Detection of Hg²⁺ with NBD-based colorimetric chemosensor: Practical application to water samples and test strips

A new nitrobenzoxadiazole (NBD)-based chemosensor N′-(7-nitrobenzo[c][1,2,5]oxadiazol-4-yl)thiophene-2-carbohydrazide (NTCH) was synthesized for detecting Hg²⁺. NTCH could sense Hg²⁺ through a color change method from pale yellow to pink. Binding ratio of NTCH and Hg²⁺ was determined to be 1:1 with the analysis of electrospray ionization mass spectrometry and Job plot. Detection limit turned out to be 0.69 μM. In addition, NTCH could be successfully utilized for detecting Hg²⁺ in real water samples and visible color test strips. The probing mechanism of NTCH to Hg²⁺ was explained with ¹H nuclear magnetic resonance (NMR) titration, Job plot, electrospray ionization mass spectrometry (ESI-MS), and theoretical calculations.