Assessment of Deoxyribonuclease Activity Using DNA Molecules Immobilized Between Microelectrodes

Abstract

Serum deoxyribonuclease I (DNase I) can serve as a functional biomarker for the therapeutic monitoring of acute myocardial infarction and other diseases. Here, we demonstrate that the electrical properties of DNA molecules can be exploited to monitor enzymatic activity. A label-free DNA biosensor for the detection of DNase I activity was devised based on electrochemical impedance spectroscopy (EIS). Multiple lambda phage DNA molecules were immobilized between two electrodes in a polydimethylsiloxane reservoir. An equivalent circuit estimated from the EIS measurement was used to calculate the impedance of DNA molecules between the electrodes. DNase detection was then achieved by measuring the increase in impedance, after DNA cleavage by DNase I. This was assessed by the impedance-increase ratio, defined as R_after/R_before (where R_before and R_after represent the resistance between the electrode-immobilized DNA molecules before and after DNase I treatment, respectively). After treatment with DNase I at a concentration 10⁻² unit/μL, a reproducible impedance-increase ratio of approximately 3.3 times was obtained, with a standard deviation of less than 20%. When DNase solutions of various concentrations were introduced, we succeeded in obtaining a definite correlation between DNase concentration and impedance-increase rate, within the range of 10⁻⁴ unit/μL to 10⁻¹ unit/μL.