A Facile Colorimetric Sensor for Sensitive Detection of Nitrite in the Simulated Saliva

Rapid on-site monitoring of nitrite as a diagnostic biomarker has drawn considerable attention in recent years. However, conventional detection techniques face limitations in terms of portability and ease of usage. In this work microfluidic paper based colorimetric sensor (µPCS) is developed for detection of nitrite from simulated saliva sample using Griess reagent. We discovered that the chemical nature of the filter papers has significant effect on the analytical sensitivity of nitrite detection. Among different paper substrate tested, the glass microfiber filter (GMF) paper exhibits exceptional detection sensitivity. The µPCS was fabricated using GMF as the substrate material through a lamination process. We have fabricated a portable light box using 3D printing and coupled it with µPCS device for image acquisition. This helps to maintain uniform lighting and avoid external interference during image acquisition. Under optimal conditions, a linear change in response with respect to nitrite concentration was observed for 0.5–200 µM with a limit of detection of 3.22 µM and a limit of quantification of 10.72 µM. The proposed method was validated with UV–Vis spectrophotometer. The device developed in this work showed good accuracy (recovery of 103–113%), and precision (RSD < 9.21%). This work demonstrates an end-to-end portable procedure for nitrite detection and its potential as a preliminary screening device in clinical applications.