A novel optical DNA biosensor for detection of trace amounts of mercuric ions using gold nanoparticles introduced onto modified glass surface

摘要

In this work we report a DNA spectrophotometric biosensor for detection of Hg~(2+) ions in which a pair of oligonucleotides with four thymine–thymine (T–T) mismatched bases was immobilized onto modified glass surface. Firstly, glass surface modified with 3-(mercaptopropyl) trimethoxysilane (MSPT) and gold nano-particles respectively and then one oligonucleotide (P_1) modified with hexanthiol at 5-terminal was immobilized on gold nano-particles via self-assembly and inserted in methylene blue. Methylene blue can intercalate on single strand DNA (ss-DNA) and its absorption peak can measure spectrophotometrically. Then the other oligonucleotide was able to hybridize with P_1 by forming thymine–Hg~(2+)–thymine (T–Hg~(2+)–T) complexes in the presence of Hg~(2+), and absorption signal of methylene blue reduced upon Hg~(2+) increasing concentration because inaccessibility of guanine base in DNA duplex. However, when Hg~(2+) was absent, the two oligonucleotides could not hybridize due to the T–T mismatched bases, and P_2 could not be fixed on the modified glass surface and any change in absorption peak of methylene blue takes place. The UV–Vis spectrum showed a linear correlation between the absorption peak of methylene blue and the concentration of Hg~(2+) over the range from 10 nM to 10 μM (R~2 = 0.9985) with a detection limit of 6 nM. This spectrophotometric biosensor could be widely used for selective detection of Hg~(2+).