A "turn-on" Michler's ketone-benzimidazole fluorescent probe for selective detection of serum albumins

Interaction of Michler's ketone-benzimidazole derivatives (MK-1 and MK-2) with serum albumin proteins was examined by absorption, steady-state, time-resolved fluorescence, molecular docking and circular dichroism methods. In the presence of albumins, a remarkable increase in fluorescence intensity and the quantum yield along with a dominant color response was observed for cationic derivative 1 while neutral derivative 2 showed a weaker effect. The studies reveal synergistic effects of electrostatic, hydrophobic and H-bonding interactions in protein binding with the fluorophores. Competitive binding studies reveal selective binding of the probe to the albumin proteins over other commonly occurring analytes in the serum matrix. Bioimaging studies in HeLa cells showed the cytoplasmic distribution of the fluorophore with an intense fluorescence signal. Serum depletion studies show a significant reduction in the fluorescence intensity that indicates binding affinity with albumins and their potential use for albumin detection.