Colloidal metal‐halide perovskite nanocrystals (MHP NCs) are gaining significant attention for a wide range of optoelectronics applications owing to their exciting properties, such as defect ...tolerance, near‐unity photoluminescence quantum yield, and tunable emission across the entire visible wavelength range. Although the optical properties of MHP NCs are easily tunable through their halide composition, they suffer from light‐induced halide phase segregation that limits their use in devices. However, MHPs can be synthesized in the form of colloidal nanoplatelets (NPls) with monolayer (ML)‐level thickness control, exhibiting strong quantum confinement effects, and thus enabling tunable emission across the entire visible wavelength range by controlling the thickness of bromide or iodide‐based lead‐halide perovskite NPls. In addition, the NPls exhibit narrow emission peaks, have high exciton binding energies, and a higher fraction of radiative recombination compared to their bulk counterparts, making them ideal candidates for applications in light‐emitting diodes (LEDs). This review discusses the state‐of‐the‐art in colloidal MHP NPls: synthetic routes, thickness‐controlled synthesis of both organic–inorganic hybrid and all‐inorganic MHP NPls, their linear and nonlinear optical properties (including charge‐carrier dynamics), and their performance in LEDs. Furthermore, the challenges associated with their thickness‐controlled synthesis, environmental and thermal stability, and their application in making efficient LEDs are discussed.
This review provides a comprehensive overview of the research progress and challenges associated with thickness‐controlled synthesis, stability, surface passivation, doping, optical (linear and nonlinear) properties of both organic and organic–inorganic hybrid lead and lead‐free halide perovskite nanoplatelets along with recent progress on their application to light‐emitting diodes.
This work focuses on the systematic investigation of the shape, size, and composition‐controlled synthesis of perovskite nanocrystals (NCs) under inert gas‐free conditions and using pre‐synthesized ...precursor stock solutions. In the case of CsPbBr3 NCs, we find that the lowering of reaction temperature from ∼175 to 100 °C initially leads to a change of morphology from bulk‐like 3D nanocubes to 0D nanocubes with 3D‐quantum confinement, while at temperatures below 100 °C the reaction yields 2D nanoplatelets (NPls) with 1D‐quantum confinement. However, to our surprise, at higher temperatures (∼215 °C), the reaction yields CsPbBr3 hexapod NCs, which have been rarely reported. The synthesis is scalable, and their halide composition is tunable by simply using different combinations of precursor solutions. The versatility of the synthesis is demonstrated by applying it to relatively less explored shape‐controlled synthesis of FAPbBr3 NCs. Despite the synthesis carried out in the air, both the inorganic and hybrid perovskite NCs exhibit nearly‐narrow emission without applying any size‐selective separation, and it is precisely tunable by controlling the reaction temperature.
The morphology of both inorganic and hybrid halide perovskite nanocrystals is tunable from 3D nanocubes with no‐confinement to 0D nanocubes and 2D nanoplatelets with 3D and 1D‐quantum confinement, respectively by a decrease of the reaction temperature in the hot‐plate approach under inert gas‐free conditions. The synthesis is scalable, and their halide composition is tunable by simply using different combinations of precursor stock solutions.
We describe a simple and efficient methodology for the aqueous synthesis of stable, uniform, and size tunable Au@Ag core–shell nanoparticles (NPs) that are stabilized by citrate ions. The synthetic ...route is based on the stepwise Ag reduction on preformed Au NPs. The final size of the core–shell NPs and therefore their optical properties can be modulated at least from 30 to 110 nm by either tuning the Ag shell thickness or changing the size of the Au core. The optical properties of the Au@Ag core–shell NPs resemble those of pure Ag NPs of similar sizes, which was confirmed by means of Mie extinction calculations. We additionally evaluated the surface-enhanced raman scattering (SERS) enhancing properties of Au@Ag core–shell NP colloids with three different laser lines (532, 633, and 785 nm). Importantly, such core–shell NPs also exhibit a higher SERS efficiency than Ag NPs of similar size under near-infrared excitation. The results obtained here serve as a basis to select Au@Ag core–shell NPs of specific size and composition with maximum SERS efficiency at their respective excitation wavelengths for SERS-based analytical and bioimaging applications.
Chiral transition metal oxide nanoparticles (CTMOs) are attracting a lot of attention due to their fascinating properties. Nevertheless, elucidating the chirality induction mechanism often remains a ...major challenge. Herein, the synthesis of chiral cobalt oxide nanoparticles mediated by histidine (Co3O4@L‐His and Co3O4@D‐His for nanoparticles synthesized in the presence of L‐ and D‐histidine, respectively) is investigated. Interestingly, these CTMOs exhibit remarkable and tunable chiroptical properties. Their analysis by x‐ray photoelectron, Fourier transform infrared, and ultraviolet‐visible absorption spectroscopy indicates that the ratio of Co2+/Co3+ and their interactions with the imidazole groups of histidine are behind their chiral properties. In addition, the use of chiral Co3O4 nanoparticles for the development of sensitive, rapid, and enantioselective circular dichroism‐based sensors is demonstrated, allowing direct molecular detection and discrimination between cysteine or penicillamine enantiomers. The circular dichroism response of the chiral Co3O4 exhibits a limit of detection and discrimination of cysteine and penicillamine enantiomers as low as 10 µm. Theoretical calculations suggest that the ligand exchange and the coexistence of both species adsorbed on the oxide surface are responsible for the enantiomeric discrimination. This research will enrich the synthetic approaches to obtain CTMOs and enable the extension of the applications and the discovery of new chiroptical properties.
The effect of chemical states on the chirality origin and chiroptical activity of chiral cobalt oxide nanoparticles mediated by histidine (Co3O4@His NPs) is investigated theoretically and experimentally. In addition, the chiral Co3O4@His NPs are applied for the enantiomeric discrimination and quantification of cysteine and penicillamine enantiomers.
The synthesis of discrete nanostructures with a strong, persistent, stable plasmonic circular dichroism (PCD) signal is challenging. We report a seed‐mediated growth approach to obtain discrete Au ...nanorods with high and stable chiroptical responses (c‐Au NRs) in the visible to near‐IR region. The morphology of the c‐Au NRs was governed by the concentration of l‐ or d‐cysteine used. The amino acids encapsulated within the discrete gold nanostructure enhance their PCD signal, attributed to coupling of dipoles of chiral molecules with the near‐field induced optical activity at the hot spots inside the c‐Au NRs. The stability of the PCD signal and biocompatibility of c‐Au NRs was improved by coating with silica or protein corona. Discrete c‐Au NR@SiO2 with Janus or core–shell configurations retained their PCD signal even in organic solvents. A side‐by‐side assembly of c‐Au NRs induced by l‐glutathione led to further PCD signal enhancement, with anisotropic g factors as high as 0.048.
Discrete gold nanorods (Au NRs) with strong chiroptical responses in the visible and near infrared region were synthesized by a seed‐mediated approach in the presence of l‐ or d‐cysteine. The chiral Au NRs can be further stabilized by a silica coating (lower pictures). Assembly of the chiral Au NRs (right pictures) with glutathione further improved the g factor.
Most bacteria in nature exist as biofilms, which support intercellular signalling processes such as quorum sensing (QS), a cell-to-cell communication mechanism that allows bacteria to monitor and ...respond to cell density and changes in the environment. As QS and biofilms are involved in the ability of bacteria to cause disease, there is a need for the development of methods for the non-invasive analysis of QS in natural bacterial populations. Here, by using surface-enhanced resonance Raman scattering spectroscopy, we report rationally designed nanostructured plasmonic substrates for the in situ, label-free detection of a QS signalling metabolite in growing Pseudomonas aeruginosa biofilms and microcolonies. The in situ, non-invasive plasmonic imaging of QS in biofilms provides a powerful analytical approach for studying intercellular communication on the basis of secreted molecules as signals.
We studied the controlled growth of triangular prismatic Au nanoparticles with different beveled sides for surface-enhanced Raman spectroscopy (SERS) applications. First, in a seedless synthesis ...using 3-butenoic acid (3BA) and benzyldimethylammonium chloride (BDAC), gold nanotriangles (AuNTs) were synthesized in a mixture with gold nanooctahedra (AuNOCs) and separated by depletion-induced flocculation. Here, the influence of temperature, pH, and reducing agent on the reaction kinetics was initially investigated by UV–vis and correlated to the size and yield of AuNT seeds. In a second step, the AuNT size was increased by seed-mediated overgrowth with Au. We show for the first time that preformed 3BA-synthesized AuNT seeds can be overgrown up to a final edge length of 175 nm and a thickness of 80 nm while maintaining their triangular shape and tip sharpness. The NT morphology, including edge length, thickness, and tip rounding, was precisely characterized in dispersion by small-angle X-ray scattering and in dry state by transmission electron microscopy and field-emission scanning electron microscopy. For sensor purposes, we studied the size-dependent SERS performance of AuNTs yielding analytical enhancement factors between 0.9 × 104 and 5.6 × 104 and nanomolar limit of detection (10–8–10–9 M) for 4-mercaptobenzoic acid and BDAC. These results confirm that the 3BA approach allows the fabrication of AuNTs in a whole range of sizes maintaining the NT morphology. This enables tailoring of localized surface plasmon resonances between 590 and 740 nm, even in the near-infrared window of a biological tissue, for use as colloidal SERS sensing agents or for optoelectronic applications.
Microbes produce bioactive chemical compounds to influence the physiology and growth of their neighbors, and our understanding of their biological activities may be enhanced by our ability to ...visualize such molecules in vivo. We demonstrate here the application of surface-enhanced Raman scattering spectroscopy for simultaneous detection of quorum-sensing-regulated pyocyanin and violacein, produced respectively by Pseudomonas aeruginosa and Chromobacterium violaceum bacterial colonies, grown as a coculture on agar-based plasmonic substrates. Our plasmonic approach allowed us to visualize the expression and spatial distribution of the microbial metabolites in the coculture taking place as a result of interspecies chemical interactions. By combining surface-enhanced Raman scattering spectroscopy with analysis of gene expression we provide insight into the chemical interplay occurring between the interacting bacterial species. This highly sensitive, cost-effective, and easy to implement approach allows spatiotemporal imaging of cellular metabolites in live microbial colonies grown on agar with no need for sample preparation, thereby providing a powerful tool for the analysis of microbial chemotypes.
In recent years, new strategies for silica coating of inorganic nanoparticles and organic nanomaterials, which differ from the classical methodologies, have emerged at the forefront of materials ...science. Silica as a coating material promises an unparalleled opportunity for enhancement of colloidal properties and functions by using core–shell rational designs and profiting from its synthetic versatility. This contribution provides a brief overview of recent progress in the synthesis of silica‐coated nanomaterials and their significant impact in different areas such as spectroscopy, magnetism, catalysis, and biology.
Novel strategies for silica coating of inorganic nanoparticles and organic nanomaterials differ from classical materials science methodologies. Silica is a coating material with unparalleled potential for enhancement of colloidal properties and functions. A brief overview is presented of various methods recently developed for silica coating of nanomaterials and their impact in areas such as spectroscopy, magnetism, catalysis, and biology.
PDF
