Detection of ascorbic acid by persistent luminescent nanoparticles based on CoOOH nanosheets modification.

Persistent luminescent nanomaterials (PLNPs) Zn0.8Ga2O4: Cr3+, Zr3+ with high brightness and good dispersion were prepared by hydrothermal method. The PLNPs were used as luminescent units, and CoOOH nanosheets were used as quenching agents. Based on the fluorescence internal filtering effect, the luminescence of PLNPs were effectively quenched by CoOOH modification on the surface of PLNPs. However, the introduction of ascorbic acid (AA) restored the luminescence of PLNPs and successfully achieved highly sensitive and selective detection of AA. This was due to a selective redox reaction between CoOOH and AA, in which CoOOH was reduced to Co2+. The degree of luminescence recovery of PLNPs showed a good linear relationship with AA concentration in the range 5-250 µM, with a detection limit of 0.72 µM. The recovery of actual spiked samples were 97.9-102.2%. This method is expected to provide reference for the study of other redox substances in biological systems.

A ratiometric fluorescent probe with dual-targeting capability for heat shock imaging.

HSO3- is an important reactive sulfur species that maintains the normal physiological activities of living organisms and participates in a variety of redox homeostatic processes. It has been found that changes in HSO3- levels is closely related to the heat stroke phenomenon of the organism. Heat stroke causes damage to normal cells, which in turn causes damage to the body and even death. It is crucial to accurately monitor and track the physiological behavior of HSO3- during heat stroke. Herein, a ratiometric multifunctional fluorescent probe DRM-SO2 with dual-targeting ability to rapidly and precisely recognize HSO3- being constructed based on the FRET mechanism. DRM-SO2 has extra Large Stokes shift (216 nm), very high sensitivity (DL = 12.2 nM), fast response time and good specificity. When DRM-SO2 undergoes Michael addition with HSO3-, the fluorescence emission peak was blue-shifted from 616 nm to 472 nm, and a clear ratiometric signal appeared. The interaction between lysosomes and mitochondria in maintaining cellular homeostasis was investigated by the dual-targeting ability of the probe using HSO3- as a mediator. DRM-SO2 achieved successful targeting and real-time monitoring of exogenous and endogenous HSO3- in the cells. More importantly, imaging experiments in heat stroke mice revealed high HSO3- expression in intestinal tissues. This provides new ideas and research tools for early prevention of heat stroke-induced diseases such as intestinal injuries. In addition, the semi-quantitative monitoring experiments for paper-based visualization of HSO3- make the probe promising for the design of portable detectors.

Construction of nanohybrid Tb@CDs/GSH-CuNCs as a ratiometric probe to detect phosphate anion based on aggregation-induced emission and FRET mechanism.

The simple preparation of a nanohybrid of terbium-doped carbon dots/glutathione-capped copper nanoclusters (Tb@CDs/GSH-CuNCs) was for the first time developed for ratiometric detection of phosphate anion (Pi). Blue-emission of Tb@CDs can trigger non-luminescence of GSH-CuNCs for aggregation-induced emission (AIE) performance due to the strong reserved coordination capacity of Tb3+. Thus, Tb@CDs/GSH-CuNCs rapidly generated dual-emission signals at 630 nm and 545 nm by directly mixing the two individual materials via the AIE effect, alongside fluorescence resonance energy transfer (FRET) process. However, by the introduction of Pi, both AIE and FRET processes were blocked because of the stronger binding affinity of Tb3+ and Pi than that of Tb3+ and -COOH on Tb@CDs, thus realizing successful ratiometric detection of Pi. The linear concentration range was 0-16 µM, with the limit of detection (LOD) of 0.32 µM. The proposed method provided new ideas for designing nanohybrid of CDs and nanoclusters (MNCs) as ratiometric fluorescent probes for analytical applications.

Synthesis of molecularly imprinted polymers based on nitrogen-doped carbon dots for specific detection of chlortetracycline by reversed phase microemulsion method.

Among the tetracycline antibiotics, chlortetracycline (CTC) is the most frequently used antibiotic except for tetracycline (TC) for enhancing the ability of the organism to fight bacterial infections. The poor metabolism and degradability of CTC can cause serious health effects. Most studies have focused on the detection and analysis of TC, and research on CTC is relatively scarce. This is because the structures of CTC and TC and oxytetracycline (OTC) are extremely similar, and even indistinguishable. In this study, CTC was used as a template molecule and a molecularly imprinted layer was coated on the surface of highly fluorescent N-CDs using a reversed-phase microemulsion method to form N-CDs@MIPs. It was possible to specifically identify CTC without the influence of TC and OTC, which are extremely similar in structure. By comparing with the non-imprinted polymer (N-CDs@NIPs), it exhibited high sensitivity and selectivity with an imprinting factor of 2.02. And it was used in the determination of CTC in milk with recoveries and relative standard deviations of 96.7%-109.8% and 0.64%-3.27%, respectively, with high accuracy and precision. The specificity of the measurement is excellent compared with other assays, and it is a valid and reliable assay.

Ce4+/Ce3+ as the switch of AIE-copper nanoclusters for highly selective detection of ascorbic acid in soft drinks.

An ultrasimple "turn-on" sensor for indirectly detecting ascorbic acid (AA) was prepared using N-acetyl-L-cysteine stabilized copper nanoclusters (NAC-CuNCs) via the AIE (aggregation-induced emission) effect controlled by Ce4+/Ce3+ redox reaction. This sensor fully utilizes the different properties of Ce4+ and Ce3+. Non-emissive NAC-CuNCs were synthesized by a facile reduction method. NAC-CuNCs easily aggregate in the presence of Ce3+ due to AIE, resulting in fluorescence enhancement. However, this phenomenon cannot be observed in the presence of Ce4+. Ce4+ possesses strong oxidizing ability and produces Ce3+ by reacting with AA via a redox reaction, followed by switching on the luminescence of NAC-CuNCs. Moreover, the fluorescence intensity (FI) of NAC-CuNCs increases with the concentration of AA in the range of 4-60 µM, with the limit of detection (LOD) as low as 0.26 µM. This probe with excellent sensitivity and selectivity was successfully used in the determination of AA in soft drinks.

A review: Small organic molecule dual/multi-organelle-targeted fluorescent probes.

In recent years, the dual/multi-organelle-targeted fluorescent probe based on small organic molecules has good biocompatibility and can visualize the interaction between different organelles, which has attracted much attention. In addition, these probes can also be used to detect small molecules in the organelle environment, such as active sulfur species (RSS), reactive oxygen species (ROS), pH, viscosity and so on. However, the review of dual/multi-organelle-targeted fluorescent probe for small organic molecules lacks a systematic summary, which may hinder the development of this field. In this review, we will focus on the design strategies and bioimaging applications of dual/multi-organelle-targeted fluorescent probe, and classify them into six classes according to different organelles targeted. The first class probe targeted mitochondria and lysosome. The second class probe targeted endoplasmic reticulum and lysosome. The third class probe targeted mitochondria and lipid droplets. The fourth class probe targeted endoplasmic reticulum and lipid droplets. The fifth class probe targeted lysosome and lipid droplets. The sixth class multi-targeted probe. The mechanism of these probes targeting organelles and the visualization of the interaction between different organelles are emphasized, and the prospect and future development direction of this research field are prospected. This will provide a systematic idea for the development and functional research of dual/multi-organelle-targeted fluorescent probe, and promote its research in related physiological and pathological medicine field in the future.

Synthesis of fluorescent probe based on molecularly imprinted polymers on nitrogen-doped carbon dots for determination of tobramycin in milk.

Tobramycin (TOB) plays a considerable role in combating milk spoilage and preventing disease in dairy cows. However, overuse of TOB can lead to nephrotoxicity, ototoxicity, neuromuscular blockade, and hypersensitivity reactions. Here, nitrogen-doped carbon dots (N-CDs) were prepared with ethylenediamine and citric acid, then molecularly imprinted layers were obtained by imprinting of surface on the N-CDs to prepare Nitrogen-doped carbon dot-based molecularly imprinted polymers (N-CDs@MIPs). The fluorescence emission spectrum of this probe showed a linear enhancement with the TOB concentration in the 1-12 µM. Meanwhile, a detection limit of 99.2 nM was obtained. This probe was not affected by the structural analogs of the TOB and can show high sensitivity and selectivity compared to non-imprinted polymers (N-CDs@NIPs). Therefore, it can be successfully used for the trace analysis of TOB in milk with advantages over other reported techniques such as liquid chromatography coupled with tandem mass spectrometry or various aptamer sensors.

Ce3+-induced Fluorescence Amplification of Copper Nanoclusters Based on Aggregation-induced Emission for Specific Sensing 2,6-pyridine Dicarboxylic Acid.

A straightforward, cost-effective and biocompatible reduction approach was applied to fabricate soluble but non-luminous glutathione-stabilized copper nanocluster (GSH-CuNCs). Surprisingly, as high as 1 × 103 times fluorescence enhancement was acquired when Ce3+ was injected at an extremely low concentration of only 18 µM. Ce3+ outperformed other rare-earth metal ions in terms of inducing fluorescence amplification of the non-luminous GSH-CuNCs. Furthermore, Ce3+ was employed as inducer for aggregation-induce emission (AIE) effect as well as reactant to coordinate with target of 2,6-pyridine dicarboxylic acid (DPA) due to the stronger coordination ability between Ce3+ and DPA than that of Ce3+ and GSH. As a result, the Ce3+/GSH-CuNCs ensemble was developed as a novel sensor to detect DPA in the "on-off" mode. When DPA was introduced into the sensor, Ce3+ failed to interact with GSH and detached from the surface of GSH-CuNCs, leading to fluorescence quenching. In addition, static quenching process and internal filtration effect (IFE) between Ce3+/GSH-CuNCs and DPA were also responsible for fluorescence quenching effect. A good linear relationship was obtained from 0.3 µM to 18 µM, with a limit of detection (LOD) of 0.19 µM. The as-proposed probe displayed high specificity to DPA and provided a simple, fast rapid and cheap method for construction this type of ensemble sensors to detect other targets.

A novel ratiometric sensor prepared based aggregation-induced emission for ultrafast detection of SO2 derivatives in food samples and living cells.

As one of the gaseous signaling molecules, aberrant levels of SO2 are usually associated with many diseases. it is of great significance to develop sensitive methods for detection SO2 on real. In this paper, a D-π-A near-infrared aggregation-induced fluorescent probe (DPA-CN) was built using diphenylamino-4-benzaldehyde and malononitrile for sensing SO2. The DPA-CN exhibit AIE characterization that can quickly recognize SO2 via the Michael addition mechanism. The DPA-CN displayed emission blue drift from 650 nm to 560 nm after adding SO2, thereby realizing rapid and sensitive colorimetric detection of SO2. The mechanism for recognition of SO2 was verified via magnetic resonance imaging (1H NMR), electrospray ionization mass spectrometry (ESI-MS), scanning electron microscopy (SEM) and dynamic light scattering (DLS). The DPA-CN realized rapid and sensitive recognition of SO2 with high specificity in 10 s within the concentration range of 0-100 µM. The limit of detection (LOD) is as low as 0.31 µM. Owing to its high sensitivity and low toxicity, the DPA-CN can be applied in monitoring of SO2 in living cells and food analysis. Furthermore, the DPA-CN was used to prepare a visible and ultrafast semiquantitative paper-based SO2 sensor with low cost and easy operation.

Novel ratiometric probe based on the use of rare earth-carbon dots nanocomposite for the visual determination of doxycycline.

Rare earth-carbon dots (RE-CDs) hybrid nanomaterials with the merits of both RE and CDs have rapidly emerging as highly promising functional materials in biochemical analysis. In this work, a new kind of water-soluble RE-CDs nanocomposite (CDs@CaF2:Eu3+) was developed for the ratiometric determination of doxycycline (DOX). The CDs@CaF2:Eu3+ under the excitation at 365 nm displayed blue emission of CDs at 440 nm and no obvious emission of Eu3+. With the addition of DOX, substantial fluorescence quenching of the CDs at 440 nm and enhancement of Eu3+ at 613 nm were observed, resulting in a ratiometric fluorescent response toward DOX. A wide linear range from 0.1 µM to 30 µM was achieved in the detection of DOX with a lowest detection limit of 43 nM. In particular, the probe could discriminate DOX from other tetracycline antibiotics through unique fluorescence response. Moreover, we have successfully applied the method for the determination of DOX in milk and honey samples.

Morphological analysis of chromium in carbon quantum dots pairs Co-doped with zirconium and nitrogen and their applications in imaging of living cells.

As a new nanomaterial in the biochemistry field, carbon quantum dots (CDs) have been widely applied by scientists. In this study, CDs co-doped with zirconium and nitrogen (Zr-N-CDs) were synthesized quickly with lemon, ethylenediamine, and zirconium chloride through a hydrothermal method. The yield of Zr-N-CDs reached as high as 82.7%. The Zr-N-CDs showed outstanding water solubility in aqueous solution. The formation of Zr-N-CDs was verified by characterization technologies, such as high-resolution transmission electron microscopy (HRTEM), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). Moreover, the optical properties of Zr-N-CDs were investigated through fluorophotometer and ultraviolet spectroscopy. The synthesized Zr-N-CDs were applied to test hexavalent chromium (Cr (VI)), which showed a good linear relationship with the fluorescence quenching of Zr-N-CDs. The limit of detection was 0.52 µM. An analytical method for Cr morphology in natural water areas was developed in this experiment. The sensor showed good stability. The results demonstrate that the sensor detected 98.35%-100.9% Cr (VI) recovery rate in water samples. Based on the cytotoxicity of Zr-N-CDs to human cervical cancer cells (HeLa cells), the Zr-N-CDs had no evident cytotoxicity. The applications of Zr-N-CDs in bioimaging of cells were determined through laser scanning confocal microscopy.

A novel AIE active NIR fluorophore based triphenylamine for sensing of Hg2+ and CN- and its multiple application.

New strategies still need to be proposed that can be used to sense and remove toxic environmental pollutants in a sensing system. In this research, a novel NIR fluorescence sensor 1 was designed and prepared with aggregation induced emission (AIE) property. The fluorescence intensity of the sensor 1 in DMSO/H2O mixed solvent was changed along with the proportion of water. The sensor 1 can be successfully used for real-time detection and removal of Hg2+ in 20% DMSO aqueous solution with high selectivity, quick response and so on. Furthermore it can be efficiently reused and recycled without any loss through Na2S. In addition, the sensor 1 displayed high sensitivity and selectivity to cyanide ions in 1% DMSO aqueous solution with the presence of other interference anions. The sensing mechanism for Hg2+ and cyanide ion was evaluated by 1H NMR spectra, Mass spectrometry. The sensor 1 exhibited low cytotoxicity for biological applications, which was used as an outstanding fluorescent transducer for detection of cyanide ion in living cells. Based on the visible fluorescence change for the sensor 1 to cyanide ion, the measurement was performed for food materials containing cyanide, such as potato, cassava powder and almond. This research provides perspective potential in solving the problem of other pollution and stimulating new thinking for designing of the novel fluorescence materials.

A large-Stokes-shift fluorescent probe for Zn2+ based on AIE, and application in live cell imaging.

A fluorescence-enhanced sensor based on aggregation-induced emission (AIE) was synthesized using a di(2-picolyl)amine (DPA) group as a highly selective metal chelating agent for Zn2+. The combination of the probe and Zn2+ was achieved in an environment where the volume fraction of water was 90%, giving the probe good biocompatibility, and a large Stokes shift (100 nm) occurred after Zn2+ was combined with the probe. The obvious color change makes the probe visible to the naked eye, and gives it a high signal-to-noise ratio, and high contrast, and minimizes self-absorption. Because of the high selectivity of the DPA group to Zn2+, the sensitivity of the probe to detect Zn2+ has been improved. The mechanism of the formation of complexes between the probe and Zn2+ was confirmed by nuclear magnetic resonance spectroscopy (NMR), high-resolution mass spectrometry (HRMS), and particle size distribution. Under the optimal experimental conditions, the linear fluorescence reaction of Zn2+ was good, between 0.2 and 18 µM, and the detection limit was 1.3 × 10-7 M. The low toxicity and excellent membrane permeability of the probe in living cells enable it to be efficiently applied for Zn2+ imaging in cells. Graphical abstract.

Using zinc ion-enhanced fluorescence of sulfur quantum dots to improve the detection of the zinc(II)-binding antifungal drug clioquinol.

A turn on-off fluorometric assay for clioquinol (CQ) is described here. It is based on modulation of the fluorescence of sulfur quantum dots (SQDs; best measured at excitation/emission wavelengths of 360/426 nm) by using the Zn2+-CQ affinity pair. Although the fluorescence enhancement effect of Zn2+ on SQDs was not obvious, a good quenching modulation effect was observed in the presence of CQ. This resulted in a linear analytical range that is increased by two orders of magnitude (from 0.024 µM to 0.24 µM, and 0.62 µM to 30 µM), with a detection limit (3 s) of 0.015 µM. The selectivity of the method is also improved. Graphical abstractSchematic illustration of the turn on-off fluorometric assay for for clioquinol (CQ) based on Zn2+-modulated sulfur quantum dots (SQDs).

An AIE active pyrene based fluorescent probe for selective sensing Hg2+ and imaging in live cells.

A novel fluorescence probe pyrene based derivatives (1) with aggregation induced emission (AIE) properties was synthesized by an easy procedure. The probe 1 was characterized by UV-vis, Fluorescent, NMR, MS, SEM etc. It displayed high sensitivity and selectivity to Hg2+ compared with other metal ions in H2O/DMF solvent and the detection limit was 4.2 × 10-7 M. Upon addition of Hg2+, the 1 - Hg2+ compound was formed with the formation of 2:1. More importantly, the probe exhibited very low cytotoxicity and strong fluorescence emission in live cells. This showed that the probe had potential applications for detection of Hg2+ in environment and biosystems.

Aggregation-induced phosphorescence quenching method for the detection of picric acid based on melamine-passivated Mn-doped ZnS quantum dots.

Melamine (MA)-passivated Mn-doped ZnS quantum dots (QDs) were synthesized by a hydrothermal method. The MA-passivated QDs can form a charge-transfer complex with picric acid (PA) at 80 °C, thereby quenching the phosphorescence of the QDs. A sensitive method for detecting PA was established based on this principle of phosphorescence quenching. When the PA concentration ranged from 2.0 to 180 ng mL-1, the concentration was linearly related to the quenching intensity of the QDs, with a detection limit of 1.4 ng mL-1. When applied to detect PA in environmental water samples, the proposed method showed superior analytical performance compared with other PA analysis methods. Furthermore, we verified the static quenching mechanism by density functional theory. MA on the surface of QDs and PA formed a stable structure with a binding energy of 12.43 eV.

Preparation of metal-organic framework UiO-66-incorporated polymer monolith for the extraction of trace levels of fungicides in environmental water and soil samples.

A zirconium terephthalate metal-organic framework-incorporated poly(N-vinylcarbazole-co-divinylbenzene) monolith was fabricated in a capillary by a thermal polymerization method. The optimized monolith had a homogeneous structure, good permeability, and stability. The monolith could be used for the effective enrichment of fungicides through π-π interactions, electrostatic forces, and hydrogen bonds. The potential factors that affect the extraction efficiency, including ionic strength, solution pH, sample volume, and eluent volume, were investigated in detail. The monolith-based in-tube solid-phase microextraction coupled with ultra-high-performance liquid chromatography and high-resolution Orbitrap mass spectrometry was performed for the analysis of five fungicides (pyrimethanil, tebuconazole, hexaconazole, diniconazole, and flutriafol) in environmental samples. Under the optimized conditions, the linear ranges were 0.005-5 ng/mL for pyrimethanil, 0.01-5 ng/mL for flutriafol, and 0.05-5 ng/mL for other fungicides, respectively, with coefficients of determination ≥0.9911. The limits of detection were 1.34-14.8 ng/L. The columns showed good repeatability (relative standard deviations ≤9.3%, n = 5) and desirable column-to-column reproducibility (relative standard deviations 5.3-9.4%, n = 5). The proposed method was successfully applied for the simultaneous detection of five fungicides in water and soil samples, with recoveries of 90.4-97.5 and 84.0-95.3%, respectively.

Determination of cholic acid in body fluids by ß­cyclodextrin-modified N-doped carbon dot fluorescent probes.

An easy, dependable, and sensitive cholic acid activity experiment was designed based on ß­cyclodextrin-modified carbon dot (ß­CD-CD) nanoprobes with specific host-guest recognizing ability and photoelectron transfer capability. The ß­CD-CD nanoprobes were characterized by infrared, ultraviolet-visible, and fluorescence spectroscopy and transmission electron microscopy. The fluorescence of the probes under optimized conditions linearly responded to cholic acid concentration from 0 to 650 µmol·L-1 with a detection limit of 25 nmol·L-1. The probes also performed well in detecting cholic acid in serum and urine samples with an average recovery rate of 97.1%-103.4%. Thus, this study provides a reliable, rapid, and easy method of cholic acid detection in body fluids that can be potentially applied in medical studies.

An active fluorescent probe based on aggregation-induced emission for intracellular bioimaging of Zn2+ and tracking of interactions with single-stranded DNA.

A novel dual-sensing fluorescence probe L was designed and synthesized for highly selective and sensitive detection of Zn2+ and DNA. The probe L achieved a detection limit of 3.8 nM for Zn2+, which is lower than the acceptable level of Zn2+ in living cells. The probe L displayed high selectivity toward Zn2+ over other interference metal ions and amino acids. Moreover, the probe L displayed low cytotoxicity and good cell permeability, indicating its potential for detecting and bio-imaging of Zn2+. In addition, the probe L-Zn2+ exhibited enhanced fluorescence signal for DNA detection through the metal-coordination interaction between Zn2+ and DNA. The enhanced signal is higher than that of the classical ethidium bromide probe. The experiments in aqueous media verified the feasibility of applying probe L in real samples.

Aptamer based fluorometric sulfamethazine assay based on the use of graphene oxide quantum dots.

The authors have developed a homogeneous "off-on" fluorometric method for the determination of the antibiotic sulfamethazine (SMZ). Aptamer against SMZ was labeled with graphene oxide quantum dots upon which the Graphene oxide quenched the blue fluorescence of the GOQDs. On addition of SMZ, the aptamers will bind SMZ and this will cause the release of GOQDs. As a result, fluorescence will be regenerated. Fluorescence, best measured at excitation/emission wavelengths of 365/455 nm, increases linearly in the 8 pg·mL-1 to 60 ng·mL-1 SMZ concentration range, with a 5 pg·mL-1 detection limit. The method is reliable and was successfully applied to the determination of SMZ in spiked milk samples, with recoveries ranging from 89 to 96% depending on analyte concentration. Graphical abstract Graphene oxide quantum dots (GOQDs) were covalently bound to the aptamer (apt) against sulfamethazine (SMZ) and adsorbed on the surface of graphene oxide (GO). This results in quenching of the fluorescence of GOQDs. On addition of SMZ, fluorescence is restored due to the release of GOQD@apt from GO.