A label-free nano-probe for sequential and quantitative determination of Cr(VI) and ascorbic acid in real samples based on S and N dual-doped carbon dots

A fluorescent sulfur and nitrogen dual-doped carbon dots (S,N-CDs) was prepared by a simple and one-step acid-base neutralization and exothermic carbonization method. Hexavalent chromium (Cr(VI)) could effectively quench the fluorescence of S,N-CDs based on inner filter effect (IFE) and dynamic quenching, whereas ascorbic acid (AA) could recover the fluorescence of S,N-CDs/Cr(VI) because of IFE weakening. So an "on-off-on" and label-free nano-probe consecutive determination of Cr(VI) and AA was constructed. This nano-probe system demonstrated excellent selectivity and sensitivity to Cr(VI) and AA with linear range of 0.065-198 μmol/L (3.38-10,296 μg/L) and 6.6-892 μmol/L (1.16-157 mg/L), respectively. Meanwhile, the as-prepared S,N-CDs possess low toxicity and could be used for multi-color cell imaging in SMMC 7721 cells. More importantly, this nano-probe was successfully employed for detection of Cr(VI) in tap water and AA in food samples. In view of its simple detection condition, rapid response, wide linear range, low detection limit and inexpensive instrument, the as-constructed nano-probe system could have a wide range of potential application, including water quality monitoring and evaluation, food inspection and testing and biomedical analysis.

The Fluorescent Quenching Mechanism of N and S Co-Doped Graphene Quantum Dots with Fe3+ and Hg2+ Ions and Their Application as a Novel Fluorescent Sensor

The fluorescence intensity of N, S co-doped graphene quantum dots (N, S-GQDs) can be quenched by Fe3+ and Hg2+. Density functional theory (DFT) simulation and experimental studies indicate that the fluorescence quenching mechanisms for Fe3+ and Hg2+ detection are mainly attributed to the inner filter effect (IFE) and dynamic quenching process, respectively. The electronegativity difference between C and doped atoms (N, S) in favor to introduce negative charge sites on the surface of N, S-GQDs leads to charge redistribution. Those negative charge sites facilitate the adsorption of cations on the N, S-GQDs' surface. Atomic population analysis results show that some charge transfer from Fe3+ and Hg2+ to N, S-GQDs, which relate to the fluorescent quenching of N, S-GQDs. In addition, negative adsorption energy indicates the adsorption of Hg2+ and Fe2+ is energetically favorable, which also contributes to the adsorption of quencher ions. Blue fluorescent N, S-GQDs were synthesized by a facile one-pot hydrothermal treatment. Fluorescent lifetime and UV-vis measurements further validate the fluorescent quenching mechanism is related to the electron transfer dynamic quenching and IFE quenching. The as-synthesized N, S-GQDs were applied as a fluorescent probe for Fe3+ and Hg2+ detection. Results indicate that N, S-GQDs have good sensitivity and selectivity on Fe3+ and Hg2+ with a detection limit as low as 2.88 and 0.27 nM, respectively.

Highly luminescent N-doped carbon dots from black soya beans for free radical scavenging, Fe3+ sensing and cellular imaging

The novel N doped carbon dots (N-CDs) were readily fabricated through one-step pyrolysis method from black soya beans. The obtained N-CDs possessed excellent photoluminescence properties with quantum yield of 38.7 ± 0.64% and dual responsive properties towards free radical and Fe3+. The N-CDs exhibited favorable radical scavenging activity (RSA) against 1,1-diphenyl-2-picrylhydrazyl (DPPH) and superoxide anion radicals. Fe3+ could induce photoluminescence quenching of N-CDs through static quenching characteristics. The possible quenching mechanism was presented. Combining with negligible toxicity and preferable biocompatibility, the N-CDs were extended to imaging intracellular Fe3+. As an attractive candidate, the N-CDs demonstrated a great potential in free radical scavenging, sensing and cellular imaging.

Green Synthesis of Fluorescent Carbon Dots from Gynostemma for Bioimaging and Antioxidant in Zebrafish

Fluorescent carbon dots (CDs) have been synthesized via the calcination method using natural gynostemma as the precursor, without any toxic ingredients or surface passivation chemicals. CDs have a narrow size distribution, and the mean particle size is about 2.5 nm. CDs exhibit good water dispersibility and can emit intense blue fluorescence under 365 nm UV light in an aqueous solution, which can be stable in different conditions. The biotoxicity of CDs on the embryonic development of zebrafish is evaluated, the hatch rate and survival rate of embryos are around 90%, and the malformation rate is less than 10%. Because of the excellent fluorescence stability and biocompatibility, CDs can be used in zebrafish for bioimaging. In addition, the antioxidative stress property of CDs is investigated both in vitro and in vivo, and the presence of CDs can promote the mRNA expression of related genes to encode more antioxidant proteins in zebrafish. Therefore, fluorescent CDs would be a potential candidate for bioimaging and treating diseases caused by excessive oxidation damage, such as cancer, senility, and other diseases associated with aging.

Nitrogen and phosphorus doped polymer carbon dots as a sensitive cellular mapping probe of nitrite

Nitrite (NO₂ ^-) is one of the important pollutants in food and the environment, which can seriously endanger the health of human beings. Therefore, detecting nitrite in food, environmental and biological samples is very significant for health monitoring. Herein, polymer carbon dots (PCDs) doped with nitrogen and phosphorus were prepared by polymerization of ascorbic acid (AA) and polyethylenimine (PEI) with phosphoric acid, and exhibited excellent stability, adjustable fluorescence emissions and good biocompatibility. It was found that the PCDs presented a sensitive response to nitrite (NO₂ ^-), and they were successfully applied for NO₂ ^- analysis in water and milk samples, and the dynamic monitoring of nitrite entry into Hep-2 cells.

One-pot synthesis of dual carbon dots using only an N and S co-existed dopant for fluorescence detection of Ag. SPECTROCHIMICA ACTA. PART A, MOLECULAR AND BIOMOLECULAR SPECTROSCOPY 2019;208:162-171. [PMID: 30312843 DOI: 10.1016/j.saa.2018.10.004]

Luminescent carbon-based nanoparticles, named often as carbon dots (CDs), were synthesized from citric acid (CA) and guanidine thiocyanate (GITC) via an N and S co-doped hydrothermal procedure. In the present structure characterization, N and S elements could be sufficiently doped by means of the heteroatom or the functional groups bonded on the surface of CDs. The as-prepared CDs solution showed blue color fluorescence under ultraviolet excitation, yet the PL spectra exhibited a repetitive emission process from excitation-independent to excitation-dependent. In view of the triexponential feature of fluorescence lifetimes of CDs, one possibility was proposed to be co-existence of two types of CDs with different surface states. Additionally, the as-prepared CDs were used as a sensing probe for the detection of Ag⁺ taking into consideration of the possible interactions between Ag⁺ and various fluorophores attached to the CD surface. As expected, the changes of fluorescence intensities were linearly proportional to the different concentration ranges of Ag⁺, which suggests the complex nature of the quenching mechanism. And for the first time, the SCN group was found to accelerate the quenching of CDs towards Ag⁺, promising a new approach for efficient detection of Ag⁺ for the application in industrial pollutants.

A di-functional and label-free carbon-based chem-nanosensor for real-time monitoring of pH fluctuation and quantitative determining of Curcumin

A nitrogen and sulfur dual-doped carbon nanodots (N,S-CNDs) sample was fabricated by an one-step hydrothermal treatment of acid fuchsin. The obtained N,S-CNDs possess yellow fluorescent, excellent water solubility, high fluorescence stability and religious biocompatibility, which can be used as a di-functional and label-free chem-nanosensor for the determination of pH and curcumin (Cur). When the pH is decreased from 8.0 to 4.4, the N,S-CNDs reveals an extraordinary emission escalation at emission wavelength (λ_em) of 543 nm, and the pK_a value of the N,S-CNDs was calculated as 6.06. The N,S-CNDs displays a favourable linear relationship in the physiological pH range of 5.0-7.4, which is meaningful for the research of near-neutral cytosolic pH. Furthermore, the laser scanning confocal microscopic images of intracellular distribution and the determination of pH in HeLa cells were successfully carried out, implying that the N,S-CNDs possess excellent cell membrane permeability and are capable of being further applied to real-time pH fluctuations monitoring in live cells with negligible autofluorescence. More importantly, the fluorescence of N,S-CNDs may be dramatically quenched by Cur via a combination of electrostatic and hydrogen-bond interaction and fluorescence inner filter effect (FIFE). The limit of detection is as low as 81 nmol/L Cur, and the linearity range is 0.5-20 μmol/L Cur. Ultimately, a satisfactory result was obtained when applying the as-constructed fluorescent chem-nanosensing system for the analyses of Cur in practical samples.

Photoluminescence enhancement via microwave irradiation of carbon quantum dots derived from solvothermal synthesis of l-arginine

Photoluminescence enhancement of carbon quantum dots was achieved via solvothermal synthesis followed by microwave irradiation.

Facile synthesis of orange fluorescence carbon dots with excitation independent emission for pH sensing and cellular imaging

High-efficient orange fluorescence nitrogen-doped carbon dots (N-CDs) were facilely prepared from P-phenylenediamine as a precursor via hydrothermal method. The as-prepared N-CDs with an average diameter of 3.65 nm displayed excitation-independent emission at 590 nm. The N-CDs demonstrated a remarkable fluorescence enhancement behavior with the increase of pH. A sigmoidal curve was well fitted using BiDoseResp equation with pK_a1 3.57 and pK_a2 6.01, which can be ascribed to the unique surface properties of N-CDs. Two-segment linear ranges of 2.6-4.6 and 5.0-6.8 broaden the response range to pH of the orange-emission N-CDs to some extent. The confocal fluorescent microscopic images of SMMC7721 cells were performed successfully, which demonstrating that N-CDs possess exceptional cell membrane permeability and can implement as biosensing platform to monitor pH fluctuations in living cells.

A Facile Synthesis of Highly Nitrogen-Doped Carbon Dots for Imaging and Detection in Biological Samples

A facile, green, and high-output hydrothermal synthesis was proposed for the fabrication of highly fluorescent nitrogen-doped carbon quantum dots (N-doped CDs). The nitrogen content in N-doped CDs reached 19.2% and demonstrated strong blue fluorescence emission was obtained with fluorescence quantum yield (QY) of up to 32.9%, which exhibit high fluorescence quantum yield, high photostability, and excellent biocompatibility. The N-doped CDs possess high photostability, low toxicity, and excellent biocompatibility, based on which the N-doped CDs were successfully applied as a fluorescence probe for cell imaging. Moreover, it was then successfully demonstrated for sensitive and selective detection of Fe3+ in serum.

Highly passivated phosphorous and nitrogen co-doped carbon quantum dots and fluorometric assay for detection of copper ions

Carbon quantum dots are becoming powerful fluorophore materials for metal ion analysis. Here, highly passivated green phosphorous and nitrogen co-doped carbon quantum dots (C-dots) were prepared using low-temperature carbonization route. Strong green fluorescence emission around 490 nm and excitation wavelength independent C-dots were obtained. Morphological, surface, and optical properties of the C-dots were characterized. Fluorescence emission of C-dots was quenched selectively by copper ions and restored by adding copper chelators, such as EDTA and sulfide ions. Thus, C-dots were successfully used for direct determination of copper ions. Detection limit as low as 1.5 nM (s/n = 3) was achieved for copper ions. Such a low detection limit is very significant for metal analysis using our proposed facile method and low-cost substrates. Experimental results showed that the prepared C-dots demonstrated high sensitivity and selectivity for Cu²⁺ ion detection and the method is robust and rugged. Graphical abstract ᅟ.

Facile preparation of bright orange fluorescent carbon dots and the constructed biosensing platform for the detection of pH in living cells

Long wavelength (i.e., orange- to red-light) fluorescence emission and functionality are critically longing for the development and applications of carbon dots (CDs) toward biosensor and bioimaging analysis. Herein, the N-doped carbon dots (N-CDs) with bright orange fluorescence emission at 592 nm were facilely synthesized via p-phenylenediamine as a carbon precursor by microwave method. The as-prepared N-CDs exhibit favorable biocompatibility, excellent water solubility, highly optical stabilities and display sensitive pH response behavior. When the pH is decreased from 9.45 to 2.45, its emission fluorescence intensity will be significantly enhanced. The pKa value of N-CDs is 5.80 and it shows linear response to the physiological pH range of 4.45-7.00. Moreover, the N-CDs also possess high selectivity of hydrogen ions over common metal ions and some bioactive molecules, excellent photostability and reversibility. Based on this, a fluorescence sensing platform is established for the detection of pH in the environment. The N-CDs were successfully used as the fluorescent probe for cellular imaging and applied to monitor pH fluctuations in live cells based on its biocompatibility and cell membrane permeability. It is also anticipated that the N-CDs are potential bio-nano-materials for real-time tracking of the intracellular pH especially under physiological conditions in the disease diagnosis, biosensing and biomedical fields.

Conversion of Carbon Dots from Fluorescence to Ultralong Room-Temperature Phosphorescence by Heating for Security Applications

Stimuli-responsive optical materials have received tremendous interest in the last several decades due to their numerous promising applications. Here, fluorescence emissive polymer carbon dots (F-CDs), prepared with a simple heating treatment from ethylenediamine and phosphoric acid, are found to produce unexpected ultralong room-temperature phosphorescence (URTP), which lasts for about 10 s with a lifetime of 1.39 s. This is the first example to achieve the conversion of a fluorescence material to URTP by means of an external heating stimulus. Further investigations reveal that the doping of N and P elements and self-immobilization of the excited triplet species are likely mainly responsible for the observed URTP after the heating treatment, due to the facilitation of the intersystem crossing and formation of more compact cores for effective intraparticle hydrogen bonds, respectively. Importantly, this study also demonstrates the potential for aqueous dispersion of the F-CDs as an advanced security ink for information encryption and anticounterfeiting; this is a feature that has not been reported before. This study is believed to open possibilities to extend stimuli-responsive optical materials to rarely exploited phosphorescence-relevant systems and applications, and also to provide a novel strategy to easily prepare URTP materials.

N,S,P Co-Doped Carbon Nanodot Fabricated from Waste Microorganism and Its Application for Label-Free Recognition of Manganese(VII) and l-Ascorbic Acid and AND Logic Gate Operation

A novel fluorescent probe based on N,S,P codoped carbon nanodots (N,S,P-CND_Sac) is very simple and quickly fabricated by a one-step hydrothermal pyrolysis of Saccharomyces cerevisiae and utilized for label-free and "on-off-on" sequential detection of manganese(VII) and l-ascorbic acid (l-AA). The fluorescence of N,S,P-CND_Sac can be effectively quenched by Mn(VII) based on an inner filter effect (IFE) and recovered upon the addition of l-AA due to the easy conversion of Mn(VII) to reduced states (i.e., Mn(IV), Mn(II), and Mn(0)) by l-AA. This probe exhibited favorable selectivity and sensitivity toward Mn(VII) and l-AA with detection limits of 50 nmol/L and 1.2 μmol/L, respectively. Simultaneously, an "AND" logic gate based on the as-fabricated N,S,P-CND_Sac has been constructed. Also, the as-proposed fluorescent probe was extended to detect Mn(VII) and l-AA in biosystems. Furthermore, the as-constructed fluorescent probe system was successfully applied to the analyses of Mn(VII) in tap water, Fenhe River water, and medicinal herb samples with satisfactory results. The proposed method is simple and easily accessible, demonstrating the great potential of N,S,P-CND_Sac in biosensing, disease diagnosis, cellular labeling, and environmental monitoring.

An "on-off-on" fluorescent nanoprobe for recognition of chromium(VI) and ascorbic acid based on phosphorus/nitrogen dual-doped carbon quantum dot

Chromium (VI) [Cr(VI)] is a harsh environmental contaminates and has been proved to be highly toxic, carcinogenic and mutagenic. Therefore, developing an inexpensive, good selective and highly sensitive nanoprobe for the detection of Cr(VI) is in urgent demand. Recently, the highly fluorescent carbon quantum dots (CQDs) have been successfully utilized as efficient fluorescent nanoprobes for the detection of ions, pH and molecular substances. In this work, an "on-off" fluorescence phosphorus/nitrogen dual-doped CQDs (PNCQDs) probe was developed for the determination of Cr(VI) based on inner filter effect (IFE). The proposed PNCQDs nanoprobe shows its distinct merits of simplicity, convenience, fast implementation, good selectivity and high sensitivity towards Cr(VI), allowing its potential application in the determination of Cr(VI) in environment and biosystem. In addition, the chelation effect of the functional groups in reductant and Cr(VI), and the easy-conversion of Cr(VI) to reduced states (i.e. Cr(III) and Cr(0)) by reductants makes the minimization of IFE with a concomitant recovery of PNCQDs fluorescence possible. Hence, the PNCQDs/Cr(VI) hybrid was used as an "off-on" fluorescence probe for sensing ascorbic acid (AA), which is a model reductant. For the detection of Cr(VI), the linear range and the limit of detection achieved were 1.5-30 μmol/L and 23 nmol/L, respectively. For the detection of AA, the linear range and the limit of detection obtained were 5.0-200 μmol/L and 1.35 μmol/L, respectively. The as-constructed "on-off-on" PNCQDs fluorescent nanoprobe was successfully applied for detecting Cr(VI) and AA in biosystem. Furthermore, the as-constructed fluorescent sensing system was successfully applied to the analyses of AA in fresh fruits and in commercial fruit juices with satisfactory results.

Formation of N, S-codoped fluorescent carbon dots from biomass and their application for the selective detection of mercury and iron ion

Biomass is regarded as an excellent candidate for the preparation of heteroatom-doped carbon nanomaterials. We have developed a simple and facile one-pot synthesis of nitrogen and sulfur codoped fluorescent carbon dots from pigeon feathers, egg and manure via the pyrolysis carbonization method. The as-prepared four PCDs have high fluorescence quantum yield about 24.87% (PCDs-f), 17.48% (PCDs-w), 16.34% (PCDs-y), 33.50% (PCDs-m), respectively, which is higher than the other carbon dots preparing from biomass. We found that the preparation of PCDs-m with pigeon manure has no favourable selectively with heavy metal ions. However, other PCDs exhibit highly sensitive and selective detection behavior of Hg²⁺/Fe³⁺ ions with a low detection limit of 10.3 and 60.9nM. They were applied to imaging of human umbilical vein endothelial cells, showing low cytotoxicity and good biocompatibility.

N-Doped carbon dots: green and efficient synthesis on a large-scale and their application in fluorescent pH sensing

A green and efficient anhydrous method was developed to synthesize nitrogen doped carbon dots (N-CDs) on a large-scale, and the N-CDs exhibited excellent reversible pH-sensitive property.

Nitrogen-doped carbon dots originating from unripe peach for fluorescent bioimaging and electrocatalytic oxygen reduction reaction

This paper reports the robust hydrothermal synthesis of nitrogen doped carbon dots (N-CDs) using the unripe fruit of Prunus persica (peach) as the carbon precursor and aqueous ammonia as the nitrogen source. The optical properties of synthesized N-CDs were characterized by ultraviolet visible (UV-Vis) and fluorescence spectroscopy techniques. The synthesized N-CDs were emitted blue light when excitated with a portable UV lamp. The materials with the optical properties were characterized further by high resolution transmission electron microscope (HRTEM), X-ray diffraction (XRD), Raman, Fourier transform infrared (FT-IR) and X-ray photoelectron spectroscopy (XPS). The mean size of the N-CDs was approximately 8nm, as calculated from the HRTEM image. The d-spacing of N-CDs, calculated using Bragg law, was approximately 0.21nm, which was consistent with the interlayer distance calculated from the HRTEM image. FT-IR spectroscopy and XPS revealed the presence of the phytoconstituents functionalities of peach fruit over the N-CDs surface and a high level of nitrogen doping on carbon dots (CDs) was confirmed by XPS studies. These results suggest that the unripe fruit extract of peach is an ideal candidate for the preparation of N-CDs. The resulting N-CDs showed excellent optical properties in water. The synthesized N-CDs exhibited a high fluorescence quantum yield and low cytotoxicity, and can be used as fluorescence imaging probes. In addition, the N-CDs were catalytically activite towards the oxygen reduction reaction (ORR). The N-CDs exhibited good catalytic activity in an alkaline medium (0.1M KOH) with a remarkable ORR of approximately 0.72V vs reversible hydrogen electrode (RHE), and O2 reduction follows mainly a 2 electron pathway by being reduced to hydrogen peroxide. The 2-electron reduction pathway is used in industry for H2O2 production.

Synthesis and formation mechanistic investigation of nitrogen-doped carbon dots with high quantum yields and yellowish-green fluorescence

Heteroatom doped carbon dots (CDs) have received increasing attention due to their unique properties and related applications. However, previously reported CDs generally show strong emission only in the blue-light region, thus restricting their further applications. And the fundamental investigation on the preparation process is always neglected. Herein, we have developed a simple and solvent-free synthetic strategy to fabricate nitrogen-doped CDs (N-CDs) from citric acid and dicyandiamide. The as-prepared N-CDs exhibited a uniform size distribution, strong yellowish-green fluorescence emission and a high quantum yield of 73.2%. The products obtained at different formation stages were detailedly characterized by transmission electron microscopy, X-ray diffraction spectrometer, X-ray photoelectron spectroscopy and UV absorbance spectroscopy. A possible formation mechanism has thus been proposed including dehydration, polymerization and carbonization. Furthermore, the N-CDs could serve as a facile and label-free probe for the detection of iron and fluorine ions with detection limits of 50 nmol L(-1) and 75 nmol L(-1), respectively.

Phosphorus and Nitrogen Dual-Doped Hollow Carbon Dot as a Nanocarrier for Doxorubicin Delivery and Biological Imaging

Innovative phosphorus and nitrogen dual-doped hollow carbon dots (PNHCDs) have been fabricated for anticancer drug delivery and biological imaging. The functional groups of PNHCDs are introduced by simply mixing glucose, 1,2-ethylenediamine, and concentrated phosphoric acid. This is an automatic method without external heat treatment to rapidly produce large quantities of PNHCDs, which avoid high temperature, complicated operations, and long reaction times. The as-prepared PNHCDs possess small particle size, hollow structure, and abundant phosphate/hydroxyl/pyridinic/pyrrolic-like N groups, endowing PNHCDs with fluorescent properties, improving the accuracy of PNHCDs as an optical monitoring code both in vitro and in vivo. The investigation of PNHCDs as an anticancer drug nanocarrier for doxorubicin (DOX) indicates a better antitumor efficacy than free DOX owing to its enhanced nuclear delivery in vitro and tumor accumulation in vivo, which results in highly effective tumor growth inhibition and improved targeted therapy for cancer in clinical medicine.

Multicolour fluorescent carbon nanoparticle probes for live cell imaging and dual palladium and mercury sensors

Carbon based nanomaterials are emerging as a desirable alternative to semiconducting quantum dots due to their unique optical properties and biocompatibility. The present study demonstrates the design and synthesis of highly fluorescent carbon nanoparticles (CNPs). The CNPs are investigated for their biocompatibility and henceforth successfully employed as promising multicolor bioimaging probes in A375 and DU145 cell lines. Furthermore, a "turn off" mode has been established for the detection of noble metal palladium (Pd²⁺) and heavy metal mercury (Hg²⁺) by quenching the fluorescence of CNPs. The CNP sensor responded to the detection of Pd²⁺ (5-100 μM) and Hg²⁺ (1-18 μM) in a wide range with the limit of detection (LOD) of 58 nM for Pd²⁺ and 100 nM for Hg²⁺. The CNP sensor was employed for the detection of Pd²⁺ and Hg²⁺ in real water samples and detection of leftover palladium catalysts in a model reaction system. Also, the CNPs were successfully employed as intracellular mercury and palladium sensors using confocal microscopy.

A hydrothermal reaction of an aqueous solution of BSA yields highly fluorescent N doped C-dots used for imaging of live mammalian cells

In the current study, we present a new and facile synthesis of N doped C-dots (N@C-dots) by hydrothermally reacting an aqueous solution of Bovine Serum Albumin (BSA) for imaging of live mammalian cells.

Effective synthesis of highly fluorescent nitrogen doped carbon nanoparticles for selective sensing of Hg2+ in food and cosmetics samples

The as prepared N-doped CNPs could serve as an effective fluorescent sensing probe for Hg²⁺ detection.

In situ sonochemical synthesis of luminescent Sn@C-dots and a hybrid Sn@C-dots@Sn anode for lithium-ion batteries

A facile sonochemical approach is employed for the in situ formation of Sn@C-dots via ultrasonic irradiation of polyethylene glycol (PEG) as a solvent with molten tin and its decomposition.

One-pot and ultrafast synthesis of nitrogen and phosphorus co-doped carbon dots possessing bright dual wavelength fluorescence emission

Very brief microwave heating of aniline, ethylene diamine, and phosphoric acid in water at ambient pressure generated nitrogen and phosphorus co-doped carbon dots (N,P-CDs) that exhibit bright dual blue (centred at 450 nm; 51% quantum yield) and green (centred at 510 nm, 38% quantum yield) fluorescence emission bands. The N,P-CDs were characterized using TEM, XRD, XPS, IR, UV-vis, and fluorescence spectroscopy, demonstrating their partially crystalline carbon, partially amorphous structures, and the incorporation of O, N, and P into the carbogenic scaffold. The N,P-CDs demonstrated excitation-dependent and nearly pH-independent emission properties. The unique dual emission properties lay the foundation for the use of N,P-CDs in ratiometric sensing applications.