Abstract
A novel, facile sensor was further developed for microcystin-LR (MC-LR) determination by visible spectroscopy. Antibody-functionalized SiO2-coated magnetic nanoparticles (Fe3O4@SiO2) and aptamer-functionalized polydopamine nanospheres decorated with Cu nanoparticles (PDA/CuNPs) recognized specific sites in MC-LR and then the sandwich-type composites were separated magnetically. The Cu in the separated composites was converted to Cu2+ ions in solution and turn-on visible absorption was achieved after reaction with bis(cyclohexanone)oxaldihydrazone (BCO) (λmax = 600 nm). There was a quantitative relationship between the spectral intensity and MC-LR concentration. In addition, under the optimum conditions, the sensor turns out to be a linear relationship from 0.05 to 25 nM, with a limit of detection of 0.05 nM (0.05 μg/L) (S/N = 3) for MC-LR. The sensitivity was dependent on the low background absorption from the off-to-on spectrum and label amplification by the polydopamine (PDA) surface. The sensor had high selectivity, which shows the importance of dual-site recognition by the aptamer and antibody and the highly specific color formed by BCO with Cu2+. The bioassay was complete within 150 min, which enabled quick determination. The sensor was successfully used with real spiked samples. These results suggest it has potential applications in visible detection and could be used to detect other microcystin analogs.
Highlights
Microcystins (MCs) are mainly formed as products of cyanobacterial metabolism
Copper chloride, BCO, tetraethyl orthosilicate (TEOS), NaOH, tris(hydroxymethyl)aminomethane (Tris), poly(diallyldimethylammonium chloride) (PDDA, 20%, w/w in water, MW = 200,000–350,000), poly(acrylic acid) (PAA, 35%, w/w in water, MW = 100,000), 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC), N-hydroxysuccinimide (NHS), ethanol and methanol were bought from the Aladdin Reagent Co., Ltd. (Shanghai, China)
When PDA/Cu nanoparticles (CuNPs)-aptamer and Fe3O4@SiO2-antibody probes were used after storage at 4 ◦C for a month, the UV-Vis absorption intensity retained over 97.7% of the initial response to MC-LR
Summary
Microcystins (MCs) are mainly formed as products of cyanobacterial metabolism. They are widely present in water. There is an urgent need to develop alternative enzyme-free labels that offer high reproducibility, ease of use, accuracy and portable detection to manage the health risks associated with MC-LR [22,23]. MC-LR was captured in one step and it was enriched using magnetic nanoparticles Such particles provide a proper platform for eliminating pretreatment, with signal amplification and removal of matrix effects from many samples, leading to an off-to-on colorimetric complex. This straightforward assay enables effective detection with high sensitivity and specificity, with a performance that is better than those of previous analytical methods
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