Photocatalytic degradation of methyl blue dye with H2O2 sensing

A condensation polymer (urea-formaldehyde resin) passivated ZnO nanoparticles were used as an efficient photocatalyst for methyl blue degradation in the presence of H2O2 involving a Fenton-like reaction. The formation of OH˙ radicals were attributed to the pivotal factor for the degradation process. The method was easy and recyclable. The dose of photocatalyst, initial dye concentration, pH variation, variations of the composition of the photocatalyst, and the effect of scavengers were gauged. The degraded product was highly fluorescent and fluorometric detection of H2O2 was achieved along with a colorimetric recognition pathway. No other dye could be degraded under similar experimental conditions, implying the novel utility of methyl blue for environmental remediation.

Highly fluorescent quinone-capped silver hydrosol for environmental remediation and sensing applications

A metal-enhanced fluorescence was achieved from in situ-generated Ag0 nanoparticles in the proximity of 2-hydroxy benzaldehyde (2HB). Such nanoparticles eliminated methyl blue (MB) dye from water exclusively in the presence of Zn2+ and were proven to be an efficient adsorbent for environmental remediation (maximum uptake capacity 1065 mg·g-1). Ag was zero valent in the absorbent, while Zn2+ was in Zn(OH)2 form. Fe3+ brought back MB in the aqueous medium due to the strong interaction of MB with Fe3+ and the regeneration of blue color helped to design a selective and sensitive Fe3+ sensing platform colorimetrically (linear detection range 10-4-10-6 M; linear detection limit 10-6 M). The silver nanoparticle-induced metal-enhanced fluorescence was quenched efficiently with MB. Pb2+ restored the quenched fluorescence by removing MB from the proximity of the metalized surface of silver, and Pb2+ sensing was performed fluorometrically (linear detection range; 10-5-5 × 10-8 M limit of detection 5 × 10-8 M). Iron and lead were also estimated in a variety of natural water sources, including rainfall, drinking water from taps, and water from the Ganga River via spiking method.

Role of transition metals in coinage metal nanoclusters for the remediation of toxic dyes in aqueous systems

A difficult issue in chemistry and materials science is to create metal compounds with well-defined components. Metal nanoclusters, particularly those of coinage groups (Cu, Ag, and Au), have received considerable research interest in recent years owing to the availability of atomic-level precision via joint experimental and theoretical methods, thus revealing the mechanisms in diverse nano-catalysts and functional materials. The textile sector significantly contributes to wastewater containing pollutants such as dyes and chemical substances. Textile and fabric manufacturing account for about 7 × 105 tons of wastewater annually. Approximately one thousand tons of dyes used in textile processing and finishing has been recorded as being discharged into natural streams and water bodies. Owing to the widespread environmental concerns, research has been conducted to develop absorbents that are capable of removing contaminants and heavy metals from water bodies using low-cost technology. Considering this idea, we reviewed coinage metal nanoclusters for azo and cationic dye degradation. Fluorometric and colorimetric techniques are used for dye degradation using coinage metal nanoclusters. Few reports are available on dye degradation using silver nanoclusters; and some of them are discussed in detailed herein to demonstrate the synergistic effect of gold and silver in dye degradation. Mostly, the Rhodamine B dye is degraded using coinage metals. Silver nanoclusters take less time for degradation than gold and copper nanoclusters. Mostly, H2O2 is used for degradation in gold nanoclusters. Still, all coinage metal nanoclusters have been used for the degradation due to suitable HOMO-LUMO gap, and the adsorption of a dye onto the surface of the catalyst results in the exchange of electrons and holes, which leads to the oxidation and reduction of the adsorbed dye molecule. Compared to other coinage metal nanoclusters, Ag/g-C3N4 nanoclusters displayed an excellent degradation rate constant with the dye Rhodamine B (0.0332 min-1). The behavior of doping transition metals in coinage metal nanoclusters is also reviewed herein. In addition, we discuss the mechanistic grounds for degradation, the fate of metal nanoclusters, anti-bacterial activity of nanoclusters, toxicity of dyes, and sensing of dyes.

Copper enhanced fluorescence: A novel platform for sensing of hydrogen peroxide

A small molecule of salicylaldehyde was used to achieve copper enhanced fluorescence. The fluorescence was investigated at various physicochemical conditions. Such fluorescence was utilized to obtain a selective sensing platform...

Natural Kaolin: Sustainable Technology for the Instantaneous and Energy-Neutral Recycling of Anthropogenic Mercury Emissions

Kaolin, a natural and inexpensive clay mineral, is ubiquitous in soil, dirt, and airborne particles. Amongst four commonly available clay minerals, kaolin, as a result of its layered structure, is the most efficient natural gaseous Hg adsorbent to date (Langmuir maximum adsorption capacity Q_m =574.08 μg g^-1 and Freundlich Q_m =756.49 μg g^-1 ). The Hg uptake proceeds by homogeneous monolayer and heterogeneous processes. Hg physisorption on kaolin occurs in the dark, yet the adsorption rate is enhanced upon irradiation. The effects of several metal complexes, salts, halides and solvents on the Hg uptake were examined. The addition of CuCl₂ particles leads to a significant enhancement of the Hg uptake capacity (>30 times) within second timescales and without irradiation. The physisorption with kaolin is switched to chemisorption upon the addition of CuCl₂ to kaolin. This process is entirely reversible upon the addition of Zn/Sn granules at room temperature without any added energy. However, the investment of a small amount of renewable energy can speed up the process. This technology demonstrates the facile and efficient capture and recycling of elemental Hg⁰ from air. A wide range of metal particles and diverse physicochemical processes, which include the microphysics of nucleation, are herein examined to explore the potential reaction mechanism by using a suite of complementary analytical techniques. These new mechanistic insights open a new era of energy-neutral environmental remediation based on natural soil/airborne particles.

Novel Technology for the Removal of Brilliant Green from Water: Influence of Post-Oxidation, Environmental Conditions, and Capping

Chemical dyes are used in a wide range of anthropogenic activities and are generally not biodegradable. Hence, sustainable recycling processes are needed to avoid their accumulation in the environment. A one-step synthesis of Fe_core-maghemite_shell (Fe-MM) for facile, instantaneous, cost-effective, sustainable, and efficient removal of brilliant green (BG) dye from water has been reported here. The homogenous and monolayer type of adsorption is, to our knowledge, the most efficient, with a maximum uptake capacity of 1000 mg·g^-1, for BG on Fe-MM. This adsorbent was shown to be efficient in occurring in time-scales of seconds and to be readily recyclable (ca. 91%). As iron/iron oxide possesses magnetic behavior, a strong magnet could be used to separate Fe-MM coated with BG. Thus, the recycling process required a minimum amount of energy. Capping Fe-MM by hydrophilic clay minerals further enhanced the BG uptake capacity, by reducing unwanted aggregation. Interestingly, capping the adsorbent by hydrophobic plastic (low-density polyethylene) had a completely inverse effect on clay minerals. BG removal using this method is found to be quite selective among the five common industrial dyes tested in this study. To shed light on the life cycle analysis of the composite in the environment, the influence of selected physicochemical factors (T, pH, hν, O₃, and NO₂) was examined, along with four types of water samples (melted snow, rain, river, and tap water). To evaluate the potential limitations of this technique, because of likely competitive reactions with metal ion contaminants in aquatic systems, additional experiments with 13 metal ions were performed. To decipher the adsorption mechanism, we deployed four reducing agents (NaBH₄, hydrazine, LiAlH₄, and polyphenols in green tea) and NaBH₄, exclusively, favored the generation of an efficient adsorbent via aerial oxidation. The drift of electron density from electron-rich Fe_core to maghemite shells was attributed to be responsible for the electrostatic adsorption of N⁺ in BG toward Fe-MM. This technology is deemed to be environmentally sustainable in environmental remediation, namely, in waste management protocol.

Fast, Cost-effective and Energy Efficient Mercury Removal-Recycling Technology

We herein present a novel and sustainable technology for mercury recycling, with the maximum observed uptake capacity. Facile synthesis of the most efficient (~1.9 gg-1) nano-trap, made of montmorillonite-Fe-iron oxides, was performed to instantaneously remove mercury(II) ions from water. Elemental Hg was recovered from the adduct, by employing Fe granules, at ambient conditions. Varied pHs and elevated temperatures further enhanced this already highly efficient recycling process. The reduction of Hg(II) to Hg(I) by the nano trap and Hg(I) to Hg(0) by Fe granules are the main driving forces behind the recycling process. Facile sustainable recycling of the nano-trap and Fe granules require no additional energy. We have further developed a recyclable model for Hg nano-trap, which is inexpensive (<$5 CAD), and can remove mercury in a few seconds. This technology has multiple applications, including in the communities exposed to mercury contamination.

Purely Inorganic Highly Efficient Ice Nucleating Particle

To evaluate the role of atmospheric heterogeneous reactions on the ice nucleation ability of airborne dust particles, we investigated the systematic study of ice nucleation microphysics with a suite of atmospherically relevant metals (10), halides (4), and oxyhalides (2). Within a minute, a kaolin-iron oxide composite (KaFe) showed efficient reactions with aqueous mercury salts. Among the different mercury salts tested, only HgCl₂ reacting with KaFe generated HgKaFe, a highly efficient ice nucleating particle (HEIN). When added to water, HgKaFe caused water to freeze at much warmer temperatures, within a narrow range of -6.6 to -4.7 °C. Using a suite of optical spectroscopy, mass spectrometry, and microscopy techniques, we performed various experiments to decipher the physical and chemical properties of surface and bulk. KaFe was identified as a mixture of different iron oxides, namely, goethite, hematite, magnetite, and ε-Fe₂O₃, with kaolin. In HgKaFe, HgCl₂ was reduced to Hg₂Cl₂ and iron was predominantly in maghemite form. Reduction of Fe²⁺ by NaBH₄, followed by aerial oxidation, helped KaFe to be an exact precursor for the synthesis of HEIN HgKaFe. Kaolin served as a template for synthesizing iron oxide, opposing unwanted aggregation. No other metal or metal halide was found to have more efficient nucleating particles than HgCl₂ with KaFe composite. The chelation of Hg(II) hindered the formation of HEIN. This study is useful for investigating the role of morphology and how inorganic chemical reactions on the surface of dust change morphology and thus ice nucleation activity. The understanding of the fundamentals of what makes a particle to be a good ice nucleating particle is valuable to further understand and predict the amount and types of atmospheric ice nucleating particles.

Fluorescence enhancement via varied long-chain thiol stabilized gold nanoparticles: A study of far-field effect

Metal enhanced fluorescence of carbon dots has been reported in aqueous solution. Moderately fluorescing carbon dots (λ_ex=360nm and λ_em=440nm) of 6-8nm diameters (CDA) have been synthesized from freshly prepared aqueous ascorbic acid solution under modified hydrothermal treatment. The CDA fluorescence is quenched at the close proximity with gold nanoparticles (AuNPs). Here, a substrate specific near-field electric field distribution is pronounced. Anticipating distance dependent fluorescence enhancement phenomenon, long-chain aliphatic thiol capped AuNPs are introduced to improve fluorescence of moderately fluorescing CDAs. The long-chain aliphatic thiols act as spacers between CDA and AuNP. Interestingly, the fluorescence of CDA is observed to be enhanced successively as the chain lengths of aliphatic thiols are increased. Fluorescing CDA, upon excitation, transfers energy to the nearby AuNP and a plasmon is induced. This plasmon radiates in the far-field resulting in fluorescence enhancement of CDAs. Such an interesting enhancement in emission with metallic gold is termed as gold enhanced fluorescence. This far-field effect for fluorescence enhancement of CDA particles becomes a general consensus in solution with varied long-chain aliphatic amine ligand capped silver nanoparticles (AgNPs). Finally, consequence of far-field effect of fluorescence enhancement has been observed while derivatized AuNP and AgNP are introduced into the CDA solution simultaneously which is described as reinforced fluorescence enhancement due to coupled plasmonic radiation.

Boron Precursor-Dependent Evolution of Differently Emitting Carbon Dots

Attention has been directed toward electron-deficient boron doping in carbon dots (CDs) with the expectation of revealing new photophysical aspects in accordance with varying amounts of boron content. It has been emphatically shown that boron uptake in CDs varies with different boron precursors evolving altered emissive CDs. Boron doping in CDs causes definite surface defect due to the generation of electron-deficient states. Modified hydrothermal treatment of a mixture of ascorbic acid (AA) and different boron precursor compounds (borax/boric acid/sodium borate/sodium borohydride) produces different kinds of boron-doped CDs (BCDs). These BCDs (<6 nm) differ in size, emission maxima (∼15 nm), and fluorescence intensity but carry unchanged excitation maxima (365 nm). These differences are related to the nature of boron precursor compounds. The most fluorescing BCD (quantum yield ≈ 5%) is identified from the borax-mediated reaction and is used for the detection of Fe(III) on a nanomolar level in water via the fluorescence "Turn Off" phenomenon. Again, Fe(III)-infested CD solution regains its lost fluorescence, with AA paving the way for nanomolar level AA detection from the same pot. The proposed method has been tactfully made interference free for the quantitative measure of Fe(III) and AA in real samples. Furthermore, new photophysical properties of the CDs with variable boron contents supplement information that is hitherto unknown. Theoretical calculations also justify the observed optical behavior of the as-synthesized BCDs. The calculations describe the variable amount of boron doping-related huge charge polarization within the carbon surface, leading to the formation of surface defects. Thus, subsequent electronic transition-related red shift in the absorption spectrum authenticates experimental findings.

A Segregated, Partially Oxidized, and Compact Ag10 Cluster within an Encapsulating DNA Host

Silver clusters develop within DNA strands and become optical chromophores with diverse electronic spectra and wide-ranging emission intensities. These studies consider a specific cluster that absorbs at 400 nm, has low emission, and exclusively develops with single-stranded oligonucleotides. It is also a chameleon-like chromophore that can be transformed into different highly emissive fluorophores. We describe four characteristics of this species and conclude that it is highly oxidized yet also metallic. One, the cluster size was determined via electrospray ionization mass spectrometry. A common silver mass is measured with different oligonucleotides and thereby supports a Ag10 cluster. Two, the cluster charge was determined by mass spectrometry and Ag L3-edge X-ray absorption near-edge structure spectroscopy. Respectively, the conjugate mass and the integrated white-line intensity support a partially oxidized cluster with a +6 and +6.5 charge, respectively. Three, the cluster chirality was gauged by circular dichroism spectroscopy. This chirality changes with the length and sequence of its DNA hosts, and these studies identified a dispersed binding site with ∼20 nucleobases. Four, the structure of this complex was investigated via Ag K-edge extended X-ray absorption fine structure spectroscopy. A multishell fitting analysis identified three unique scattering environments with corresponding bond lengths, coordination numbers, and Debye-Waller factors for each. Collectively, these findings support the following conclusion: a Ag10(+6) cluster develops within a 20-nucleobase DNA binding site, and this complex segregates into a compact, metal-like silver core that weakly links to an encapsulating silver-DNA shell. We consider different models that account for silver-silver coordination within the core.

Synergism of gold and silver invites enhanced fluorescence for practical applications

Synergism of gold and silver improves fluorescence behavior of gold–silver bimetallic clusters with practical applications.

Enlightening surface plasmon resonance effect of metal nanoparticles for practical spectroscopic application

Pictorial depiction of applications of metal nanoparticles in different fields enlightening surface plasmon resonance effect.

DNA-Directed Fluorescence Switching of Silver Clusters

Silver clusters with ≲30 atoms are molecules with diverse electronic spectra and wide-ranging emission intensities. Specific cluster chromophores form within DNA strands, and we consider a DNA scaffold that transforms a pair of silver clusters. This ~20-nucleotide strand has two components, a cluster domain (S1) that stabilizes silver clusters and a recognition site (S2) that hybridizes with complementary oligonucleotides (S2C). The single-stranded S1-S2 exclusively develops clusters with violet absorption and low emission. This conjugate hybridizes with S2C to form S1-S2:S2C, and the violet chromophore transforms to a fluorescent counterpart with λex ≈ 490 nm/λem ≈ 550 nm and with ~100-fold stronger emission. Our studies focus on both the S1 sequence and structure that direct this violet → blue-green cluster transformation. From the sequence perspective, C4X sequences with X = adenine, thymine, and/or guanine favor the blue-green cluster, and the specificity of the binding site depends on three factors: the number of C4X repeats, the identity of the X nucleobase, and the number of contiguous cytosines. A systematic series of oligonucleotides identified the optimal S1 sequence C4AC4T and discerned distinct roles for the adenine, thymine, and cytosines. From the structure perspective, two factors guide the conformation of the C4AC4T sequence: hybridization with the S2C complement and coordination by the cluster adduct. Spectroscopic and chromatographic studies show that the single-stranded C4AC4T is folded by its blue-green cluster adduct. We propose a structural model in which the two C4X motifs within C4AC4T are cross-linked by the encapsulated cluster. These studies suggest that the structures of the DNA host and the cluster adduct are interdependent.

Ten-atom silver cluster signaling and tempering DNA hybridization

Silver clusters with ∼10 atoms are molecules, and specific species develop within DNA strands. These molecular metals have sparsely organized electronic states with distinctive visible and near-infrared spectra that vary with cluster size, oxidation, and shape. These small molecules also act as DNA adducts and coordinate with their DNA hosts. We investigated these characteristics using a specific cluster-DNA conjugate with the goal of developing a sensitive and selective biosensor. The silver cluster has a single violet absorption band (λ(max) = 400 nm), and its single-stranded DNA host has two domains that stabilize this cluster and hybridize with target oligonucleotides. These target analytes transform the weakly emissive violet cluster to a new chromophore with blue-green absorption (λ(max) = 490 nm) and strong green emission (λ(max) = 550 nm). Our studies consider the synthesis, cluster size, and DNA structure of the precursor violet cluster-DNA complex. This species preferentially forms with relatively low amounts of Ag(+), high concentrations of the oxidizing agent O2, and DNA strands with ≳20 nucleotides. The resulting aqueous and gaseous forms of this chromophore have 10 silvers that coalesce into a single cluster. This molecule is not only a chromophore but also an adduct that coordinates multiple nucleobases. Large-scale DNA conformational changes are manifested in a 20% smaller hydrodynamic radius and disrupted nucleobase stacking. Multidentate coordination also stabilizes the single-stranded DNA and thereby inhibits hybridization with target complements. These observations suggest that the silver cluster-DNA conjugate acts like a molecular beacon but is distinguished because the cluster chromophore not only sensitively signals target analytes but also stringently discriminates against analogous competing analytes.

Aggregation of nitroaniline in tetrahydrofuran through intriguing H-bond formation by sodium borohydride

The participation of sodium borohydride (NaBH4) in hydrogen bonding interactions and transient anion radical formation has been proved. Thus, the properties of NaBH4 are extended beyond the purview of its normal reducing capability and nucleophilic property. It is reported that ortho- and para-nitroanilines (NAs) form stable aggregates only in tetrahydrofuran (THF) in the presence of NaBH4 and unprecedented orange/red colorations are observed. The same recipe with nitrobenzene instead of nitroanilines (NAs) in the presence of NaBH4 evolves a transient rose red solution due to the formation of a highly fluorescent anion radical. Spectroscopic studies (UV-vis, fluorescence, RLS, Raman, NMR etc.) as well as theoretical calculations supplement the J-aggregate formation of NAs due to extensive hydrogen bonding. This is the first report where BH4(-) in THF has been shown to support such an aggregation process through H-bonding. It is further confirmed that stable intermolecular hydrogen bond-induced aggregation requires a geometrical match in both the nitro- and amino-functionalities attached to the phenyl ring with proper geometry. On the contrary, meta-nitroaniline remains as the odd man out and does not take part in such aggregation. Surprisingly, Au nanoparticles dismantle the J-aggregates of NA in THF. Explicit hydrogen bond formation in NA has been confirmed experimentally considering its promising applications in different fields including non-linear optics.

Precursor salt assisted syntheses of high-index faceted concave hexagon and nanorod-like polyoxometalates

This paper describes an effective method for a precursor salt assisted fabrication and reshaping of two different polyoxometalates [(NH4)2Cu(MoO4)2 (ACM) and Cu3(MoO4)2(OH)2 (CMOH)] into five distinctive shapes through straightforward and indirect routes. Explicit regulation of the structural arrangements of ACM and CMOH has been studied in detail with altered precursor salt concentration employing our laboratory developed modified hydrothermal (MHT) method. Morphologically different ACM 3D architectures are evolved with higher molybdate concentration, whereas 1D growth of CMOH is observed with increased copper concentration. Interesting morphological transformation of the products has been accomplished employing one precursor salt at a time without using any other foreign reagent. It has been proven that large ACMs become labile in the presence of incoming Cu(II) and NH4(+) ions of the precursor salts. A new strategy for the conversion of faceted ACMs (hexagonal plate, circular plate and hollow flower) to exclusive CMOH nanorods through a Cu(II) assisted reaction has been adopted. According to thermodynamic consideration, the synthesis of rare concave nanostructures with high index facet is still challenging due to their higher reactivity. In this study, concave hexagonal ACM with high index facet {hkl} has been successfully prepared for the first time from hexagonal ACM through simple etching with ammonium heptamolybdate (AHM), which is another precursor salt. Hexagonal ACM corrugates to a concave hexagon because of the higher reactivity of the {001} crystal plane than that of the {010} plane. It has been shown that high index facet exposed concave hexagonal ACM serves as a better catalyst for the photodegradation of dye than the other microstructures enclosed by low index facets.

Imine (–CHN–) brings selectivity for silver enhanced fluorescence

Strong silver and gold stimulated fluorescence enhancement of alkaline salicylaldehyde solution have been observed. Ammonia or primary amine quantitatively eliminates gold enhanced fluorescence, keeping silver enhanced fluorescence unaffected.

Orange-red silver emitters for sensing application and bio-imaging

Strongly fluorescent HFL-containing Ag@Au particles are synthesized via a modified hydrothermal technique. This solution is used for sulfide sensing and cell imaging.

Silver nanoparticle anchored carbon dots for improved sensing, catalytic and intriguing antimicrobial activity

Catalytic, sensing and efficient antimicrobial activity of silver nanoparticle anchored hybrid carbon dots.

Fabrication of superhydrophobic copper surface on various substrates for roll-off, self-cleaning, and water/oil separation

Superhydrophobic surfaces prevent percolation of water droplets and thus render roll-off, self-cleaning, corrosion protection, etc., which find day-to-day and industrial applications. In this work, we developed a facile, cost-effective, and free-standing method for direct fabrication of copper nanoparticles to engender superhydrophobicity for various flat and irregular surfaces such as glass, transparency sheet (plastic), cotton wool, textile, and silicon substrates. The fabrication of as-prepared superhydrophobic surfaces was accomplished using a simple chemical reduction of copper acetate by hydrazine hydrate at room temperature. The surface morphological studies demonstrate that the as-prepared surfaces are rough and display superhydrophobic character on wetting due to generation of air pockets (The Cassie-Baxter state). Because of the low adhesion of water droplets on the as-prepared surfaces, the surfaces exhibited not only high water contact angle (164 ± 2°, 5 μL droplets) but also superb roll-off and self-cleaning properties. Superhydrophobic copper nanoparticle coated glass surface uniquely withstands water (10 min), mild alkali (5 min in saturated aqueous NaHCO3 of pH ≈ 9), acids (10 s in dilute HNO3, H2SO4 of pH ≈ 5) and thiol (10 s in neat 1-octanethiol) at room temperature (25-35 °C). Again as-prepared surface (cotton wool) was also found to be very effective for water-kerosene separation due to its superhydrophobic and oleophilic character. Additionally, the superhydrophobic copper nanoparticle (deposited on glass surface) was found to exhibit antibacterial activity against both Gram-negative and Gram-positive bacteria.

Intriguing cysteine induced improvement of the emissive property of carbon dots with sensing applications

A simple fluorometric technique has been adopted for cysteine (Cys) sensing in alkaline medium down to the nM level. The huge fluorescent signal of the solution is a consequence of fluorescent carbon dots (CDs) produced in situ from modified hydrothermal (MHT) reaction between Cys and dopamine (DA). It has been observed that the inherent fluorescence of DA is drastically quenched in alkaline solution. Cys can selectively rescue the fluorescence of DA. Thus, Cys determination in a straightforward way, but only to a micro molar (10(-7) M i.e. 0.1 μM) level is possible through such fluorescence enhancement. Sensitive Cys determination remains associated with the in situ generated CDs, but the external addition of pre-formed CDs to Cys solution fails miserably towards Cys detection. However, CDs prepared from the Cys-DA system in alkaline solution admirably increase the limit of detection (LOD) of Cys at least two orders higher (10(-9) M) than that observed without hydrothermal technique i.e., without CDs. This method finds applications for Cys determination in biological samples and pharmaceutical preparations.

A complementary palette of NanoCluster Beacons

NanoCluster Beacons (NCBs), which use few-atom DNA-templated silver clusters as reporters, are a type of activatable molecular probes that are low-cost and easy to prepare. While NCBs provide a high fluorescence enhancement ratio upon activation, their activation colors are currently limited. Here we report a simple method to design NCBs with complementary emission colors, creating a set of multicolor probes for homogeneous, separation-free detection. By systematically altering the position and the number of cytosines in the cluster-nucleation sequence, we have tuned the activation colors of NCBs to green (C8-8, 460 nm/555 nm); yellow (C5-5, 525 nm/585 nm); red (C3-4, 580 nm/635 nm); and near-infrared (C3-3, 645 nm/695 nm). At the same NCB concentration, the activated yellow NCB (C5-5) was found to be 1.3 times brighter than the traditional red NCB (C3-4). Three of the four colors (green, yellow, and red) were relatively spectrally pure. We also found that subtle changes in the linker sequence (down to the single-nucleotide level) could significantly alter the emission spectrum pattern of an NCB. When the length of linker sequences was increased, the emission peaks were found to migrate in a periodic fashion, suggesting short-range interactions between silver clusters and nucleobases. Size exclusion chromatography results indicated that the activated NCBs are more compact than their native duplex forms. Our findings demonstrate the unique photophysical properties and environmental sensitivities of few-atom DNA-templated silver clusters, which are not seen before in common organic dyes or luminescent crystals.

Account of nitroarene reduction with size- and facet-controlled CuO-MnO2 nanocomposites

In this work, we propose a systematic and delicate size- and shape-controlled synthesis of CuO-MnO2 composite nanostructures from time-dependent redox transformation reactions between Cu2O and KMnO4. The parental size and shape of Cu2O nanostructures are retained, even after the redox transformation, but the morphology becomes porous in nature. After prolonged reaction times (>24 h), the product shapes are ruptured, and as a result, tiny spherical porous nanocomposites of ∼100 nm in size are obtained. This method is highly advantageous due to its low cost, its easy operation, and a surfactant or stabilizing agent-free approach with high reproducibility, and it provides a facile but new way to fabricate porous CuO-MnO2 nanocomposites of varied shape and size. The composite nanomaterials act as efficient recyclable catalysts for nitroarene reduction in water at room temperature. The time-dependent reduction kinetics can be easily monitored by using UV-vis spectrophotometer. The catalytic system is found to be very useful toward the reduction of nitro compounds, regardless of the type and position of the substituent(s). Furthermore, it is revealed that CuO-MnO2 composite nanomaterials exhibit facet-dependent catalytic activity toward nitroarene reduction, where the (111) facet of the composite stands to be more active than that of the (100) facet. The results are also corroborated from the BET surface area measurements. It is worthwhile to mention that porous tiny spheres (product of 48 h reaction) exhibit the highest catalytic activity due to pronounced surface area and smaller size.

Morphology controlled synthesis of SnS₂ nanomaterial for promoting photocatalytic reduction of aqueous Cr(VI) under visible light

A mild, template free protocol has been demonstrated for SnS2 nanoflake formation at the gram level from SnCl2 and thioacetamide (TAA). The SnS2 nanoflakes congregate to nanoflowers and nanoyarns with variable TAA concentrations. BET measurements reveal that the synthesized nanomaterials are highly porous having very high surface area, and the nanoflower has higher surface area than the nanoyarn. The synthesized nanomaterial finds application for promoting photoreduction of extremely toxic and lethal Cr(VI) under visible light irradiation due to their porous nature. The nanoflowers photocatalyst is proved to be superior to nanoyarn due to the increased surface area and higher pore volume. It was also inferred that increased pH decreased the reaction rate. The present result suggests that the morphology-dependent photoreduction of Cr(VI) by SnS2 nanomaterial under visible light exposure will endorse a new technique for harvesting energy and purification of wastewater.

Selective dopamine chemosensing using silver-enhanced fluorescence

Condensation product of salicylaldehyde and 1,3 propylenediamine becomes a diiminic Schiff base, which is oxidized by AgNO3 in alkaline solution, and in turn, stable Ag(0) is produced at room temperature. Under this condition, the solution exhibits intense silver nanoparticle enhanced fluorescence (SEF) with the λ(em) at 412 nm. Dopamine is selectively detected down to the nanomolar level via exclusive fluorescence quenching of the SEF. Dopamine-infested solution regains the fluorescence [i.e., SEF in the presence of Hg(II) ions]. Thus dopamine and Hg(II) in succession demonstrate "turn off/on" fluorescence due to the change in the scattering cross section of Ag(0) and gives a quantitative measure of dopamine in real samples. The proposed method is free from interferences of common biocompetitors.

Photoproduced fluorescent Au(I)@(Ag2/Ag3)-thiolate giant cluster: an intriguing sensing platform for DMSO and Pb(II)

Synergistic evolution of fluorescent Au(I)@(Ag2/Ag3)-thiolate core-shell particles has been made possible under the Sun in presence of the respective precursor coinage metal compounds and glutathione (GSH). The green chemically synthesized fluorescent clusters are giant (∼600 nm) in size and robust. Among all the common water miscible solvents, exclusively DMSO exhibits selective fluorescence quenching (Turn Off) because of the removal of GSH from the giant cluster. Again, only Pb(II) ion brings back the lost fluorescence (Turn On) leaving aside all other metal ions. This happens owing to the strong affinity of the sulfur donor of DMSO for Pb(II). Thus, employing the aqueous solution containing the giant cluster, we can detect DMSO contamination in water bodies at trace level. Besides, a selective sensing platform has emerged out for Pb(II) ion with a detection limit of 14 × 10(-8) M. Pb(II) induced fluorescence recovery is again vanished by I(-) implying a promising route to sense I(-) ion.

Green synthesis and reversible dispersion of a giant fluorescent cluster in solid and liquid phase

A water-soluble highly fluorescent silver cluster on Au(I) surface has been synthesized with green chemistry under sunlight. The evolution of the silver cluster is synergistic, demanding gold and glutathione. The fluorescent Au(I)core-Ag(0)shell particles are huge in size and at the same time they are robust. That is why they become a deliverable fluorescing solid upon drying. Again, the giant particles run into common water miscible solvents. As a result, the fluorescence intensity increases to a great extent without any alteration of emission maxima. In this respect, acetone has been found to be the best-suited solvent. To have a universal applicability of the fluorescent clusters, the particles in the water pool of a reverse micelle have been prepared to transfer the particles into different water immiscible solvents. The comparatively lower fluorescence intensity of the particles has been ascribed to a space confinement effect. Finally, giant-cluster-impregnated yellow-orange fluorescent polymer film and fluorescent cotton wool, as well as paper substrate, have been prepared. The antibacterial activity of the fluorescent particle has also been tested involving modified cotton wool and paper substrate for Gram-negative and -positive Escherichia coli and Staphylococcus aureus, respectively.

Fabrication of porous β-Co(OH)2 architecture at room temperature: a high performance supercapacitor

A facile, cost-effective, surfactant-free chemical route has been demonstrated for the fabrication of porous β-Co(OH)2 hierarchical nanostructure in gram level simply by adopting cobalt acetate as a precursor salt and ethanolamine as a hydrolyzing agent at room temperature. A couple of different morphologies of β-Co(OH)2 have been distinctly identified by varying the mole ratio of the precursor and hydrolyzing agent. The cyclic voltammetry measurements on β-Co(OH)2 displayed significantly high capacitance. The specific capacitance obtained from charge-discharge measurements made at a discharge current of 1 A/g is 416 F/g for the Co(OH)2 sample obtained at room temperature. The charge-discharge stability measurements indicate retention of specific capacitance about 93% after 500 continuous charge-discharge cycles at a current density of 1 A g(-1). The capacitive behavior of the other synthesized morphology was also accounted. The nanoflower-shaped porous β-Co(OH)2 with a characteristic three-dimensional architecture accompanied highest pore volume which made it promising electrode material for supercapacitor application. The porous nanostructures accompanied by high surface area facilitates the contact and transport of electrolyte, providing longer electron pathways and therefore giving rise to highest capacitance in nanoflower morphology. From a broad view, this study reveals a low-temperature synthetic route of β-Co(OH)2 of various morphologies, qualifying it as supercapacitor electrode material.

Synthesis of highly fluorescent silver clusters on gold(I) surface

Evolution of fluorescence from a giant core-shell particle is new and synergistic, which requires both gold and silver ions in an appropriate ratio in glutathione (GSH) solution. The formation of highly fluorescent Ag(2)/Ag(3) clusters on the surface of Au(I) assembly results in giant Au(I)(core)-Ag(0)(shell) water-soluble microparticles (~500 nm). Here, Au(I) acts as the template for the generation of fluorescent Ag clusters. The presence of gold under the synthetic strategy is selective, and no other metal supports such synergistic evolution. The core-shell particle exhibits stable and static emission (emission maximum, 565 nm; quantum yield, 4.6%; and stroke shift, 179 nm) with an average lifetime of ~25 ns. The drift of electron density by the Au(I) core presumably enhances the fluorescence. The positively charged core offers unprecedented long-term stability to the microparticles in aqueous GSH solution.

Cervical mediastinoscopy: re-evaluation of an old technique in era of new imaging technology

CONTEXT

With the advent of modern anatomical and functional imaging technologies, application of cervical mediastinoscopy has decreased in diagnosis and staging of mediastinal diseases.

AIM

To evaluate the usefulness of cervical mediastinoscopy in assessing the mediastinal disease when imaging modalities are non-diagnostic.

SETTINGS AND DESIGN

Retrospective analysis of records of a tertiary care hospital.

PATIENTS AND METHODS

Thirty-nine patients with mediastinal pathology of varied aetiologies underwent cervical mediastinoscopy. Pre- and post-operative diagnosis was compared.

RESULTS

In 34 out of 39 cases (87.5%), cervical mediastinoscopy provided a confirmatory final diagnosis. One case had a major complication in the form of recurrent laryngeal nerve palsy.

CONCLUSION

Cervical mediastinoscopy is useful, minimally invasive modality in a scenario where anatomical and functional imaging tools are non-diagnostic.

Tracheal necrosis with surgical emphysema following thyroidectomy

Tracheal necrosis after thyroidectomy is an extremely rare event with only a few published reports. We present a case of a 65-year-old male who developed rapidly progressive surgical emphysema of face and upper thorax on the seventh day following total thyroidectomy. Prompt surgical exploration of neck revealed a tracheal rent at the level of the second tracheal ring. This hole was then refashioned into a formal tracheostomy. Patient had an eventful recovery. Tracheostomy was closed by the 14th day. The complication was probably related to tracheal injury sustained due to electro-coagulation and subsequent secondary infection.

Assessment and occurrence of various heavy metals in surface water of Ganga river around Kolkata: a study for toxicity and ecological impact

A study was conducted during November, 2005-October, 2006 to evaluate the surface water quality of river Ganga around Kolkata. The samples were analyzed for a number of physico-chemical parameters using standard laboratory procedures and giving prime thrust to determine the heavy metal concentrations (Fe, Mn, Cu, Zn, Pb, Cd, Cr, and Ni) of surface water at four different locations of the river Ganga around Kolkata from two points (middle of the river stream and a discharge point) at each location. Out of 96 samples analyzed, Fe, Mn, Cu, Zn, and Ni were detected in 71, 47, 38, 60, and 45 samples in the concentrations ranging from 0.013 to 5.49, 0.022 to 1.78, 0.003 to 0.033, 0.005 to 0.293, and 0.045 to 0.24 mg L(-1), respectively. Cd and Pb were detected in six and 21 samples in the range of 0.005 to 0.006 and 0.05 to 0.53 mg L(-1), respectively. But Cr was not detected in any of the samples analyzed. The metals exhibited no significant variation with respect to sampling locations as well as discharge points. However, the concentration of those metals varied with season, being higher in rainy and lower in winter season.

PINK1 protein in normal human brain and Parkinson's disease

Parkinson's disease is a common incurable neurodegenerative disease whose molecular aetiology remains unclear. The identification of Mendelian genes causing rare familial forms of Parkinson's disease has revealed novel proteins and pathways that are likely to be relevant in the pathogenesis of sporadic Parkinson's disease. Recently, mutations in a novel gene, PINK1, encoding a 581 amino acid protein with both mitochondrial targeting and serine/threonine kinase domains, were identified as a cause of autosomal recessive parkinsonism. This provided important evidence for the role of the mitochondrial dysfunction and kinase pathways in neurodegeneration. In this study, we report the first characterization of the PINK1 protein in normal human and sporadic Parkinson's brains, in addition to Parkinson's cases with heterozygous PINK1 mutations. The possible role of the PINK1 protein was also assessed in a number of neurodegenerative diseases characterized by proteinaceous inclusions. For these studies, rabbit polyclonal antibodies were raised against two peptide sequences within the N-terminal hydrophilic loops of PINK1 protein. Using immunohistochemistry and western blotting we were able to demonstrate that PINK1 is a ubiquitous protein expressed throughout the human brain and it is found in all cell types showing a punctate cytoplasmic staining pattern consistent with mitochondrial localization. Fractionation studies of human and rat brain confirm that PINK1 is localized to the mitochondrial membranes. In addition, we show that PINK1 is detected in a proportion of Lewy bodies in cases of sporadic Parkinson's disease and Parkinson's disease associated with heterozygous mutations in the PINK1 gene, which are clinically and pathologically indistinguishable from the sporadic cases. PINK1 was absent in cortical Lewy bodies, in neurofibrillary tangles in Alzheimer's disease, progressive supranuclear palsy and corticobasal degeneration, and in the glial and neuronal alpha-synuclein positive inclusions in multiple system atrophy. These studies provide for the first time in vivo morphological and biochemical evidence to support a mitochondrial localization of PINK1 and underpin the significance of mitochondrial dysfunction in the pathogenesis of nigral cell degeneration in Parkinson's disease.