A novel fluorescent receptor L was synthesized by Schiff base condensation of 1-pyrenemethylamine with the vitamin B₆ cofactor pyridoxal. The receptor L is highly selective and sensitive towards Zn²⁺ ions among other tested metal ions. Upon interaction with Zn²⁺, the receptor L showed a distinct fluorescence enhancement at 485 nm due to the excimer formation leading to the fluorescent colour change from blue to bluish-green. Subsequently, when the in situ generated ZnL₂ complex interacted with various anions and amino acids, the addition of H₂PO₄ ⁻ and cysteine reinstated the fluorescence of the receptor L due to the demetalation of Zn²⁺ from the ZnL₂ complex. Accordingly, the receptor L was developed for the highly selective, specific and sensitive detection of three important bioactive analytes, i.e., Zn²⁺, H₂PO₄ ⁻ and cysteine with a detection limit down to 2.3 × 10⁻⁶ M, 2.18 × 10⁻⁷ M and 1.59 × 10⁻⁷ M, respectively. Additionally, the receptor L was applied to the detection of intracellular Zn²⁺ ions in live HeLa cells.

The morphology and physicochemical properties of polydopamine are not totally inherent and undergo changes with differing reaction conditions like the choice of solvent used for polymerization. The polymerisation of dopamine to polydopamine carried out in different solvents like sodium hydroxide, sodium bicarbonate, PBS and Tris leads to polydopamine with exceptionally different morphological and physicochemical features with each solvent. Additionally, the different physicochemical characteristics and morphologies bestow the polymer films with different extents of antimicrobial activity. Moreover, the findings supported by chemical evidence from X-ray photoelectron spectroscopy reveal that higher antibacterial activities were obtained against E. coli and S. aureus with polydopamine films prepared by Tris and NaOH solvent induced polymerization. The antibacterial activity observed in saline was found to be higher than that in PBS medium for both E. coli and S. aureus. The higher antibacterial activity of polydopamine films prepared in Tris and NaOH solvents was attributed to the covalent incorporation of –OH groups on the surface provided by nucleophilic Tris and NaOH solvents during the polymerisation process. The distinct physicochemical and morphological changes were supported by the results from contact angle measurements, FE-SEM, EDAX, AFM, and XPS analysis. The present finding provides insight into the different chemistry, morphologies and properties of the designed polydopamine films with controlled antibacterial/antifouling properties. Additionally, new insights into the mechanism of formation, physicochemical changes in morphology and properties of polydopamine coatings were revealed.

Polydopamine (pDA)-modified iron oxide core-shell nanoparticles (IONPs) are developed and designed as nanovectors of drugs. Reactive quinone of pDA enhances the binding efficiency of various biomolecules for targeted delivery. Glutathione disulfide (GSSG), an abundant thiol species in the cytoplasm, was immobilized on the pDA-IONP surface. It serves as a cellular trigger to release the drug from the nanoparticles providing an efficient platform for the drug delivery system. Additionally, GSSG on the surface was further modified to form S-nitrosoglutathione that can act as nitric oxide (NO) donors. These NPs were fully characterized using a transmission electronic microscopy (TEM), thermogravimetric analysis (TGA), dynamic light scattering (DLS), zeta potential, X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) and UV-vis spectroscopies. Doxorubicin (DOX) and docetaxel (DTX) are two anticancer drugs, which were loaded onto nanoparticles with respective loading efficiencies of 243 and 223 µmol/g of IONPs, calculated using TGA measurements. DOX release study, using UV-vis spectroscopy, showed a pH responsive behavior, making the elaborated nanocarrier a potential drug delivery system. (3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl) -2H-tetrazolium (MTS) and apoptosis assays were performed on PC3 cell lines to evaluate the efficiency of the developed nanocarriers. These nanoparticles thus can prove their worth in cancer treatment on account of their easy access to the site and release of drug in response to changes to internal parameters such as pH, chemicals, etc.

We developed pyridoxal conjugated gold nanoparticles (CAPy-AuNPs) for the selective colorimetric detection of Cr³⁺ and iodide ions in an aqueous medium.