Room-Temperature Deep-UV Photoluminescence from Low-Dimensional Hexagonal Boron Nitride Prepared Using a Facile Synthesis.

Identification and evaluation of defect levels in low-dimensional materials is an important aspect in quantum science. In this article, we report a facile synthesis method of low-dimensional hexagonal boron nitride (h-BN) and study light emission characteristics due to the defects. The thermal annealing procedure is optimized to obtain clean multilayered h-BN as revealed by transmission electron microscopy. UV-vis spectroscopy shows the optical energy gap of 5.28 eV, which is comparable to the reported energy gap for exfoliated, clean h-BN samples. X-ray photoelectron spectroscopy reveals the location of the valence band edge at 2 eV. The optimized synthesis route of h-BN generates two kinds of defects, which are characterized using room-temperature photoluminescence (PL) measurements. The defects emit light at 4.18 eV [deep-UV (DUV)] and 3.44 eV (UV) photons. The intensity of PL has an oscillatory dependence on the excitation energy for the defect emitting DUV light. A series of spectral lines are observed with the energy ranging between 2.56 and 3.44 eV. The average peak-to-peak energy separation is about 125 meV. The locations of the spectral lines can be modeled using Franck-Condon-type transition and associated with displaced harmonic oscillator approximation. Our facile route gives an easier approach to prepare clean h-BN, which is essential for classical two-dimensional material-based electronics and single-photon-based quantum devices.

Enhanced antibacterial, antioxidant and anticancer activity of caffeic acid by simple acid-base complexation with spermine/spermidine.

Caffeic acid (CA) is a naturally occurring plant-derived polyphenol possessing diverse biological properties. However, the poor water-solubility of CA restricts its widespread applications. On the other hand, biogenic amines such as spermine and spermidine are natural constituents in eukaryotes. In this work, we present water-soluble complexes of CA with spermine and spermidine by exploiting the acid-base interaction. Four different compositions have been prepared by varying the CA to amine ratios, whose chemical structures have been probed in detail using Fourier-transform infrared spectroscopy (FT-IR) and nuclear magnetic resonance (NMR) studies that have revealed the acid-base interaction between the constituent precursors. The obtained acid-base complexes at their native pH values have shown enhanced antibacterial and antioxidant activities than pristine CA. Further, the CA-polyamine complexes have shown high anticancer performances in the concentration range that is compatible with the normal cell lines.

Water-soluble caffeic acid-dopamine acid-base complex exhibits enhanced bactericidal, antioxidant, and anticancer properties.

Despite the highly potent biological characteristics, the poor water-solubility of caffeic acid (CA) limits its applications in various domains. Here, we present a facile approach, wherein CA has been treated with dopamine hydrochloride (Dopa.HCl) to obtain a water-soluble acid-base complex, which does not possess any covalent bond between the individual components and thus retains their nativity. Simple mixing of CA and Dopa.HCl did not provide water solubility to CA, but the complex became readily soluble in water when the mineral acid was scavenged using sodium bicarbonate. The obtained CA-Dopa complex had been characterized using FT-IR, 1H NMR, 13C NMR, 2D 1H-1H NOESY NMR, XPS, and DSC techniques. The complex was found to exhibit excellent bactericidal, antibiofilm, antioxidant, and anticancer properties in the physiologically relevant pH range of 5.5 to 7.5. The results have revealed the high potential of the simple acid-base complex of CA in diverse domains.

Lactobacillus amylovorus derived lipase-mediated silver derivatization over poly(ε-caprolactone) towards antimicrobial coatings.

Owing to the probiotic origin, lipases-derived from the Lactobacilli sp. are considered to be promising biomaterials for in vivo applications. On a different note, poly(ε-caprolactone) (PCL)-an FDA-approved polymer for implantable applications-lacks inherent antimicrobial property, because of which suitable modifications are required to render it with bactericidal activity. Here, we employ Lactobacillus amylovorous derived lipase to surface derivatize the PCL films with silver that is a highly efficient inorganic broad-spectrum antimicrobial substance. Two different surface functionalization strategies have been employed over the alkaline hydrolyzed PCL films towards this purpose: In the first strategy, lipase-capped silver nanoparticles (Ag NPs) have been synthesized in a first step, which have been covalently immobilized over the activated carboxylic groups on the PCL film surface in a subsequent step. In the second strategy, the lipase was covalently immobilized over the activated carboxylic groups of the PCL film surface in the first step, over which silver was deposited in the second step using the dip-coating method. While the characterization study using X-ray photoelectron spectroscopy (XPS) has revealed the successful derivatization of silver over the PCL film, the surface characterization using field-emission scanning electron microscopy (FE-SEM) study has shown a distinct morphological change with higher silver loading in both strategies. The antimicrobial studies employing E. coli have revealed 100 % inhibition in the bacterial growth in 4-6 h with the Ag NPs-immobilized PCL films as opposed to >8 h with those prepared through the dip-coating method. Additionally, the cytotoxicity assay using mouse fibroblast cells has shown that the PCL films immobilized with lipase-capped Ag NPs exhibit high cell compatibility, similar to that of pristine PCL film, and thereby making it suitable for in vivo applications.

Genotyping simplified: rationally designed antisense oligonucleotide-mediated PCR amplification-free colorimetric sensing of viral RNA in HCV genotypes 1 and 3.

Molecular diagnosis of viral genotyping devoid of polymerase chain reaction (PCR) amplification in clinical cohorts has hitherto been challenging. Here we present a simplified molecular diagnostic strategy for direct genotyping of hepatitis C virus (HCV) 1 and 3 (prevalent worldwide) using a combination of rationally designed genotype-specific antisense oligonucleotides (ASOs) and plasmonic gold nanoparticles. The ASOs specific to genotypes 1 and 3 have been designed from the nonstructural region 5A (NS5A) of the viral genome using the ClustalW multiple sequence alignment tool. A total of 79 clinical samples including 18 HCV genotype 1, 18 HCV genotype 3, one HIV positive, one HBV positive, and 41 healthy controls have been tested against both the designed ASOs. The study reveals 100% specificity and sensitivity with the employed samples and thereby opens up new avenues for PCR-free direct genotyping of other viruses as well, through the rational design of ASOs.

Naked-eye colorimetric detection of HCV RNA mediated by a 5' UTR-targeted antisense oligonucleotide and plasmonic gold nanoparticles.

The increasing incidence of hepatitis C viral (HCV) infection worldwide is a major concern for causing liver cirrhosis and hepatocellular carcinoma, leading to increased morbidity and mortality. Currently, the prevalence of HCV infection is estimated to be in the range of ∼3%. According to the World Health Organization, antiviral drugs can cure more than 95% of the HCV infected cases, if timely diagnosis and treatment are provided. The gold standard RT-qPCR assay is expensive and requires a minimum turnaround time of 4 h. Hence, a rapid and cost-effective detection assay that can be used even in resource-limited settings would be highly beneficial for mass level screening. Herein, we present an Au NP based facile strategy for rapid, early-stage, and sensitive detection of HCV RNA in clinical samples which avoids thiol tagging to the antisense oligonucleotide and expensive infrastructure. This technique utilizes the hybridization of a short-chain antisense oligonucleotide from the 5' untranslated region (UTR) of the viral genome with the isolated HCV RNA samples. Using a specific sequence universal to all HCV genotypes-obtained through the NCBI BLASTn tool-the HCV positive samples have stabilized the citrate capped Au NPs against salt-induced aggregation, retaining their red color. On the other hand, negative controls, including HBV and HIV positive samples, do not stabilize the Au NPs, which results in purple coloration. Besides, the assay is successfully tested with a RNase A enzyme-treated HCV positive sample, which does not stabilize the Au NPs, thus confirming the role of the viral HCV RNA in this strategy. This Au NP based assay takes about 30 min using the viral RNA isolate and has high specificity with a detection limit of 100 IU mL-1, which is ∼10 fold lower than the state-of-the-art Au NP based strategy.

Quaternized Polydopamine Coatings for Anchoring Molecularly Dispersed Broad-Spectrum Antimicrobial Silver Salts.

Because of the broad-spectrum antimicrobial efficacy, silver-based coatings have emerged as the popular choice to apply over frequently touched surfaces for mitigating the spread of nosocomial infections. Despite the advancements through various coating strategies, clustering of the active component remains a bottleneck in achieving the molecular-scale dispersion of silver. To circumvent this, the current study takes advantage of the recent findings of quaternary ammonium moieties forming molecular complexes with silver salts that differ from the simple adduct between the individual components. Here we demonstrate the quaternization of oxidatively cross-linked polydopamine coatings over magnetite nanoparticles to anchor ionic silver at a molecular-scale dispersion. The silver-derivatized materials exhibit remarkable broad-spectrum antimicrobial properties against representative microbes like E. coli, S. aureus, and A. niger. Also, the study reveals the materials' antibiofilm efficacy (∼80-90%) against both bacteria. Further recyclability studies have proven the sustained bactericidal properties up to five cycles. The surface derivatization strategy has then been extended to cover glass slips that have also shown the retention of the bactericidal properties even after wiping 20 times with artificial sweat. The biocompatibility of the materials has been ascertained with treated water against the mouse fibroblast and human embryonic kidney cell lines. The current study offers insights in developing coatings with molecular-scale dispersion of ionic silver to achieve broad-spectrum antimicrobial properties in an atom-economical and sustainable manner.

Anatase versus Triphasic TiO2: Near-identical synthesis and comparative structure-sensitive photocatalytic degradation of methylene blue and 4-chlorophenol.

Studies on photocatalytic activity of monophasic and biphasic TiO2 have been well explored. However, detailed studies on the photocatalytic activity of triphasic titania, as opposed to monophasic or biphasic TiO2 are scarce. Here we report a comparative structure-sensitive photocatalytic study of triphasic versus anatase TiO2, both have been synthesized under near-identical conditions through a customized sol-gel approach. The composition of the phases is tuned just by varying the thermal pre-treatment conditions of TiO2 gel that has been subsequently subjected to calcination at 300 °C. Interestingly, when the pre-treatment temperature of the gel is systematically increased from 50 to 250 °C, a transition from anatase to triphasic (anatase, rutile, and brookite) and then again to anatase has been observed. The synthesized TiO2 phase compositions have been thoroughly characterized for their structural, optical, electrical, surface and morphological properties. Among the different phase compositions, triphasic titania having a significant proportion of rutile has been found to exhibit the highest photocatalytic activity, as probed using model organic pollutants, Methylene Blue (MB) and 4-Chlorophenol (4-CP). In addition to the earlier known factors such as effective heterojunction, and favorable position of the valence band (VB), an important contribution to the high photocatalytic activity of triphasic TiO2 has been experimentally found to stem from the additional electron density in VB that is attributed to the lattice contraction of anatase phase owing to the coexistence of other two phases. The study provides fundamental insights into the energetics that impact the photocatalytic activity of triphasic versus anatase TiO2.

Highly Dispersed Nanocomposite of AgBr in g-C3N4 Matrix Exhibiting Efficient Antibacterial Effect on Drought-Resistant Pseudomonas putida under Dark and Light Conditions.

Synthesis of nanocomposites possessing intimately mixed components is highly challenging to bring out the best possible properties of the materials. The challenge is mainly due to the difficulties associated with controlling the phase segregation of individual components as a result of high interfacial tension between them and cohesive forces within each component during the synthesis. Here, we show a single-step synthesis of representative nanocomposites of g-C3N4/AgBr through a rationally designed approach, wherein melamine, the precursor of g-C3N4, has been intimately mixed with the AgBr precursor, silver-tetraoctylammonium bromide. Subsequent calcination of the obtained solid at 500 °C has resulted in the formation of highly dispersed g-C3N4/AgBr. The key to such a high dispersion lies in the surfactant-based AgBr precursor that minimized the interfacial tension during the process. The AgBr content has been varied between 2 and 20 wt % with respect to the g-C3N4 content. The obtained nanocomposites have been thoroughly characterized using XRD, XPS, ED-XRF, FE-SEM, HR-TEM, DRS, TCSPC, and BET surface area techniques. The studies revealed a high dispersion of AgBr in the g-C3N4 matrix. The nanocomposites have been found to exhibit remarkable antimicrobial properties over a drought-resistant bacterial strain of Pseudomonas putida under both dark and light conditions compared with similar compositions obtained through other methods reported so far. The present study offers a new approach for synthesizing highly dispersed and efficient nanocomposites.