Silicon Quantum Dots Research Articles

Biodistributions and Imaging of Poly(ethylene glycol)-Conjugated Silicon Quantum Dot Nanoparticles in Osteosarcoma Models via Intravenous and Intratumoral Injections.

Osteosarcoma is a malignant tumor with relatively high mortality rates in children and adolescents. While nanoparticles have been widely used in assisting the diagnosis and treatment of cancers, the biodistributions of nanoparticles in osteosarcoma models have not been well studied. Herein, we synthesize biocompatible and highly photoluminescent silicon quantum dot nanoparticles (SiQDNPs) and investigate their biodistributions in osteosarcoma mouse models after intravenous and intratumoral injections by fluorescence imaging. The bovine serum albumin (BSA)-coated and poly(ethylene glycol) (PEG)-conjugated SiQDNPs, when dispersed in phosphate-buffered saline (PBS), can emit red photoluminescence with the photoluminescence quantum yield more than 30% and have very low in vitro and in vivo toxicity. The biodistributions after intravenous injections reveal that the SiQDNPs are mainly metabolized through the livers in mice, while only slight accumulation in the osteosarcoma tumor is observed. Furthermore, the PEG conjugation can effectively extend the circulation time. Finally, a mixture of SiQDNPs and indocyanine green (ICG), which complement each other in the spectral range and diffusion length, is directly injected into the tumor for imaging. After the injection, the SiQDNPs with relatively large particle sizes stay around the injection site, while the ICG molecules diffuse over a broad range, especially in the muscular tissue. By taking advantage of this property, the difference between the osteosarcoma tumor and normal muscular tissue is demonstrated.

The combined plasma membrane coating and cluster bombing strategy for improved tumor-targeting gene delivery of silicon nanoclusters

With the promising biosafety and favorable cell imaging efficiency, silicon quantum dots (SiQDs) was broadly exploited as non-viral gene carriers in recent years. However, the low transfection efficiency and weak targeting ability hindered its further clinical applications. In this study, the combined plasma membrane coating and cluster bombing strategy was adopted to enhance the gene delivery potential of silicon quantum dots nanoclusters (SiNC). Initially, SiNC was generated via 3, 3′-Dithiodipropionic acid (DipA) crosslinking of SiQDs, then the obtained nanoclusters were coated by distinct plasma membrane. Interestingly, cell membrane coated SiNC (CM-SiNC) underwent particle size change, the typical character of “cluster bombing”, when exposed to high GSH concentration, which was observed in the tumor microenvironment. Meanwhile, CM-SiNC can be efficiently uptaken by HEK 293T and HeLa cells, therefore transferring DNA into those cells. More importantly, among the particles coated by HeLa (HeLa-M), Red Blood (RBC-M) or RAW267.4 (RAW-M) cell membrane, HeLa cell membrane coating exhibited better cellular uptake and transfection efficiency in HeLa cells, which suggested the encouraging tumor targeting ability. In sum, these data suggested that cluster bombing of SiNC could be beneficial for physical stability and biodistribution, the additional plasma membrane coating further endowed SiNC the efficient gene delivery and tumor targeting ability. Therefore, CM-SiNC had the potential as a gene delivery vector and its application should be further addressed in vivo.

Development of a biomimetic DNA delivery system by encapsulating polyethyleneimine functionalized silicon quantum dots with cell membranes.

Quantum dots (QDs) are renowned for their remarkable optoelectronic properties, making them suitable for applications such as bioimaging and optoelectronics. However, their use in gene delivery has been restricted due to the low DNA loading capacity. This study aimed to develop a biomimetic DNA delivery system by encapsulating polyethyleneimine (PEI) functionalized silicon QDs (SiQDs) with cell membranes and evaluate its potential as a gene vector in vitro. To achieve this, hydrophilic dispersed silicon QDs (PQDs) were prepared through a one-pot hydrothermal reaction of PEI and 3-Aminopropyltrimethoxysilane (APTMS). Subsequently, red blood cell membrane (RBCM) encapsulated biomimetic QDs (CM-PQDs) was obtained through the extrusion method. The CM-PQDs exhibited higher DNA loading capacity and better stability than naked SiQDs. The CM-PQDs/DNA complex was effectively taken up by cells, as observed through the fluorescence characteristics of QDs themselves. Both CM-P10QDs (prepared with PEI10k) and CM-P25QDs (prepared with PEI25k) could deliver DNA into cells and express the reporter protein successfully. CM-P25QDs showed a higher transfection efficiency of 77.32% in 293T cells and 47.11% in HeLa cells than SiQDs and CM-P10QDs. The results also indicated that cell membrane encapsulation could effectively reduce the cytotoxicity of SiQDs further. Therefore, the study concludes that CM-PQDs have the potential to serve as a safe and traceable biomimetic gene delivery system.

Single-Electron Transistor Operation of a Physically Defined Silicon Quantum Dot Device Fabricated by Electron Beam Lithography Employing a Negative-Tone Resist

We have proposed and demonstrated a device fabrication process of physically defined quantum dots utilizing electron beam lithography employing a negative-tone resist toward high-density integration of silicon quantum bits (qubits). The electrical characterization at 3.8 K exhibited so-called Coulomb diamonds, which indicates successful device operation as single-electron transistors. The proposed device fabrication process will be useful due to its high compatibility with the large-scale integration process.

(Invited) Silicon Quantum Dot Single-Electron Pumps for the Closure of the Quantum Metrology Triangle

We have developed silicon quantum dot single-electron pumps for the application to quantum electrical standards. High-speed silicon pumps operated at GHz frequencies, generating a large current at a sub-nanoampere level, are promising for the realization of a precise closure of the quantum metrology triangle; it is a consistency check experiment with the quantum Hall resistance standard and Josephson voltage standard. We have found that, to improve the pump accuracy which is governed by the dynamical charge quantization process in a quantum dot, the optimal design and operation of pumps regarding the gate length and cross coupling to the quantum dot is important. The Japanese project, which aims at a precise closure of the quantum metrology triangle, is described with its recent progress.

Facile Fabrication of Transparent Hydrophobic Spectral Converting Thin Film of Cyclic Silica-Silane Structure

There is a growing demand for advanced coatings with remarkable physical properties such as high transparency, water resistance, spectrum conversion, and dust repellence, which can be used in a variety of applications. In this study, we built thin films using silicon quantum dots and a silane-based material composite, resulting in a unique mix of hydrophobicity, self-cleaning and the ability to convert ultraviolet (UV) to visible spectrum. The use of silicon quantum dots in the film results in spectrum conversion from UV to visible wavelengths, taking advantage of their broad UV absorption and concurrent visible light emission. Concurrently, a silica-silane based layer of tetraethyl orthosilicate, N, N dimethyl amino propyl trimethoxy silane, and 3-chloro-propyl trimethoxy silane is integrated, imparting not only water resistance but also dust resistance. The challenging synthesis chemistry exemplifies the several stages required to create a spectral-converting hydrophobic layer. Given its inherent transparency, coupled with UV-to-visible spectrum conversion capabilities, this novel layered structure have a potential in outer coating of solar photovoltaic systems and various outdoor glass applications.

Ultrasensitive quantifying copper ions in serum by tapered optical fiber fluorescent sensor based on static quenching effect

As an essential trace element, abnormal levels of copper ions (Cu2+) in body are associated with various disease. Various methods have been developed for Cu2+ sensing, but the construction of portable sensors for online and sensitive detection of Cu2+ in complex samples is still urgent. In this work, a portable and in-situ optical fiber fluorescent sensor was firstly operated by combining tapered optical fiber and fluorescent silicon quantum dots (SiQDs) via hydrogel strategy and used for ultrasensitive detection of Cu2+ in serum. The hydrothermally synthesized SiQDs of blue fluorescence exhibited excellent specificity of response to Cu2+ due to the static quenching effect. Good linear correlations were obtained over Cu2+ concentration from 0.01 to 50 μM. The sensor was successfully used for rapid detection of Cu2+ in serum samples avoiding tedious pretreatment. The sensor provided a portable and effective platform for online and ultrasensitive determination of Cu2+ in complex samples with the detection limit of 3.58 nM, as well as promising for the detection of biomolecule mediated by Cu2+. This method demonstrated superiority in high sensitivity and selectivity, convenient practicability and easy fabrication. It is of significance for the analysis in narrow space, remote sensing and emergency analysis.

Dangling Bonds as Possible Contributors to Charge Noise in Silicon and Silicon-Germanium Quantum Dot Qubits.

Spin qubits based on Si and Si1-xGex quantum dot architectures exhibit among the best coherence times of competing quantum computing technologies, yet they still suffer from charge noise that limit their qubit gate fidelities. Identifying the origins of these charge fluctuations is therefore a critical step toward improving Si quantum-dot-based qubits. Here, we use hybrid functional calculations to investigate possible atomistic sources of charge noise, focusing on charge trapping at Si and Ge dangling bonds (DBs). We evaluate the role of global and local environment in the defect levels associated with DBs in Si, Ge, and Si1-xGex alloys, and consider their trapping and excitation energies within the framework of configuration coordinate diagrams. We additionally consider the influence of strain and oxidation in charge-trapping energetics by analyzing Si and GeSi DBs in SiO2 and strained Si layers in typical Si1-xGex quantum dot heterostructures. Our results identify that Ge dangling bonds are more problematic charge-trapping centers both in typical Si1-xGex alloys and associated oxidation layers, and they may be exacerbated by compositional inhomogeneities. These results suggest the importance of alloy homogeneity and possible passivation schemes for DBs in Si-based quantum dot qubits and are of general relevance to mitigating possible trap levels in other Si, Ge, and Si1-xGex-based metal-oxide-semiconductor stacks and related devices.

Plasma electrochemical synthesis of silicon quantum dots

Environmentally friendly and fast synthesis of silicon quantum dots (SiQDs) is realized with the assistance of plasma. The precursors used are N-(β-aminoethyl)-γ-aminopropyl trimethoxysilane (DAMO) and citric acid. When the excitation wavelength was 370 nm, the photoluminescence emission peak of the SiQDs appeared at 452.5 nm. The optimization of precursor concentration, reaction time and other parameters can effectively improve the quantum yield (QY) of SiQDs. The results show that the amidation and condensation of DAMO and citric acid plays an important role in the improvement of QY, as this means that more fluorescent molecules are produced and therefore QY is increased. This paper increases QY from 4.23% to 23.9%, providing a promising way to improve QY even more.

Chiral Melanin-like Particle-Inspired Fluorescent Silicon Quantum Dots for Sensitively Detecting Inflammation in Cells

Chiral Melanin-like Particle-Inspired Fluorescent Silicon Quantum Dots for Sensitively Detecting Inflammation in Cells

A 2D quantum dot array in planar 28Si/SiGe

Semiconductor spin qubits have gained increasing attention as a possible platform to host a fault-tolerant quantum computer. First demonstrations of spin qubit arrays have been shown in a wide variety of semiconductor materials. The highest performance for spin qubit logic has been realized in silicon, but scaling silicon quantum dot arrays in two dimensions has proven to be challenging. By taking advantage of high-quality heterostructures and carefully designed gate patterns, we are able to form a tunnel coupled 2 × 2 quantum dot array in a 28Si/SiGe heterostructure. We are able to load a single electron in all four quantum dots, thus reaching the (1,1,1,1) charge state. Furthermore, we characterize and control the tunnel coupling between all pairs of dots by measuring polarization lines over a wide range of barrier gate voltages. Tunnel couplings can be tuned from about 30 μeV up to approximately 400 μeV. These experiments provide insightful information on how to design 2D quantum dot arrays and constitute a first step toward the operation of spin qubits in 28Si/SiGe quantum dots in two dimensions.

An Efficient Design of Multiplier for Using in Nano-Scale IoT Systems Using Atomic Silicon

Because of recent technological developments, such as Internet of Things (IoT) devices, power consumption has become a major issue. Atomic silicon quantum dot (ASiQD) is one of the most impressive technologies for developing low-power processing circuits, which are critical for efficient transmission and power management in micro IoT devices. On the other hand, multipliers are essential computational circuits used in a wide range of digital circuits. Therefore, the multiplier design with a low occupied area and low energy consumption is the most critical expected goal in designing any micro IoT circuits. This paper introduces a low-power atomic silicon-based multiplier circuit for effective power management in the micro IoT. Based on this design, a 4×4-bit multiplier array with low power consumption and size is presented. The suggested circuit is also designed and validated using the SiQAD simulation tool. The proposed ASiQD-based circuit significantly reduces energy consumption and area consumed in the micro IoT compared to most recent designs.

Photoresponsivity Enhancement of Monolayer MoS2 by Silicon Quantum Dots

Hybrid 2D/0D structures with various 2D materials and 0D quantum dots (QDs) have been studied to overcome the limitations of 2D materials. In this work, a hybrid structure with MoS2 and silicon quantum dots (Si QDs) as a photodetector is developed. The I–V transfer characteristics show a threshold voltage shift after decorating Si QDs on MoS2, which results from an n‐type doping effect to the MoS2 channel from the Si QDs. The field‐effect mobility of the MoS2/Si QDs device is increased by ≈5.8 times compared with that of the bare MoS2 device. It is understood that the mobility enhancement is attributed to the surface defect passivation of MoS2 at the interface with Si QDs. It is observed that the photoresponsivity of the MoS2/Si QDs structure is improved by ≈7.7 times compared with that of the bare MoS2 device under 500 nm illumination. Additionally, it is observed that the photoluminescence (PL) intensity of MoS2 is increased about 4.5 times after decoration of Si QDs. The band alignment as type I at the interface between the Si QDs and MoS2 is interpreted. The mobility enhancement and the photoexcited charge transfer (CT) between the MoS2 and the Si QDs due to the illumination lead to enhancing the photoresponsivity of the MoS2/Si QDs hybrid structure.

Lysosome-targeted silicon quantum dots theranostics for simultaneous fluorescent imaging and photodynamic therapy

As an emerging treatment method, photodynamic therapy (PDT) has attracted considerable interest due to the characteristics of non-invasiveness, repeatable treatment, high spatiotemporal resolution and few side effects. However, the life span (<40 ns) and diffusion distance (<20 nm) of reactive oxygen species such as singlet oxygen (1O2) in tumor cells are extremely short, which has seriously limited therapeutic efficacy of PDT. The enrichment site of photosensitizers in cancer cells is usually the first site of PDT action, which will not only affect the biological signaling pathway of cancer cell death, but also is closely related to the final therapeutic effect. Therefore, the design and preparation of photosensitizers targeting specific subcellular organelles can directly break the biological function of the organelle and trigger the corresponding cell death signaling pathway, which can significantly improve the efficacy of PDT. Herein, a lysosome-targeted silicon quantum dots (L-Si QDs) was first made by diethylene glycol-mediated synthetic route as a multicolor fluorescent imaging reagents and a new photosensitizer. The as-prepared L-Si QDs exhibit bright fluorescence with excellent pH stability and time stability, excitation-dependent emission, and good biocompatibility. Furthermore, the results of cell experiments showed that L-Si QDs was accumulated in lysosomes after being taken up by cancer cells, and can efficiently produce 1O2 upon 635 nm laser irradiation, which can damage lysosomes, up-regulate cleavage caspase-3, increase Bax release, down-regulate Bcl-2 and induce cell apoptosis finally. This study significantly broadens the biomedical applications of silicon quantum dots and provides excellent nanomaterials candidates for tumor phototherapy.

Silicon-carbon anode with high interfacial stability by a facile thermal reaction involving alkaline nitrogenous carbon source for lithium ion batteries

Silicon‑carbon composites are considered one of the most promising anodes for high-energy lithium-ion batteries. In this work, NC@Si nanospheres were prepared as silicon‑carbon anode materials for lithium-ion batteries by using an alkaline nitrogenous carbon source (polydopamine, PDA) to induce the anchoring of ultra-fine and high-purity SiO2 quantum dots onto a carbon matrix, followed by a magnesium thermal reduction treatment. The small volume expansion of silicon quantum dots (<10 nm) in NC@Si nanospheres and the thin Si3N4 outerwear formed on Si quantum dots due to the diffusion of N atoms and the local high temperature of magnesium heat synergistically ensure the structural integrity of NC@Si nanospheres and inhibit the excessive formation of SEI. The multi-point solid electrical contact between the silicon quantum dots and the nitrogen-doped carbon matrix provides sufficient conductive channels for fast Li+ diffusion and charge transfer. The as-prepared NC@Si anode exhibits a specific capacity of 497.2 mAh g−1 at 0.1 A g−1 with a capacity retention of 75.4% after 100 cycles, demonstrating a stable cycling performance. In the NC@Si||LFP full cell, the anode maintains a reversible capacity of 260.8 mAh g−1 after 80 cycles. The investigation of NC@Si composite anode proves that the silicon‑carbon anode by a facile thermal reaction involving alkaline nitrogenous carbon source can effectively improve the defects of silicon, offering the possibility of commercial application of silicon-based anode.

Chemically modified starch with silicon quantum dots: Structures and properties

Attachment of Silicon quantum dots (Si QDs) onto starch via sol-gel controlled covalent bonding to form hybrid starch particles was developed to modulate the optical, physical, and mechanical features of starch. Fabricated Si QDs chemically interacted with –OH side groups due to the sol-gel reactions on the starch molecules providing a detectable new molecular bonding to result in fluorescent emission. The produced structures formed nonlinear morphological orientations that provide a nanocomposite material platform for a facile molecular marking in daily applications.

Simulation of 1/f charge noise affecting a quantum dot in a Si/SiGe structure

Due to presence of magnetic field gradient needed for coherent spin control, dephasing of single-electron spin qubits in silicon quantum dots is often dominated by 1/f charge noise. We investigate theoretically fluctuations of ground state energy of an electron in gated quantum dot in a realistic Si/SiGe structure. We assume that the charge noise is caused by motion of charges trapped at the semiconductor–oxide interface. We consider a realistic range of trapped charge densities, ρ ∼1010 cm−2, and typical lenghtscales of isotropically distributed displacements of these charges, δr≤ 1 nm, and identify pairs (ρ,δr) for which the amplitude and shape of the noise spectrum are in good agreement with spectra reconstructed in recent experiments on similar structures.

Efficient photon upconversion enabled by strong coupling between silicon quantum dots and anthracene.

Hybrid structures formed between organic molecules and inorganic quantum dots can accomplish unique photophysical transformations by taking advantage of their disparate properties. The electronic coupling between these materials is typically weak, leading photoexcited charge carriers to spatially localize to the dot or to a molecule at its surface. However, we show that by converting a chemical linker that covalently binds anthracene molecules to silicon quantum dots from a carbon-carbon single bond to a double bond, we access a strong coupling regime where excited carriers spatially delocalize across both anthracene and silicon. By pushing the system to delocalize, we design a photon upconversion system with a higher efficiency (17.2%) and lower threshold intensity (0.5 W cm-2) than that of a corresponding weakly coupled system. Our results show that strong coupling between molecules and nanostructures achieved through targeted linking chemistry provides a complementary route for tailoring properties in materials for light-driven applications.

Exploring the Core Parameters of CNC-Based Chiral Nematic Structures for Enhancing the Dissymmetry Factor of Right-Handed Circularly Polarized Luminescence.

The chiral nematic nanostructure formed from cellulose nanocrystal (CNC) self-assembly has shown great potential as a matrix for generating circularly polarized luminescent (CPL) light with a high dissymmetry factor. Exploring the relationship between the device composition and structure and the light dissymmetry factor is crucial to a common strategy for a strongly dissymmetric CPL light. In this study, we have compared the single-layered and double-layered CNC-based CPL devices with different luminophores, such as rhodamine 6G (R6G), methylene blue (MB), crystal violet (CV), and silicon quantum dots (Si QDs). We demonstrated that forming a double-layered structure of CNCs nanocomposites is a simple but effective pathway for enhancing the CPL dissymmetry factor for CNC-based CPL materials containing different luminophores. The |glum| values of double-layered CNC devices (dye@CNC5||CNC5) versus that of single-layered devices (dye@CNC5) are 3.25 times for Si QDs, 3.7 times for R6G, 3.1 times for MB, and 2.78 times for CV series. The different enhancement degrees of these CNC layers with a similar thickness may be due to the different pitch numbers in the chiral nematic liquid crystal layers whose photonic band gap (PBG) has been modified to match the emission wavelengths of dyes. Furthermore, the assembled CNC nanostructure has great tolerance to the addition of nanoparticles. Gold nanorods coated with the SiO2 layer (Au NR@SiO2) were added for enhancing the dissymmetry factor of MB in CNC composites (named MAS devices). When the strong longitudinal plasmonic band of the Au NR@SiO2 matched the emission wavelength of MB and the PBG of assembled CNC structures simultaneously, the increase in the glum factor and quantum yield of MAS composites was obtained. The good compatibility of the assembled CNC nanostructures makes it a universal platform for developing strong CPL light sources with a high dissymmetry factor.

Bifunctional manganese-doped silicon quantum dot-responsive smartphone-integrated paper sensor for visual multicolor/multifluorescence dual-mode detection of nitrite

Considering great threats of nitrite in food toward public health, it is significant to develop portable, dependable, and cost-effective methods to detect the target. In comparison with traditional colorimetric or fluorometric strategies relying on the intensity variation at a single wavelength, multimodal measurement with notable color changes is a more attractive paradigm because of its stronger resistance against external conditions, expanded application scenario, improved reliability, and naked-eye distinguishable readouts. However, it remains a challenge on how to attain this goal. Here we proposed a smartphone-integrated paper sensor based on manganese-doped silicon quantum dots (Mn-SiQDs) for the visual dual-mode multicolor/multifluorescence determination of nitrite. The Mn-SiQDs featured both photoluminescence and oxidase-mimetic catalytic activity, and could stimulate the colorless 3,3′,5,5′-tetramethylbenzidine (TMB) oxidation to a blue species TMB+. When nitrite existed, the generated TMB+ selectively reacted with the analyte to produce yellow diazotized TMB+. Meanwhile, the photoluminescence of Mn-SiQDs could be suppressed by the diazotized TMB+ via inner filter effect. As a result, with a facile electrostatic assembly of Mn-SiQDs and [Ru(bpy)3]2+, the formed complex Mn-SiQDs/[Ru(bpy)3]2+ led to the variations of both color and photoluminescence upon different levels of nitrite. By combining the principle with paper strips and smartphone sensing, the fabricated sensor offered naked-eye visible multicolor/multifluorescence dual-mode response toward nitrite, exhibiting excellent specificity, performance stability, and practicability in food analysis. Our work provides an effective tool to achieve the multicolor/multifluorescence bimodal measurement of nitrite, and it will inspire future effort on designing versatile materials for advanced sensing applications.