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

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

Buenos Aires

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

CNEA - CONICET - AGENCIA

Here we present a ￿eld-deployable biosensor platform that quantitatively determines chlorpyrifos (CPS) in river water samples. An innovative readout takes advantage of the omnipresent phe- nomenon that occurs after the evaporation of sessile droplets containing suspended particles, i.e., the co￿ee-ring (CR) e￿ect￿. E￿ectively, 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-speci￿c 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 e￿ect after evaporation over a paper (Fig.￿-a): when CPS was absent, aptamer-stabilized AuNPs left the typical CR stain, whereas a suppression of the CR e￿ect was evident when CPS was present (Fig.￿-b). A strong correlation between CPS level and alteration of stain patterns was established (Fig.￿-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 de￿ned detection spots. Once the drops placed on the spots fully evaporated, the card was imaged with the smartphone using the LED ￿ash. 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.