Colorimetric and fluorimetric detection of Hg2 + and Cr3 + by boronic acid conjugated rhodamine derivatives: Mechanistic aspects and their bio-imaging application in bacterial cells

Abstract

Colorimetric and fluorimetric detection of toxic metal ions such as Hg2+ and Cr3+ has gained tremendous popularity over the conventional methods due to their operational simplicity, high selectivity, and speediness. Although numerous colorimetric and fluorescent receptors for Hg2+ or Cr3+ were reported in the literature, boronic acid-based receptors for these metal ions are rather scarce in the literature. Hence, in the present study dual function boronic acid conjugated rhodamine derivatives were developed, and their toxic metal ion detection abilities were studied by absorption, emission and visual detection methods. Absorption and emission spectral studies revealed that these derivatives displayed selectivity towards Hg2+, Cr3+ and Fe3+ among the other metal ions studied by forming new absorption band. Both the derivatives exhibited colorimetric response towards Hg2+ and Cr3+ by the change in color of the solution to pink and reddish pink with Fe3+. The detailed mechanism involved in the detection of Hg2+ was deduced by 1H NMR and ESI-MS studies. Further, these derivatives were used for fluorescence imaging of Hg2+ and Cr3+ in S. aureus bacterial cells. Thus the present manuscript demonstrated the use of boronic acid conjugated rhodamine derivatives as a dual function (colorimetric and fluorescent) probes and as imaging agents for Hg2+ and Cr3+, which are known for their toxic influence on bacterial cells.