Colorimetric sensors based on Sudan-III (1) and Alizarin red S (2) have been developed for the detection of a trace amount of water in organic solvents such as THF, acetone, acetonitrile, and DMSO. The deprotonated (anionic) forms of 1 and 2 namely 1.F and 2.F are reprotonated by using a trace amount of water. Deprotonation of 1 and 2 was obtained by using fluoride anion. Test papers of 1.F and 2.F in organic solvents with and without moisture showed dramatic changes in color. Receptor 1.F exhibits high sensitivity for water in acetone and THF with the detection limit as low as 0.0042 and 0.0058 wt %. Remarkably, probes 1.F and 2.F are reversible in nature both in solution and in test strips. 1.F and 2.F are reversible and reusable for sensing moisture in the organic solvents with high selectivity, high sensitivity, and fast response. The reversible moisture sensor 1.F has also been used for application in inkless writing.

Copper complex based on a new class of fluorescence OFF-ON sensor 1.Cu has been reported for the detection of trace amounts of water in various organic solvents such as CHOH, THF, CHCN, and acetone by means of fluorescence emission intensity. The probe is highly responsive to water in THF (DL = 0.003 wt %). The dissociation of copper from probe 1.Cu in the presence of water is responsible for the fluorescence change and it was confirmed by electrospray ionization-mass spectrometry (ESI-MS), proton nuclear magnetic resonance (H-NMR), and fluorescence lifetime studies. Real application of the probe was successfully applied for the detection of moisture content in commercial products such as salt, sugar, wheat, and washing powder.

A new Alizarin Red S based fluorescent ensemble ARS–Zn(ii) for the selective detection of H2S is reported. It exhibited H2S selectivity and also detected H2S in serum under physiological conditions. The calculated detection limit of H2S was 92 nM.

A simple off-the-shelf dye molecule quinizarin (1), has been investigated for the effective detection of moisture in organic solvents and building materials. Anion-induced deprotonation followed by re-protonation with moisture is the working principle of the sensor system.

Moisture or trace water detection at a very low level in organic solvents and other chemical reagents has great significance in the chemical and industrial process. At present, reports on chemical sensors for moisture are still in the early development phase and need continuous improvements. Recently, several approaches have been proposed for the easier detection of water content in the organic solvents. In this review article, we have summarized recent reports on chemical sensors used to detect water in organic solvents. The discussion is focused on optical methods, including fluorescent and colorimetric probes exploring solvatochromism, displacement of ligand or metal and water-induced protonation. Besides, water detection in organic solvents by NMR spectroscopy is also discussed. Probe structure, sensitivity with organic solvents, spectroscopy detection limits, and possible application in various other research areas, including ink-less writing, sweat pore mapping, food products and engineering materials are described in detail.