Detection of Ag(+) using graphite carbon nitride nanosheets based on fluorescence quenching

Ultrasensitive detection of Ag+and Ce3+ions using highly fluorescent carboxyl-functionalized carbon nitride nanoparticles

The fluorescence quenching of carboxyl-rich g-C3N4nanoparticles was found to be selective to Ag+and Ce3+with a limit of detection as low as 30 pM for Ag+ions. A solid-state thermal polycondensation reaction was used to produce g-C3N4nanoparticles with distinct green fluorescence and high water solubility. Dynamic light scattering indicated an average nanoparticle size of 95 nm. The photoluminescence absorption and emission maxima were centered at 405 nm and 540 nm respectively which resulted in a large Stokes shift. Among different metal ion species, the carboxyl-rich g-C3N4nanoparticles were selective to Ag+and Ce3+ions, as indicated by strong fluorescence quenching and a change in the fluorescence lifetime. The PL sensing of heavy metal ions followed modified Stern-Volmer kinetics, and CNNPs in the presence of Ag+/Ce3+resulted in a higher value ofKapp(8.9 × 104M-1) indicating a more efficient quenching process and stronger interaction between CNNP and mixed ions. Sensing was also demonstrated using commercial filter paper functionalized with g-C3N4nanoparticles, enabling practical on-site applications.

A proof-of-concept electroreduction-free anodic stripping voltammetry analysis of Ag(I) based on S,N-Ti3C2Tx MXene nanoribbons

Herein, by preparing sulfur and nitrogen co-doped Ti3C2Tx MXene nanoribbons (S,N-Ti3C2TxR) as a sensing material, a sensitive and novel electroreduction-free anodic stripping voltammetry strategy was designed to detect Ag(I) (Ag+) for the first time, which can successfully avoid the power-consuming electroreduction step, achieving simple, sensitive and efficient detection for Ag+ with a low detection limit and wide linearity.

Graphitic carbon nitride derived probes for the recognition of heavy metal pollutants of environmental concern in water bodies

Graphitic carbon nitride (g-CN) has a number of valuable features that have been recognized during the studies related to its photocatalytic activity enhancement derived by visible light. Because of these characteristics, g-CN can be used as a detecting signal transducer with different transmission modalities. The latest up-to-date detection capabilities of modified g-CN nanoarchitectures are covered in this study. The structural features and synthetic methodologies have been discussed in a number of reports. Herein, employment of the g-CN as a promising probing modality for the recognition of different toxic heavy metals is the promising feature of the present study.

A facile aptamer-based sensing strategy for dopamine detection through the fluorescence energy transfer between dye and single-wall carbon nanohorns

Dopamine (DBA) as an important biomarker, plays a crucial role in disease diagnosis. In this study, we have developed a fast and simple aptamer-based fluorescence strategy which used single-wall carbon nanohorns (SWCNHs) as a quencher for dopamine detection. SWCNHs were negatively charged after pretreated, which improved its dispersion in solution. 5-carboxy-fluorescein (FAM) was used to label dopamine aptamer. In the absence of dopamine, FAM-modified aptamer could be absorbed onto the SWCNHs surface due to π-π interaction, resulting in the fluorescence intensity decreased. Dopamine could specifically bind with FAM-DNA to form G-quadruplex, which could not be absorbed onto the surface of SWCNHs. Hence, the fluorescence of FAM-DNA recovered, and the fluorescent intensity as a function of different concentrations of dopamine was measured. We obtained a detection limit of 5 μM for this detection system with a linear detection range of 0.02-2.20 mM. Furthermore, the feasibility of the innovative detection system has been verified by detecting dopamine in spiked serum samples.

Current advances on g-C3N4-based fluorescence detection for environmental contaminants

The development of highly-sensitive fluorescence detection systems for environmental contaminants has become high priority research in the past years. Special attention has been paid to graphitic carbon nitride (g-C₃N₄)-based nanomaterials, whose unique and superior optical property makes them promising and attractive candidates for this purpose. It is necessary to enhance the current understanding of the various classes of g-C₃N₄-based fluorescence detection systems and their mechanisms, as well as find suitable approaches to improve detection performance for environmental monitoring, protection, and management. In this review, the recent progresses on g-C₃N₄-based fluorescence detections for environmental contaminants, mainly including their basic principles, mechanisms, applications, modification strategies, and conclusions, are summarized. A particular emphasis is placed on the design and development of modification strategies for g-C₃N₄ with the objective of improving detection performance. High photoluminescence quantum yield, tunable fluorescence emission characteristics, and strong adsorption capacity of g-C₃N₄ could ensure the ultrasensitivity and selectivity of fluorescence detection of environmental contaminants. Concluding perspectives on the challenges and opportunities to design highly efficient g-C₃N₄-based fluorescence detection system are intensively put forward as well.

Preparation of bis-Schiff base immobilized mesoporous SBA-15 nanosensor for the fluorogenic sensing and adsorption of Cu2+

The inorganic−organic chemosensing material (MS-NSP) was developed by anchoring the bis-Schiff base fluorophore onto the channel surface of SBA-15 mesoporous silica surface with a quaternary ammonium linker. The mesostructure, morphology,...

A simple enzyme-catalyzed reaction induced "switch" type fluorescence biosensor based on carbon nitride nanosheets for the assay of alkaline phosphatase activity

An enzyme-catalyzed fluorescence "switch" type sensor was constructed for the determination of alkaline phosphatase (ALP) activity by combining the fluorescence quenching effect of Ag+ on ultrathin g-C3N4 nanosheets (CNNSs) with the simple redox reaction of AA and Ag+. Briefly, Ag+ exhibits a significant quenching effect on the fluorescence of CNNSs. Thus the fluorescence signal of the CNNS-Ag+ system is extremely weak even in the presence of l-ascorbic acid-2-phosphate (AAP) ("off" state). When ALP coexists in the system, the enzyme can specifically catalyze the hydrolysis of AAP to form ascorbic acid (AA), which reduces Ag+ to Ag0. In this case, the fluorescence signal of the system is recovered ("on" state). Based on this principle, a signal-enhanced CNNS fluorescence sensor was developed to determine the activity of alkaline phosphatase. The experimental results show that the detection range of alkaline phosphatase is 0.5-20 U L-1, and the detection limit is 0.05 U L-1 (S/N = 3). Meanwhile, this method was used to assay ALP in serum samples.

Water-soluble graphitic carbon nitride for clean environmental applications

The removal of halogenated dye and sensing of pharmaceutical products in the water bodies with quick purification time is of high need due to the scarcity of drinking water. The present work reported on the preparation of graphitic carbon nitride (g-C₃N₄) for quick time water contaminant adsorption, followed by synthesizing silver nanoparticles decorated graphitic carbon nitride for pharmaceutical product sensing using in-situ SERS technique. The prepared graphitic carbon nitride is used to study the adsorption behavior of water contaminants at room temperature, in the presence of methylene blue (MB) as an adsorbate model. The water-soluble graphitic carbon nitride, even at low concentration, possesses an excellent ability to adsorb halogenated organic dye. As a result, the dyes are found to adsorb within ∼5s even without any additional physical or chemical activation. From the UV-Vis absorption investigations, it has been perceived that in the presence of graphitic carbon nitride (g-C₃N₄) the dye adsorption efficacy is observed nearly 80% with the well fitted linearly of R² = 0.9731. Effective in-situ surface-enhanced Raman scattering (SERS) studies for Ag nanoparticles decorated graphitic carbon nitride has been carried out and the obtained result shows good sensing performance of the material towards acetaminophen drug. This method opens the possibility of the Nobel metal decorated graphitic carbon nitride for real-time sensing of SERS-based drug products along with the development of high-performance sensing of the target analyte in the future.

Carboxymethyl chitosan crosslinked ꞵ-cyclodextrin containing hydrogen bonded NC QDs nanocomposites to design fluorescence probes for manganese ion (II) sensing

The direct determination Mn²⁺ using carboxymethyl chitosan crosslinked with cyclodextrin containing hydrogen-bonded NC QDs (NC QD/CCSCD nanocomposites). The probable mechanism of the NC QD/CCSCD nanocomposites' fluorescence was quenched by Mn²⁺ could be interpreted as acyclic crown ether chelation. Mn²⁺ induced the NC QD/CCSCD clusters assembly to form large aggregates, which resulted in aggregation-caused quenching. The linear detection (I = 479.93-15.94C (R² = 0.9954)) can be established at Mn²⁺ concentrations from 0 to 21.11 × 10^-6 mol/L. Common metal ions, except iron and magnesium, showed minimal effect on detection. It could satisfy the standard range of Mn²⁺ in actual water samples. The method which using chelating assembly mechanism to build a novel sensor would provide a new model for the application of polymer materials in this field, but the precise assembly of polymer is an unsolved challenge.

A fluorescent probe using phosphorus-doped graphite carbon nitride nanosheets for the detection of silver ions and cell imaging

The fluorescent phosphorus-doped graphite carbon nitride (P-g-C3N4) nanosheets have been synthesized as a fluorescence probe using an ultrasonic exfoliating method. The as-prepared P-g-C3N4 nanosheets were characterized by multiple analytical techniques such as transmission electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and infrared spectroscopy. The fluorescence intensity of P-g-C3N4 nanosheets decreases with the increase in concentration of silver ions. A good linear relationship was achieved between the corresponding fluorescence intensity of P-g-C3N4 nanosheets and the concentration of silver ions in the range of 20 nmol/L – 3.2 μmol/L. The quenching mechanism of interaction between P-g-C3N4 nanosheets and silver ions was primarily discussed. The proposed fluorescence probe has been successfully applied to detect silver ions in real water samples and the recoveries range from 96.8% to 103.7%.

Fluorescent MoS2 QDs based on IFE for turn-off determination of FOX-7 in real water samples

A novel method for turn-off sensing 1,1-diamino-2,2-dinitroethylene (FOX-7) in aqueous medium was first proposed based on the inner filter effect (IFE) of FOX-7 on the fluorescence of molybdenum disulfide quantum dots (MoS₂ QDs). Water-soluble MoS₂ QDs as the fluorophore were prepared by the simple hydrothermal method. The morphology, structure, composition and optical properties of the prepared MoS₂ QDs were characterized by Transmission electron microscopy (TEM), Fourier transform infrared (FT-IR), X-ray photoelectron spectroscopy (XPS), UV-vis absorption and photoluminescence spectra. The results showed that the MoS₂ QDs had good water dispersibility and emitted strong photoluminescence with a particle size of 2 nm. Under the optimal experimental conditions, the fluorescence signal of MoS₂ QDs was quenched in the concentrations range of FOX-7 (0.5-100 μM) and the limit of detection (LOD) of the sensor was 0.19 μM. The method had been applied to analyze the real water samples with good selectivity and stability. Moreover, the quenching mechanism was studied systematically by the Fourier transform infrared (FT-IR), UV-vis absorption spectra, fluorescence lifetime, and Stern-Volmer equation, which had been proved to be static quenching. The fluorescence quenching mechanism is mainly IFE and electron transfer.

Fluorescent assay based on phenyl-modified g-C3N4 nanosheets for determination of thiram

Phenyl-modified graphitic carbon nitride nanosheets (Ph-g-C₃N₄ NSs) were synthesized by a thermal copolymerization and ultrasonic exfoliation method. The Ph-g-C₃N₄ NSs are used as a fluorescent assay for determination of thiram. The results of X-ray photoelectron spectroscopy, ¹³C solid-state nuclear magnetic resonance and Fourier transform infrared spectra confirm that phenyl group is integrated into the heptazine network of g-C₃N₄. Compared to the g-C₃N₄ NSs, the Ph-g-C₃N₄ NSs show bigger stokes shift about 185 nm and higher fluorescence intensity. The fluorescence of Ph-g-C₃N₄ NSs is quenched by Cu²⁺ via the photo-induced electron transfer mechanism, which then recovers in the presence of thiram. The fluorescence restoring of Ph-g-C₃N₄ NSs is correlated with the concentration of thiram. Under the optimized conditions, the fluorescent intensity of g-C₃N₄ NSs at excitation/emission wavelengths of 310/455 nm give a linear range of 33.0-670 nM with detection limit of 9.90 nM. While fluorescent assay based on the Ph-g-C₃N₄ NSs show the linear range of 6.70-1300 nM at excitation/emission wavelengths of 310/495 nm with detection limit of 2.01 nM. Graphical abstract Schematic representation of fluorescent "on-off-on" assay based on phenyl-modified graphitic carbon nitride nanosheets (Ph-g-C₃N₄ NSs) for determination of thiram.

A Water-Soluble Fluorescent Probe for the Selective Sensing of Ag+ and its Application in Imaging of Living Cells and Nematodes

In this study, an imidazole-coumarin based fluorescent probe was developed for the selective and sensitive detection of Ag+ in aqueous solution. Using a combination of Job plot, NMR titrations, and DFT calculations, the binding properties between Ag+ and the probe were deeply investigated, and the results revealed a 1:1 binding stoichiometry between the probe and Ag+ with a binding constant of 1.02 × 106 M-1. The detection limit was found to be 150 nM, which satisfies the requirement for the quantitative detection of Ag+ in real water samples. Moreover, the new probe, Ic, was successfully applied to sense Ag+ in HeLa and HepG2 cells as well as in C. elegans, indicating that it could be a useful tool for the environmental monitoring of Ag+ pollution. These results demonstrated that Ic could serve as a high-efficiency and low-cost fluorescent probe for tracking Ag+ in an aquatic environment and biological organisms.

Fluorescence covalent interaction enhanced sensor for lead ion based on novel graphitic carbon nitride nanocones

Novel graphitic carbon nitride nanocones (g-CNNCs) were synthesized for the first time in this study. The SEM, TEM, XPS and FT-IR were used to research the structure of the g-CNNCs. We found that the g-CNNCs showed high selective and sensitive for fluorescence enhancement detection of Pb²⁺ ion via covalent interaction. In addition, the g-CNNCs exhibit stable and specific concentration-dependent fluorescence intensity in the presence of Pb²⁺ ion in the range of 1-200 μmol·dm^-3, and the limit of detection was estimated to be 0.0438 μmol·dm^-3 (3S/k). More importantly, the g-CNNCs were used to detect practical samples with satisfactory results.

A high-performance fluorescent probe for dopamine detection based on g-C3N4 nanofibers

A novel fluorescent sensor based on g-C₃N₄ nanofibers for the sensitive detection of dopamine (DA) has been proposed. We synthesized g-C₃N₄ nanofibers by directly hydrolyzing bulk g-C₃N₄ in the alkaline atmosphere (3 M NaOH). The obtained ultrathin g-C₃N₄ nanofibers were verified by characterizations of Transmission electronic microscope (TEM), X-ray diffractometer (XRD), Fourier transformation-infrared (FT-IR) and X-ray photoelectron spectroscopy (XPS). It was found that the fluorescence intensity of g-C₃N₄ nanofibers was obviously quenched by DA. Fluorescence resonance energy transfer (FRET) between DA and g-C₃N₄ nanofibers led to the fluorescence reduction of g-C₃N₄ nanofibers. The fluorescent probe based on g-C₃N₄ nanofibers exhibits linear responses to the concentration of DA in the range from 0 to 4 μM and 4 to 20 μM, the limit of detection is 17 nM. The fluorescent probe shows excellent stability, good selectivity with its application in serums.

Fe3+-selective and sensitive "on-off" fluorescence probe based on the graphitic carbon nitride nanosheets

An effective and facile "on-off" fluorescence sensing approach for the determination of Fe³⁺ ion using a large area and relatively uniform size graphitic carbon nitride nanosheets (GCNS) was developed. The prepared GCNS have blue and stable emission, as well as excellent water dispersion, and were applied as an effective fluorescent probe that based on the quenched fluorescence for selective and sensitive detection of Fe³⁺ ion. Herein, we explain the ambiguous fluorescence quenching mechanism between the GCNS and Fe³⁺, which mainly springs from the redox potential and empty d orbital of Fe³⁺. The redox potential and unfilled d orbit of Fe³⁺ endow it excellent binding force with GCNS, which generates most obvious fluorescence quenching effect with respect to other metal ions. The limit of detection (LOD) for Fe³⁺ was found to be about 2.06 μM. Therefore, the prepared GCNS has the potential to be used as a fluorescent probe for detection.

Dual Functional S-Doped g-C₃N₄ Pinhole Porous Nanosheets for Selective Fluorescence Sensing of Ag⁺ and Visible-Light Photocatalysis of Dyes

This study explores the facile, template-free synthesis of S-doped g-C₃N₄ pinhole nanosheets (SCNPNS) with porous structure for fluorescence sensing of Ag⁺ ions and visible-light photocatalysis of dyes. As-synthesized SCNPNS samples were characterized by various analytical tools such as XRD, FT-IR, TEM, BET, XPS, and UV⁻vis spectroscopy. At optimal conditions, the detection linear range for Ag⁺ was found to be from 0 to 1000 nM, showing the limit of detection (LOD) of 57 nM. The SCNPNS exhibited highly sensitive and selective detection of Ag⁺ due to a significant fluorescence quenching via photo-induced electron transfer through Ag⁺⁻SCNPNS complex. Moreover, the SCNPNS exhibited 90% degradation for cationic methylene blue (MB) dye within 180 min under visible light. The enhanced photocatalytic activity of the SCNPNS was attributed to its negative zeta potential for electrostatic interaction with cationic dyes, and the pinhole porous structure can provide more active sites which can induce faster transport of the charge carrier over the surface. Our SCNPNS is proposed as an environmental safety tool due to several advantages, such as low cost, facile preparation, selective recognition of Ag⁺ ions, and efficient photocatalytic degradation of cationic dyes under visible light.

Novel dual-functional fluorescent sensors based on bis(5,6-dimethylbenzimidazole) derivatives for distinguishing of Ag+ and Fe3+ in semi-aqueous medium

Three novel bisbenzimidazole derivatives have been synthesized and developed as dual-functional fluorescent sensors for the rapid and highly selective detection of Ag⁺ and Fe³⁺ ions in semi-aqueous medium with distinct spectral response for the first time. The absorption intensity is drastically decreased after the addition of Ag⁺. Contrarily, it is markedly increased upon the addition of Fe³⁺. And there is a good linear relation at low concentration of both Ag⁺ and Fe³⁺, which provides a quantitative method for their detection. Similarly, the sensors show a distinct fluorescence response towards Ag⁺ and Fe³⁺ with a different fluorescence color change under UV light. In addition, no significant changes and interference can be observed with other metal ions. The sensing mechanism studies confirm that the N atom in CN of benzimidazole ring of sensor 4a may bind with Ag⁺ or Fe³⁺ ion to form metal complex. And there is only a static quenching process for the 4-Ag⁺ complex system, but both dynamic and static quenching processes occur in the 4-Fe³⁺ complex system. Moreover, sensors 4 can steadily work in solution with a wide range of pH 4-13 and rapidly respond to Ag⁺ and Fe³⁺ with a response time of 10 s. Finally, the sensors have been successfully applied to the visual detection of Ag⁺ and Fe³⁺ not only in solution, but also in test paper.

A specific electrochemiluminescence sensor for selective and ultra-sensitive mercury(ii) detection based on dithiothreitol functionalized copper nanocluster/carbon nitride nanocomposites

A novel electrochemiluminescence sensor based on the combination of copper nanoclusters and carbon nitride nanosheets was fabricated for detecting Hg²⁺.

Fluorometric determination of quercetin by using graphitic carbon nitride nanoparticles modified with a molecularly imprinted polymer

The authors describe a fluorescent probe for sensitive and selective determination of quercetin, an indicator for the freshness of drinks. The probe consists of silica ball encapsulated graphitic carbon nitride (g-C₃N₄) modified with a molecularly imprinted polymer (MIP). It was synthesized via reverse microemulsion. The resulting MIP@g-C₃N₄ nanocomposite was characterized by fluorescence spectroscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, and X-ray powder diffraction. Quercetin quenches the fluorescence of the MIP@g-C₃N₄ probe. The effect was used to quantify quercetin in grape juice, tea juice, black tea, and red wine by fluorometry (λ_exc = 350 nm, λ_em = 460 nm). Response is linear in the 10-1000 ng mL^-1 quercetin concentration range. The detection limit is 2.5 ng mL^-1, recoveries range between 90.7 and 94.1%, and relative standard deviations are between 2.1 and 5.5%. Graphical abstract Schematic of the synthesis of the MIP@g-C₃N₄ by a reverse microemulsion method. The probe was applied for the selective recognition and fluorometric determination of quercetin.

Development of graphite carbon nitride based fluorescent immune sensor for detection of alpha fetoprotein

A novel fluorescent immunosensor for determination of alpha fetoprotein (AFP) in serum samples has been developed based on the nano graphite carbon nitride (g-C₃N₄) as fluorophore and immunomagnetic beads (MBs) as separation material. The bulk g-C₃N₄ was obtained by thermal polymerization of melamine, and then carboxylated and exfoliated to acquire the carboxylated nano g-C₃N₄ (c-n-g-C₃N₄), which has been characterized and the results showed that it had excellent fluorescent properties. The antibodies of AFP (Ab₁, Ab₂) were conjugated to the MBs and the c-n-g-C₃N₄, respectively. In assay of AFP detection, the magnetic part of the immunosensor, MBs-Ab₁, would form the sandwich type complex with the signal part of the sensor, c-n-g-C₃N₄-Ab₂. The developed immunosensor could simplify the process of separation due to the MBs. The results illustrated that proposed approach held a good linearity between the fluorescence intensity of the sensor and the AFP concentration ranging from 5-600ng/mL with the limit of detection as low as 0.43ng/mL, and its spiking recoveries ranged from 98.2% to 105.9% with RSD from 2.1% to 3.5%. The fabricated fluorescent immunosensor possesses the merits of good sensitivity, excellent selectivity, high biocompatibility and low cost, and the results provide a novel clue to develop immunosensor for determination of the biomarkers in complex matrices.

Electrochemically prepared oxygen and sulfur co-doped graphitic carbon nitride quantum dots for fluorescence determination of copper and silver ions and biothiols

Although great advances have been achieved in synthesis of fluorescent graphitic carbon nitride quantum dots (g-C₃N₄-dots), it is still challenging to develop g-C₃N₄-dots with high fluorescence quantum yield (FLQY) and multiple sensing functionalities. Herein, the oxygen and sulfur co-doped graphitic carbon nitride quantum dots (OS-g-C₃N₄-dots) with high FLQY of 33.9% were firstly synthesized by a simple electrochemical "tailoring" process. It was found that OS-g-C₃N₄-dots could specifically bind copper ions (Cu²⁺) and silver ions (Ag⁺), accompanied with a dramatic "turn-off" fluorescence response. With the help of different masking agents, OS-g-C₃N₄-dots are able to selectively detect Cu²⁺ and Ag⁺. Furthermore, the generated OS-g-C₃N₄-dots/Ag⁺ displayed a "turn-on" fluorescent response specific to biothiols (HCy, Cys and GSH). Therefore, the multiple functional sensing platforms based on "ON-OFF-ON" fluorescence response of OS-g-C₃N₄-dots for the detection of Cu²⁺, Ag⁺ and biothiols were constructed. Under the optimal conditions, the detection limits of Cu²⁺, Ag⁺, HCy, Cys and GSH were as low as 7.0 × 10^-10 M, 2.0 × 10^-9 M, 1.0 × 10^-8 M, 1.0 × 10^-8 M and 8.4 × 10^-9 M, respectively. Moreover, the prepared platforms could be successfully applied to the determination of Cu²⁺, Ag⁺ and biothiols in practical samples and exhibited excellent sensitivity and selectivity.

DNA-functionalized gold nanoparticle-based fluorescence polarization for the sensitive detection of silver ions

Despite their practical applications, Ag⁺ ions are environmental pollutants and affect human health. So the effective detection methods of Ag⁺ ions are imperative. Herein, we developed a simple, sensitive, selective, and cost-effective fluorescence polarization sensor for Ag⁺ detection in aqueous solution using thiol-DNA-functionalized gold nanoparticles (AuNPs). In this sensing strategy, Ag⁺ ions can specifically interact with a cytosine-cytosine (CC) mismatch in DNA duplexes and form stable metal-mediated cytosine-Ag⁺-cytosine (C-Ag⁺-C) base pairs. The formation of the C-Ag⁺-C complex results in evident changes in the molecular volume and fluorescence polarization signal. To achieve our aims, we prepared two complementary DNA strands containing C-base mismatches (probe A: 5'-SH-A₁₀-TACCACTCCTCAC-3' and probe B: 5'-TCCTCACCAGTCCTA-FAM-3'). The stable hybridization between probe A and probe B occurs with the formation of the C-Ag⁺-C complex in the presence of Ag⁺ ions, leading to obvious fluorescence quenching in comparison to the system without AuNP enhancement. The assay can be used to identify nanomolar levels of Ag⁺ within 6 min at room temperature, and has extremely high specificity for Ag⁺, even in the presence of higher concentrations of interfering metal ions. Furthermore, the sensor was successfully applied to the detection of Ag⁺ ions in environmental water samples and showed excellent selectivity and high sensitivity, implying its promising application in the future.

One-step synthesis of graphitic carbon nitride nanosheets with the help of melamine and its application for fluorescence detection of mercuric ions

A facile, simple, and relatively environment-friendly hydrothermal approach was developed for one-step synthesis of graphitic carbon nitride nanosheets (GCNNs) using melamine and sodium citrate as the precursors. The prepared GCNNs emit strong fluorescence with a high quantum yield of 48.3%. The GCNNs were then characterized by various techniques including transmission electron microscopy, atomic force microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and UV-Vis absorption spectroscopy. In addition, the fluorescence quenching behavior of the GCNNS by mercuric ions (Hg²⁺) was exploited to fabricate a label-free fluorescence quenching sensor for sensitive and selective detection of Hg²⁺. The results showed that there existed a linear relationship between the fluorescence intensity and the concentration of Hg²⁺ from 0.001 to 1.0μM with a detection limit of 0.3nM. Finally, the sensor was successfully used to detection of Hg²⁺ in water and milk samples.