Probing surface interactions in CdSe quantum dots with thiocyanate ligands.

Surface chemistry dictates the optoelectronic properties of semiconductor quantum dots (QDs). Tailoring these properties relies on the meticulous selection of surface ligands for efficient passivation. While long-chain organic ligands boast a well-understood passivation mechanism, the intricacies of short inorganic ionic ligands remain largely unexplored. This study sheds light on the surface-passivation mechanism of short inorganic ligands, particularly focusing on SCN- ions on CdSe QDs. Employing steady-state and time-resolved infrared spectroscopic techniques, we elucidated the surface-ligand interactions and coordination modes of SCN--capped CdSe QDs. Comparative analysis with studies on CdS QDs unveils intriguing insights into the coordination behavior and passivation efficacy of SCN- ions on Cd2+ rich QD surfaces. Our results reveal the requirement of both surface-bound (strong binding) and weakly-interacting interfacial SCN- ions for effective CdSe QD passivation. Beyond fostering a deeper understanding of surface-ligand interactions and highlighting the importance of a comprehensive exploration of ligand chemistries, this study holds implications for optimizing QD performance across diverse applications.

Ultrafast Dynamics of Self-Trapped Excitons in Cs2AgInCl6:Al3+ Double Perovskite Nanocrystals.

It is a huge challenge to increase the photoluminescence (PL) of lead-free halide perovskites, and understanding the mechanism behind exciton dynamics can provide a valuable solution. Herein, we achieved enhanced broad-band emission at ambient conditions in Cs2AgInCl6 by tuning self-trapped excitons (STEs) through Al3+ doping. Cryogenic measurements showed an inhomogeneous nature of STE emission due to the presence of defect states and is subject to thermal quenching. An increased Huang-Rhys factor (S-factor) resulted in better electron-phonon coupling and high-density STE states post Al3+ doping. Femtosecond transient absorption (fs-TA) results provided insights into the distribution dynamics of excitons, which occurs through gradient energy levels from free excitons (FE) to STEs, where each STE state potentially possesses higher quantized energy states. Overall, this study aims to comprehend the origins of self-trapping and decay of STEs in Cs2AgInCl6:Al3+ and emphasizes the potential of compositional engineering to mitigate self-trapping in this material.

Prevention of ion migration in lead halide perovskites upon plugging the anion vacancies with PbSe islands.

To circumvent the issue of halide ion exchange in perovskites, we have decorated CsPbBr3 and CsPbI3 nanocrystals with different sized PbSe nanoparticles and demonstrated that it effectively prevents anion exchange reaction in CsPbBr3/CsPbI3 nanoheterostructures (NHSs) as a consequence of halide vacancy passivation by the more covalent selenide anion.

On the unique temperature-dependent interplay of a B-exciton and its trion in monolayer MoSe2.

Plasmonics in metal nanoparticles can enhance their near field optical interaction with matter, promoting emission into selected optical modes. Here, using Ga nanoparticles with carefully tuned plasmonic resonance in proximity to MoSe2 monolayers, we show selective photoluminescence enhancement from the B-exciton and its trion with no observable A-exciton emission. The nanoengineered substrate allows for the first direct experimental observation of the B-trion binding energy in semiconducting monolayers. Using temperature-dependent photoluminescence measurements, we show the following features of the MoSe2 B-exciton family: (i) the trion binding energy has an observable temperature dependence with a decreasing trend towards low temperatures and (ii) the exciton-trion emission ratio varies non-monotonically with temperature with a steep increase in the trion emission at lower temperatures. Using detailed models, we identify the particle size required for selective excitation and describe the underlying physical processes. This opens newer avenues for selectively promoting excitonic species and tuning the effective particle lifetimes in monolayer semiconductors. These results demonstrate the excellent plasmonic properties of Ga nanoparticles, which along with facile processing techniques makes it an attractive alternative to the prevalent noble metal plasmonics having applications in flexible/stretchable materials and textiles.

Nano-Formulation of Antioxidants as Effective Inhibitors of γD-Crystallin Aggregation.

The aggregation of crystallin proteins is related to cataracts and age-related macular degeneration. Apart from surgical replacement of the cataract lens, no other alternative treatment is available till date for this ailment. In the current work, we carried out an in-depth investigation of the effect of polyphenol-loaded nano-formulations on the aggregation of γD-crystallin. At first, the protein was allowed to form amorphous aggregates under denaturing conditions. Several polyphenols were then tried to inhibit the aggregation of the protein. Among the polyphenols tested, resveratrol and quercetin were found to be the most effective. Since polyphenols are prone to degradation, they were encapsulated in chitosan nanoparticles in order to provide ambient conditions for them to function effectively. The loading efficiency and polyphenol release kinetics were subsequently tested. Finally, the efficacy of resveratrol/quercetin-loaded chitosan nano-particles as inhibitors of γD-crystallin aggregation was confirmed in a series of experiments demonstrating the potency of the system in the prospective therapeutic intervention of eye ailments concerning self-assembly of γD-crystallin proteins.

Hesperidin: A Potential Therapeutic Agent against COVID-19.

COVID-19, aka Coronavirus Disease 2019, triggered by new severe acute respiratory syndrome coronavirus-2 or SARS-CoV-2, is now a public health emergency due to its rapid spread, high transmission efficiency, and severe viral pandemic that is significantly increasing the number of patients and associated deaths. Currently, no specific treatment is available for this highly contagious virus. The unavailability of effective and specific treatments and the severity of this epidemic situation potentiate medicinal chemists' in supporting new prophylactic or therapeutic interventions against COVID-19. This study discusses the therapeutic potential of hesperidin, a traditionally used herbal medicine with an exceptional safety profile. Recent studies on hesperidin advocate its promising potential in the prevention and management of COVID-19. This paper also discusses the recent clinical studies based on the previously documented antiviral activity of hesperidin. Herein, we propose the detailed preclinical and clinical manifestations of hesperidin based on its multifaceted bioactivities to develop a novel anti-COVID-19 lead.

Doping Mn2+in hybrid Ruddlesden-Popper phase of layered double perovskite (BA)4AgBiBr8.

The layered hybrid double perovskites emerged as excellent semiconductor materials owing to their environment compatibility and stability. However, these materials are weakly luminescent, and their photoluminescence (PL) properties can be modulated via doping. While Mn2+doping in perovskites is well known, but to the best of our knowledge the doping of Mn2+in layered double perovskites (LDPs) is yet to be explored. Herein, for the first time, we demonstrate the doping of Mn2+in hybrid inorganic-organic two-dimensional (2D) LDPs, (BA)4AgBiBr8(BA = n-butyl amine) via a simple solid-state mechanochemical route. The powder x-ray diffraction pattern, and electron paramagnetic resonance analysis confirm the successful incorporation of Mn2+ions inside (BA)4AgBiBr8lattice. The Mn2+doped 2D LDP shows energy transfer from host excitons to d-electrons of Mn2+ions, which results in red-shifted broad Mn2+emission band centered at 625 nm, attributed to thespin-forbidden4T1to6A1internal transition. This work opens up new possibilities to dope metal ions in 2D LDPs to tune the optical as well as magnetic properties.

Impact of Bifunctional Ligands on Charge Transfer Kinetics in CsPbBr3-CdSe/CdS/ZnS Nanohybrids.

Mixed dimensional nanohybrids (MDNHs) between zero-dimensional (0D) perovskites and two-dimensional (2D) II-VI semiconductors hold great potential for photonic device applications. An in-depth study to understand the shuttling of charge carriers is carried out utilizing bifunctional ligands such as 4-aminothiophenol (4-ATP), p-aminobenzoic acid, and 6-amino-2-naphthoic acid in the synthesis of MDNHs of CsPbBr3 nanocrystals (NCs) and CdSe/CdS/ZnS core/shell/shell (CSS) nanoplatelets (NPLs). These MDNHs form donor-bridge-acceptor systems, where the electronic interaction is greatly influenced by the nature of ligands. The smaller size and stronger binding affinity of 4-ATP to CSS NPLs lead to a faster rate of charge transfer as compared to other linkers. Electronic structure calculations under the framework of density functional theory (DFT) confirms that in 4-ATP capped CSS NPLs, stronger electronic overlap occurs between CSS NPLs and 4-ATP at the valence band maxima (VBM). Furthermore, Poisson distribution modeling proposes that in 4-ATP linked MDNHs, the number of CSS NPLs around CsPbBr3 NCs is highest.

Development of magnetic nanoparticle assisted aptamer-quantum dot based biosensor for the detection of Escherichia coli in water samples.

The contamination of food and potable water with microorganisms may cause food-borne and water-borne diseases. The common contaminants include Escherichia coli (E. coli), Salmonella sp. etc. The conventional methods for monitoring the water quality for the presence of bacterial contaminants are time-consuming, expensive, and not suitable for rapid on-spot detection in field conditions. In the current study, super paramagnetic iron oxide nanoparticles (SPIONs) were synthesized and conjugated with E. coli specific Aptamer I to detect E. coli cells qualitatively as well as quantitatively. The sludge consisting of E. coli- SPION complex was separated via magnetic separation. The presence of E. coli cells was confirmed with the help of standard techniques and confocal laser scanning microscopy (CLSM) employing Aptamer II conjugated CdTe-MPA quantum dots (QDs). Finally, an ATmega 328P prototype biosensor based on Aptamer II conjugated CdTe MPA QDs exhibited quantitative and qualitative abilities to detect E.coli. This prototype biosensor can even detect low bacterial counts (up to 1 × 102 cfu) with the help of a photodiode and plano-convex lens. Further, the prototype biosensor made up of ultraviolet light-emitting diode (UV LED), liquid crystal display (LCD) and ATmega328Pmicrocontroller offers on-spot detection of E.coli in water samples with high resolution and sensitivity. Similarly, this in-house developed prototype biosensor can also be utilized to detect bacterial contamination in food samples.

Insight into morphology dependent charge carrier dynamics in ZnSe-CdS nanoheterostructures.

Semiconductor nanoheterostructures (NHSs) are being increasingly used for the photocatalytic conversion of solar energy in which photo-induced charge separation is an essential step and hence it is necessary to understand the effect of various factors such as size, shape, and composition on the charge transfer dynamics. Ultrafast transient absorption spectroscopy is used to investigate the nature and dynamics of photo-induced charge transfer processes in ZnSe-CdS NHSs of different morphologies such as nanospheres (NSs), nanorods (NRs), and nanoplates (NPs). It demonstrates the fast separation of charge carriers and localization of both charges in adjacent semiconductors, resulting in the formation of a charge-separated (CS) state. The lifetime of the charge-separated state follows the order of NSs < NPs < NRs, emphasizing the effect of morphology on the enhancement of photo-induced charge separation and suppression of backward recombination. The separated charge carriers have been utilized in visible light driven hydrogen production and the hydrogen generation activity follows the same order as that for the lifetime of the CS state, underlining the role of charge separation efficiency. Therefore, the variation of the morphology of NHSs plays a significant role in their charge carrier dynamics and hence the photocatalytic hydrogen production activity.

Enhanced Photocurrent Owing to Shuttling of Charge Carriers across 4-Aminothiophenol-Functionalized MoSe2-CsPbBr3 Nanohybrids.

Mixed-dimensional van der Waals nanohybrids (MvNHs) of two-dimensional transition-metal dichalcogenides (TMDs) and zero-dimensional perovskites are highly promising candidates for high-performance photonic device applications. However, the growth of perovskites over the surface of TMDs has been a challenging task due to the distinguishable surface chemistry of these two different classes of materials. Here, we demonstrate a synthetic route for the design of MoSe2-CsPbBr3 MvNHs using a bifunctional ligand, i.e., 4-aminothiophenol. Close contact between these two materials is established via a bridge that leads to the formation of a donor-bridge-acceptor system. The presence of the small conjugated ligand facilitates faster charge diffusion across MoSe2-CsPbBr3 interfaces. Density functional theory calculations confirm the type-II band alignment of the constituents within the MvNHs. The MoSe2-CsPbBr3 nanohybrids show much higher photocurrent (∼2 × 104-fold photo-to-dark current ratio) as compared to both pure CsPbBr3 nanocrystals and pristine MoSe2 nanosheets owing to the synergistic effect of pronounced light-matter interactions followed by efficient charge separation and transportation. This study suggests the use of a bifunctional ligand to construct a nanohybrid system to tune the optoelectronic properties for potential applications in photovoltaic devices.

Band Gap Engineering in Cs2(NaxAg1-x)BiCl6 Double Perovskite Nanocrystals.

Lead-free double perovskite materials, A2M(I)M'(III)X6, have recently attracted attention as environment-friendly alternatives to lead-based perovskites, APbX3, because of both rich fundamental science and potential applications. We report band gap tuning via alloying of Cs2AgBiCl6 nanocrystals (NCs) with nontoxic, abundant Na. It results in a series of Cs2NaxAg1-xBiCl6 (x = 0, 0.25, 0.5, 0.75, and 1) double perovskite NCs, leading to increase in optical band gap from 3.39 eV (x = 0) to 3.82 eV (x = 1) and 30-fold increment in weak photoluminescence. The tuning of band gap has been further explored by electronic structure calculation under the framework of density functional theory (DFT). The latter confirms that the increase in band gap is due to reduction of Ag contribution near valence band maxima (VBM) on incorporation of Na ion in place of Ag. These alloyed double perovskites can have useful potential applications in optoelectronic devices.

Fluorescence resonance energy transfer in multifunctional nanofibers designed via block copolymer self-assembly.

In the present study, we demonstrate the fabrication of multifunctional nanofibers, loaded with CdSe quantum dots (QDs) and sulforhodamine 101 (S101) dye, via the self-assembly process of a polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) block copolymer (BCP). The CdSe QDs and S101 dye were simultaneously incorporated in the cylindrical domains, constituted of P4VP blocks, of the self-assembled BCP structure. The cylindrical domains subsequently were isolated as individual nanofibers via the selective-swelling approach. The confinement imposed due to the nano-dimension geometry of the cylindrical domains enabled the QDs and S101 dye to localize within their Förster radius enabling an efficient fluorescence resonance energy transfer (FRET) between them. The mean lifetime of donor emission varied from 4.56 to 3.38 ns with the change in the ratio of S101 dye and CdSe QDs within the nanofibers. Furthermore, using efficiency measurements and the corresponding Förster distances, donor-acceptor distances were determined. Moreover, the kinetics of energy transfer from CdSe QDs to S101 was studied by the Poisson binding model, to understand the interactions between CdSe QDs and S101 dye molecules. The numbers of dye molecules per CdSe QD were determined, by assuming random distribution of S101 dye molecules around the CdSe QDs in the nanofibers. The results showed that the number of dye molecules per QD increased with increasing concentration of dye molecules in the nanofibers. The resulting multifunctional nanofibers could have potential applications in optoelectronics, photonics and sensors which utilize the FRET process.

MoSe2-Cu2S Vertical p-n Nanoheterostructures for High-Performance Photodetectors.

Heterostructures based on atomically thin two-dimensional layered transition metal dichalcogenides are highly promising for optoelectronic device applications owing to their tunable optical and electronic properties. However, the synthesis of heterostructures with desired materials having proper interfacial contacts has been a challenging task. Here, we develop a colloidal synthetic route for the design of MoSe2-Cu2S nanoheterostructures, where the Cu2S islands grow vertically on top of the defect sites present on the MoSe2 surface, thereby forming a vertical p-n junction having plasmonic characteristics. These MoSe2-Cu2S nanoheterostructures are used to fabricate photodetectors with superior photoresponse characteristics. The fabricated device exhibits a broad-band spectral photoresponse over the visible to near-infrared range with a peak responsivity of 410 mA W-1 at -2.0 V and over 3000-fold photo-to-dark current ratio. The superior device performance of MoSe2-Cu2S over only MoSe2 devices is due to the combined effect of the formation of the p-n junction, pronounced light-matter interactions, and passivation of surface defects. This study would pave the way for designing a new class of nanoheterostructured materials for their potential applications in next-generation photonic devices.

Nickel Selenide Nanoparticles as a Cheap Alternative for Pt-Counter Electrode in Dye-Sensitized Solar Cells.

Colloidal nickel selenide nanocrystals (NCs) of two different compositions i.e., Ni3Se2 and Ni3Se4, where one is Ni-rich while another is Se-rich are synthesized using the hot injection method by merely changing the injection and growth temperature while keeping the rest of the reaction conditions like solvent, ligands, amount of precursors and reaction time identical. These nanocrystals exhibit electrocatalytic activity in the reduction of triiodide (I-3) to iodide (3I-), therefore employed as counter electrodes (CE) in dye-sensitized solar cells (DSCs). The DSC based on nickel selenides displays an efficiency of 6.4%, comparable to the Pt-based cells prepared by us.

Evaluation of remineralization potential and mechanical properties of pit and fissure sealants fortified with nano-hydroxyapatite and nano-amorphous calcium phosphate fillers: An in vitro study.

OBJECTIVES: The aim of this study was: (i) to formulate pit and fissure sealants (PFS) containing nano-hydroxyapatite (nHAP) filler; nHAP filler and silica co-filler; nHAP and nano-Amorphous Calcium Phosphate (nACP) co-filler, (ii) to evaluate physical properties; degree of conversion (DOC), curing depth (CD) and mechanical properties; microshear bond strength (MBS) of fortified PFS, and (iii) to assess remineralization potential and release of Ca2= and PO4 ions from newly synthesized sealants. MATERIALS AND METHODS: Four PFS were prepared using monomers with mixture of 35.5 wt % BisGMA, 35.5 wt % triethylene glycol dimethacrylate and 28 wt % hydroxyethyl methacrylate. Bioactive nanofillers (nHAP and n-ACP) were added in various concentrations (0%-30%). Three commercial sealants were used as follows: unfilled (Clinpro; 3M ESPE), Fluoride releasing (Delton FS plus, Dentsply), ACP filled (Aegis, Bosworth). The samples (n = 35.5/gp) were tested for MBS, DOC, and CD. Remineralization potential was assessed by scanning electron microscopy (SEM). The concentrations of Ca2= and PO4 released from the sealant specimens were analyzed with Ultraviolet-visible Spectrophotometer. Data obtained was statistically analyzed (one-way analysis of variance, Tukey's test, P < 0.05). RESULTS: 10% hydroxyapatite (HAP) =20% ACP sealant showed significantly higher DOC. A remineralized region on the surface between fissure sealant and tooth enamel was observed by SEM in all three HAP filled bioactive sealants. Decreasing the solution pH significantly increased ion release from sealant filled with 10% nHAP = 20% nACP (P ≤ 0.001). CONCLUSION: Results suggested that admixture of nHAP and nACP to PFS showed remineralizing capability, without declining their mechanical and physical properties.

Facile Green Synthesis of BiOBr Nanostructures with Superior Visible-Light-Driven Photocatalytic Activity.

Novel green bismuth oxybromide (BiOBr-G) nanoflowers were successfully synthesized via facile hydrolysis route using an Azadirachta indica (Neem plant) leaf extract and concurrently, without the leaf extract (BiOBr-C). The Azadirachta indica leaf extract was employed as a sensitizer and stabilizer for BiOBr-G, which significantly expanded the optical window and boosted the formation of photogenerated charge carriers and transfer over the BiOBr-G surface. The photocatalytic performance of both samples was investigated for the degradation of methyl orange (MO) and phenol (Ph) under the irradiation of visible light. The leaf extract mediated BiOBr-G photocatalyst displayed significantly higher photocatalytic activity when compared to BiOBr-C for the degradation of both pollutants. The degradation rate of MO and Ph by BiOBr-G was found to be nearly 23% and 16% more when compared to BiOBr-C under visible light irradiation, respectively. The substantial increase in the photocatalytic performance of BiOBr-G was ascribed to the multiple synergistic effects between the efficient solar energy harvesting, narrower band gap, high specific surface area, porosity, and effective charge separation. Furthermore, BiOBr-G displayed high stability for five cycles of photocatalytic activity, which endows its practical application as a green photocatalyst in the long run.

Tuning the Electronic and Magnetic Properties of CuAlO2 Nanocrystals Using Magnetic Dopants.

Optoelectronic applications with transparent conducting oxides have been made possible by modulating the carrier density of wide band gap oxides with doping. We demonstrate the modulation of the density of states (DOS) at the Fermi level in nanocrystalline CuAlO2 particles synthesized using a sol-gel technique, as a function of doping with a magnetic impurity (Ni). This behavior is directly correlated with structural studies using X-ray diffraction and magnetic properties which show a similar trend. Our results can be understood in a picture where charge hopping occurs through surface or defect states, rather than by direct hopping between the quantum-confined states of the nanocrystal, and an increase in the DOS at the Fermi level caused by the substitution of Ni atoms at the Al site.

Biofabricated BiOI with enhanced photocatalytic activity under visible light irradiation.

In the recent past, there has been a large-scale utilization of plant extracts for the synthesis of various photocatalysts. The biofabrication technology eliminates the usage of harmful chemicals and serves as an eco-friendly approach for environmental remediation. Herein, a comparative analysis between bismuth oxyiodide synthesized via Azadirachta indica (neem) leaf extract (BiOI-G) and without leaf extract (BiOI-C) has been envisaged. The BiOI-G and BiOI-C samples were characterized by spectral and microscopic techniques, which revealed that the Azadirachta indica assisted BiOI-G attained enhanced features over BiOI-C such as narrower band gap, large surface area, porosity, increased absorption range of visible light and effectual splitting of the photogenerated e--h+ pairs. Benefiting from these enhanced features, BiOI-G degraded methyl orange (MO), rhodamine B (RhB), and benzotriazole (BT) at a significantly higher rate in comparison to BiOI-C. The degradation rate of MO, RhB and BT by BiOI-G was observed to be 1.3, 1.25 and 1.29 times higher in comparison to BiOI-C. Moreover, BiOI-G displayed high stability upto five cycles of the photocatalytic activity, which endow its effectiveness as a highly-efficient green photocatalyst.

Functionalized 2D-MoS2-Incorporated Polymer Ternary Solar Cells: Role of Nanosheet-Induced Long-Range Ordering of Polymer Chains on Charge Transport.

In this paper, we demonstrated the enhancement in power conversion efficiency (PCE) of solar cells based on poly(3-hexylthiophene-2,5-diyl) (P3HT)/[6,6]-phenyl C71 butyric acid methyl ester (PC71BM) by incorporation of functionalized 2D-MoS2 nanosheets (NSs) as an additional charge-transporting material. The enhancement in PCE of ternary solar cells arises due to the synergic enhancement in exciton dissociation and the improvement in mobility of both electrons and holes through the active layer of the solar cells. The improved hole mobility is attributed to the formation of the long-range ordered nanofibrillar structure of polymer phases and improved crystallinity in the presence of 2D-MoS2 NSs. The improved electron mobility arises due to the highly conducting 2D network of MoS2 NSs which provides additional electron transport channels within the active layer. The nanosheet-incorporated ternary blend solar cells exhibit 32% enhancement in PCE relative to the binary blend P3HT/PC71BM.