ELECTROCHEMICAL DETECTION OF ORGANIC AND BIOLOGICAL COMPOUNDS WITH MODIFIED ELECTRODE

Abstract

In this dissertation, analytical method/devices based on electrochemical detection are described for determining the important compounds/biomarkers in pharmaceutical and medical diagnostic applications, which can be separated into five parts. In the first part, electrochemical method for N-acetyl-L-cysteine (NAC) detection in drug formulations was developed using boron doped diamond (BDD) sensor coupled with flow injection analysis (FIA) system. The proposed method offers a linear range of 0.5 − 50 µmol/L, a limit of detection (LOD) of 10 nM, excellent response precision, and high stability. In the second part, an electrochemical cholesterol sensor was developed using silver nanoparticles modified glassy carbon electrode (AgNPs/GCE). Hydrogen peroxide (H2O2) produced from the enzymatic reaction was monitored for indirect cholesterol quantification. AgNPs showed the catalytic activity of H2O2 reduction, with no observed interference from easily oxidizable species. The proposed method displayed wide linear range of 3.87 - 773.40 mg/dL with LOD of 0.99 mg/dL. In the third part, a selective non-enzymatic glucose sensor was successfully developed using bimetallic Pt/Au modified BDD electrode. Pt/Au nanocatalyts possess high electrocatalytic activity for glucose oxidation in physiological conditions. A linear range of 0.01 -7.5 mM and a LOD of 0.01 mM were obtained. In the fourth part, a silver nanoparticle-modified boron-doped diamond (AgNP/BDD) electrode coupled with paper-based analytical devices (PADs) was developed for cholesterol detection. Cholesterol and cholesterol oxidase (ChOx) were directly drop-casted onto the hydrophilic area of PAD followed by monitoring of H2O2 from the enzymatic reaction using chronoamperometry. A linear range and a LOD were obtained at 0.01 - 7 mM and 6.5 uM, respectively. In the final part, the disposable boron doped diamond paste electrodes (BDDPEs) for microfluidic paper-based analytical devices (µPADs) were developed and employed for two applications; the quantitative detection of norepinephrine (NE) and serotonin (5-hydroxytryptamine, 5-HT), and the anodic stripping voltammetry of heavy metals. In case of biological species, the electrochemical paper-based analytical device (ePAD) was capable of simultaneously detecting NE and 5-HT in concentration ranges of 2.5−100 µM and 0.5−7.5 µM, respectively. For heavy metal quantitation, a flow-through µPAD design using square-wave anodic stripping voltammetry (SWASV) to enhance the efficiency of metal deposition was presented, thereby improving the detection sensitivity compared to a static ePAD system. The results demonstrated that all proposed method/sensors provide high sensitivity, selectivity, low cost, and portability.