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

MACAGNO, JOANA; GERLERO, GABRIEL S.; SATUF, MARÍA LUCILA; CLAUDIO L. A. BERLI

Congreso; III Brazil-Argentine Microfluidics Congress VI Congreso de Microfluídica Argentina; 2022

Here we present a field-deployable biosensor platform that quantitatively determines chlorpyrifos (CPS) in river water samples. An innovative readout takes advantage of the omnipresent phenomenon that occurs after the evaporation of sessile droplets containing suspended particles, i.e., the coffee-ring (CR) effect. Effectively, we correlated the variation of the CR patterns with the target level, for a wide range of concentrations.A smartphone-based Python program was written for fully automated image capture and processing. The sensing principle makes use of gold nanoparticles stabilized by a CPS-specific aptamer. When competing CPS molecules are present, colloidal destabilization occurs, yielding a visible color change. However, instead of reading color shift, we implemented the reaction in sessile drops and then quantitatively analyzed the CR effect after evaporation over a paper (Fig.1-a): when CPS was absent, aptamer-stabilized AuNPs left the typical CR stain, whereas a suppression of the CR effect was evident when CPS was present (Fig.1-b). A strong correlation between CPS level and alteration of stain patterns was established (Fig.1-c).In order to translate the assay to a portable format prone to software analysis, wax-printed paper cards were prototyped. These cards (designated as CR code cards) included computer detectable features and four defined detection spots. Once the drops placed on the spots fully evaporated, the card was imaged with the smartphone using the LED flash. Only uniform illumination is required, no other external devices are needed as distance and perspective corrections are performed by the software. The aptamer-based biosensor constitutes a reliable system to detect and quantify CPS in environmental samples.