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Ultrasensitive immunoassay of microcystins-LR using G-quadruplex DNAzyme as an electrocatalyst

Tian, Junping, Zhao, Huimin, Yuan, Fang, Quan, Xie, Chen, Shuo
International journal of environmental analytical chemistry 2014 v.94 no.10 pp. 988-1000
carbon nanotubes, correlation, detection limit, electrochemistry, electrodes, equations, horseradish, hydrogen peroxide, immunoassays, linear models, microcystin-LR, monitoring, water quality, water reservoirs
An electrochemical immunoassay for microcystin-LR (MC-LR) detection was developed using multi-labeled horseradish peroxidase-mimicking DNAzyme on carbon nanotubes (CNTs) as electrocatalyst for signal amplification. CNTs were covalently conjugated to multiple DNAzyme along with MC-LR for a competitive immunoassay. The as-prepared DNAzyme/CNTs/MC-LR biolabel was specifically captured on the electrode surface, and current responses were obtained upon the electro-catalytic reduction of hydrogen peroxide by the captured biolabels. Under optimal conditions, the electro-catalytic current decreased linearly with the increase amount of MC-LR in the range from 0.01 to 7.0 µg L ⁻¹. The linear regression equation was I (µA) = 12.96 − 1.48 X [MC–LR] (µg L ⁻¹), with a correlation coefficient of 0.989. The limit of detection of MC-LR was 2.31 ng L ⁻¹. Application of the immunoassay method and LC/MS/MS method for MC-LR determination on spiked reservoir water gave recovery range of 91.7–105.2% and 94.0–105.0%, respectively. The resulting versatile immunoassay exhibited high sensitivity, good precision and satisfactory reproducibility, which could have vast potential in routine water quality monitoring for various environmental toxins.