Luminescent Silicon Nanoparticles Research Articles

Study of Mask Fibers for Protection Against SARS-Cov-2 Via Luminescent Aerosolized Silicon Nanoparticles

During the 2020-current COVID-19 pandemic, the importance of wearing a mask to reduce infection and spread is key. The mask works as filter for the different microorganisms. In this work the geometrical part of the filtration process of the N95 and surgical masks was studied using luminescent ultra-small silicon nanoparticles (Si-NPs) to represent the SARS-CoV-2 by spraying it on the mask using atomizer. Scanning electron microscopy (SEM), and optical microscope were used to check the mask. The obtained images show that the Si nanoparticles to are trapped by the PE fiber network, indicating its ability to filter SARS-CoV-2. This visualization using nanotechnology can help to further improve mask designs for better filtration.

Synthesis and characterization of organic ligand capped luminescent silicon nanoparticles

The confinement effects on the optical characteristics of silicon nanoparticles (Si-NPs) are very attractive for a variety of low-cost applications of this nontoxic material in light emitting devices and photovoltaics. However, effective utilization of these properties in devices have been limited as chemically prepared Si-NPs are highly prone towards oxidation to form amorphous silica. Surface modified luminescent Si-NPs are synthesized by an inexpensive wet-chemical solution-based route by hydrolyzing the silicon tetrachloride (SiCl4) and terminating the Si dangling bonds by using different capping ligands. Structural, optical and electrical properties are studied and the photoluminescence (PL) characteristics are correlated to its core–shell structure. The photoluminescence characteristics of the surface modified Si-NPs of virtually identical sizes in the core was accounted in terms of effects from the variations in the cell-structure on the surface of Si-NPs introduced by changes in the nature of siloxane capping.

Study of Polyethylene Fibers Used in Masks Via Luminescent Aerosolized Silicon Nanoparticles

Commercial polyethylene (PE) fiber-based masks are currently used as personal filters for protection against various microorganisms. Due to the coronavirus (SARS-CoV-2) pandemic of 2020, the use of masks has become the critical mechanism in reducing the spread. The PE mask filter uses a sieve (geometry) in a spider web fashion to filter out microorganisms using Van der Waals atomic forces. However, the non-geometrical part of the filtration process is not fully understood. In this work, we utilized luminescent ultra-small silicon nanoparticles, which are Si-H or/and Si-OH terminated to examine how the filter operates at a chemical level. The particles were sprayed onto the fiber network by an atomizer and we used scanning electron microscopy (SEM), optical microscope and fluorescence spectroscopy under UV radiation. The images and measurements clearly showed that the Si nanoparticles bonded to the PE fiber network. The results were analyzed in terms of chemical bonding between Si nanoparticle and fiber. Our findings suggest that the PE fibers could act as a chemical filter via hydrogen or hydrolysis–based bonding or via Si-C bonding, which is complementary to their physical filtration ability via the geometric sieve process.Graphic

Silicon Quantum Dot-Polymer Fabry-Pérot Resonators with Narrowed and Tunable Emissions.

Luminescent silicon nanoparticles have been widely recognized as an alternative for metal-based quantum dots (QDs) for optoelectronics partly because of the high abundance and biocompatibility of silicon. To date, the broad photoluminescence line width (often >100 nm) of silicon QDs has been a hurdle to achieving competitive spectral purity and incorporating them into light-emitting devices. Herein we report fabrication and testing of straightforward configuration of Fabry-Pérot resonators that incorporates a thin layer of SiQD-polymer hybrid/blend between two reflective silver mirrors; remarkably these devices exhibit up-to-14-fold narrowing of SiQD emission and achieve a spectral bandwidth as narrow as ca. 9 nm. Our polymer-based, SiQD-containing Fabry-Pérot resonators also provide convenient spectral tunability, can be prepared using a variety of polymer hosts and substrates, and enable rigid as well as flexible devices.

Luminescent silicon nanoparticles for distinctive tracking of cellular targeting and trafficking.

Developing therapeutic nanoparticles that actively target disease cells or tissues by exploiting the binding specificity of receptors presented on the cell surface has extensively opened up biomedical applications for drug delivery and imaging. An ideal nanoparticle for biomedical applications is required to report confirmation of relevant targeting and the ultimate fate in a physiological environment for further verification, e.g. to adapt dosage or predict response. Herein, we demonstrate tracking of silicon nanoparticles through intrinsic photoluminescence (PL) during the course of cellular targeting and uptake. Time-resolved analysis of PL characteristics in cellular microenvironments provides dynamic information on the physiological conditions where the silicon nanoparticles are exposed. In particular, the PL lifetime of the silicon nanoparticles is in the order of microseconds, which is significantly longer than the nanosecond lifetimes exhibited by fluorescent molecules naturally presented in cells, thus allowing discrimination of the nanoparticles from the cellular background autofluorescence in time-gated imaging. The PL lifetime is a physically intensive property that reports the inherent characteristics of the nanoparticles regardless of surrounding noise. Furthermore, we investigate a unique means to inform the lifespan of the biodegradable silicon nanoparticles responsive to local microenvironment in the course of endocytosis. A multivalent strategy of nanoparticles for enhanced cell targeting is also demonstrated with complementary analysis of time-resolved PL emission imaging and fluorescence correlation spectroscopy. The result presents the promising potential of the photoluminescent silicon nanoparticles toward advanced cell targeting systems that simultaneously enable tracking of cellular trafficking and tissue microenvironment monitoring.

Luminescent Porous Silicon Nanoparticles for Continuous Wave and Time-Gated Photoluminescence Imaging.

Luminescent porous silicon nanoparticles (LpSiNPs) display red-orange photoluminescence (PL) that provides large penetration depth for precise deep-tissue imaging and diagnostics. Herein, we describe in detail the fabrication process of porous silicon nanoparticles (pSiNPs), activation of photoluminescence, quantum yield measurement, and PL imaging. LpSiNPs perform as imaging probe for both the continuous wave and time-gated PL imaging.

One-pot green synthesis of highly luminescent silicon nanoparticles using Citrus limon (L.) and their applications in luminescent cell imaging and antimicrobial efficacy

Strongly luminescent and water dispersible silicon nanoparticles were synthesised by one-pot synthesis from venyl-trimethoxy-silane and (3-aminopropyl)-triethoxy-silane using both chemical and green reducing agents, sodium ascorbate and Citrus limon (L.) respectively. Unlike sodium ascorbate, the reduction using lemon extracts produces smaller nanoparticles with average size of 20 and 57 nm. The antimicrobial efficacy of the nanoparticles is examined against various microorganisms and is noted that these particles possessed antibacterial property if used in concentrations above the threshold value of 1.5 μg/ml. In addition, these silicon nanoparticles emit intense blue-green emission which is successfully utilised for the luminescent cell imaging of human white blood cells and mice epithelial cells.

One-Pot Synthesis of Gel Glass Embedded with Luminescent Silicon Nanoparticles.

Preparation of highly luminescent glasses involves expensive and complicated processes and usually requires high temperature. In this work, we show that luminescent silicon (Si) nanoparticle (NP)-embedded silicate gel glasses can be developed under near-ambient conditions by a remarkably simple, one-pot strategy, without using any sophisticated instrumentation or technique. Simultaneous hydrolysis and reduction of (3-aminopropyl)triethoxysilane leads to the formation of colloidal Si nanocrystals that can be transformed to a glassy phase upon slow evaporation followed by freezing. Structural investigations reveal the formation of a sodium silicate gel glass framework having discernible shear bands, along with embedded Si NPs. High photoluminescence quantum yield (ca. 35-40%), low glass-transition temperature ( Tg ≈ 66-73 °C), strain-tolerant mechanical stability, and inexpensive preparation make the glass attractive for applications as display materials and photonic converters.

Atomically precise cluster-based white light emitters $$^{\S }$$ §

Materials emitting white luminescence are receiving increasing attention due to their potential applications in electroluminescent devices, information displays and fluorescent sensors. To produce white light, one must have either three primary colors, blue, green and red or two colors, blue and orange. In this paper, we have used thiol/phosphine protected red luminescent silver nanoclusters (Ag NCs), $$[\hbox {Ag}_{29}(\hbox {BDT})_{12}(\hbox {PPh}_{3})_{4} ]^{3\hbox {-}}\, (\hbox {BDT}=1,\!3\hbox {-benzenedithiol})$$ , $$[\hbox {Au}_{\mathrm{x}}\hbox {Ag}_{29\hbox {-}\mathrm{x}}(\hbox {BDT})_{12} (\hbox {PPh}_{3})_{4}]^{3\hbox {-}}$$ and $$\hbox {Ag}_{29}(\hbox {LA})_{12}$$ ( $$\hbox {LA}= \hbox {lipoic acid}$$ ) as one of the fluorophores for white light emission. These clusters are mixed with blue luminescent silicon nanoparticles (Si NPs) and green luminescent fluorescein isothiocyanate (FITC). The mixtures show white luminescence with CIE coordinates of (0.31, 0.34), (0.33, 0.35) and (0.29, 0.31) which are in good agreement with pure white light (0.33, 0.33). The other clusters with yellow, blue, orange, etc., luminescence can also be used to make white light. This work provides a prospective pathway for white light emission based on atomically precise noble metal NCs. Synopsis Monolayer protected noble metal nanoclusters such as $$[\hbox {Ag}_{29}(\hbox {BDT})_{12}(\hbox {PPh}_{3})_{4}]^{3\hbox {-}}\, (\hbox {BDT}=1,3\hbox {-benzenedithiol})$$ , $$[\hbox {Au}_{\mathrm{x}}\hbox {Ag}_{29\hbox {-}\mathrm{x}}(\hbox {BDT})_{12} (\hbox {PPh}_{3})_{4}]^{3\hbox {-}}$$ and $$\hbox {Ag}_{29}(\hbox {LA})_{12}$$ ( $$\hbox {LA}= \hbox {lipoic acid}$$ ) are used as red luminophores which can produce white light emission when mixed with blue luminescent silicon nanoparticles (Si NPs) and green luminescent fluorescein isothiocyanate (FITC). The mixtures produce white luminescence with CIE (Commission Internationale d’Eclair) coordinates of (0.31, 0.34), (0.33, 0.35) and (0.29, 0.31), respectively. All-cluster-based white light emission is indeed possible.

Luminescence of silicon nanoparticles from oxygen implanted silicon

Oxygen with a kinetic energy of 20 keV is implanted in a silicon wafer (100) at different fluences, followed by post-implantation thermal annealing (PIA) performed at temperatures ranging from 1000 to 1200 °C, in order to form luminescent silicon nanoparticles (SiNPs) and also to reduce the damage induced by the implantation. As a result of this procedure, a surface SiOx layer (with 0 < x < 2) with embedded crystalline Si nanoparticles has been created. The samples yield similar luminescence in terms of peak wavelength, lifetime, and absorption as recorded from SiNPs obtained by the more conventional method of implanting silicon into silicon dioxide. The oxygen implantation profile is characterized by elastic recoil detection (ERD) technique to obtain the excess concentration of Si in a presumed SiO2 environment. The physical structure of the implanted Si wafer is examined by grazing incidence X-ray diffraction (GIXRD). Photoluminescence (PL) techniques, including PL spectroscopy, time-resolved PL (TRPL), and photoluminescence excitation (PLE) spectroscopy are carried out in order to identify the PL origin. The results show that luminescent SiNPs are formed in a Si sample implanted by oxygen with a fluence of 2 × 1017 atoms cm−2 and PIA at 1000 °C. These SiNPs have a broad size range of 6–24 nm, as evaluated from the GIXRD result. Samples implanted at a lower fluence and/or annealed at higher temperature show only weak defect-related PL. With further optimization of the SiNP luminescence, the method may offer a simple route for integration of luminescent Si in mainstream semiconductor fabrication.

Imparting optical functionality to aromatic thermosetting copolyester by luminescent silicon nanoparticles cross-linked via in situ thermal polymerization reaction

Aromatic thermosetting copolyester (ATSP) enables high- to low-k tunability as well as providing reliable thermomechanical performance from cryogenic to elevated temperatures, so it is a promising polymer system for silicon-based microelectronics and spacecraft applications. Here we reported on imparting strong photoluminescence to otherwise weak luminescent ATSP matrix by incorporating H-terminated Si nanoparticles (Sinps) to obtain luminescent polymer nanocomposites without degenerating the polymer backbone chain configuration. We employed photoluminescence and ultraviolet-visible (UV-Vis) spectroscopies along with electron microscopy analysis to characterize pre- and post-thermal polymerization processes. In the pre-polymerization stage, a size-dependent convection-like motion was observed in a liquid medium under thermal gradient, which caused the nanocomposites to accumulate and be trapped. Scanning electron microscope (SEM) images revealed the formation of 2-D nanosheets, as small as 50–100 nm, decorated with 10–15 nm size complexes of Sinps and oligomers. The post-polymerization analysis showed that the Sinps homogenously incorporated, with insignificant aggregation, into the polymerization process as a secondary cross-linker neither losing their red-luminescence functionality nor deteriorating the physical properties of the ATSP matrix. Chain relaxation characteristics, measured by dynamic mechanical analysis (DMA), in the glass transition regime likewise indicated the effective conjugation of the Sinps with the cross-linked polymer backbone. The ATSP–Sinps composite structure manifested bandgap imprints of both Sinps and ATSP in the ultraviolet–visible spectral region. Via superb thermomechanical properties enriched with luminescence, the ATSP–Sinps nanocomposite may potentially afford UV shielding to mitigate photo-degradation and enhance operational efficiency for photonics applications.

Fabricating highly luminescent solid hybrids based on silicon nanoparticles: a simple, versatile and green method.

In this work, we report a simple but novel method to transfer highly luminescent silicon nanoparticles (Si NPs) from solutions to solids without sacrificing their excellent photoluminescence (PL) properties. Hybrid Si NP/clay phosphors that glowed ultrabright and had colorful PL properties were first obtained. More importantly, large-area and flexible films with superior PL properties can be easily obtained via combining the Si NP/clay hybrids with different kinds of polymer. The Si NP-based phosphors and films from our method show high stabilities with no significant loss of PL performance after long-term storage (several months). In addition, bright yellow-emitting Si NPs were prepared and used as down-converters for white-light-emitting diodes (W-LEDs). Overall, this work presents a simple, versatile and green method to fabricate Si NP-based solid hybrids with superior PL properties, which has promise to be applied in the future in solid-state lighting fields.

Luminescent Silicon Nanocrystal embedded Sodium Silicate Glass

Green luminescent silicon nanoparticles (Si NPs), embedded in sodium silicate (SS) based glass, have been prepared by a simple green chemical synthesis route. (3-aminopropyl) triethoxysilane (APTES) was reduced by sodium ascorbate (SA) in a one-step synthesis method to prepare Si NPs. Extending the same route SS based glass was synthesised by slow evaporation of the aqueous solution of colloidal Si NPs at room temperature. Colloids of Si NPs and the SS-based glass exhibit intense room temperature greenish photoluminescence (PL) that can be detected with the naked eye. Structural investigations reveal that the Si NP sample contains dominant amorphous phase with trace amount of Si nanocrystals (NCs). Analysis of optical properties of the Si NP sample indicates that green PL is dominantly due to the contribution of oxide enriched surface states rather than quantum confinement of excitons and likewise the PL from the SS based glass is due to the presence of trace amount of Si NCs along with agglomerated amorphous oxide embedded in the glass. There is a clear indication of selective reflectance from the prepared SS based glass.

Hydrophilic Luminescent Silicon Nanoparticles in Steric Colloidal Solutions: Their Size, Agglomeration, and Toxicity

Luminescent silicon nanoparticles are promising for intracellular biological research as luminescent probe for in vitro and in vivo studies. We prepared nanoclusters of hydrophilic highly porous silicon having the size around 100 nm, composed of nanocrystals ∼2.5 nm in size, by electrochemical etching. Colloidal suspensions of the nanoparticles in steric organics (bovine serum albumin (BSA), glutamic acid, dextran, and glycine) were prepared to attempt to stabilize the nanoparticles and prevent their further agglomeration. The zeta potential differs from sample to sample – BSA and glycine solutions have zeta potential between −30 and −40 mV indicating good stability of nanoparticles in the solutions, while the zeta potentials of water (−24 mV), dextran (−10 mV), and glutamic acid (−14 mV) are showing that nanoparticles tend to agglomerate. Strong orange luminescence of nanoparticles is situated between 600 and 700 nm and remains stable in all used organic colloidal solutions. Performed study of in vitro toxicity revealed that sterically stabilized silicon nanoparticles are cytotoxic only at the highest used concentration (500 μg ml−1) of the silicon nanoparticles in water and BSA. Only in the case of glycine a significant decrease of the cell viability was observed already at a lower concentration of 250 μg ml−1 and is caused probably by glycine itself.

Nanosecond pulsed laser ablated sub-10 nm silicon nanoparticles for improving photovoltaic conversion efficiency of commercial solar cells

In this paper, we demonstrate the enhancement of photovoltaic (PV) solar cell efficiency using luminescent silicon nanoparticles (Si-NPs). Sub-10 nm Si-NPs are synthesized via pulsed laser ablation technique. These ultra-small Si nanoparticles exhibit photoluminescence (PL) character tics at 425 and 517 nm upon excitation by ultra-violet (UV) light. Therefore, they can act as secondary light sources that convert high energetic photons to ones at visible range. This down-shifting property can be a promising approach to enhance PV performance of the solar cell, regardless of its type. As proof-of-concept, polycrystalline commercial solar cells with an efficiency of ca 10% are coated with these luminescent Si-NPs. The nanoparticle-decorated solar cells exhibit up to 1.64% increase in the external quantum efficiency with respect to the uncoated reference cells. According to spectral photo-responsivity characterizations, the efficiency enhancement is stronger in wavelengths below 550 nm. As expected, this is attributed to down-shifting via Si-NPs, which is verified by their PL characteristics. The results presented here can serve as a beacon for future performance enhanced devices in a wide range of applications based on Si-NPs including PVs and LED applications.

Biodegradable and Magnetic-Fluorescent Porous Silicon@Iron Oxide Nanocomposites for Fluorescence/Magnetic Resonance Bimodal Imaging of Tumor in Vivo.

Considering future clinical transactions, biodegradable and luminescent porous silicon nanoparticles instead of traditional heavy-metal quantum dots have an important significance on the construction of biodegradable and magnetic-fluorescent nanocomposites. Herein, to fabricate PSiNPs@Fe3O4 nanocomposites, superparamagnetic iron oxide nanoparticles were covalently incorporated into luminescent porous silicon nanoparticles by microwave-induced hydrosilylation. These resultant nanocomposites had near-infrared fluorescence (500 nm-800 nm) and superparamagnetism with high magnetic saturation value of 141 emu/g. The aqueous-dispersibility of PSiNPs@Fe3O4 nanocomposites could be significantly improved via simple ultrasonication in water. Furthermore, they also exhibited an excellent biodegradability and biocompatibility, whether in vitro or in vivo. Finally, their ability of fluorescence/magnetic resonance bimodal imaging had been successfully demonstrated for cancer cells in vitro or tumor tissues in vivo.

Glucose-Modified Silicon Nanoparticles for Cellular Imaging.

Luminescent silicon nanoparticles have recently attracted attention due to their remarkable stability, covalent functionalisation and tunable photoemission properties. Owing to their biocompatibility, low toxicity, and the small particle size that can be achieved by different synthetic approaches, these nanomaterials are candidates as cellular probes in the field of bioimaging, and potentially for in vivo applications. Tailoring the surface of the particles with active biomolecules such as sugar moieties can be an interesting strategy to increase the kinetics of internalisation or to vary the localisation of nanosystems in living cells. In this study, we synthesised and modified ultrasmall silicon nanoparticles with glucose covalently linked on their surface. Moreover, by varying the ratio between the amount of silicon nanoparticles and the saccharide groups, the amount of glucose, as a capping moiety, can be well controlled. FTIR spectroscopy, NMR spectroscopy, zeta potential measurements and anisotropy decay analysis confirmed the covalent binding of glucose to the nanoparticles. The photophysical behaviour of the surface-functionalised silicon quantum dots was not significantly different to that of the unmodified nanoparticles. In vitro studies demonstrated faster internalisation of the glucose-functionalised nanoparticles into HeLa cells. Different localisation and uptake kinetics of the glucose-modified particles compared to the unmodified particles are discussed in order to reveal the role played by the sugar molecules.

Structural and luminescence properties of silicon nanocrystals in colloidal solutions for bio applications

Luminescent silicon nanoparticles are promising not only for optoelectronics or photovoltaics, but also for biological and medical research, e.g., as luminescent markers, for drug delivery, or toxicity studies. For intracellular biological research, it is necessary to prepare water-based or isotonic colloidal solutions of nanoparticles which are stable and non-toxic. In this work, we compare structural and optical properties of silicon nanocrystals in colloidal solutions, obtained by two fundamentally different methods: A microplasma-based synthesis (a “bottom-up” technique) and porous silicon prepared by electrochemical etching of a silicon wafer (a “top–down” method). Low-pressure microwave plasma synthesis produces ∼5–8 nm large silicon nanocrystals while the porous siliconcontains clusters ∼60–70 nm in diameter, composed of nanometer-sized luminescent nanocrystals. However, both types of nanoparticles are prone to agglomeration, as was confirmed by dynamic light scattering and zeta potential measurements. We have attempted to stabilize the nanoparticles via modification of the their surface by methyl groups; however, the mechano-photo-chemical treatment procedure leading to coverage with methyl groups is less efficient in the case of plasma-synthesized nanoparticles than in porous silicon. The first attempt of steric stabilization of the colloidal solutions of the silicon nanoparticles was succesfully carried out too; good candidates for stabilization are bovine serum albumin and glycine.

Domino-Like Intercellular Delivery of Undecylenic Acid-Conjugated Porous Silicon Nanoparticles for Deep Tumor Penetration.

Improving the intratumoral distribution of anticancer agents remains the critical challenge for developing efficient cancer chemotherapy. Luminescent porous silicon nanoparticles (PSiNPs) have attracted considerable attention in the biomedical field especially in drug delivery. Here, we described the lysosomal exocytosis-mediated domino-like intercellular delivery of undecylenic acid-conjugated PSiNPs (UA-PSiNPs) for deep tumor penetration. UA-PSiNPs with significantly improved stability in physiological conditions were internalized into tumor cells by macropinocytosis-, caveolae-, and clathrin-mediated endocytosis and mainly colocalized with Golgi apparatus and lysosomes. Substantial evidence showed that UA-PSiNPs was excreted from cells via lysosomal exocytosis after cellular uptake. The exocytosed UA-PSiNPs induced a domino-like infection of adjacent cancer cells and allowed encapsulated doxorubicin (DOX) to deeply penetrate into both three-dimensional tumor spheroids and in vivo tumors. In addition, DOX-loaded UA-PSiNPs exhibited strong antitumor activity and few side effects in vivo. This study demonstrated that UA-PSiNPs as a drug carrier might be applied for deep tumor penetration, offering a new insight into the design of more efficient delivery systems of anticancer drugs.

A New Generation of Primary Luminescent Thermometers Based on Silicon Nanoparticles and Operating in Different Media

Luminescence nanothermometry is nowadays a highly‐dynamic research topic that is being driven by the challenging demands arising from dissimilar areas such as microelectronics, microfluidics and nanomedicine. Although the technique is rapidly evolving from the initial breakthrough to real applications, there are still major challenges regarding the conciliation of nanometric probes with the high sensitivity and predictability of the thermal response of the system. In the past five years, luminescent thermometers operating at the nanoscale, where the conventional methods are ineffective, have emerged as a very active field of research. Luminescent silicon nanoparticles (SiNPs) are a promising choice for nanothermometry, combining the Si biocompatibility with the compatibility with the current microelectronic technology. Here, the thermal dependence of the emission peak position of SiNPs, used as the thermometric parameter, is well‐described by the Varshni's law, enabling the development of a self‐calibrated nanothermometer with a calibration curve predicted by a well‐stablished state equation, avoiding new calibration procedures whenever the thermometer operates in different media. For the first time, temperature sensing using SiNPs‐based luminescent thermometers in different media without the need of new calibration procedures is demonstrated. The thermometer reveals reversibility and repeatability higher than 99.98%, and a maximum relative sensitivity of 0.04% K−1.