Rhodamine hydrazone derivatives as Hg²⁺ selective fluorescent and colorimetric chemosensors and their applications to bioimaging and microfluidic system

In this paper, we report new rhodamine hydrazone derivatives bearing thiol and carboxylic acid groups as selective fluorescent and colorimetric chemosensors for Hg²⁺. The ring-opening process of spirolactam enables the large fluorescent enhancement and colorimetric change upon the addition of Hg²⁺. The sample containing Hg²⁺ was mixed with one of the chemosensors in a microchannel where the sensor was examined using confocal laser scanning microscopy. A plot of the fluorescent intensities of both chemosensors versus the log concentration of Hg²⁺ exhibited a linear response (r² = 0.95) in the range of 1 nM-1 μM, and the detection limits were 1 nM and 4.2 nM, respectively. Both chemosensors also enable the visualization of Hg²⁺ accumulated in the nematode Caenorhabditis elegans previously exposed to nanomolar concentrations of Hg ²⁺.