Efficient Charge-Transfer Studies for Selective Detection of Bilirubin Biomolecules Using CsPbBr3 as the Fluorescent Probe.

Bright luminescence hybrid halide perovskite nanocrystals (PNCs) as a novel fluorophore class have not been broadly explored in biological sensing. Herein, we synthesized highly fluorescent CsPbBr3 PNCs through the LARP method using oleic acid and oleyl amine as capping ligands. Morphological and optical properties of as-synthesized PNCs were studied using transmission electron microscopy, X-ray diffraction, UV-vis, and emission spectroscopic analysis. Oleic acid- and oleyl amine-capped PNCs are employed for sensitive and selective detection of bilirubin (BR). A panel of characterizations (time-correlated single-photon count spectroscopy and photoluminescence (PL)) was carried out to investigate the detailed sensing study of PNCs-BR composite for quenching the PL emission of CsPbBr3 with BR. It has been noticed that the synthesized nanoparticles are highly capable of detecting BR and thus act as a biological material sensor.

Air stable highly luminescent 2D tin halide perovskite nanocrystals as photodetectors.

Hybrid and inorganic perovskite nanocrystals are a hot topic in materials chemistry due to their versatile optoelectronic properties. Herein, we report highly luminescent water stable lead-free orange emissive (OleylAm)2SnBr4 (OleylAm = oleylammonium cation) 2D tin halide perovskite nanocrystals in humid conditions in a solution-based process. The photoresponse study performed with the synthesized nanocrystals exhibits a responsivity of 4.9 mA W-1 at a 5 V operating voltage.

Efficient charge transfer from organometal lead halide perovskite nanocrystals to free base meso-tetraphenylporphyrins.

The efficient charge transfer from methylammonium lead halide, MAPbX3 (X = Br, I), perovskite nanocrystals (PNCs) to 5,10,15,20-tetraphenylporphyrin (TPP) molecules has been investigated in detail. The hydrophobically-capped MAPbX3 PNCs exhibited bright fluorescence in the solution state. However, in the presence of TPP, the fluorescence intensity was quenched, which is ascribed to the electron transfer from the PNCs to TPP. Photoluminescence (PL) spectroscopy and absolute quantum yield measurements were used to evaluate the fluorescence quenching. This efficient fluorescence quenching leads to an increase in the quenching efficiency value. The quenching of fluorescence intensity is not attributed to the change in lifetime, as evidenced by time-correlated single-photon counting (TCSPC) measurements, suggesting a static electron transfer from the PNCs to TPP molecules. Such a static fluorescence quenching corresponds to the adsorption of TPP onto the surface of hydrophobic PNCs, and has been examined via transmission electron microscopy (TEM). Cyclic voltammetry (CV) studies were used to compare the PNCs and PNCs@TPP nanocomposites, revealing that the electron transfer process takes place from the PNCs to the organic acceptor TPP molecules.

Aromatic Amino Acid-Mediated Perovskite Nanocrystals: Fluorescence Tuning and Morphological Evolution.

Lead halide perovskites with high fluorescent and tunable morphology appeared at the forefront of materials chemistry because of their corresponding impressive optoelectronic properties. The current advancement of metal halide perovskites put forward the functional and bidentate ligand to expand their utilization in modified ligand chemistry. We successfully introduced nontoxic aromatic amino acid as a capping ligand to synthesize the perovskite nanocrystals (PNCs). The implementation of aromatic amino acid for the construction of CsPbX3 nanocrystals (NCs) provides the synergetic service of the carboxylic and amine groups with the phenyl residue, which prompts the formation of NCs with high fluorescence intensity. The experimental results demonstrate the emissive property of PNCs in a whole visible region with long-term stability. Additionally, the morphology of the NCs has been tuned. We performed several characterization techniques to investigate the nature of the NCs in the solid and solution phases.

Significant boost of the stability and PLQYof CsPbBr3 NCs by Cu-BTC MOF.

Developing stable perovskite nanocrystals (NCs) with enhancing luminescent properties holds great importance for future potential applications in optoelectronics. Here, we engaged perovskite NCs in Cu2+ ion-based metal-organic framework (MOF) Cu-BTC (BTC = 1,3,5-benzene tricarboxylate) by physical mixing of MOF with CsPbBr3 NCs in toluene solution. MOF-protected perovskite NCs achieved high photoluminescence quantum yield 96.51% than pristine state CsPbBr3 NCs (51.66%). Along with the improvement in optical properties, the long-term stability of CsPbBr3 NCs in the solution phase also increases considerably upon loading in Cu-BTC MOF. Moreover, the changes in the luminescent intensity of the samples have been observed for 3 months in the solution. After 1 month, pristine CsPbBr3 NCs lose their emission intensity 68% from the initial, while the MOF-protected CsPbBr3 NCs show only a 10% reduction from the initial. These results indicate that the effective passivation of Cu-BTC MOF inhibits the aggregation of NCs, protecting them from the defective atmosphere. The excellent photoluminescence findings provide a new pathway for future optoelectronic applications.

Antibacterial and Antiviral Functional Materials: Chemistry and Biological Activity toward Tackling COVID-19-like Pandemics.

The ongoing worldwide pandemic due to COVID-19 has created awareness toward ensuring best practices to avoid the spread of microorganisms. In this regard, the research on creating a surface which destroys or inhibits the adherence of microbial/viral entities has gained renewed interest. Although many research reports are available on the antibacterial materials or coatings, there is a relatively small amount of data available on the use of antiviral materials. However, with more research geared toward this area, new information is being added to the literature every day. The combination of antibacterial and antiviral chemical entities represents a potentially path-breaking intervention to mitigate the spread of disease-causing agents. In this review, we have surveyed antibacterial and antiviral materials of various classes such as small-molecule organics, synthetic and biodegradable polymers, silver, TiO2, and copper-derived chemicals. The surface protection mechanisms of the materials against the pathogen colonies are discussed in detail, which highlights the key differences that could determine the parameters that would govern the future development of advanced antibacterial and antiviral materials and surfaces.

Investigating the property of water driven lead-free stable inorganic halide double perovskites.

Lead free halide double perovskite materials, A2BB́X6 (where A, B and B́ are cations and X is a halide anion) have achieved considerable attention in the field of optoelectronic devices due to their high thermal along with the moisture stability and less toxicity as lead halide perovskites suffer from the stability and toxicity issues which inhibit them to be commercialized. Therefore, synthesis of low cost and stable perovskite materials are the main focus of perovskite family nowadays. Herein, we have reported lead free Cs2AgBiCl6 and Cs2AgBiBr6 double perovskite microcrystals in both organic and a mixture of the aqueous-organic medium. Our studies are not only eradicating the toxicity of lead but also explored towards the stability of perovskite materials in the aqueous medium. Morphology is investigated using SEM and TEM imaging along with the enhancement in emission peak by increasing the content of water.

Aqueous Precursor Induced Morphological Change and Improved Water Stability of CsPbBr3 Nanocrystals.

In the literature, lead halide perovskites are very notable for their degradation in the presence of polar solvents, such as water. In contrast, in this research, it is observed that adding a minor amount of water into the precursor solution can improve the stability and photoluminescence quantum yield of CsPbBr3 nanocrystals through a ligand-assisted reprecipitation (LARP) method. In this way, the shape and phase transformation from CsPbBr3 nanoplates to CsPbBr3 /Cs4 PbBr6 nanorods and Cs4 PbBr6 nanowires can be controlled with increasing water content in the precursor solution. Upon adding water up to an ideal amount, CsPbBr3 maintains its phase and nanoplate morphology. The key role of water amount for tuning the crystallinity, stability, morphology, optical properties, and phase transformation of cesium lead halide perovskite nanocrystals will be beneficial in the future commercialization of optoelectronics.

Charge transfer between lead halide perovskite nanocrystals and single-walled carbon nanotubes.

A charge transfer study between lead halide-based perovskite nanocrystals and single-walled carbon nanotubes (PNC@CNT nanocomposite) was performed. Solution-processed MAPbX3 PNCs displayed very bright luminescence, but it quenched in the presence of CNTs. This was attributed to the electron transfer from PNCs to CNTs. The detailed changes in fluorescence lifetime were investigated through time-correlated single-photon counting (TCSPC), which suggested mixed static and dynamic quenching along with a decrease in the lifetime. Morphological changes were investigated via transmission electron microscopy (TEM) and attributed to the incorporation of PNCs on long CNTs. Also, the PNC@CNT nanocomposite was explored for photoinduced current response, which indicated an ∼3 fold increase in photoconductivity under light illumination (with a 1 mV bias). This electron transfer study between PNCs and CNTs contributes to the exploration of charge dynamics.

Nitrate Ion-Incorporated Stable Perovskite Nanocrystals by a Solvent-Free Mechanochemical Reaction.

We have synthesized a new class of organolead halide perovskite nanocrystals by a solvent-free mechanochemical green approach. We have developed a new combination of precursor by incorporating nitrate ions into the MAPbBr3 perovskite core. While the presence of nitrate ion is evidenced by Fourier-transform infrared spectra, X-ray diffraction data shows the formation of perovskite nanocrystals. By altering the precursor composition, the morphology of the nanocrystals changes. Photoluminescence properties of these nanocrystals are preserved. Moreover, the stability of these nanocrystals is monitored for a long time, which shows that the incorporation of nitrate ions into the perovskite nanocrystal core does not have any decremental effect on its stability. Nonetheless, this strategy to synthesize perovskite nanocrystals reduces the solvent toxicity.

Ultralong micro-belts of luminescent lead halide-based perovskites.

Ultralong micro-belts of MAPbI3 show bright and stable fluorescence in solution. Luminescent perovskites have been synthesized through centrifugation of a solution processed with a ligand-assisted reprecipitation technique (LARP). All electron spectroscopic analysis provided evidence for stacking of nanocrystals as bundles of self-assembled micro-belts. Under an applied bias, migration of free charge carriers through the long axis is feasible. Thus, long micro-belts are promising channel materials for two-electrode nanodevices for good electrical conductivity.

Surface modulation of solution processed organolead halide perovskite quantum dots to large nanocrystals integrated with silica gel G.

We demonstrated a facile method to grow organometal halide perovskite quantum dots in a solid silica matrix. The photoluminescence measurements of the MAPbBr3 quantum dots and corresponding large particles show a shift from blue to green emission with morphological changes. The nanocrystals impregnated on the silica matrix improve the stability and may be useful as functional materials in all solid state light emitting devices.

In-Situ Hydrothermal Synthesis of Bi-Bi2O2CO3 Heterojunction Photocatalyst with Enhanced Visible Light Photocatalytic Activity.

Bismuth containing nanomaterials recently received increasing attention with respect to environmental applications because of their low cost, high stability and nontoxicity. In this work, Bi-Bi2O2CO3 heterojunctions were fabricated by in-situ decoration of Bi nanoparticles on Bi2O2CO3 nanosheets via a simple hydrothermal synthesis approach. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and high-resolution TEM (HRTEM) were used to confirm the morphology of the nanosheet-like heterostructure of the Bi-Bi2O2CO3 composite. Detailed ultrafast electronic spectroscopy reveals that the in-situ decoration of Bi nanoparticles on Bi2O2CO3 nanosheets exhibit a dramatically enhanced electron-hole pair separation rate, which results in an extraordinarily high photocatalytic activity for the degradation of a model organic dye, methylene blue (MB) under visible light illumination. Cycling experiments revealed a good photochemical stability of the Bi-Bi2O2CO3 heterojunction under repeated irradiation. Photocurrent measurements further indicated that the heterojunction incredibly enhanced the charge generation and suppressed the charge recombination of photogenerated electron-hole pairs.

A novel nanohybrid for cancer theranostics: folate sensitized Fe2O3 nanoparticles for colorectal cancer diagnosis and photodynamic therapy.

Organic-inorganic nanohybrids are becoming popular for their potential biological applications, including diagnosis and treatment of cancerous cells. The motive of this study is to synthesise a nanohybrid for the diagnosis and therapy of colorectal cancer. Here we have developed a facile and cost-effective synthesis of folic acid (FA) templated Fe2O3 nanoparticles with excellent colloidal stability in water using a hydrothermal method for the theranostics applications. The attachment of FA to Fe2O3 was confirmed using various spectroscopic techniques including FTIR and picosecond resolved fluorescence studies. The nanohybrid (FA-Fe2O3) is a combination of two nontoxic ingredients FA and Fe2O3, showing remarkable photodynamic therapeutic (PDT) activity in human colorectal carcinoma cell lines (HCT 116) via generation of intracellular ROS. The light induced enhanced ROS activity of the nanohybrid causes significant nuclear DNA damage, as confirmed from the comet assay. Assessment of p53, Bax, Bcl2, cytochrome c (cyt c) protein expression and caspase 9/3 activity provides vivid evidence for cell death via an apoptotic pathway. In vitro magnetic resonance imaging (MRI) experiments in folate receptor (FR) overexpressed cancer cells (HCT 116) and FR deficient human embryonic kidney cells (HEK 293) reveal the target specificity of the nanohybrid towards cancer cells, and are thus pronounced MRI contrasting agents for the diagnosis of colorectal cancer.

Facile synthesis of reduced graphene oxide-gold nanohybrid for potential use in industrial waste-water treatment.

Here, we report a facile approach, by the photochemical reduction technique, for in situ synthesis of Au-reduced graphene oxide (Au-RGO) nanohybrids, which demonstrate excellent adsorption capacities and recyclability for a broad range of dyes. High-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) data confirm the successful synthesis of Au-RGO nanohybrids. The effect of several experimental parameters (temperature and pH) variation can effectively control the dye adsorption capability. Furthermore, kinetic adsorption data reveal that the adsorption process follows a pseudo second-order model. The negative value of Gibbs free energy (ΔG0) confirms spontaneity while the positive enthalpy (ΔH0) indicates the endothermic nature of the adsorption process. Picosecond resolved fluorescence technique unravels the excited state dynamical processes of dye molecules adsorbed on the Au-RGO surface. Time resolved fluorescence quenching of Rh123 after adsorption on Au-RGO nanohybrids indicates efficient energy transfer from Rh123 to Au nanoparticles. A prototype device has been fabricated using Au-RGO nanohybrids on a syringe filter (pore size: 0.220 µm) and the experimental data indicate efficient removal of dyes from waste water with high recyclability. The application of this nanohybrid may lead to the development of an efficient reusable adsorbent in portable water purification.

Carbon nanoparticles for ferric ion detection and novel HFCNs-Fe3+ composite for NH3 and F- estimation based on a "TURN ON" mechanism.

In this study we have synthesised and characterised hollow fluorescent carbon nanoparticle (HFCNs) and solid fluorescent carbon nanoparticle (SFCNs) separately using Syzygium cumini extract via a self-catalysis method in large scale for commercialization without providing any external heat. The characterisation of both HFCNs and SFCNs was performed by employing various techniques like UV-Vis, PL, IR, Raman, XPS, TCSPC, FESEM and TEM. The hollow interior of the HFCNs was corroborated by the TEM images. The average particle size distribution of the HFCNs was ∼20-40 nm and their pore size was ∼10-15 nm while the average particle size distribution range of the SFCNs was ∼12 nm. We have further extended our study by exploring the application of the as-synthesised CNs as excellent bio-imaging agents with appreciable cell viability. In addition, the produced CNs were shown to be excellent when applied as fluorescent ink for security purposes. The CNs were also shown to be excellent nanoprobes for Fe3+ ion detection via a "TURN-OFF" mechanism. Furthermore, we utilized the CNs-Fe3+ nanocomposite as a novel nanoprobe for the detection of NH3 and F- using the promising nano carrier ability of the CNs based on a "TURN-ON" mechanism.

Enhanced Charge Separation and FRET at Heterojunctions between Semiconductor Nanoparticles and Conducting Polymer Nanofibers for Efficient Solar Light Harvesting.

Energy harvesting from solar light employing nanostructured materials offer an economic way to resolve energy and environmental issues. We have developed an efficient light harvesting heterostructure based on poly(diphenylbutadiyne) (PDPB) nanofibers and ZnO nanoparticles (NPs) via a solution phase synthetic route. ZnO NPs (~20 nm) were homogeneously loaded onto the PDPB nanofibers as evident from several analytical and spectroscopic techniques. The photoinduced electron transfer from PDPB nanofibers to ZnO NPs has been confirmed by steady state and picosecond-resolved photoluminescence studies. The co-sensitization for multiple photon harvesting (with different energies) at the heterojunction has been achieved via a systematic extension of conjugation from monomeric to polymeric diphenyl butadiyne moiety in the proximity of the ZnO NPs. On the other hand, energy transfer from the surface defects of ZnO NPs (~5 nm) to PDPB nanofibers through Förster Resonance Energy Transfer (FRET) confirms the close proximity with molecular resolution. The manifestation of efficient charge separation has been realized with ~5 fold increase in photocatalytic degradation of organic pollutants in comparison to polymer nanofibers counterpart under visible light irradiation. Our results provide a novel approach for the development of nanoheterojunctions for efficient light harvesting which will be helpful in designing future solar devices.

Direct observation of key photoinduced dynamics in a potential nano-delivery vehicle of cancer drugs.

In recent times, significant achievements in the use of zinc oxide (ZnO) nanoparticles (NPs) as delivery vehicles of cancer drugs have been made. The present study is an attempt to explore the key photoinduced dynamics in ZnO NPs upon complexation with a model cancer drug protoporphyrin IX (PP). The nanohybrid has been characterized by FTIR, Raman scattering and UV-Vis absorption spectroscopy. Picosecond-resolved Förster resonance energy transfer (FRET) from the defect mediated emission of ZnO NPs to PP has been used to study the formation of the nanohybrid at the molecular level. Picosecond-resolved fluorescence studies of PP-ZnO nanohybrids reveal efficient electron migration from photoexcited PP to ZnO, eventually enhancing the ROS activity. The dichlorofluorescin (DCFH) oxidation and no oxidation of luminol in PP/PP-ZnO nanohybrids upon green light illumination unravel that the nature of ROS is essentially singlet oxygen rather than superoxide anions. Surface mediated photocatalysis of methylene blue (MB) in an aqueous solution of the nanohybrid has also been investigated. Direct evidence of the role of electron transfer as a key player in enhanced ROS generation from the nanohybrid is also clear from the photocurrent measurement studies. We have also used the nanohybrid in a model photodynamic therapy application in a light sensitized bacteriological culture experiment.

Impact of metal ions in porphyrin-based applied materials for visible-light photocatalysis: key information from ultrafast electronic spectroscopy.

Protoporphyrin IX-zinc oxide (PP-ZnO) nanohybrids have been synthesized for applications in photocatalytic devices. High-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), and steady-state infrared, absorption, and emission spectroscopies have been used to analyze the structural details and optical properties of these nanohybrids. Time-resolved fluorescence and transient absorption techniques have been applied to study the ultrafast dynamic events that are key to photocatalytic activities. The photocatalytic efficiency under visible-light irradiation in the presence of naturally abundant iron(III) and copper(II) ions has been found to be significantly retarded in the former case, but enhanced in the latter case. More importantly, femtosecond (fs) transient absorption data have clearly demonstrated that the residence of photoexcited electrons from the sensitizer PP in the centrally located iron moiety hinders ground-state bleach recovery of the sensitizer, affecting the overall photocatalytic rate of the nanohybrid. The presence of copper(II) ions, on the other hand, offers additional stability against photobleaching and eventually enhances the efficiency of photocatalysis. In addition, we have also explored the role of UV light in the efficiency of photocatalysis and have rationalized our observations from femtosecond- to picosecond-resolved studies.

Photosensitization of nanoparticulate TiO2 using a Re(I)-polypyridyl complex: studies on interfacial electron transfer in the ultrafast time domain.

We have synthesized a new photoactive rhenium(i)-complex having a pendant catechol functionality [Re(CO)(3)Cl(L)] (1) (L is 4-[2-(4'-methyl-2,2'-bipyridinyl-4-yl)vinyl]benzene-1,2-diol) for studying the dynamics of the interfacial electron transfer between nanoparticulate TiO(2) and the photoexcited states of this Re(i)-complex using femtosecond transient absorption spectroscopy. Our steady state absorption studies revealed that complex 1 can bind strongly to TiO(2) surfaces through the catechol functionality with the formation of a charge transfer (CT) complex, which has been confirmed by the appearance of a new red-shifted CT band. The longer wavelength absorption band for 1, bound to TiO(2) through the proposed catecholate functionality, could also be explained based on the DFT calculations. Dynamics of the interfacial electron transfer between 1 and TiO(2) nanoparticles was investigated by studying kinetics at various wavelengths in the visible and near infrared regions. Electron injection into the conduction band of the nanoparticulate TiO(2) was confirmed by detection of the conduction band electron in TiO(2) ([e(-)](TiO(2)(CB))) and the cation radical of the adsorbed dye (1˙(+)) in real time as monitored by transient absorption spectroscopy. A single exponential and pulse-width limited (<100 fs) electron injection was observed. Back electron transfer dynamics was determined by monitoring the decay kinetics of 1˙(+) and .