| The pollution situation of lead(Pb) and mercury(Hg), detection methods for Pb and Hg, aptamer, gold label silver stain and electrochemiluminescence were systematically reviewed. Aptamer has been widely used in biomedical research and analytical chemistry due to its diverse targets, high specificity, good chemical stability and cheapness. In this study, a series of analytical methods for Pb2+ and Hg2+ detection based on aptamers having specificity for Pb2+ and Hg2+ respectively were developed by combining with gold label silver stain and electrochemiluminescence technology. The detailed contents were described as follows:1. Determination of nanomolar levels of Hg2+ by exploiting the silver stain enhancement of the aggregation of aptamer-functionalized gold nanoparticlesAn ultrasensitive method for the determination of Hg2+ was developed based on Hg2+-induced strong and selective binding of thymine-thymine mismatches between aptamers on gold nanoparticles and a signal amplification effect caused by a silver stain. The gold nanoparticles were first coated with a single-stranded DNA aptamer rich in thymine. In the presence of Hg2+, the functionalized gold nanoparticles aggregated due to the formation of thymine-Hg2+-thymine complexes resulting in a largely reduced surface area of the gold nanoparticles when exposed to silver ions during staining. Therefore, fewer silver ions were reduced, and the average grey values, as measured by a scanner, were lower. The average grey values were linearly related to the logarithm of Hg2+ concentration from 1 to 500 nM. In addition, there were no significant interference by common metal ions due to the high specificity of the interaction between Hg2+ and the aptamer. The method offers high sensitivity, good selectivity, and the absence of large equipment that makes it suitable field analysis.2. Scanometric nanomolar Pb2+ detection using DNA-functionalized gold nanoparticles and silver stain enhancementBased on gold label silver stain method, a facile, sensitive and selective scanometric method for the detection of Pb2+ was developed. The main components of the method include “8-17†DNAzyme functionalized gold nanoparticles(AuNP1), capture DNA functionalized gold nanoparticles(AuNP2), and silver staining. In presence of Pb2+, AuNP1 was cleaved into different pieces that were captured by AuNP2; and became aggregated and formed network structures. These aggregate structures hindered the exposure of gold particles during the silver staining, resulting in a reduced grey values compared with that in the absence of Pb2+. Using the grey value of silver stain signals, the developed scanometric assay realized quantitative detection of nanomolar levels of Pb2+, ranging from 2 to 1000 nM, without significant interference from other metal ions. Results suggested that this scanometric method is a simple, sensitive, selective, and portable tool for the onsite detection of nanomolar levels of Pb2+.3. An electrochemiluminescence biosensor for Hg2+ detection based on gamma-polyglutamic acid-graphene-luminol composite and oligonucleotidesAn ultrasensitive electrochemiluminescence(ECL) biosensor based on gamma-polyglutamic acid-graphene-luminol(γ-PGA-G-luminol) composite and oligonucleotides for the detection of Hg2+ was developed. γ-PGA-G-luminol composite coated on the glassy carbon electrode could produce a strong and stable ECL signal by luminol, and provide carboxyl groups to cross-link with amino-modified DNA1 enriching in thymine(T) by γ-PGA. Upon addition of Hg2+ and biotin-modified DNA2 enriching in T, T-Hg2+-T interaction occurred and mediated the coordination between DNA1 and DNA2. Afterwards, streptavidin was connected to the end of DNA2 through specific binding of streptavidin to biotin, which obviously reduced the ECL intensity due to the inert protein layer with poor electron transfer ability. Based on the specific T-Hg2+-T coordination chemistry and the specific binding of streptavidin-biotin system, ultrahigh sensitivity and selectivity for Hg2+ detection were obtained. Results revealed that the ECL intensity was logarithmically linear with the concentration of Hg2+ in a wide range from 0.01 to 100 nM. Moreover, the biosensor also exhibited excellent selectivity for Hg2+ ions without significant interference from commonly co-existing metal ions in the sample matrix. Excellent sensitivity and selectivity make the developed biosensor a potential and simple tool for the detection of Hg2+. |
