A Rapid and Versatile Colorimetric Sensor for the Visual Detection of Zinc Ions in Urine and Drinking Water

The rapid detection of zinc in different aqueous matrices is very relevant. For example, a Zn²⁺ level above ca. 50 µM affects drinking water quality, while levels below ca. 25 µM in urine are related to higher probability of prostate cancer. Herein, a simple and rapid qualitative colorimetric sensor for the detection of zinc ions in aqueous samples is developed. The sensor exploits the reaction between 1,5-diphenylthiocarbazone and Zn²⁺ to form colored chelates whose color changes with increasing Zn²⁺ concentration. The chelating agent has been immobilized in a dried form on various cellulose- and synthetic-based materials to obtain a sensor that can be used for in situ analysis. The procedure to obtain the colorimetric device is easy and straightforward. Moreover, it requires neither specialized personnel to perform the analysis nor specialized personnel for the interpretation of the analytical results. The analysis requires only 20 µL of sample, and a reliable colorimetric output is obtained within 10 min and is stable up to 30 min. The sensor allows Zn²⁺ visual detection in drinking water and urine without any sample pre-treatment with excellent efficiency and repeatability. Considering the ability to distinguish between Zn²⁺ concentrations equal to 0.5 and 2× the cut-off level, the sensor showed sensitivity and specificity of 100% for fortified tap water analysis and 100% sensitivity and 88.9% specificity for urine samples. The almost-perfect concordance with the reference atomic absorption spectrometer and the 94.1% accuracy demonstrated the sensor's excellent potential to be applied for selective qualitative Zn²⁺ detection in real-life situations.