Electrochemical and electronic detection of biomarkers in serum: a systematic comparison using aptamer-functionalized surfaces

Sensitive and selective detection of biomarkers in serum in a short time has a significant impact on health. The enormous clinical importance of developing reliable methods and devices for testing serum levels of cardiac troponin I (cTnI), which are directly correlated to acute myocardial infarction (AMI), has spurred an unmatched race among researchers for the development of highly sensitive and cost-effective sensing formats to be able to differentiate patients with early onset of cardiac injury from healthy individuals with a mean cTnI level of 26 pg mL(-1). Electronic- and electrochemical-based detection schemes allow for fast and quantitative detection not otherwise possible at the point of care. Such approaches rely largely on voltammetric and field-effect-based readouts. Here, we systematically investigate electric and electrochemical point-of-care sensors for the detection of cTnI in serum samples by using the same surface receptors, cTnI aptamer-functionalized CVD graphene-coated interdigated gold electrodes. The analytical performances of both sensors are comparable with a limit of detection (LoD) of 5.7 +/- 0.6 pg mL(-1)(electrochemical) and 3.3 +/- 1.2 pg mL(-1) (electric). However, both sensors exhibit different equilibrium dissociation constant (K-D) values between the aptamer-linked surface receptor and the cTnI analyte, being 160 pg mL(-1) for the electrochemical and about three times lower for the electrical approach with K-D = 51.4 pg mL(-1). This difference is believed to be related to the use of a redox mediator in the electrochemical sensor for readout. The ability of the redox mediator to diffuse from the solution to the surface via the cTnI/aptamer interface is hindered, correlating to higher K-D values. In contrast, the electric readout has the advantage of being label-free with a sensing limitation due to ionic strength effects, which can be limited using poly(ethylene) glycol surface ligands.

Automated summary

The study investigates electric and electrochemical point-of-care sensors for the detection of cTnI in serum samples using aptamer-functionalized CVD graphene-coated interdigated gold electrodes. Both sensors have comparable analytical performances with different equilibrium dissociation constant (K-D) values, indicating the advantage of label-free electric readout over electrochemical sensor when detecting cTnI in serum samples.