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We demonstrate that the polarity influence on the pyrene fluorescence band ratios (I3/I1) termed as the Ham effect can be effectively utilized to study the electrostatic interaction of CdTe nanoparticles (ζ = −46 mV) with the oppositely charged organic molecule, pyrenemethylamine hydrochloride (PMAH). As compared to water, the less polar nature of the QD's surface resulted in an increase in I3/I1 peak ratio of PMAH (from 0.34 to 0.54) when brought into close proximity. The lowering of the asymmetric stretching frequency of the carboxylate group of thioglycolic acid (1570 cm−1 to ∼1550 cm−1) and the drop in zeta potential of the nanoparticle from −46 mV to −8 mV indicate the interaction of PMAH with the nanoparticles. Control experiments with capping ligands, QDs with different surface charges (−46, −39, −35, −31, −20 and +21 mV) and negatively charged pyrene molecules invariably support the role of nanoparticles and their surface charge. The combined effects of charge neutralization and hydrophobicity increase lead to the organization of QDs into 2D sheet like superstructures, preserving their initial individuality.

Anisotropic nanocrystals of gold and silver are promising candidates for sensing and therapeutic applications because of their high extinction coefficient, increased NIR response and localization of hot spots at their tips. Herein, we report a viable room temperature synthetic strategy to prepare multi-branched gold nanocrystals of varying morphologies without the aid of additional nanoseeds or shape directing agents. By systematically modulating the bifunctional ligand to the Au3+ ion molar ratio ([L-DOPA]/[HAuCl4] = 0.15–1), the plasmon absorption was tuned from visible (530 nm) to NIR (930 nm). The corresponding microscopic studies showed a gradual transformation of the nanomaterial's morphology from multiply twinned spheres to branched stars and flowers. The detailed spectroscopic and microscopic studies have revealed that evolution of these branched nanocrystals proceeds through aggregation and subsequent overgrowth of initially produced spherical particles.