Synthesis and electronic properties of semiconductor nanoparticles/quantum dots

Green, HF-Free Synthesis of MXene Quantum Dots and their Photocatalytic Activity for Hydrogen Evolution

A general methodology to prepare MXene quantum dots (MxQDs) with yields over 20% by liquid-phase laser ablation of the MAX phase is reported. Mechanical and thermal shock by 532 nm laser pulses (7 ns fwhp, 50 mJ × pulse^-1 , 1 Hz pulse frequency) produces MAX etching and exfoliation to form MXene QDs, avoiding the use of HF. The process can be followed by absorption and emission spectroscopy and by dynamic laser scattering and it appears to be general, being applied to Ti₃ AlC₂ , Ti₂ AlC, Nb₂ AlC, and V₂ AlC MAX phases. Density functional theory calculations indicate that, depending on the surface terminal groups, the diminution of the MXene size to the nanometric scale makes it possible to control the band gap of the MXene. The photocatalytic activity of these MXene QDs for hydrogen evolution has been observed, reaching an H₂ production for the most efficient Ti₃ C₂ QDs as high as 2.02 mmol × g^-1 × h^-1 .

Modeling of Advanced Silicon Nanomaterial Synthesis Approach: From Reactive Thermal Plasma Jet to Nanosized Particles

A three-dimensional numerical modelling of a time-dependent, turbulent thermal plasma jet was developed to synthetize silicon nanopowder. Computational fluid dynamics and particle models were employed via COMSOL Multiphysics® v. 5.4 (COMSOL AB, Stockholm, Sweden) to simulate fluid and particle motion in the plasma jet, as well as the heat dependency. Plasma flow and particle interactions were exemplified in terms of momentum, energy, and turbulence flow. The transport of nanoparticles through convection, diffusion, and thermophoresis were also considered. The trajectories and heat transfer of both plasma jet fields, and particles are represented. The swirling flow controls the plasma jet and highly affects the dispersion of the nanoparticles. We demonstrate a decrease in both particles’ velocity and temperature distribution at a higher carrier gas injection velocity. The increase in the particle size and number affects the momentum transfer, turbulence modulation, and energy of particles, and also reduces plasma jet parameters. On the other hand, the upstream flame significantly impacts the particle’s behavior under velocity and heat transfer variation. Our findings open the door for examining thermal plasma impact in nanoparticle synthesis, where it plays a major role in optimizing the growth parameters, ensuring high quality with a low-cost technique.

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.

Dendronised Polymers as Templates for In Situ Quantum Dot Synthesis

The utility of dendrimers as effective carriers for targeted drug delivery and imaging has been facilitated by a high degree of molecular uniformity, narrow molecular weight distribution, tunable size and shape characteristics, and multivalency. Dendrimer–quantum dot (QD) nanocomposites have traditionally been synthesised by electrostatic self-assembly of preformed dendrimers and QDs, but higher generations are associated with limited flexibility and increased cytotoxicity. In this paper, we report the fabrication of CdTe QD nanoparticles using a dendronised linear copolymer bearing thiolated fourth-generation poly(amido amine) (PAMAM) dendrons as the capping and stabilising agent. We demonstrate this approach enables synthesis of nanocomposites with aqueous and photophysical stability.

Polymer-guided assembly of inorganic nanoparticles

The self-assembly of inorganic nanoparticles is of great importance in realizing their enormous potentials for broad applications due to the advanced collective properties of nanoparticle ensembles. Various molecular ligands (e.g., small molecules, DNAs, proteins, and polymers) have been used to assist the organization of inorganic nanoparticles into functional structures at different hierarchical levels. Among others, polymers are particularly attractive for use in nanoparticle assembly, because of the complex architectures and rich functionalities of assembled structures enabled by polymers. Polymer-guided assembly of nanoparticles has emerged as a powerful route to fabricate functional materials with desired mechanical, optical, electronic or magnetic properties for a broad range of applications such as sensing, nanomedicine, catalysis, energy storage/conversion, data storage, electronics and photonics. In this review article, we summarize recent advances in the polymer-guided self-assembly of inorganic nanoparticles in both bulk thin films and solution, with an emphasis on the role of polymers in the assembly process and functions of resulting nanostructures. Precise control over the location/arrangement, interparticle interaction, and packing of inorganic nanoparticles at various scales are highlighted.

Synthesis and Growth Mechanism of Stable Prenucleated (≈0.8 nm Diameter) PbS Quantum Dots by Medium Energy Ion Scattering Spectroscopy

In the current work, stable prenucleated PbS quantum dots (QDs) with a sub-nanometer (0.8 nm) size have been successfully synthesized via a systematically designed experiment. A detailed analysis of critical nucleation, growth, and stability for such ultrasmall prenucleated clusters is done. The experimental strategy is based on controlled concentration, temperature and injection of respective precursors, thus enabling us to control nucleation rate and separation of stable sub-nanometer PbS QDs with size 0.8 nm. Significantly, by providing additional thermal energy to sub-nanometer PbS QDs, we achieved the fully nucleated cubic crystalline structure of PbS with size of around 1.5 nm. The size and composition of the prenucleated QDs are investigated by sophisticated tools like X-ray photoelectron spectroscopy (XPS) and medium energy ion scattering (MEIS) spectroscopy which confirms the synthesis of PbS with Pb²⁺ rich surface while the UV-Vis spectroscopy and X-ray diffraction (XRD) data suggests an alternative crystallization path. Non-classical nucleation theory is employed to substantiate the growth mechanism of prenucleated PbS QDs.

Phosphate Favors the Biosynthesis of CdS Quantum Dots in Acidithiobacillus thiooxidans ATCC 19703 by Improving Metal Uptake and Tolerance

Recently, we reported the production of Cadmium sulfide (CdS) fluorescent semiconductor nanoparticles (quantum dots, QDs) by acidophilic bacteria of the Acidithiobacillus genus. Here, we report that the addition of inorganic phosphate to Acidithiobacillus thiooxidans ATCC 19703 cultures favors the biosynthesis of CdS QDs at acidic conditions (pH 3.5). The effect of pH, phosphate and cadmium concentrations on QDs biosynthesis was studied by using Response Surface Methodology (RSM), a multivariate technique for analytical optimization scarcely used in microbiological studies to date. To address how phosphate affects intracellular biosynthesis of CdS QDs, the effect of inorganic phosphate on bacterial cadmium-uptake was evaluated. By measuring intracellular levels of cadmium we determined that phosphate influences the capacity of cells to incorporate this metal. A relation between cadmium tolerance and phosphate concentrations was also determined, suggesting that phosphate participates in the adaptation of bacteria to toxic levels of this metal. In addition, QDs-biosynthesis was also favored by the degradation of intracellular polyphosphates. Altogether, our results indicate that phosphate contributes to A. thiooxidans CdS QDs biosynthesis by influencing cadmium uptake and cadmium tolerance. These QDs may also be acting as a nucleation point for QDs formation at acidic pH. This is the first study reporting the effect of phosphates on QDs biosynthesis and describes a new cadmium-response pathway present in A. thiooxidans and most probably in other bacterial species.

An organic phase transmetallation approach for synthesis of hollow Ni–Au nanocomposites with tunable cavity size

Hydrophobized HAuCl₄ entered Ni nanoparticles through the fractures on the surface initiating transmetallation at the centre, yielding hollow Ni–Au composites.

Core/Shell Nanocomposites Produced by Superfast Sequential Microfluidic Nanoprecipitation

Although a number of techniques exist for generating structured organic nanocomposites, it is still challenging to fabricate them in a controllable, yet universal and scalable manner. In this work, a microfluidic platform, exploiting superfast (milliseconds) time intervals between sequential nanoprecipitation processes, has been developed for high-throughput production of structured core/shell nanocomposites. The extremely short time interval between the sequential nanoprecipitation processes, facilitated by the multiplexed microfluidic design, allows us to solve the instability issues of nanocomposite cores without using any stabilizers. Beyond high throughput production rate (∼700 g/day on a single device), the generated core/shell nanocomposites harness the inherent ultrahigh drug loading degree and enhanced payload dissolution kinetics of drug nanocrystals and the controlled drug release from polymer-based nanoparticles.

Self-Assembled Nanoparticle Arrays on Chemical Nanopatterns Prepared Using Block Copolymer Lithography

We present a high-throughput and inexpensive fabrication approach that uses self-assembled block copolymer (BCP) films as templates to generate dense nanoscale chemical patterns of polymer brushes for the selective immobilization of Au nanoparticles (NPs). A cross-linked random copolymer mat that contains styrene and methyl methacrylate units serves both as a base layer for perpendicular assembly of nanoscale domains of poly(styrene-block-methyl methacrylate) (PS-b-PMMA) films and as a nonadsorbing background layer that surrounds the chemical patterns. The selective removal of the PMMA block and the underlying mat via oxygen plasma etching generates binding sites which are then functionalized with poly(2-vinylpyridine) (P2VP) brushes. Au NPs with a diameter of 13 nm selectively immobilize on the patterned P2VP brushes. An essential aspect in fabricating high quality chemical patterns is the superior behavior of methyl methacrylate containing cross-linked mats in retaining their chemistry during the grafting of P2VP brushes. The use of BCPs with different molecular weights and volume fractions allows for preparation of chemical patterns with different geometries, sizes, and pitches for generating arrays of single particles that hold great promise for applications that range from molecular sensing to optical devices.

Investigation of the size-property relationship in CuInS2 quantum dots

In this work we investigated fundamental properties of CuInS2 quantum dots in dependence of the particle size distribution (PSD). Size-selective precipitation (SSP) with acetone as poor solvent was performed as an adequate post-processing step. Our results provide deep insight into the correlation between particle size and various optical characteristics as bandgap energy, absorption and emission features and the broadness of the emission signal. These structure-property relationships are only achieved due to the unique combination of different analytical techniques. Our study reveals that the removal of 10 wt% of smallest particles from the feed results in an enhancement of the emission signal. This improvement is ascribed to a decreased quenching of the emission in larger particles. Our results reveal the impact of PSDs on the properties and the performance of an ensemble of multicomponent QDs and anticipate the high potential of controlling PSDs by well-developed post-processing.

Fluorescence-tagged metallothionein with CdTe quantum dots analyzed by the chip-CE technique

ABSTRACT

Quantum dots (QDs) are fluorescence nanoparticles (NPs) with unique optic properties which allow their use as probes in chemical, biological, immunological, and molecular imaging. QDs linked with target ligands such as peptides or small molecules can be used as tumor biomarkers. These particles are a promising tool for selective, fast, and sensitive tagging and imaging in medicine. In this study, an attempt was made to use QDs as a marker for human metallothionein (MT) isoforms 1 and 2. Four kinds of CdTe QDs of different sizes bioconjugated with MT were analyzed using the chip-CE technique. Based on the results, it can be concluded that MT is willing to interact with QDs, and the chip-CE technique enables the observation of their complexes. It was also observed that changes ranging roughly 6-7 kDa, a value corresponding to the MT monomer, depend on the hydrodynamic diameters of QDs; also, the MT sample without cadmium interacted stronger with QDs than MT saturated with cadmium. Results show that MT is willing to interact with smaller QDs (blue CdTe) rather than larger ones QDs (red CdTe). To our knowledge, chip-CE has not previously been applied in the study of CdTe QDs interaction with MT.

GRAPHICAL ABSTRACT

Anodic stripping voltammetry of anti-Vi antibody functionalized CdTe quantum dots for the specific monitoring of Salmonella enterica serovar Typhi

CdTe QD based stripping voltammetry for Vi capsular polysaccharide detection. The technique has provided an insight into the competence of CdTe QD and GNP immuno-conjugates. This is a novel approach to characterize the efficiency of immuno-conjugates of QDs and GNPs.

Inorganic Nanoparticles for Therapeutic Delivery: Trials, Tribulations and Promise

Inorganic nanomaterials have a wide array of physical and structural properties that make them attractive candidates for imaging and therapeutic delivery. Nanoparticle platforms have been intensely studied for these applications, and examples are starting to enter the clinic. This review looks at why inorganic particles provide promising platforms for biomedicine, and what issues need to be addressed for them to reach their potential.

DNA nanotechnology: from sensing and DNA machines to drug-delivery systems

DNA/nanoparticle hybrid systems combine the unique electronic and optical properties of nanomaterials with the recognition and catalytic properties of nucleic acids. These materials hold great promise for the development of new sensing platforms, the programmed organization of nanoparticles, the switchable control of plasmonic phenomena in the nanostructures, and the controlled delivery of drugs. In this Perspective, we summarize recent advances in the application of DNA/nanoparticle (NP) hybrids in these different disciplines. Nucleic acid-semiconductor quantum dot hybrids are implemented to develop multiplexed sensing platforms for targeted DNA. The chemiluminescence resonance energy transfer mechanism is introduced as a new transduction signal, and the amplified detection of DNA targets through the biocatalytic regeneration of analytes is demonstrated. DNA machines consisting of catenanes or tweezers, and modified with fluorophore/Au NP pairs are used as functional devices for the switchable "mechanical" control of the fluorescence properties of the fluorophore. Also, nucleic acid nanostructures act as stimuli-responsive caps for trapping drugs in the pores of mesoporous SiO2 nanoparticles. In the presence of appropriate biomarker triggers, the pores are unlocked, leading to the controlled release of anticancer drugs. Selective cancer-cell death is demonstrated with the stimuli-responsive SiO2 nanoparticles.

Nucleic acid/quantum dots (QDs) hybrid systems for optical and photoelectrochemical sensing

Nucleic acid/semiconductor quantum dots (QDs) hybrid systems combine the recognition and catalytic properties of nucleic acids with the unique photophysical features of QDs. These functions of nucleic acid/QDs hybrids are implemented to develop different optical sensing platforms for the detection of DNA, aptamer-substrate complexes, and metal ions. Different photophysical mechanisms including fluorescence, electron transfer quenching, fluorescence resonance energy transfer (FRET), and chemiluminescence resonance energy transfer (CRET) are used to develop the sensor systems. The size-controlled luminescence properties of QDs are further implemented for the multiplexed, parallel analysis of several DNAs, aptamer-substrate complexes, or mixtures of ions. Similarly, methods to amplify the sensing events through the biocatalytic regeneration of the analyte were developed. An additional paradigm in the implementation of nucleic acid/QDs hybrids for sensing applications involves the integration of the systems with electrodes, and the generation of photocurrents as transduction signals for the sensing events. Finally, semiconductor QDs conjugated to functional DNA machines, such as "walker" systems, provide an effective optical label for probing the dynamics and mechanical functions of the molecular devices. The present article addresses the recent advances in the application of nucleic acid/QDs hybrids for sensing applications and DNA nanotechnology, and discusses future perspectives of these hybrid materials.

Fluorescence in nanobiotechnology: sophisticated fluorophores for novel applications

Nanobiotechnology is one of the fastest growing and broadest-ranged interdisciplinary subfields of the nanosciences. Countless hybrid bio-inorganic composites are currently being pursued for various uses, including sensors for medical and diagnostic applications, light- and energy-harvesting devices, along with multifunctional architectures for electronics and advanced drug-delivery. Although many disparate biological and nanoscale materials will ultimately be utilized as the functional building blocks to create these devices, a common element found among a large proportion is that they exert or interact with light. Clearly continuing development will rely heavily on incorporating many different types of fluorophores into these composite materials. This review covers the growing utility of different classes of fluorophores in nanobiotechnology, from both a photophysical and a chemical perspective. For each major structural or functional class of fluorescent probe, several representative applications are provided, and the necessary technological background for acquiring the desired nano-bioanalytical information are presented.

Surfactant-assisted synthesis and characterization of stable silver bromide nanoparticles in aqueous media

Colloidal dispersions of silver bromide (AgBr) in aqueous surfactant medium have been prepared using a surfactant-assisted synthesis approach with hexadecyltrimethylammonium bromide (CTAB). The surfactant acts both as source of bromide ion as well as the stabilizing agent. Upon progressive addition of silver nitrate to aqueous CTAB solution, stable AgBr dispersions were obtained. Formation of surfactant cation (CTA(+)) stabilized AgBr was confirmed by way of XRD, FTIR and NMR studies. Thermal behavior of the isolated nanoparticles was investigated by differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA), where the occurrence of phase transition in the surfactant-stabilized nanoparticles was observed. Kinetics of the particle growth was investigated by dynamic light scattering measurements, which predicted the formation of surfactant bilayered structures associated with the nanoparticles of AgBr. Band gap of the nanoparticles was determined by suitably analyzing the UV-visible spectral data, which concluded that the particles behaved like insulators. Morphology of the particles, studied by TEM measurements, was found to be spherical. Finally, enthalpy of formation of surfactant-stabilized AgBr, determined calorimetrically, was found to be dependent on the concentration of the precursors.

Electron-transfer quenching of nucleic acid-functionalized CdSe/ZnS quantum dots by doxorubicin: a versatile system for the optical detection of DNA, aptamer-substrate complexes and telomerase activity

The optical detection of DNA or the sensing of low-molecular-weight substrates or proteins by aptamer nucleic acids is a long term challenge in the design of biosensors. Similarly, the detection of the telomerase activity, a versatile biomarker of cancer cells, is important for rapid cancer diagnostics. We implement the luminescence quenching of the CdSe/ZnS quantum dots (QDs) as a versatile process to develop DNA sensors and aptasensors, and to design an analytical platform for the detection of telomerase activity. The formation of nucleic acid duplexes on QDs, or the assembly of aptamer-substrate complexes on the QDs (substrate=cocaine or thrombin) is accompanied by the intercalation of doxorubicin (DB) into the duplex domains of the resulting recognition complexes. The intercalated DB quenches the luminescence of the QDs, thus leading to the detection readout signal. Similarly, the telomerase-induced formation of the telomere chains on the QDs is followed by the hybridization of nucleic-acid units complementary to the telomere repeat units, and the intercalation of DB into the resulting duplex structure. The resulting luminescence quenching of the QDs provides an indicating signal for the activity of telomerase.

Glucose biosensor based on nanocomposite films of CdTe quantum dots and glucose oxidase

A blood glucose sensor has been developed based on the multilayer films of CdTe semiconductor quantum dots (QDs) and glucose oxidase (GOD) by using the layer-by-layer assembly technique. When the composite films were contacted with glucose solution, the photoluminescence of QDs in the films was quickly quenched because the enzyme-catalyzed reaction product (H2O2) of GOD and glucose gave rise to the formation of surface defects on QDs. The quenching rate was a function of the concentration of glucose. The linear range and sensitivity for glucose determination could be adjusted by controlling the layers of QDs and GOD. The biosensor was used to successfully determine the concentration of blood glucose in real serum samples without sample pretreatment and exhibited satisfactory reproducibility and accuracy.

Nano-adsorbents for the removal of metallic pollutants from water and wastewater

Of the variety of adsorbents available for the removal of heavy and toxic metals, activated carbon has been the most popular. A number of minerals, clays and waste materials have been regularly used for the removal of metallic pollutants from water and industrial effluents. Recently there has been emphasis on the application of nanoparticles and nanostructured materials as efficient and viable alternatives to activated carbon. Carbon nanotubes also have been proved effective alternatives for the removal of metallic pollutants from aqueous solutions. Because of their importance from an environmental viewpoint, special emphasis has been given to the removal of the metals Cr, Cd, Hg, Zn, As, and Cu. Separation of the used nanoparticles from aqueous solutions and the health aspects of the separated nanoparticles have also been discussed. A significant number of the latest articles have been critically scanned for the present review to give a vivid picture of these exotic materials for water remediation.

Magnetic particle-based hybrid platforms for bioanalytical sensors

Biomagnetic nano and microparticles platforms have attracted considerable interest in the field of biological sensors due to their interesting physico-chemical properties, high specific surface area, good mechanical stability and opportunities for generating magneto-switchable devices. This review discusses recent advances in the development and characterization of active biomagnetic nanoassemblies, their interaction with biological molecules and their use in bioanalytical sensors.

Dip-pen-nanolithographic patterning of metallic, semiconductor, and metal oxide nanostructures on surfaces

Dip-pen nanolithography (DPN) is a powerful method to pattern nanostructures on surfaces by the controlled delivery of an "ink" coating the tip of an atomic force microscope upon scanning and contacting with surfaces. The growing interest in the use of nanoparticles as structural and functional elements for the fabrication of nanodevices suggests that the DPN-stimulated patterning of nanoparticles on surfaces might be a useful technique to assemble hierarchical architectures of nanoparticles that could pave methodologies for functional nanocircuits or nanodevices. This Review presents different methodologies for the nanolithographic patterning of metallic, semiconductor, and metal oxide nanostructures on surfaces. The mechanisms involved in the formation of the nanostructures are discussed and the effects that control the dimensions of the resulting patterns are reviewed. The possible applications of the nanostructures are also addressed.

Facile aqueous synthesis and growth mechanism of CdTe nanorods

Single-crystal CdTe nanorods with diameters of 50-100 nm were synthesized under a surfactant-assisted hydrothermal condition. The experimental results indicated that with a temporal dependence the morphologies of CdTe nanocrystallites changed from nanoparticles to smooth surface nanorods. The crystal structure, morphology and optical properties of the products were investigated by x-ray diffraction (XRD), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM) and fluorescence spectrophotometer. Furthermore, the formation mechanisms of the nanorods were investigated and discussed on the basis of the experimental results.