One-Pot Green Synthesis of Ultrabright N-Doped Fluorescent Silicon Nanoparticles for Cellular Imaging by Using Ethylenediaminetetraacetic Acid Disodium Salt as an Effective Reductant

A smartphone sensing fluorescent detection of mercury ion based on silicon quantum dots in environment water

Mercury ion (Hg2+) pose a significant hazard to the natural environment. Conventional techniques like Inductively coupled plasma mass spectrometry, X-ray absorption spectroscopy, among others, pose some disadvantages as they demand a lot of money, need trained employees, and cannot provide on-site detection in real-time. A smartphone sensing technique based on silicon quantum dots (Si-QDs) was presented to detect Hg2+ in the environment without the usage of sophisticated equipment. Meanwhile, the technology was built by utilizing a smartphone to capture gray values of fluorescent images of the Si-QDs-Hg2+ system. Microwave-assisted Si-QDs with tiny particle size, high fluorescence, and good optical stability were created. The fluorescence of the Si-QDs was gradually quenched by raising the Hg2+ concentration from 0.5 μmol/L to 5.0 μmol/L for fluorescent detection with a detection limit of 28 nmol/L. The 94.8-97.1 % recovery demonstrated the viability of the Si-QDs approach for detecting Hg2+. Meanwhile, a smartphone sensing strategy was built by recording the gray value of the fluorescent images of the Si-QDs-Hg2+ systems using a smartphone, and the detection limit of the established approach was 3 nmol/L. The accuracy and reliability of the smartphone strategy were verified with the recovery rates of 80.3-92.5 % in tap water and 87.6-109 % in river water. Electron transfer quenching mechanism between Si-QDs and Hg2+ was evidenced by ultraviolet-visible spectroscopy, fluorescent decay curves, cyclic voltammetry, and Zeta potential. Finally, the suggested approach was used to detect Hg2+ in water samples from various environments.

Designing a Hypoxia-Activated Sensing Platform Using an Azo Group-Triggered Reaction with the Formation of Silicon Nanoparticles

Hypoxia is known as a specific signal of various diseases, such as liver fibrosis. We designed a hypoxia-sensitive fluorometric approach that cleaved the azo bond (N═N) in the presence of hypoxia-controlled agents (sodium dithionite and azoreductase). 4-(2-Pyridylazo) resorcinol (Py-N═N-RC) bears a desirable hypoxia-responsive linker (N═N), and its azo bond breakup can only occur in the presence of sodium dithionite and azoreductase and leads to the release of 2,4-dihydroxyaniline, which can react with 3-[2-(2-aminoethylamino)ethylamino]propyltrimethoxysilane to generate yellow fluorescent silicon nanoparticles. This approach exhibited high selectivity and sensitivity toward both sodium dithionite and azoreductase over other potential interferences. The mouse liver microsome, which is known to contain azoreductase, was applied and confirmed the feasibility of the designed platform. Py-N═N-RC is expected to be a practical substrate for hypoxia-related biological analyses. Furthermore, silicon nanoparticles were successfully applied for Hela cell imaging owing to their negligible cytotoxicity and superb biocompatibility.

Magnetoplasmonic Metasurface-Modulated Electrochemiluminescence Strategy for Extracellular Vesicle Detection

Due to the ideal optical manipulation ability, the metasurface has broad prospects in the development of novel optical research. In particular, an active metasurface can control optical response through external stimulus, which has attracted great research interest. However, achieving effective modulation of the optical response is a significant challenge. In this work, we have developed a novel electrochemiluminescence (ECL) signal modulation strategy by an active magnetoplasmonic metasurface under an external magnetic field. The magnetoplasmonic metasurface was assembled based on yolk-shell Fe3O4@Au nanoparticles (Fe3O4@Au YS-NPs). On the one hand, the yolk-shell structure of Fe3O4@Au YS-NPs possessed the surface plasmon coupling effect and cavity-based Purcell effect, which provided high-intensity electromagnetic hot spots in the magnetoplasmonic metasurface. On the other hand, due to the strong magnetic response of the Fe3O4 core, the local magnetic field was induced by the external magnetic field, which further generated Lorentz force acting on the free electrons of Au nanoshells with strong optical anisotropy. The plasmon frequency of the metasurface can be effectively modulated by the Lorentz force effect. As a result, the ECL signal of nitrogen dots (N dots) was dynamically modulated and significantly enhanced at a specific polarization angle by the magnetoplasmonic metasurface under the variable external magnetic field. Based on the luminescence modulation ability and structure feature, the magnetoplasmonic metasurface was further established successfully as a sensing interface for gastric cancer (GC) extracellular vesicle (EV) detection. This study illustrated that the electromagnetic response of the active metasurface can effectively improve the optical modulation ability and luminescence sensing performance.

A fluorescent method for bisphenol A detection based on enzymatic oxidation-mediated emission quenching of silicon nanoparticles

As a common raw material of industrial products, bisphenol A (BPA) is widely used in the production of food contact materials, and there is a high risk of exposure in food. However, BPA is a well-known endocrine disruptor and poses a serious threat to human health. Herein, a fluorescent sensing platform of BPA based on enzymatic oxidation-mediated fluorescence quenching of silicon nanoparticles (SiNPs) is established and used to the detection of BPA in food species. The SiNPs are prepared with a facile one-step synthesis and emit bright green fluorescence. BPA can be oxidized by horseradish peroxidase (HRP) and hydrogen peroxide (H2O2) to form a product which can quench the fluorescence of SiNPs through electron transfer. There is a good linear relationship between the fluorescence intensity and BPA concentration in the range of 1-100 μM. Therefore, a fluorometry of BPA is established with a low limit of detection (LOD) of 0.69 μM. This method has been applied to the determination of BPA in mineral drinking water, orange juice, and milk with satisfactory results. The fluorescent sensor of BPA based on SiNPs has favorable application foreground in the field of food safety analysis.

Synergistic effect-triggered fluorescence quenching enables rapid and sensitive detection of alkaline phosphatase

The development of biosensors mediated by synergistic quenching effect is of great significance for rapid and accurate clinical diagnosis. Hence, we prepared a cyan-emitting fluorescent Si dots for alkaline phosphatase (ALP) detection through the synergistic quenching effect of inner filter effect (IFE) and photo-induced electron transfer (PET). Si dots were prepared by microwave-assisted method, which displayed high quantum yield (28.7%), as well as good physiochemical properties, such as photo-stability, pH stability, and chemical stability. As the hydrolysate of 4-nitrophenyl phosphate disodium salt hexahydrate catalyzed by ALP, both IFE and PET of 4-nitrophenyl to Si dots were used for the turn-off mode detection of ALP. The linear relationships were established between the change of fluorescence intensity and ALP concentration in the range of 0.05 U L^-1 to 5.0 U L-1, and 5.0 U L^-1 to 80.0 U L^-1, respectively. The detection limit was 0.01 U L^-1. The synergistic quenching effect caused the turn-off mode detection to be more sensitive, and it can also be used for the accurate detection of ALP in human serum, thereby showing great anti-interference ability in complex environments.

Small-Molecule Probe-Induced In Situ-Sensitized Photoelectrochemical Biosensor for Monitoring α-Glucosidase Activity

Semiconductor-based photoelectrochemical (PEC) biosensors have garnered significant attention in the field of disease diagnosis and treatment. However, the recognition units of these biosensors are mainly limited to bioactive macromolecules, which hinder the photoelectric response due to their insulating characteristics. In this study, we develop an in situ-sensitized strategy that utilizes a small-molecule probe at the interface of the photoelectrode to accurately detect α-glucosidase (α-Glu) activity. Silane, a prototype small-molecule probe, was surface-modified on graphitic carbon nitride to generate Si nanoparticles upon reacting with hydroquinone, the enzymatic product of α-Glu. The in situ formed heterojunction enhances the light-harvesting property and photoexcited carrier separation efficiency. As a result, the in situ-sensitized PEC biosensor demonstrates excellent accuracy, a low detection limit, and outstanding anti-interference ability, showing good applicability in evaluating α-Glu activity and its inhibitors in human serum samples. This novel in situ sensitization approach using small-molecule probes opens up new avenues for developing simple and efficient PEC biosensing platforms by replacing conventional biorecognition elements.

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 Nanoparticle-Based Ratiometric Fluorescence Probes for Highly Sensitive and Visual Detection of VB2

In this work, blue fluorescent silicon nanoparticles (SiNPs) were prepared by a simple one-step hydrothermal method using (3-aminopropyl) triethoxy silane (APTES) and eriochrome black T as raw materials. The SiNPs showed favorable water solubility, thermal stability, pH stability, salt tolerance, and photobleaching resistance. At an excitation wavelength of 376 nm, the SiNPs emitted bright blue fluorescence at 460 nm. In the presence of vitamin B₂ (VB₂), the fluorescence intensity (FL intensity) of the SiNPs at 460 nm decreased obviously, and a new peak appeared at 521 nm. Based on this, a novel ratiometric fluorescence method was established for VB₂ detection. There was a good linear relationship between the fluorescence intensity ratio (F ₅₂₁/F ₄₆₀) and VB₂ concentration from 0.5 to 60 μM with a detection limit of 135 nM. This method was successfully applied to detect VB₂ content in the samples of vitamin B₂ drugs and beverages. Additionally, a simple paper sensor based on the SiNPs was designed to visualize detection of VB₂. With the support of color recognition software on a smartphone, the visual quantitative analysis of VB₂ was realized, ranging from 40 to 800 μM.

Dual-Signal Triple-Mode Optical Sensing Platform for Assisting in the Diagnosis of Kidney Disorders

As known biomarkers of kidney diseases, N-acetyl-β-d-glucosaminidase (NAG) and β-galactosidase (β-GAL) are of great importance for the diagnosis and treatment of diseases. The feasibility of using multiplex sensing methods to simultaneously report the outcome of the two enzymes in the same sample is even more alluring. Herein, we establish a simple sensing platform for the concurrent detection of NAG and β-GAL using silicon nanoparticles (SiNPs) as a fluorescent indicator synthesized by a one-pot hydrothermal route. p-Nitrophenol (PNP), as a common enzymatic hydrolysis product of the two enzymes, led to the attenuation of fluorometric signal caused by the inner filter effect on SiNPs, the enhancement of colorimetric signal due to the increase of intensity of the characteristic absorption peak at around 400 nm with increasing reaction time, and the changes of RGB values of images obtained through a color recognition application on a smartphone. The fluorometric/colorimetric approach combined with the smartphone-assisted RGB mode was able to detect NAG and β-GAL with good linear response. Applying this optical sensing platform to clinical urine samples, we found that the two indicators in healthy individuals and patients (glomerulonephritis) with kidney diseases were significantly different. By expanding to other renal lesion-related specimens, this tool may show great potentials in clinical diagnosis and visual inspection.

Significance of Capping Agents of Colloidal Nanoparticles from the Perspective of Drug and Gene Delivery, Bioimaging, and Biosensing: An Insight

The over-growth and coagulation of nanoparticles is prevented using capping agents by the production of stearic effect that plays a pivotal role in stabilizing the interface. This strategy of coating the nanoparticles’ surface with capping agents is an emerging trend in assembling multipurpose nanoparticles that is beneficial for improving their physicochemical and biological behavior. The enhancement of reactivity and negligible toxicity is the outcome. In this review article, an attempt has been made to introduce the significance of different capping agents in the preparation of nanoparticles. Most importantly, we have highlighted the recent progress, existing roadblocks, and upcoming opportunities of using surface modified nanoparticles in nanomedicine from the drug and gene delivery, bioimaging, and biosensing perspectives.

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.

Highly luminescent pH-responsive carbon quantum dots for cell imaging

Carbon quantum dots (CDs) have attracted tremendous interest owing to their idiosyncratic functions and wide-ranging applications. However, it remains a great challenge to empolder an integrated CDs combining high luminescence, biocompatibility and luminescence color tunability for bioimaging via simple approach. In this work, pH-responsive carbon quantum dots (Si-CDs) with high luminescence (quantum yield = 74.8%) were fabricated by one-step hydrothermal method using (3-mercaptopropyl) triethoxysilane (KH-580) as modifier for the first time. The optical properties of the as-prepared Si-CDs can be controlled from obvious green-blue-violet transformation by altering the pH. More importantly, the change is reversible and repeatable. In addition, the Si-CDs have good biocompatibility and chemically inertin vitrocell system simulation. Such non-toxic, environmental friendly, low-cost, inert CDs materials are promising candidates for biomedical and pH-sensitive sensors.

Ligand-Induced Ground- and Excited-State Chirality in Silicon Nanoparticles: Surface Interactions Matter

Silicon-based light-emitting materials have emerged as a favorable substitute to various organic and inorganic systems due to silicon's high natural abundance, low toxicity, and excellent biocompatibility. However, efforts on the design of free-standing silicon nanoparticles with chiral non-racemic absorption and emission attributes are rather scare. Herein, we unravel the structural requirements for ligand-induced chirality in silicon-based nanomaterials by functionalizing with D- and L-isomers of a bifunctional ligand, namely, tryptophan. The structural aspects of these systems are established using high-resolution high-angle annular dark-field imaging in the scanning transmission electron microscopy mode, solid-state nuclear magnetic resonance, Fourier transform infrared, and X-ray photoelectron spectroscopy. Silicon nanoparticles capped with L- and D-isomers of tryptophan displayed positive and negative monosignated circular dichroic signals and circularly polarized luminescence indicating their ground- and excited-state chirality. Various studies supported by density functional theory calculations signify that the functionalization of indole ring nitrogen on the silicon surface plays a decisive role in modifying the chiroptical characteristics by generating emissive charge-transfer states. The chiroptical responses originate from the multipoint interactions of tryptophan with the nanoparticle surface through the indole nitrogen and -CO₂^- groups that can transmit an enantiomeric structural imprint on the silicon surface. However, chiroptical properties are not observed in phenylalanine- and alanine-capped silicon nanoparticles, which are devoid of Si-N bonds and chiral footprints. Thus, the ground- and excited-state chiroptics in tryptophan-capped silicon nanoparticles originates from the collective effect of ligand-bound emissive charge-transfer states and chiral footprints. Being the first report on the circularly polarized luminescence in silicon nanoparticles, this work will open newer possibilities in the field of chirality.

Two-photon-excited tumor cell fluorescence targeted imaging based on transferrin-functionalized silicon nanoparticles

Transferrin-functionalized silicon nanoparticles (Trf-SiNPs) were fabricated and utilized for targeted fluorescence imaging in tumor cells. Silicon nanoparticles (SiNPs) was firstly synthesized by microwave irradiation method, and then coupled with transferrin in the presence of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS). The structural informations of Trf-SiNPs were measured by transmission electron microscope and Fourier transform infrared spectrometer. The optical properties of Trf-SiNPs were characterized by ultraviolet absorption spectrum, fluorescence emission spectrum, fluorescence quantum yield, fluorescence lifetime, photo-stability, and so on. MTT assay evidenced the low toxicity of Trf-SiNPs. Finally, Trf-SiNPs were successfully applied in HeLa cells and HepG2 cells for targeted fluorescence imaging under single-photon excitation and two-photon excitation.

Synthesis of metal ion-tolerant Mn-doped fluorescence silicon quantum dots with green emission and its application for selective imaging of ·OH in living cells

Monitoring hydroxyl radical (·OH) in living cells remains a big challenge on account of its high reactivity and short half-life. In this work, we designed a fluorescent probe based on manganese-doped silicon quantum dots (Mn-SiQDs) for detecting and imaging of ·OH with good water solubility. The manganese was doped in its ethylene diamine tetra-acetic acid (EDTA) complex form and effectively improved the metal ion tolerance of fluorescence of SiQDs. And m-dihydroxybenzene was used as the reductant to extend the emission of SiQDs to the green region at 515 nm when the excitation wavelength was 424 nm. Basing on the fluorescence quenching of Mn-SiQDs, a linear response of ·OH was observed in the range 0.8-50 μM with a limit of detection (LOD) of 88.4 nM, which is lower than those reported with SiQDs. The interference from other ROS or RNS has been assessed and no impact was found. In fully aqueous systems, the Mn-SiQDs have been applied to monitor and image the endogenous ·OH in HeLa cells. Our work provided a new strategy for designing SiQDs with good biocompatibility, high selectivity and long monitoring wavelength. Synthesis of green-emitting silicon quantum dots with N-[3 -(trimethoxysilyl) propyl] ethylenediamine (DAMO), Ethylenediamine tetraacetic acid disodium salt dehydrate (EDTA-2Na·2H₂O), manganese acetate tetrahydrate (Mn(CH₃COO)₂·4H₂0) and m-dihydroxybenzene. The green fluorescence of the silicon quantum dots can be selectively quenched by hydroxyl radicals.

"Switch-Off-On" Detection of Fe3+ and F- Ions Based on Fluorescence Silicon Nanoparticles and Their Application to Food Samples

An approach to the detection of F⁻ ions in food samples was developed based on a “switch-off-on” fluorescence probe of silicon nanoparticles (SiNPs). The fluorescence of the synthetic SiNPs was gradually quenched in the presence of Fe³⁺ ion and slightly recovered with the addition of F⁻ ion owing to the formation of a stable and colorless ferric fluoride. The fluorescence recovery exhibited a good linear relationship (R² = 0.9992) as the concentration of F⁻ ion increased from 0 to 100 μmol·L⁻¹. The detection limit of the established method of F⁻ ion was 0.05 μmol·L⁻¹. The recovery experiments confirmed the accuracy and reliability of the proposed method. The ultraviolet–visible spectra, fluorescence decays, and zeta potentials evidenced the fluorescence quenching mechanism involving the electron transfer between the SiNPs and Fe³⁺ ion, while the fluorescence recovery resulted from the formation of ferric fluoride. Finally, SiNPs were successfully applied to detect F⁻ ions in tap water, Antarctic krill, and Antarctic krill powder.

One-pot synthesis of poly(vinylpyrrolidone)-encapsulated color-emitting silicon quantum dots for sensitive and selective detection of 2,4,6-trinitrophenol

Here, we illustrate an efficient, convenient, and simple method for the sensitive and selective detection of nitro explosive 2,4,6-trinitrophenol (TNP) in 100% water medium by bright cyan-blue color emitting colloidal...

A dual-signal fluorometric-colorimetric sensing platform and visual detection with a smartphone for the determination of β-galactosidase activity based on fluorescence silicon nanoparticles

As one of primary biomarkers of ovarian cancer in early stages, β-galactosidase (β-Gal) is significant in the discovery and diagnosis of the disease. In this work, we constructed a multi-signal sensing platform based on silicon nanoparticles (Si NPs) for β-Gal activity determination. When β-Gal was introduced to the sensing system, 2-Nitrophenyl β-D-galactopyranoside (ONPG) could be converted to o-Nitrophenol (o-NP), which had a characteristic absorption peak at 416 nm and the colorless solution turned yellow. The fluorescence emission of Si NPs at 450 nm can be greatly quenched by o-NP as a consequence of inner filter effect (IFE). This dual-signal fluorometric and colorimetric determination approach could be utilized to detect β-Gal in the range of 2-120 U/L and 6-120 U/L. The limits of detection were 1.36 U/L and 1.07 U/L, respectively. This sensing platform could be successfully utilized to detect β-Gal in real samples. Additionally, a visual detection method was designed to achieve quantitative analysis of β-Gal with the assistance of the smartphone.

Dual-channel fluorescent signal readout strategy for cysteine sensing

Cysteine (Cys) is a biological thiol. Aberrant changes in thiol levels are associated with the development and pathogenesis of various diseases, including liver damage, Alzheimer's disease, weakness, and cardiovascular diseases. Therefore, thiol detection in biological samples has great importance in health monitoring and disease prediction. In this study, we developed a ratiometric fluorescence nanosensor combined with carbon dots (CDs)-doped mesoporous silica and fluorescein-based fluorescent probes loaded in pores for Cys detection. The nanosensor emitted fluorescence at 450 nm upon excitation at 370 nm. In the presence of Cys, the fluorescence emission from the probe could be selectively enhanced, whereas that from CDs could be changed. Thus, a ratiometric fluorescent sensor was developed. This sensor can eliminate the potential influence of background fluorescence and other analyte-independent external environmental factors. The nanosensor was utilized to monitor Cys levels in human serum, and satisfactory results were obtained. Results indicated that the nanosensor can be utilized as an excellent fluorescent nanocomposite material in practical biological applications.

Synthesis of orange-emissive silicon nanoparticles as "off-on" fluorescence probe for sensitive and selective detection of l-methionine and copper

Fluorescent silicon nanoparticles (Si NPs) are of great interest as they are free of heavy ions. However, most of Si NPs exhibit blue or green emission, while orange or red-emitting Si NPs are required for an extensive range of applications. Copper ion (Cu²⁺) and l-methionine (L-Met) detection is critically valuable point since their abnormal level is an indicator of various diseases. In this work, we illustrate an "off-on" method for sensitively and selectively determination of Cu²⁺ and L-Met using Si NPs as fluorescent probe. The Si NPs emitting orange fluorescence with the quantum yield of 2.23% were prepared via one and easy step of hydrothermal treatment of 3(2-aminoethylamino) propyl (dimethoxymethylsilane) (AEAPDMMS) and 2-aminophenol as precursors. The fluorescence of Si NPs was quenched in the presence of Cu²⁺ due to the strong metal-ligand coordination and electrostatic interactions between the large amount of amino and hydroxyl groups on the surface of Si NPs and Cu²⁺. Surprisingly, the resulted non-fluorescent Si NPs-Cu²⁺ complex displayed a fluorescence "turn-on" toward L-Met, due to the competitive coordination of Cu²⁺ between L-Met and Si NPs which leads to the unique "off-on" response to L-Met after the release of free Si NPs. The as-proposed approach is fast, simple, low cost and environmental-friendly. More importantly, it has been applied in the determination of Cu²⁺ and L-Met in water and urine samples, respectively with satisfactory recoveries. Furthermore, the approach could detect Cu²⁺ and L-Met with detection limit of 0.012 μM and 0.07 μM, which are lower than the level of Cu²⁺ in drinking water and of L-Met in human urine sample (maximum ~20 μM and ~5.9 μM, respectively).

Determination of Fe(Ⅲ) ion and cellular bioimaging based on a novel photoluminescent silicon nanoparticles

The determination approaches of Fe (Ⅲ) in biological samples were developed by a novel water-soluble silicon nanoparticles (SiNPs). The SiNPs were synthesized by a facile microwave-assisted method, and simultaneously featured strong blue fluorescence (photoluminescence quantum yield: 25.2%), long lifetime (~13.29 ns) and good photo-stability. The fluorescence intensities of SiNPs were gradually quenched with Fe (Ⅲ) concentration increasing from 2.0 to 50 μmol/L. The detection limit of the established method was 0.56 μmol/L and the precision for eleven replicate detections of 20 μmol/L Fe (Ⅲ) was 3.2% (relative standard deviation, RSD). The spiked recoveries were 99.0%-104.5%. Results of the lifetime decay and cyclic voltammetry (CV) evidenced that the electron transfer was responsible for the fluorescence quenching mechanism of SiNPs and Fe (Ⅲ). Moreover, the SiNPs were successfully applied in the determination of Fe(Ⅲ) in different environmental waters and human serum. Finally, the resulting SiNPs exhibited the green fluorescence in HeLa cells as the optical probe.

Microwave-assisted synthesis of fluorescent silicon quantum dots for ratiometric sensing of Hg (II) based on the regulation of energy transfer

The rapid and sensitive detection of Hg²⁺ is highly required to protect the environmental safety and human healthy. In the present work, a ratiometric fluorescent sensing platform, consisting of silicon quantum dots (SiQDs), Rox-labelled DNA (Rox-DNA), and Exonuclease III (Exo III), is developed for the accurate detection of Hg²⁺. As for fluorescent probe, we report the first use of glutathione as reduction reagent for the microwave synthesis of SiQDs, achieving the facile (using a house-hold microwave oven) and rapid (within 8 min) synthesis. Such SiQDs show pH-independent spectra and reversible fluorescent behavior with temperature. Moreover, experimental results revealed that the electrostatic interaction-induced aggregation of Rox-DNA and SiQDs facilitated the occurring of energy transfer (ET). And detection principle based on the regulation of ET between Rox and SiQDs with Exo III was designed for analysis. ET effect resulted in the fluorescent fading of Rox while that of SiQDs kept stable. For analysis, the addition of Hg²⁺ led to the formation of double-stranded Rox-DNA via T-Hg²⁺-T. Exo III would cut these double-stranded DNA to release Rox and Hg²⁺, thereby impeding the ET effect and recovering the fluorescent of Rox. Such SiQDs/Rox-DNA/Exo III ratiometric fluorescent sensing platform exhibited a linear response concentration range of 0.02 nM-10 nM with a detection limit of 0.01 nM. It was successfully used to analyze the water and soil samples. The reliability was validated by ICP-MS. Our work should promote the practical application of ratiometric fluorescent assay.

Facile Synthesis, Enhanced Photostability, and Long-term Cellular Imaging of Bright Red Luminescent Organosilica Nanoparticles

We herein demonstrate a facile approach for the preparation of red luminescent organosilica nanoparticles (OSi NPs) via the addition reaction of indocyanine green (ICG) and (3-aminopropyl)trimethoxysilane (APTMS). Photoluminescent quantum yield (PLQY) of the resulting OSi NPs was tunable by simply changing the molar ratio of ICG and APTMS used in the reactions. Under the optimized molar ratio of ICG and APTMS, that is, 1:4, PLQY of the red luminescent OSi NPs was as high as 32%. The resulting OSi NPs presented greatly enhanced photostability, attributing to the promoted decay rate of the excited state and thus suppressed the generation of the reactive oxygen species in the OSi NPs. The integrated superiorities of high PLQY, enhanced photostability, low toxicity, and excellent biocompatibility endow the red luminescent OSi NPs extremely promising for long-term cellular imaging.

Rational Design of Far-Red to Near-Infrared Emitting Carbon Dots for Ultrafast Lysosomal Polarity Imaging

Carbon dots (CDs) have been widely studied for their excellent properties. However, most of the prepared CDs only show strong emission in the blue to green region, which greatly limits the application of CDs in the biomedical field. In this report, a new design strategy of long-wavelength CDs was reported. The orange phenyl-CDs with good optical properties and biocompatibility were successfully prepared by changing the substituted group of the o-phenylenediamine and the main emission band of phenyl-CDs was in the far-red region. With the increase of polarity, the wavelength of phenyl-CDs red-shifts and the fluorescence intensity decreases, demonstrating their sensitive polarity response function. In addition, phenyl-CDs can achieve ultrafast target imaging of lysosome within 40 s through clathrin-mediated endocytosis. Finally, phenyl-CDs were successfully applied for monitoring lysosomal polarity induced by drugs, which is helpful in getting a better understanding of the physiological and pathological processes of lysosomes. This report provides an important theoretical basis for the rational design and precise synthesis of long-wavelength fluorescent CDs.

A turn-on fluorescent nanoprobe based on N-doped silicon quantum dots for rapid determination of glyphosate

N-Doped silicon quantum dots (N-SiQD) were synthesized using N-[3-(trimethoxysily)propyl]-ethylenediamine and citric acid as silicon source and reduction agent, respectively. The N-SiQD shows a strong blue fluorescence with a high quantum yield of about 53%. It is found that a selective static quenching process occurs between N-SiQDs and Cu2+. Glyphosate can inhibit this phenomenon and trigger the rapid fluorescence enhancement of the quenched N-SiQDs/Cu2+ system due to the specific interaction between Cu2+ and glyphosate. With such a design, a turn-on fluorescent nanoprobe based on N-SiQD/Cu2+ system was established for rapid determination of glyphosate. The determination signal of N-SiQD/Cu2+ was measured at the optimum emission wavelength of 460 nm after excitation at 360 nm. Under optimal conditions, the turn-on nanoprobe showed a linear relationship between fluorescent response and glyphosate concentrations in the range 0.1 to 1 μg mL-1. The limit of determination was calculated to 7.8 ng mL-1 (3σ/S). Satisfactory recoveries were obtained in the determination of spiked water samples, indicating the potential use for environmental monitoring. Graphical abstract Schematic representation of N-SiQD/Cu2+ system for glyphosate determination. Fluorescence quenching of N-SiQDs induced by copper ions and the succedent fluorescent "turn on" triggered by glyphosate.

High photoluminescence nitrogen, phosphorus co-doped carbon nanodots for assessment of microbial viability

Assessment of microbial viability plays a key role in human health protection. Optical imaging based on fluorescent dyes is a simple and convenient way to assess microbial viability. However, it is still a challenge to obtain stable, nontoxic and low-cost dyes. Herein, we prepared a nitrogen and phosphorus co-doped carbon nanodots (N, P-CDs) via a one-step solvothermal method. The prepared CDs possess plenty of functional groups and exhibit high stability, good biocompatibility, excellent photoluminescent and low toxicity. Especially, the properties of high quantum yield (89.9%) and highly negative surface charge (-41.9 mV) make the prepared N, P-CDs ideal materials for microbial differentiation. Compared with commercial dyes, our CDs are more stable, cost less, which can rapidly distinguish dead microorganisms from living ones with higher specificity.

Intrinsic lysosomal targeting fluorescent carbon dots with ultrastability for long-term lysosome imaging

Intrinsic lysosomal targeting carbon dots were synthesized with ultrastability for long-term lysosome imaging of living cells and drug-induced apoptotic cells.

Introductory lecture: origins and applications of efficient visible photoluminescence from silicon-based nanostructures

This review highlights many spectroscopy-based studies and selected phenomenological studies of silicon-based nanostructures that provide insight into their likely PL mechanisms, and also covers six application areas.

One-Step Synthesis of Silica-Coated Carbon Dots with Controllable Solid-State Fluorescence for White Light-Emitting Diodes

Carbon dots (CDots)-based solid-state luminescent materials have important applications in light-emitting devices owing to their outstanding optical properties. However, it still remains a challenge to develop multiple-color-emissive solid-state CDots, due to the serious self-quenching of the CDots in the aggregation or solid state. Herein, a one-step synthesis of multiple-color-emissive solid-state silica-coated CDots (silica/CDots) composites by controlling CDots loading fraction and composite morphology to realize the adjustment of emitting color is reported. The emission of resultant silica/CDots composites shifts from blue to orange with the photoluminescence quantum yields of 57.9%, 34.3%, and 32.7% for blue, yellow, and orange emitting, respectively. Furthermore, the yellow emitting silica/CDots composites exhibit an excellent fluorescence thermal stability, and further have been applied to fabricate white-light-emitting devices with a high color rendering index of above 80.

Endocytosis and Lack of Cytotoxicity of Alkyl-Capped Silicon Quantum Dots Prepared from Porous Silicon

Freely-dissolved silicon quantum dots were prepared by thermal hydrosilation of 1-undecene at high-porosity porous silicon under reflux in toluene. This reaction produces a suspension of alkyl-capped silicon quantum dots (alkyl SiQDs) with bright orange luminescence, a core Si nanocrystal diameter of about 2.5 nm and a total particle diameter of about 5 nm. Previous work has shown that these particles are rapidly endocytosed by malignant cell lines and have little or no acute toxicity as judged by the standard 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay for viability and the Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay for apoptosis. We have extended this work to the CACO-2 cell line, an established model for the human small intestinal mucosa, and demonstrate that neither acute nor chronic (14 days) toxicity is observed as judged by cell morphology, viability, ATP production, ROS production and DNA damage (single cell gel electrophoresis) at doses of 50–200 μg mL−1. Quantitative assessment of the extent of uptake of alkyl SiQDs by CACO-2, HeLa, HepG2, and Huh7 cell lines by flow cytometry showed a wide variation. The liver cell lines (HepG2 and Huh7) were the most active and HeLa and CACO-2 showed comparable activity. Previous work has reported a cholesterol-sensitivity of the endocytosis (HeLa), which suggests a caveolin-mediated pathway. However, gene expression analysis by quantitative real–time polymerase chain reaction (RT-PCR) indicates very low levels of caveolins 1 and 2 in HepG2 and much higher levels in HeLa. The data suggest that the mechanism of endocytosis of the alkyl SiQDs is cell-line dependent.

Lysosome-targeted carbon dots for ratiometric imaging of formaldehyde in living cells

Formaldehyde (FA) is involved in many biological processes and is closely connected with many diseases including Alzheimer's disease and cancer. Therefore, methods for sensitive and selective detection of FA in living cells are highly demanded. As a new class of carbon nanomaterials, carbon dots (CDs) have attracted great attention owing to their robust photostability, good biocompatibility and environmental friendliness. In this manuscript, the first lysosome-targeted CDs for ratiometric fluorescence detection of FA were efficiently prepared from dexamethasone and 1,2,4,5-tetraaminobenzene through the microwave-assisted hydrothermal method. These CDs show highly selective and sensitive sensing ability towards FA with fast response and great changes of ratio values. The CDs exhibit robust photostability and good biocompatibility and were successfully employed in ratiometric fluorescence bioimaging of FA fluctuations in lysosomes of living cells, which demonstrates their great practicability in FA-related bioanalysis and biological studies.

Preparation of a Ruthenium-Complex-Functionalized Two-Photon-Excited Red Fluorescence Silicon Nanoparticle Composite for Targeted Fluorescence Imaging and Photodynamic Therapy in Vitro

Silicon nanoparticles (SiNPs), especially those emitting red fluorescence, have been widely applied in the field of bioimaging. However, harsh synthetic conditions and strong biological autofluorescence caused by short wavelength excitation restrict the further development of SiNPs in the field of biological applications. Here, we report a method for synthesizing a ruthenium-complex-functionalized two-photon-excited red fluorescence silicon nanoparticle composite (SiNPs-Ru) based on fluorescence resonance energy transfer under mild experimental conditions. In the prepared SiNPs-Ru composite, silicon nanoparticles synthesized by atmospheric pressure microwave-assisted synthesis served as a fluorescence energy donor, which had two-photon fluorescence properties, and tris(4,4'-dicarboxylic acid-2,2-bipyridyl)ruthenium(II) dichloride (L_Ru) acted as a fluorescence energy acceptor, which could emit red fluorescence as well as had the ability to produce singlet-oxygen for photodynamic therapy. Therefore, the synthesized SiNPs-Ru could emit red fluorescence by two-photon excitation based on fluorescence resonance energy transfer, which could effectively avoid the interference of biological autofluorescence. Fluorescence imaging tests in zebrafish and nude mice indicated that the as-prepared SiNPs-Ru could act as a new kind of fluorescence probe for fluorescence imaging in vivo. By coupling folic acid (FA) to SiNPs-Ru, the prepared composite (FA-SiNPs-Ru) could not only serve as a targeted two-photon fluorescence imaging probe but also kill cancer cells via photodynamic therapy in vitro.

One-Step Hydrothermal Synthesis of Yellow and Green Emitting Silicon Quantum Dots with Synergistic Effect

The concept of synergistic effects has been widely applied in many scientific fields such as in biomedical science and material chemistry, and has further attracted interest in the fields of both synthesis and application of nanomaterials. In this paper, we report the synthesis of long-wavelength emitting silicon quantum dots based on a one-step hydrothermal route with catechol (CC) and sodium citrate (Na-citrate) as a reducing agent pair, and N-[3-(trimethoxysilyl)propyl]ethylenediamine (DAMO) as silicon source. By controlling the reaction time, yellow-emitting silicon quantum dots and green-emitting silicon quantum dots were synthesized with quantum yields (QYs) of 29.4% and 38.3% respectively. The as-prepared silicon quantum dots were characterized by fluorescence (PL) spectrum, UV⁻visible spectrum, high resolution transmission electron microscope (HRTEM), Fourier transform infrared (FT-IR) spectrometry energy dispersive spectroscopy (EDS), and Zeta potential. With the aid of these methods, this paper further discussed how the optical performance and surface characteristics of the prepared quantum dots (QDs) influence the fluorescence mechanism. Meanwhile, the cell toxicity of the silicon quantum dots was tested by the 3-(4,5-dimethylthiazolyl-2)-2,5-diphenyltetrazolium (MTT) bromide method, and its potential as a fluorescence ink explored. The silicon quantum dots exhibit a red-shift phenomenon in their fluorescence peak due to the participation of the carbonyl group during the synthesis. The high-efficiency and stable photoluminescence of the long-wavelength emitting silicon quantum dots prepared through a synergistic effect is of great value in their future application as novel optical materials in bioimaging, LED, and materials detection.

Fluorescein sodium ligand-modified silicon nanoparticles produce ultrahigh fluorescence with robust pH- and photo-stability

Water-dispersed silicon nanoparticles (SiNPs) feature ultrahigh fluorescence (photoluminescent quantum yield (PLQY): ∼90%), robust pH- and photo-stability, and favourable biocompatibility.

A facile synthesis of hybrid silicon quantum dots and fluorescent detection of bovine hemoglobin

A new type of hybrid SiQDs was synthesized with a higher nitrogen content, fluorescence intensity and longer fluorescence lifetime.