A Label-Free Electrochemical Biosensing Approach for Modern Diagnostics Using Screen-Printed Electrodes

Abstract

Electrochemical biosensors are renowned for their ability to detect a wide range of analytes in biological fluids for clinical diagnosis. The implementation of biomarkers in electrochemical biosensors for clinical diagnosis is essential for the specific and accurate diagnosis of the disease with high sensitivity and selectivity. Therefore, this thesis evaluates the challenges pertaining to the stability, reproducibility, and obtaining a low limit of detection for the internal/external biomarkers associated with two distinct electrochemical biosensors. The first study tackles the challenge of detecting low analyte concentrations in a label-free biosensor. It introduces an innovative label-free electrochemical biosensing method for the detection of glycosylated hemoglobin (HbA1c) and C-reactive protein (CRP) to predict Coronary Heart Disease (CHD) progression using tailored redox probes, proposing a dual biomarker biosensing platform for future research. Calibration curves reveal an LOD of 5 mg/mL in PBS (8) FeCN (II) and 6 mg/mL in SB for a linear range of 0 – 30 mg/mL of HbA1c. Similarly, an LOD of 0.007 mg/mL and 0.008 mg/mL in PBS (7.4) PcA-NO2 and SB, respectively, is reported for a linear range of 0 – 0.05 mg/mL of CRP. The second study focuses on stabilizing a biomolecule-free sensor for the ultra-low detection of Δ9-tetrahydrocannabinol (THC) in roadside testing. Pre-depositing THC, an external biomarker for drug-impaired driving, onto the biosensor's working electrode enhances its interaction with analytes. However, THC's oxidative nature compromises sensor stability during manufacturing. Consequently, optimal electrode storage conditions were explored, indicating frozen storage as ideal for up to six months, effectively preventing THC oxidation at -18°C, while degradation occurs at 4°C. Modified electrodes stored under optimal conditions exhibit improved calibration curves when exposed to various THC samples.