Highly photoluminescent silicon nanocrystals for rapid, label-free and recyclable detection of mercuric ions

Luminescent Silicon Nanocrystals as Metal Ion Sensors

At relatively low concentrations in aqueous solution, Fe3+, Fe2+, Cu2+, and Ni2+ quench the photoluminescence (PL) of the undecenoic acid-capped silicon (Si) nanocrystals. The PL could be restored by adding a chelating agent, such as ethylenediaminetetraacetic acid (EDTA), to remove the ions. Fe3+ and Cu2+ also significantly increase the PL lifetime. Other metal ions, including Cd2+, Mn2+, Pb2+, Zn2+, In3+, K+, and Ca2+, had no effect on the Si nanocrystal PL. The limits of detection (LODs) for Fe3+ and Cu2+ of 370 and 150 nM, respectively, are low enough for metal ion sensing applications.

Highly fluorescent hydroxyl groups functionalized graphitic carbon nitride for ultrasensitive and selective determination of mercury ions in water and fish samples

Heavy metal ion pollution is always a serious problem worldwide. Therefore, monitoring heavy metal ions in environmental water is a crucial and difficult step to ensure the safety of people and the environment. A mercury ion (Hg2+) fluorescence probe with excellent sensitivity and selectivity is described here. The functionalized graphitic carbon nitride nanosheets (T/G-C3N4) fluorescence probe was fabricated using melamine as a precursor by the pyrolysis technique, followed by a rapid KOH heat treatment method for 2 min. The chemical structure and morphology of the T/G-C3N4 probe were characterized using multiple analytical techniques including UV–Vis, SEM, XPS, XRD, and fluorometer spectroscopy. Geometry optimization of T/G-C3N4 as a modified probe was performed to assess its stability and interaction ability with Hg(II) via using the density function approach. The T/G-C3N4 probe showed a linear response based on quenching over the range 0–1.25 × 103 nM Hg(II); the detection limit was 27 nM. The remarkable sensitivity of T/G-C3N4 towards the Hg2+ ions was explained by the intense coordination and fast chelation kinetics of Hg2+ with the NH2, CN, C=N, and OH groups of T/G-C3N4 nanoprobe. The T/G-C3N4 probe demonstrates exceptional selectivity for Hg2+ ions among other metal ions including (Na+, Ag+, Mg2+, Fe2+, Fe3+, Co2+, Ni2+, Cd2+, K+, Ca2+, Cu2+, Pb2+, Mn2+ and Hg2+) and over a broad pH range (6–10), together with remarkable long-term fluorescence stability in water (> 30 days) and minimal toxicity. T/G-C3N4 was used to detect and quantify Hg2+ ions in tuna and mackerel fish and the results compared to ICP-AES. The results obtained offer a new simple and green technique for the design of multifunctional fluorescent probe appropriate for environmental applications.

Graphical Abstract

Incorporation of perovskite nanocrystals into lanthanide metal-organic frameworks with enhanced stability for ratiometric and visual sensing of mercury in aqueous solution

In-situ growth of CsPbBr₃ nanocrystal into Eu-BTC was realized for synthesis of dual-emission CsPbBr₃@Eu-BTC by a facile solvothermal method, and a novel ratiometric fluorescence sensor based on the CsPbBr₃@Eu-BTC was prepared for rapid, sensitive and visual detection of Hg²⁺ in aqueous solution. The transmission electron microscopy (TEM), X-ray diffraction pattern (XRD), X-ray photoelectron spectroscopy (XPS) and Brunauer-Emmett-Teller (BET) analysis were used to verify the successful incorporation of CsPbBr₃ into the Eu-BTC. Meanwhile, the CsPbBr₃@Eu-BTC nanocomposite maintained high fluorescence performance and stability in aqueous solution. After adding Hg²⁺, the green fluorescence of CsPbBr₃ was quenched and the red fluorescence of Eu³⁺ remained unchanged, while the color changed from green to red obviously. The occurrence of dynamic quenching and electron transfer were verified by fluorescence lifetime, Stern-Volmer quenching constant and XPS analysis. The ratiometric fluorescence sensor shows high analytical performance for Hg²⁺ detection with a wide linear range of 0-1 μM and a low detection limit of 0.116 nM. In addition, it also shows high selectivity for the detection of Hg²⁺ and can be successfully applied to detect Hg²⁺ in environmental water samples. More importantly, a novel paper-based sensor based on the CsPbBr₃@Eu-BTC ratiometric probe was successfully manufactured for the visual detection of Hg²⁺ by naked eyes. This new type of ratiometric fluorescent sensor shows great potential for applications in point-of-care diagnostics.

Single-step acid-catalyzed synthesis of luminescent colloidal organosilica nanobeads

We present a single-step, room-temperature synthesis of fluorescent organosilica nanobeads (FOS NBs). The FOS NBs were synthesized under aqueous conditions using (3-aminopropyl)triethoxysilane (APTES) as the silicon source in the presence of L-ascorbic acid (L-AA). In the APTES/L-AA/water ternary phase, the hydrolysis and condensation reaction of APTES occurred under acidic conditions to form spherical FOS NBs with an average diameter of 426.8 nm. FOS NBs exhibit excellent colloidal stability in aqueous media. The formation of FOS NBs was complete within a 10 min reaction time, which indicates potential for large-scale mass-production synthesis of luminescent colloidal NBs. The FOS NBs exhibited blue photoluminescence (PL) under UV excitation in the absence of an additional high temperature calcination process or with the incorporation of any fluorophores. This phenomenon is attributed to the presence of carbon-containing defects, which act as luminescent centers formed by the reaction between amino groups in the APTES and L-ascorbic acid reductant. Finally, the results of a cytotoxicity test and cellular uptake experiments revealed that the FOS NBs showed potential as optical contrast agents for bioimaging.

Hairpin oligosensor using SiQDs: Förster resonance energy transfer study and application for miRNA-21 detection

MicroRNAs are known to be tumor suppressors and promoters and can be used as cancer markers. In this work, a novel oligosensor was designed using Si quantum dots (SiQDs) for the detection of miRNAs. Five-nanometer SiQDs were synthesized, with a band gap of 2.8 eV, fluorescence lifetime of 4.56 μs (τ1/2 = 3.26 μs), quantum yield of 25%, fluorescence rate constant of 6.25 × 104, and non-radiative rate constant of 1.60 × 105 s-1. They showed excellent water dispersibility, good stability (with 95% confidence for 6-month storage) without photobleaching, and high biocompatibility, with an IC50 value of 292.2 μg/L. The SiQDs and Black Hole Quencher-1 (BHQ1) were conjugated to the 5' and 3' terminals of an oligomer, respectively. The resulting hairpin molecular beacon showed resonance energy transfer efficiency of 63%. A distance of 0.91 R (Förster distance) between SiQD and BHQ1 was obtained. In the presence of a stoichiometric amount of the complementary oligonucleotide (ΔGhybridization = -35.09 kcal mol-1), 98% of the fluorescence was recovered due to loop opening of the hairpin structure. The probe showed good selectivity toward miRNA-21, with a limit of detection of 14.9 fM. The oligosensor recoveries of miRNA-21 spiked in human serum and urine were 94-98% and 93-108%, respectively.

"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.

Rapid Determination of Sunset Yellow in Soft Drinks Using Silicon Nanoparticles Synthesized under Mild Conditions

Sunset yellow (SY) is a synthetic colorant which can cause allergies, diarrhea and other symptoms in sensitive people. When ingested too much, it can accumulate in the body and cause damage to the kidneys and liver. Therefore, the content of SY in food must be strictly controlled. In order to regulate their use and ensure food quality, simple and cost-effective methods need to be developed to identify them. In this experiment, fluorescent silicon nanoparticles (SiNPs) were prepared by a one-step method, which is simple, mild and less time-consuming. The fluorescent SiNPs prepared had good thermal stability, excellent salt resistance and pH stability. SY effectively quenched the fluorescence of SiNPs by fluorescence resonance energy transfer when added to the system as an interfering substance. The method had a good linear relationship in the range of SY concentration of 0.050 - 14.0 μg mL^-1 and the detection limit is 0.023 μg mL^-1. The established sensor was applied to the detection of SY in beverages, and the recovery rate was 93.8 - 102.4%. Based on the excellent selectivity and sensitivity of the method, it could provide a convenient way for the detection of SY in food samples.

Turning waste into treasure: chicken eggshell membrane derived fluorescent carbon nanodots for the rapid and sensitive detection of Hg2+ and glutathione

Herein, a green, economical, and waste-utilization approach is reported for the synthesis of water-soluble carbon nanodots (C-Dots) with a high fluorescence quantum yield of 19.5%. As a common protein-rich waste, eggshell membrane was selected as a cost-effective and ideal precursor to prepare C-Dots using the microwave method. The as-prepared C-Dots showed a maximum emission at 375 nm with an excitation wavelength at 235 nm. The fluorescent C-Dots were adopted as a sensitive probe for the rapid detection of Hg²⁺ and glutathione (GSH) based on the fluorescence off and on (turn-off-on) strategy. This was ascribed to the fact that Hg²⁺ could effectively quench the fluorescence of the C-Dots and GSH was able to prevent fluorescence quenching owing to the specific binding between Hg²⁺ and GSH. The designed method exhibited a high sensitivity and selectivity towards the detection of Hg²⁺ and GSH. Under the optimized conditions, the method showed a good linear relationship with Hg²⁺ concentration in the range from 100 nM to 50 μM with a detection limit of 32.0 nM. For GSH detection, it displayed a linear range from 50 nM to 10 μM with a detection limit of 9.8 nM. Moreover, this method was successfully applied to detect GSH in human serum samples. The eggshell derived fluorescent C-Dots pave the way for economical environmental and biological analyses.

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.

Ratiometric Fluorescence Detection of DNA Based on the Inner Filter Effect of Ru(bpy)2(dppx)2+ toward Silicon Nanodots

A ratiometric DNA sensor was developed based on fluorescent silicon nanodots (SiNDs) and Ru(bpy)₂(dppx)²⁺. The absorption spectrum of Ru(bpy)₂(dppx)²⁺ has significant overlap with both the excitation and emission spectra of SiNDs. Therefore, fluorescence quenching of Ru(bpy)₂(dppx)²⁺ toward SiNDs can occur on account of the strong inner filter effect. The effect of quenching is not influenced by the specific binding between Ru(bpy)₂(dppx)²⁺ and DNA. Fluorescence turn-on detection of DNA can be performed employing Ru(bpy)₂(dppx)²⁺ and SiNDs as the response and reference signals, respectively. Using SiND-Ru(bpy)₂(dppx)²⁺, a convenient, sensitive, rapid, and precise method could be developed for DNA detection. In aqueous solutions, the I ₆₀₁/I ₄₄₈ fluorescence intensity ratio of SiND-Ru(bpy)₂(dppx)²⁺ increases linearly in the DNA concentration range of 20-1500 nM. The limit of detection and precision of the method is 4.3 nM and 3.5% (50 nM, n = 13), respectively. The ratiometric sensor was tested for visual detection of trace DNA. Moreover, this method was found suitable for the ratiometric detection of DNA in a simulated sample and a human serum sample, and the recoveries were in the range of 98-119%.

Color-switchable hybrid dots/hydroxyethyl cellulose ink for anti-counterfeiting applications

Many anti-counterfeiting inks have been explored recently, most of them are commonly involved in weak fastness, high cost and long-term toxicity, impeding their real-life applications. Herein, an environment-friendly and inexpensive anti-counterfeiting ink with excellent fastness is reported. The untifake ink is developed by combining hybrid dots (silicon/carbon) with hydroxyethyl cellulose (HEC) binder. Interestingly, the HEC binder can effectively prevent from aggregation-induced quenching of hybrid dots. Subsequently, the customized patterns are successfully transferred onto different surfaces of various substrates including cotton fabric, cellulosic paper, glass, metal, silicon wafer and PET film, using the as-prepared ink by screen-printing technique, exhibiting that the hybrid dots/HEC ink possesses widespread practicability. Notably, fluorescent color of these patterns can be switchable by adjusting environmental pH-value, further imparting the as-prepared ink with excellent covert performance. This new fluorescent hybrid dots/HEC ink will be promising candidates for high-level anti-counterfeiting applications including food packaging, apparel and documents.

Recent progress in using hybrid silicon polymer composites for wastewater treatment

Heavy metal ions, oil and organic pollutants in water does not only cause serious water pollution, but also pose serious threats to ecosystems and human health. To this end, water pollution has gradually gained human attention, and various wastewater treatment methods are emerging. Organosilicon polymer composites are a class of materials that contain organic-inorganic hybrid structures with the characteristics of hydrophobicity, thermal stability and easy modification, which provides a brand new solution for wastewater treatment. In this review, various structural features including amorphous, linear, and cage structure of silicon containing polymer composites and the removal mechanism targeting at heavy metal ions, oil and organic pollutants of silicon containing polymer composites are summarized. The viewpoints and challenges in adsorption and engineering application are discussed, and possible solutions are proposed.

Facile preparation of FITC-modified silicon nanodots for ratiometric pH sensing and imaging

A ratiometric fluorescent pH sensor was facilely constructed by covalent modification of amino-terminated silicon nanodots (SiND) with pH-sensitive fluorescein isothiocyanate (FITC). After optimization, the SiND-FITC(40:1) material with a SiND:FITC initial mass ratio of 40:1 was selected for the sensing of hydrogen ions. It was observed that the material inherits the unique features of SiND and FITC, and there is significant improvement of SiND acid-base stability, which is a favorable factor in terms of providing fluorescence reference signal. The SiND-FITC(40:1) material displays not only high pH sensitivity, but also good stability and anti-interference ability, and the response process is highly reversible. Deploying the SiND-FITC(40:1) material, we have made available a simple, sensitive, and precise approach for pH sensing. In aqueous solutions, the I₅₁₇/I₄₆₆ fluorescence intensity ratio of SiND-FITC(40:1) increases linearly in the pH range of 5.40-7.76. This dual emission nanosensor was successfully applied for pH sensing and cellular fluorescence imaging.

Novel mulberry silkworm cocoon-derived carbon dots and their anti-inflammatory properties

Mulberry silkworm cocoon (MSC) carbonisata has been used for the treatment of inflammatory diseases for hundreds of years; however, after years of research efforts, little information is available on its anti-inflammatory components and underlying mechanism. We developed novel carbon dots (CDs) derived from MSC carbonisata (MSC-CDs), for the first time, with an average diameter of 2.26-9.35 nm and a quantum yield (QY) of 6.32%. The MSC-CDs were prepared using a modified pyrolysis method, and no further modification and external surface passivation agent was required. With abundant surface groups, MSC-CDs showed distinct solubility and bioactivity. In this study, we innovatively used three classical experimental models of inflammation to evaluate the anti-inflammatory bioactivity of MSC-CDs. The results indicated that MSC-CDs exhibited marked anti-inflammatory bioactivity which was likely mediated by inhibition of the expression of interleukin-6 and tumour necrosis factor-α. These results suggest that MSC-CDs possess a remarkable anti-inflammatory property, which provides evidence to support further investigation of the considerable potential and effective material basis of this traditional Chinese medicine.

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.

Multifunctional mesoporous silica nanoplatform based on silicon nanoparticles for targeted two-photon-excited fluorescence imaging-guided chemo/photodynamic synergetic therapy in vitro

Currently, the nanocomposites based on silicon nanoparticles (SiNPs) are usually limited to a single therapeutic modality, and the design of the SiNPs nanohybrids with multi-modal synergistic therapeutic functions is still worth being explored to achieve more effective treatment. Herein, we used mesoporous silica nanoparticle (MSN) as a nanoplatform, SiNPs and the photosensitizer 5,10,15,20-tetrakis (1-methyl 4-pyridinio) porphyrin tetra (p-toluenesulfonate) (TMPyP) were first embedded in the MSN and was further modified with folic acid (FA) to obtain the mesoporous silica nanocomposite (MSN@SiNPs@TMPyP-FA) for targeted two-photon-excited fluorescence imaging-guided photodynamic therapy (PDT) and chemotherapy. The embedded TMPyP could generate singlet oxygen to perform PDT under light irradiation, meanwhile the anticancer drugs doxorubicin (DOX) could be loaded for chemotherapy. Moreover, due to the two-photon excited fluorescence of SiNPs, the nanocomposite successfully achieved targeted two-photon fluorescence cellular imaging at the near-infrared (NIR) laser excitation, which could effectively avoid the interference of biological auto-fluorescence. And in vitro cytotoxicity assays revealed that the synergistic therapy combining PDT and chemotherapy exhibited high therapeutic efficacy for cancer cells.

Application of Silicon Quantum Dots in the Detection of Formaldehyde in Water and Organic Phases

Background:

Formaldehyde is widely acknowledged as a carcinogen, but as an important organic reagent, it has also been widely employed in the fields of chemical synthesis, industrial production and biomedicine. It is therefore of great practical significance for the detection of formaldehyde in food, clothing, daily necessities, construction materials and environments.

Methods:

The two silicon QDs, that are, DAMO-Si-QDs (with N-[3-(Trimethoxysilyl) propyl] ethylenediamine as silicon source) and APTMS-Si-QDs (with (3-Aminopropyl) trimethoxysilane as silicon source) as the fluorescence probe to detect formaldehyde in both water and organic phases.

Results:

Silicon QDs prepared by different silicon sources exhibit an obvious difference in their tolerances to the environment and the responses to formaldehyde. However, APTMS-Si-QDs show better selectivity in both water and organic phases. In Tris-HCl solution (20.00mmol•L-1, pH=5), the formaldehyde concentration maintains an excellent linear relationship with the fluorescence intensity of APTMS-Si-QDs in the range of 3.125×10-7-3.125×10-5 mol•L-1, with correlation coefficient R2= 0.9998. In methanol, the formaldehyde concentration maintains an excellent linear relationship with the fluorescence intensity of APTMS-Si-QDs in the range of 1.563×10-7-3.125×10-5 mol•L-1, with correlation coefficient R2= 0.9992.

Conclusion:

It is found that DAMO-Si-QDs show poor response to the presence of formaldehyde, while APTMS-Si-QDs got a strong, sensitive and selective response to that in both aqueous and organic phases. In the Tris-HCl buffer (20 mmol•L-1, pH=5), the linear range for formaldehyde detection reaches 3.125×10-7-3.125×10-5 mol•L-1, and for the detection in the organic phase, the linear range reaches 1.563×10-7-3.125×10-5 mol•L-1, in methanol solution. The paper provides a sensitive, selective and simple means for formaldehyde detection in both aqueous and organic phase

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.

Highly sensitive and selective "off-on" fluorescent sensing platform for ClO- in water based on silicon quantum dots coupled with nanosilver

We present a new "off-on" fluorescence probe for detecting hypochlorite (ClO^-) based on silicon quantum dots coupled with silver nanoparticles (SiQDs/AgNPs) as nanocomplexes. Via introducing N-[3-(trimethoxysilyl)propyl]ethylenediamine and catechol as initial reactants, silicon quantum dots (SiQDs) with excellent properties were synthesized through a simple hydrothermal method. Transmission electron microscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy were used to characterize the morphology and structure of quantum dots. The fluorescence of SiQDs could be quenched by the silver nanoparticles (AgNPs) by surface plasmon-enhanced energy transfer (SPEET) from SiQDs (donor) to AgNPs (acceptor). The AgNPs could be etched by adding ClO^-, thus freeing the SiQDs from the AgNP surfaces and restoring the SiQDs' fluorescence. The sensing system exhibits many advantages, such as wide linear response range, high sensitivity, and excellent selectivity. Under optimized conditions, wide linear ranges (from 0.1 to 100.0 μM) and low detection limits (0.08 μM) were obtained for ClO^-. Graphical Abstract.

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.

Polymethyldopa Nanoparticles-Based Fluorescent Sensor for Detection of Tyrosinase Activity

Being a typical copper-containing oxidase, tyrosinase plays critical roles in biological activity, and its aberrant expression might cause diverse skin diseases. Herein, we, for the first time, have found an interesting green fluorogenic reaction between methyldopa and ethanolamine. By combining transmission electron microscopy, UV-vis absorption spectroscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and MALDI-TOF mass spectrum analysis, we have confirmed that there is a reliable method for preparing the bright green fluorescent polymethyldopa nanoparticles (PMNPs) by simply mixing methyldopa and ethanolamine at room temperature. Inspired by such a simple and convenient fluorogenic reaction, a novel polymethyldopa nanoparticles-based fluorescent sensor for detection of tyrosinase activity was developed by using the commercially available metyrosine as a substrate, accompanied by the tyrosinase-catalyzed specific conversion of metyrosine into methyldopa. According to the intrinsic sensitivity/selectivity of fluorescence technology and unambiguous response mechanism, our fluorescent sensor exhibits excellent sensing performance and can be utilized in the determination of the tyrosinase activity in real biological samples and inhibitor screening.

Graphitic carbon nitride quantum dots as an "off-on" fluorescent switch for determination of mercury(II) and sulfide

A rapid method has been developed for the determination of Hg(II) and sulfide by using graphitic carbon nitride quantum dots (g-CNQDs) as a fluorescent probe. The interaction between Hg(II) and g-CNQDs leads to the quenching of the blue g-CNQD fluorescence (with excitation/emission peaks at 390/450 nm). However, the fluorescence can be recovered after addition of sulfide such that the "turn-off" state is switched back to the "turn-on" state. The g-CNQDs were fully characterized by transmission electron microscopy, X-ray diffractometry, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, UV-vis absorption and fluorescence spectroscopy. Under the optimal experimental conditions, this probe is highly selective and sensitive to Hg(II). The linear response to Hg(II) extends from 0.20 to 21 μM with a detection limit of 3.3 nM. In addition, sulfide can be detected via the recovery of fluorescence. The linear response range for sulfide species is from 8.0 to 45 μM with a detection limit of 22 nM. The mechanism of the "turn-off-on" scheme is discussed. The methods have been applied to the analysis of spiked tap water, lake water and wastewater samples. Graphical abstract Schematic of an off-on fluorescent probe for mercury(II). The fluorescence of graphitic carbon nitride quantum dots (g-CNQDs) is quenched by Hg²⁺ but is recovered after reacting with S^2- as it can combine with Hg²⁺ on the surface of g-CNQDs.

The influence of conjugated alkynyl(aryl) surface groups on the optical properties of silicon nanocrystals: photoluminescence through in-gap states

Developing new methods, other than size and shape, for controlling the optoelectronic properties of semiconductor nanocrystals is a highly desired target. Here we demonstrate that the photoluminescence (PL) of silicon nanocrystals (SiNCs) can be tuned in the range 685-800 nm solely via surface functionalization with alkynyl(aryl) (phenylacetylene, 2-ethynylnaphthalene, 2-ethynyl-5-hexylthiophene) surface groups. Scanning tunneling microscopy/spectroscopy on single nanocrystals revealed the formation of new in-gap states adjacent to the conduction band edge of the functionalized SiNCs. PL red-shifts were attributed to emission through these in-gap states, which reduce the effective band gap for the electron-hole recombination process. The observed in-gap states can be associated with new interface states formed via (-Si-C≡C-) bonds in combination with conjugated molecules as indicated by ab initio calculations. In contrast to alkynyl(aryl)s, the formation of in-gap states and shifts in PL maximum of the SiNCs were not observed with aryl (phenyl, naphthalene, 2-hexylthiophene) and alkynyl (1-dodecyne) surface groups. These outcomes show that surface functionalization with alkynyl(aryl) molecules is a valuable tool to control the electronic structure and optical properties of SiNCs via tuneable interface states, which may enhance the performance of SiNCs in semiconductor devices.

Sonication-assisted liquid-phase exfoliated α-GeTe: a two-dimensional material with high Fe3+ sensitivity

We describe sonication-assisted liquid-phase exfoliation of rhombohedral germanium telluride (α-GeTe) to obtain a good dispersion of α-GeTe nanosheets in ethanol. The thickness of the α-GeTe nanosheets is dependent on the exfoliation conditions, and few-layer α-GeTe nanosheets of 2-4 layers and even monolayer α-GeTe were obtained. We use first-principles calculations to investigate the structural, electronic, and optical properties of monolayer and bulk α-GeTe and compare the optical band gap of centrifugally fractionated α-GeTe nanosheet dispersions with the computational predictions. We demonstrate that few layer α-GeTe nanosheets are purified selectively through centrifugation, and they exhibit high sensitivity to Fe3+. The scalable production of two-dimensional α-GeTe nanosheets can be used in the future optoelectronic industry.

The influence of surface functionalization methods on the performance of silicon nanocrystal LEDs

The influence of silicon nanocrystal (SiNC) surface characteristics obtained from different functionalization methods on the performance of LEDs was investigated. The surface of SiNCs was functionalized with hexyl chains via hydrosilylation (HS) or with organolithium reagents (OLR) and resulting SiNCs were incorporated as the emissive layer in hybrid organic/inorganic LEDs. Devices utilizing SiNCs functionalized with OLR consistently exhibited lower turn-on voltages, higher luminances and external quantum efficiencies compared to those obtained from the HS method. These improvements were attributed to the less dense and monolayer surface coverage of the SiNCs obtained by the OLR method, as well as their higher absolute quantum yield.

Ratiometric fluorescent test paper based on silicon nanocrystals and carbon dots for sensitive determination of mercuric ions

Classical dye absorption-based pH test papers are widely used to measure the degree of acidity of media for quantification or semi-quantification by the observation of the naked eye on the variation of colour. However, it remains a challenging task to extend portable and cheap methods to a wide range of analytes for accurate quantification. Here, we report a dosage-sensitive test paper for the assay of mercury ions (Hg2+) with wide colour evolution. The ratiometric fluorescent probe was prepared by mixing blue-emission silicon nanocrystals (Si NCs) and red-emission carbon dots (r-CDs). The Si NCs serve as the reaction site and the r-CDs as the internal reference. Upon the addition of Hg2+, the blue fluorescence of the Si NCs was quenched, while the red fluorescence of the r-CDs remained constant, resulting in the consecutive fluorescence colour changes from blue to orange red. The probe demonstrates high selectivity and sensitivity of the visualization assay of Hg2+ with a detection limit of 7.63 nM. Moreover, we printed the ratiometric fluorescence probe result onto a piece of filter paper to prepare a test paper, which represents an on-site, sensitive, rapid and cost-effective method for the visual determination of Hg2+ by the naked eye.

One-pot hydrothermal preparation of gadolinium-doped silicon nanoparticles as a dual-modal probe for multicolor fluorescence and magnetic resonance imaging

One-pot hydrothermal preparation of gadolinium-doped silicon nanoparticles as a dual-modal probe for multicolor fluorescence and magnetic resonance imaging.

Recent Advances in Silicon Nanomaterial-Based Fluorescent Sensors

During the past decades, owing to silicon nanomaterials' unique optical properties, benign biocompatibility, and abundant surface chemistry, different dimensional silicon nanostructures have been widely employed for rationally designing and fabricating high-performance fluorescent sensors for the detection of various chemical and biological species. Among of these, zero-dimensional silicon nanoparticles (SiNPs) and one-dimensional silicon nanowires (SiNWs) are of particular interest. Herein, we focus on reviewing recent advances in silicon nanomaterials-based fluorescent sensors from a broad perspective and discuss possible future directions. Firstly, we introduce the latest achievement of zero-dimensional SiNP-based fluorescent sensors. Next, we present recent advances of one-dimensional SiNW-based fluorescent sensors. Finally, we discuss the major challenges and prospects for the development of silicon-based fluorescent sensors.

Thermostable polymeric nanomicelles of iridium(iii) complexes with aggregation-induced phosphorescence emission characteristics and their recyclable double-strand DNA monitoring

Thermostable polymeric nanomicelles of iridium(iii) complexes with AIPE characteristics were synthesized, which can be recycled and used for DNA monitoring.

Water-Dispersible Fluorescent Silicon Nanoparticles and their Optical Applications

Fluorescent silicon nanoparticles (SiNPs) attract considerable attention owing to their intrinsic advantages, including relatively strong fluorescence coupled with robust photostability, rich resource support and relatively low cost, industrial maturity, and good biocompatibility. Extensive efforts are devoted to developing effective methods for the synthesis of hydrogen or halogen-terminated SiNPs, which nevertheless need further surface modification to improve their stability and solubility for wide-ranging applications. Notably, recent years have witnessed the development of various aqueous synthetic strategies for direct preparation of highly fluorescent and photostable SiNPs in the aqueous phase, facilitating the promotion of this promising material for myriad optical applications. Here, a concise discussion of the latest exciting research progress of the preparation of SiNPs is given, with a focus on water-dispersible SiNPs synthesized in the aqueous phase. In addition, representative optical applications of SiNPs in bioimaging and sensing are also summarized. Finally, the opportunities and challenges of fluorescent-SiNP-based optical applications are discussed.

Origin of the Photoluminescence Quantum Yields Enhanced by Alkane-Termination of Freestanding Silicon Nanocrystals: Temperature-Dependence of Optical Properties

On the basis of the systematic study on temperature dependence of photoluminescence (PL) properties along with relaxation dynamics we revise a long-accepted mechanism for enhancing absolute PL quantum yields (QYs) of freestanding silicon nanocrystals (ncSi). A hydrogen-terminated ncSi (ncSi:H) of 2.1 nm was prepared by thermal disproportination of (HSiO_1.5)_n, followed by hydrofluoric etching. Room-temperature PL QY of the ncSi:H increased twentyfold only by hydrosilylation of 1-octadecene (ncSi-OD). A combination of PL spectroscopic measurement from cryogenic to room temperature with structural characterization allows us to link the enhanced PL QYs with the notable difference in surface structure between the ncSi:H and the ncSi-OD. The hydride-terminated surface suffers from the presence of a large amount of nonradiative relaxation channels whereas the passivation with alkyl monolayers suppresses the creation of the nonradiative relaxation channels to yield the high PL QY.

In situ growth of fluorescent silicon nanocrystals in a monolithic microcapsule as a photostable, versatile platform

A facile, one-step method was developed for the in situ formation of fluorescent silicon nanocrystals (SiNC) in a microspherical encapsulating matrix. The obtained SiNC encapsulated polymeric microcapsules (SiPM) possess uniform size (0.1-2.0 μm), strong fluorescence, and nanoporous structure. A unique two stage, time dependent reaction was developed, as the growth of SiNC was slower than the formation of polymeric microcapsules. The resulting SiPM with increasing reaction time exhibited two levels of stability, and correspondingly, the release of SiNC in aqueous media showed different behavior. With reaction time <1 h, the obtained low-density SiPM (LD-SiPM) as matrix microcapsules, would release encapsulated SiNC on demand. With >1 h reaction time, resulting high-density SiPM (HD-SiPM) became stable SiNC reservoirs. SiPM exhibit stable photoluminescence. The porous structure and fluorescence quenching effects make SiPM suitable for bioimaging, drug loading and sorption of heavy metals (Hg(2+) as shown) as an intrinsic indicator. SiPM were able to reduce metal ions, forming SiPM/metal oxide and SiPM/metal hybrids, and their applications in bio-sensing and catalysis were also demonstrated.

The preparation of high-quality water-soluble silicon quantum dots and their application in the detection of formaldehyde

This paper reports the synthesis of water-soluble fluorescence silicon quantum dots (Si QDs) through a hydrothermal route with urea propyl triethoxysilane (UPTES) as the source of silicon and sodium citrate as the deoxidizer.

Germanium nanocrystals as luminescent probes for rapid, sensitive and label-free detection of Fe3+ ions

Luminescent water-soluble germanium nanocrystals (Ge NCs) have been developed as a fluorescent sensing platform for the highly selective and sensitive detection of Fe3+ via quenching of their strong blue luminescence, without the need for analyte-specific labelling groups. The amine-terminated Ge NCs were separated into two discrete size fractions with average diameters of 3.9±0.4 nm and 6.8±1.8 nm using centrifugation. The smaller 3.9 nm NCs possessed a strong blue luminescence, with an average lifetime of 6.1 ns and a quantum yield (QY) of 21.5%, which is strongly influenced by solution pH. In contrast, 6.8 nm NCs exhibited a green luminescence with a longer lifetime of 7.8 ns and lower QY (6.2%) that is insensitive to pH. Sensitive detection of Fe3+ was successfully demonstrated, with a linear relationship between luminescence quenching and Fe3+ concentration observed from 0-800 μM, with a limit of detection of 0.83 μM. The Ge NCs show excellent selectivity toward Fe3+ ions, with no quenching of the fluorescence signal induced by the presence of Fe2+ ions, allowing for solution phase discrimination between ions of the same element with different formal charges. The luminescence quenching mechanism was confirmed by static and time-resolved photoluminescence spectroscopies, while the applicability for this assay for detection of Fe3+ in real water samples was successfully demonstrated.

Ionic liquid-assisted synthesis of multicolor luminescent silica nanodots and their use as anticounterfeiting ink

Here we propose a simple route for the fabrication of silica nanodots which are strongly photoluminescent in both solution and the solid state based on the use of ionic liquids (ILs). It is found that the ILs not only provides the environment for the reaction but also contributes to the quantum yield (QY) of the silica nanodots. In particular, the produced silica nanodots also displayed excitation-dependent photoluminescence and temperature sensitive properties. Based on the unique optical properties, the as-prepared nanomaterial was used for anticounterfeiting application and the results demonstrated the great potential of the silica nanodots alone or combined with other fluorescent material of unicolor for an improved anticounterfeiting technology. This simple approach and the resulting outstanding combination of properties make the prepared silica nanodots highly promising for myriad applications in areas such as fluorescent anticounterfeiting, optoelectronic devices, medical diagnosis and biological imaging.

Role of novel silicon nanoparticles in luminescence detection of a family of antibiotics

The design, synthesis, photophysical properties and practical application of fluorescent silicon nanoparticles (SiNPs) of a quantum-size (∼3 nm) have been studied.