Rapid Electrical Immunoassay of the Cardiac Biomarker Troponin I through Dielectrophoretic Concentration using Imbedded Electrodes

Abstract

Rapidity and high sensitivity are critical factors for the diagnoses of heart attacks, and cardiac troponin I (cTnI) is at present a clinical standard for its diagnosis. Here we report a rapid, label-free, and highly sensitive single-walled carbon nanotube (SWCNT) electrical immunosensor, featuring two pairs of electrodes. Two concentration electrodes (gaps: 25 and 80 μm) and two detection electrodes (source and drain; gap: 20 μm; width: 50 μm) were used for dielectrophoretic concentration of cTnI on the SWCNT channels and resistance measurements of the dielectrophoresis (DEP)-concentrated cTnI, respectively. The two concentration electrodes were imbedded between upper and lower dielectric layers, facing each other, underneath the -COOH-functionalized SWCNT channels deposited between the detection electrodes. Therefore, the gap between these imbedded concentration electrodes can be reduced to maximize the electric field intensity for DEP-mediated concentration of cTnI, thereby greatly reducing the detection time (1 min) and enhancing the limit of detection (0.7-0.8 pg mL- 1). Relative resistance changes of the SWCNTs were measured as cTnI concentration in Tris-Borate-EDTA (TBE; 0.0025×) and human serum diluted 500-fold with 0.0025× TBE decreased from 100 ng mL- 1 to 1 pg mL-1, and they were shown to be linear with the logarithm of cTnI concentration (R2=0.99 and 0.97, respectively). These immunosensors also showed high specificity over another cardiac biomarker, myoglobin, TBE medium (0.0025×), and 500-fold diluted human serum. The DEP-capture of cTnI depended on the frequency of the applied electric field, demonstrating the qualitative nature of the real part of the Clausius-Mossotti factor for cTnI.