Monitoring disinfection in the Covid-19 era. A reagent-free nanostructured smartphone-based device for the detection of oxidative disinfectants

Abstract

In this work, a ready-to-use colorimetric device for oxidative disinfectants (i.e., H2O2, C2H4O3, and NaClO) detection has been developed and proved for the evaluation of disinfection treatments in the COVID-19 containment framework.The sensing element of the proposed colorimetric indicator consists of a transparent flexible PET substrate integrating gold and silver nanostructures. The nano-equipped indicator was integrated into different devices realized using a craft-cutting plotter taking advantage of adhesive/thermo-adhesive flexible pouches and filter paper. In particular, two devices are presented (i) a flexible multi-analysis sampling plate and (ii) a paper-based sampling pipette, for the determination of oxidant disinfectants concentration, evaluation of disinfection treatments by spraying/fogging, and for the analysis of disinfectant residues.The sensing strategy relies on the ability of the disinfectants to oxidize the silver nanostructures of the indicator substrate, producing a colorimetric variation monitorable by a smartphone, maximizing the sensitivity using a colored background. The proposed colorimetric assay occurs in 5 min and does not use external reagents; contact of the disinfectant with the sensing surface is the only requirement. The devices had very low limits of detection (∼1 ppb) and good reproducibility (RSD ≤ 2 %, n = 3) for direct disinfectants analysis. They were challenged for the evaluation of indoor disinfection treatments, allowing to evaluate spraying and fogging treatments, as well as residues monitoring.The here proposed system is disposable, low-cost both in therm of material and reagents (0.05 €) and instruments required, portable, and able to return information on the good practices recommended for environmental disinfection.