Ultra-Sensitive and Selective Detection based on Oligonucleotide/Nanoparticle Biosensors

Abstract

This thesis describes research efforts aimed at developing novel biosensors, based on oligonucleotide-modified metal nanoparticles, for ultrasensitive metal ion and DNA detections. In Chapter 2, we have demonstrated a gold nanoparticle/DNA biosensor for colorimetric detection of mercuric ions (Hg2+) at room temperature. Our novel DNA biosensor can easily detect mercuric ions in aqueous solutions and in the presence of excessive other metal ions. Compared with instrument-based ultrahigh sensitive methods for accurate metal ion identification, this instrument-free assay provided a practical and convenient solution for rapid screening of Hg2+ contamination, especially in remote areas. In Chapter 3, a chip-based approach, combined with silver amplification, for rapid and ultra-high sensitive detection of single nucleotide polymorphisms in DNA sequences has been presented. More importantly, the silver amplification method provides the ability to quickly identify the precise location of the single-base mismatch in a target DNA sequence. In Chapter 4, an enzyme-based colorimetric method has been demonstrated for ultrahigh-sensitive detection of single stranded oligonucleotides and long stranded DNA sequences. The preliminary detection limit of this colorimetric system is about 0.5 fmol. Significantly, upon modification, the approach presented herein could also be extended to detect a broad range of other targets including biological macromolecules, aptamer-binding small molecules, and metal ions at ultra-low concentrations. In Chapter 5, a novel wet DNA sensing method, based on PMMA-protected sub-2 nm nanogaps, has been reported for in-situ biological detection directly in aqueous solutions under near-physiological conditions. In Chapter 6, a proof-of-concept fluorescence resonance energy transfer system involving upconversion nanoparticles as energy donors and Au nanoparticles as energy acceptors have been demonstrated. This new optical detection approach provides an opportunity for multiplex sensing of various biological analytes.