Red emission nitrogen, boron, sulfur co-doped carbon dots for "on-off-on" fluorescent mode detection of Ag+ ions and l-cysteine in complex biological fluids and living cells

Redox induced dual-signal optical sensor of carbon dots/MnO2 nanosheets based on fluorescence and second-order scattering for the detection of ascorbic acid

In order to detect ascorbic acid (AA) sensitively, a dual-signal optical sensor of a nanosystem with carbon dots (CDs)/MnO₂ nanosheets based on fluorescence and second-order scattering (SOS) has been constructed. Here, MnO₂ nanosheets, both as a fluorescence quencher and signal transducer of SOS, quench the blue fluorescence of CDs by an inner filter effect. Under the excitation of 300 nm, the nanosystem shows a fluorescence emission peak at 405 nm and a SOS peak at 610 nm, respectively. With the increase of AA , the lamellar structure of MnO₂ nanosheets is etched into a smaller nanostructure, causing a decrease of the fluorescence recovery of CDs (405 nm) and decrease of the SOS signal of the MnO₂ nanosheets (610 nm). According to the simultaneous changes of fluorescence and SOS signals, a dual-signal optical sensor toward AA is successfully constructed. Satisfactorily, the optical sensor for AA detection shows a detection limit of 88 and 105 nM for fluorescence and SOS, respectively. The practical application of the designed sensor is verified through the detection of AA content in vitamin C tablets, and satisfactory results are obtained Graphical Abstract A dual-signal sensor of fluorescence (FL) and second-order scattering (SOS) based on the carbon dot (CD) and MnO₂ nanosheet system for ascorbic acid (AA) detection is constructed, in which CDs are used for the FL mode and MnO₂ nanosheets are used for the SOS mode.

Dual-QDs ratios fluorescent probe for sensitive and selective detection of silver ions contamination in real sample

Silver ions, as a commonly used industrial heavy metal, tends to deposit in the body and induce many diseases. In this work, modified CdTe QDs with green and red emission were synthesized to assemble dual-QDs, which could be efficient and selective utilized for Ag⁺ determination through the electron transfer progress between surface functional group of dual-QDs and Ag⁺, and the aggregation of Ag⁺ on the surface of dual-QDs. Under the appropriate pH value and volume ratio, the interaction between the surface functional groups of assembled dual-QDs reduce the affinity of Hg²⁺ in this system. The fluorescent signal of dual-QDs simultaneously attenuation or enhancement in the same proportion remove the interference of Cu²⁺ and other metal ions. Therefore, this method can selectively detect Ag⁺ without any masking agents. The linear region of detection was from 0 to 800 nmol/L (R² > 0.998), and low of detection (LOD) was 7.7 nmol/L, which could meet the corresponding standards of World Health Organization (WHO) and Environmental Protection Agency (EPA). This effective proposed dual-QDs ratios fluorescent probe has been applied to detect Ag⁺ in real environment water, tea and Citri Reticulatae Pericarpium (CRP) water.

One-step synthesis of mitochondrion-targeted fluorescent carbon dots and fluorescence detection of silver ions

Silver ions (Ag+) are the most representative harmful ions found in polluted water and widely used in many industries; excessive ingestion of Ag+ in the human body may result in interaction with different metabolites in the human body and in aquatic microorganisms, leading to many diseases. Therefore, there is a great desire to develop good fluorescent probes for Ag+. Herein, a kind of mitochondrion-targeted fluorescent carbon dot was developed. These carbon dots exhibit 29.5% fluorescence quantum yield in water, good photostability and thermal stability. The as-fabricated carbon dots can quickly detect Ag+ in 100% water solution with good selectivity and anti-interference ability. Further, the carbon dots have been successfully applied to monitor Ag+ in living cells via the dual-channel method.

Facile fabrication of N/S/P tri-doped carbon dots for tetracycline detection by an internal filtering effect of a two-way matching strategy

We have developed a facile ultrasound-assisted route to synthesize N/S/P co-doped carbon dots (N/S/P-CDs) in an alkaline solution at room temperature. They demonstrate brightly luminescent and thermo-tunable fluorescence properties and show ultra-high sensitivity for the detection of TC in milk via the inner filter effect (IFE) of a two-way matching strategy.

A review: recent advances in preparations and applications of heteroatom-doped carbon quantum dots

Carbon quantum dots (CQDs) are widely used in optoelectronic catalysis, biological imaging, and ion probes owing to their low toxicity, stable photoluminescence, and ease of chemical modification. However, the low fluorescence yield and monochromatic fluorescence of CQDs limit their practical applications. This review summarizes the commonly used approaches for improving the fluorescence efficiency of CQDs doped with non-metallic (heteroatom) elements. Herein, three types of heteroatom-doped CQDs have been investigated: (1) CQDs doped with a single heteroatom; (2) CQDs doped with two heteroatoms; and (3) CQDs doped with three heteroatoms. The limitations and future perspectives of doped CQDs from the viewpoint of producing CQDs for specific applications, especially for bioimaging and light emitting diodes, have also been discussed herein.

Label-free iodide detection using functionalized carbon nanodots as fluorescent probes

A label-free fluorescent nanoprobe for iodide ion (I^-) detection was developed based on the direct fluorescence quenching of spermine-functionalized carbon dots (SC-dots), whether in complex biological fluids or living cells. The positively charged SC-dots were fabricated via one-step microwave synthesis and exhibited excellent optical properties. Due to the strong quenching ability of I^-, SC-dots were utilized for I^- detection with high sensitivity and excellent selectivity, which offered a relatively low detection limit of 0.18 μM. This strategy was also successfully applied for I^- detections in human serum and HeLa cells. The detection process is facile, highly sensitive and selective, providing a new insight into the potential applications of SC-dots for anion nanoprobe designs in clinical diagnosis and other biologically related areas. Graphical abstract.

Carbon dots: Current advances in pathogenic bacteria monitoring and prospect applications

Pathogenic bacterial infections are a significant threat to human safety and health. Recent researches on the application of nanoparticles as imaging, detecting agents have evidenced their huge potential for infectious disease management. Among these nanoparticles, carbon dots (CDs) have attracted much attention as a new and innovative nanoparticle owing to their unique optical and physicochemical properties as well as their higher biosafety. Thus, CDs are becoming superior candidates for imaging and detection of pathogenic bacteria. This review provides an overview of research advances and the mechanisms in the imaging and detection pathogenic bacteria such as "switch on" sensor, "on-off" sensor, förster resonance energy transfer (FRET), etc. Further, our discussion extends to exploring the antibacterial effects of CDs, which is considered to be a potentially promising antibacterial agent. This review would provide the basis and the direction for the further commercial applications of CDs in imaging, detecting and eliminating pathogenic bacteria. The challenges associated with CDs in monitoring of pathogenic bacteria and future directions in this field are also presented.

Manganese oxide doped carbon dots for temperature-responsive biosensing and target bioimaging

We report on the synthesis of manganese oxide doped CDs (MnO_x-CDs) by a hydrothermal strategy using manganese (III) acetylacetonate (Mn(III) (C₅H₇O₂)₃) as the only raw materials. The MnO_x-CDs exhibit water solubility, favorable biocompatibility, low cytotoxicity, and show blue fluorescence with excitation/emission maxima at 326/442 nm with a quantum yield of 11.3%, allowing efficient cellular imaging. The MnO_x-CDs have a reversible temperature-sensitive fluorescent property in vitro within 10-60 °C, which can also be used as a sensitive thermometer in living cells. By a scratch assay, the MnO_x-CDs can restrain the migration of HepG2 cancer cells, which make the MnO_x-CDs be attractive candidates for liver cancer adjuvant treatment. Besides, the fluorescence of the MnO_x-CDs is quenched in the presence of Fe³⁺ due to the formation of a nonfluorescent MnO_x-CDs-Fe³⁺ complex between oxygen-containing groups on the surface of MnO_x-CDs and Fe³⁺, and the quenched fluorescence of MnO_x-CDs can be turn-on by dissociation of MnO_x-CDs-Fe³⁺ complexes by biothiols including L-cysteine, homocysteine and glutathione. Therefore, the Fe³⁺ and biothiols can be sequentially detected with high reliability and accuracy via exploiting the on-off-on nanosensor at room temperature, respectively. Further application to detection biothiols in human serum indicated that the probe was practicality and feasibility in medical field.

Red emissive carbon dots obtained from direct calcination of 1,2,4-triaminobenzene for dual-mode pH sensing in living cells

Red emissive carbon dots with colorimetric/fluorescent responses to pH fluctuations were prepared by direct calcination of 1,2,4-triaminobenzene.

Recent Advances in Functionalized Carbon Dots toward the Design of Efficient Materials for Sensing and Catalysis Applications

Since the past decade, enormous research efforts have been devoted to the detection/degradation and quantification of environmental toxic pollutants and biologically important molecules due to their ubiquitous necessity in the fields of environmental protection and human health. These fields of sensor and catalysis are advanced to a new era after emerging of nanomaterials, especially, carbon nanomaterials including graphene, carbon nanotube, carbon dots (C-dots), etc. Among them, the C-dots in the carbon family are rapidly boosted in the aspect of synthesis and application due to their superior properties of chemical and photostability, highly fluorescent with tunable, non/low-toxicity, and biocompatibility. The C-dot-based functional materials have shown great potential in sensor and catalysis fields for the detection/degradation of environmental pollutants. The major advantage of C-dots is that they can be easily prepared from numerous biomass/waste materials which are inexpensive and environment-friendly and are suitable for a developing trend of sustainable materials. This review is devoted to the recent development (since 2017) in the synthesis of biomass- and chemical-derived C-dots as well as diverse functionalization of C-dots. Their capability as a sensor and catalyst and respective mechanism are summarized. The future perspectives of C-dots are also discussed.

Red-Emissive Guanylated Polyene-Functionalized Carbon Dots Arm Oral Epithelia against Invasive Fungal Infections

Oral candidiasis as a highly prevalent and recurrent infection in medically compromised individuals is mainly caused by the opportunistic fungal pathogen Candida albicans. This epithelial infection, if not controlled effectively, can progress to life-threatening systemic conditions and complications. The efficacy of current frontline antifungals is limited due to their poor bioavailability and systemic toxicity. As such, an efficient intervention is essential for controlling disease progression and recurrence. Herein, a theranostic nanoplatform (CD-Gu⁺-AmB) was developed to track the penetration of antifungals and perturb the invasion of C. albicans at oral epithelial tissues, via decorating the homemade red-emissive carbon dots (CD) with positively charged guanidine groups (Gu⁺) followed by conjugation with antifungal polyene (amphotericin B, AmB) in a reacting site-controllable manner. The generated CD-Gu⁺-AmB favorably gathered within the Candida cells and exhibited potent antifungal effects in both planktonic and biofilm forms. It selectively accumulated in the nuclei of human oral keratinocytes and exhibited undetectable toxicity to the host cells. Moreover, we reported for the first time the penetration and exfoliation profiles of CD in a three-dimensional organotypic model of human oral epithelial tissues, demonstrating that the extra- and intracellular accumulation of CD-Gu⁺-AmB effectively resisted the invasion of C. albicans by forming a "shielding" layer throughout the entire tissue. This study establishes a multifunctional CD-based theranostic nanoplatform functioning as a traceable and topically applied antifungal to arm oral epithelia, thereby shedding light on early intervention of mucosal candidiasis for oral and general health.

A phenanthro[9,10-d]imidazole-based AIE active fluorescence probe for sequential detection of Ag+/AgNPs and SCN- in water and saliva samples and its application in living cells

Ag⁺ and SCN^- play extremely important roles in the fields of the physiology and environment. In this work, on the basis of phenanthro[9,10-d]imidazole derivative (DIPIP) which can exhibit the aggregation-induced emission (AIE) properties in aqueous solution, we achieved a sequential on-off-on switch for Ag⁺ and SCN^- with high selectivity and sensitivity. A remarkable fluorescence quenching effect of Ag⁺ on the probe DIPIP was observed with 1:2 stoichiometry, Subsequently, the fluorescence intensity of in situ generated DIPIP-Ag⁺ ensemble was easily switched on after the interaction between Ag⁺ and SCN^-, which was attributed to the stronger affinity of SCN^- to capture Ag⁺. In particular, the extreme limits of detection (LOD) for Ag⁺ and SCN^- in standard solutions were as low as to be 74.5 nM and 7.8 nM, respectively. Furthermore, the probe DIPIP and the DIPIP-Ag⁺ ensemble could be used to detect Ag⁺ in the real water and SCN^- in smoker saliva samples, respectively. In addition, the sequential "on-off-on" fluorescence mode of DIPIP to Ag⁺ and SCN^- were also successfully applied in living HeLa cells.

Nitrogen, phosphorus and sulfur tri-doped carbon dots are specific and sensitive fluorescent probes for determination of chromium(VI) in water samples and in living cells

A rapid, sensitive, and selective fluorometric assay is described for the determination of chromium(VI) in real waters and living cells. The method is making use of nitrogen, phosphorus, and sulfur tri-doped carbon dots (NPS-CDs) which have absorption/emission maxima at 360/505 nm/nm. Cr(VI) has an absorption maximum at 350 nm and causes an inner filter effect (IFE) on the blue fluorescence of the NPS-CDs. The NPS-CDs were hydrothermally synthesized using p-aminobenzenesulfonic acid and tetrakis(hydroxymethyl)phosphonium chloride as precursors. The NPS-CDs were characterized by transmission electron microscopy, X-ray diffraction, and several spectroscopic methods. They are biocompatible and negligibly cytotoxic when tested with HeLa cells and MCF-7 cells even after 48 h of incubation. The NPS-CDs were used as fluorescent probes for Cr(VI). The detection limit is 0.23 μM (three times standard deviation versus slope), and the linear response covers the 1 to 500 μM chromate concentration range. The NPS-CDs were applied to the determination of Cr(VI) in real waters and living cells (HeLa and MCF-7) and gave satisfying results. Graphical abstractSchematic representation of hydrothermal synthesis of nitrogen, phosphorus, and sulfur tri-doped carbon dots (NPS-CDs) for Cr(VI) detection via inner filter effect (IFE). NPS-CDs were applied to the determination of Cr(VI) in living cells (HeLa and MCF-7) with satisfying results.

Highly selective antenna effect of graphene quantum dots (GQDs): A new fluorescent sensitizer for rare earth element terbium in aqueous media

This study focused on the fluorescence antenna-sensitizing effect of graphene quantum dots (GQDs) in a case on the detection of terbium ions. A simple one-step chemical oxidation method was applied for the preparation of GQDs starting from the regular multilayer graphene oxide (GO) via the refluxing in a concentrated mixture of strong acids. The as-prepared GQDs were further evaluated as a fluorescent sensitizer to the terbium ion. An expanded in-deep mechanism study on the fluorescence phenomena during the interaction of the as-prepared GQDs and REEs was made. The highly selective antenna effect of GQDs on one of REEs' aqueous media, which was terbium (III), was identified. The excited terbium ion emitted its long-living fluorescence based on its own characteristic line-typed f-f transition, contrasting to a undetectable fluorescence in a very poor quantum yield in its aqueous solution induced by water collisions. This study, in the first place, identified the significant sensitization effect of the as-prepared GQDs on the terbium ion in a high selectivity in aqueous media. The detectable linear range and the detection limit of the terbium ion was 0-30 × 10^-6 mol L^-1 (R² = 0.9960) of 0.3 × 10^-6 mol L^-1, respectively. The excitation wavelength and the optimal fluorescence wavelength were 230 nm 546 nm, respectively. Further material characterizations, involving XPS, FTIR, Raman and the Zeta potential, verified the important participation of carboxyl function groups on the as-prepared GQDs.

Fluorescence "Off-On" Probe for L-Cysteine Detection Based on Nitrogen Doped Carbon Dots

Herein, a simple and efficient fluorescence analysis method for L-Cysteine (L-Cys) was established. The method was based on the fluorescent "off-on" mode of nitrogen doped carbon dots (NCDs). The NCDs were prepared via a facile one-step solvothermal method. In the process of exploring the bio-functional application of these newly synthesized NCDs, we found these NCDs with rich functional groups exhibited excellent optical properties. In addition, these newly synthesized NCDs showed an excitation-dependent emissions photolumine-scent (PL) property and exhibited good performance in the detection of Fe³⁺ ions by quenching the blue emission fluorescence. Interestingly, the quenched fluorescence of NCDs was recovered with the addition of L-Cys, which provided a novel approach for L-Cys detection. The NCDs-based fluorescent "off-on" sensor has a wide linear detection range (0-100 μM), and a relatively low detection limits (0.35 μM) for L-Cys. This simple fluorescent "off-on" approach is, very sensitive and selective for L-Cys detection, which also provides a new insight on NCDs biosensor application.

Nucleolus-Targeted Red Emissive Carbon Dots with Polarity-Sensitive and Excitation-Independent Fluorescence Emission: High-Resolution Cell Imaging and in Vivo Tracking

Red-emitting carbon dots (CDs) have attracted tremendous attention due to their wide applications in areas including imaging, sensing, drug delivery, and cancer therapy. However, it is still highly challenging for red-emitting CDs to simultaneously achieve high quantum yields (QYs), nucleus targeting, and super-resolution fluorescence imaging (especially the stimulated emission depletion (STED) imaging). Here, it is found that the addition of varied metal ions during the hydrothermal treatment of p-phenylenediamine (pPDA) leads to the formation of fluorescent CDs with emission wavelengths up to 700 nm. Strikingly, although metal ions play a crucial role in the synthesis of CDs with varied QYs, they are absent in the formed CDs, that is, the obtained CDs are metal-free, and the metal ions play a role similar to a "catalyst" during the CD formation. Besides, using pPDA and nickel ions (Ni²⁺) as raw materials, we prepare Ni-pPCDs which have the highest QY and exhibit various excellent fluorescence properties including excitation-independent emission (at ∼605 nm), good photostability, polarity sensitivity, and ribonucleic acid responsiveness. In vitro and in vivo experiments demonstrate that Ni-pPCDs are highly biocompatible and can realize real-time, wash-free, and high-resolution imaging of cell nuclei and high-contrast imaging of tumor-bearing mice and zebrafish. In summary, the present work may hold great promise in the synthesis and applications of red emissive CDs.

Designing an "Off-On" Fluorescence Sensor Based on Cluster-Based CaII-Metal-Organic Frameworks for Detection of l-Cysteine in Biological Fluids

Recently, luminescent metal-organic framework (MOF) materials have attracted considerable attention in fluorescence sensing. In this essay, we prepared a new cluster-based Ca^II-MOFs {[Ca_1.5(μ₈-HL₁)(DMF)₂]·DMF}_n (1) with good water dispersibility, excellent photoluminescence properties (FL quantum yield of 20.37%) and great fluorescence stability. Further, it was employed to design as an "off-on" fluorescence sensor for sensitive detection of l-cysteine. This proposed strategy was that fluorescence of Ca^II-MOFs 1 was quenched for providing a low fluorescence background by the introduction of Pb²⁺ forming the Ca^II-MOFs 1/Pb²⁺ hybrid system. The quenching effect could be ascribed to the static quenching mechanism because of the formation of ground-state complexes and coordination interactions between the free carboxyl of H₄L₁ ligands of Ca^II-MOFs 1 and Pb²⁺. Then, with the addition of l-cysteine into the Ca^II-MOFs 1/Pb²⁺ hybrid system, the fluorescence signal was immediately restored. This result was because the Pb²⁺ was gradually released from the hybrid system by chelation interactions between the -SH groups of l-cysteine and Pb²⁺. This method received a relative wide linear range varying from 0.05 to 40 μM and a low detection limit of 15 nM for detection of l-cysteine. This proposed strategy was also successfully applied to detect l-cysteine in human serum samples with satisfactory recoveries from 95.9 to 101.5%.

Nitrogen atom free polythiophene derivative as an efficient chemosensor for highly selective and sensitive Cu2+ and Ag+ detection

A new nitrogen atom free polythiophene derivative bearing methoxy-ethoxy units of poly{3-[2-(2-methoxy-ethoxy)-ethoxy]-thiophene} (PM) was successfully synthesized by introducing multiple ether bonds on the thiophene unit. The special (ether bonds) coordination structure was constructed and these fluorescence characteristics of PM to metal ions detection were investigated. This polythiophene-based material displays a specific fluorescence quenching effect on Cu²⁺ and Ag⁺, and correspondingly emerges some color changes that are visible to the naked eyes. In addition, it even performs a low detection limit to Cu²⁺ for only 0.45 μM, which exhibits a higher selective detection to Cu²⁺ than other reported N-containing chemosenors. These discoveries are helpful to indicate an original aspect for development on nitrogen atom free polythiophene-based fluorescent-sensing materials.

Nitrogen, Cobalt Co-doped Fluorescent Magnetic Carbon Dots as Ratiometric Fluorescent Probes for Cholesterol and Uric Acid in Human Blood Serum

Detection of cholesterol and uric acid biomarkers is of great importance for clinical diagnosis of several serious diseases correlated with their variations in human blood serum. In this study, a new kind of well selective and highly sensitive ratiometric fluorescent probe for cholesterol and uric acid determination in human blood serum was innovatively developed on the basis of the inner filter effect (IFE) process of nitrogen, cobalt co-doped carbon dots (N,Co-CDs) with 2,3-diaminophenazine (DAP). DAP was the oxidative product during the oxidation reaction between o-phenylenediamine and H2O2. Fluorescent magnetic N,Co-CDs possessing blue emission and magnetic property were prepared through a facile one-pot hydrothermal strategy by using citric acid, diethylenetriamine, and cobalt(II) chloride hexahydrate as precursors. N,Co-CDs exhibited good ferromagnetic property and excellent optical properties even in extremely harsh environmental conditions, implying the huge potential applications of such N,Co-CDs in biological areas. On the basis of the IFE process between N,Co-CDs and DAP, N,Co-CDs were applied to establish ratiometric fluorescent probes for the indirect detection of cholesterol and uric acid that participated in enzyme-catalyzed H2O2-generation reactions. The established IFE-based fluorescent probes exhibited relatively low detection limits of 3.6 nM for cholesterol and 3.4 nM for uric acid, respectively. The fluorescent probe was successfully utilized for the determination of cholesterol and uric acid in human blood serum with satisfying results, which provided an informed perspective on the applications of such doped CDs to explore the specific and sensitive nanoprobe in disease diagnoses and clinical therapy.

A fluorometric clenbuterol immunoassay using sulfur and nitrogen doped carbon quantum dots

A fluorometric clenbuterol immunoassay is described that uses S- and N-co-doped carbon quantum dots as the fluorescent probe. Strongly fluorescent S/N-doped carbon quantum dots (S/N-CDs) were synthesized by hydrothermal method using fructose as the carbon precursor and L-cysteine as S/N sources. The S/N-CDs were characterized by transmission electron microscopy, energy dispersive spectroscopy and Fourier transform infrared spectroscopy (FTIR). Under 350 nm photoexcitation, they display strong purple fluorescence with an emission peak at 405 nm. In pH 4.0 solution, the amino groups (confirmed by FTIR) on the carbon quantum dots were coupled to clenbuterol antibody (Ab) by amine-amine coupling reaction to quench the fluorescence. If clenbuterol (Clen) is added, it binds to the Ab to generate a stable Ab-Clen immunocomplex and free S/N-CD. This causes the fluorescence of nanoprobe to be restored. The fluorescence of the system increases linearly in the 0.07-1.7 ng·mL^-1 Clen concentration range. The probe of type S/N₄-CD displays the best sensitivity. The detection limit is 23 pg·mL^-1. Graphical abstract Schematic presentation of clenbuterol fluorometric immunoassay using sulfur and nitrogen doped carbon quantum dots.

A novel dithiourea-appended naphthalimide "on-off" fluorescent probe for detecting Hg2+ and Ag+ and its application in cell imaging

An effective dithiourea-appended 1,8-naphthalimide fluorescent probe was designed and synthesized. This probe could recognize Hg²⁺ and Ag⁺ sensitively and selectively in neutral and alkaline conditions. Moreover, the probe detected Hg²⁺ alone at pH between 2 and 6. The sensing ability of the probe was explored by UV-vis, fluorescence, FTIR and ¹H NMR spectroscopy. The probe was quenched by Hg²⁺ and Ag⁺ with 1:1 binding ratios in MeCN/H₂O (4/1, v/v) mixed solution with binding constants of 3.76 × 10⁴ L mol^-1 and 2.47 × 10⁴ L mol^-1, respectively. The linear concentration ranges for Hg²⁺ and Ag⁺ were 0-17 μmol L^-1 and 0-24 μmol L^-1 with detection limits of 0.83 μmol L^-1 and 1.20 μmol L^-1, respectively, which allowed for the quantitative determination of Hg²⁺ and Ag⁺. The new probe, 3a, was successfully applied to the fluorescence imaging of Hg²⁺ and Ag⁺ in HepG2 cells, demonstrating its potential application in biological science. Moreover, 3a was used to measure Hg²⁺ and Ag⁺ in tap water, drinking water and ultrapure water samples. The recoveries of Hg²⁺ and Ag⁺ in water samples were 96-99% and 98-103%, respectively. Therefore, the proposed method showed promising perspectives for its application, aimed at detecting Hg²⁺ and Ag⁺ in fluorescence imaging and real water samples.

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.

Synthesis of novel cationic carbon dots and application to quantitative detection of K+ in human serum samples

Novel cationic carbon dots were synthesized in a simple way and applied to detect K⁺ in human serum samples with ultra-high sensitivity.

S,N-Co-doped carbon nanoparticles with high quantum yield for metal ion detection, IMP logic gates and bioimaging applications

S,N-CNPs with high quantum yield exhibited potential multiple applications including metal ion detection, IMP logic gate fabrication and bioimaging.