Fluorescent Silicon Research Articles

A dual-signal colorimetric and ratiometric fluorescent nanoprobe for enzymatic determination of uric acid by using silicon nanoparticles.

The authors describe a dual-signal colorimetric and ratiometric fluorescent probe for uric acid (UA). It is based on cascade catalysis and an inner filter effect. The method involves uricase-catalyzed oxidation of UA and iodide-catalyzed oxidation of the colorless peroxidase substrate o-phenylenediamine (OPD) to form yellow 2,3-diaminophenazine (oxOPD). This can be visually observed or monitored by measuring absorbance at 417nm. Furthermore, oxOPD quenches the fluorescence of silicon nanoparticles (SiNPs) (with peaks at 450 and 565nm) via an inner filter effect. The change in the ratio of emissions peaking 565 and 450 (at excitation wavelength of 380 nm) increases linearly in the 0.01-0.8mM UA concentration range). The lower detection limits are 8.4 and 0.75μM when using the colorimetric and ratiometric fluorometric method, respectively. The assay was successfully applied to the quantitation of UA in spiked serum samples. Graphical abstractA dual-signal colorimetric and ratiometric fluor ometric assay was developed for uric acid (UA). The fluorometric assay is based on the inner filter effect between fluorescent silicon nanoparticles and 2,3-diaminophenazine. It involves uricase-catalyzed oxidation of UA, and iodide-catalyzed oxidation of o-phenylenediamine.

Temperature-dependent photoluminescence properties of porous fluorescent SiC

A comprehensive study of surface passivation effect on porous fluorescent silicon carbide (SiC) was carried out to elucidate the luminescence properties by temperature dependent photoluminescence (PL) measurement. The porous structures were prepared using an anodic oxidation etching method and passivated by atomic layer deposited (ALD) Al2O3 films. An impressive enhancement of PL intensity was observed in porous SiC with ALD Al2O3, especially at low temperatures. At temperatures below 150 K, two prominent PL emission peaks located at 517 nm and 650 nm were observed. The broad emission peak at 517 nm was attributed to originate from the surface states in the porous structures, which was supported by X-ray photoelectron spectra characterization. The emission peak at 650 nm is due to donor-acceptor-pairs (DAP) recombination via nitrogen donors and boron-related double D-centers in fluorescent SiC substrates. The results of the present work suggest that the ALD Al2O3 films can effectively suppress the non-radiative recombination for the porous structures on fluorescent SiC. In addition, we provide the evidence based on the low-temperature time-resolved PL that the mechanism behind the PL emission in porous structures is mainly related to the transitions via surface states.

Photoluminescence Quantum Yield of Fluorescent Silicon Carbide Determined by an Integrating Sphere Setup.

The excitation-dependent photoluminescence quantum yield (PL-QY) of strong n-type nitrogen–boron codoped 6H fluorescent silicon carbide (f-SiC) at room temperature is experimentally determined for the first time. The PL-QY measurements are realized by an integrating sphere system based on a classical two-measurement approach. In particular, in accordance to the difference between our in-lab setup and the standard setup of the two-measurement approach, we have technically modified the experimental design, the data processing algorithm, and the estimation of relative uncertainty. The measured highest PL-QY of f-SiC samples is found to reach above 30%. We compare the PL-QYs at a certain excitation power of all f-SiC samples by considering their intrinsic defect densities. Finally, the evolution of the excitation power-dependent PL-QY of f-SiC is attributed to both band-to-band and impurity-assisted Auger recombination.

Fluorescent Silicon Nanorods-Based Nanotheranostic Agents for Multimodal Imaging-Guided Photothermal Therapy

HighlightsA kind of multifunctional silicon-based theranostic agent is fabricated and exploited for imaging-guided tumor-targeted photothermal therapy.The obtained gold nanoparticles-decorated fluorescent silicon nanorods featuring high photothermal conversion performance and good photothermal stability enable a total ablation of tumors and prolong the survival time of mice.

Multifunctional nanoagents for ultrasensitive imaging and photoactive killing of Gram-negative and Gram-positive bacteria

Simultaneous imaging and treatment of infections remains a major challenge, with most current approaches being effective against only one specific group of bacteria or not being useful for diagnosis. Here we develop multifunctional nanoagents that can potentially be used for imaging and treatment of infections caused by diverse bacterial pathogens. The nanoagents are made of fluorescent silicon nanoparticles (SiNPs) functionalized with a glucose polymer (e.g., poly[4-O-(α-D-glucopyranosyl)-D-glucopyranose]) and loaded with chlorin e6 (Ce6). They are rapidly internalized into Gram-negative and Gram-positive bacteria by a mechanism dependent on an ATP-binding cassette (ABC) transporter pathway. The nanoagents can be used for imaging bacteria by tracking the green fluorescence of SiNPs and the red fluorescence of Ce6, allowing in vivo detection of as few as 105 colony-forming units. The nanoagents exhibit in vivo photodynamic antibacterial efficiencies of 98% against Staphylococcus aureus and 96% against Pseudomonas aeruginosa under 660 nm irradiation.

Synthesis and characterization of a novel, reactive, yellow fluorescent organosilicon dye and its polysiloxanes

A novel, reactive, yellow fluorescent organosilicon dye, N-propyl-(diethoxy)methyl-silane-4-dimethylamino-naphthalimide, is designed and synthesized and is used to fabricate a covalently yellow fluorescent silicone oil by polycondensation of hydroxy-terminated polydimethylsiloxane. The chemical structure and optical properties of the N-propyl-(diethoxy)methyl-silane-4-dimethylamino-naphthalimide and covalently yellow fluorescent silicone oil are characterized by 1H nuclear magnetic resonance, 13C nuclear magnetic resonance, mass spectrometry, Fourier transform infrared, UV–Vis, and fluorescence spectra. The results indicate that the fluorescence quantum yields of N-propyl-(diethoxy)methyl-silane-4-dimethylamino-naphthalimide and covalently yellow fluorescent silicone oil are 2.61% and 3.5%, respectively. The λmax values of their dichloromethane solutions are 416 nm, and their λex and λem are 430 and 509 nm, respectively. Furthermore, covalently yellow fluorescent silicone rubbers are prepared using tetraethoxysilane as a cross-linker, and some of their properties are investigated. Thermogravimetric analysis and dynamic mechanical analysis show that heat resistance and tan δ of the covalently yellow fluorescent silicone rubber are improved in comparison with silicone rubbers without N-propyl-(diethoxy)methyl-silane-4-dimethylamino-naphthalimide moieties. Solvent extraction experiments indicate that the solvent resistance of the covalently yellow fluorescent silicone rubber is much better than that of noncovalently yellow fluorescent silicone rubber.

One-step synthesis of amine-functionalized fluorescent silicon nanoparticles for copper(II) ion detection

Amine-functionalized silicon nanoparticles (A-SiNPs) with intense green fluorescence and photostability are synthesized via a one-step, low-cost hydrothermal method under mild conditions using 3-aminopropyl triethoxysilane (APTES) as a silicon source and L-ascorbic acid (AA) as a reducing reagent. The amine-rich surface not only improves water dispersability and stability of the A-SiNPs but also offers a specificcopper(II) ion (Cu2+) coordination capability. The as-prepared A-SiNPs can be directly employed forCu2+ detection in "turn-off" mode, resulting from Cu2+ coordination-induced fluorescence quenching effect. Under optimal conditions, Cu2+ detection was accomplished with a linear range from 1 to 500μM and a limit of detection (LOD) at 0.1μM, which was much lower than the maximum level (~ 20μM) of Cu2+ in drinking water permitted by the US Environmental Protection Agency (EPA). In addition, the A-SiNPs were successfully used to detect Cu2+ in spiked river water, demonstrating its good selectivity and potential application for analysis of surface water samples. Graphical abstract.

Highly Sensitive Fluorescence Assay for Glucose Using Amine-Terminated Silicon Quantum Dots As a Non-enzymatic Bioprobe

This work presents a simple, economic and green technique for functionalizing fluorescent silicon quantum dots (Si QDs) as a bioprobe to measure blood glucose levels. The functionalized Si QDs are synthesized by adding 3-aminopropyltriethoxysilane to a colloidal solution of Si QDs, freshly prepared by laser ablation of a silicon target in distilled water. The amine-terminated surface of Si QDs is confirmed using Fourier transform infrared spectroscopy, energy dispersive x-ray spectroscopy and UV–visible absorption spectroscopy. The photoluminescence of the colloid exhibits high photo-stability and good reproducibility making it a good candidate for fluorescent probes in biosensor studies. We have investigated the use of such functionalized Si QDs as a probe for fluorescent glucose detection application based on its effective fluorescence quenching by hydrogen peroxide, which is produced from glucose. The room temperature fluorescent glucose sensor, based on amine-functionalized Si QDs, gave a detection limit of 0.97 μM and a linear range from 20 to 700 μM. This non-enzymatic fluorescent biosensor system shows high sensitivity, excellent selectivity and extreme stability toward glucose.

Fluorescent silicon nanomaterials: from synthesis to functionalization and application

Abstract In the last decade, we have witnessed the giant achievement in the field of silicon materials. Among of them, fluorescent silicon nanomaterials have attracted considerable attentions owing to their unique advantages, including strong fluorescence coupled with robust photostability, rich resource support, low cost, industrial maturity, and good biocompatibility. Extensive efforts are devoted to developing effective methods for the synthesis and functionalization of fluorescent silicon nanomaterials with different nanostructures, facilitating the promotion of this promising material for myriad optical applications. In this review article, we systematically summarize representative progresses for the design and synthesis of fluorescent silicon nanomaterials during the last decade. We also present an in-depth description of functionalization strategies toward fluorescent silicon nanomaterials, with a particular focus on organic ligands-modification, doping and biological species-modification methods. Furthermore, typical optical applications (e.g., bioimaging, sensing, anti-counterfeiting and anti-bacterial applications) are introduced based on latest research achievements. Finally, future trends and current challenges are highlighted as a roadmap proposal for research in this field.

Photostable and Biocompatible Fluorescent Silicon Nanoparticles for Imaging-Guided Co-Delivery of siRNA and Doxorubicin to Drug-Resistant Cancer Cells

HighlightsA novel all-in-one fluorescent nanomedicine platform based on silicon nanoparticles (SiNPs) was developed for imaging-guided co-delivery of short interfering RNA (siRNA) and doxorubicin (DOX).The intracellular time-dependent release behaviors of siRNA and DOX were visually monitored by tracking the strong and stable fluorescence of SiNPs.The SiNPs-based nanocarriers displayed pronounced therapeutic efficiency on drug-resistant breast cancer cells.

One-step hydrothermal synthesis of ultrabright water-soluble silicon nanoparticles for folate-receptor-mediated bioimaging

Fluorescent silicon nanoparticles (SiNPs) exhibiting excellent photostability and colloidal stability and favorable biocompatibility are emerging as novel fluorescent nanoprobes for biological and biomedical imaging. However, studies on the synthesis of highly bright SiNPs and their specific targeted biolabeling are still limited. Herein, we report a facile one-pot hydrothermal approach for the synthesis of ultrabright SiNPs, in which N-[3-(trimethoxysilyl)propyl]ethylenediamine (DAMO) molecules and trisodium citrate acted as silicon precursor and reducing agents, respectively. Remarkably, the prepared SiNPs were small (~ 3.5 nm diameter) and showed ultrahigh photoluminescence quantum yield of 85.2% and long-term stability (in pH range of 4–13 and almost saturated NaCl solution, and at 80 °C). The low cytotoxicity of the resultant SiNPs facilitated conjugation with biomolecules such as folic acid (FA) for bioimaging. The FA-conjugated SiNPs specifically bound receptor-positive HepG2 cells over receptor-negative A549 cells, indicating the potential of these SiNPs as robust bioprobe both in vitro and in vivo.

One-pot synthesis of highly fluorescent silicon nanoparticles for sensitive and selective detection of hemoglobin.

In this work, a simple, selective, and sensitive probe for hemoglobin based on the quenched fluorescence of silicon nanoparticles (SiNPs) was fabricated. The SiNPs were synthesized by a simple hydrothermal treatment from N-[3-(trimethoxysilyl)propyl]ethylenediamine and sodium citrate. The as-prepared SiNPs exhibited good water-solubility and high fluorescence with the quantum yield of 70%. The fluorescence of the SiNPs could be remarkably quenched by hemoglobin. A wide linear range was obtained from 50 nM to 4000 nM with a LOD of 40 nM. The quenching mechanism was investigated by UV-Vis absorption spectrometry and time-resolved fluorescence spectrometry.

Determination of potassium ferrocyanide in table salt and salted food using a water-soluble fluorescent silicon quantum dots

The addition of potassium ferrocyanide (K4[Fe(CN)6]) in table salt as anti-caking agent has a crucial role in preventing the formation of lumps. However, the excess of K4[Fe(CN)6] and its decomposers are harmful to both human health and environment. To date, there are still lack of suitable methods for simple and rapid analysis of K4[Fe(CN)6] in table salt and salted food. Herein, a novel fluorescent Si QDs probe for sensitive, selective and rapid detection of K4[Fe(CN)6] was synthesized by facile one-step strategy. Notably, the fluorescence of Si QDs could be remarkably quenched by K4[Fe(CN)6] via electrostatic interaction. Based on this phenomenon, a new method of determination of K4[Fe(CN)6] was established. A wide linear range was obtained from 0.05 to 8.0 µg/mL with a detection limit of 30 ng/mL. The established fluorescent new method was suitable for detecting K4[Fe(CN)6] in table salt and salted food samples with satisfactory results.

Ratiometric target-triggered fluorescent silicon nanoparticles probe for quantitative visualization of tyrosinase activity

Tyrosinase is the key enzyme in the treatment of vitiligo. Development of rapid, simple, and visual methods for screening bioactive compounds with tyrosinase activity from natural compounds is interesting for new drug discovery. Herein, a novel visual ratiometric fluorescent assay for screening tyrosinase activators and/or inhibitors based on silicon nanoparticles (Si NPs) was explored. Inspired by the changes in both of the solution color and the fluorescence emission due to the sensing between Si NPs and dopamine (DA), we employed tyramine as the model substrate, which can transfer into DA by tyrosinase. It was found that the tyrosinase-incubated tyramine solution exhibited pale yellow under nature light or yellow fluorescence under UV light in the presence of Si NPs, where the color/fluorescence intensity were directly related to the concentration of tyrosinase. The established method showed good detection selectivity, and the LOD for tyrosinase was 0.14 U mL−1. Eventually, this assay was successfully applied to screen tyrosinase activators or inhibitors from a natural product-like library, and a tyrosinase activator with EC50 of 2.62 μM, more potent than the commonly used tyrosinase activator 8-MOP, was discovered.

Controllable silicon nanostructures featuring stable fluorescence and intrinsic in vitro and in vivo anti-cancer activity.

In this manuscript, we demonstrate that the in situ growth of fluorescent silicon (Si) nanomaterials is stimulated when organosilicane molecules interact with different green teas, producing multifunctional Si nanomaterials with controllable zero- (e.g., nanoparticles), two- (e.g., nanosheets), and three- (e.g., nanospheres) dimensional nanostructures. Such green tea-originated Si nanomaterials (GTSN) exhibit strong fluorescence (quantum yield: ∼19-30%) coupled with ultrahigh photostability, as well as intrinsic anti-cancer activity with high specificity (e.g., the GTSN can accurately kill various cancer cells, rather than normal cells). Taking advantage of these unique merits, we further performed systematic in vitro and in vivo experiments to interrogate the mechanism of the green tea- and GTSN-related cancer prevention. Typically, we found that the GTSN entered the cell nuclei and induced cell apoptosis/death of cancer cells. The prepared GTSN were observed in vivo to accumulate in the tumour tissues after 14-d post-injection, leading to an efficient inhibition of tumour growth. Our results open new avenues for designing novel multifunctional and side-effect-free Si nanomaterials with controllable structures.

One-step rapid synthesis of fluorescent silicon nanodots for a hydrogen peroxide-related sensitive and versatile assay based on the inner filter effect.

In this work, a kind of environment-friendly and water-dispersible silicon nanodot (SiND) was rapidly synthesized by using the mild reagents (3-aminopropyl)triethoxysilane (APTES) and glucose. It was found that the fluorescence of the as-prepared SiNDs can be quenched obviously by permanganate due to the inner filter effect. Inspired by this finding, a novel fluorescent sensor for sensitive detection of hydrogen peroxide (H2O2) was developed through the oxidation-reduction reaction between permanganate and H2O2. The detection limit of H2O2 is down to 2.8 nM. Since H2O2 is an important molecule and involved in various studies, this sensor could be applied in various H2O2-related biological analyses. As a proof-of-application demonstration, a sensitive biosensor for glucose detection was constructed through the catalytic oxidation of glucose to generate H2O2. The as-constructed sensor showed good linear response to glucose over the range from 0.16 to 16 μM with a detection limit of 0.11 μM. Moreover, the biosensor can be readily extended to other sensors for different targets, which indicates the broad applications of the proposed sensing strategy in biomedical analysis.

Biomimetic preparation of silicon quantum dots and their phytophysiology effect on cucumber seedlings.

In this study, a biomimetic synthetic strategy was proposed for a facile preparation of red fluorescent silicon quantum dots (SiQDs) using unicellular algae of diatoms as reaction precursor. The resultant nontoxic SiQDs of ∼2.0 nm diameter display remarkable red luminescence, high quantum yield (∼15%) and narrow full width at half maximum (FWHM, ∼35 nm). Specifically, as-prepared SiQDs show promise as regulators of plant growth. After cultivating cucumber seedlings with SiQDs, the growth of cucumber seedlings has been significant promoted within a wide range of SiQDs concentrations (0.01-0.3 mg mL-1). The total weight of cucumber seedlings significantly increased by 51.91% (P < 0.001) compared with weight of the control group after incubation for 10 days. Moreover, it was discovered that the growth of cucumber seedlings is positively correlated with the water uptake rate of roots. After a 5 day incubation, the optimum concentration of SiQDs significantly increased water uptake rate of roots by 74.6% compared with that of the control group. Real-time fluorescence quantitative polymerase chain reaction (RT-PCR) analysis revealed that the expression of aquaporin gene in cucumber roots treated with SiQDs increased significantly compared to that of the control group. This is the first report regarding a phytophysiology effect of red fluorescent SiQDs on cucumber seedlings growth. The results widen the range of applications of SiQDs in plant science.

Monitoring the trans-membrane transport of single fluorescent silicon nanoparticles based on the force tracing technique

Based on the force tracing technique, the dynamic trans-membrane transport process of single SiNPs in living cells was monitored.

Fluorescent silicon nanoparticles inhibit the amyloid fibrillation of insulin.

Amyloid fibrillation of proteins is likely a key factor leading to the development of amyloidosis-associated diseases. Inhibiting amyloid fibrillation has become a crucial therapeutic strategy. Water-soluble, fluorescent silicon nanoparticles (SiNPs) have great potential in biomedicine for various therapeutic and diagnostic purposes; however, it is unclear whether SiNPs have the ability to inhibit amyloid fibrillation. Herein, insulin was chosen as a protein model, and SiNPs of varying sizes were synthesized upon UV irradiation. The influence of size and concentration of the SiNPs on insulin fibrillation was investigated, and it has been observed that these variables were crucial in regulating insulin fibrillation. Using an average particle size of 6.6 nm and increasing the concentration of the SiNPs to 5.0 μg mL-1, the Thioflavin T (ThT) fluorescence intensity decreased significantly by 90%, with an increased lag time of 76.8 h, compared to that of the control. Insulin aggregates were short, thin fibrils or clusters when incubated with SiNPs, compared to the long, thick fibrils formed for insulin alone. Additionally, we found that the SiNPs prevent the conformational transition of insulin from its initial structure to β-sheets, and thus inhibit nucleation, which is necessary for the formation of large fibrils. The inhibitory activity is attributed to the interactions between the SiNPs and insulin during the nucleation period. Our results demonstrate that the SiNPs disrupt insulin amyloid fibrillation, and thus, may play a useful role in new therapeutic and diagnostic strategies for amyloid-related disorders.

Preparation of Double-Shelled Fluorescent Silicon Nanocrystals and Fabrication of Its Thin Layer by Electrophoretic Deposition Process

Preparation of Double-Shelled Fluorescent Silicon Nanocrystals and Fabrication of Its Thin Layer by Electrophoretic Deposition Process