Smartphone-based Quantitative Colorimetric Detection Of Water Samples On Three Dimensional Microfluidic Devices

At present, rapid industrialization and increasing human activities are gradually introducing large amounts of pollutants into water environment, among these pollutants, heavy metals have persistence and severe toxicity whichis threatening the human life and health. The problems existing in the traditional water quality testing methodsincludes: the instruments used are large in size and expensive in price, requires professional operation, the popularity is not high and so on. Aiming at these problems, the development of fast, low-cost and portable biochemical detection technology has become one of the research focuses, recently.Microfluidic paper-based devices(μPAD) is not only small in reagent consumption, environmental protection, but also easy to operate, high-throughput in detection and high in detection efficiency. Therefore, it has a great application prospect in clinical diagnosis, food hygiene, environmental monitoring and biochemistry.Towards this end, we come up with a rapid quantitative detection method, with the help of 3D μPADs and a custom-designedsmartphone application(App). In this paper, hydrophobic filter paper was obtained by coupling structurally distinct organosilane precursors(e.g., octadecyltrichlorosilane and methyltrichlorosilane) to paper fibers under controlled reaction conditions to gain nanostructured morphology on it. Desirable superhydrophobic and superoleophilic surface was achieved by this method on conventional filter paper. On this basis, we fabricated three dimensional microfluidic paper-based analytical devices(3D μPADs), and finished the rapid quantitative detection of nitrite and Cr(VI) in actual water samples, combining with the custom-designed smartphone application “μPAD_DET”. Main research contents of this article are as follows:Hydrophobic filter paper was achieved by coupling the mixture of octadecyltrichlorosilane and methyltrichlorosilane to paper fibers. The modified filter paper is very stable in both aqueous solutions and organic solvents. Employing the lipophilic and hydrophobic feature of modified filter paper, we carried out oil/water separation experiment with it. And it was proved to be a promising candidate for future oil/water separation in industrial and environmental settings for its great separation efficiency and recyclability.On the basis of hydrophobic treatment of filter paper,a“cut and paste” method for the fabrication of 3D μPAD was introduced by stacking several layers of hydrophobic bases and hydrophilic channels together. The perfect capillary action of cellulose filter paper drove water samples flow along the hydrophilic channels, so there is no need for an external drive pump. The device is lightweight, low in reagent consumption, easy to store and transport and its preparation is quite simple and low in cost.The continuous improvement of smartphone and its application popularity are of great significance for mobile phone-based rapid detection. In this paper, a custom-designedsmartphone application(App) “μPAD_DET” was written based on colorimetric analysis to perform quantitative detection of nitrite and Cr(VI) in water samples with minimum sample volume added to the above 3D μPAD.Theperformance of this Appwas evaluated bycomparing itsdetection results of tapewater samples to that of a standardspectrophotometry method, from which we find the combination of 3D μPAD and μPAD_DET possesses an extensive application prospect in the preliminary screening of environmental monitoring, food hygiene, disease diagnosis and so on.