Enantioselective Glutamic Acid Discrimination and Nanobiological Imaging by Chiral Fluorescent Silicon Nanoparticles.

Enantioselective discrimination of chiral molecules is essential in chemistry, biology, and medical science due to the configuration-dependent activities of enantiomers. Therefore, identifying a specific amino acid and distinguishing it from its enantiomer by using nanomaterials with outstanding performance are of great significance. Herein, blue- and green-emitting chiral silicon nanoparticles named bSiNPs and gSiNPs, respectively, with excellent water solubility, salt resistance, pH stability, photobleaching resistance, biocompatibility, and ability to promote soybean germination, were fabricated in a facile one-step method. Especially, chiral gSiNPs presented excellent fluorescence recognition ability for glutamic acid enantiomers within 1 min, and the enantiomeric recognition difference factor was as high as 9.0. The mechanism for enantiomeric fluorescence recognition was systematically explored by combining the fluorescence spectra with density functional theory (DFT) calculation. Presumably, the different Gibbs free energy and hydrogen-bonding interaction of the chiral recognition module with glutamic acid enantiomers mainly contributed to the difference in the fluorescence signals. Most noteworthy was the fact that the chiral gSiNPs can showcase not only the ability to recognize l- and d-glutamic acids in living cells but also the test strips fabricated by soaking gSiNPs can be applied for d-glutamic acid visual detection. As a result, this study provided insights into the design of multifunctional chiral sensing nanoplatforms for enantiomeric detection and other applications.

Facile synthesis of yellow-green fluorescent silicon nanoparticles and their application in detection of nitrophenol isomers.

A clear formation mechanism is essential for the controllable synthesis of nanomaterials with different optical properties, which is also one of the challenges facing the preparation of fluorescent silicon nanomaterials. In this work, a one-step room temperature synthesis method was established to prepare yellow-green fluorescent silicon nanoparticles (SiNPs). The obtained SiNPs exhibited excellent pH stability, salt tolerance, anti-photobleaching ability and biocompatibility. Based on X-ray photoelectron spectroscopy, transmission electron microscopy, ultra high performance liquid chromatography tandem mass spectrometry and other characterization data, the formation mechanism of the SiNPs was proposed, which provided a theoretical basis and important reference for the controllable preparation of SiNPs and other fluorescent nanomaterials. In addition, the obtained SiNPs illustrated excellent sensitivity for nitrophenol isomers, the linear range of o-nitrophenol, m-nitrophenol, p-nitrophenol was 0.05-600 µM, 20-600 µM and 0.01-600 µM under the λex and λem were set as 440 nm and 549 nm, and related limit detection was 16.7 nM, 6.7 µM and 3.3 nM, respectively. The developed SiNP-based sensor achieved satisfactory recoveries in detecting nitrophenol isomers in a river water sample, showing great promise in practical applications.

Green- and Red-Emitting Fluorescent Silicon Nanoparticles: Synthesis, Mechanism, and Acid Phosphatase Sensing.

Until now, the green and facile synthesis of multicolor fluorescent silicon nanoparticles (SiNPs) with favorable biocompatibility for cellular imaging and biosensors is still a challenge. Herein, a facile one-step room temperature method for preparing fluorescent SiNPs displayed different emission wavelengths was reported. Green and red fluorescent SiNPs (G-SiNPs and R-SiNPs) were synthesized by adjusting the concentration of the reducing agent 2,4-diaminophenol hydrochloride when the amount of N-[3-(trimethoxysilyl)-propyl]-ethylenediamine was consistent. Characterized by Fourier transform infrared spectroscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy, the results revealed that the G-SiNPs and R-SiNPs were assembled by polymerization of different building blocks, and the emission characteristics of these SiNPs were attributed to the difference in their structural composition and particle size. Interestingly, these fluorescent SiNPs exhibited excellent water solubility, salt tolerance, pH stability, photobleaching resistance, and low cytotoxicity, which facilitated multicolor cell imaging, and further led to these SiNPs were highly attractive in a variety of applications, such as multi-channel sensing and biological imaging. Furthermore, the R-SiNPs have shown the potential to detect acid phosphatase, which is a biomarker of prostate cancer.

Fabrication and application of 2,4,6-trinitrophenol sensors based on fluorescent functional materials.

2,4,6-Trinitrophenol (TNP) has been widely used for a long time. The adverse effects of TNP on ecological environment and human health have promoted researchers to develop various methods for detecting TNP. Among multifarious technologies utilized for the TNP detection, fluorescence strategy based on different functional materials has become an effective and efficient method attributed to its merits such as preferable sensitivity and selectivity, rapid response speed, simple operation, and lower cost, which is also the focus of review. This review summarizes the development status of fluorescence sensors for TNP in a detailed and systematic way, especially focusing on the research progress since 2015. The sensing properties of fluorescent materials for TNP are the core of this review, including nanomaterials, organic small molecules, emerging supramolecular systems, aggregation induced emission materials and others. Moreover, the development direction and prospect of fluorescence sensing method in the field of TNP detection are introduced and discussed at the end of review.

Construction of a Carbon Dots/Cobalt Oxyhydroxide Nanoflakes Biosensing Platform for Detection of Acid Phosphatase.

Because abnormal acid phosphatase (ACP) can disrupt the normal physiological processes, determination of ACP level is extremely important for early diagnosis, treatment, and prognostic evaluation of diseases. Herein, a fluorescence platform for monitoring ACP level was established based on the assembly of red-emitting carbon dots (RCDs) on cobalt oxyhydroxide (CoOOH) nanoflakes. RCDs displayed excellent water solubility, pH stability, salt resistance, and photobleaching resistance. Interestingly, the fluorescence of the RCDs assembled on the surface of the CoOOH nanoflakes could be quenched due to the energy transfer caused by the nanoflakes. However, the ascorbic acid (AA) produced by the hydrolysis of ascorbic acid-2-phosphate trisodium salt (AAP) catalyzed by ACP could quickly and effectively reduce CoOOH nanoflakes, leading to the fluorescence recovery of the RCDs. Therefore, an "off-on" biosensor platform for rapid, sensitive, and selective detection of ACP was constructed with a limit of detection of 0.25 mU/L. With the assistance of the biosensor, the level of ACP in human serum samples was evaluated, and the spike recovery values ranged from 94.0% to 104.5%.

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.

A review on optical sensors based on layered double hydroxides nanoplatforms.

In recent years, significant efforts have been devoted towards the fabrication and application of layered double hydroxides (LDHs) due to their tremendous features such as excellent biocompatibility with negligible toxicity, large surface area, high conductivity, excellent solubility, and ion exchange properties. Most impressive, LDHs offer a favorable environment to attach several substances such as quantum dots, fluorescein dyes, proteins, and enzymes, which leads to strengthening the catalytic properties or increasing the sensing selectivity and sensitivity of the resulted hybrids. With the extensive ongoing research on the application of nanomaterials, many studies have led to remarkable achievements in exploring LDHs as sensing nanoplatforms. In optical sensors, for instance, many sensing strategies were tailored based on the enzyme-mimicking properties of LDHs, including colorimetric and chemiluminescence procedures. Meanwhile, others were designed based on intercalating some fluorogenic substrates on the LDHs, whereby the sensing signal can be acquired by quenching or enhancing their fluorescence after the addition of analytes. In this review, we aim to summarize the recent advances in optical sensors that use layered double hydroxides as sensing platforms for the determination of various analytes. By outlining some representative examples, we accentuate the change of spectral absorbance, chemiluminescence, and photoluminescence phenomena triggered by the interaction of LDH or functionalized-LDH with the indicators and analytes in the system. And finally, current limitations and possible future orientation in designing further LDHs-based optical sensors are presented. It is hoped that this review will be helpful in assisting the establishment of more improved sensors based on LDHs features. Optical sensors based on layered double hydroxides (LDHs) nanoplatforms were reviewed. The sensing system and detection approaches were rationally reviewed. Possible future orientations were highlighted.

Advances and prospects on acid phosphatase biosensor.

Acid phosphatase (ACP) is a lysosomal enzyme widely found in animals and plants. Particularly, abnormal ACP levels are often closely related to many diseases of the individual and are therefore widely used as biomarkers in clinical diagnosis. With the rapid development of precision medicine, the improvement or enhancement of the selectivity, sensitivity and broad target sample types of ACP biosensors based on the established methods has become an emerging demand for the treatment of diseases related to ACP levels. Therefore, a large number of ACP detection strategies have been used to improve these problems. In this review, the types and advantages/disadvantages of ACP detection methods were summarized and compared. According to the previous reports, the prospects and development trends of ACP detection were discussed. It was expected to provide some insights and inspiration for future research work.

Deep eutectic solvent-assisted facile synthesis of copper hydroxide nitrate nanosheets as recyclable enzyme-mimicking colorimetric sensor of biothiols.

In the quest for alternative products that would conquer natural enzyme drawbacks, enzyme-like nanomaterials with controllable morphology, high catalytic activity, excellent stability, and reusability have gained extensive attention in recent years. Herein, a simple and versatile strategy based on basic deep eutectic solvents was used to create layered copper hydroxide nitrate (Cu2(OH)3NO3) with a well-structured nanosheet-like morphology. The present nanosheets exhibited extraordinary oxidase and peroxidase-like activity. More importantly, these nanosheets have shown the ability to operate at low and high temperatures with appreciable stability and multiple reusabilities. Based on inhibiting the oxidase-like activity of the prepared Cu2(OH)3NO3, we designed a colorimetric sensing technique with a high-efficiency detection of biothiols in serum samples. Because of the simplicity and low-cost fabrication approach, our findings would be beneficial to the artificial enzyme research community as another facile and green tactics to fabricate heterogeneous artificial enzymes. Graphical abstract.

Chiral Fluorescent Silicon Nanoparticles for Aminopropanol Enantiomer: Fluorescence Discrimination and Mechanism Identification.

As an important chiral molecule for the preparation of levofloxacin, the optical purity of L-aminopropanol has a crucial effect on the pharmacology and pharmacodynamics of levofloxacin. Therefore, it is of great significance to discriminate D-aminopropanol and L-aminopropanol. In this paper, an effective aminopropanol enantiomer recognition method was established on the basis of the chiral fluorescent silicon nanoparticles (SiNPs) probe. The chiral fluorescent SiNPs were fabricated via a one-step aqueous solution synthesis strategy, which avoided multiple steps, pressurizing operation, and time-consuming postmodified procedures. Significantly, D-aminopropanol could significantly enhance the fluorescence of the chiral SiNPs, while L-aminopropanol could not affect the fluorescence of the chiral SiNPs. This could have occurred because of the stronger interaction between the chiral SiNPs and D-aminopropanol than that of L-aminopropanol. Thus, the rapid and selective recognition of the aminopropanol enantiomer was ideally realized. The mechanism of the chiral SiNPs recognizing aminopropanol was simulated by density functional theory quantum mechanical calculations. Interestingly, this was also proved by the separation of aminopropanol enantiomer using this chiral SiNPs-modified silica column in normal phase liquid chromatography. To the best of our knowledge, this is the first time that the chiral fluorescent SiNPs were synthesized and used to detect the aminopropanol enantiomer successfully. This work will inspire additional syntheses of chiral silicon nanomaterials and other nanomaterials with excellent properties and will enable application of chiral nanomaterials to other fields.

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.

Recent progress and prospects of alkaline phosphatase biosensor based on fluorescence strategy.

Alkaline phosphatase (ALP) is a membrane-bound enzyme widely present in biological tissues and is extensively used as a biomarker in clinical diagnosis because abnormal ALP levels in organisms are often closely related to many diseases. In order to meet the urgent needs of human health and the development of precision medicine, the classic method of detecting ALP seems to be unable to meet a "tailor-made" treatment plan for patients. In order to get the best therapeutic effect and the lowest side effects, the researchers have made considerable efforts and established numerous strategies for detecting ALP. In this review, we focus on the current development and basic principles of fluorescence strategy to detect ALP, and compare the advantages and disadvantages of detecting ALP based on different fluorescent detection modes. In addition, to more intuitively understand the performance of different materials for detecting ALP, a table is presented. Finally, the future trends and prospective in this field will be discussed, it could be speculated that invent and design the detection mechanism based on the relationship between the new material and ALP is the key to effective detection of ALP, and process data with a computer analog digital platform will be a welcome and obsessive technology. It is hoped that some insights and inspiration for future research work will be provided.

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%).

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.

Fluorescent carbon nanoparticles: A low-temperature trypsin-assisted preparation and Fe(3+) sensing.

In recent years, extensive researches are focused on the fluorescent carbon nanoparticles (CNPs) due to their excellent photochemical, biocompatible and water-soluble properties. However, these synthesis methods are generally suffered from tedious processes. In this paper, fluorescent carbon nanoparticles are synthesized by a facile, one-pot, low-temperature method with trypsin and dopamine as precursors. The synthesis process avoids any heating operation and organic solvent, which provides a "green" and effective preparation route. The obtained CNPs exhibit excellent water-solubility, salt-tolerance and photostability. Based on the synergistic action of the inner filter effect and static quenching mechanism, the CNPs are exploited as a "turn-off" fluorescence sensor for sensitive and selective detection of Fe(3+) ions. The probe shows a wide linear range from 0.1 to 500 µM, with a limit of detection of 30 nM. Furthermore, the as-fabricated fluorescent sensing system is successfully applied to the analysis of Fe(3+) in biological samples such as human urine and serum samples with satisfactory recoveries (92.8-113.3%).