Analysing the interlinkage between diarrhoea and drinking water faecal contamination in India.

Diarrhoea is one of the major waterborne diseases spread through the faecal-oral route causing over 10 million cases and over 1,000 deaths per year in India. This study critically evaluates the interlinkage between bacteriological water quality, i.e. faecal coliforms and diarrhoea cases for the three pre-pandemic years 2017, 2018 and 2019 based on multiple sources. With around 17% of households tap water connectivity as of August 2019, the majority of the Indian population depends on raw groundwater (GW) and surface water sources. For this, faecal coliform (FC) levels in surface and GW have been mapped at district levels using data from India's National Water Quality Monitoring Programme. Health Management Information System's data on diarrhoea have been used to understand the monthly and district-wise variation of diarrhoea. The trends of FC, diarrhoea inpatient cases, and diarrhoea inpatient rates have been discussed. The analysis showed issues associated with the reliability and usefulness of these datasets with 43% of total India districts with no reported FC values for the study period. This study reveals a clear gap in the interlinkage between diarrhoea and bacteriological water quality with the unavailability of granular water quality data as a major challenge.

Photoinduced Stitching of Self-Assembled Triangular Silver Nanoprisms at the Air-Water Interface.

This study investigates the influence of optical excitation on the self-assembly of triangular nanoprisms of silver into a continuous monolayer at the air-water interface. Langmuir monolayers of octadecylamine (ODA) have been used to electrostatically assemble citrate-capped silver triangular nanoprisms (AgTNPs) in the presence and absence of light. Under optical excitation, the nanoprisms were observed to assemble into a well-ordered monolayer through plasmon-mediated stitching, whereas the particles were merely in close contact during assembly in the dark. These findings suggest new avenues for tailoring particle properties through light-mediated assembly in two dimensions.

Ultra-low level optical detection of mercuric ions using biogenic gold nanotriangles.

Mercury is a serious environmental pollutant known to have detrimental health effects in all life forms. Here, we report the use of biologically synthesized aqueous gold nanotriangles for sensitive and selective optical detection of femto-molar levels of mercury ions by exploiting the high amalgamation tendency of mercury metal towards gold. Aqueous chloroaurate ions were reduced using lemongrass (Cymbopogon flexuosus) leaf extract at room temperature to form gold nanotriangles. Mercuric (Hg(2+)) ions were reduced in the presence of these triangles to facilitate amalgamation and the optical properties were monitored. We observe a significant change in the longitudinal plasmon absorption band of the nanotriangles even at femto-molar concentrations of mercuric ions. High-resolution transmission electron microscopy confirms changes in particle morphology at such low concentrations. This protocol shows no sensitivity to other environmentally relevant metal ions, including Pb(2+), Zn(2+), Cd(2+), Fe(2+), Ni(2+), Sr(2+), Ca(2+), Mn(2+), and Cu(2+), confirming further that change in the optical properties of gold nanotriangles in the presence of reduced mercuric ions is solely due to the strong amalgamation tendency of mercury metal.

Size and Shape Directed Novel Green Synthesis of Plasmonic Nanoparticles Using Bacterial Metabolites and Their Anticancer Effects.

The growing need for developing new synthesis methods of plasmonic nanoparticles (PNPs) stems from their various applications in nanotechnology. As a result, a variety of protocols have been developed for the synthesis of PNPs of different shapes, sizes, and compositions. Though widely practiced, the chemical synthesis of PNPs demands stringent control over the experimental conditions, often employs environmentally hazardous chemicals for surface stabilization, and is frequently energy-intensive. Additionally, chemically obtained PNPs require subsequent surface engineering steps for various optoelectronic and biomedicine applications to minimize the toxic effects and render them useful for targeted drug delivery, sensing, and imaging. Considering the pressing need to develop environmentally-friendly technology solutions, "greener" methods of nanoparticle synthesis are gaining importance. Here, we report on the biological synthesis of plasmonic nanoparticles using bacterial metabolites. A peptide-based siderophore pyoverdine and a blue-green pigment pyocyanin obtained from a marine strain of Pseudomonas aeruginosa rapidly produced plasmonic nanoparticles of gold and silver in an aqueous environment. The morphology of plasmonic nanoparticles could be modulated by tuning the concentration of these metabolites and the reaction time. The exposure of pyoverdine to chloroauric acid resulted in anisotropic gold nanoparticles. On the other hand, pyocyanin produced a highly monodispersed population of gold nanoparticles and anisotropic silver nanoparticles. Biologically obtained gold and silver nanoparticles retained pyoverdine and pyocyanin on the nanoparticle surface and were stable for an extended period of time. The biologically obtained gold and silver plasmonic nanoparticles displayed potent anticancer activities against metastatic lung cancer cells. Biogenic nanoparticles were rapidly internalized by cancer cells in high quantity to affect the cellular organization, and karyoplasmic ratio, indicating the potential of these nanoparticles for cancer nanomedicine.

Charge and hydrophobicity of amyloidogenic protein/peptide templates regulate the growth and morphology of gold nanoparticles.

Biomolecules are known to interact with metals and produce nanostructured hybrid materials with diverse morphologies and functions. In spite of the great advancement in the principles of biomimetics for designing complex nano-bio structures, the interplay between the physical properties of biomolecules such as sequence, charge, and hydrophobicity with predictable morphology of the resulting nanomaterials is largely unknown. Here, using various amyloidogenic proteins/peptides and their corresponding fibrils in combination with different pH, we show defined principle for gold nanocrystal growth into triangular and supra-spheres with high prediction. Using a combination of different biophysical and structural techniques, we establish the mechanism of nucleation and crystal growth of gold nanostructures and show the effective isolation of intact nanostructures from amyloid templates using protein digestion. This study will significantly advance our design principle for bioinspired materials for specific functions with great predictability.

Graphene and Graphene Oxide as a Support for Biomolecules in the Development of Biosensors.

Graphene and graphene oxide have become the base of many advanced biosensors due to their exceptional characteristics. However, lack of some properties, such as inertness of graphene in organic solutions and non-electrical conductivity of graphene oxide, are their drawbacks in sensing applications. To compensate for these shortcomings, various methods of modifications have been developed to provide the appropriate properties required for biosensing. Efficient modification of graphene and graphene oxide facilitates the interaction of biomolecules with their surface, and the ultimate bioconjugate can be employed as the main sensing part of the biosensors. Graphene nanomaterials as transducers increase the signal response in various sensing applications. Their large surface area and perfect biocompatibility with lots of biomolecules provide the prerequisite of a stable biosensor, which is the immobilization of bioreceptor on transducer. Biosensor development has paramount importance in the field of environmental monitoring, security, defense, food safety standards, clinical sector, marine sector, biomedicine, and drug discovery. Biosensor applications are also prevalent in the plant biology sector to find the missing links required in the metabolic process. In this review, the importance of oxygen functional groups in functionalizing the graphene and graphene oxide and different types of functionalization will be explained. Moreover, immobilization of biomolecules (such as protein, peptide, DNA, aptamer) on graphene and graphene oxide and at the end, the application of these biomaterials in biosensors with different transducing mechanisms will be discussed.

Machine-Free Polymerase Chain Reaction with Triangular Gold and Silver Nanoparticles.

Photothermal effects of metal nanoparticles (NPs) are used for various biotechnological applications. Although NPs have been used in a polymerase chain reaction (PCR), the effects of shape on the photothermal properties and its efficiency on PCR are less explored. The present study reports the synthesis of triangular gold and silver NPs, which can attain temperatures up to ∼90 °C upon irradiation with 808 nm laser. This photothermal property of synthesized nanoparticles was evaluated using various concentrations, irradiation time, and power to create a temperature profile required for variable-temperature PCR. This study reports a cost-effective, machine-free PCR using both gold and silver triangular NPs, with efficiency similar to that of a commercial PCR machine. Interestingly, addition of triangular NPs increases PCR efficiency in commercial PCR reactions. The higher PCR efficiencies are due to the direct binding and unfolding of double-stranded DNA as suggested by circular dichroism and UV spectroscopy. These findings suggest that triangular NPs can be used to develop cost-effective, robust machine-free PCR modules and can be used in various other photothermal applications.

Photomodulated Spatially Confined Chemical Reactivity in a Single Silver Nanoprism.

Single-atom and single-particle catalysis is an area of considerable topical interest due to their potential in explaining important fundamental processes and applications across several areas. An interesting avenue in single-particle catalysis is spatial control of chemical reactivity within the particle by employing light as an external stimulus. To demonstrate this concept, we report galvanic replacement reactions (GRRs) as a spatial marker of subparticle chemical reactivity of a silver nanoprism with AuCl4- ions under optical excitation. The location of a GRR within a single Ag nanoprism can be spatially controlled depending on the plasmon mode excited. This leads to chemomorphological transformation of Ag nanoprisms into interesting Ag-Au structures. This spatial biasing effect is attributed to localized hot electron injection from the tips and edges of the silver nanoprisms to the adjacent reactants that correlate with excitation of different surface plasmon modes. The study also employs low-energy-loss EELS mapping to additionally probe the spatially confined redox reaction within a silver nanoprism. The findings presented here allow the visualization of a plasmon-driven subparticle chemical transformation with high resolution. The selective optical excitation of surface plasmon eigenmodes of anisotropic nanoparticles offers opportunities to spatially modulate chemical transformations mediated by hot electron transfer.

Synthesis of catalytically active porous platinum nanoparticles by transmetallation reaction and proposition of the mechanism.

A facile method for the synthesis of porous platinum nanoparticles by transmetallation reactions between sacrificial nickel nanoparticles and chloroplatinic acid (H(2)PtCl(6)) in solution, as well as at the constrained environment of the air-water interface, using a Langmuir-Blodgett instrumental setup is presented. To carry out the transmetallation at the air-water interface hydrophobized nickel nanoparticles are assembled as a monolayer on the sub phase containing platinum ions. The porous Pt nanoparticles obtained as a result of the reaction are found to act as extremely good catalysts for hydrogenation reaction. The products are well characterized by TEM, HRTEM, EDAX, and STEM. Attempts are made to postulate the plausible mechanism of this reaction to generate this kind of nanoparticle with controllable geometric shape and structure. This simple strategy has the potential to synthesize other nanomaterials of interest too.

Porous anisotropic metal nanostructures through controlled transmetallation across a dialysis membrane.

Nanostructured metals with hollow interiors are of technological importance due to their unique optoelectronic properties and enhanced surface area. We describe herein, a novel method for the synthesis of anisotropic gold and palladium nanoparticles through a simple galvanic replacement reaction across a semi-permeable dialysis membrane. The control over the reaction kinetics achieved by the presence of membrane enables one to tune the bimetal composition, particle porosity and morphology. Rapid outward diffusion of silver ions generated from the sacrificial silver nanoparticles even at room temperatures prevents the precipitation of high quantities of silver chloride, thereby circumventing the need for product purification. The porous anisotropic nanostructures have potential applications in catalysis, cell imaging and therapeutics.

Extracellular synthesis of crystalline silver nanoparticles and molecular evidence of silver resistance from Morganella sp.: towards understanding biochemical synthesis mechanism.

There has been significant progress in the biological synthesis of nanomaterials. However, the molecular mechanism of synthesis of such bio-nanomaterials remains largely unknown. Here, we report the extracellular synthesis of crystalline silver nanoparticles (AgNPs) by using Morganella sp., and show molecular evidence of silver resistance by elucidating the synthesis mechanism. The AgNPs were 20+/-5 nm in diameter and were highly stable at room temperature. The kinetics of AgNPs formation was investigated. Detectable particles were formed after an hour of reaction, and their production remained exponential up to 18 h, and saturated at 24 h. Morganella sp. was found to be highly resistant to silver cations and was able to grow in the presence of more than 0.5 mM AgNO(3). Three gene homologues viz. silE, silP and silS were identified in silver-resistant Morganella sp. The homologue of silE from Morganella sp. showed 99 % nucleotide sequence similarity with the previously reported gene, silE, which encodes a periplasmic silver-binding protein. The homologues of silP and silS were also highly similar to previously reported sequences. Similar activity was totally absent in closely related Escherichia coli; this suggests that a unique mechanism of extracellular AgNPs synthesis is associated with silver-resistant Morganella sp. The molecular mechanism of silver resistance and its gene products might have a key role to play in the overall synthesis process of AgNPs by Morganella sp. An understanding of such biochemical mechanisms at the molecular level might help in developing an ecologically friendly and cost-effective protocol for microbial AgNPs synthesis.

Spider silk as an active scaffold in the assembly of gold nanoparticles and application of the gold-silk bioconjugate in vapor sensing.

Spider silk is being viewed with interest by materials scientists due to its excellent resilience and mechanical properties. In this paper we show that spider silk is an excellent scaffold for the one-step synthesis and assembly of gold nanoparticles. Formation of a gold nanoparticle-spider-silk bioconjugate material is accomplished by simple reaction of the fibers with aqueous chloroauric acid. The gold nanoparticles thus formed are strongly bound to the spider-silk fiber surface enabling study of the electrical properties of the nanobioconjugate. Using the well-known contraction/expansion behavior of the fibers in solvents of varying polarity, we show that exposure of the gold nanoparticle-spider silk bioconjugate to vapors of methanol and chloroform leads to changes in electrical transport through the nanoparticles and thus, the possibility of developing a vapor sensor. The bioconjugate shows excellent response time and cycling efficiency to methanol vapors. The activation energy of electron transport from one gold nanoparticle to another in the nanobiocojugate was determined from temperature-dependent electron-transport measurements to be approximately 1.7 eV.

Bacterial enzyme mediated biosynthesis of gold nanoparticles.

Development of synthesis methods for anisotropic metal nanoparticles is of considerable interest due to their remarkable optoelectronic properties. Various shapes ranging from rods to cubes to tetrapods and prisms may be obtained by chemical methods. Here we show that anisotropic gold nanoparticles can be synthesized biologically by the bacterium Actinobacter spp. when challenged with gold chloride in the presence of Bovine serum albumin (BSA). We also observed that synthesis of gold nanoparticles occur with simultaneous induction of the protease enzyme secreted by the bacterium in the presence of BSA. The presence of BSA helps to enhance the rate of gold nanoparticles biosynthesis and may also impart some shape control. Controlling simple experimental conditions like incubation temperature and presence or absence of oxygen have drastic effect on the reaction rate and the morphology of the particles. Various assay experiments show that the presence of enzyme protease can act as a reducing as well as shape directing agent.

Fabrication, characterization, and enzymatic activity of fungal protease--nanogold membrane bioconjugate.

This study describes the synthesis of a free-standing nanogold membrane by the spontaneous reduction of aqueous chloroaurate ions by the diamine molecule DAEE at a liquid-liquid interface. The free standing nanogold membrane, provides a biocompatible surface for the immobilization of proteins. F-Protease (F-Prot) was then bound to the nanogold membrane via interaction with the gold nanoparticles leading to a new class of biocatalyst. A highlight of the new biocatalyst wherein the enzyme is bound to the nanogold membrane is the ease with which separation from the reaction medium may be achieved by simple filtration. In relation to the free enzyme in solution, the F-Prot in the bioconjugate material exhibited a slightly higher biocatalytic activity and significantly enhanced pH and temperature stability. The F-Prot nanogold membrane bioconjugate material also exhibited excellent biocatalytic activity over ten successive reuse cycles.

Synthesis of gold nanorods in organic media.

A seed mediated approach for the synthesis of anisotropic rod shaped gold nanoparticles in organic media (toluene) is demonstrated. Pre-formed gold nanoparticles stabilized in toluene by 4-hexadecylaniline (HDA) are used as seeds. These when reacted with 1-octadecylamine (ODA) hydrophobised chloroaurate ions in toluene lead to the formation of gold nanorods. ODA or alkylamines of different chain lengths which are the chloroaurate ion phase transfer agent have been found to play a key role in the formation of the nanorods. The gold nanorods that have a five-fold symmetry evolve from multiply twinned particles and are bound at the tips by [1 11] faces and at the sides by [100] faces. The gold nanorods have been shown to grow under the shape directing effect of the alkylamines which stabilize the high energy [100] faces. The concentration of the alkylamines has been found to play a critical role in the formation of the gold nanorods. Higher concentrations of the alkylamines lead to formation of spherical particles, at times of narrow size distribution.

Interfacial deposition of Ag on Au seeds leading to AucoreAgshell in organic media.

A seed mediated procedure for the synthesis of hydrophobic Au(core)Ag(shell) nanoparticles in toluene is demonstrated. The reaction proceeds by way of the interfacial reduction of silver ions by 3-pentadecylphenol followed by their deposition on hydrophobized Au nanoparticles. Such a hitherto unreported interfacial seeded growth reaction leads to the formation of phase pure Au(core)Ag(shell) nanoparticles that retain the hydrophobicity of the seed particles and remain stable in toluene. Such core-shell structures are however not formed in the aqueous phase. The core-shell architecture was verified using TEM analysis and the formation process was studied by recording the UV-vis spectra of the organic phase nanoparticles as a function of time. TEM kinetics also showed gradual increase in the silver layer thickness. Conclusive evidence was however obtained on examination of the HRTEM images of the products formed. Elemental analysis using X-ray photoelectron spectroscopy of the Au(core)Ag(shell) nanostructure revealed the presence of metallic silver. Moreover changing the surface capping of the Au seed does not affect the formation of the Au(core)Ag(shell) nanostructure.

Extracellular biosynthesis of magnetite using fungi.

The development of synthetic processes for oxide nanomaterials is an issue of considerable topical interest. While a number of chemical methods are available and are extensively used, the collaborations are often energy intensive and employ toxic chemicals. On the other hand, the synthesis of inorganic materials by biological systems is characterized by processes that occur at close to ambient temperatures and pressures, and at neutral pH (examples include magnetotactic bacteria, diatoms, and S-layer bacteria). Here we show that nanoparticulate magnetite may be produced at room temperature extracellularly by challenging the fungi, Fusarium oxysporum and Verticillium sp., with mixtures of ferric and ferrous salts. Extracellular hydrolysis of the anionic iron complexes by cationic proteins secreted by the fungi results in the room-temperature synthesis of crystalline magnetite particles that exhibit a signature of a ferrimagnetic transition with a negligible amount of spontaneous magnetization at low temperature.

Synthesis of gold nanotriangles and silver nanoparticles using Aloe vera plant extract.

Biogenic gold nanotriangles and spherical silver nanoparticles were synthesized by a simple procedure using Aloe vera leaf extract as the reducing agent. This procedure offers control over the size of the gold nanotriangle and thereby a handle to tune their optical properties, particularly the position of the longitudinal surface plasmon resonance. The kinetics of gold nanotriangle formation was followed by UV-vis-NIR absorption spectroscopy and transmission electron microscopy (TEM). The effect of reducing agent concentration in the reaction mixture on the yield and size of the gold nanotriangles was studied using transmission electron microscopy. Monitoring the formation of gold nanotriangles as a function of time using TEM reveals that multiply twinned particles (MTPs) play an important role in the formation of gold nanotriangles. It is observed that the slow rate of the reaction along with the shape directing effect of the constituents of the extract are responsible for the formation of single crystalline gold nanotriangles. Reduction of silver ions by Aloe vera extract however, led to the formation of spherical silver nanoparticles of 15.2 nm +/- 4.2 nm size.

Assembly of phase transferred nickel nanoparticles at air-water interface using Langmuir-Blodgett technique.

Development of simple and efficient protocol for the synthesis of Ni nanoparticles in aqueous media and their subsequent phase transfer to organic media is reported. The synthesis of nickel nanoparticles in aqueous medium is accomplished by reducing the nickel nitrate with sodium borohydride in presence of oleic acid. It results in the formation of nickel nanoparticles capped with oleic acid. The pristine oleic acid capped nickel nanoparticles were then phase transferred to nonpolar solvents such as toluene using stearic acid. The phase transfer was effective probably due to the space exchange between the oleic acid moiety and stearic acid molecules. The hydrophobized Ni thus obtained was organized at the air-water interface and it was observed that by controlling the pressure and concentration of hydrophobized Ni nanoparticles at air-water interface, linear ribbon like assemblies could be obtained. The organization process was followed by surface pressure-area isotherm measurement and Brewster Angle Microscopy.

Transmetalation reaction between hydrophobic silver nanoparticles and aqueous chloroaurate ions at the air-water interface.

The transmetalation reaction between a sacrificial nanoparticle and more noble metal ions in solution has emerged as a novel method for creating unique hollow and bimetallic nanostructures. In this report, we investigate the possibility of carrying out the transmetalation reaction between hydrophobic silver nanoparticles assembled and constrained at the air-water interface and subphase gold ions. We observe that facile reduction of the subphase gold ions by the sacrificial silver nanoparticles occurs resulting in the formation of elongated gold nanostructures that appear to cross-link the sacrificial silver particles. This transmetalation reaction may be modulated by the insertion of an electrostatic barrier in the form of an ionizable lipid monolayer between the silver nanoparticles and the aqueous gold ions that impacts the gold nanoparticle assembly. Transmetalation reactions between nanoparticles constrained into a close-packed structure and appropriate metal ions could lead to a new strategy for metallic cross-linking of nanoparticles and generation of coatings with promising optoelectonic behavior.