Capillary Flow-Driven, Disposable Device for Dissolved Oxygen Sensing in Water Samples

A decline in dissolved oxygen (DO) levels in many waterbodies have been observed in the last few decades. While a well-established technology for DO monitoring exists, it is rather expensive and requires user training to use. Here, we propose a simple, user-friendly, and disposable capillary flow-driven microfluidic device for colorimetric DO determination. The device is constructed with a transparent PET film, double-sided adhesive, and glass microfiber with immobilized reagents in such a way that the sample is taken by dipping the device in the analyzed water to yield the results. Modified Winkler colorimetric assay has been employed to transform oxygen into colored species. The limit of detection of the developed device was 1.7 ppm. Field applicability assessment was performed to ensure that the devices are not susceptible to interference and that measurements can be performed in various environmental conditions by untrained users. The developed devices were validated with freshwater samples from various waterbodies as well as with aquarium water, demonstrating high accuracy. The findings presented here open possibilities to deploy these sensors for citizen-based water quality monitoring campaigns.