Small-Molecule Probe for Sensing Serum Albumin with Consequential Self-Assembly as a Fluorescent Organic Nanoparticle for Bioimaging and Drug-Delivery Applications.

The recognition of a specific protein in blood serum amidst similar proteins is a challenging and vital endeavor in clinical diagnostics. Herein, we have described a small-molecule probe (DFPAC-OH) that can induce self-assembly of human serum albumin (HSA) and bovine serum albumin (BSA) to generate a highly sustainable fluorescent organic nanoparticle (NP), useful for imaging and in vitro drug-delivery applications. In the midst of similar proteins, DFPAC-OH selectively binds in a noncovalent manner to serum albumin. The specific binding tailors the fluorescence properties of DFPAC-OH. The lowest detection limit for BSA is 47 nM with a binding constant of 1.03 × 10 5 M -1 . The probe can efficiently detect HSA in an artificial urine sample. Furthermore, the subsequent bovine albumin self-assembled nanoparticle (DFPAC-OH@BSA-NPs) displays a strong emission at 580 nm both in solution and in solid state. The nanoparticle is highly stable over a long pH range, covering the physiologic pH, and shows an excellent bioavailability to be used for sustainable cell imaging and drug-delivery applications. In addition, the cellular internalization and the pH-responsive drug-release behavior of a hydrophobic drug thymoquinone (TQ) encapsulated in DFPAC-OH@BSA-NPs (TQ-DFPAC-OH@BSA-NPs) have also been evaluated in A549 cell lines. The cytotoxic effect and quantification of intracellular reactive oxygen species (ROS) generation were further examined carefully to observe the anticancer property of TQ-DFPAC-OH@BSA-NPs. Therefore, the present system can simultaneously deliver drug molecules and image the event of delivery. The entire nanoparticles are characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), dynamic light scattering (DLS), and infrared (IR) spectroscopy. The specific binding of DFPAC-OH is well supported by the molecular docking study, fluorescence lifetime measurement, and circular dichroism analysis.