Abstract
Here, we designed a simple, rapid, and ultrasensitive colorimetric aptasensor for detecting anatoxin-a (ATX-a). The sensor employs a DNA aptamer as the sensing element and gold nanoparticles (AuNPs) as probes. Adsorption of the aptamer onto the AuNP surface can protect AuNPs from aggregation in NaCl solution, thus maintaining their dispersion state. In the presence of ATX-a, the specific binding of the aptamer with ATX-a results in a conformational change in the aptamer, which facilitates AuNP aggregation and, consequently, a color change of AuNPs from red to blue in NaCl solution. This color variation is directly associated with ATX-a concentration and can be easily measured using a UV/Vis spectrophotometer. The absorbance variation is linearly proportional to ATX-a concentration across the concentration range of 10 pM to 200 nM, with a detection limit of 4.45 pM and high selectivity against other interferents. This strategy was successfully applied to the detection of ATX-a in lake water samples. Thus, the present aptasensor is a promising alternative method for the rapid detection of ATX-a in the environment.
Highlights
After incubation with 40 mM NaCl, the intensity of the absorbance peak at 524 nm dramatically decreased, implying that the AuNPs aggregated. This is due to the negative charges of citrates coated on the AuNP surface being neutralized by Na+ ions, leading to a reduction in electrostatic repulsion and subsequent AuNP aggregation [9,24]
DNA aptamers have been reported to be adsorbed onto the AuNP surface, enhancing the electrostatic repulsion between nanoparticles, and protecting AuNPs from NaCl-induced aggregation [22,33]
The change in AuNP aggregation was controlled by the interactions among the aptamer, AuNPs, and ATX-a in the presence of
Summary
Anatoxin-a (ATX-a) is a natural organophosphate neurotoxin, produced by various cyanobacteria including Aphanizomenon gracile, Oscillatoria acuminata, and Anabaena flosaquae, which occur naturally in freshwater [1,2]. This toxin can irreversibly bind to nicotinic acetylcholine receptors, leading to disruption of oxygen supply to the brain, causing respiratory paralysis, acute asphyxia, and death [2,3]. Exposure to ATX-a primarily occurs through the ingestion of contaminated water [1,3]. An increase in animal intoxication due to ATX-a has been observed [2]. The development of a sensitive and accurate method for ATX-a detection is urgently needed to monitor and control the quality of both environmental water and drinking water
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