sensitive colorimetric aptasensor for methylphosphonic acid detection in water samples

Detection of methylphosphonic acid (mpa) is important as several nerve agents can be hydrolysed to mpa after a certain period of their applications. given the need for simple and rapid mpa detection, the colorimetric method is considered the most suitable sensor. to enhance the selectivity of this sensor, dna or rna aptamers, which can bind to a target molecule with high affinity and specificity, can be integrated. in this study, the optimum conditions for detection of mpa was determined using an aptamer-citrate capped gold nanoparticle (apt-cit-aunps) colorimetric assay. the optimum conditions of the detection based on color change were: 300 µl of cit-aunps and 1 µl of 1 µm of dna aptamer. under the optimised experimental conditions, the colorimetric response is linearly proportional to mpa concentration range from 5.0 to 30.0 mm, with a detection limit of 0.3 mm. these values are much lower than the ld50 for mpa, indicating the practicability of the sensor. in addition, the aptasensor was successfully applied for the determination of mpa in lake and tap water samples, showing great potential for on-site detection of mpa.