A self-assembled nanoprobe based on Schiff base for the rapid and selective detection of serum albumin with cell imaging applications

Here, we report the design and synthesis of a Schiff base probe, DBNHC ((E)-2-(2,4-dihydroxybenzylidene)-N-(naphthalen-1-yl)hydrazine-1-carbothioamide), and its interaction with bovine serum albumin (BSA). In similar to 100% PBS buffer, the probe DBNHC can self-assemble into nonfluorescent nanoaggregates due to the aggregation caused quenching (ACQ) effect. However, it becomes highly fluorescent (similar to 14 fold) in the presence of BSA which facilitates the disassembly of nanoaggregates into its monomer. The site-selective fluorescence displacement assay and molecular docking simulations reveal that mainly hydrogen bonding, pi MIDLINE HORIZONTAL ELLIPSISsulphur and pi MIDLINE HORIZONTAL ELLIPSISalkyl interactions are responsible for the disassembly of nanoaggregates leading to encapsulation of DBNHC monomer at site II in BSA, resulting in a cyan green emission. The detection limit determined by the 3 sigma/slope method was found to be 58 nM, and the lower dissociation constant [Kd = (1.506 +/- 0.196) mu M] value suggests strong binding between the probe and BSA. Further, DBNHC was used for cell incubation and in vitro fluorescence imaging of BSA. A Schiff base based probe, DBNHC was found to undergo self aggregation in PBS buffer resulting very weakly fluorescence, but in the presence of BSA it becomes highly fluorescent due to disassembly of nanoaggregates into monomer and trapping at site II in BSA.