Microfluidic Impedance Biosensor Chip with DNA-Based Self-Assembled Monolayers for Label-Free Detection of Cardiac Biomarker Troponin I ^†

A microfluidic chip for electrochemical impedance spectroscopy (EIS) is presented as biosensor for the detection of cardiac troponin I (cTnI). Troponin I is one of the most specific diagnostic serum biomarkers for myocardial infarction. As impedimetric biosensors allow direct and label-free analyte detection, they are particularly suitable for fast biomarker detection. This is essential in the diagnosis of cardiac infarctions to enable an early treatment promoting a positive outcome. The microfluidic impedance biosensor chip presented here consists of a microscope glass slide serving as base plate, sputtered electrodes, and a polydimethylsiloxane (PDMS) microchannel. Electrode functionalization protocols were developed considering a low initial impedance in addition to analyte-specific binding by corresponding antibodies and reduction of non-specific protein adsorption to prevent false-positive signals. Reagents tested for self-assembled monolayers (SAMs) on gold electrodes included thiolated hydrocarbons and thiolated oligonucleotides, where SAMs based on the latter showed a better performance. The corresponding antibody (anti-cTnI) was covalently coupled on the SAM using carbodiimide chemistry. The PDMS microchannel was bonded on the glass slide with the functionalized electrodes, and the completed microfluidic impedance biosensor chip was connected to the readout system. Sampling and measurement took only a few minutes. Application of a human serum albumin (HSA) sample, 1000 ng/mL, led to negligible signal changes, while application of a troponin I sample, 1 ng/mL, led to a significant signal shift in the Nyquist plot. The results are promising regarding specific detection of clinically relevant concentrations of cardiac markers with the newly developed impedance biosensor chip.