferrocene derivatives in solution and covalently attached to ovalbumin adsorbed on the electrode. It is shown that chemiluminescence is initiated by electrochemical oxidation of the ferrocene derivative.

Enzyme immunosensors based on electropolymerized polytyramine modified electrodes

Highly sensitive amperometric enzyme immunosensors for human immunoglobulin G (IgG) were prepared on the basis of electrogenerated polytyramine (PTy, tyramine = p-(2-aminoethyl)-phenol) modified electrodes. Properties of PTy films changed depending on electrolysis conditions. On the basis of the found properties of the films, an effective IgG sensor was prepared: a PTy film was formed first from an acid solution on a Pt electrode, and the surface was further covered with a PTy film from an alkaline methanol solution to give a PTy doubly coated electrode on which anti-IgG was then immobilized. This electrode provided a large surface area with little non-specific adsorption of proteins. By means of the competitive enzyme immunoassay technique using glucose oxidase (GOD) labeled IgG conjugates, IgG was determined in the concentration range of c. 10 pg/ml-1 mg/ml from the oxidation current of H2O2 generated by the enzyme (GOD) reaction using the above IgG sensor. Also, an anti-IgG immobilized electrode, prepared by using a Pt electrode singly covered with a PTy film from an alkaline methanol solution, acted as an effective IgG sensor with a detection limit for IgG of c. 100 pg/ml.

Adsorptive stripping voltammetry of human chorionic gonadotropin and two of its specific antibodies

The electrochemical behaviour of human chorionic gonadotropin (hCG), as well as rat anti-beta hCG and rabbit anti-beta hCG antibodies, has been studied using cyclic voltammetry and adsorptive stripping voltammetry. Conditions have been optimised for the determination of these species by differential pulse adsorptive stripping voltammetry with respect to accumulation potential, accumulation time, scan rate, pulse amplitude and drop size. This technique has also been used to investigate the interaction of hCG with each of its specific antibodies in solution.

Potentiometric (bioselective electrodes) assay systems: utility and limitations

Numerous potentiometric assays utilizing bioselective electrodes are fast revolutionizing many areas of biotechnology. Adequately discussing the utility and limitations of these electrochemical systems is the purpose of this review. A general overview introduces bioselective potentiometry by presenting basic concepts, historical background, and current developments. Essentially, the review consists of several sections describing electrode architecture, operational concepts, different biosensors, assay systems, applications, and future trends. Advantages and disadvantages of the different bioselective assay systems discussed are included throughout each section. Electrode design discussion covers conventional liquid probes and the newer solid-state transitor biosensors. Limitations and advantages of different chemoreceptors, biocatalysts, and potentiometric transducers are presented. Operational characteristics include: linear behavior, sensitivity, stability, specificity, response, recovery, and the influence of interfering factors. Enzyme, organelle, tissue, and microbial biocatalytic sensors are discussed. Bioligand systems include: affinity, immunoselective enzyme, and liposome sensors. Potentiometric bioselective drug, microbial, and immunoassay systems are also included.

Potentiometric studies of selective reactions of bioactive substances on the surface-modified tantalum electrodes

The method of highly selective potentiometric detection of bioactive substances developed by us has been much improved by using tantalum metal as a electrode material, by employment of a new method of modification (using gamma-aminopropyltriethoxysilane and cyanogen bromide), and by the pretreatment with inert protein before the measurement. As the consequence, the response in the electrode potential shift has been increased and the reproducibility of the data reached almost 100%.

A simple, inexpensive, disposable electrochemical sensor for clinical and immuno-assay

An inexpensive, rapid, disposable electrochemical system has been developed for both clinical and immunochemical assays. The three-electrode planar configuration is produced by silk screening graphite paint on to cardboard. Assays are carried out amperometrically using constant voltage and monitoring current produced by the oxidation of an electron mediator. In the case of immuno-assay the system described uses the enzyme glucose oxidase with 1,4-benzoquinone as the mediator. The assay is carried out by effecting a separation of the bound and free fractions of the immunoreactants via immobilizing the antibodies on to magnetic particles which are magnetically concentrated on the electrode surface for analysis. This concentration of the bound antigen-antibody complex with the glucose oxidase label effectively increases the concentration of the reduced mediator in the electrode vicinity, thus increasing the amperometric response to the bound fraction of the label.