A paper-based colorimetric assay with non-instrumental detection for determination of boron in water samples.

The present work reports on the combination of paper-based analytical devices (PADs) and information technology (IT) equipment for non-instrumental determination of boron. PADs prepared with curcumin as a receptor and ethanolic extracts of Curcuma longa L. powder were evaluated for sensing. The colorimetric assay is based on a two step-strategy involving initially the formation of rosocyanin in the PAD under acidic conditions, with subsequent color change (from red to blue-green) at alkaline pH. The color change produced in the PAD is then exploited for determination of boron by digitization and image processing with IT devices (scanner and tablet camera) and an image analysis program, respectively. Under optimal conditions, the proposed assay showed limits of detection in the range 0.2-0.8 mg/L depending on the PADs and IT devices used for colorimetric reaction and digitization, respectively. In addition, the repeatability, expressed as relative standard deviation, was found to be below 5% (5 mg/L, N = 10). PADs prepared with curcumin and ethanolic extracts of Curcuma longa L. powder showed excellent lifetime and successful applicability to the analysis of water samples of different complexity with recoveries in the range 93-105%.