title: Smartphone-based simultaneous pH and nitrite colorimetric determination for paper microfluidic devices.
abstract: In this work, an Android application for measurement of nitrite concentration and pH determination in combination with a low-cost paper-based microfluidic device is presented. The application uses seven sensing areas, containing the corresponding immobilized reagents, to produce selective color changes when a sample solution is placed in the sampling area. Under controlled conditions of light, using the flash of the smartphone as a light source, the image captured with the built-in camera is processed using a customized algorithm for multidetection of the colored sensing areas. The developed image-processing allows reducing the influence of the light source and the positioning of the microfluidic device in the picture. Then, the H (hue) and S (saturation) coordinates of the HSV color space are extracted and related to pH and nitrite concentration, respectively. A complete characterization of the sensing elements has been carried out as well as a full description of the image analysis for detection. The results show good use of a mobile phone as an analytical instrument. For the pH, the resolution obtained is 0.04 units of pH, 0.09 of accuracy, and a mean squared error of 0.167. With regard to nitrite, 0.51% at 4.0 mg L(-1) of resolution and 0.52 mg L(-1) as the limit of detection was achieved.
authors.affiliation: ECsens-CITIC, Department of Electronics and Computer Technology, ETSIIT, University of Granada , 18071, Granada, Spain.
authors.forename: Nuria
authors.initials: N
authors.lastname: Lopez-Ruiz
authors.forename: Vincenzo F
authors.initials: VF
authors.lastname: Curto
authors.forename: Miguel M
authors.initials: MM
authors.lastname: Erenas
authors.forename: Fernando
authors.initials: F
authors.lastname: Benito-Lopez
authors.forename: Dermot
authors.initials: D
authors.lastname: Diamond
authors.forename: Alberto J
authors.initials: AJ
authors.lastname: Palma
authors.forename: Luis F
authors.initials: LF
authors.lastname: Capitan-Vallvey
mesh_terms: D040421:Cell Phone; D003124:Colorimetry / Q000379:methods*; D006863:Hydrogen-Ion Concentration; D044085:Microfluidics / Q000295:instrumentation*; D009573:Nitrites / Q000032:analysis*; D010209:Paper
chemical_list: D009573:Nitrites