A Single-Step Bottom-up Approach for Synthesis of Highly Uniform Mie-Resonant Crystalline Semiconductor Particles at Visible Wavelengths.

Optically Mie-resonant crystalline silicon nanoparticles have long attracted interest for their unique scattering behaviors. Here, we report a bottom-up nonthermal plasma process that produces highly monodisperse particles, with diameters controllable between 60 and 214 nm, by temporarily electrostatically trapping nanoparticles inside a continuous-flow plasma reactor. The particle size is tuned by adjusting the gas residence time in the reactor. By dispersing the nanoparticles in water, optical extinction measurements indicate colloidal solutions of a particle-based metafluid in which particles support both strong magnetic and electric dipole resonances at visible wavelengths. The spectral overlap of the electric and magnetic resonances gives rise to directional Kerker scattering. The extinction measurements show excellent agreement with Mie theory, supporting the idea that the fabrication process enables particles with narrow distributions in size, shape, and composition. This single-step gas-phase process can also produce Mie-resonant nanoparticles of dielectric materials other than silicon and directly deposit them on the desired substrates.

The Pattern of Granuloma Formation in the Liver of Rats as a Reflection of the Mechanism of Internalization of Submicron Silicon Particles.

A morphological analysis of the liver of Wistar rats was performed 2 months after a single intravenous injection of porous silicon particles of different sizes (60-80, 250-300, and 500-600 nm; 2 mg/ml, 1 ml). Histological, immunohistochemical, and electron microscopic methods showed the development of CD68+ granulomas in all experimental groups. Injection of 60-80-nm porous silicon particles led to the formation of single large granulomas (>2000 µm2), while 500-600-nm nanoparticles caused the formation of numerous smaller granulomas. The mechanism of involution of granulomas by apoptosis of Kupffer cells and the absence of subsequent connective tissue remodeling of the organ tissue is shown.

Regulatory effects of silicon nanoparticles on the growth and photosynthesis of cotton seedlings under salt and low-temperature dual stress.

BACKGROUND: Silicon nanoparticles (SiO2-NPs) play a crucial role in plants mitigating abiotic stress. However, the regulatory mechanism of SiO2-NPs in response to multiple stress remains unclear. The objectives of this study were to reveal the regulatory mechanism of SiO2-NPs on the growth and photosynthesis in cotton seedlings under salt and low-temperature dual stress. It will provide a theoretical basis for perfecting the mechanism of crop resistance and developing the technology of cotton seedling preservation and stable yield in arid and high salt areas. RESULTS: The results showed that the salt and low-temperature dual stress markedly decreased the plant height, leaf area, and aboveground biomass of cotton seedlings by 9.58%, 15.76%, and 39.80%, respectively. While SiO2-NPs alleviated the damage of the dual stress to cotton seedling growth. In addition to reduced intercellular CO2 concentration, SiO2-NPs significantly improved the photosynthetic rate, stomatal conductance, and transpiration rate of cotton seedling leaves. Additionally, stomatal length, stomatal width, and stomatal density increased with the increase in SiO2-NPs concentration. Notably, SiO2-NPs not only enhanced chlorophyll a, chlorophyll b, and total chlorophyll content, but also slowed the decrease of maximum photochemical efficiency, actual photochemical efficiency, photochemical quenching of variable chlorophyll, and the increase in non-photochemical quenching. Moreover, SiO2-NPs enhanced the activities of ribulose-1,5-bisphosphate carboxylase/oxygenase and phosphoenolpyruvate carboxylase, improved leaf water potential, and decreased abscisic acid and malondialdehyde content. All the parameters obtained the optimal effects at a SiO2-NPs concentration of 100 mg L- 1, and significantly increased the plant height, leaf area, and aboveground biomass by 7.68%, 5.37%, and 43.00%, respectively. Furthermore, significant correlation relationships were observed between photosynthetic rate and stomatal conductance, stomatal length, stomatal width, stomatal density, chlorophyll content, maximum photochemical efficiency, actual photochemical efficiency, photochemical quenching of variable chlorophyll, and Rubisco activity. CONCLUSION: The results suggested that the SiO2-NPs improved the growth and photosynthesis of cotton seedlings might mainly result from regulating the stomatal state, improving the light energy utilization efficiency and electron transport activity of PSII reaction center, and inducing the increase of Rubisco activity to enhance carbon assimilation under the salt and low-temperature dual stress.

A Brief Overview of Silicon Nanoparticles as Anode Material: A Transition from Lithium-Ion to Sodium-Ion Batteries.

The successful utilization of silicon nanoparticles (Si-NPs) to enhance the performance of Li-ion batteries (LIBs) has demonstrated their potential as high-capacity anode materials for next-generation LIBs. Additionally, the availability and relatively low cost of sodium resources have a significant influence on developing Na-ion batteries (SIBs). Despite the unique properties of Si-NPs as SIBs anode material, limited study has been conducted on their application in these batteries. However, the knowledge gained from using Si-NPs in LIBs can be applied to develop Si-based anodes in SIBs by employing similar strategies to overcome their drawbacks. In this review, a brief history of Si-NPs' usage in LIBs is provided and discuss the strategies employed to overcome the challenges, aiming to inspire and offer valuable insights to guide future research endeavors.

A Multifunctional Porous Silicon Nanocarrier for Glioblastoma Treatment.

Clinical treatment of glioblastoma (GBM) remains a major challenge because of the blood-brain barrier, chemotherapeutic resistance, and aggressive tumor metastasis. The development of advanced nanoplatforms that can efficiently deliver drugs and gene therapies across the BBB to the brain tumors is urgently needed. The protein "downregulated in renal cell carcinoma" (DRR) is one of the key drivers of GBM invasion. Here, we engineered porous silicon nanoparticles (pSiNPs) with antisense oligonucleotide (AON) for DRR gene knockdown as a targeted gene and drug delivery platform for GBM treatment. These AON-modified pSiNPs (AON@pSiNPs) were selectively internalized by GBM and human cerebral microvascular endothelial cells (hCMEC/D3) cells expressing Class A scavenger receptors (SR-A). AON was released from AON@pSiNPs, knocked down DRR and inhibited GBM cell migration. Additionally, a penetration study in a microfluidic-based BBB model and a biodistribution study in a glioma mice model showed that AON@pSiNPs could specifically cross the BBB and enter the brain. We further demonstrated that AON@pSiNPs could carry a large payload of the chemotherapy drug temozolomide (TMZ, 1.3 mg of TMZ per mg of NPs) and induce a significant cytotoxicity in GBM cells. On the basis of these results, the nanocarrier and its multifunctional strategy provide a strong potential for clinical treatment of GBM and research for targeted drug and gene delivery.

Silicon nanoparticles as a fluorometric probe for sensitive detection of cyanide ion and its application in C. elegans bio-imaging.

In recent years, silicon nanoparticles (Si NPs) have been explored as a promising alternative to traditional organic fluorophores in optical sensing and bioimaging applications owing to their exceptional optical properties and negligible toxicity. In this study, water-dispersible Si NPs were prepared from a 3-aminopropyl trimethoxysilane precursor using a facile one-pot process. The as-prepared Si NPs exhibited excitation-wavelength-dependent fluorescence properties and bright green fluorescence at 530 nm upon excitation at 420 nm. The fluorescence properties of Si NPs remained unperturbed under various physiological conditions, such as varying pH, ionic strength, and incubation time. A sensitive fluorometric turn-off sensor for cyanide ion (CN-) detection was devised based on the unique fluorescence properties of Si NPs. The Si NPs-based detection assay showed a good linear response toward CN- ranging between 0 and 33 µM, with a limit of detection as low as 0.90 nM. Caenorhabditis elegans is used as a model organism to evaluate the in vivo toxicity and molecular imaging capability of Si NPs.

Silicon nanoparticles: Comprehensive review on biogenic synthesis and applications in agriculture.

Recent advancements in nanotechnology have opened new advances in agriculture. Among other nanoparticles, silicon nanoparticles (SiNPs), due to their unique physiological characteristics and structural properties, offer a significant advantage as nanofertilizers, nanopesticides, nanozeolite and targeted delivery systems in agriculture. Silicon nanoparticles are well known to improve plant growth under normal and stressful environments. Nanosilicon has been reported to enhance plant stress tolerance against various environmental stress and is considered a non-toxic and proficient alternative to control plant diseases. However, a few studies depicted the phytotoxic effects of SiNPs on specific plants. Therefore, there is a need for comprehensive research, mainly on the interaction mechanism between NPs and host plants to unravel the hidden facts about silicon nanoparticles in agriculture. The present review illustrates the potential role of silicon nanoparticles in improving plant resistance to combat different environmental (abiotic and biotic) stresses and the underlying mechanisms involved. Furthermore, our review focuses on providing the overview of various methods exploited in the biogenic synthesis of silicon nanoparticles. However, certain limitations exist in synthesizing the well-characterized SiNPs on a laboratory scale. To bridge this gap, in the last section of the review, we discussed the possible use of the machine learning approach in future as an effective, less labour-intensive and time-consuming method for silicon nanoparticle synthesis. The existing research gaps from our perspective and future research directions for utilizing SiNPs in sustainable agriculture development have also been highlighted.

Silicon nanoparticles: Synthesis, uptake and their role in mitigation of biotic stress.

In the current scenario of global warming and climate change, plants face many biotic stresses, which restrain growth, development and productivity. Nanotechnology is gaining precedence over other means to deal with biotic and abiotic constraints for sustainable agriculture. One of nature's most beneficial metalloids, silicon (Si) shows ameliorative effect against environmental challenges. Silicon/Silica nanoparticles (Si/SiO2NPs) have gained special attention due to their significant chemical and optoelectronic capabilities. Its mesoporous nature, easy availability and least biological toxicity has made it very attractive to researchers. Si/SiO2NPs can be synthesised by chemical, physical and biological methods and supplied to plants by foliar, soil, or seed priming. Upon uptake and translocation, Si/SiO2NPs reach their destined cells and cause optimum growth, development and tolerance against environmental stresses as well as pest attack and pathogen infection. Using Si/SiO2NPs as a supplement can be an eco-friendly and cost-effective option for sustainable agriculture as they facilitate the delivery of nutrients, assist plants to mitigate biotic stress and enhances plant resistance. This review aims to present an overview of the methods of formulation of Si/SiO2NPs, their application, uptake, translocation and emphasize the role of Si/SiO2NPs in boosting growth and development of plants as well as their conventional advantage as fertilizers with special consideration on their mitigating effects towards biotic stress.

A dual-mode nanoprobe based on silicon nanoparticles and Fe(II)-phenanthroline for the colorimetric and fluorescence determination of nitrite.

A fluorometric and colorimetric dual-modal nanoprobe (denoted as Fe2+-Phen/SiNPs) has been developed for selective and sensitive determination of nitrite (NO2-). The mechanism is based on fluorescence quenching between silicon nanoparticles (SiNPs) and Fe(II)-phenanthroline complex (Fe2+-Phen) via inner filter effect and redox. With the addition of increasing NO2-, Fe2+ is oxidized to Fe3+, recovering the fluorescence of SiNPs. Meanwhile, the color of the system gradually changes from orange-red to colorless, which enables colorimetric measurement. The NO2- concentration shows a wide linear relationship with fluorescence intensity from 0.1 to 1.0 mM (R2 = 0.9955) with a detection limit of 2.4 µM in the fluorometric method (excitation wavelength: 380 nm). By contrast, the linear range of the colorimetric method ranges from 0.01 to 0.35 mM (R2 = 0.9953) with a limit of detection of 6.8 µM (proposed selective absorbance: 510 nm). The probe has been successfully applied to nitrite determination in water, salted vegetables, and hams demonstrating broad application prospects for the determination of nitrite in complicated matrices.

Using Single-Crystal Graphene to Form Arrays of Nanocapsules Enabling the Observation of Light Elements in Liquid Cell Transmission Electron Microscopy.

We have designed and fabricated a TEM (transmission electron microscopy) liquid cell with hundreds of graphene nanocapsules arranged in a stack of two Si3N4-x membranes. These graphene nanocapsules are formed on arrays of nanoholes patterned on the Si3N4-x membrane by focused ion beam milling, allowing for better resolution than for the conventional graphene liquid cells, which enables the observation of light elements, such as atomic structures of silicon. We suggest that multiple nanocapsules provide opportunities for consecutive imaging under the same conditions in a single liquid cell. The use of single-crystal graphene windows offers an excellent signal-to-noise ratio and high spatial resolution. The motion of silicon nanoparticles (a low atomic number (Z) material) interacting with nanobubbles was observed, and analyzed, in detail. Our approach will help advance liquid-phase TEM observations by providing a straightforward method to encapsulate liquid between monolayers of various 2-dimensional materials.

Antibacterial Effect of Acoustic Cavitation Promoted by Mesoporous Silicon Nanoparticles.

As-prepared mesoporous silicon nanoparticles, which were synthesized by electrochemical etching of crystalline silicon wafers followed by high-energy milling in water, were explored as a sonosensitizer in aqueous media under irradiation with low-intensity ultrasound at 0.88 MHz. Due to the mixed oxide-hydride coating of the nanoparticles' surfaces, they showed both acceptable colloidal stability and sonosensitization of the acoustic cavitation. The latter was directly measured and quantified as a cavitation energy index, i.e., time integral of the magnitude of ultrasound subharmonics. The index turned out to be several times greater for nanoparticle suspensions as compared to pure water, and it depended nonmonotonically on nanoparticle concentration. In vitro tests with Lactobacillus casei revealed a dramatic drop of the bacterial viability and damage of the cells after ultrasonic irradiation with intensity of about 1 W/cm2 in the presence of nanoparticles, which themselves are almost non-toxic at the studied concentrations of about 1 mg/mL. The experimental results prove that nanoparticle-sensitized cavitation bubbles nearby bacteria can cause bacterial lysis and death. The sonosensitizing properties of freshly prepared mesoporous silicon nanoparticles are beneficial for their application in mild antibacterial therapy and treatment of liquid media.

Preparation of Mesoporous Si Nanoparticles by Magnesiothermic Reduction for the Enhanced Reactivity.

In this study, mesoporous silicon nanoparticles (M-Si) were successfully prepared by a magnesiothermic reduction of mesoporous silica nanoparticles, which were synthesized by a templated sol-gel method and used as the precursors. M-Si exhibited a uniform size distribution with an average diameter of about 160 nm. The measured BET surface area was 93.0 m2 g-1, and the average pore size calculated by the BJH method was 16 nm. The large internal surface area provides rich reaction sites, resulting in unique interfacial properties and reduced mass diffusion limitations. The mechanism of the magnesiothermic reduction process was discussed. The reactivity of prepared M-Si was compared with that of commercially available non-porous Si nanopowder (with the average diameter of about 30 nm) by performing simultaneous thermogravimetry and differential scanning calorimetry in the air. The results showed that the reaction onset temperature indicated by weight gain was advanced from 772 °C to 468 °C, indicating the promising potential of M-Si as fuel for metastable intermolecular composites.

Ultrabright silicon nanoparticle fluorescence probe for sensitive detection of cholesterol in human serum.

A highly sensitive fluorescence-based assay for cholesterol detection was developed using water-dispersible green-emitting silicon nanoparticles (SiNPs) as a fluorescence indicator and enzyme-catalyzed oxidation product PPDox (Bandrowski's base) as a quencher. The SiNPs were facilely synthesized via a simple, one-step hydrothermal treatment using 3-[2-(2-aminoethylamino)ethylamino]propyl-trimethoxysilane (AEEA) as the silicon source, which has ultrahigh quantum yield and low phototoxicity. Under the catalysis of cholesterol oxidase (ChOx), hydrogen peroxide (H2O2) was generated as a result of cholesterol oxidation. Utilizing p-phenylenediamine (PPD) as the substrate for horseradish peroxidase (HRP) in the presence of H2O2 led to the production of PPDox. Based upon the inner filter effect (IFE), the established ultrasensitive fluorescent assay could accurately measure cholesterol. The limit of detection (LOD) of the assay was 0.018 µM with a linear range of 0.025-10 µM. The results for the detection of real serum samples by the proposed assay were comparable to those by a commercial reagent kit, demonstrating that our proposed strategy has high application potential in disease diagnosis and other related biological studies.

Antenna effect of pyridoxal phosphate on the fluorescence of mitoxantrone-silicon nanoparticles and its application in alkaline phosphatase assay.

As a kind of sensing and imaging fluorescent probe with the merit of low toxicity, good stability, and environment-friendly, silicon nanoparticles (SiNPs) are currently attracting extensive research. In this work, we obtained mitoxantrone-SiNPs (MXT-SiNPs) with green emission by one-pot synthesis under mild temperature condition. The antenna based on pyridoxal phosphate (PLP) was designed for light-harvesting to enhance the luminescence of MXT-SiNPs and to establish a novel sensing strategy for alkaline phosphatase (ALP). PLP transfers the absorbed photon energy to MXT-SiNPs by forming Schiff base. When PLP is dephosphorized by ALP, the released free hydroxyl group reacts with aldehyde group to form internal hemiacetal, which leads to the failure of Schiff base formation. Based on the relationship between antenna formation ability and PLP hydrolysis degree, the activity of ALP can be measured. A good linear relationship was obtained from 0.2 to 3.0 U/L, with a limit of detection of 0.06 U/L. Furthermore, the sensing platform was successfully used to detect ALP in human serum with recovery of 97.6-106.2%. The rational design of antenna elements for fluorescent nanomaterials can not only provide a new pathway to manipulate the luminescence, but also provide a new direction for fluorescence sensing strategy.

A dual-signal sensing strategy based on ratiometric fluorescence and colorimetry for determination of Cu2+ and glyphosate.

Herein, a dual-signal sensing strategy based on ratiometric fluorescence and colorimetry for Cu2+ and glyphosate determination was constructed. Fluorescence silicon nanoparticles (SiNPs) were prepared by hydrothermal reaction, which has maximum fluorescence intensity under the excitation of 355 nm. o-Phenylenediamine (OPD) was oxidized through Cu2+ to generate 2,3-diaminophenazine (oxOPD). The obtained oxOPD showed a strong absorption peak at 417 nm and quenched the fluorescence of SiNPs at 446 nm due to fluorescence resonance energy transfer (FRET). Meanwhile, oxOPD produced a new fluorescence emission at 556 nm forming a ratiometric state. With increasing Cu2+, the original solution changed from colorless to yellow. When glyphosate was present, the interaction between Cu2+ and the functional groups of glyphosate could reduce the oxidation of oxOPD, resulting in the enhancement of fluorescence at 446 nm and the decrease of fluorescence at 556 nm. Furthermore, the addition of glyphosate changed yellow solution to colorless. Under the optimal conditions of OPD (1 mM), 20 mM Tris-HCl buffer (pH 7.5), and incubation time (4 h), the ratiometric fluorescence sensor had good selectivity and showed a wide linear range of 0.025-20 µM with the LOD of 0.008 µM for Cu2+ and 0.15-1.5 µg/mL with the LOD of 0.003 µg/mL for glyphosate, respectively. Besides, it is worth mentioning that this developed sensing system showed good performance in real samples, providing a simple and reliable dual-signal detection strategy.

Fluorescent silicon nanoparticle-based quantitative hemin assay.

Hemin with functions such as oxygen carrying, oxygen storing, promoting redox, and performing electron transfer is important for the health of organisms. In this paper, green synthetic silicon nanoparticles (Si-NPs) were synthesized and used for free hemin detection in serum (a low limit of detection (LOD), 29.5 nM). The quenching mechanism was investigated by UV-vis absorption spectra, time-resolved luminescence decay curve, and circular dichroism (CD) spectra. It was confirmed that multiple redox centers of hemin led to intensified effective collision and increased the electron transfer rate, therefore enhancing the dynamic quenching, and it was undeniable that the inner filter effect (IFE) also played a role in the quenching.

A green method for removing chromium (VI) from aqueous systems using novel silicon nanoparticles: Adsorption and interaction mechanisms.

In the present study, we used the horsetail plant (Equisetum arvense) as a green source to synthesize silicon nanoparticles (GS-SiNPs), considering that it could be an effective adsorbent for removing chromium (Cr (VI)) from aqueous solutions. The characterization of GS-SiNPs was performed via Brunauer-Emmett-Teller (BET), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and X-ray photo electron spectroscopy (XPS) techniques. The batch test results of Cr (VI) adsorption on GS-SiNPs showed a high adsorption capacity, reaching 87.9% of the amount added. The pseudo-second order kinetic model was able to comprehensively explain the adsorption kinetics and provided a maximum Cr (VI) adsorption capacity (Qe) of 3.28 mg g-1 (R2 = 90.68), indicating fast initial adsorption by the diffusion process. The Langmuir isotherm model fitted the experimental data, and accurately simulated the adsorption of Cr (VI) on GS-SiNPs (R2 = 97.79). FTIR and XPS spectroscopy gave further confirmation that the main mechanism was ion exchange with Cr and surface complexation through -OH and -COOH. Overall, the results of the research can be of relevance as regards a green and new alternative for the removal of Cr (VI) pollution from affected environments.

Fluorometric assay based on the in situ formation of silicon nanoparticles for the determination of ß-glucuronidase.

As a prodrug-converting enzyme, ß-glucuronidase (ß-GCase) is a lysosomal enzyme participating in the release of glucose from glucopyranosyl glycoside. In this work, for the first time, we have developed an analytical method exhibiting fluorometric signals for straightforward determination of ß-GCase using silicon nanoparticles (Si NPs). Via hydrothermal treatment, in the water bath of 70 °C for 50 min, dopamine (DA) reacts with (3-[2-(2-aminoethylamino) ethylamino] propyltrimethoxysilane) (AEEA) to produce green fluorescent Si NPs. Enlightened by such easy reaction and ß-GCase-triggered specific hydrolysis of dopamine-4-ß-D-glucuronide (DA-GCU) into DA, we have designed an analytical method for ß-GCase sensing through the production of Si NPs. Therefore, through the designed sensing platform, ß-GCase activity was monitored, and the limit of detection (LOD) for this study was 0.02 U/L. Furthermore, the feasibility of the method was assessed by measuring ß-GCase activity in human serum where recoveries and RSD were in the ranges 99-104% and 1.37-3.44, respectively.

Determination of cyanide based on a dual-emission ratiometric nanoprobe using silver sulfide quantum dots and silicon nanoparticles.

A novel ratiometric fluorescent nanoprobe was designed for the sensitive determination of cyanide anion (CN-) by the electrostatic attraction between positively charged silicon nanoparticles (Si NPs) and negatively charged silver sulfide quantum dots (Ag2S QDs). The nanoprobe exhibited two well-resolved emission peaks at 446 nm and 540 nm under a single excitation wavelength (360 nm). In the presence of CN-, the fluorescence of Ag2S QDs at 540 nm was remarkably quenched, while the fluorescence of the Si NPs at 446 nm remained constant, establishing the desired conditions for ratiometric fluorescence detection. Under optimal conditions, the ratiometric fluorescence assay showed good linearity (R2 = 0.9921) within the range 0.05-15 µM, and the limit of detection was calculated to be 56 nM (at an S/N ratio of 3). The proposed Ag2S QD/Si NP nanoprobe has been successfully used to determine CN- in water and sprouting potato samples with satisfactory recoveries in the range 97-110.5%.

Water-Based Graphene Oxide-Silicon Hybrid Nanofluids-Experimental and Theoretical Approach.

In the current paper, a new hybrid nanofluid based on graphene oxide sheets and silicon nanoparticles is proposed for thermal applications. GO sheets and Si nanoparticles with different mixture ratios are dispersed in distilled water. Dynamic viscosity is measured at temperatures within the range 20-50 °C and the values are compared to the results available in the literature. The results indicated that the viscosity increases with increasing the mixture ratio of graphene oxide. A new correlation for the dynamic viscosity based on the experimental findings is proposed. Finally, the criteria for the performance of new hybrid nanofluid for thermal applications are analyzed.