Water soluble blue-emitting AuAg alloy nanoparticles and fluorescent solid platforms for removal of dyes from water

Chicken egg shell membrane, a naturally abundant protein membrane, was used to synthesize gold (Au), silver (Ag) and their bimetallic (AuAg) alloy nanoclusters at room temperature without the use of any reducing agent or catalyst. The as-formed gold and alloy clusters were highly fluorescent and exhibited intense blue emission around 435 +/- 5 and 440 +/- 5 nm, respectively. This is the first report confirming the formation of fluorescent alloy clusters exhibiting nanosecond lifetimes by a biomembrane-induced reduction process. We have also explored the capability of these metal cluster immobilized inexpensive ESMs in removing organic dyes from water. The results confirmed that it is the strong adsorption of the dye molecules in the presence of the metal particles that has helped to convert ESM into an effective platform for water purification. This process has the dual advantages of utilizing an inexpensive, abundant and eco-friendly food waste (egg shell membrane) for in situ reduction and formation of metal nanoparticles and the utilization of the same as an effective platform for the removal of anionic dyes from waste water. An Au-immobilized ESM showed a better efficiency in dye molecules removal than those of the Ag-ESM and AuAg-ESM membranes

Development of N and S heteroatom co-doped stable dual emitting carbon ink in aqueous media for sensing applications

In recent times great attention has been given to the synthesis of fluorescent carbon nanomaterials with high quantum yield and multicolor eye catching fluorescence emission for various applications. In this work, a facile hydrothermal method has been adapted for the synthesis of nitrogen and sulfur co-doped water soluble highly fluorescent carbon ink with a dual emission zone. Incorporation of heteroatoms induces different surface states leading to excellent tunable fluorescence properties. The synthesized carbon material exhibited a maximum quantum yield of 52% and 14% for blue emission at 440 nm and green emission at 510 nm, respectively. The observed fluorescence properties were sensitive towards toxic Hg2+ ions in water with a lower detection limit of 5 nM. The (N, S)-CNPs are able to detect Hg2+ at a much lower level compared to the maximum concentration allowed in normal drinking water, set by the Environmental Protection Agency (USA). In addition, the emission characteristics of the synthesized carbon are very sensitive to the pH of the medium as well

Current-Perpendicular-to-Plane Magnetoresistance in Chemical Vapor Deposition-Grown Multilayer Graphene

Current-perpendicular-to-plane (CPP) magnetoresistance (MR) effects are often exploited in various state-of-the-art magnetic field sensing and data storage technologies. Most of the CPP-MR devices are artificial layered structures of ferromagnets and non-magnets, and in these devices, MR manifests, due to spin-dependent carrier transmission through the constituent layers. In this work, we explore another class of artificial layered structure in which multilayer graphene (MLG) is grown on a metallic substrate by chemical vapor deposition (CVD). We show that depending on the nature of the graphene-metal interaction, these devices can also exhibit large CPP-MR. Magnetoresistance ratios (>100%) are at least two orders of magnitude higher than “transferred” graphene and graphitic samples reported in the literature, for a comparable temperature and magnetic field range. This effect is unrelated to spin injection and transport and is not adequately described by any of the MR mechanisms known to date. The simple fabrication process, large magnitude of the MR and its persistence at room temperature make this system an attractive candidate for magnetic field sensing and data storage applications and, also, underscore the need for further fundamental investigations on graphene-metal interactions

Current-Perpendicular-to-Plane Magnetoresistance in Chemical Vapor Deposition-Grown Multilayer Graphene

Current-perpendicular-to-plane (CPP) magnetoresistance (MR) effects are often exploited in various state-of-the-art magnetic field sensing and data storage technologies. Most of the CPP-MR devices are artificial layered structures of ferromagnets and non-magnets, and in these devices, MR manifests, due to spin-dependent carrier transmission through the constituent layers. In this work, we explore another class of artificial layered structure in which multilayer graphene (MLG) is grown on a metallic substrate by chemical vapor deposition (CVD). We show that depending on the nature of the graphene-metal interaction, these devices can also exhibit large CPP-MR. Magnetoresistance ratios (>100%) are at least two orders of magnitude higher than “transferred” graphene and graphitic samples reported in the literature, for a comparable temperature and magnetic field range. This effect is unrelated to spin injection and transport and is not adequately described by any of the MR mechanisms known to date. The simple fabrication process, large magnitude of the MR and its persistence at room temperature make this system an attractive candidate for magnetic field sensing and data storage applications and, also, underscore the need for further fundamental investigations on graphene-metal interactions

Egg-shell derived carbon dots for base pair selective DNA binding and recognition

The development of base pair selective fluorescent binding probes and their interaction mode with nucleic acids have created great interest for sensing and biomedical applications. Herein, we have used chicken egg shell membrane (ESM) as a cost effective easily available protein source for the synthesis of highly fluorescent carbon dots. The detailed characterizations have confirmed the in situ formation of heteroatom doped graphitic carbon nanodots (CDs) from ESM. The intrinsic fluorescence property of the material has been utilized for the label free binding of duplex deoxyribonucleic acid (DNA). The interaction of different natural and synthetic DNAs with carbon dots resulted in the enhancement of fluorescence characteristics of the latter. Analysis of the binding data obtained from steady state fluorescence studies revealed a selective and stronger affinity of CDs to the adenine-thymine (AT) base pair rich double stranded DNA (ds DNA) than that of the guanine-cytosine (GC) pair rich ds DNA. Base pair specific binding was further validated from isothermal titration calorimetry (ITC) and melting temperature data. The thermodynamic profile revealed endothermic binding that was driven by the hydrophobic interaction at the nano-bio interfaces. The results reveal the potential of carbon dots as a new and promising fluorescent probe for base pair selective and sequence specific DNA recognition

A new insight into the interaction of ZnO with calf thymus DNA through surface defects

Experimental evidences on the binding interaction of ZnO and Calf Thymus (CT) DNA using several biophysical techniques are the centre of interest of the present study. The interaction of ZnO with CT DNA has been investigated in detail by absorption spectral study, fluorescence titration, Raman analysis, zeta potential measurement, viscometric experiment along with thermal melting study and microscopic analysis. Steady-state fluorescence study revealed the quenching (48%) of the surface defect related peak intensity of ZnO on interaction with DNA. The optimized concentration of ZnO and DNA to obtain this level of quenching has been found to be 0.049 mM and 1.027 mu M, respectively. Additional fluorescence study with 8-hydroxy-5-quinoline (HQ) as a fluorescence probe for Zn2+ ruled out the dissolution effect of ZnO under the experimental conditions. DNA conjugation on the surface of ZnO was also supported by Raman study. The quantitative variation in conductivity as well as electrophoretic mobility indicated significant interaction of ZnO with the DNA molecule. Circular dichroism (CD) and viscometry titration provided clear evidence in support of the conformational retention of the DNA on interaction with ZnO. The binding interaction was found to be predominantly entropy driven in nature. The bio-physical studies presented in this paper exploring ZnO-CT DNA interaction could add a new horizon to understand the interaction between metal oxide and DNA

Selective detection of Escherichia coli DNA using fluorescent carbon spindles

We investigate the interaction of hydrophilic blue emitting carbon spindles with various deoxyribonucleic acids (DNA) having different base pair compositions, such as Herring testes (HT), calf thymus (CT),Escherichia coli (EC) and Micrococcus lysodeikticus (ML) DNA, to understand the mode of interaction. Interestingly, the fluorescent carbon spindles selectively interacted with E. coli DNA resulting in enhanced fluorescence of the former. Interaction of the same carbon with other DNAs exhibited insignificant changes in fluorescence. In addition, in the presence of EC DNA, the D band in the Raman spectrum attributed to the defect state completely disappeared, resulting in enhanced crystallinity. Microscopy images confirmed the wrapping of DNA on the carbon spindles leading to the assembly of spindles in the form of flowers. Dissociation of double-stranded DNA occurred upon interaction with carbon spindles, resulting in selective E. coli DNA interaction. The carbon spindles also exhibited a similar fluorescence enhancement upon treating with E. coli bacteria. These results confirm the possibility of E. coli detection in water and other liquid foods using such fluorescent carbo

Unraveling the Interaction of Silver Nanoparticles with Mammalian and Bacterial DNA

The focus of this study was to understand and unravel the interaction of silver nanoparticles (AgNPs) with different types of Deoxyribonucleic acid (DNA), mammalian and bacterial, having different base pair compositions. Binding of spherical silver nanoparticles (AgNPs) to Calf thymus (CT) DNA, Escherichia coli (EC) DNA and Micrococcus lysodeikticus (ML) DNA has been studied to gain insights into their mode of interaction and specificity. Interaction of AgNPs with synthetic DNA has also been carried out. On the basis of absorption, thermal melting, isothermal calorimetry and viscosity studies, we could establish the mode of binding and specificity of the synthesized silver nanoparticles with mammalian and bacterial DNA. Thermal melting (Tm) studies indicated a decrease in the Tm of all the DNAs, confirming the destabilization of DNA stacks on interaction with AgNPs. Comparative interaction studies with single stranded (ss) and double stranded (ds) DNAs further confirmed the specificity of the particles toward ds DNA. On the basis of the results we could confirm that the synthesized AgNPs could be used for selective detection of DNA through their DNA binding mechanism. In addition, the AgNPs−DNA complexes exhibited distinct differences in the SERS spectra making it an interesting SERS platform for identifying ds DNA. The optical and physical properties of AgNPs help in differentiating the DNAs of different base pair compositions through their binding affinity and specificit

Selective Binding of Genomic Escherichia coli DNA with ZnO Leads to White Light Emission: A New Aspect of Nano−Bio Interaction and Interface

Here, we report for the first time, a novel and intriguing application of deoxyribonucleic acid (DNA) in the area of optics by demonstrating white light emission by tuning the emission of a nanomaterial, ZnO rods, exhibiting surface defects, in the presence of genomic Escherichia coli DNA with a comparatively high quantum efficiency. In order to understand the DNA specificity, we have also studied the interaction of ZnO with CT, and ML DNA, ss EC DNA, synthetic polynucleotides and different mononucleosides and bases. Further, in order to understand the effect of particle shape and defects present in ZnO, we have also extended our study with ZnO rods prepared at higher temperature exhibiting red emission and ZnO particles exhibiting yellow emission. Interestingly, none of the above studies resulted in white light emission from ZnO−DNA complex. Our studies unequivocally confirmed that the concentration and the nature of DNA and ZnO together plays a crucial role in obtaining CIE coordinates (0.33, 0.33) close to white light. The much enhanced melting temperature (Tm) of EC DNA and the energetics factors confirm enhanced hydrogen bonding of ZnO with EC DNA leading to a new emission band. Our experimental observations not only confirm the selective binding of ZnO to EC DNA but also open a new perspective for developing energy saving light emitting materials through nano-bio interactions

Multiband Fluorescent Graphitic Carbon Nanoparticles from Queen of Oils

Here, we report a facile and rapid approach for the synthesis of multiband fluorescent graphitic carbon nanoparticles (CNPs) from queen of oils exhibiting multifarious applications. The as-prepared and calcined CNPs exhibited excitation dependent multiband emission that has been explored for detection of deoxyribonucleic acid (DNA) and removal of water pollutant cationic dye. We report here selective detection of Escherichia coli (E. coli-DNA) using fluorescent graphitic carbon nanoparticles through fluorescence enhancement of the nanoparticle. On the basis of thermal melting, CD and calorimetric studies, we could conclude that the interaction of CNPs are stronger with E. coli-DNA resulting in preferential selectivity for E. coli-DNA. The as-derived CNPs could be an emerging cost-effective material for the selective detection of E. coli-DNA and a sorbent for removal of basic pollutant dyes from water