Optical biosensor with automated analysis of coffee-ring patterns for the detection of chlorpyrifos in water

MACAGNO, J.; GERLERO, G.S.; SATUF, M.L.; BERLI, C.L.A.

Buenos Aires

Congreso; III Brazil-Argentine Microfluidics Congress; 2022

CNEA, Conicet, Agencia I+D+i

Here we present a field-deployable biosensor platform that quantitatively determineschlorpyrifos (CPS) in river water samples. An innovative readout takesadvantage of the omnipresent phenomenon that occurs after the evaporation ofsessile droplets containing suspended particles, i.e., the coffee-ring (CR) effect1.Effectively, we correlated the variation of the CR patterns with the target level,for a wide range of concentrations. A smartphone-based Python program waswritten for fully automated image capture and processing.The sensing principle makes use of gold nanoparticles stabilized by a CPSspecificaptamer. When competing CPS molecules are present, colloidal destabilizationoccurs, yielding a visible color change. However, instead of readingcolor shift, we implemented the reaction in sessile drops and then quantitativelyanalyzed the CR effect after evaporation over a paper (Fig.1-a): when CPS wasabsent, aptamer-stabilized AuNPs left the typical CR stain, whereas a suppressionof the CR effect was evident when CPS was present (Fig.1-c). A strongcorrelation between CPS level and alteration of stain patterns was established.In order to translate the assay to a portable format prone to software analysis,wax-printed paper cards were prototyped2. These cards (designated as CRcode cards) included computer detectable features and four defined detectionspots. Once the drops placed on the spots fully evaporated, the card was imagedwith the smartphone using the LED flash (Fig.1-b). It is worth to remarkthat no other external devices are needed. The aptamer-based optical biosensorconstitutes a reliable system to detect and quantify CPS in environmentalsamples.