Colorimetric detection of water content in organic solvents: Via a smartphone with fluorescent Ag nanoclusters

We detected the water content in ethanol and dimethyl sulfoxide (DMSO) solvents via a smartphone with the help of fluorescent Ag nanoclusters (Ag NCs). The Ag NCs intrinsically have two emission peaks, among which the long-wavelength emission intensified with decreasing water content due to the aggregation induced emission enhancement (AIEE) effect, but in contrast the short-wavelength emission was relatively insensitive to water content. This fact makes the Ag NCs an ideal colorimetric indicator of water content in organic solvents. A smartphone was applied to take pictures of Ag NC samples and read the R, G, and B values from the images. When the water content increased from 20% to 55% in ethanol, the G/B values displayed a good linear relationship with the water content, and a limit of detection (LOD) of 4.48% was achieved. Moreover, good consistency was observed when the colorimetric fluorescent Ag NCs were applied to detect water content in real samples such as white wine and medical alcohol. These studies demonstrated a convenient and practical method for the detection of water content via a smartphone.