Carbon Nitride Dots Research Articles

Influence of Carbon-Nitride Dot-Emitting Species and Evolution on Fluorescence-Based Sensing and Differentiation.

Carbon dots have attracted widespread interest for sensing applications based on their low cost, ease of synthesis, and robust optical properties. We investigate structure-function evolution on multiemitter fluorescence patterns for model carbon-nitride dots (CNDs) and their implications on trace-level sensing. Hydrothermally synthesized CNDs with different reaction times were used to determine how specific functionalities and their corresponding fluorescence signatures respond upon the addition of trace-level analytes. Archetype explosives molecules were chosen as a testbed due to similarities in substituent groups or inductive properties (i.e., electron withdrawing), and solution-based assays were performed using ratiometric fluorescence excitation-emission mapping (EEM). Analyte-specific quenching and enhancement responses were observed in EEM landscapes that varied with the CND reaction time. We then used self-organizing map models to examine EEM feature clustering with specific analytes. The results reveal that interactions between carbon-nitride frameworks and molecular-like species dictate response characteristics that may be harnessed to tailor sensor development for specific applications.

Localized states in carbon dots: Structural and optical investigation of three systems with varying degrees of carbonization

Carbon dots (CDs) have been widely researched in recent years, mainly to investigate their potential in various applications such as drug delivery, photocatalysis, and sensing. However, understanding of their fundamental properties, including physical and electronic structure, has lagged behind their development in applied sciences. To address this, it is necessary to use novel methods which go beyond the current level of characterization in the literature. In this work, we utilize time of flight-secondary ion mass spectrometry (ToF-SIMS) to generate specific knowledge of the structural components of three CDs generated in our lab. This work revealed that black CDs (B-CDs) possess a highly carbonic structure with nitrogen and oxygen functionalization throughout the particle structure. Carbon nitride dots (CNDs) possess some of these same carbonic structures, but also show the presence of more organic structures which would be expected through a bottom-up approach. In terms of carbonization, CNDs lie between B-CDs and the third sample, yellow-CDs (Y-CDs). Y-CDs are believed to be almost completely polymeric/organic in structure and the groups detected through this mass analysis supports this idea. The structural information from ToF-SIMS is compared with other structural techniques. Additionally, the optical properties of CDs before and after oxidation and reduction are used to craft a proposed photoluminescence (PL) mechanism for each system. The analysis contained herein enables further understanding of the structure of these three samples, and the attained understanding of the surface structure is particularly important for future biomedical applications.

Carbon nitride dots do not impair the growth, development, and telomere length of tadpoles

Carbon nanoparticles, or carbon dots, can have many beneficial uses. However, we must consider whether they may have any potential negative side effects on wildlife or the ecosystem when these particles end up in wastewater. Early development stages of amphibians are particularly sensitive to contaminants, and exposure to carbon dots could disrupt their development and cause morbidity or death. Past studies have investigated short-term exposure to certain types of nanoparticles, but if these particles get into wastewater exposure may not be short term. Therefore, we tested whether chronic exposure to different concentrations of carbon dots affects the growth, metamorphosis, and telomere length of Cuban tree frog (Osteopilus septentrionalis) tadpoles. We exposed 12 groups of five tadpoles each to different concentrations of carbon dots and a control for three months and tracked survival, growth and metamorphosis. We used carbon nitride dots approximately 2 nm in size at concentrations of 0.01 mg/ml and 0.02 mg/ml, known to interrupt development in zebrafish embryos. After three months, we measured telomere length from tissue samples. We found no difference in tadpole survivorship, growth, development rate, or telomere length among any of the groups, suggesting that carbon dots at these concentrations do not disrupt tadpole development.

Computational Investigation of Interactions between Carbon Nitride Dots and Doxorubicin.

The study of carbon dots is one of the frontiers of materials science due to their great structural and chemical complexity. These issues have slowed down the production of solid models that are able to describe the chemical and physical features of carbon dots. Recently, several studies have started to resolve this challenge by producing the first structural-based interpretation of several kinds of carbon dots, such as graphene and polymeric ones. Furthermore, carbon nitride dot models established their structures as being formed by heptazine and oxidized graphene layers. These advancements allowed us to study their interaction with key bioactive molecules, producing the first computational studies on this matter. In this work, we modelled the structures of carbon nitride dots and their interaction with an anticancer molecule (Doxorubicin) using semi-empirical methods, evaluating both geometrical and energetic parameters.

Engineering the Surface Chemistry and Morphology of Polymeric Carbon Nitrides Towards Greener Heterogeneous Catalysts for Biodiesel Synthesis.

Biodiesel remains one of the most promising alternatives to replace fossil fuel-derived petrodiesel. Nonetheless, conventional biodiesel synthesis relies on homogeneous alkali-based catalysts that involve long and tedious purification steps , increasing biodiesel production costs. Heterogeneous catalysts have emerged as promising alternatives to circumvent these drawbacks, as they can easily be recovered and reused. Herein, polymeric carbon nitride dots and nanosheets are synthesized through a solid-phase reaction between urea and sodium citrate. Their morphology and surface chemistry are tuned by varying the precursor's ratio, and the materials are investigated as catalysts in the transesterification reaction of canola oil to biodiesel. A conversion of > 98% is achieved using a 5 wt% catalyst loading, oil to methanol ratio of 1:36 at 90 °C for 4 h, with the performance maintained over at least five reuse cycles. In addition, the effect of the transesterification reaction parameters on the reaction kinetics is evaluated, which follows a pseudo-first-order (PFO) regime. Combined with a deep understanding of the catalyst's surface, these results have allowed us to propose a reaction mechanism similar to the one observed for homogenous alkali catalysts. These carbon nitride-based nanoparticles offer a metal-free and cost-effective alternative to conventional homogeneous and metal-based heterogeneous catalysts.

G-C3N4 Dots Decorated with Hetaerolite: Visible-Light Photocatalyst for Degradation of Organic Contaminants

In this paper, a facile hydrothermal approach was used to integrate graphitic carbon nitride dots (CNDs) with hetaerolite (ZnMn2O4) at different weight percentages. The morphology, microstructure, texture, electronic, phase composition, and electrochemical properties were identified by field emission scanning electron microscopy (FESEM), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), Fourier transform-infrared (FT-IR), ultraviolet-visible diffuse reflectance (UV-vis DR), photoluminescence (PL), electrochemical impedance spectroscopy (EIS), Brunauer–Emmett–Teller (BET), Barrett–Joyner–Halenda (BJH), and photocurrent density. The results of XRD, FT-IR, EDX, and XPS analyses confirmed the synthesis of CNDs/ZnMn2O4 (20%) nanocomposite. As per PL, EIS, and photocurrent outcomes, the binary CNDs/ZnMn2O4 nanocomposite revealed superior features for interfacial transferring of charge carriers. The developed p–n heterojunction at the interface of CNDs and ZnMn2O4 nanoparticles partaken a significant role in the impressive charge segregation and migration. The binary nanocomposites were employed for the photodegradation of several dye pollutants, including rhodamine B (RhB), fuchsin, malachite green (MG), and methylene blue (MB) at visible wavelengths. Amongst the fabricated photocatalysts, the CNDs/ZnMn2O4 (20%) nanocomposite gave rise to about 98% RhB degradation efficiency within 45 min with the rate constant of 747 × 10−4 min−1, which was 66.5-, 3.44-, and 2.72-fold superior to the activities of CN, CNDs, and ZnMn2O4 photocatalysts, respectively. The impressive photodegradation performance of this nanocomposite was not only associated with the capacity for impressive visible-light absorption and boosted separation and transport of charge carriers, but also with its large surface area.

Dual functional carbon nitride dots as electrochemical sensor and anticancer agent with chemotherapic and photodynamic effect

We report the facile single-step synthesis of carbon nitride dots (CND) from l-ascorbic acid and urea as precursors. The as-synthesized carbon dots were water-soluble, displaying green fluorescence in UV light with a high quantum yield. Electrochemical studies manifest carbon nitride dots' excellent stability, sensitivity, and selectivity for mercuric ions and drug tetracycline detection. The former and latter's detection limit is 0.055 µM and 0.18 µM, respectively. Furthermore, cytotoxic studies with the carbon nitride dots exposed its selective toxicity towards cancer cells, which steered anticancer studies on B16 murine melanoma cells. These non-functionalized carbon nitride dots could induce cell death by cell apoptosis derived from chemotherapic and photodynamic effects.

One-pot synthesized multifunctional carbon nitride dots for fluorescent sensing, bioimaging, and selective cytotoxic effect on cancer cells

Heavy metals are one of the significant contributors to environmental pollution; they can occur naturally or through anthropogenic activities. On the other hand, antibiotics are emerging contaminants that can pollute water bodies. In the present work, versatile metal-free oxygen-doped carbon nitrides dots (O-GCNQD) having multiple applications like rapid fluorescent sensing of heavy metal mercury (Hg2+), antibiotic tetracycline (TC), in-vitro cellular imaging, and selective cytotoxicity for cancerous cells have been developed. In the first part of the work, the intrinsic property exhibited by O-GCNQDs is used in the selective and sensitive sensing of Hg2+ and tetracycline. Additionally, iodide ion (I−) sensitivity is employed to reverse fluorescence quenched by Hg2+ inducing ‘on-off’ fluorescence. The metal and drug detection limit was 250 nM and 410 nM, respectively. The sensor could sense more than 98.7 % of respective metal ions and drug molecules in spiked actual water samples. There is a lot of study on carbon dots (CD) in nanomedicine, particularly in imaging and drug administration. Still, there is less focus on its intracellular activity and possible anticancer processes. So in the second part, the biological applications of O-GCNQDs are explored. Their bright green fluorescence in long UV and biocompatibility were investigated for imaging of cancer cells. The cytotoxic studies showed the carbon dots have exceptional selective toxicity towards cancer B16murine melanomacells compared to fibroblast cells. The anticancer studies also reveal that our carbon dots could induce cell apoptosis at lower concentrations without external stimuli like light or heat.

Room Temperature Phosphorescence of Chlorine Doped Carbon Nitride Dots.

Metal free room temperature phosphorescent materials have been the subject of considerable attention due to their potential applications in optoelectronic devices sensing, and security and safety signage. This study discusses how efficient fluorescent and phosphorescent chlorine doped carbon nitride dots (Cl-CNDs) were prepared by thermal treatment of guanidine hydrochloride. The Cl-CNDs prepared were characterized by field emission scanning electron microscope, dynamic light scattering, PXRD, EDX, Thermo gravimetric analysis, FT-IR, and UV-Visible spectroscopy. The Cl-CNDs exhibit a long phosphorescence lifetime of 657 ms and the phosphorescence quantum yield was found to be 2.32% upon being excited at 360 nm in ambient conditions. Formation of compact coreparticles via condensation along with hydrogen bonding of Cl-CNDs by its functional groups facilitate intersystem crossing and stabilizes the triplet states, favoring room temperature phosphorescence. The cost effective preparation and tunable optical properties of Cl-CNDs may find applications in security encryption and optoelectronic devices.

Structure-activity relationship of carbon nitride dots in inhibiting Tau aggregation

Due to the numerous failed clinical trials of anti-amyloid drugs, microtubule associated protein tau (MAPT) now stands out as one of the most promising targets for AD therapy. In this study, we report for the first time the structure-dependent MAPT aggregation inhibition of carbon nitride dots (CNDs). CNDs have exhibited great promise as a potential treatment of Alzheimer's disease (AD) by inhibiting the aggregation of MAPT. In order to elucidate its structure-activity relationship, CNDs were separated via column chromatography and five fractions with different structures were obtained that were characterized by multiple spectroscopy methods. The increase of surface hydrophilic functional groups is consistent with the increase of polarity from fraction 1 to 5. Particle sizes (1–2 nm) and zeta potentials (∼-20 mV) are similar among five fractions. With the increase of polarity from fraction 1 to 5, their MAPT aggregation inhibition capacity was weakened. This suggests hydrophobic interactions between CNDs and MAPT, validated via molecular dynamics simulations. With a zebrafish blood-brain barrier (BBB) model, CNDs were observed to cross the BBB through passive diffusion. CNDs were also found to inhibit the generation of multiple reactive oxygen species, which is an important contributor to AD pathogenesis.

Drug delivery of memantine with carbon dots for Alzheimer’s disease: blood–brain barrier penetration and inhibition of tau aggregation

Neurofibrillary tangle, composed of aggregated tau protein, is a pathological hallmark of Alzheimer’s disease (AD). The inhibition of tau aggregation is therefore an important direction for AD drug discovery. In this work, we explored the efficacy of two types of carbon dots in targeting tau aggregation, as versatile nano-carriers for the development of carbon dots (CDs)-based AD therapy. We carried out synthesis, biophysical and biochemical characterizations of two types of CDs, namely, carbon nitride dots (CNDs) and black carbon dots (B-CDs). CDs, which are biocompatible and non-toxic, were successfully conjugated with memantine hydrochloride (MH) through EDC/NHS mediated amidation reactions followed by systematic characterizations using various biophysical techniques including UV–vis spectroscopy (UV–vis), photoluminescence (PL), Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), mass spectrometry (MS), Transmission electron microscopy (TEM) and atomic force microscopy (AFM). The surface diversity along with small particle sizes of CDs allowed facile delivery of MH across the blood–brain barrier (BBB), as demonstrated using a zebrafish in vivo model. The tau aggregation inhibition experiments were conducted using the thioflavin-T (ThT) assay to identify the most effective inhibitor. The kinetics and magnitude of tau aggregation were measured in the presence of CDs, which demonstrates that both B-CDs-MH and B-CDs alone are the most effective inhibitors of tau aggregation with IC50 values of 1.5 ± 0.3 and 1.6 ± 1.5 μg/mL, respectively. Taken together, our findings hold therapeutic significance to enhance the efficient delivery of MH to target AD pathology in the brain for improved efficacy.

An insight into embryogenesis interruption by carbon nitride dots: can they be nucleobase analogs?

The carbon nitride dot (CND) is an emerging carbon-based nanomaterial. It possesses rich surface functional moieties and a carbon nitride core. Spectroscopic data have demonstrated the analogy between CNDs and cytosine/uracil. Recently, it was found that CNDs could interrupt the normal embryogenesis of zebrafish. Modifying CNDs with various nucleobases, especially cytosine, further decreased embryo viability and increased deformities. Physicochemical property characterization demonstrated that adenine- and cytosine-incorporated CNDs are similar but different from guanine-, thymine- and uracil-incorporated CNDs in many properties, morphology, and structure. To investigate the embryogenesis interruption at the cellular level, bare and different nucleobase-incorporated CNDs were applied to normal and cancerous cell lines. A dose-dependent decline was observed in the viability of normal and cancerous cells incubated with cytosine-incorporated CNDs, which matched results from the zebrafish embryogenesis experiment. In addition, nucleobase-incorporated CNDs were observed to enter cell nuclei, demonstrating a possibility of CND-DNA interactions. CNDs modified by complementary nucleobases could bind each other via hydrogen bonds, which suggests nucleobase-incorporated CNDs can potentially bind the complementary nucleobases in a DNA double helix. Nonetheless, neither bare nor nucleobase-incorporated CNDs were observed to intervene in the amplification of the zebrafish polymerase-alpha 1 gene in quantitative polymerase chain reactions. Thus, in conclusion, the embryogenesis interruption by bare and nucleobase-incorporated CNDs might not be a consequence of CND-DNA interactions during DNA replication. Instead, CND-Ca2+ interactions offer a plausible mechanism that hindered cell proliferation and zebrafish embryogenesis originating from disturbed Ca2+ homeostasis by CNDs. Eventually, the hypothesis that raw or nucleobase-incorporated CNDs can be nucleobase analogs proved to be invalid.

Dual Functional Carbon Nitride Dots as Electrochemical Sensor and Anticancer Agent with Chemotherapic and Photodynamic Effect

Dual Functional Carbon Nitride Dots as Electrochemical Sensor and Anticancer Agent with Chemotherapic and Photodynamic Effect

Surface modification of carbon nitride dots by nanoarchitectonics for better drug loading and higher cancer selectivity.

Carbon Dots (CDs) have recently attracted a considerable amount of attention thanks to their well-documented biocompatibility, tunable photoluminescence, and excellent water solubility. However, CDs need further analysis before their potential use in clinical trials. Previously, we reported a new type of carbon nitride dot (CND) that displayed selective cancer uptake traits attributed to structural resemblances between CNDs and glutamine. Here, the effects of surface structural differences on the cellular uptake of CNDs are further investigated to understand their selective cancer cell uptake trend. Beyond enhanced drug loading on modified CNDs, our cytotoxicity, western blotting and bioimaging studies proposed that modified CNDs' cellular uptake mechanism is thoroughly linked with ASCT2 and LAT1 transporters. Therefore, CNDs have a promising trait of selective cancer cell targeting by utilizing highly expressed transporters on cancer cells. Additionally, drug loaded CNDs exhibited improved anti-cancer efficacies towards cancer cells along with good non-tumor biocompatibilities.

Drug Loading of Anthracycline Antibiotics on Carbon Dots Using Circular Dichroism Spectrometry.

Drug delivery systems using nanoparticles are currently in the panorama of nanomedicine studies. In oncology, chemotherapeutic regimens using anthracycline antibiotics rely on the dosage of treatments to minimize the severity of side effects on the patient. Therefore, even in targeted delivery systems it is of great importance to quantify the level of drug administrated for dosage and quality control of the treatment. Herein, as a feasible pathway to shed light on improving nano drug quantification procedures, we proposed a simple analytical protocol to quantify the anthracyclines loaded on our nonchiral carbon nitride dots (CNDs) with circular dichroism spectrometry (CD). The calibration curves from the linear relation between ellipticity and concentration of the anthracycline drugs followed by measurements on the CNDs conjugates were used in achieving the quantification technique which showed different drug loading for each anthracycline used such as daunorubicin, doxorubicin, and epirubicin.

Optimized Doxorubicin Chemotherapy for Diffuse Large B-cell Lymphoma Exploits Nanocarrier Delivery to Transferrin Receptors.

New treatments are needed to address persistent unmet clinical needs for diffuse large B-cell lymphoma (DLBCL). Overexpression of transferrin receptor 1 (TFR1) is common across cancer and permits cell-surface targeting of specific therapies in preclinical and clinical studies of various solid tumors. Here, we developed novel nanocarrier delivery of chemotherapy via TFR1-mediated endocytosis, assessing this target for the first time in DLBCL. Analysis of published datasets showed novel association of increased TFR1 expression with high-risk DLBCL cases. Carbon-nitride dots (CND) are emerging nanoparticles with excellent in vivo stability and distribution and are adaptable to covalent conjugation with multiple substrates. In vitro, linking doxorubicin (Dox) and transferrin (TF) to CND (CND-Dox-TF, CDT) was 10-100 times more potent than Dox against DLBCL cell lines. Gain- and loss-of-function studies and fluorescent confocal microscopy confirmed dependence of these effects on TFR1-mediated endocytosis. In contrast with previous therapeutics directly linking Dox and TF, cytotoxicity of CDT resulted from nuclear entry by Dox, promoting double-stranded DNA breaks and apoptosis. CDT proved safe to administer in vivo, and when incorporated into standard frontline chemoimmunotherapy in place of Dox, it improved overall survival by controlling patient-derived xenograft tumors with greatly reduced host toxicities. Nanocarrier-mediated Dox delivery to cell-surface TFR1, therefore, warrants optimization as a potential new therapeutic option in DLBCL. SIGNIFICANCE: Targeted nanoparticle delivery of doxorubicin chemotherapy via the TRF1 receptor presents a new opportunity against high-risk DLBCL tumors using potency and precision.

A deep investigation into the structure of carbon dots

Since their discovery, carbon dots (CDs) have been a promising nanomaterial in a variety of fields including nanomedicine. Despite their potential in this area, there are many obstacles to overcome for CDs to be approved for biomedical use. One major hindrance to CDs’ approval is related to their poorly defined structure. Herein a structural study of CDs is presented in order to rectify this shortcoming. The properties of three CDs which have significant promise in biomedical applications, black CDs (B-CDs), carbon nitride dots (CNDs), and yellow CDs (Y-CDs), are compared in order to develop a coherent structural model for each nanosystem. Absorption coefficients were measured for each system and this data gave insight on the level of disorder in each system. Furthermore, extensive structural characterization has been performed in order to derive structural information for each system. This data showed that B-CDs and CNDs are functionalized to a greater degree and are also more disordered and amorphous than Y-CDs. These techniques were used to develop a structural model consistent with the obtained data and what is known for carbonic nanostructures. These models can be used to analyze CD emission properties and to better understand the structure-property relationship in CDs.

Abstract PO-48: Cytotoxic mechanism of a novel transferrin receptor-targeting chemotherapeutic nanocarrier for use in diffuse large B-cell lymphoma

Abstract Diffuse large B-cell lymphoma (DLBCL), the most common hematologic malignancy, is an aggressive form of non-Hodgkin lymphoma. Approximately 60% of DLBCL patients achieve long-term disease-free survival from frontline R-CHOP (rituximab, cyclophosphamide, doxorubicin, vincristine, prednisone), but patients with relapsed or refractory disease have poor prognosis. Doxorubicin (Dox) remains the most active anti-lymphoma agent, but its use is limited by well-characterized toxicities, including potentially irreversible cardiac damage. Targeted and specific delivery of Dox to tumors to overcome these limitations has been an area of active research. Targeted delivery of Dox via the transferrin receptor (TFR1) has preclinical efficacy in solid malignancies but has yet to be explored in lymphoma. We have uncovered for the first time a significant association between TFR1 expression and poor prognosis in DLBCL. Carbon-nitride dots (CNDs) are third-generation nanocarriers with inherent photoluminescence, which are easily conjugated with a wide variety of substrates. We conjugated Dox and transferrin (TF), the ligand for TFR1, to CNDs to develop CND-Dox-TF (CDT). CDT is uniquely designed to enhance Dox delivery to TFR1-expressing DLBCL tumors while limiting effects on nonmalignant tissues. BJAB and Farage cell lines treated with CDT for 24 hours underwent apoptosis at a significantly lower concentration when compared to Dox (50 nM vs. 1000 nM). Overall, CDT was 1-2 Log10 more potent than Dox against DLBCL cell lines. Co-incubation with 250 uM of antagonist holo-transferrin significantly decreased BJAB and Farage sensitivity to CDT, confirming activity through TFR1. Confocal microscopy of BJAB cells incubated up to 24 hours with 250 nM Dox and 30 nM CDT reveled enhanced nuclear colocalization of Dox at a significantly lower concentration. Prior dose-finding experiments in non-tumor bearing mice identified a CDT safe working dose of 33.0 mg/kg containing 16% moles of Dox in comparison to Dox maximum-tolerated dose (MTD) 3.3 mg/kg. We engrafted 2 groups of 10 NSG mice with a Dox-sensitive high-TFR1 expressing patient-derived xenograft (PDX) tumor. Mice were dosed with CDT and Dox on day 0, 14, and 24. CDT demonstrated similar anti-lymphoma efficacy with reduced toxicity: CDT-treated mice displayed no significant decline in body weight, which is characteristic and was observed following each single-agent Dox treatment. Histology analyses revealed little to no obvious damage to CDT-treated nonmalignant tissues, including myocardium. With a working dose of CDT identified, we now have under way clinically relevant R-CHOP vs. R-nanoCHOP (CDT substituted for Dox) assessments in our PDX mouse model. Capitalizing on the unique design, we expect to observe improved anti-lymphoma efficacy, with decreased toxicities and an improvement in overall survival. In sum, we provide mechanistic insight for novel DLBCL nano-chemotherapy and illustrate preclinical efficacy for a promising new therapeutic approach. Citation Format: Artavazd Arumov, Piumi Y. Liyanage, Asaad Trabolsi, Evan R. Roberts, Braulio Ferreira, Daniel Bilbao, Roger M. LeBlanc, Jonathan H. Schatz. Cytotoxic mechanism of a novel transferrin receptor-targeting chemotherapeutic nanocarrier for use in diffuse large B-cell lymphoma [abstract]. In: Proceedings of the AACR Virtual Meeting: Advances in Malignant Lymphoma; 2020 Aug 17-19. Philadelphia (PA): AACR; Blood Cancer Discov 2020;1(3_Suppl):Abstract nr PO-48.

Gemcitabine-carbon nitride dots as nanocarrier to target specifically pediatric glioma tumors

The article discusses a study to target-specific gemcitabine delivery to pediatric glioblastoma tumors across the blood-brain barrier (BBB) using carbon nitride dots (CNDs) as a nanocarrier . CNDs can be identified as a third-generation novel nano dot material after semiconductor metal quantum dots and carbon dots. Similar to its predecessor carbon dots, CNDs have excellent stability, water dispersibility and non-toxic properties in comparison to the metal quantum dots.

A new strategy for determination of trace PO43− using CNDAu as resonance Rayleigh scattering and fluorescence dual-mode probe

The hydrophilic carbon nitride dots (CNDs) and gold-carbon nitride dots (CNDAu) were prepared by microwave digestion instrument with citric acid, thiourea and chloroauric acid as precursors. The morphology and properties of the nanomaterial were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), resonance Rayleigh scattering (RRS), fluorescence (FL), Fourier transform infrared spectrometer (FTIR) and particle size analysis. The acidified ammonium molybdate and CNDs are combined to form complex by intermolecular forces, the system's fluorescence and RRS signals are decreased. After adding PO43−, the ammonium molybdate and PO43− form stable phosphomolybdate heteropoly acid (PMo) with hydrophobic properties, the PMo particles are separated from CNDs, and the released CNDs lead to the increase of FL signal. At the same time, PMo particles are simultaneously aggregate forming large particles, which are manifested by an increase in the RRS signal. We can establish a sensitive, rapid, selective method for the determination of trace PO43− by combining RRS and FL signals. Within a certain range, the signals of the two methods show a linear relationship with the concentration of PO43−. The linear range of dual-mode determination method is 1.4–21 nmol/L PO43−, with a detection limit of 0.60 nmol/L.