Converting solution viscosity to distance-readout on paper substrates based on enzyme-mediated alginate hydrogelation: Quantitative determination of organophosphorus pesticides

Abstract Quantitatively paper-based senor is performed with simple distance-readout on mixed cellulose ester (MCE) filter paper based on acetylcholinesterase (AChE)-mediated alginate hydrogel. The method is accomplished with the aid of the inhibition effect of target samples on the AChE enzyme-catalyzed hydrolysis of acetylcholine, which changes the pH value of the solution to release Ca 2+ and trigger alginate hydrogelation. The viscosity of the solution is thus regulated with the presence of target samples in the reaction mixture, leading to a significant change in the diffusion diameter of the solution spotted on the filter paper. The concentration in the sample is quantitatively determined by ruler-measureable diffusion diameter of the spot on the paper. With successfully application for quantitatively sensing of organophosphorus pesticides (OPs), we show that the method exhibits excellent reproducibility with RSD (n = 5) as low as 0.09% and good selectivity for detection of OPs. The dynamic range of the method is up to 66.7 ng/mL with the limit-of-detection (LOD) of 3.3 ng/mL. The present study provides a new approach for developing paper-based sensors with quantitative distance-readout, by utilizing enzymatic inhibition to modulate liquid viscosity, which would be of value for target detection in complex samples.