ELECTROCHEMICAL SENSORS FOR HUMAN PAPILLOMAVIRUS DNA, C-REACTIVE PROTEIN AND FOOD COLORANTS DETECTIONS

Abstract

In this dissertation, electrochemical sensors for determination of medical biomolecular markers and food colorants were developed. The research can be divided into two parts. In the first part, electrochemical sensors for determination of clinically important biomarkers were studied. There was two subprojects based on the target markers. The first subproject was the development of electrochemical sensor for the simultaneous detection of high-risk human papillomaviruses (HPV) DNA type 16 and 18 as biomarkers for cervical cancer. In this work, a highly specific pyrrolidinyl peptide nucleic acid was employed as DNA capture probe for both target DNAs. A second PNA probe labeled with a redox-active anthraquinone (AQ) tag was used to generate the electrochemical signal upon binding to the DNA target. The developed sensor showed a linear range between 0.1 and 100 nM, and the limits of detection (LODs) of 40 and 60 pM (S/N = 3) for HPV types 16 and 18 were found, respectively. This developed sensor was highly sensitive and selective, and was successfully applied to detect DNAs obtained cell lines after amplification by polymerase chain reaction (PCR). For the second subproject, a sandwich-type electrochemical immunosensor was designed to detect C-reactive protein (CRP) - a biomarker for cardiovascular diseases. The observed electrochemical signal increased proportionally to CRP level presented in the system with a linear range from 0.01 to 150 µg/mL and LOD of be 1.50 ng/mL. This developed sensor was successfully applied to determine CRP in practical samples, giving results that are in agreement with certified samples. For the second part of the research, an electrochemical sensor for the determination of synthetic colorants, sunset yellow (SY) and tartrazine (TZ) was developed. The employed electrode was modified using graphene oxide to enhance detection. Furthermore, a screen-printed electrode type was a low-cost screen-printed carbon electrode (SPCE) modified with graphene oxide to enhance the performance of the detection. The graphene film was coated onto the electrode surface via a simple electrochemical reduction process that does not require toxic chemicals and generates no toxic wastes. From the obtained results, the modified electrode exhibited higher electrochemical signal response compared to the unmodified electrode. Linearity of detection was in the range of 0.01 – 20 µM and 0.02 – 20 µM, and LODs were 0.50 and 4.5 nM for SY and TZ, respectively. All developed electrochemical sensors were highly sensitive and selective, inexpensive and portable which are suitable for use as alternative sensors for pharmaceutical, environmental and other analyses.