Bipattaran Paramanik

Detection of Hg2+ and F- ions by using fluorescence switching of quantum dots in an Au-cluster-CdTe QD nanocomposite.

A single probe of an Au nanocluster-CdTe quantum dots nanocomposite has been developed by using tripeptide-capped CdTe quantum dots (QD) and bovine serum albumin (BSA) protein-conjugated Au25 nanocluster (NC) for detection of both Hg(2+) ion and F(-) ion. The formation of Au-NC-CdTe QD nanocomposite has been confirmed by TEM, steady state and time resolved spectroscopy, CD and FTIR studies. A significant signal off (74 % PL quenching at 553 nm) phenomenon of this nanocomposite is observed in presence of 6.56×10(-7)  M Hg(2+) ion, due to salt-induced aggregation. However, a dramatic PL enhancement (128 %) of the Au-NC-CdTe QD nanocomposite is observed in presence of 8.47×10(-7)  M F(-) anion. The calculated limit of detections (LOD) of Hg(2+) ion concentration and F(-) ion concentration are found to be 9 and 117 nM, respectively, which are within the safety range set by the United States Environment Protection Agency. Thus, the simple Au-NC-CdTe QD optical-based sensor is very useful to detect both toxic cations and anions.

Fluorescent AuAg alloy clusters: synthesis and SERS applications

Fluorescent metal nanoclusters have recently emerged as a new class of functional materials because of their potential in photocatalysis, water splitting, light harvesting and other applications. Herein, we demonstrate the synthesis of highly blue luminescent AuAg bimetallic alloy clusters using a simple one pot bottom up method. Transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and photoluminescence (PL) have been used to characterize the alloy clusters. A dramatic blue shift of the PL peak (from 608 nm to 444 nm) reveals a drastic change in the electronic transitions in the presence of Ag+, due to the formation of a new cluster. We have given emphasis to the influence of the capping ligand, pH and metal ions on the formation of the clusters and their stability. Based on controlled experiments and galvanic theory, an anti-galvanic reaction mechanism has been proposed for the formation of the bimetallic AuAg alloy clusters. The Surface Enhanced Raman Scattering (SERS) intensity is found to be increased in the presence of the AuAg alloy clusters and the enhancement factor (EF) is found to be 1.44 × 106 for the AuAg alloy nanocluster.

Energy/Hole Transfer Phenomena in Hybrid α-Sexithiophene (α-STH) Nanoparticle–CdTe Quantum-Dot Nanocomposites

Considerable attention has been paid to hybrid organic-inorganic nanocomposites for designing new optical materials. Herein, we demonstrate the energy and hole transfer of hybrid hole-transporting α-sexithiophene (α-STH) nanoparticle-CdTe quantum dot (QD) nanocomposites using steady-state and time-resolved spectroscopy. Absorption and photoluminescence studies confirm the loss of planarity of the α-sexithiophene molecule due to the formation of polymer nanoparticles. Upon photoexcitation at 370 nm, a nonradiative energy transfer (73 %) occurs from the hole-transporting α-STH nanoparticles to the CdTe nanoparticles with a rate of energy transfer of 6.13×10(9) s(-1). However, photoluminescence quenching of the CdTe QDs in the presence of the hole-transporting α-STH nanoparticles is observed at 490 nm excitation, which is due to both static-quenching and hole-transfer-based dynamic-quenching phenomena. The calculated hole-transporting rate is 7.13×10(7) s(-1) in the presence of 42×10(-8)  M α-STH nanoparticles. Our findings suggest that the interest in α-sexithiophene (α-STH) nanoparticle-CdTe QD hybrid nanocomposites might grow in the coming years because of various potential applications, such as solar cells, optoelectronic devices, and so on.

Structural evolution, photoinduced energy transfer in Au nanocluster–CdTe QD nanocomposites and amino acid sensing

Metal–semiconductor heterostructures/composites are found to be a new class of functional materials because of their unprecedented properties and potential applications. Various strategies have been adopted to design such materials with unique properties. Here, we have synthesized Au–CdTe nanocomposites using Au nanoclusters, and the growth rate is controlled by changing the Au : Cd ratio. The structural characterization of Au–CdTe nanocomposites is done by SAXS (small angle X-ray scattering), TEM (transmission electron microscopy), X-ray photoelectron spectroscopy (XPS), FTIR (Fourier transformed infrared), and steady state and time resolved spectroscopy. The blue shifting of the absorption band of CdTe QDs and strong photoluminescence quenching in the presence of Au suggest the metal cluster–semiconductor composite formation. A time resolved spectroscopy study confirms the Forster resonance energy transfer from QDs to proximal Au nanoclusters by changing the non-radiative decay rate. Interestingly, turn on of the signal i.e. the enhancement of photoluminescence (PL) intensity of the nanocomposite is observed in the presence of amino acid and the limit of detection (LOD) for L-cystein amino acid is found to be 192 nM. These nanocomposites open up new platforms to design optical based probes for selective sensing of amino acids.

Light Harvesting and White‐Light Generation in a Composite of Carbon Dots and Dye‐Encapsulated BSA‐Protein‐Capped Gold Nanoclusters

Several strategies have been adopted to design an artificial light-harvesting system in which light energy is captured by peripheral chromophores and it is subsequently transferred to the core via energy transfer. A composite of carbon dots and dye-encapsulated BSA-protein-capped gold nanoclusters (AuNCs) has been developed for efficient light harvesting and white light generation. Carbon dots (C-dots) act as donor and AuNCs capped with BSA protein act as acceptor. Analysis reveals that energy transfer increases from 63 % to 83 % in presence of coumarin dye (C153), which enhances the cascade energy transfer from carbon dots to AuNCs. Bright white light emission with a quantum yield of 19 % under the 375 nm excitation wavelength is achieved by changing the ratio of components. Interesting findings reveal that the efficient energy transfer in carbon-dot-metal-cluster nanocomposites may open up new possibilities in designing artificial light harvesting systems for future applications.

Study of binding interactions between MPT63 protein and Au nanocluster

The use of protein–nanocluster conjugates in the field of bio-nanotechnology provides exciting opportunities in live cell imaging, drug delivery and detecting pathogens. Here, we have demonstrated the interactions between Mycobacterium tuberculosis derived protein MPT63 and gold nanoclusters (Au NCs). Two single cysteine mutants of MPT63, namely G20C and G75C have been used to study the position dependence of cysteine residues on nanocluster–protein interactions. In the presence of MPT63, the enhancement of fluorescence intensity and the decay time of the Au nanocluster confirm the binding of MPT63 to Au NC. The decrease in non-radiative relaxation of Au NC by solvent molecules inside the protein environment might be responsible for the increase in fluorescence intensity and decay time of Au NC. The determination of the binding constant for protein–Au NC complex reveals the difference in binding ability of wild type MPT63 and its two cysteine mutants. We have also studied the effects of pH and salt on protein–Au NC interactions. Based on these results, it is suggested that both electrostatics and other factors play crucial roles to define the complexity of protein–Au NC interactions.