Construction of an effective ratiometric fluorescent sensing platform for specific and visual detection of mercury ions based on target-triggered the inhibition on inner filter effect

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

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

An ultrasensitive cellulose-based fluorescent sensor for Al3+ detection and its applications in plant tissue and food samples

Fluorescent sensors available for metal ions detection have been extensively developed in recent years. However, developing an ultrasensitive fluorescent sensor for highly selectively detecting Al3+ based on cellulose remains a challenge. In this study, an ethylcellulose-based flavonol fluorescent sensor named EC-BHA was synthesized by the esterification of ethylcellulose (EC) with a new flavonol derivative 4-(2-(2,3-bis(ethoxymeothy)phenyl)-3-hydroxy-4-oxo-4-H-chromen-7-yl) benzoic acid (BHA). The fluorescence intensity of EC-BHA exhibited a 180-fold increase at 490 nm after binding with Al3+ and provided an ultralow detection limit of 13.0 nM. The sensor showed some exceptional sensing properties including a broad pH range (4-10), large Stokes shifts (190 nm), and a short response time (3 min). This sensor was successfully applied for determining trace Al3+ in food samples as well as in plant tissue. Moreover, the electrostatic spun film EBP was fabricated by blending EC-BHA with PS (polystyrene) via electrostatic spinning technique and utilized for selective detection of Al3+ as soon as possible.

Fabrication of Eu-MOFs rod-shaped nanospheres with dual emissions for ratiometric fluorescence detecting Hg2+ in water

The incorporation of novel nanostructure has been proven to significantly improve the performance of fluorescence-based sensors in terms of sensitivity, selectivity, and detection capability. Herein, a lanthanide metal-organic framework (BTC-Eu-BDC-NH2) with dual ligands of 2-aminobenzoic acid (BDC-NH2) and 1,3,5-benzene tricarboxylic acid (BTC) has been prepared for ratiometric fluorescent detection of Hg2+ through the rational one-step synthetic approach. Through adjusting the ratio of two ligands, this dual-ligands strategy not only provided two independent emissions at peaks of 435 nm and 615 nm to resist the influence of external conditions, but also introduced the visual detection with an obvious color change. Moreover, the specific rod-shaped nanospheres morphology substantially enlarged the surface area of BTC-Eu-BDC-NH2 to ensure good dispersion and rapid response during sensing. Upon the addition of Hg2+, the fluorescence at 435 nm of BTC-Eu-BDC-NH2 was obviously quenched because of the interaction between Hg2+ and -NH2 from the ligand, while the red fluorescence at 615 nm remains almost unchanged. As a result, the synthesized BTC-Eu-BDC-NH2 showed excellent performances for visual sensing detection of Hg2+ with a clear luminescent color conversion from blue to red, and the detecting range was 0-40 μM with a low detection limit of 67 nM. Finally, the developed sensor was applied to actual tap water, and a handy sensing kit was constructed by hydrogel with BTC-Eu-BDC-NH2, demonstrating its potential practical applications.

Carbon dots/Ruthenium(III) nanocomposites for FRET fluorescence detection and removal of mercury (II) via assembling into nanofibers

The determination and removal of mercury(II) (Hg2+) are essential for human health and environmental ecosystems. Herein, an ingenious carbon dots (CDs)-based Förster resonance energy transfer (FRET) system (N, S-CDs/Ru) was fabricated employing CDs and Ru3+ units as energy-transfer doner/acceptor pairs for visual detection and efficient removal of Hg2+. The treatment of Hg2+ induced a remarkable linear enhancement of the ratiometric fluorescence (F613 nm/F478 nm) with a detection limit (LOD) of 95 nM, along with continuous fluorescence color variations from blue to red. Given that the fluorescence color recognition and processing realized the real-time and rapid quantitation of Hg2+ by paper-based smartphone sensing platform. The mechanistic study revealed that the N/S/O-rich surface of the system enabled the Hg2+-triggered self-assembly from dots to nanofibers, combing with the active FRET process. Also, the efficient removal of Hg2+ with a removal efficiency of ∼98 % and an adsorption capacity of ∼372 mg/g was obtained. Furthermore, it was found that N, S-CDs/Ru loaded commercialized SiO2 or SBA-15 could facilitate the removal of Hg2+ with a removal efficiency over 99 % and an adsorption capacity up to ∼562 mg/g. This study provides a potential strategy for environmental monitoring and remediation.

Constructing an eco-friendly and ratiometric fluorescent sensor for highly efficient detection of mercury ion in environmental samples

Mercury ion (Hg2+) is a highly toxic and ubiquitous pollutant, whose effective detection has aroused widespread concern. A novel ratiometric fluorescent sensor has been designed to rapidly and efficiently detect Hg2+ based on blue/red carbon dots (CDs) with environmental friendliness. This sensor was well characterized via TEM, FTIR, XPS, UV-vis, and zeta potential analysis and displayed excellent fluorescence properties and stability. The fluorescence of blue CDs at 447 nm was significantly quenched with the addition of Hg2+ resulted from the static quenching, whereas that of red CDs at 650 nm remained invariable. A sensitive method for Hg2+ determination was constructed in the range of 0.05-7.0 nmol mL-1 with optimal conditions, and the detection limit was down to 0.028 nmol mL-1. Meanwhile, compared to other 17 metal ions, the ratiometric fluorescent sensor exhibited high selectivity for Hg2+. Furthermore, satisfied recoveries had also been obtained for measuring trace Hg2+ in practical environmental samples. This developed ratiometric fluorescent sensor provided a reliable, environmental-friendly, rapid, and efficient platform for the detection of Hg2+ in environmental applications.

Tetraphenylporphyrin-based Chelating Ligand Additive as a Molecular Sieving Interfacial Barrier toward Durable Aqueous Zinc Metal Batteries

The sustained water consumption and uncontrollable dendrite growth strongly hamper the practical applications of rechargeable zinc (Zn) metal batteries (ZMBs). Herein, for the first time, we demonstrate that trace amount of chelate ligand additive can serve as a "molecular sieve-like" interfacial barrier and achieve highly efficient Zn plating/stripping. As verified by theoretical modeling and experimental investigations, the benzenesulfonic acid groups on the additive molecular not only facilitates its water solubility and selective adsorption on the Zn anode, but also effectively accelerates the de-solvation kinetics of Zn2+ . Meanwhile, the central porphyrin ring on the chelate ligand effectively expels free water molecules from Zn2+ via chemical binding against hydrogen evolution, and reversibly releases the captured Zn2+ to endow a dendrite-free Zn deposition. By virtue of this non-consumable additive, high average Zn plating/stripping efficiency of 99.7 % over 2100 cycles together with extended lifespan and suppressed water decomposition in the Zn||MnO2 full battery were achieved, thus opening a new avenue for developing highly durable ZMBs.

Lysosome-targeted dual-emissive carbon dots for ratiometric optical dual-readout and smartphone-assisted visual determination of Hg2+ and SO32

Smartphone-assisted visual assay not only expands quantitative analysis but also enhance real-time on-site sensing capabilities. Herein, lysosome-targeted dual-emissive carbon dots (L-CDs) can not only recognize Hg2+ and SO32- by ratiometric fluorescence and ratiometric absorption, but also visually quantify Hg2+ and SO32- by smartphone-assisted method. With monitoring of intrinsic ratiometric fluorescent variation (I580/I468), L-CDs are developed as an effective sensing platform for ratiometric fluorescent successive identification of Hg2+ and SO32- accompanying with continuous fluorescence variation of blue, purplish pink, pink, and light yellow. With detecting of inherent ratiometric absorption change (A538/A206), L-CDs are also constructed as an efficacious sensing terrace for ratiometric absorption consecutive discrimination of Hg2+ and SO32-. More crucially, integrating continuous fluorescence color change and color recognizer APP in the smartphone, visual quantification of Hg2+ and SO32- can be accomplished on the basis of the ratio of red value and blue value (R/B) with linear ranges of 0-130 and 0-850 µM, respectively, as well as LOD of 8.4 and 12.9 nM, respectively. More interestingly, confocal fluorescent imaging of HeLa cells further verifies that L-CDs can be regarded as favorable biosensors for on-site, real-time differentiation of Hg2+ and SO32- in vitro and in vivo with ratiometric manners.

A Portable Smartphone-Based System for the Detection of Blood Calcium Using Ratiometric Fluorescent Probes

Hypocalcemia is a disease that adversely affects the production and reproduction of dairy cows. A portable device for rapid bovine blood calcium sensing has been growing in demand. Herein, we report a smartphone-based ratiometric fluorescence probe (SRFP) platform as a new way to detect and quantify calcium ions (Ca²⁺) in blood serum. Specifically, we employed a cost-effective and portable smartphone-based platform coupled with customized software that evaluates the response of Ca²⁺ ions to ratiometric fluorescence probe in bovine serum. The platform consists of a three-dimensional (3D) printed housing and low-cost optical components that excite fluorescent probe and selectively transmit fluorescence emissions to smartphones. The customized software is equipped with a calibration model to quantify the acquired fluorescence images and quantify the concentration of Ca²⁺ ions. The ratio of the green channel to the red channel bears a highly reproducible relationship with Ca²⁺ ions concentration from 10 μM to 40 μM in bovine serum. Our detection system has a limit of detection (LOD) of 1.8 μM in bovine serum samples and the recoveries of real samples ranged from 92.8% to 110.1%, with relative standard deviation (RSD) ranging from 1.72% to 4.89%. The low-cost SRFP platform has the potential to enable campesino to rapidly detect Ca²⁺ ions content in bovine serum on-demand in any environmental setting.

Tris(bipyridine)ruthenium(II)-functionalized metal-organic frameworks for the ratiometric fluorescence determination of aluminum ions

A novel ratiometric fluorescence probe was designed for the determination of Al³⁺ by self-assembling of NH₂-MIL-101(Fe) and [Ru(bpy)₃]²⁺. Under the excitation wavelength of 360 nm, the NH₂-MIL-101(Fe)@[Ru(bpy)₃]²⁺ presented a dual-emitting luminescent property at 440 and 605 nm, respectively. In the presence of Al³⁺, the blue fluorescence of NH₂-MIL-101(Fe)@[Ru(bpy)₃]²⁺ at 440 nm was enhanced remarkably, while the red emission at 605 nm was almost not influenced. Therefore, taking the fluorescence at 440 nm as the report signal and 605 nm as the reference signal, quantitative determination was achieved for Al³⁺ concentration in the ranges 0.2-25 μM and 25-250 μM. The limit of detection (LOD) and limit of quantification (LOQ) were calculated to be 73 nM and 244 nM, respectively. The sensing mechanisms were studied by theoretical calculation and optical spectra. The analysis of real food samples confirmed the suitability of the proposed method. More importantly, portable fluorescent test papers were successfully manufactured to provide a strategy for visual, rapid, and on-site detection of Al³⁺.

Thioether-functionalized porphyrin-based polymers for Hg2+ efficient removal in aqueous solution

In this paper, thioether-functionalized porphyrin-based polymers (TPPs) were constructed according to two different "bottom-up" and "top-down" strategies and they were applied for Hg²⁺ capture in aqueous solution. TPP1, which was constructed by one-step polycondensation of 2,5-bis(methylthio) terephthalaldehyde (BMTA) with pyrrole according to the "bottom-up" strategy, owned high Brunauer-Emmett-Teller (BET) surface area (S_BET, 554 m²/g), pore volume (V_total, 0.32 cm³/g), and S content (16.8%), resulting in high Hg²⁺ capture (913 mg/g) with high removal efficiency (> 99%). The adsorption mechanism clarified that the strong coordination between the S species and Hg²⁺ was the main driving force. In comparison, TPP2 and TPP3 were fabricated by the thioether functionalization of the porphyrin-based polymers according to the "top-down" strategy. They showed much lower S_BET, V_total, and S content for the reason that the post-functionalization process greatly blocked the pores and the functional sites were hardly fully post-functionalized, resulting in much lower Hg²⁺ capture (555 mg/g and 609 mg/g, respectively). This work reveals the advantage of the "bottom-up" strategy for the construction of the thioether-functionalized polymers and it offers the guidance for the construction of some other thioether-functionalized polymers.

Ultrasensitive ratiometric fluorescent probes for Hg(ii) and trypsin activity based on carbon dots and metalloporphyrin via a target recycling amplification strategy

A ultrasensitive ratiometric fluorescent probe was developed for Hg(ii) and trypsin based on CDs and TPPS via a target recycling amplification strategy. The detection limits of Hg2+ and trypsin were 0.086 nM and 0.013 ng mL−1.

A ratiometric fluorescent sensing of proanthocyanidins by MnO2 nanosheets simultaneously tuning the photoluminescence of Au/AgNCs and thiamine

By simultaneously regulating the photoluminescence of alloy Au/Ag nanoclusters (NCs) and thiamine (VB1) through MnO₂ nanosheets (MnO₂ NS), a novel ratiometric fluorescent probe (RF-probe) was established for sensitively and selectively monitoring proanthocyanidins (PAs). The introduction of Ag (I) ions could enhance significantly the quantum yields (QYs, 11.1%) of AuNCs based on the synthetic method of UVI (UV irradiation) combined with MWH (microwave heating). MnO₂ NS could quench the fluorescence (FL) of Au/AgNCs mainly coming from Förster resonance energy transfer (FRET), while it could act as a nanozyme catalyst for directly catalyzing the oxidation of VB1 to produce highly fluorescent oxVB1. In the presence of PAs, MnO₂ was reduced to Mn²⁺, which caused that its quenching capacity and oxidase-like activity were vanished, thus the FL of oxVB1 and Au/AgNCs was reduced and recovered. The concentration of PAs could be monitored by the RF-probe with a linear range of 0.27-22.4 μmol L^-1 and corresponding limit of detection (LOD) and limit of quantification (LOQ) were calculated to be 75.9 and 250.5 nmol L^-1. Furthermore, the RF-probe was successfully used for the determination of PAs in mineral water, PAs additive and PAs capsule with satisfactory results compared to the standard HPLC method.

Ingenious dual-emitting Ru@UiO-66-NH2 composite as ratiometric fluorescence sensor for detection of mercury in aqueous

The increasing deterioration of ecosystem derived from heavy metals residues brings about the environmental and food contamination, which presses the exploration of facile platform for monitoring heavy metals. Herein, a ratiometric fluorescence sensor was designed for Hg²⁺ detection based on the compound of UiO-66-NH₂ and Ru(bpy)₃²⁺ (Ru@UiO-66-NH₂) which was synthesized by situ encapsulation. The innovative composite displayed two emission peaks at 437 and 604 nm, and the addition of Hg²⁺ could only quench the blue fluorescence due to static quenching and photo-induced electron transfer mechanism, providing an internal standard to promote the precision. Under optimal conditions, the ratiometric Ru@UiO-66-NH₂ probe revealed outstanding anti-interference capability and performed with a great limit of detection (LOD) of 0.053 μM for Hg²⁺, which was 2-fold lower than that of single-color UiO-66-NH₂. By merit of Ru@UiO-66-NH₂, test hydrogels were fabricated to provide a tactics for visual, rapid and on-site detection of Hg²⁺. Additionally, the dual-emitting sensing platform presented satisfactory recoveries and reliabilities in lake water, tap water, and drink water, demonstrating the application potential of this proposed ratiometric fluorescence sensor for monitoring Hg²⁺.

A simple sensitive ratiometric fluorescent probe for the detection of mercury ions in living cells and zebrafish

Mercury, as a highly toxic heavy metal, can cause very serious harm to human health and even death in severe cases. Therefore, we synthesized a novel ratiometric fluorescent probe for detecting mercury ions, with mercaptoethanol as the recognition receptor. Probe CMER could determine mercury ions in 0-1.6 μM and the detection limit is 7.6 nM. Moreover, CMER manifested a fast response for Hg²⁺ (within 5 s) and simultaneously observed that the color changed from light yellow to orange by naked eye. In addition to these preeminent spectral properties, the probe also had satisfactory bioimaging results in RAW 264.7 macrophage cells and zebrafish.

Ratiometric fluorescence determination of alkaline phosphatase activity based on dual emission of bovine serum albumin-stabilized gold nanoclusters and the inner filter effect

A novel and convenient method for the ratiometric fluorescence detection of alkaline phosphatase (ALP) activity was proposed based on dual emission of bovine serum albumin-templated gold nanoclusters (BSA-AuNCs) and the mechanism of the inner filter effect between BSA-AuNCs and p-nitrophenol (PNP). First, ALP catalyzed the hydrolysis of the substrate p-nitrophenyl phosphate (PNPP) to produce PNP. PNP effectively quenched the emission peak of BSA-AuNCs at 410 nm because of the overlap in absorbance feature of PNP and the fluorescence spectrum of BSA-AuNCs, and the peak at 650 nm was almost unaffected. Thus, a sensitive ratiometric method for detection of ALP activity was developed using the fluorescence intensity of BSA-AuNCs at 650 nm as a reference signal. ALP activity versus the ratio of fluorescence intensities at 410 and 650 nm showed good linearity between 0.2 and 5 mU mL^-1 (R² = 0.9931) and high sensitivity with a detection limit of 0.03 mU mL^-1 (S/N = 3). The developed sensing method was successfully applied to investigate ALP inhibitors and detect ALP in serum samples.

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

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

Molecularly imprinted ratiometric fluorescent probe for visual and fluorescent determination of aristolochic acid I based on a Schiff-base fluorescent compound

A molecularly imprinted ratiometric fluorescent probe (MIRF probe) was synthesized for the determination of aristolochic acid I (AAI) based on the Schiff-base fluorescent compound N,N'-bis(o-carboxybenzylidene)-p-4,4'-diaminobiphenyl (BDDB). The BDDB was immobilized in the silica nanoparticle (BDDB@SiO₂) as an internal standard material. The blue-emitting BDDB@SiO₂ and the yellow-emitting carbon quantum dots (y-CDs) were wrapped in the molecularly imprinted polymer (MIP) to provide a reliable reference signal at 440 nm and a fluorescent response signal at 530 nm at the excitation wavelength of 365 nm, respectively. In the preparation of the MIP of the MIRF probe, 4-vinylbenzoic acid as the functional monomer and AAI as the template molecule were used. An imprinting factor of 2.25 was obtained. Under the optimum conditions, the fluorescent response signal at 530 nm was quenched gradually by AAI in the range 1.0 to 120.0 μmol/L, while the reference signal at 440 nm remained unchanged. The limit of detection was 0.45 μmol/L, and the fluorescent color of the MIRF probe changed gradually from yellow to green to blue, which illustrated that the developed probe had a specific AAI recognition ability, a good anti-interference ability, and a sensitively visual determination ability. The probe was successfully applied to the AAI determination in traditional Chinese medicine (TCM) Asarum. The results showed that it had satisfactory recoveries (95.5-107.3%) and low relative standard deviations (2.0%). Furthermore, this method has a potential for the onsite naked eye determination of AAI in TCM samples.Graphical abstract.

Ratiometric Fluorescent Probe Based on Diazotization-Coupling Reaction for Determination of Clenbuterol

In view of the potential harm caused by illegal feeding of clenbuterol (CLB) in the livestock industry, herein, a novel ratiometric fluorescent probe based on graphene quantum dots (GQDs)@[Ru(bpy)₃]²⁺ was elaborately constructed for CLB detection. In this probe, GQDs acted as response signals, and their fluorescence was remarkably quenched by CLB through the diazotization-coupling reaction. As for [Ru(bpy)₃]²⁺ as a reference signal, its fluorescence was hardly affected. The intensity ratio of two fluorophores showed good linearity with CLB concentration in the range of 0.05-40 μM, accompanied by visualization of fluorescence variation from yellow to red. The detection limit was as low as 0.029 μM. Particularly, the probe was successfully used to detect CLB in pork and beef samples with satisfactory recoveries. To our knowledge, this is the first report on a ratiometric fluorescent probe for the detection of CLB, which possesses broad application prospects in food safety risk monitoring.

Smartphones and Test Paper-Assisted Ratiometric Fluorescent Sensors for Semi-Quantitative and Visual Assay of Tetracycline Based on the Target-Induced Synergistic Effect of Antenna Effect and Inner Filter Effect

Development of selective and sensitive methods for on-site assay of tetracycline (TC) is of great significance for public health and food safety. Herein, a valid ratiometric fluorescence strategy using g-C₃N₄ nanosheets coupled with Eu³⁺ is designed for the assay of TC. In this strategy, both Eu³⁺ and g-C₃N₄ nanosheets serve as the recognition units of TC. The blue fluorescence of g-C₃N₄ nanosheets can be quenched by TC via the inner filter effect (IFE); meanwhile, the red fluorescence of Eu³⁺ can be enhanced by TC through the antenna effect (AE). The synergistic effect of AE and IFE caused by TC makes the developed ratiometric fluorescent sensor display a wide linear range for TC from 0.25 to 80 μM with a detection limit of 6.5 nM and a significant fluorescence color evolution from blue to red. Given its simplicity, free-label, excellent selectivity, high sensitivity, and recognizable color change, point-of-care testing systems, including smartphones and test paper-based assays, are developed for the visual sensing of TC. The integration of smartphones and test paper on a ratiometric fluorescent sensor greatly reduces the detection cost and time, providing a promising method for the qualitative discernment and semi-quantitative assay of TC on-site. Moreover, the potential application of the approach is also verified by detecting TC in milk.

Visual monitoring of trace water in organic solvents based on ecofriendly b/r-CDs ratiometric fluorescence test paper

Developing a green, non-toxic and easy to synthesize of fluorescence probe for fast and visual detecting trace water in various organic solvents was an important task. Here, a novel dual-emission fluorescence probe (b/r-CDs) was designed based on the red CDs (r-CDs) and blue CDs (b-CDs) to detect the trace water and enhance the visualization for naked-eye observation in different organic solvents. Among, the red fluorescence carbon dots (CDs) was found to have the capability to monitor trace amounts of water, which synthesized with green tea by facile ultrasonic method. Further, Such a dual-emission probe could fast monitor trace water in various organic solvents with high stability and fast response. Importantly, a synergistic mechanism of the dynamic process (b-CDs) and static quenching (r-CDs) was proved for the study of water detection. Moreover, the test paper was made for detecting trace water in different organic solvents, achieving convenient and effective detection.

Ratiometric fluorescent nanoprobes based on Resonance Rayleigh Scattering and inner filter effect for detecting alizarin red and Pb2

A new ratiometric fluorescent strategy for detection of alizarin red (ARS) was designed based on the fluorescence of CDs and scattered light of scatterer. The CDs-ARS system can be used to detect Pb²⁺ based on that the complexation between ARS and Pb²⁺. With the addition of ARS, the fluorescence of CDs was apparently quenched via inner filter effect (IFE). Resonance Rayleigh Scattering (RRS) at 350 nm was enhanced by an increase in the number of scatterer. The value of ln(I₃₅₀/I₄₂₅) was linearly correlated with ARS concentration in the range of 0-80 μM, and the detection limit for ARS was calculated to be 68.1 nM. When Pb²⁺ was added to the CDs-ARS system, the complexation of ARS with Pb²⁺ increased the size of the scatterer, resulting in the increase of the RRS intensity at 350 nm. Due to the affinity between ARS and Pb²⁺, the overlap of the emission spectra of CDs and the absorption spectra of ARS was reduced, resulting in the IFE effect was inhibited and the recovery of the fluorescence of CDs. The value of I₃₅₀/I₄₂₅ linearly increased with the addition of Pb²⁺ within the range of 10-50 μM, the limit of detection was 36.8 nM. As for practical application, CDs and CDs-ARS were applied to detect ARS and Pb²⁺ in tap water and poor water, respectively. The recovery values were obtained to be 95.4-98.8% and 93.4-101.7%. Furthermore, the system of CDs-ARS has been successfully applied to H1299 cell imaging.