Synthesis of Silicon Nanoparticles Emitting Yellow-Green Fluorescence for Visualization of pH Change and Determination of Intracellular pH of Living Cells.

In order to understand related pathogenesis of some diseases and design new intracellular drug delivery systems, investigation of pH change in living cells in real time is important. In this paper, a new style of fluorescent silicon nanoparticles (SiNPs) as a pH-sensitive probe and for the visualization of the pH changes in cells was designed and prepared using 4-aminophenol as a reducing agent and N-aminoethyl-γ-aminopropyltrimethyl as a silicon source by a one-pot hydrothermal method. It was particularly noteworthy that the fluorescence intensity emitted from the SiNPs positively correlated with the pH value of solutions, making the SiNPs a viable probe used for sensitive sensing of pH. At the same time, a response of the probe to the pH was found in 5.0-10.0, and the SiNPs have an excellent biocompatibility (e.g., ∼74% of cell viability was remained after treatment for 24 h at 500 µg/mL of the SiNPs). The proposed method that could display the change in pH of live cells provided an effective means for visually diagnosing diseases related to intracellular pH.

Determination of pathogenic bacteria-Bacillus anthrax spores in environmental samples by ratiometric fluorescence and test paper based on dual-emission fluorescent silicon nanoparticles.

Many lanthanide ions-based probes have been widely used for detecting anthrax spores biomarker-dipicolinic acid (DPA). However, little work has realized detection of bacillus anthrax spores in real environmental samples. In this work, a novel ratiometric fluorescent nanoprobe based on europium (Eu)-doped silicon nanoparticles (Eu@SiNPs) was fabricated for the first time by one-pot method without post-modification for determination of the DPA in bacillus subtilis spores (simulant bacillus anthrax spores). Based on Eu(III) in the Eu@SiNPs could be sensitized by DPA to emit intrinsic fluorescence and the fluorescence intensity of SiNPs in the Eu@SiNPs almost remained stable, a new ratiometric fluorescent method for determination of micro DPA in bacillus subtilis spores and bacillus subtilis spores in real environmental samples, such as Yellow river water, tap water and soil was established. Under the optimum conditions, the limit of detection (LOD) of the method toward bacillus subtilis spores was as low as 2.38×104 spore/mL. Simple, fast and visual DPA and bacillus subtilis spores determination was also achieved by the Eu@SiNPs-based test paper. Therefore, the newly established method was expected to be a powerful tool for efficiently determination of bacillus anthrax spores to avoid anthrax threats.

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.

Investigation of nitrogen content effect in reducing agent to prepare wavelength controllable fluorescent silicon nanoparticles and its application in detection of 2-nitrophenol.

Fluorescent silicon nanoparticles (SiNPs) displayed different emission wavelengths have been synthesized, but it has not been reported that the preparation of wavelength controllable SiNPs by adjusting the nitrogen content of reducing agents. In this paper, the wavelength-controlled fluorescent SiNPs were prepared by selecting the dopamine (DA) with nitrogen content between catechol and 2-aminophenol as the reducing agent and N-[3-(trimethoxysilyl) propyl]-ethylenediamine (DAMO) as the silicon source via one-step hydrothermal method. The emission wavelength of the prepared SiNPs was in direct proportion to the nitrogen content in the reducing agent. To the best of our knowledge, this is the first time for exploring the nitrogen content in reducing agents could affect the optical properties of SiNPs so far. In addition, the obtained SiNPs could be applied to determinate 2-nitrophenol (2-NP). Based on the combination action of inner filter effect (IFE) and static quenching effect (SQE) mechanism, a wide linear range was obtained from 0.1 to 500 µM, and the limit of detection was 0.029 µM for 2-NP, which was comparable to or even lower than some previous reports. This SiNPs probe was also successfully employed for sensing of 2-NP in industrial effluent with satisfactory results (98.6%-103.4%).

A peptide-WS2 nanosheet based biosensing platform for determination of ß-secretase and screening of its inhibitors.

ß-Secretase (BACE1) is an important drug target in the treatment of Alzheimer's disease (AD). Therefore, sensitive detection of BACE1 is essential for AD treatment and drug discovery. In this work, a facile and sensitive fluorescence biosensing platform was developed for BACE1 detection. This sensing platform was constituted based on the interaction between a WS2 nanosheet and a peptide sequence. In the absence of BACE1, a FAM-labeled peptide substrate could be adsorbed on the surface of the WS2 nanosheet, thereby quenching its fluorescence. However, in the presence of BACE1, the hydrolysis of the peptide substrate by BACE1 triggers could occur with the subsequent release of short FAM-linked peptide fragments which could not be adsorbed on the surface of the WS2 nanosheet. This resulted in weak fluorescence quenching, thus restoring the fluorescence signal. By measuring the change in the fluorescence of the FAM-labeled peptide substrate, the fluorescence sensing platform based on the WS2 nanosheet could monitor BACE1. The proposed WS2 nanosheet-based platform exhibited excellent specificity and high sensitivity with a detection limit of 66 pM for BACE1. Importantly, we also demonstrated that this platform was suitable for the screening of BACE1 inhibitors. The proposed sensing platform not only provides a novel strategy for the BACE1 assay but also offers a potential tool for screening drugs.

One-step synthesis of red/green dual-emissive carbon dots for ratiometric sensitive ONOO- probing and cell imaging.

The synthesis of dual-emissive carbon dots (CDs) with a longer emission wavelength by using a facile strategy is of great importance for the fabrication of ratiometric fluorescent nanoprobes. Herein, red/green dual-emissive carbon dots (RGDE CDs) were synthesized in one step using 2,5-diaminotoluene sulfate (DATS) as a carbon source. The as-prepared RGDE CDs not only exhibited dual emission fluorescence peaks (525 nm, 603 nm) at the single excitation wavelength of 370 nm, but also possessed good water solubility and excellent fluorescence stability. Moreover, the as-prepared RGDE CDs could be directly utilized as a ratiometric fluorescent probe for the determination of trace ONOO- due to the electron transfer process from ONOO- to the excited RGDE CDs. Under optimal conditions, the linear range was 0.03-60 µM with the limit of detection of 11.6 nM. Importantly, this RGDE CD probe could be applied for the detection of intracellular ONOO- with excellent biocompatibility and cellular imaging capability, indicating great promise in biomedical applications.

Ratiometric fluorescent detection of chromium(VI) in real samples based on dual emissive carbon dots.

As we know, hexavalent chromium (Cr(VI)) was usually used as an additive to improve the color fastness during the printing and dyeing process, and thus posing tremendous threat to our health and living quality. In this work, the dual emissive carbon dots (DECDs) were synthesized through hydrothermal treatment of m-aminophenol and oxalic acid. The obtained DECDs not only exhibited dual emission fluorescence peaks (430 nm, 510 nm) under the single excitation wavelength of 380 nm, but also possessed good water solubility and excellent fluorescence stability. A ratiometric fluorescent method for the determination of Cr(VI) was developed using the DECDs as a probe. Under the optimal conditions, a linear range was obtained from 2 to 300 µM with a limit of detection of 0.4 µM. Furthermore, the proposed ratiometric fluorescent method was applied to the analysis of Cr(VI) in textile, steel, industrial wastewater and chromium residue samples with satisfactory recoveries (88.4-106.8%).

One-Pot Synthesis of Fluorescent Silicon Nanoparticles for Sensitive and Selective Determination of 2,4,6-Trinitrophenol in Aqueous Solution.

Because 2,4,6-trinitrophenol (TNP) and its analogues such as 2,4,6-trinitrotoluene (TNT) possess similar chemical structures and properties, the reliable and accurate detection of TNP from its analogues still remains a challenging task. In the present work, a selective and sensitive method based on the water-soluble silicon nanoparticles (SiNPs) for the determination of TNP was established. The SiNPs with good thermostability and excellent antiphotobleaching capability were prepared via a simple one-pot method. Compared with the synthesized time of other nanomaterials with respect to the detection of TNP, this method avoided a multistep and time-consuming synthesis procedure. Significantly, the fluorescence of the SiNPs could be remarkably quenched by TNP via an inner filter effect. A wide linear range was obtained from 0.02 to 120 µg/mL with a limit of detection of 6.7 ng/mL. The method displayed excellent selectivity toward TNP over other nitroaromatic explosives. The proposed fluorescent method was successfully applied to the analysis of TNP. Moreover, a straightforward and convenient fluorescent filter paper sensor was developed for the detection of TNP, providing a valuable platform for TNP sensing in public safety and security.

pH-Regulated Synthesis of Trypsin-Templated Copper Nanoclusters with Blue and Yellow Fluorescent Emission.

In this article, a simple protocol to prepare water-soluble fluorescent copper nanoclusters (CuNCs) using trypsin as a stabilizer and hydrazine hydrate as a reducing agent was reported. It was found that the pH of the reaction solution was critical in determining the fluorescence of CuNCs. CuNCs with blue and yellow fluorescent emission were obtained under basic and acidic conditions, respectively. Although the detailed formation mechanisms of these CuNCs required further analysis, the synthetic route was promising for preparing different fluorescent metal NCs for applications. With good water solubility and excellent photostability, the yellow-emitting CuNCs could serve as a fluorescence probe for detection of Hg2+ based on the aggregation-induced quenching mechanism. The fluorescence quenching efficiency had fantastic linearity to Hg2+ concentrations in the range of 0.1-100 µM, with a limit of detection of 30 nM. Additionally, the yellow-emitting CuNCs exhibited negligible cytotoxicity and were successfully applied to bioimaging of HeLa cells.

One-Step Synthesis of Water-Dispersible and Biocompatible Silicon Nanoparticles for Selective Heparin Sensing and Cell Imaging.

A sensitive and selective fluorescence "turn-off" sensor to detect heparin using water-soluble silicon nanoparticles (Si NPs) was developed for the first time. The Si NPs were synthesized by a simple one-step procedure, which did not need high-temperature and complex modification. The as-prepared Si NPs featured strong fluorescence, favorable biocompatibility, and robust photo- and pH stability. Significantly, the Si NPs were induced to assemble or aggregate via hydrogen bonding, which resulted in the fluorescence of Si NPs quenched. Under the optimized conditions, the linear range was obtained from 0.02 to 2.0 µg/mL, with a limit of detection of 18 ng/mL (equal to 0.004 U/mL). It was lower than the proper therapeutic level of heparin during cardiovascular surgery and long-term therapy. This proposed method was relatively free of interference from heparin analogues, which commonly existed in heparin samples and could possibly affect heparin detection. Moreover, it did not need to introduce any control medium. As expected, the method was successfully applied to detect heparin in human serum samples with satisfactory recovery ranging from 98.8 to 102.5%. The Si NPs were superbly suitable for cell imaging owing to the negligible cytotoxicity and excellent biocompatibility.

"Switch-On" Fluorescent Sensing of Ascorbic Acid in Food Samples Based on Carbon Quantum Dots-MnO2 Probe.

This work describes a "switch-on" fluorescence approach for sensing of ascorbic acid (AA) in food samples. In the present method, the fluorescence intensity (FL) of carbon quantum dots (CQDs) was first quenched by addition of MnO2 nanosheets through an inner filter effect to form a CQDs-MnO2 probe. When reductive AA was introduced into the quenched CQDs solution, the added MnO2 was destroyed due to the redox reaction between AA and MnO2 nanosheets, and the FL of the system was recovered. Under the optimal conditions, the limit of detection for AA was 42 nM, with a wide concentration linear range of 0.18-90 µM. Furthermore, the as-fabricated fluorescent sensing system was successfully applied to the analysis of AA in fresh fruits, vegetables, and commercial fruit juices samples with satisfactory results.

The peroxidase/catalase-like activities of MFe2O4 (M=Mg, Ni, Cu) MNPs and their application in colorimetric biosensing of glucose.

MFe2O4 (M=Mg, Ni, Cu) magnetic nanoparticles (MNPs) were found to have catalytic activities similar to those of biological enzymes such as catalase and peroxidase. These nanomaterials, as bifunctional catalase/peroxidases (KatGs), not only could catalyze H2O2 to produce hydroxyl radicals, which oxidized peroxidase substrate to produce color, but also could catalyze the decomposition reaction of H2O2 into water and oxygen directly in the same condition through the catalase-like activity. And it was also found that the amount of generated hydroxyl radicals and oxygen was related to the concentration of MFe2O4 (M=Mg, Ni, Cu) MNPs. The peroxidase-like catalytic behavior of MFe2O4 MNPs was analyzed in detail. Under the optimized conditions, NiFe2O4 MNPs were used as a colorimetric biosensor for the detection of 9.4×10(-7)-2.5×10(-5) mol L(-1) glucose with a limit of detection (LOD) of 4.5×10(-7) mol L(-1). The sensor was successfully applied to glucose detection in urine sample.