Department of Chemistry
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Item Electrostatically driven multielectron transfer for the photocatalytic regeneration of nicotinamide cofactor(ACS, 2020) Rao, AnishDeveloping generic strategies that are capable of driving multielectron processes are essential to realize important photocatalytic conversions. Here, we present the idea of introducing favorable catalyst–reactant interaction in achieving efficient photocatalytic regeneration of nicotinamide (NADH) cofactor by gold nanoparticles (AuNPs). The electrostatic attraction emanating from the ligands on the surface of NP increases the channeling and local concentration of NAD+ reactants around AuNP photocatalysts, thereby enhancing the probability of the electron transfer process. Detailed kinetics- and intensity-dependent studies confirm the involvement of multiple electron transfer from the AuNP photocatalyst to the NAD+ reactant. The photocatalytic performances of AuNPs presented here are comparable to or greater than most of the catalytic systems reported based on plasmonic NP, with the added advantage of being structurally less complex. The use of electrostatics mimics the underlying force involved in various enzyme catalysis, which can serve as a generic approach for other important artificial multielectron photocatalytic reactions as well.Item Temporal fluctuations in interparticle interactions drive the formation of transiently stable nanoparticle precipitates(2020-04) Rao, AnishThe pH and ionic strength dependence of electrostatic interactions was explored to introduce temporal fluctuations in the strengths of interparticle interactions and choreograph a transient self-assembly response in plasmonic nanoparticles. The assembly process was triggered by the electrostatic attraction between positively-charged gold nanoparticles (AuNPs) and an aggregating agent, ethylenediaminetetraacetic acid (EDTA). The autonomous changes in the pH and ionic strength of the solution, under the influence of atmospheric CO2, weaken the aggregating ability of EDTA and initiate the complete disassembly of [+] AuNP - EDTA precipitates. The non-destructive way of disassembly minimizes the generation of waste, which helped in achieving some of the desirable feats in the area of dynamic self-assembly like easy removal of waste, transiently stable precipitates and negligible dampness. The chemical strategy adopted in the present work, to introduce transientness, can act as a generic tool in creating the next generation of complex matter.Item Electrostatically directed long-range self-assembly of nucleotides with cationic nanoparticles to form multifunctional bioplasmonic networks(Wiley, 2022-05) Rao, AnishPrecise control over interparticle interactions is essential to retain the functions of individual components in a self-assembled superstructure. Here, we report the design of a multifunctional bioplasmonic network via an electrostatically directed self-assembly process involving adenosine 5′-triphosphate (ATP). The present study unveils the ability of ATP to undergo a long-range self-assembly in the presence of cations and gold nanoparticles (AuNP). Modelling and NMR studies gave a qualitative insight into the major interactions driving the bioplasmonic network formation. ATP-Ca2+ coordination helps in regulating the electrostatic interaction, which is crucial in transforming an uncontrolled precipitation into a kinetically controlled aggregation process. Remarkably, ATP and AuNP retained their inherent properties in the multifunctional bioplasmonic network. The generality of electrostatically directed self-assembly process was extended to different nucleotide–nanoparticle systems.Item Self-assembled colloidal gold nanoparticles as substrates for plasmon enhanced fluorescence(Taylor & Francis, 2023) Rao, AnishDecades of intense research in the field of nanoscience have led to the ability to produce nanoparticles (NPs) with controlled composition, shape, and size. One of the next key challenges is the self-assembly of appropriate NP building blocks into larger systems to obtain micro- or macroscale materials. To achieve this, self-assembly protocols must not only produce high-quality structures, but also deliver the assemblies of interest to desired locations on a substrate. In this review, we discuss different self-assembly strategies, focusing on colloidal gold NPs and applications as plasmon-enhanced fluorescence (PEF) platforms. These plasmonic substrates have been used for biosensing and cell imaging, based on the enhancement of fluorescent emitters, and applied to improve the emission efficiency of luminescent NPs. It is important to note that higher fluorescence enhancement relies on precise control of the location of gold NPs and fluorescent emitters on the plasmonic substrate. Despite the diversity of available self-assembly strategies, many of them provide similar levels of structural control over the placement of gold NPs on the substrate. To highlight this, we have organized the discussion according to strategies that result in similar degrees of structural control over the placement of gold NPs and its associated PEF effect.Item Choreographing oscillatory hydrodynamics with DNA-coated gold nanoparticles(ACS, 2024-06) Rao, AnishPeriodic responses to nonperiodic energy inputs, such as oscillations, are hallmarks of living systems. Nanoparticle-based systems have largely remained unexplored in the generation of oscillatory features. Here, we demonstrate a nanosystem featuring hierarchical response to light, where thermoplasmonic effects and reversible DNA-hybridization generate thermal convective forces and ultimately, oscillatory hydrodynamic flows. The slow aggregation of gold nanoparticles (AuNPs) serves as a positive feedback, while fast photothermal disassembly acts as negative feedback. These asymmetric feedback loops, combined with thermal hysteresis for time-delay, are essential ingredients for orchestrating an oscillating response.