New improvements to electrochemical methods for the detection of lead ions and cancer biomarker in aqueous media

Abstract

Electrochemical techniques have been established as one class of the most important and successful methods in qualitative and quantitative chemical and biochemical analysis with extensive applications in environmental and biomedical detections. The main thrust of this thesis is to explore how the sensitivity, selectivity, and quantitative dynamic range can be improved in the electrochemical detection of a typical environmental analyte (Pd²⁺ ion) and a typical biomedical analyte(a cancer-biomarker CA 72-4) in aqueous media, by experimentally examining three important factors: (1) the effect of the chemical modification of the working electrode by new types of composite nano-materials, (2) the effect of the electrochemical parameters employed in the potential-excitation in DPASV technique, and (3) the effect of the selection of redox reporters in case that the analyte is redox-inactive. Chapter 1 briefly introduces the background of the two works reported in this thesis and outlines the thesis objectives. Chapter 2 demonstrates a sensitive and selective screen-printing carbon electrode with a hybrid of gold amalgam (Au₄Hg) and graphene modification for Pb²⁺ ions detection by differential pulse anodic stripping voltammetry (DPASV). Upon optimization of fabrication conditions and DPASV parameters, the hybrid of Au₄Hg(amal) and graphene-modified SPCE shows excellent electrochemical sensing performance with a linear range from 1 to 80 μg/L and a lower limit of detection (LOD) of 0.040 μg/L, with a correlation coefficient of 0.999. The recovery of Pb²⁺ concentrations in four different water samples ranged from 92.41% to 103.87%. The main scientific contribution of this chapter is the introduction of a composition-specific gold amalgam as a component in the hybrid chemical modifier for the detection of lead ions. The dependence of the detection performance on electrochemical parameters in the DPASV technique is systematically examined and optimized for the first time. Chapter 3 reports a traditional sandwich-type electrochemical immunosensing method with a new type of redox-reporter, the anodic stripping of silver nanoparticles (AgNPs) hybridized with other nanomaterials as the chemical modifiers for the working electrode, for the detection of cancer antigen 72-4 (CA 72-4). AuNPs/MXene@PAMAM capture probe (Ab₁) and DMSNs/AuNPs@Ag reporting probe (Ab₂) were designed to implement the sandwich immunosensor. The highlight of this immunoassay is the utilization of the DMSNs/AuNPs@Ag probe for amplifying electrochemical signals based on Ag anodic stripping responses. The designed immunosensor showed a good linear range from 0 to 80 U/mL with a quite low LOD (0.0014 U/mL). Under optimum conditions, the immunosensor demonstrated good selectivity, stability, and reproducibility, providing promising prospects for detecting other cancer biomarkers. Chapter 4 summarizes the main achievements of this thesis and presents my prospectives for the future work along the results obtained in this thesis.

Date of Award	2024
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology
Supervisor	Xiaoyuan LI (Supervisor) & Hongkai WU (Supervisor)