A New Disposable Paper-Based Chemosensor for the Rapid and Direct Detection of Hexavalent Chromium in Aqueous Media

Abstract Hexavalent chromium (Cr 6+ ) poses significant risks to both individuals and the environment. However, direct detection of Cr 6+ in fully aqueous media with high sensitivity and selectivity is extremely challenging. Herein, an isoindigo-derived chemosensor (II-MT) is developed and utilized as a single use paper-based sensor. This sensor allows for quick and simple screening of Cr 6+ in water through a significant color change that is visible to the naked eyes. Moreover, via a simple UV detection method, the new sensor enables an accurate trace-level detection of Cr 6+ at concentration as low as 0.1 µM. This detection capability is one order of magnitude lower than the recommended limit for drinking water (0.960 µM) set by World Health Organization (WHO). More importantly, the sensor delivers an average recovery of 104.5% and 98.25% for the detection of tap water samples. This convenient, yet accurate, quantification method for Cr 6+ in spiked tap water was compared to the certified inductive coupled plasma (ICP) method. The agreement between the measurements obtained by our sensor and the ICP method was 93.57%. Mechanistic studies using Fourier Transform Infrared Spectroscopy (FT-IR) indicate a nucleophilic attack to the carbonyl group of II-MT by HCrO 4 − , resulting in the dye color changing from brown to colorless. Overall, this novel chemosensor has a high potential for application as a selective, sensitive, and disposable paper sensor for direct and rapid screening of Cr 6+ in real world environments.