Sai Sathish Ramamurthy

Synthesis and characterization of gold graphene composite with dyes as model substrates for decolorization: a surfactant free laser ablation approach.

A facile surfactant free laser ablation mediated synthesis (LAMS) of gold-graphene composite is reported here. The material was characterized using transmission electron microscopy, field emission scanning electron microscopy, energy dispersive X-ray spectroscopy, powdered X-ray diffraction, Raman spectroscopy, Zeta potential measurements and UV-Visible spectroscopic techniques. The as-synthesized gold-graphene composite was effectively utilized as catalyst for decolorization of 4 important textile and laser dyes. The integration of gold nanoparticles (AuNPs) with high surface area graphene has enhanced the catalytic activity of AuNPs. This enhanced activity is attributed to the synergistic interplay of pristine golds electronic relay and π-π stacking of graphene with the dyes. This is evident when the Rhodamine B (RB) reduction rate of the composite is nearly twice faster than that of commercial citrate capped AuNPs of similar size. In case of Methylene blue (MB) the rate of reduction is 17,000 times faster than uncatalyzed reaction. This synthetic method opens door to laser ablation based fabrication of metal catalysts on graphene for improved performance without the aid of linkers and surfactants.

1-Minute Spacer Layer Engineering for Tunable Enhancements in Surface Plasmon-Coupled Emission

In this work, we report green advancements in surface plasmon-coupled emission (SPCE) spacer layer engineering with the shortest preparation time to realize ≥35-fold enhancements in the fluorescence emission intensity. A simple linker free spin coat of polyvinyl alcohol (PVA) dispersed nanoparticles on a SPCE substrate was employed as a spacer layer to achieve tunable enhancements in plasmon-coupled fluorescence emission intensities. Based on the current findings, the enhancements achieved in the SPCE can be tuned simply by varying the nanomaterial and its size. In the technique developed by us, nanomaterials having any capping agent, shape, and origin can be used as a spacer material as the nanomaterials are coated on the silver thin film in the form of a PVA-embedded hybrid spacer without the use of any linker or bond forming chemicals. We also demonstrate the use of biogenic nanoparticles as SPCE spacer layers for enabling tuning of SPCE enhancements.

Earth Abundant Iron-Rich N-Doped Graphene Based Spacer and Cavity Materials for Surface Plasmon-Coupled Emission Enhancements

We demonstrate for the first time the use of Fe-based nanoparticles on N-doped graphene as spacer and cavity materials and study their plasmonic effect on the spontaneous emission of a radiating dipole. Fe-C-MF was produced by pyrolizing FeOOH and melamine formaldehyde precursor on graphene, while Fe-C-PH was produced by pyrolizing the Fe-phenanthroline complex on graphene. The use of the Fe-C-MF composite consisting of Fe-rich crystalline phases supported on N-doped graphene presented a spacer material with 116-fold fluorescence enhancements. On the other hand, the Fe-C-PH/Ag based cavity resulted in an 82-fold enhancement in Surface Plasmon-Coupled Emission (SPCE), with high directionality and polarization of Rhodamine 6G (Rh6G) emission owing to Casimir and Purcell effects. The use of a mobile phone as a cost-effective fluorescence detection device in the present work opens up a flexible perspective for the study of different nanomaterials as tunable substrates in cavity mode and spacer applications.

Ag-CNT Architectures for Attomolar Dopamine Detection and 100-Fold Fluorescence Enhancements with Cellphone-based Surface Plasmon-Coupled Emission Platform

We report cellphone-based detection of dopamine with attomolar sensitivity in clinical samples with the use of a surface plasmon-coupled emission (SPCE) platform. To this end, silver-coated carbon nanotubes were used as spacer and cavity materials on SPCE substrates to obtain up to 100-fold fluorescence enhancements. The presence of silver on the carbon nanotubes helped to overcome fluorescence quenching arising due to π-π interactions between the carbon nanotube and rhodamine 6G. The competing adsorption of dopamine versus rhodamine 6G on graphene oxide was utilized to develop this sensing platform.

Cellphone Monitoring of Multi-Qubit Emission Enhancements from Pd-Carbon Plasmonic Nanocavities in Tunable Coupling Regimes with Attomolar Sensitivity

We demonstrate for the first time the tuning of qubit emission based on cavity engineering on plasmonic silver thin films. This tunable transition from weak to strong coupling regime in plasmon-coupled fluorescence platform was achieved with the use of palladium nanocomposites. In addition to our recently established correlation between Purcell factor and surface plasmon-coupled emission enhancements, we now show that the qubit-cavity environment experiences the Purcell effect, Casimir force, internal fano resonance, and Rabi splitting. Finite-difference time-domain simulations and time correlated single photon counting studies helped probe the molecular structure of the radiating dipole, rhodamine-6G, in palladium-based nanocavities. The sensitivity of the qubit-cavity mode helped attain a DNA detection limit of 1 aM (attomolar) and multianalyte sensing at picomolar concentration with the use of a smartphone camera and CIE color space. We believe that this low-cost technology will lay the groundwork for mobile phone-based next-gen plasmonic sensing devices.

Elecrochemical Determination of Ethanol by a Palladium Modified Graphene Nanocomposite Glassy Carbon Electrode

ABSTRACT Pristine palladium nanoparticles were decorated on graphene nanosheets for the development of a low-cost, nonenzymatic ethanol sensor. The nanocomposite was characterized by ultraviolet–visible absorbance spectroscopy, infrared spectroscopy, and field emission scanning electron microscopy equipped with energy dispersive X-ray spectroscopy. Cyclic voltammetry and chronoamperometry were used to quantify ethanol in alkaline media. A graphene palladium nanocomposite-modified glassy carbon electrode provided a detection limit of 2 mM with a linear dynamic range of 2–210 mM for ethanol determination. The nanocomposite exhibited excellent stability for 100 cyclic voltammetry scans. Ethanol oxidation was performed across a range of temperatures, unlike enzymatic based sensors. Moreover, the catalytic material showed a low activation energy and low onset potentials for the oxidation of ethanol. Interference studies with congeners of ethanol in fermentation chambers showed good selectivity for the analyte. The enhanced catalytic activity for ethanol detection involves the combination of pristine palladium nanoparticles with the enhanced conductivity of graphene.

Low-Cost Plasmonic Carbon Spacer for Surface Plasmon-Coupled Emission Enhancements and Ethanol Detection: a Smartphone Approach

Surface plasmon-coupled emission (SPCE) has led to significant advancements in analytical techniques on account of its unique characteristics that include highly polarized photon-sorting ability. In this study, we report the use of a low-cost activated carbon as a plasmonic spacer in the SPCE substrate for achieving 30-fold enhancement in fluorescence emission. We extend the use of this spacer in the presence of Rhodamine B Base, a lactone dye as the sensing material for smartphone-based ethanol detection on the SPCE platform. Ethanol detection from 1 to 6% concentration highlights the potential use of this technique in monitoring fermentation processes.

Novel Synthesis of Nanoparticles for Enhancements in Surface Plasmon Coupled Emission

We report a novel synthesis route for nanomaterials namely SnSe and SnTe and their application as a simple thin film spacers for achieving 30–45 fold fluorescence enhancements using Surface Plasmon Coupled Emission platform.

Smartphone Plasmonics for Doxycycline Detection with Silver-Lignin Bio-spacer at Attomolar Sensitivity

We demonstrate the achievement of 100-fold fluorescence enhancement and attomolar doxycycline (DC) detection with the use of Ag-lignin nanocomposite in spacer architecture in surface plasmon-coupled emission (SPCE) platform. Fluorescence quenching on π-π stacking of Rhodamine 6G (Rh6G) on lignin has been overcome due to the presence of silver nanoparticles (AgNPs) on the lignin surface. The use of cellphone camera as the detector opens the door to next-gen plasmonics based portable diagnostic devices.

Endophytic Fungi from Aegle marmelos Plant: A Potent and Innovative Platform for Enhanced Cellulolytic Enzyme Production

Fungi have a prominent status in fermentation for the production of different bio-products. Endophytic fungi isolated from medicinal plants are particularly formidable in their adaptability to solid state fermentation as an extension of its natural habitat and are also a potent source of broad-spectrum cellulolytic enzymes. We report for the first time the use of endophytic fungus isolated from Aegle marmelos for enhanced cellulolytic enzymes production from groundnut shell (GNS) as substrate. ImageJ software identified Trichoderma harzianum as an endophytic fungus having maximum radial growth rate. A systematic comparison of the endophytic fungus with Aspergillus oryzae , under solid state fermentation (SSF) and submerged fermentation (SmF) conditions was performed and enhanced cellulase production was observed by the endophytic fungus (4.27 FPU/ml) under SSF environment compared to SmF (2.35 FPU/ml). A comprehensive understanding of the systemic breakdown in the structural integrity of the biomass has been achieved using a synergy of enzyme assay protocols, spectral and thermal based techniques. The use of endophytic fungi in SSF systems in our study lays the basis for the production of other industrially important enzymes. The present study opens the door for the synergistic use of endophytic and epiphytic fungi for the production of cellulolytic enzyme.