Surface charge-dependent cytokine production using near-infrared emitting silicon quantum dots.

Toll-like receptor 9 (TLR-9) is a protein that helps our immune system identify specific DNA types. Upon detection, CpG oligodeoxynucleotides signal the immune system to generate cytokines, essential proteins that contribute to the body's defence against infectious diseases. Native phosphodiester type B CpG ODNs induce only Interleukin-6 with no effect on interferon-α. We prepared silicon quantum dots containing different surface charges, such as positive, negative, and neutral, using amine, acrylate-modified Plouronic F-127, and Plouronic F-127. Then, class B CpG ODNs are loaded on the surface of the prepared SiQDs. The uptake of ODNs varies based on the surface charge; positively charged SiQDs demonstrate higher adsorption compared to SiQDs with negative and neutral surface charges. The level of cytokine production in peripheral blood mononuclear cells was found to be associated with the surface charge of SiQDs prior to the binding of the CpG ODNs. Significantly higher levels of IL-6 and IFN-α induction were observed compared to neutral and negatively charged SiQDs loaded with CpG ODNs. This observation strongly supports the notion that the surface charge of SiQDs effectively regulates cytokine induction.

Rational ligand design for enhanced carrier mobility in self-powered SWIR photodiodes based on colloidal InSb quantum dots.

Solution-processed colloidal III-V semiconductor quantum dot photodiodes (QPDs) have potential applications in short-wavelength infrared (SWIR) imaging due to their tunable spectral response range, possible multiple-exciton generation, operation at 0-V bias voltage and low-cost fabrication and are also expected to replace lead- and mercury-based counterparts that are hampered by reliance on restricted elements (RoHS). However, the use of III-V CQDs as photoactive layers in SWIR optoelectronic applications is still a challenge because of underdeveloped ligand engineering for improving the in-plane conductivity of the QD assembled films. Here, we report on ligand engineering of InSb CQDs to enhance the optical response performance of self-powered SWIR QPDs. Specifically, by replacing the conventional ligand (i.e., oleylamine) with sulfide, the interparticle distance between the CQDs was shortened from 5.0 ± 0.5 nm to 1.5 ± 0.5 nm, leading to improved carrier mobility for high photoresponse speed to SWIR light. Furthermore, the use of sulfide ligands resulted in a low dark current density (∼nA cm-2) with an improved EQE of 18.5%, suggesting their potential use in toxic-based infrared image sensors.

Highly efficient, self-powered UV photodiodes based on leadfree perovskite nanocrystals through interfacial engineering.

Double perovskite crystals are promising alternatives for lead-based perovskites that has potential to address toxicity and instability issues. In this study, Cs2AgBiCl6nanocrystals (NCs) with high absorption coefficients were synthesized by hot-injection method. The bandgap engineering was realized by tuning the halide composition in Cs2AgBiCl6to Cs2AgBiBr6. Both NCs were used as light-absorbing layers in lead-free perovskite photodiodes that exhibit wavelength-selectivity for UV-visible light operatable even at a bias voltage of 0 V. Cs2AgBiBr6-based photodiode exhibits a characteristic detection peak at 340 nm with a responsivity of 3.21 mA W-1, a specific detectivity up to 8.91 × 1010Jones and a fast response speed with a rise/fall time of 30/35 ms. The excellent performance of self-driven photodiodes lights up the prospect of lead-free perovskite NCs in highly efficient optoelectronic devices.

Analysis of Silicon Quantum Dots and Serum Proteins Interactions Using Asymmetrical Flow Field-Flow Fractionation.

Semiconductor nanocrystals or quantum dots (QDs) have gained significant attention in biomedical research as versatile probes for imaging, sensing, and therapies. However, the interactions between proteins and QDs, which are crucial for their use in biological applications, are not yet fully understood. Asymmetric flow field-flow fractionation (AF4) is a promising method for analyzing the interactions of proteins with QDs. This technique uses a combination of hydrodynamic and centrifugal forces to separate and fractionate particles based on their size and shape. By coupling AF4 with other techniques, such as fluorescence spectroscopy and multi-angle light scattering, it is possible to determine the binding affinity and stoichiometry of protein-QD interactions. Herein, this approach has been utilized to determine the interaction between fetal bovine serum (FBS) and silicon quantum dots (SiQDs). Unlike metal-containing conventional QDs, SiQDs are highly biocompatible and photostable in nature, making them attractive for a wide range of biomedical applications. In this study, AF4 has provided crucial information on the size and shape of the FBS/SiQD complexes, their elution profile, and their interaction with serum components in real time. The differential scanning microcalorimetric technique has also been employed to monitor the thermodynamic behavior of proteins in the presence of SiQDs. We have investigated their binding mechanisms by incubating them at temperatures below and above the protein denaturation. This study yields various significant characteristics such as their hydrodynamic radius, size distribution, and conformational behavior. The compositions of SiQD and FBS influence the size distribution of their bioconjugates; the size increases by intensifying the concentration of FBS, with their hydrodynamic radii ranging between 150 and 300 nm. The results signify that in the alliance of SiQDs to the system, there is an augmentation of the denaturation point of the proteins and hence their thermal stability, providing a more comprehensive understanding of the interactions between FBS and QDs.

Nano-bio interaction between human immunoglobulin G and nontoxic, near-infrared emitting water-borne silicon quantum dot micelles.

In recent years, the field of nanomaterials has exponentially expanded with versatile biological applications. However, one of the roadblocks to their clinical translation is the critical knowledge gap about how the nanomaterials interact with the biological microenvironment (nano-bio interactions). When nanomaterials are used as drug carriers or contrast agents for biological imaging, the nano-bio interaction-mediated protein conformational changes and misfolding could lead to disease-related molecular alterations and/or cell death. Here, we studied the conformation changes of human immunoglobulin G (IgG) upon interaction with silicon quantum dots functionalized with 1-decene, Pluronic-F127 (SiQD-De/F127 micelles) using UV-visible, fluorescence steady state and excited state kinetics, circular dichroism, and molecular modeling. Decene monolayer terminated SiQDs are accumulated inside the Pluronic F127 shells to form SiQD-De/F127 micelles and were shown to bind strongly with IgG. In addition, biological evaluation studies in cell lines (HeLa, Fibroblast) and medaka fish (eggs and larvae) showed enhanced uptake and minimal cytotoxicity. Our results substantiate that engineered QDs obviating the protein conformational changes could have adept bioefficacy.

Impact of coherent core/shell architecture on fast response in InP-based quantum dot photodiodes.

Solution-processed, cadmium-free quantum dot (QD) photodiodes are compatible with printable optoelectronics and are regarded as a potential candidate for wavelength-selective optical sensing. However, a slow response time resulting from low carrier mobility and a poor dissociation of charge carriers in the optically active layer has hampered the development of the QD photodiodes with nontoxic device constituents. Herein, we report the first InP-based photodiode with a multilayer device architecture, working in photovoltaic mode in photodiode circuits. The photodiode showed the fastest response speed with rising and falling times of τ r = 4 ms and τ f = 9 ms at a voltage bias of 0 V at room temperature in ambient air among the Cd-free photodiodes. The single-digit millisecond photo responses were realized by efficient transportation of the photogenerated carriers in the optically active layer resulting from coherent InP/ZnS core/shell QD structure, fast separation of electron and hole pairs at the interface between QD and Al-doped ZnO layers, and optimized conditions for uniform deposition of each thin film. The results suggested the versatility of coherent core/shell QDs as a photosensitive layer, whose structures allow various semiconductor combinations without lattice mismatch considerations, towards fast response, high on/off ratios, and spectrally tunable optical sensing.

A facile approach to preparing personalized cancer vaccines using iron-based metal organic framework.

Background: Considering the diversity of tumors, it is of great significance to develop a simple, effective, and low-cost method to prepare personalized cancer vaccines. Methods: In this study, a facile one-pot synthetic route was developed to prepare cancer vaccines using model antigen or autologous tumor antigens based on the coordination interaction between Fe3+ ions and endogenous fumarate ligands. Results: Herein, Fe-based metal organic framework can effectively encapsulate tumor antigens with high loading efficiency more than 80%, and act as both delivery system and adjuvants for tumor antigens. By adjusting the synthesis parameters, the obtained cancer vaccines are easily tailored from microscale rod-like morphology with lengths of about 0.8 µm (OVA-ML) to nanoscale morphology with sizes of about 50~80 nm (OVA-MS). When cocultured with antigen-presenting cells, nanoscale cancer vaccines more effectively enhance antigen uptake and Th1 cytokine secretion than microscale ones. Nanoscale cancer vaccines (OVA-MS, dLLC-MS) more effectively enhance lymph node targeting and cross-presentation of tumor antigens, mount antitumor immunity, and inhibit the growth of established tumor in tumor-bearing mice, compared with microscale cancer vaccines (OVA-ML, dLLC-ML) and free tumor antigens. Conclusions: Our work paves the ways for a facile, rapid, and low-cost preparation approach for personalized cancer vaccines.

Postproduction Approach to Enhance the External Quantum Efficiency for Red Light-Emitting Diodes Based on Silicon Nanocrystals.

Despite bulk crystals of silicon (Si) being indirect bandgap semiconductors, their quantum dots (QDs) exhibit the superior photoluminescence (PL) properties including high quantum yield (PLQY > 50%) and spectral tunability in a broad wavelength range. Nevertheless, their low optical absorbance character inhibits the bright emission from the SiQDs for phosphor-type light emitting diodes (LEDs). In contrast, a strong electroluminescence is potentially given by serving SiQDs as an emissive layer of current-driven LEDs with (Si-QLEDs) because the charged carriers are supplied from electrodes unlike absorption of light. Herein, we report that the external quantum efficiency (EQE) of Si-QLED was enhanced up to 12.2% by postproduction effect which induced by continuously applied voltage at 5 V for 9 h. The active layer consisted of SiQDs with a diameter of 2.0 nm. Observation of the cross-section of the multilayer QLEDs device revealed that the interparticle distance between adjacent SiQDs in the emissive layer is reduced to 0.95 nm from 1.54 nm by "post-electric-annealing". The shortened distance was effective in promoting charge injection into the emission layer, leading improvement of the EQE.

Effect of the surface coverage of an alkyl carboxylic acid monolayer on waterborne and cellular uptake behaviors for silicon quantum dots.

This article reports the development of highly waterborne silicon quantum dots (Si QDs) terminated with a reactive group for grafting of biomolecules. Hydrogen-terminated QDs were prepared by thermal disproportionation of amorphous hydrogen silsesquioxane derived from triethoxysilane followed by hydrofluoric etching. Next, the hydrogenated Si surfaces were exposed to 10-undecenoic acid at different temperatures in Ar atmosphere, yielding the termination of the QDs with a carboxyl group. The thermal hydrosilylation of 10-undecenoic acid yielded the termination of the QDs with a carboxyl group. An increase in molecular coverage of an undecanoic acid (UA) monolayer resulted in both the enhanced increase of zeta-potential in a negative direction for a greater water-dispersity and the increase of absolute quantum yield (QY) of photoluminescence (PL). PLQY improved for ~ 1% to 26% with increasing UA coverage. We assessed the molecular interaction between the UA-SiQDs and HeLa cells by means of cellular uptake experiments using the QDs with different UA coverages. Results showed that the QDs with the highest dispersity in water were not internalized in the cells under confocal fluorescence microscopic observation. In contrast, the QDs with lower coverage of UA monolayer were internalized by endocytosis when incubated with HeLa cells. This contrasting observation opens the possibility of successfully preparing carboxy-capped SiQDs that do not allow cellular uptake but are targeted to specific cells by appropriate conjugation with biomolecules.

Impact of bismuth-doping on enhanced radiative recombination in lead-free double-perovskite nanocrystals.

Lead-free double-perovskite nanocrystals (NCs) have received considerable attention as promising candidates for environmentally friendly optical applications. Furthermore, double-perovskite nanostructures are known to be physically stable compared to most other inorganic halide perovskites, with a generic chemical formula of ABX3 (e.g., A = Cs+; B = Sn2+ or Ge2+; X = Cl-, Br-, I-, or their combination). However, relevant experimental studies on the photophysical properties are still insufficient for Pb-free double-perovskite NCs. Herein, we synthesized Cs2Ag0.65Na0.35InCl6 NCs doped with bismuth (Bi3+) ions and investigated their photophysical properties to reveal the role of the dopant on the enhanced photoemission properties. Specifically, it was found that the photoluminescence quantum yield (PLQY) increased up to 33.2% by 2% Bi-doping. The optical bandgap of the NCs decreased from 3.47 eV to 3.41 eV as the amount of the dopant increased from 2% to 15%. To find out the effect of Bi-doping, the temperature-dependent PL properties of the undoped and doped NCs were investigated by utilizing steady-state and time-resolved PL spectroscopy. With increasing the temperature from 20 K to 300 K, the PL intensities of the doped NCs decreased slower than the undoped ones. The correlated average PL lifetimes of both the bismuth-doped and undoped NCs decreased with increasing the temperature. The experimental results revealed that all the NC samples showed thermal quenching with the temperature increasing, and the PL quenching was suppressed in bismuth-doped NCs.

Generating Lifetime-Enhanced Microbubbles by Decorating Shells with Silicon Quantum Nano-Dots Using a 3-Series T-Junction Microfluidic Device.

Long-term stability of microbubbles is crucial to their effectiveness. Using a new microfluidic device connecting three T-junction channels of 100 µm in series, stable monodisperse SiQD-loaded bovine serum albumin (BSA) protein microbubbles down to 22.8 ± 1.4 µm in diameter were generated. Fluorescence microscopy confirmed the integration of SiQD on the microbubble surface, which retained the same morphology as those without SiQD. The microbubble diameter and stability in air were manipulated through appropriate selection of T-junction numbers, capillary diameter, liquid flow rate, and BSA and SiQD concentrations. A predictive computational model was developed from the experimental data, and the number of T-junctions was incorporated into this model as one of the variables. It was illustrated that the diameter of the monodisperse microbubbles generated can be tailored by combining up to three T-junctions in series, while the operating parameters were kept constant. Computational modeling of microbubble diameter and stability agreed with experimental data. The lifetime of microbubbles increased with increasing T-junction number and higher concentrations of BSA and SiQD. The present research sheds light on a potential new route employing SiQD and triple T-junctions to form stable, monodisperse, multi-layered, and well-characterized protein and quantum dot-loaded protein microbubbles with enhanced stability for the first time.

Coherent InP/ZnS core@shell quantum dots with narrow-band green emissions.

We report, for the first time, that the coherent growth of zinc sulfide (ZnS) on a colloidal indium phosphide (InP) quantum dot (QD) yields a InP/ZnS core/shell structure with a single lattice constant of 0.563 nm. Compared to the bulk crystal of zinc-blend (cubic) InP, the lattice of the core QD is compressed by 4.1%. In contrast, the lattice of the shell expands by 4.1% relative to the bulky ZnS crystal throughout the core/shell QD if the shell is thinner than or equal to 0.81 nm and the diameter of the core QD is smaller than 2.64 nm. Under these conditions, the bandgap of the core QD increases, resulting in a blueshift of absorption and photoluminescence (PL) spectra. The PL peak is centered at 523 nm. Furthermore, the PL quantum yield is enhanced up to 70% and the PL bandwidth narrows to 36 nm based on the strengthened quantum confinement effect. The temperature dependence of the PL properties is investigated to discuss the effect of the core/shell lattice coherency on the improved PL performances.

Photosensitizer Encryption with Aggregation Enhanced Singlet Oxygen Production.

Chromophores that generate singlet oxygen (1O2) in water are essential to developing noninvasive disease treatments using photodynamic therapy (PDT). A facile approach for formation of stable colloidal nanoparticles of 1O2 photosensitizers, which exhibit aggregation enhanced 1O2 generation in water toward applications as PDT agents, is reported. Chromophore encryption within a fuchsonarene macrocyclic scaffold insulates the photosensitizer from aggregation induced deactivation pathways, enabling a higher chromophore density than typical 1O2 generating nanoparticles. Aggregation enhanced 1O2 generation in water is observed, and variation in molecular structure allows for regulation of the physical properties of the nanoparticles which ultimately affects the 1O2 generation. In vitro activity and the ability of the particles to pass through the cell membrane into the cytoplasm is demonstrated using confocal fluorescence microscopy with HeLa cells. Photosensitizer encryption in rigid macrocycles, such as fuchsonarenes, offers new prospects for the production of biocompatible nanoarchitectures for applications involving 1O2 generation.

Water-Soluble Silicon Quantum Dots toward Fluorescence-Guided Photothermal Nanotherapy.

We report carboxy-terminated silicon quantum dots (SiQDs) that exhibit high solubility in water due to the high molecular coverage of surface monolayers, bright light emission with high photoluminescence quantum yields (PLQYs), long-term stability in the PL property for monitoring cells, less toxicity to the cells, and a high photothermal response. We prepared water-soluble SiQDs by the thermal hydrosilylation of 10-undecenoic acid on their hydrogen-terminated surfaces, provided by the thermal disproportionation of triethoxysilane hydrolyzed at pH 3 and subsequent hydrofluoric etching. The 10-undecanoic acid-functionalized SiQDs (UA:SiQDs) showed long-term stability in hydrophilic solvents including ethanol and water (pH 7). We assess their interaction with live cells by means of cellular uptake, short-term toxicity, and, for the first time, long-term cytotoxicity. Results show that UA:SiQDs are potential candidates for theranostics, with their good optical properties enabling imaging for more than 18 days and a photothermal response having a 25.1% photothermal conversion efficiency together with the direct evidence of cell death by laser irradiation. UA:SiQDs have low cytotoxicity with full viability of up to 400 µg/mL for the short term and a 50% cell viability value after 14 days of incubation at a 50 µg/mL concentration.

Phosphatidylcholine-mediated regulation of growth kinetics for colloidal synthesis of cesium tin halide nanocrystals.

Cesium tin halide (CsSnX3, where X is halogen) perovskite nanocrystals (NCs) are one of the most representative alternatives to their lead-based cousins. However, a fundamental understanding of how to regulate the growth kinetics of colloidal CsSnX3 NCs is still lacking and, specifically, the role of surfactants in affecting their growth kinetics remains incompletely understood. Here we report a general approach for colloidal synthesis of CsSnX3 perovskite NCs through a judicious combination of capping agents. We demonstrate that introducing a small amount of zwitterionic phosphatidylcholine in the reaction is of vital importance for regulating the growth kinetics of CsSnX3 NCs, which otherwise merely leads to the formation of large-sized powders. Based on a range of experimental characterization, we propose that the formation of intermediate complexes between zwitterionic phosphatidylcholine and the precursors and the steric hindrance effect of branched fatty acid side-chains of phosphatidylcholine can regulate the growth kinetics of CsSnX3, which enables us to obtain CsSnX3 NCs with emission quantum yields among the highest values ever reported. Our finding of using zwitterionic capping agents to regulate the growth kinetics may inspire more research on the synthesis of high-quality tin-based perovskite NCs that could speed up their practical applications in optoelectronic devices.

Theory-Guided Synthesis of Highly Luminescent Colloidal Cesium Tin Halide Perovskite Nanocrystals.

The synthesis of highly luminescent colloidal CsSnX3 (X = halogen) perovskite nanocrystals (NCs) remains a long-standing challenge due to the lack of a fundamental understanding of how to rationally suppress the formation of structural defects that significantly influence the radiative carrier recombination processes. Here, we develop a theory-guided, general synthetic concept for highly luminescent CsSnX3 NCs. Guided by density functional theory calculations and molecular dynamics simulations, we predict that, although there is an opposing trend in the chemical potential-dependent formation energies of various defects, highly luminescent CsSnI3 NCs with narrow emission could be obtained through decreasing the density of tin vacancies. We then develop a colloidal synthesis strategy that allows for rational fine-tuning of the reactant ratio in a wide range but still leads to the formation of CsSnI3 NCs. By judiciously adopting a tin-rich reaction condition, we obtain narrow-band-emissive CsSnI3 NCs with a record emission quantum yield of 18.4%, which is over 50 times larger than those previously reported. Systematic surface-state characterizations reveal that these NCs possess a Cs/I-lean surface and are capped with a low density of organic ligands, making them an excellent candidate for optoelectronic devices without any postsynthesis ligand management. We showcase the generalizability of our concept by further demonstrating the synthesis of highly luminescent CsSnI2.5Br0.5 and CsSnI2.25Br0.75 NCs. Our findings not only highlight the value of computation in guiding the synthesis of high-quality colloidal perovskite NCs but also could stimulate intense efforts on tin-based perovskite NCs and accelerate their potential applications in a range of high-performance optoelectronic devices.

Nano-Bio Interaction between Blood Plasma Proteins and Water-Soluble Silicon Quantum Dots with Enabled Cellular Uptake and Minimal Cytotoxicity.

A better understanding of the compatibility of water-soluble semiconductor quantum dots (QDs) upon contact with the bloodstream is important for biological applications, including biomarkers working in the first therapeutic spectral window for deep tissue imaging. Herein, we investigated the conformational changes of blood plasma proteins during the interaction with near-infrared light-emitting nanoparticles, consisting of Pluronic F127 shells and cores comprised of assembled silicon QDs terminated with decane monolayers. Albumin and transferrin have high quenching constants and form a hard protein corona on the nanoparticle. In contrast, fibrinogen has low quenching constants and forms a soft protein corona. A circular dichroism (CD) spectrometric study investigates changes in the protein's secondary and tertiary structures with incremental changes in the nanoparticle concentrations. As expected, the addition of nanoparticles causes the denaturation of the plasma proteins. However, it is noteworthy that the conformational recovery phenomena are observed for fibrinogen and transferrin, suggesting that the nanoparticle does not influence the ordered structure of proteins in the bloodstream. In addition, we observed enabled cellular uptake (NIH3T3 Fibroblasts) and minimal cytotoxicity using different cell lines (HeLa, A549, and NIH3T3). This study offers a basis to design QDs without altering the biomacromolecule's original conformation with enabled cellular uptake with minimal cytotoxicity.

Emerging Atomic Energy Levels in Zero-Dimensional Silicon Quantum Dots.

Driven by the emergence of colloidal semiconductor quantum dots (QDs) of tunable emission wavelengths, characteristic of exciton absorption peaks, outstanding photostability and solution processability in device fabrication have become a key tool in the development of nanomedicine and optoelectronics. Diamond cubic crystalline silicon (Si) QDs, with a diameter larger than 2 nm, terminated with hydrogen atoms are known to exhibit bulk-inherited spin and valley properties. Herein, we demonstrate a newly discovered size region of Si QDs, in which a fast radiative recombination on the order of hundreds of picoseconds is responsible for photoluminescence (PL). Despite retaining a crystallographic structure like the bulk, controlling their diameters in the 1.1-1.7 nm range realizes the strong PL with continuous spectral tunability in the 530-580 nm window, the narrow spectral line widths without emission tails, and the fast relaxation of photogenerated carriers. In contrast, QDs with diameters greater than 1.8 nm display the decay times on the microsecond order as well as the previous Si QDs. In addition to the five-orders-of-magnitude variation in the PL decay time, a systematic study on the temperature dependence of PL properties suggests that the energy structure of the smaller QDs does not retain an indirect band gap character. It is discussed that a 1.7 nm diameter is critical to undergo changes in energy structure from bulky to molecular configurations.

High Aspect Ratio and Post-Processing Free Silver Nanowires as Top Electrodes for Inverted-Structured Photodiodes.

Silver nanowires (Ag NWs) as transparent conducting electrodes are widely used in many applications such as organic light-emitting diodes (OLEDs), polymer light-emitting diodes, touch screens, solar cells, and transparent heaters. In this work, using a large-scale synthesis, the synthesized Ag NWs had a high aspect ratio of 2820. The Ag NWs could be applied as a top transparent electrode in a device by simple drop-casting without any post-processing steps. The fabricated device comprised 4,4'-bis(carbazol-9-yl)biphenyl/MoO3 organic/inorganic layers which are parts of the inverted structure OLEDs or solar cells. The photodiode characteristics at the UV range were observed in the device. The ability of Ag NWs to replace opaque metals as top electrodes in a device has been demonstrated.

Recent advances on fluorescent biomarkers of near-infrared quantum dots for in vitro and in vivo imaging.

Luminescence probe has been broadly used for bio-imaging applications. Among them, near-infrared (NIR) quantum dots (QDs) are more attractive due to minimal tissue absorbance and larger penetration depth. Above said reasons allowed whole animal imaging without slice scan or dissection. This review describes in vitro and in vivo imaging of NIR QDs in the regions of 650-900 nm (NIR-I) and 1000-1450 nm (NIR-II). Also, we summarize the recent progress in bio-imaging and discuss the future trends of NIR QDs including group II-VI, IV-VI, I-VI, I-III-VI, III-V, and IV semiconductors.