Green-Synthesized Amino Carbons for Impedimetric Biosensing of E. coli O157:H7.

This study describes the synthesis of amino-functionalized carbon nanoparticles derived from biopolymer chitosan using green synthesis and its application toward ultrasensitive electrochemical immunosensor of highly virulent Escherichia coli O157:H7 (E. coli O157:H7). The inherent advantage of high surface-to-volume ratio and enhanced rate transfer kinetics of nanoparticles is leveraged to push the limit of detection (LOD), without compromising on the selectivity. The prepared carbon nanoparticles were systematically characterized by employing CO2-thermal programmed desorption (CO2-TPD), Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), ultraviolet-visible (UV-visible), and transmission electron microscopy (TEM). The estimated limit of detection of 0.74 CFU/mL and a sensitivity of 5.7 ((ΔRct/Rct)/(CFU/mL))/cm2 in the electrochemical impedance spectroscopy (EIS) affirm the utility of the sensor. The proposed biosensor displayed remarkable selectivity against interfering species, making it well suited for real-time applications. Moreover, the chitosan-derived semiconducting amino-functionalized carbon shows excellent sensitivity in a comparative analysis compared to highly conducting amine-functionalized carbon synthesized via chemical modification, demonstrating its vast potential as an E. coli sensor.

Dual-color photoluminescence modulation of zero-dimensional hybrid copper halide microcrystals.

Zero-dimensional hybrid copper(I) halides (HCHs) are attractive due to their interesting photoluminescence (PL) properties and the high abundance and low toxicity of copper. In this study, we report green-red dual emission from rhombic 1-butyl-1-methyl piperidinium copper bromide [(Bmpip)2Cu2Br4] microcrystals (MCs) prepared on borosilicate glass. The structure and elemental composition of the MCs are characterized by single crystal X-ray diffraction analysis, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. Interestingly, MCs prepared on an ITO-coated glass plate show an intense green emission compared to the dual emission on a bare glass or plastic substrate. Furthermore, the intensity of the green emission from the MC is enormously increased by powdering using a conductive material, suggesting the deactivation of the red-emitting state by a charge transfer interaction with the conductor. These findings open a new strategy to suppress the self-trapping of excitons by longitudinal optical phonons and control the dual emitting states in HCHs.

Toll-like receptor-immobilized carbon paste electrodes with plasma functionalized amine termination: Towards real-time electrochemical based triaging of gram-negative bacteria.

Chronic wounds caused due to bacterial biofilms are detrimental to a patient, and an immediate diagnosis of these bacteria can aid in an effective treatment, which is still an unmet clinical need. An instant and accurate identification of bacterial type could be made by utilizing the Toll-Like Receptors (TLRs) combined with Myeloid Differentiation factor 2 (MD-2). Given this, we have developed an electrochemical sensing platform to identify the gram-negative (gram-ve) bacteria using TLR4/MD-2 complex. The nonthermal plasma (NTP) technique was utilized to functionalize amine groups onto the carbon surface to fabricate cost-effective carbon paste working electrodes (CPEs). The proposed electrochemical sensor platform with a specially engineered electrochemical cell (E-Cell) identified the Escherichia coli (E. coli) in a wide linear range of 1.5×10° - 1.5×106 C.F.U./mL, accounting for a very low detection limit of 0.087 C.F.U./mL. The novel and cost-effective sensor platform identified gram-ve bacteria predominantly in a mixture of gram positive (gram+ve) bacteria and fungi. Further, towards real-time detection of bacteria and point-of-care (PoC) applications, the effect of the pond water matrix was studied, which was minimal, and the sensor could identify E. coli concentrations selectively, showing the potential application of the proposed platform towards real-time bacterial detection.

Photoinduced interfacial electron transfer from perovskite quantum dots to molecular acceptors for solar cells.

Bandgap-engineered inorganic and hybrid halide perovskite (HP) films, nanocrystals, and quantum dots (PQDs) are promising for solar cells. Fluctuations of photoinduced electron transfer (PET) rates affect the interfacial charge separation efficiencies of such solar cells. Electron donor- or acceptor-doped perovskite samples help analyze PET and harvest photogenerated charge carriers efficiently. Therefore, PET in perovskite-based donor-acceptor (D-A) systems has received considerable attention. We analyzed the fluctuations of interfacial PET from MAPbBr3 or CsPbBr3 PQDs to classical electron acceptors such as 7,7,8,8-tetracyanoquinodimethane (TCNQ) and 1,2,4,5-tetracyanobenzene (TCNB) at single-particle and ensemble levels. The significantly negative Gibbs free energy changes of PET estimated from the donor-acceptor redox potentials, the donor-acceptor sizes, and the solvent dielectric properties help us clarify the PET in the above D-A systems. The dynamic nature of PET is apparent from the decrease in photoluminescence (PL) lifetimes and PL photocounts of PQDs with an increase in the acceptor concentrations. Also, the acceptor radical anion spectrum helps us characterize the charge-separated states. Furthermore, the PL blinking time and PET rate fluctuations (108 to 107 s-1) provide us with single-molecule level information about interfacial PET in perovskites.

Label-free miniaturized electrochemical nanobiosensor triaging platform for swift identification of the bacterial type.

In chronic wounds, rapid identification of the bacterial type is critical for immediate clinical assessment. A novel, cost-effective, and label-free electrochemical nanobiosensor was developed with the help of an indigenously fabricated carbon paste working electrode to rapidly identify the bacterial type. The proposed platform made use of gold nanoparticles (AuNPs) to boost electrochemical activity, and the strong affinity of boronic acid moieties for diols allowed for detection and differentiation of gram + ve and gram -ve bacteria on the same platform. A scalable and robust miniaturized Electrochemical Cell (E-Cell) designed for the developed electrodes assisted in reducing sample waste, detection time, and Limit of Detection (LOD). Within 15 min, the proposed nano biosensing platform identified Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) bacteria with an excellent recovery rate for the blind samples. Because of its size and the extra lipopolysaccharides (LPS) layer containing diols, the bioelectrode demonstrated a superior response to E. coli, effectively distinguishing it from S. aureus. Furthermore, the proposed biosensing platform demonstrated an excellent shelf-life and reproducibility with acceptable selectivity and exhibited an excellent specificity towards bacteria, making it an ideal candidate for rapid identification of the bacterial type.

Plasma Functionalized Carbon Interfaces for Biosensor Application: Toward the Real-Time Detection of Escherichia coli O157:H7.

Nonthermal plasma, a nondestructive, fast, and highly reproducible surface functionalization technique, was used to introduce desired functional groups onto the surface of carbon powder. The primary benefit is that it is highly scalable, with a high throughput, making it easily adaptable to bulk production. The plasma functionalized carbon powder was later used to create highly specific and low-cost electrochemical biosensors. The functional groups on the carbon surface were confirmed using NH3-temperature-programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS) analysis. In addition, for biosensing applications, a novel, cost-effective, robust, and scalable electrochemical sensor platform comprising in-house-fabricated carbon paste electrodes and a miniaturized E-cell was developed. Biotin-Streptavidin was chosen as a model ligand-analyte combination to demonstrate its applicability toward biosensor application, and then, the specific identification of the target Escherchia coli O157:H7 was accomplished using an anti-E. coli O157:H7 antibody-modified electrode. The proposed biosensing platform detected E. coli O157:H7 in a broad linear range of (1 × 10-1-1 × 106) CFU/mL, with a limit of detection (LOD) of 0.1 CFU/mL. In addition, the developed plasma functionalized carbon paste electrodes demonstrated high specificity for the target E. coli O157:H7 spiked in pond water, making them ideal for real-time bacterial detection.

Mechano-optical Modulation of Excitons and Carrier Recombination in Self-Assembled Halide Perovskite Quantum Dots.

Mechanically modulating optical properties of semiconductor nanocrystals and organic molecules are valuable for mechano-optical and optomechanical devices. Halide perovskites with excellent optical and electronic properties are promising for such applications. We report the mechanically changing excitons and photoluminescence of self-assembled formamidinium lead bromide (FAPbBr3) quantum dots. The as-synthesized quantum dots (3.6 nm diameter), showing blue emission and a short photoluminescence lifetime (2.6 ns), form 20-300 nm 2D and 3D self-assemblies with intense green emission in a solution or a film. The blue emission and short photoluminescence lifetime of the quantum dots are different from the delayed (ca. 550 ns) green emission from the assemblies. Thus, we consider the structure and excitonic properties of individual quantum dots differently from the self-assemblies. The blue emission and short lifetime of individual quantum dots are consistent with a weak dielectric screening of excitons or strong quantum confinement. The red-shifted emission and a long photoluminescence lifetime of the assemblies suggest a strong dielectric screening that weakens the quantum confinement, allowing excitons to split into free carriers, diffuse, and trap. The delayed emission suggests nongeminate recombination of diffusing and detrapped carriers. Interestingly, the green emission of the self-assembly blueshifts by applying a lateral mechanical force (ca. 4.65 N). Correspondingly, the photoluminescence lifetime decreases by 1 order of magnitude. These photoluminescence changes suggest the mechanical dissociation of the quantum dot self-assemblies and mechanically controlled exciton splitting and recombination. The mechanically changing emission color and lifetime of halide perovskite are promising for mechano-optical and optomechanical switches and sensors.

Promising Utilization of CO2 for Syngas Production over Mg2+- and Ce2+-Promoted Ni/γ-Al2O3 Assisted by Nonthermal Plasma.

Dry reforming of methane is conducted in a catalyst packed-bed dielectric barrier discharge (DBD) reactor aiming to improve the reaction efficiency. The MgO- and CeO2-promoted Ni/γ-Al2O3 catalyst is tested to carry out the reaction. An interesting observation is that Ni/MgO_Al2O3 integration provides ∼35 and 13% conversion of CH4 and CO2, respectively. The highest syngas ratio of 0.94 is obtained with Ni/MgO_Al2O3, whereas the ratio is only 0.57 with Ni/CeO2_Al2O3 and 0.64 with bare DBD. In addition, Ni/CeO2_Al2O3 offers the highest selectivity (68%) of CO due to the oxygen buffer property of CeO2. Finally, the optimal acid/base property is highly desirable for the dry reforming reaction.

Synthesis, optoelectronic properties and applications of halide perovskites.

Halide perovskites have emerged as a class of most promising and cost-effective semiconductor materials for next generation photoluminescent, electroluminescent and photovoltaic devices. These perovskites have high optical absorption coefficients and exhibit narrow-band bright photoluminescence, in addition to their halide-dependent tuneable bandgaps, low exciton binding energies, and long-range carrier diffusion. These properties make these perovskites superior to classical semiconductors such as silicon. Most importantly, the simple synthesis of perovskites in the form of high quality films, single crystals, nanocrystals and quantum dots has attracted newcomers to develop novel perovskites with unique optoelectronic properties for optical and photovoltaic applications. Here, we comprehensively review recent advances in the synthesis and optoelectronic properties of films, microcrystals, nanocrystals and quantum dots of lead halide and lead-free halide perovskites. Followed by the classification of synthesis, we address the ensemble and single particle properties of perovskites from the viewpoints of the confinement and transport of charge carriers or excitons. Further, we correlate the charge carrier properties of perovskite films, microcrystals, nanocrystals and quantum dots with the crystal structure and size, halide composition, temperature, and pressure. Finally, we illustrate the emerging applications of perovskites to solar cells, LEDs, and lasers, and discuss the ongoing challenges in the field.

A photoanode with plasmonic nanoparticles of earth abundant bismuth for photoelectrochemical reactions.

A wide range of technologies has been developed for producing hydrogen economically and in greener ways. Photoelectrochemical water splitting using photoelectrodes submerged in a bath electrolyte forms a major route of hydrogen evolution. The efficacy of water splitting is improved by sensitizing metal oxide photoelectrodes with narrow bandgap semiconductors that efficiently absorb sunlight and generate and transport charge carriers. Here we show that the efficiencies of photocurrent generation and photoelectrochemical hydrogen evolution by the binary TiO2/Sb2S3 anode increase by an order of magnitude upon the incorporation of the earth-abundant plasmonic bismuth nanoparticles into it. The ternary electrode TiO2/Bi nanoparticle/Sb2S3 illuminated with sunlight provides us with a photocurrent density as high as 4.21 mA cm-2 at 1.23 V, which is fourfold greater than that of the binary electrode and tenfold greater than that of pristine TiO2. By using bismuth nanoparticles, we estimate the incident photon to current conversion efficiency at 31% and solar power conversion efficiency at 3.85%. Here the overall impact of bismuth nanoparticles is attributed to increases in the open-circuit voltage (860 mV), which is by expediting the transfer of photogenerated electrons from Sb2S3 nanoparticles to the TiO2 electrode, and short-circuit current (9.54 mA cm-2), which is by the plasmonic nearfield effect. By combining the cost-effective plasmonic bismuth nanoparticles with the narrow bandgap Sb2S3 on the TiO2 electrode, we develop a stable, ternary photoanode and accomplish high-efficiency photocurrent generation and hydrogen evolution.

Extinction of Antimicrobial Resistant Pathogens Using Silver Embedded Silica Nanoparticles and an Efflux Pump Blocker.

Control measures against antimicrobial resistant bacterial pathogens are important challenges in our daily life. In this study, we discuss the sensitivity and resistance of four bacterial pathogens, Vibrio alginolyticus, Escherichia coli, Staphylococcus aureus, and Bacillus subtilis, to silver-silica hybrid nanoparticles. Successively, by combining with an efflux pump blocking agent Verapamil, we find that these hybrid nanoparticles induce complete mortality to even the most resistive S. aureus. The above pathogens are selected from a pool of 100 bacterial strains resistant to silver nitrate. While S. aureus shows increased resistance to the nanoparticles, the cell wall integrity and genetic stability of V. alginolyticus and E. coli are compromised in the presence of the hybrid nanoparticles. These studies suggest that the antimicrobial properties of the nanoparticles against Gram-negative pathogens originate from increased oxidative stress, which is confirmed by the blocking of reactive oxygen species (ROS) using scavengers such as ascorbic acid and observing DNA damage. The antimicrobial property of the nanoparticle when combined with its nontoxic nature to mammalian cells makes it a promising agent for controlling drug-resistant Gram-negative pathogens.

Bimetallic Pd-Au/TiO2 Nanoparticles: An Efficient and Sustainable Heterogeneous Catalyst for Rapid Catalytic Hydrogen Transfer Reduction of Nitroarenes.

Anilines are one of the important chemical feedstocks and are utilized for the preparation of a variety of pharmaceuticals, agrochemicals, pigments, and dyes. In this context, the catalytic reduction of nitro functionality is an industrially vital process for the synthesis of aniline derivatives. Herein, we report an efficient nanosized bimetallic Pd-Au/TiO2 nanomaterial which is proved to be quite efficient for rapid catalytic hydrogen transfer reduction of nitroarenes into corresponding amines. Significantly, the reduction process is successful under solvent-free and mild green atmospheric conditions. Bimetallic Pd-Au nanoparticles served as the active center, and TiO2 played as a support in hydrogen transfer from the source hydrazine monohydrate. Typical results highlighted that the reactions were very rapid and the products were obtained in good to excellent yields. Significantly, the process was successful in the presence of a very low amount catalyst (0.1 mol %). Furthermore, the reaction showed good chemoselectivity and compatiblity with double or triple bond, aldehyde, ketone, and ester functionalities on the aromatic ring. Typical results indicated the true heterogeneous nature of the Pd-Au/TiO2 nanocatalyst, where the catalyst retained the activity, without loss of its activity.