Pseudo-Crown ether II: Intracellular and solution-, SiNPs based test-kits for ppm level detection of H2S gas

Abstract

Perylene diimide based pseudo-Crown ether derivatives have been synthesized and characterized and their photophysical properties towards Fe3+ and H2S in 50% HEPES buffer–CH3CN and CH3CN solutions have been studied. PDI 1 showed formation of supramolecular aggregates with nanorods (dimer) morphology. Upon addition of Fe3+ ions, nanorods of PDI 1 transformed to spheres and PDI 1/2 showed a decrease in absorbance at (542 nm) and emission (578 nm) intensities supported by Job's plot, DLS, CV, WXRD and NMR techniques. The detection limits for Fe3+ are as low as 0.6 μM. We utilized PDI 1+Fe3+ complex as an ensemble for detection and discrimination of bio thiol derivatives. Upon addition of H2S (7.5 μM) and Cys (19 μM), the ensemble showed an increase at 542/578 nm (‘OFF-ON’) and further addition of H2S/Cys caused a decrease at same wavelength (‘ON-OFF’) with formation of new absorbance band at 630 nm (‘OFF-ON’). The mechanism of interaction of H2S involves reduction of Fe3+ to Fe2+ ions, followed by binding of HS− to form (PDI 1+Fe2++HS) complex. PDI 1 and PDI 1+Fe3+ complex has been successfully utilized for bioimaging of Fe3+ ions and H2S, respectively in live MG-63 cells. The solution and silica NPs based colorimetric test-kits were fabricated and detection of 30–60 ppm H2S gas has been achieved. These ‘OFF-ON-OFF’ and ‘ON-OFF-ON’ molecular switches mimic functioning of IMPLICATION, AND logic gates.