Sensitive, convenient and rapid detection devices for toxic Cr(VI) suitable for filed use are required. Smartphone can be used as the detector, but the quality of images taken with a smartphone may depend on the ambient light and the operator. In this work, two types of low-cost and portable smartphone-based devices used for fluorescence spots brightness and size dual-mode detection of Cr(VI) were constructed with the aid of the 3D printing, which avoids the effect of ambient light and maintains a fixed position of the phone camera relative to the samples. Based on the brightness reflected by the blue channel of RGB values of the images of carbon nanodots, a linear relationship between quenching efficiency and concentration of Cr(VI) in a range of 0.2-150 μM with a limit of detection of 0.058 μM was attained, which is comparable to or better than that from fluorescence spectrometers. With the size variation of fluorescence spots, a linear range of 10-350 μM was acquired and it is more intuitive for direct naked-eye estimation of the concentration of Cr(VI). The applicability of the proposed devices for the detection of Cr(VI) was verified with water and soil samples with recoveries ranging in 95.0-108.2%.
Keywords: Carbon nanodots; Cr(VI) sensing; Dual-mode sensing; Smartphone-based devices; Visualization.
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