Figure 1
(a) Multi-target water quality analysis through paper-based smartphone detection. (b) Hydrophilic channels are patterned in cellulose filter paper using SU-8 (negative) photoresist. After fabrication, channels are pre-loaded with target-sensitive reagents, providing a reference reflected intensity for the paper-surface background (Ib). (c) After a water sample is loaded, it flows along the length of the channel. If the water sample contains the reagent-specific target, an optically-detectable change in the channel’s reflected intensity is produced (Is). Two additional reference intensity values are also available: the peak reflected intensity (Ip), or “pure white” reference, indicating the maximum incident light available to the paper strip; and the wetted paper reflected intensity (Iw), indicating the change in reflected intensity that is attributable to only the saturation level of the cellulose channel. (d,e) Targets are identified and quantified optically through smartphone image analysis of each channel at empirically determined detection angles (90° for absorbance and fluorescence detection, and 65° for Mie scattering detection).
