Combining HR-TEM and XPS to elucidate the core-shell structure of ultrabright CdSe/CdS semiconductor quantum dots

A hybrid nanoparticle-protein hydrogel system for prolonged local anesthesia

Local anesthetics are effective in relieving pain, but their duration of action is short. Therefore, the development of injectable sustained release systems to prolong the effect of local anesthetics has been of interest. In such systems delivering conventional local anesthetics, it has been challenging to achieve long durations of effect, particularly without incurring tissue toxicity. To overcome these challenges, we created a platform comprising a protein hydrogel incorporating hydrophobic local anesthetic (bupivacaine) nanoparticles. The nanoparticles were prepared by anti-solvent precipitation stabilized with bovine serum albumin (BSA), followed by crosslinking with glutaraldehyde (GA). The resulting BSA hydrogels prolonged release of bupivacaine in vitro. When bupivacaine nanoparticles within crosslinked BSA were injected at the sciatic nerve in rats, a duration of nerve block of 39.9 h was obtained, compared to 5.5 h for the commercial bupivacaine liposome suspension EXPAREL®. Tissue reaction was benign. We further demonstrated that this system could control the release of the amphiphilic drug diphenhydramine and the hydrophobic paclitaxel.

Iron Oxide Nanocubes as a New Certified Reference Material for Nanoparticle Size Measurements

The rational design and increasing industrial use of nanomaterials require a reliable characterization of their physicochemical key properties like size, size distribution, shape, and surface chemistry. This calls for nanoscale reference materials (nanoRMs) for the validation and standardization of commonly used characterization methods closely matching real-world nonspherical nano-objects. This encouraged us to develop a nonspherical nanoRM of very small size consisting of 8 nm iron oxide nanocubes (BAM-N012) to complement spherical gold, silica, and polymer nanoRMs. In the following, the development and production of this nanoRM are highlighted including the characterization by transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS) as complementary methods for size and shape parameters, homogeneity and stability studies, and calculation of a complete uncertainty budget of the size features. The determination of the nanocubes' edge length by TEM and SAXS allows a method comparison. In addition, SAXS measurements can also provide the mean particle number density and the mass concentration. The certified size parameters, area equivalent circular diameter and square edge length, determined by TEM with a relative expanded uncertainty below 9%, are metrologically traceable to a natural constant for length, the very precisely known (111) lattice spacing of silicon. Cubic BAM-N012 qualifies as a certified nanoRM for estimating the precision and trueness, validation, and quality assurance of particle size and shape measurements with electron microscopy and SAXS as well as other sizing methods suitable for nanomaterials. The production of this new iron oxide nanocube RM presents an important achievement for the nanomaterial community, nanomaterial manufacturers, and regulators.

How similar is the antibacterial activity of silver nanoparticles coated with different capping agents?†

Silver nanoparticles (AgNPs) represent one of the most commercialised metal nanomaterials, with an extensive number of applications that span from antimicrobial products to electronics. Bare AgNPs are very susceptible to aggregation, and capping agents are required for their protection and stabilisation. The capping agents can endow new characteristics which can either improve or deteriorate AgNPs (bio)activity. In the present work, five different capping agents were studied as stabilizing agents for AgNPs: trisodium citrate (citrate), polyvinylpyrrolidone (PVP), dextran (Dex), diethylaminoethyl-dextran (Dex^DEAE) and carboxymethyl-dextran (Dex^CM). The properties of the AgNPs were studied using a set of methods, including transmission electron microscopy, X-ray diffraction, thermogravimetric analysis and ultraviolet-visible and infrared spectroscopy. Coated and bare AgNPs were also tested against Escherichia coli, methicillin-resistance Staphylococcus aureus and Pseudomonas aeruginosa to analyse their capacity to suppress bacterial growth and eradicate biofilms of clinically relevant bacteria. The results showed that all the capping agents endow long-term stability for the AgNPs in water; however, when the AgNPs are in bacterial culture media, their stability is highly dependent on the capping agent properties due to the presence of electrolytes and charged macromolecules such as proteins. The results also showed that the capping agents have a substantial impact on the antibacterial activity of the AgNPs. The AgNPs coated with the Dex and Dex^CM were the most effective against the three strains, due to their better stability which resulted in the release of more silver ions, better interactions with the bacteria and diffusion into the biofilms. It is hypothesized that the antibacterial activity of capped AgNPs is governed by a balance between the AgNPs stability and their ability to release silver ions. Strong adsorption of capping agents like PVP on the AgNPs endows higher colloidal stability in culture media; however, it can decrease the rate of Ag⁺ release from the AgNPs and reduce the antibacterial performance. Overall, this work presents a comparative study between different capping agents on the properties and antibacterial activity of AgNPs, highlighting the importance of the capping agent in their stability and bioactivity.

Nanosilver antibacterial activity is governed by a balance between the nanosilver stability and their ability to release/dope Ag⁺ to solution.

Conformational Heterogeneity and Interchain Percolation Revealed in an Amorphous Conjugated Polymer

Conjugated polymers are employed in a variety of application areas due to their bright fluorescence and strong biocompatibility. However, understanding the structure of amorphous conjugated polymers on the nanoscale is extremely challenging compared to their related crystalline phases. Using a bespoke classical force field, we study amorphous poly(9,9-di-n-octylfluorene-alt-benzothiadiazole) (F8BT) with molecular dynamics simulations to investigate the role that its nanoscale structure plays in controlling its emergent (and all-important) optical properties. Notably, we show that a giant percolating cluster exists within amorphous F8BT, which has ramifications in understanding the nature of interchain species that drive the quantum yield reduction and bathochromic shift observed in conjugated polymer-based devices and nanostructures. We also show that distinct conformations can be unravelled from within the disordered structure of amorphous F8BT using a two-stage machine learning protocol, highlighting a link between molecular conformation and ring stacking propensity. This work provides predictive understanding by which to enhance the optical properties of next-generation conjugated polymer-based devices and materials by rational, simulation-led design principles.

Semiconductor Quantum Dots as Target Analytes: Properties, Surface Chemistry and Detection

Since the discovery of Quantum Dots (QDs) by Alexey I. Ekimov in 1981, the interest of researchers in that particular type of nanomaterials (NMs) with unique optical and electrical properties has been increasing year by year. Thus, since 2009, the number of scientific articles published on this topic has not been less than a thousand a year. The increasing use of QDs due to their biomedical, pharmaceutical, biological, photovoltaics or computing applications, as well as many other high-tech uses such as for displays and solid-state lighting (SSL), has given rise to a considerable number of studies about its potential toxicity. However, there are a really low number of reported studies on the detection and quantification of QDs, and these include ICP-MS and electrochemical analysis, which are the most common quantification techniques employed for this purpose. The knowledge of chemical phenomena occurring on the surface of QDs is crucial for understanding the interactions of QDs with species dissolved in the dispersion medium, while it paves the way for a widespread use of chemosensors to facilitate its detection. Keeping in mind both human health and environmental risks of QDs as well as the scarcity of analytical techniques and methodological approaches for their detection, the adaptation of existing techniques and methods used with other NMs appears necessary. In order to provide a multidisciplinary perspective on QD detection, this review focused on three interrelated key aspects of QDs: properties, surface chemistry and detection.

Composition, thickness, and homogeneity of the coating of core-shell nanoparticles-possibilities, limits, and challenges of X-ray photoelectron spectroscopy

Core-shell nanoparticles have attracted much attention in recent years due to their unique properties and their increasing importance in many technological and consumer products. However, the chemistry of nanoparticles is still rarely investigated in comparison to their size and morphology. In this review, the possibilities, limits, and challenges of X-ray photoelectron spectroscopy (XPS) for obtaining more insights into the composition, thickness, and homogeneity of nanoparticle coatings are discussed with four examples: CdSe/CdS quantum dots with a thick coating and a small core; NaYF4-based upconverting nanoparticles with a large Yb-doped core and a thin Er-doped coating; and two types of polymer nanoparticles with a poly(tetrafluoroethylene) core with either a poly(methyl methacrylate) or polystyrene coating. Different approaches for calculating the thickness of the coating are presented, like a simple numerical modelling or a more complex simulation of the photoelectron peaks. Additionally, modelling of the XPS background for the investigation of coating is discussed. Furthermore, the new possibilities to measure with varying excitation energies or with hard-energy X-ray sources (hard-energy X-ray photoelectron spectroscopy) are described. A discussion about the sources of uncertainty for the determination of the thickness of the coating completes this review. Graphical abstract.

Ultrafast dynamics and ultrasensitive single particle spectroscopy of optically robust core/alloy shell semiconductor quantum dots

A "one-pot one-step" synthesis method of Core/Alloy Shell (CAS) quantum dots (QDs) offers the scope of large scale synthesis in a less time consuming, more economical, highly reproducible and high-throughput manner in comparison to "multi-pot multi-step" synthesis for Core/Shell (CS) QDs. Rapid initial nucleation, and smooth & uniform shell growth lead to the formation of a compositionally-gradient alloyed hetero-structure with very significantly reduced interfacial trap density in CAS QDs. Thus, interfacial strain gets reduced in a much smoother manner leading to enhanced confinement for the photo-generated charge carriers in CAS QDs. Convincing proof of alloy-shelling for a CAS QD has been provided from HRTEM images at the single particle level. The band gap could be tuned as a function of composition, temperature, reactivity difference of precursors, etc. and a high PLQY and improved photochemical stability could be achieved for a small sized CAS QD. From the ultrafast exciton dynamics in CdSe and InP CAS QDs, it has been shown that (a) the hot exciton thermalization/relaxation happens in <500 fs, (b) hot electron trapping dynamics occurs within a ∼1 ps time scale, (c) band edge exciton trapping occurs within a 10-25 ps timescale and (d) for CdSe CAS QDs the hot hole gets trapped in about 35 ps. From fast PL decay dynamics, it has been shown that the amplitude of the intermediate time constant can be correlated with the PLQY. A model has been provided to understand these ultrafast to fast exciton dynamical processes. At the ultrasensitive single particle level, unlike CS QDs, CdSe CAS QDs have been shown to exhibit (a) constancy of PL_max (i.e. no bluing) and (b) constancy of PL intensity (i.e. no bleaching) of the single CAS QDs for continuous irradiation for one hour under an air atmosphere. Thus, CAS QDs hold the promise of being a superior optical probe in comparison to CS QDs both at the ensemble and at the single particle level, leading to enhanced flexibility of the CAS QDs towards designing and developing next generation application devices.

Improved Characteristics of CdSe/CdS/ZnS Core-Shell Quantum Dots Using an Oleylamine-Modified Process

CdSe/CdS with ZnS/ZnO shell quantum dots (QDs) are synthesized by a one-pot method with various oleylamine (OLA) contents. The crystal structures of the QDs were analyzed by X-ray diffractometry, which showed ZnS diffraction peaks. It was represented that the ZnS shell was formed on the surface of the CdSe/CdS core. Interestingly, QDs with a high OLA concentration exhibit diffraction peaks of ZnS/ZnO. As a result, the thermal stability of QDs with ZnS/ZnO shells exhibits better performance than those with ZnS shells. In addition, the photoluminescence intensity of QDs with ZnS/ZnO shells shows a relatively slow decay of 7.1% compared with ZnS shells at 85 °C/85% relative humidity aging test for 500 h. These indicate that QDs with different OLA modifications can form ZnS/ZnO shells and have good stability in a harsh environment. The emission wavelength of QDs can be tuned from 505 to 610 nm, suitable for micro-LED display applications.

Soft Bioelectronics Based on Nanomaterials

Recent advances in nanostructured materials and unconventional device designs have transformed the bioelectronics from a rigid and bulky form into a soft and ultrathin form and brought enormous advantages to the bioelectronics. For example, mechanical deformability of the soft bioelectronics and thus its conformal contact onto soft curved organs such as brain, heart, and skin have allowed researchers to measure high-quality biosignals, deliver real-time feedback treatments, and lower long-term side-effects in vivo. Here, we review various materials, fabrication methods, and device strategies for flexible and stretchable electronics, especially focusing on soft biointegrated electronics using nanomaterials and their composites. First, we summarize top-down material processing and bottom-up synthesis methods of various nanomaterials. Next, we discuss state-of-the-art technologies for intrinsically stretchable nanocomposites composed of nanostructured materials incorporated in elastomers or hydrogels. We also briefly discuss unconventional device design strategies for soft bioelectronics. Then individual device components for soft bioelectronics, such as biosensing, data storage, display, therapeutic stimulation, and power supply devices, are introduced. Afterward, representative application examples of the soft bioelectronics are described. A brief summary with a discussion on remaining challenges concludes the review.

Analyzing the surface of functional nanomaterials-how to quantify the total and derivatizable number of functional groups and ligands

Functional nanomaterials (NM) of different size, shape, chemical composition, and surface chemistry are of increasing relevance for many key technologies of the twenty-first century. This includes polymer and silica or silica-coated nanoparticles (NP) with covalently bound surface groups, semiconductor quantum dots (QD), metal and metal oxide NP, and lanthanide-based NP with coordinatively or electrostatically bound ligands, as well as surface-coated nanostructures like micellar encapsulated NP. The surface chemistry can significantly affect the physicochemical properties of NM, their charge, their processability and performance, as well as their impact on human health and the environment. Thus, analytical methods for the characterization of NM surface chemistry regarding chemical identification, quantification, and accessibility of functional groups (FG) and surface ligands bearing such FG are of increasing importance for quality control of NM synthesis up to nanosafety. Here, we provide an overview of analytical methods for FG analysis and quantification with special emphasis on bioanalytically relevant FG broadly utilized for the covalent attachment of biomolecules like proteins, peptides, and oligonucleotides and address method- and material-related challenges and limitations. Analytical techniques reviewed include electrochemical titration methods, optical assays, nuclear magnetic resonance and vibrational spectroscopy, as well as X-ray based and thermal analysis methods, covering the last 5-10 years. Criteria for method classification and evaluation include the need for a signal-generating label, provision of either the total or derivatizable number of FG, need for expensive instrumentation, and suitability for process and production control during NM synthesis and functionalization.

Composition-tuned MAPbBr3 nanoparticles with addition of Cs+ cations for improved photoluminescence

Hybrid organic-inorganic lead halide perovskite nanoparticles are promising candidates for optoelectronic applications. This investigation describes the structural and optical properties of MA x Cs1-x PbBr3 mixed cation colloidal nanoparticles spanning the complete compositional range of Cs substitution. A monotonic progression in the cubic lattice parameter (a) with changes in the Cs+ content confirmed the formation of mixed cation materials. More importantly, time-resolved photoluminescence (TRPL) revealed the optimized 13 mol% Cs nanoparticle composition exhibits the longest charge carrier lifetime and enhancement in radiative pathways. This sample also showed the highest photoluminescence quantum yield (PLQY) of ∼88% and displays ∼100% improvement in the PLQY of pure MAPbBr3 and CsPbBr3. Prototype LEDs fabricated from MA0.87Cs0.13PbBr3 were demonstrated.