● A cellphone-based colorimetric multi-channel sensor for in-field detection.

The development of colorimetric analysis technologies for the commercial cellphone platform has attracted great attention in environmental monitoring due to the low cost, high versatility, easy miniaturization, and widespread ownership of cellphones. This work demonstrates a cellphone-based colorimetric multi-channel sensor for quantifying multiple environmental contaminants simultaneously with high sensitivity and stability. To improve the sensitivity of the sensor, a delicate optical path system was created by using a diffraction grating to split six white beams transmitting through the multiple colored samples, which allows the cellphone CMOS camera to capture the diffracted light for image analysis. The proposed sensor is a universal colorimetric detection platform for a variety of environmental contaminants with the colorimetry assay in the range of 400–700 nm. By introducing the diffraction grating for splitting light, the sensitivity was improved by over six folds compared with a system that directly photographed transmitted light. As a successful proof-of-concept, the sensor was used to detect turbidity, orthophosphate, ammonia nitrogen and three heavy metals simultaneously with high sensitivity (turbidity: detection limit of 1.3 NTU, linear range of 5–400 NTU; ammonia nitrogen: 0.014 mg/L, 0.05–5 mg/L; orthophosphate: 0.028 mg/L, 0.1–10 mg/L; Cr (VI): 0.0069 mg/L, 0.01–0.5 mg/L; Fe: 0.025 mg/L, 0.1–2 mg/L; Zn: 0.032 mg/L, 0.05–2 mg/L) and reliability (relative standard deviations of six parallel measurements of 0.37%–1.60% and recoveries of 95.5%–106.0% in surface water). The miniature sensor demonstrated in-field sensing ability in environmental monitoring, which can be extended to point-of-care diagnosis and food safety control.