Scanning Electrochemical Microscope for the Analysis of Biological Samples

Scanning electrochemical microscopy (SECM) is a noninvasive tool for analyzing the electrochemical activity of various surfaces. It can be applied to investigate biomolecules or whole cells. Also, using SECM, electrochemical immunoassays can be developed. Recently we proposed a sandwich immunoassay for the detection of hGH by SECM in generation-collection mode where glucose oxidase was used as a detecting enzyme. In this way, hGH concentrations as low as 40 nM were detected.
SECM, together with the electrochemical impedance spectroscopy (EIS) technique, can be used for the sensitive detection of antibodies, modified by enzymes or nanomaterials. Localized EIS (SEIM) allows the visualization of surfaces by plotting the parameters of equivalent circuits as dependent on coordinates. The most promising results of SEIM can be obtained when the common amperometric SECM lacks sensitivity. Our results show 0.001 ng/mL LOD, measuring gold-nanoparticle-modified human growth hormone (hGH) by SEIM in feedback mode. SEIM in redox competition mode was used to detect localized horseradish peroxidase (HRP) activity. Electrochemical impedance was evaluated by an equivalent circuit, whose parameters depend on distance and hydrogen peroxide concentration used as a substrate for HRP. The HRP-catalyzed reaction describing parameter is charge transfer resistance, showing linear dependence on hydrogen peroxide concentration. Therefore, SECM and SEIM can be used for the analysis of various biological systems, including living cells, immunoassays, and enzymes.