Electrochemical Sensors Based On Gold Nanoclusters And Electroactive Amino Acids

Electrochemical sensors possess some favorable properties of simple design, low cost, high sensitivity, portable device, easy miniaturization and automation. In the present thesis, electrochemical sensors were developed based on the enzyme-gold nanoclusters and electroactive amino acid for probing environmentally toxicants and the biomarkers of cancer diagnosis and metastasis.(1) An electrochemical detection method was developed by use of the electrical activity of tyrosine for the detectiion of organophosphorus agent(Chapter 2). Tyrosine with organophosphorus agent-sensitive electroactivity was modified onto the surface of the magnetic particles, forming FeR3ROR4R@Tyrosine. Here, the phosphation of tyrosine by the organophosphorus agents would trigger the loss of their electrochemical activities. The as prepared magnetic electrodes were applied to track the change of tyrosine electrochemical signals before and after treated with organophosphorus, achieving the highly sensitive detection of organophosphorus content in the blood. Easy to separate, irreversible oxidation of tyrosine and combination of tyrosine-organophosphorus with high stability were composited in the FeR3ROR4R@Tyrosine, the established method realized simple, rapid and specific detection of organophosphorus in the blood, with the detection limit of 0.016 n M.(2) Enzyme-gold nanocluster compounds were fabricated through the technology of protein biomineralization, aiming to improve the catalysis activities of protein enzymes by gold nanoclusters(Chapter 3). Considering that enzyme catalytic active sites are often located at the deep channels of proteins, into which AuP3+P ions were first introduced to be in situ reduced by the reducible amino acids in the surface or internal of enzymes to form gold nanoclusters in the channels resulting in the improved catalytic activities of enzymes. The activities of three common enzymes and their catalysis kinetics were systematically investigated by the colorimetric experiments. Compared with the corresponding natural enzymes, the developed enzyme-gold nanoclusters could not only present higher catalytic activity, but also higher affinity to the reaction substrates. Such a method offers a new way to improve the natural enzyme activities, promising the extensive applications of enzymes.(3) A sandwich-type ultrasensitive electrochemical sensing technology was developed for detecting low-level free micro RNAs(mi RNAs) in blood(Chapter 4). Alkaline phosphatase(ALP)-gold nanocluster(ALP-Au NCs) compounds were in situ synthesized for labelling DNA detection probes. Meantimes, DNA capture probes were covalently anchored onto magnetic particles to capture mi RNA targets to further hybridize with the DNA detection probes to form sandwich-type nucleic acid compounds. Here, DNA ligase was introduced to make the connection of two DNA probes complementary to mi RNA targets. An electrochemical sensor was thereby established for the ultrasensitive detection of mi RNAs. Herein, ALP in ALP-Au NCs would conduct the catalytic hydrolysis of phosphorylated ascorbic acid to produce reducing agent. Au NCs in ALP-Au NCs would catalyze the silver deposition on the magnetic electrode for silver signal output. Studies have shown that the use of DNA ligase, not only improved the ability of DNA probes in bearing the deposited silver precipitate on the surface of magnetic electrodes, so as to maximize the amplified silver deposition signal. With the help of selectivity of DNA ligase, single-base-mutated mi RNAs could also be determined. The silver deposition-based electrochemical sensing method might break through the detection bottleneck of mi RNAs with short chains. It can allow for the ultrasensitive detection of mi RNAs in blood(the detection limit down to 21.5 a M) for the early warning of cancer diagnosis and metastasis.