Silica Nanoparticle-based Novel Fluorescent Biosensors with Conjugated Polyelectrolyte-sensitized Signals

Abstract

The development of sensitive, low-cost and fast biomolecular detection is a key issue for clinical diagnosis of genetic and pathogenic diseases. This thesis presents the research that is focused on the design and fabrication of silica nanoparticle (NP) based fluorescent biosensors with the aid of conjugated polyelectrolytes (CPEs) for the detection of human-essential biomolecule and disease-related proteins. An overview of recent research and development emphasizing on biosensors, CPE and silica NP has been summarized in Chapter 1. Afterwards, CPE-sensitized biosensors in solution were firstly investigated in Chapter 2, which take advantage of collective response of CPEs upon external minor perturbation in sensing procedure. Label-free ATP detection was designed using DNA aptamer/ATP specific interaction as the recognition event and intercalator ethidium bromide (EB) as signal reporter. The detection limit and assay selectivity tetrahydrofluorene-sensitized EB emission via a fluorescence resonance energy transfer (FRET) process. Super-quenching property of CPE was then studied via complexation of cytochrome c (cyto c) and exploited to screen trypsin activity in the process of hydrolysis in Chapter 3. This is based on hydrolysis-induced fluorescence recovery of CPE, in that case less charge transfer from cyto c to CPE occurs. The initial velocity and kinetic parameters were also derived by measuring fluorescence recovery of CPE. The CPE-based biosensors demonstrate high assay performance in solution; however, solution-based biosensors can hardly detect analytes in biological samples due to non-specific interaction between CPE/protein and high background signal of complicated solution environment. To address this problem, silica NP serves as a novel substrate to fabricate biosensors in virtue of its versatile surface modification, biocompatibility and target/non-target separation in mixture. In Chapter 4, a general method is reported for silica NP synthesis, surface modification and probe immobilization, followed by the development of NP-based ATP detection relying on conformational switch of double-stranded DNA (dsDNA) to DNA aptmer/ATP complex. To realize silica NP-based protein detection, we design a fluoroimmunoassay for IgG with the aid of antibody-immobilized NPs and CPEs in Chapter 5. The integration of CPE offers remarkable signal amplification for enhanced immuno-sensitivity and selectivity. To further address real sample detection, aptamer-functionalized NPs as sensory platform has been employed for protein detection in Chapter 6 and Chapter 7. Thrombin detection is achieved on the basis of target-induced formation of sandwich structure on NPs, which provided sensitized-dye emission upon excitation of CPE. We also design a naked-eye lysozyme detection triggered by recognition-induced charge switching using negatively charged CPE as signal output. These NP-based detection strategies offer tremendous opportunities for developing next-generation biosensors.