Portable smartphone-based colorimetric system for simultaneous on-site microfluidic paper-based determination and mapping of phosphate, nitrite and silicate in coastal waters

Early and on-site detection of environmental contaminations and physicochemical parameters of seawater is increasingly preferred to guarantee hazard minimization in many settings. In this paper, we describe a combination of microfluidic paper-based sensors (µPADs) and an Android-based smartphone application (App) for simultaneous on-site quantification of phosphate (PO 4 -P), silicate (SiO 3 -Si) and nitrite (NO 2 -N) in coastal seawater samples. The developed App can on-site capture, process, and quantify the µPAD colorimetric outputs. This App uses an image processing algorithm for quantifying color intensity and relating the RGB components to the analyte concentrations. The GPS-tagged data can be stored on the smartphone or sent via social networks. The significant factors affecting the detection of the analytes were optimized using Box–Behnken design. Under optimized parameters, the proposed method presented the linear ranges between 5 and 100 µg L −1 for phosphate (R 2 = 0.9909), 5 to 100 µg L −1 (R 2 = 0.9819) for nitrite and 10 to 600 µg L −1 (R 2 = 0.9933) for silicate. The LODs of the method for detection of phosphate, nitrite and silicate were 1.52 µg L −1 , 0.61 µg L −1 and 3.74 µg L −1 , respectively. The device was successfully used to simultaneous analyze and map the PO 4 -P, SiO 3 -Si and NO 2 -N of Bushehr coastal seawater samples (Iran). The results were confirmed by the lab-based conventional colorimetric methods using spectrophotometer.