1. Design of positive potential barrier immunosensors
Publication:
M. Stobiecka and M. Hepel,
"Effect of buried potential barrier in label-less electrochemical
immunodetection of glutathione and glutathione-capped gold
nanoparticles"
The design of an immunosensor for GSH developed in this work is depicted in Scheme 1. It is based on an anti-GSH antibody molecules immobilized on positive potential-barrier self-assembled monolayer (SAM) of aminohexanethiol (AHT). The accessibility of binding sites for the analyte epitope at the top branches of the Y shaped antibody molecules is the key element in the sensor response. In this work, the anti-GSH antibody molecules were immobilized on an AHT SAM adsorbed on gold piezoelectrode via amide bonds between carboxylic groups of the Fc stem of an Ab and amine groups of the thiol. The carboxylic groups of Ab were activated with EDC reagent. To control nonspecific binding of proteins that might be present in analyzed samples, the electrodes were incubated with 0.001% BSA solution in 0.1M PBS pH 7.4. The main goal of this work was to evaluate electrostatic interactions in the sensory film based on the AHT basal SAM. The analyte solutions in the form of a free GSH or GSH-capped gold nanoparticle (AuNP@GSH) solution were added to investigate the antigen-antibody interactions.
The sensor response to the additions of GSH and GSH-capped gold nanoparticles is illustrated in Figure 2. The charge density distribution in a positive potential barrier sensory film was calculated using Gaussian charge distributions in subsequent layers of AHT, counterions, BSA, and IgG. The electric field distribution in the film was calculated by numerical integration of charge density profiles. A second integration results in the potential vs. distance dependence for the film. The analysis of the obtained plots of charge density profiles, electric field and potential distributions enabled defining conditions for film stability, diminished ingress of counterions, and the optimum sensitivity for voltammetric signal transduction using label-less redox probe ion (ferricyanide) reactions.
Scheme 1. The design of an electrochemical and nanogravimetric immunosensor with positive potential barrier for the detection of glutathione-capped AuNP.
Figure 2. Changes of apparent mass vs. time during binding of: (1) glutathione and (2) glutathione-capped AuNP, on a AuQC/AHT/Abmono/BSA modified gold piezoelectrode.