"Quasi-two-dimensional (2D) Semiconductor Nanoplatelets manifest strong quantum confinement with exceptional optical characteristics of narrow photoluminescence peaks with energies tunable by thickness with monolayer precision.  We employed scanning tunneling spectroscopy (STS) in conjunction with optical measurements to probe the thickness-dependent band gap and density of excited states in a series of CdSe nanoplatelets. The tunneling spectra, measured in the double-barrier tunnel junction configuration, reveal the effect of quantum confinement on the band gap taking place mainly through a blue-shift of the conduction band edge, along with a signature of 2D electronic structure intermixed with finite lateral-size and/or defects effects. The STS fundamental band gaps are larger than the optical gaps as expected from the contributions of exciton binding in the absorption, as confirmed by theoretical calculations. The calculations also point to strong valence band mixing between the light- and split-off hole levels. Strikingly, the energy difference between the heavy-hole and light-hole levels in the tunneling spectra are significantly larger than the corresponding values extracted from the absorption spectra. Possible explanations for this, including an interplay of nanoplatelet charging, dielectric confinement, and difference in exciton binding energy for light and heavy holes, are analyzed and discussed."

"Quantum Dots Offer Superior Optical Features and hold a great potential as an imaging tool in comparison to ‘conventional’ fluorescent dyes. However, in vivo application in inflammatory-associated disorders is limited due to potential toxicity following systemic administration. Vascular inflammation contributes to cardiovascular diseases such as restenosis (re-narrowing of the artery following angioplasty), and poor  prognosis is associated with the increased number of monocytes-derived macrophages (MDMs) in the arterial wall.  Local administration of a suitable delivery system targeting MDMs could provide effective fluorescent imaging while minimizing systemic exposure and toxicity. We report here on the physicochemical characteristics and the structural stability of MDMs-targeted liposomal QDs (LipQDs), cellular uptake and cytotoxicity, the systemic biodistribution of LipQDs following local intra-luminal administration of LipQDs in carotid-injured rats vs. systemic administration, and imaging of QDs in the arterial tissue. The local treatment with LipQDs was found to be a suitable approach for targeting QDs to MDMs in the injured artery. In contrast to free QDs, the LipQDs formulation exhibited unique properties including structural and fluorescent stability, increased accumulation and retention for up to 24 h, and targeting properties enabling imaging of MDMs. MDMs imaging by targeted nanoparticles (NPs) could potentially serve for the detection of MDMs density in the injured artery for diagnostic purposes."

"Semiconductor heterostructure nanocrystals, especially with core/shell architectures, are important for numerous applications.  Here we show that by decreasing the shell growth rate the morphology of ZnS shells on ZnSe quantum rods can be tuned from flat to islands-like, which decreases the interfacial strain energy. Further reduced growth speed, approaching the thermodynamic limit, leads to coherent shell growth forming unique helical-shell morphology.  This reveals a template-free mechanism for induced chirality at the nanoscale. The helical morphology minimizes the sum of the strain and surface energy and maintains band gap emission due to its coherent core/shell interface without traps, unlike the other morphologies. Reaching the thermodynamic controlled growth regime for colloidal semiconductor core/shell nanocrystals thus offers morphologies with clear impact on their applicative potential."

"The majority of developed and approved anticancer nanomedicines have been designed to exploit the dogma of the enhanced permeability and retention (EPR) effect, which is based on the leakiness of the tumor’s blood vessels accompanied by impeded lymphatic drainage. However, the EPR effect has been under scrutiny recently because of its variable manifestation across tumor types and animal species and its poor translation to human cancer therapy. To facilitate the EPR effect, systemically injected NPs should overcome the obstacle of rapid recognition and elimination by the mononuclear phagocyte system (MPS). We hypothesized that circulating monocytes, major cells of the MPS that infiltrate the tumor, may serve as an alternative method for achieving increased tumor accumulation of NPs, independent of the EPR effect. We describe here the accumulation of liposomal quantum dots (LipQDs) designed for active delivery via monocytes, in comparison to LipQDs designed for passive delivery (via the EPR effect), following IV administration in a mammary carcinoma model. Hydrophilic QDs were synthesized and entrapped in functionalized liposomes, conferring passive (“stealth” NPs; PEGylated, neutral charge) and active (monocyte-mediated delivery; positively charged) properties by differing in their lipid composition, membrane PEGylation, and charge (positively, negatively, and neutrally charged). The various physicochemical parameters affecting the entrapment yield and optical stability were examined in vitro and in vivo. Biodistribution in the blood, various organs, and in the tumor was determined by the fluorescence intensity and Cd analyses. Following the treatment of animals (intact and mammary-carcinoma-bearing mice) with disparate formulations of LipQDs (differing by their lipid composition, neutrally and positively charged surfaces, and hydrophilic membrane), we demonstrate comparable tumor uptake of QDs delivered by the passive and the active routes (mainly by Ly-6C^hi monocytes). Our findings suggest that entrapping QDs in nanosized liposomal formulations, prepared by a new facile method, imparts superior structural and optical stability and a suitable biodistribution profile leading to increased tumor uptake of fluorescently stable QDs."

"Colloidal semiconductor quantum dots (QDs) are promising for solar energy harvesting, particularly the excess energy of hot and/or high energy excitons before they relax, which would allow efficiencies beyond the Shockley-Queisser limit. Going beyond QDs, nanostructured materials such as nanorods (NRs) are attracting significant attention, as their geometrical differences with QDs imply different electronic properties, and their one-dimensional character makes them ideal building blocks for hybrid nanostructures [1,2]. Experimental observation of the charge relaxation pathways in such nanostructured systems is challenging, as high resolution in time (to resolve ultrafast processes) and in excitation energy (to distinguish the relaxation pathways of different excitons) are simultaneously required, which are incompatible with regular transient absorption (TA). Both requirements are met by two-dimensional electronic spectroscopy (2DES), which can be thought as an extension of TA employing two phase-locked pump pulses. Acquiring the data as a function of the delay t ₁ between them and using Fourier transform spectroscopy yields a correlation map between signal excitation and signal emission energies for each waiting time t ₂ [3]. As it provides resolution in the excitation energy, 2DES is ideal to study systems with spectrally congested electronic transitions and was applied to study many nanostructured systems."

"Quasi‐1D colloidal semiconductor nanorods (NRs) are at the forefront of nanoparticle (NP) research owing to their intriguing size‐dependent and shape‐dependent optical and electronic properties. The past decade has witnessed significant advances in both fundamental understanding of the growth mechanisms and applications of these stimulating materials. Herein, the state‐of‐the‐art of colloidal semiconductor NRs is reviewed, with special emphasis on heavy‐metal‐free materials. The main growth mechanisms of heavy‐metal‐free colloidal semiconductor NRs are first elaborated, including anisotropic‐controlled growth, oriented attachment, solution–liquid–solid method, and cation exchange. Then, structural engineering and properties of semiconductor NRs are discussed, with a comprehensive overview of core/shell structures, alloying, and doping, as well as semiconductor–metal hybrid nanostructures, followed by highlighted practical applications in terms of photocatalysis, photodetectors, solar cells, and biomedicine. Finally, challenges and future opportunities in this fascinating research area are proposed."

"The Electrical Functionality of an Array of Semiconductor Nanocrystals (NCs) depends critically on the free carriers that may arise from impurity or surface doping. Herein, we used InAs NC thin films as a model system to address the relative contributions of these doping mechanisms by comparative analysis of as-synthesized and Cu-doped NC-based field effect transistor (FET) characteristics. By applying FET simulation methods used in conventional semiconductor FETs, we elucidate surface and impurity-doping contributions to the overall performance of InAs NC-based FETs. As-synthesized InAs NC-based FETs show n-type characteristics assigned to the contribution of the surface electron accumulation layer that can be considered as an actual electron-donating doping level with specific doping density and is energetically located just below the conduction band. The Cu-doped InAs NC FETs show enhanced n-type conduction as expected from the Cu impurity location as an interstitial n-dopant in InAs NCs. The simulated curves reveal the additional contribution from electrons within an impurity sub-band close to the conduction band onset of the InAs NCs. The work therefore demonstrates the utility of the bulk FET simulation methodology also to NC-based FETs. It provides guidelines for control of doping of NC arrays separately from surface contributions and impurity doping in colloidal semiconductor NCs toward their future utilization as building blocks in bottom-up prepared optoelectronic devices."

"DNA nanostructures provide a powerful platform for the programmable assembly of nanomaterials. Here, this approach is extended to semiconductor nanorods that possess interesting electrical properties and could be utilized for the bottom‐up fabrication of nanoelectronic building blocks. The assembly scheme is based on an efficient DNA functionalization of the nanorods. A complete coverage of the rod surface with DNA ensures a high colloidal stability while maintaining the rod size and shape. It furthermore supports the assembly of the nanorods at defined docking positions of a DNA origami platform with binding efficiencies of up to 90 % as well as the formation of nanorod dimers with defined relative orientations. By incorporating orthogonal binding sites for gold nanoparticles, defined metal‐semiconductor heterostructures can be fabricated. Subsequent application of a seeded growth procedure onto the gold nanoparticles (AuNPs) allows for to establish a direct metal‐semiconductor interface as a crucial basis for the integration of semiconductors in self‐assembled nanoelectronic devices."

"Colloidal quantum materials are nanocrystals containing hundreds to thousands of atoms that exhibit unique properties resulting from their small finite dimensions. The extraordinary flexibility in tuning their properties via composition, size- and dimensionality-related quantum confinement effects and surface engineering combined with their scalable bottom-up manufacturing has already led to their commercialization in different light-emitting applications, such as materials for displays and as fluorescent agents for imaging and sensing. Beyond light emission, harnessing absorbed light energy to perform useful chemical work is an important new avenue for diverse applications of the colloidal quantum materials. Here, we introduce the colloidal quantum materials and their virtues, focusing on the “all-in-one system” concept for semiconductor–metal hybrid nanoparticles acting as photocatalysts. Next, their emerging photocatalytic functionalities are highlighted, including their action as photocatalysts for solar-to-fuel conversion and as photoinitiators for photo-curing and biomedical applications, such as phototherapy, sterilization, and diagnostics."

"Semiconductor nanocrystals have been shown to have unique advantages over traditional organic photoinitiators for polymerization in solution. However, efficient photoinitiation with such nanoparticles in solvent-free and additive-free formulations so far has not been achieved. Herein, the ability to use semiconductor nanocrystals for efficient bulk polymerization as sole initiators is reported, operating under modern UV-blue-LED light sources found in 3D printers and other photocuring applications. Hybrid semiconductor–metal nanorods exhibit superior photoinitiation capability to their pristine semiconductor counterparts, attributed to the enhanced charge separation and oxygen consumption in such systems. Moreover, photoinitiation by semiconductor nanocrystals overcoated by inorganic ligands is reported, thus increasing the scope of possible applications and shedding light on the photoinitiation mechanism; in light of the results, two possible pathways are discussed – ligand-mediated and cation-coordinated oxidation. A demonstration of the unique attributes of the quantum photoinitiators is reported in their use for high-resolution two-photon printing of optically fluorescing microstructures, demonstrating a multi-functionality capability. The bulk polymerization demonstrated here can be advantageous over solvent based methods as it alleviates the need of post-polymerization drying and reduces waste and exposure to toxic solvents, as well as broadens the possible use of quantum photoinitiators for industrial and research uses."

"Zinc chalcogenides nanostructures are promising newly‐studied materials for photocatalytic reactions such as water reduction for hydrogen generation and photoinitiation of radical polymerization processes. Herein, we introduced a straightforward synthesis of thin ZnS shell on ZnSe nanorods and characterized the resulting core/shell ZnSe/ZnS nanorods by electron microscopy techniques and X‐ray photoelectron spectroscopy. Then, the photocatalytic activities of the nanorods were studied by gas chromatography for hydrogen generation and by Fourier transform infrared spectroscopy for the photoinitiation capability. While such core/shell systems may limit charge transfer to the solution due to the type‐I band alignment, we find that the photochemical stability and photocatalytic activity of this system is significantly enhanced over pristine ZnSe nanorods. ZnSe/ZnS nanorods with Ni(NO₃)₂ co‐catalyst are used for hydrogen generation and the effects of the nanorods’ surface coating, pH conditions and type of hole scavenger are examined. The best performances were observed for nanorods after ligand stripping with Meerwein′s reagent using ascorbic acid as a hole acceptor at pH 4.5. All three parameters were found to affect the photocatalytic activity. Yet, the surface coating and pH dependence differ from previous reports on cadmium chalcogenides photocatalysts. The origin of their differences is discussed and attributed to the band alignment of the systems and the nature of the co‐catalyst. The stable heavy‐metal free ZnSe/ZnS nanorods system presented here holds promise for various photocatalytic applications."

"We report a solution for the challenge of having luminescence and metal conductivity from the same material. The fabrication of a hybrid metal–conductive luminescent film that manifests this dual property is described: the conductivity arising from a continuous gold thin film structure and luminescence originating from the embedded fluorescent emitters (nanoparticles of silica-coated CdSe/CdS quantum dots (QD/SiO₂ NPs)). The embedding of the QD/SiO₂ NPs is performed via a self-templating gold electroless process. The presence of the insulating silica layer on the QDs avoids quenching and enables luminescence, while still allowing plasmonic coupling of the QDs, as observed by luminescence lifetime analysis and by surface-enhanced Raman scattering. The potential applications of this special dual functionality are demonstrated by its used as a temperature probe: Passing current (heating the gold thin film) affects the emission intensity and induces a spectral red-shift of the QD/SiO₂ NPs. All properties of this metal–conductive luminescent film required the special embedding architecture and are not observed with simple adsorption of QD/SiO₂ NPs on a continuous Au film."