Red-emitting Carbon Dots Research Articles

Red-emissive carbon dots from Hibiscus rosa-sinensis: a detailed appraisal of tartrazine dye sensing properties.

Aneconomically viable and greener approach is introduced to fabricate red emissive carbon dots (R@CQDs) via employing hydrothermal means on Hibiscus rosa-sinensis leaves as precursor source. The obtained R@CQDs displayed excitation-dependent behavior, with high aqueous stability, quantum yield of 56%, and outstanding fluorescence aptitude under the conditions of varied range of ionic strength and pH (1-12). The fluorescence emission behavior of R@CQDs displayed selective turn off fluorescenceresponse to tartrazine over other interfering species with alimit of detection of 0.09µM and quantitation limit of 0.30µM. Theoretical calculations employing density functional theory (DFT) were carried out to complement experimental findings and getting insights into the underlying mechanism governing the sensing of tartrazine. The developed sensor holds significant potential for tartrazine detection in real samples and offering wider prospective in the food safety assessment.

Innovating uric acid Biosensing: Development of a GSH@Cd-Mediated Dual-Signal fluorometric method

Uric acid (UA) is a crucial biomarker for various metabolic and renal disorders, making its accurate determination essential for clinical diagnostics and disease management. This study presents a novel fluorometric method for UA detection using a glutathione@cadmium/carbon dots/uricase system (GSH@Cd/CDs/uricase system), which offers enhanced sensitivity and selectivity compared to existing techniques. The method employs a cascade reaction mechanism initiated by uricase-catalyzed oxidation of UA to produce H2O2. This H2O2 subsequently oxidizes GSH to oxidized glutathione (GSSG), releasing cadmium ions from GSH complexes. The liberated Cd2+ ions interact with two types of carbon dots (CDs) in the system: blue-emitting CDs (BCDs) and red-emitting CDs (RCDs). This interaction triggers a dual fluorescence response, characterized by a decrease in fluorescence intensity at 400 nm (BCDs) and an increase at 610 nm (RCDs), enabling ratiometric detection of UA levels. Comprehensive characterization and mechanistic investigations were conducted using various optical and morphological techniques, including transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and fluorescence spectroscopy. The method exhibits outstanding analytical performance, characterized by strong linearity (R2 = 0.9932), a broad detection range (0.05–7.0 μM), and a low detection limit of 0.015 μM. The method demonstrated excellent selectivity against common interfering substances and was successfully applied to human serum and urine samples with high recovery values (97.65 % to 99.20 %), highlighting its potential for clinical applications. This innovative approach combines the specificity of enzymatic recognition with the sensitivity of dual-emission fluorescence, offering a promising tool for accurate UA quantification in complex biological matrices.

Synthesis and application of optically stable red fluorescent carbon dots for sensitive and selective detection of ceftazidime

This study reports the successful synthesis of optically stable red-emitting carbon dots (R-CDs) through a solvothermal method, using glycine as the carbon source and o-phenylenediamine as the nitrogen-doping agent. The R-CDs exhibit long-wavelength emission characteristics with optimal excitation and emission wavelengths of 533 nm and 600 nm, respectively, and a quantum yield of 26.7 %. The results demonstrate that R-CDs possess excellent salt resistance and photostability. The R-CDs display bright fluorescence emission and show a sensitive response to ceftazidime (CF). Leveraging these properties, a fluorescent probe based on R-CDs was developed for the sensitive determination of CF. The fluorescence quenching intensity of this system exhibits a good linear relationship with CF concentration in the range of 0–0.7 mmol/L. The linear equation is (F0-F)/ F0 = 0.9564CCF (mmol/L) + 0.0089, with a linear correlation coefficient (R2) of 0.9945. The detection limit is 4.9 μmol/L, with recovery rates ranging from 94.2 % to 100.5 % and relative standard deviations between 2.2 % and 3.2 %. This work provides a theoretical basis for the detection of CF using red-emitting carbon dots and demonstrates promising potential for practical applications.

Red-emitting carbon dots for fluorescent and smartphone-assisted dual-mode detection of Cu(II), Hg(II), and Fe(III) and investigation of the sensing mechanism

Red-emitting carbon dots (R-CDs) have triggered ever-increasing interest in biochemical sensing due to their deep tissue penetration and minimal biological auto-fluorescence interference. Herein, dual-emitting intrinsic R-CDs are fabricated and well-characterized. R-CDs display ratiometric and colorimetric sensing properties for heavy metal ions (HMIs, Cu2+, Hg2+, and Fe3+), with the corresponding detection limits of 24.5, 74.2, and 170 nM, respectively. Additionally, smartphone imaging colorimetry based on red-green-blue (RGB) value variations is employed to achieve real-time and on-site detection of these HMIs. Crucially, discrimination of these HMIs is facilitated by principal component analysis. Furthermore, R-CDs demonstrate effective optical sensing of these HMIs in tap/lake water and human urine with satisfactory recoveries (95.82–104.8 %). The underlying mechanism of optical sensing, which involves metal ion-triggered aggregation-induced quenching, is elucidated by spectroscopic, morphological analysis, and quantum mechanical calculations. This work presents a feasible real-time approach for the fluorescent and smartphone-assisted dual-mode detection of HMIs.

Monitoring concentration of quinolones in human serum by fluorescence and colorimetric analysis based on red carbon dots

Bacterial infections are common and predominant concern after surgical operation despite surgical techniques have improved significantly. Monitoring of antibiotics concentration can provide critical feedback in clinical treatment so as to achieve rapid and effective treatment and avoid bacterial resistance. Quinolones (QNs) are synthetic broad-spectrum antibiotics to treat bacterial infections. In this work, we developed a high-yield (50.67 %) red-emitting carbon dots (R-CDs) as fluorescence probe for sensing of three quinolone antibiotics, ofloxacin (OFL), gatifloxacin (GAT), and ciprofloxacin (CIP). R-CDs were prepared in 30 min using tartaric acid and o-phenylenediamine as precursors via an economical and efficient microwave-assisted method. At excitation of 339 nm, R-CDs show sensing performance towards OFL, GAT, CIP. Ofloxacin can be detected in the range of 0.25–30 μM with limit of detection (LOD) of 27.01 nM. Detection concentration range of gatifloxacin is between 0.25–40 μM and LOD is 23.73 nM. Ciprofloxacin can be detected in the range of 0.75–35 μM with LOD of 75.23 nM. A smartphone-assisted analysis platform was developed based on colorimetric phenomenon which applicable in three quinolones concentration monitoring in human serum. This research setup an efficient and promising therapeutic drug monitoring method for clinical treatment and widen the applications of carbon dots.

Carbon dots as a distinctive platform fabricated through a sustainable approach for versatile applications

Red-emitting carbon dots (R-CDs) have garnered significant interest owing to its exceptional fluorescence (FL) characteristics. In this study, we present a one-pot solvothermal synthesis for producing biomass-derived R-CDs, utilizing Birch leaves as the primary raw material. The R-CDs display high solubility in ethanol and demonstrate deep-red emission at 625 nm with narrowband characteristics. After conducting a selectivity assessment with different metal ions, it is observed that R-CDs demonstrate exceptional sensitivity and specificity specifically to Fe3+. This demonstrates a linear relationship up to a concentration of 500 μM, with a detection limit of 0.302 μM (S/N=3). In this research, we created photoluminescent and transparent composites made from polyvinyl alcohol (PVA) with embedded fluorescent R-CDs, using the solution casting method for fabrication. The synthesized R-CDs exhibit robust and consistent FL in solution, whereas, the R-CDs@PVA nanocomposites (NCs) films are transparent and exceptionally flexible. The optimized 0.08 wt% R-CDs demonstrated the most effective ultra violet (UV) blockage across the UV-A (76.84 %), UV-B (74.86 %), and UV-C (78.46 %) region. However, PVA alone absorbed < 25 % of the light in all UV regions. The study explored the shape memory and FL characteristics of the R-CDs@PVA NCs changed under varying conditions such as water, temperature and pH. In alkaline conditions, the FL intensity of the R-CDs@PVA NCs increased due to the deprotonation of the R-CDs surface. In addition, R-CDs dispersed within PVA exhibit superior ink-free patterned substrates, proving to be advantageous for non-destructive template relief printing. Furthermore, R-CDs serve as effective anti-oxidants, combating 2,2-Diphenyl-1-picrylhydrazyl (DPPH) scavenging activity and mitigating the oxidative stress (OS) in red blood cells (RBCs) induced by sodium nitrite (NaNO2). They aid in the restoration of essential stress indicators, encompassing lipid peroxidation (LPO), protein carbonyl content (PCC), total thiol (TT), superoxide dismutase (SOD), and catalase (CAT). Furthermore, R-CDs restored the damaged liver, kidney, heart, and pancreas by regulating biochemical parameters. Furthermore, incorporated R-CDs into red light-emitting diodes (R-LEDs) and white light-emitting diodes (W-LEDs), thereby enhancing plant growth efficiency. The results of this study highlight the possible of R-CDs as non-toxic, UV blocking agents suitable for developing edible coatings and packaging. These properties suggest their applicability in the food industry, anti-counterfeiting (AC) measures, and biomedical applications.

Synthesis and functionalization of red-emissive carbon dots towards sensing of copper(II) and ATP in aqueous media

Red-emissive carbon dots, RCDs, were prepared in a bottom-up approach, from citric acid and urea, through a single solvothermal step, which were posteriorly surface-functionalized with di-(2-picolyl)amine (DPA) groups. The functionalized RCDs, henceforth named CD1, were analyzed through high-resolution transmission electron microscopy (HR-TEM), X-ray diffraction (XRD), dynamic light-scattering (DLS) and infrared spectroscopy (FTIR), and were found to be spherical, with diameter of circa 4 nm. UV-Vis and luminescence spectroscopic studies showed that CD1 display an absorption maximum at 550 nm, with emission maxima at around 640 nm. Fluorescence measurements indicated that Cu(II) induces the strongest changes in the emission of CD1 among eleven investigated metal ions, with a full quenching effect being observed. Further addition of an anionic species, adenosine 5-triphosphate (ATP), resulted in a recovery of the luminescence, which suggests that ATP is capable of sequestering metal ions from the surface of CD1. These results highlight the potential of simple and easy-to-make carbon nanomaterials as sensors for ions in aqueous media.

Eco-friendly synthesis of red-emissive carbon dots for visual alcohol detection and light-emitting diodes

Red-emissive carbon dots (R-CDs) is highly desired in developing full-color solid-state lighting and display applications based on CDs. Developing simple and eco-friendly methods to produce R-CDs is extremely desirable. In this work, two types of R-CDs were obtained via simple and eco-friendly grinding-heating or solvothermal methods using fresh spinach leaves as the carbon source, respectively. The obtained R-CDs naturally possess surface functional groups. These R-CDs were effectively used as sensitive probes for detecting alcohol (including alcohol gas and liquor detection) due to the synergistic effect of the nitrogen-containing surface groups on the R-CDs and the oxhydryl groups in the alcohol solution. Finally, red electroluminescence was achieved by mixing the R-CDs with polyvinyl pyrrolidone as the phosphor layer on a blue light-emitting diode (LED) chip. This work paves the way for the further development of R-CDs in fluorescence probes and full-color LED applications.

Exploiting the pH-responsive behavior of zinc-dithizone complex for fluorometric urea sensing utilizing red-emission carbon dots

This study develops a novel fluorometric method for the sensitive and selective determination of urea, based on unique system comprising nitrogen doped red-emissive carbon dots (NRECDs), zinc-dithizone complex, and the urease enzyme. The underlying principle of this method relies on the pH increase resulting from the enzymatic breakdown of urea by urease. Initially, the fluorescence of the NRECDs is quenched by the red-colored zinc-dithizone complex. However, upon the addition of urea, the subsequent release of ammonia and the consequent rise in pH lead to the dissociation of the zinc-dithizone complex, causing a color change from red to yellow. This spectral shift eliminates the quenching effect, resulting in the restoration of the CDs’ fluorescence. The prepared NRECDs were comprehensively characterized using various spectroscopic techniques, including fluorometry, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), UV–visible spectroscopy, and transmission electron microscopy (TEM) imaging. The proposed fluorometric method exhibits excellent sensitivity (Limit of detection = 0.0012 mM) and linearity (R2 = 0.9951) in the determination of urea. Notably, this approach addresses the selectivity limitations of previous pH-sensitive CDs-based methods, which relied solely on the intrinsic response of CDs, lacking specificity in either quenching or fluorescence enhancement. Furthermore, the developed method demonstrates remarkable selectivity, as evidenced by negligible interference from various potentially interfering substances, ensuring reliable and accurate urea quantification. When applied to human serum samples, the method showcased excellent recovery with low relative standard deviations, highlighting its practical applicability in biomedical and clinical applications.

Fabrication of fluorescence probe based on molecularly imprinted polymers on red emissive biomass-derived carbon dots coupled with smartphone readout for tyramine determination in fermented meat products.

A fluorescence probe based on molecularly imprinted polymers on red emissive biomass-derived carbon dots (r-BCDs@MIPs) was developed to detect tyramine in fermented meat products. The red emissive biomass-derived carbon dots (r-BCDs) were synthesized by the one-step solvothermal method using discarded passion fruit shells as raw materials. The fluorescence emission peak of r-BCDs was at 670nm, and the relative quantum yield (QY) was about 2.44%. Molecularly imprinted sensing materials were prepared with r-BCDs as fluorescent centers for the detection of trace tyramine, which showed a good linear response in the concentration range of tyramine from 1 to 40µg L-1. The linear correlation coefficient was 0.9837, and the limit of detection was 0.77µg L-1. The method was successfully applied to the determination of tyramine in fermented meat products, and the recovery was 87.17-106.02%. The reliability of the results was verified through high-performance liquid chromatography (HPLC). Furthermore, we combined the r-BCDs@MIPs with smartphone-assisted signal readout to achieve real-time detection of tyramine in real samples. Considering its simplicity and convenience, the method could be used as a rapid and low-cost promising platform with broad application prospects for on-site detection of trace tyramine with smartphone-assisted signal readout.

Enhanced dual fluorescence quenching of red and blue emission carbon dots by copper dimethyldithiocarbamate for selective ratiometric detection of ziram in foodstuff and water samples

The monitoring of ziram levels is of vital importance due to its widespread application in agriculture and the possible risks it poses to human health and the ecosystem. This work proposes an innovative approach for the highly sensitive and selective sensing of ziram, a widely used dithiocarbamate fungicide, through the formation of copper dimethyldithiocarbamate Cu)DDC)2 assisted dual quenching of red and blue emission carbon dots (R/NCDs and B/NSCDs). When ziram is added to a system containing copper-bound B/NSCDs and R/NCDs, the displacement of ziram zinc ions by copper ions leads to the formation of a yellow-colored Cu)DDC)2 complex. This complex induces significant quenching of the fluorescence emissions from both types of carbon dots, consequently enhancing the sensitivity of the detection method. Comprehensive characterization of the R/NCDs and B/NSCDs was conducted using various spectroscopic and morphological techniques to elucidate their structural and optical properties. The quenching mechanism was confirmed through different spectroscopic techniques, including fluorescence lifetime measurements, UV–vis spectroscopy, and Stern-Volmer analysis. The proposed method demonstrated high sensitivity across a wide concentration ranging from 20 to 1000 ng mL−1, making it suitable for trace-level detection of ziram. Moreover, the method exhibited excellent selectivity and recovery when applied to real samples, such as apples, grains, and water matrices. The combination of high sensitivity, selectivity, and applicability to diverse sample matrices makes this carbon dot-based dual quenching method a promising approach for fast and accurate detection of ziram in various environmental and agricultural applications.

Sensitive and reliable hybrid nanosensor (Co2+-CDs@R-CDs) for ratiometric fluorescent and colorimetric detecting NO2−

A ratiometric fluorescent and colorimetric detecting assay for NO2− was realized by a hybrid nanosensor (Co2+-CDs@R-CDs) utilizing firstly through the redox reaction of nitrite (NO2−) with Co2+, of which the hybrid nanosensor Co2+-CDs@R-CDs was fabricated by Co2+-doped carbon dots (Co2+-CDs) and a reference of red-emitting carbon dots (R-CDs). The ratiometric fluorescent linear detection range of NO2− was 2.5–45 μM and the limit of detection (LOD) was 0.068 μM with the response time of 120 s. While, the colorimetric linear detection range of NO2− was 2.5–60 μM and the LOD was 0.075 μM. In addition, a portable smartphone system which could measure the R (red), G (green), and B (blue) values of the fluorescence and the visible color of the coated Co2+-CDs@R-CDs paper strip-based sensor had also been developed and successfully applied to detect NO2− in sausage, pickles and tap water samples.

User-Friendly Multifunctional Red-Emissive Carbon Dots for Rapid Cell Nucleus Staining via Targeting Nuclear Proteins.

Cytoarchitectural staining is of great importance in disease diagnosis and cell biology research. This study developed user-friendly multifunctional red-emissive carbon dots (R-CDs) for rapid cell nucleus staining via targeting nuclear proteins. R-CDs, simply prepared by electrochemical treatment of 1,2,4-benzenetriamine, exhibit strong emission at 635 nm when excited at 507 nm. The R-CDs can rapidly stain the nucleus of human SH-SY5Y, HepG2, and HUH-7 cells with a high signal-to-noise ratio owing to fluorescence enhancement after entering the nucleus. Compared to conventional cytosolic dyes such as Hoechst and DAPI, R-CDs are cheaper, more highly dispersed in water, and more stable (requiring no stringent storage conditions). The R-CDs show stable optical properties with insignificant photobleaching over 7 days and salt resistance up to 2 M of NaCl. More importantly, R-CDs, possessing a positive charge, allow rapid staining of live cells (3 min) and dead cells (10 s) in saline. According to kinetic variation, R-CDs can distinguish live cells from dead cells. Staining exhibits high efficiency in onion epidermal cells, Aspergillus niger, Caenorhabditis elegans, and human spermatozoa. The mechanism for efficient staining is based on their fast accumulation in the nucleus due to their small size and positive charge and strong interaction with nuclear proteins at amino acid residues of histidine and arginine, resulting in fluorescence enhancement by dozens of times. The developed R-CDs do not bind to DNA and would not cause genetic damage and will find various safe applications in biological and medical fields.

Synthesis of Amphiphilic and Red Emissive Carbon Dots as Nanoprobes for Targeted Stimulated Emission Depletion Imaging of Live Cell Plasma Membranes

Synthesis of Amphiphilic and Red Emissive Carbon Dots as Nanoprobes for Targeted Stimulated Emission Depletion Imaging of Live Cell Plasma Membranes

Red emissive fluorescent carbon dots based on ternary carbon source for imaging α-synuclein fibrils

The misfolding and aggregation of α-synuclein monomers usually cause the occurrence and development of Parkinson’s disease (PD). It is important to develop effective methods for detection of α-synuclein aggregates. Carbon dots (CDs) could be the potential fluorescence probe for this purpose owing to their appreciated optical properties. However, undefined structure of CDs and complicated three-dimensional structure of protein severely hindered the design of fluorescence probe towards protein aggregates. Herein, a red emissive fluorescent amphiphilic CD, named as CL-9, was designed with a high sensitivity to α-synuclein fibrils by a one-step heating process, using the ternary carbon source, including Congo red, l-tryptophan and urea. The CL-9 exhibited turn-on red emissive fluorescence towards α-synuclein fibril, but remained no change towards its monomer. Compared with the original Congo red dye, CL-9 exhibited stronger turn-on red fluorescence towards α-synuclein fibrils with better anti-photobleaching resistance, biocompatibility and signal-to-noise ratio. The CL-9 was successful as a fluorescent probe to image α-synuclein fibrils in NL-5901 C. elegans. The present study provided a feasible approach using the multiple carbon sources to construct the CDs based fluorescence probe targeting amyloid proteins.

Formation and Fluorescent Mechanism of Multiple Color Emissive Carbon Dots from o-Phenylenediamine.

Carbon dots (CDs) have received considerable attention in many application areas owing to their unique optical properties and potential applications; however, the fluorescent mechanism is an obstacle to their applications. Herein, three-color emissive CDs are prepared from single o-phenylenediamine (oPD) by regulating the ratio of ethanol and dimethylformamide (DMF). Fluorescent mechanism of these CDs is proposed as molecular state fluorescence. Reaction intermediates are identified using liquid chromatrography-mass spectroscopy (LC-MS) and 1H nuclear magnetic resonance (NMR) spectra. 1H-Benzo[d]imidazole (BI), 2,3-diaminophenazine (DAP), and 5,14-dihydroquinoxalino[2,3-b] phenazine (DHQP) are proposed to be the fluorophores of blue, green, and red emissive CDs by comparing their optical properties. As per the LC-MS and 1H-NMR analysis, DHQP with red emission tends to form from DAP and oPD in pure ethanol. By adding DMF, BI formation is enhanced and DHQP formation is suppressed. The prepared CDs exhibit green emission with DAP. When the DMF amount is >50%, BI formation is considerably promoted, resulting in DAP formation being suppressed. BI with blue emission then turns into the fluorophore of CDs. This result provides us an improved understanding of the fluorescent mechanism of oPD-based CDs, which guides us in designing the structure and optical properties of CDs.

Meticulously designed red emission carbon dots as efficient and stable luminescent species for rapid latent fingerprint recognition and light emitting diodes

The preparation of carbon dots (CDs) emitting long wavelength has attracted more attentions due to their unique advantages in biological and optoelectronic fields, including the wide absorption, long PL lifetime and deep-tissue penetration. Herein, we prepare the nitrogen and sulfur co-doped red emission carbon dots (R-CDs) from the 2,4-diaminodiphenylamine (DDA) and thiourea via a solvothermal reaction, which exhibit reliable red emission at 613 nm and possess a high quantum yield (QY) of 34 %. Meanwhile, the structural analysis and theoretical calculation reveal that the sulfur doping from thiourea increases the nitrogen and oxygen content of CDs, leading to the red emission observed in R-CDs. Subsequently, we design an integrated fingerprints recognition system based on the R-CDs phosphors for the imaging of latent fingerprints (LFPs) and fast LFPs recognition, expanding the application of biometric identification and comparison technology based on fluorescence. Finally, we successfully apply the R-CDs into red and white light-emitting diodes, improving plant growth efficiency. As a result, this work provides a new in-depth insight of red emission CDs and expands the application in latent fingerprint recognition and light-emitting diodes.

Real-time and specific monitoring of nitric oxide and evaluating of the oxidative stress in living cells and zebrafish under the pollutant exposure using a carbon dot-based composite fluorescent probe

Nitric oxide (NO) functions as an essential signalling molecule in various physiological and pathological pathways. In vitro and vivo redox processes mediated by reactive oxygen species (ROS) and nitric oxide (NO) directly influence the intracellular state. In this study, a red-emitting fluorescent nanoprobe, N,S-CDs@Zn-ICA, was synthesized to monitor NO fluctuations in living cells and zebrafish under the exposure to various pollutants. Red-emissive carbon dots (N,S-CDs) were synthesized by a hydrothermal method using o-phenylenediamine and urea as carbon / nitrogen sources, and H2SO4 as sulfur source. Glutathione (GSH) was introduced to link N,S-CDs with metal organic complexes (Zn-ICA) through an amidation reaction to fabricate a carbon dot-based composite fluorescent probe, which greatly improved the selectivity, stability, and response time of the N,S-CDs. The composite probe has high selectivity and sensitivity with limit of detection (LOD) of 96.0 nM. Furthermore, the proposed probe was successfully used to monitor the dynamic changes in NO levels and evaluate oxidative stress in MCF-7 cells and zebrafish under the exposure to various pollutants, including seven heavy metal ions (such as Pb2+, Cd2+, and Hg2+) and nine organic pollutants at different concentrations and exposure times. This work provides a novel strategy for constructing highly selective and red-emitting fluorescent probe for real-time and dynamic monitoring of NO and further evaluating oxidative stress induced by pollutants in vitro and in vivo via fluorescence imaging.

Small Warriors of Nature: Novel Red Emissive Chlorophyllin Carbon Dots Harnessing Fenton‐Fueled Ferroptosis for In Vitro and In Vivo Cancer Treatment (Small 18/2024)

Small Warriors of Nature: Novel Red Emissive Chlorophyllin Carbon Dots Harnessing Fenton‐Fueled Ferroptosis for In Vitro and In Vivo Cancer Treatment (Small 18/2024)

Ratiometric Sensing of Azithromycin and Sulfide Using Dual Emissive Carbon Dots: A Turn On-Off-On Approach.

A novel ratiometric fluorescence probe was developed for the determination of azithromycin (AZM) and sulfide ions based on the differential modulation of red emissive carbon dots (R-N@CDs) and blue emissive carbon dots (B-NS@CDs). The addition of sulfide anion selectively quenched the red emission of R-N@CDs while the blue emission of B-NS@CDs unaffected. Upon subsequent introduction of AZM to this R-N@CDs@sulfide system, the quenched red fluorescence was restored. Comprehensive characterization of the CDs was performed using UV-Vis, fluorescence, FTIR spectroscopy, XPS, and TEM. The proposed method exhibited excellent sensitivity and selectivity, with limits of detection of 0.33 µM for AZM and 0.21 µM for sulfide. Notably, this approach enabled direct detection of sulfide without requiring prior modulation of the CDs with metal ions, as is common in other reported methods. The ratiometric probe was successfully applied for the determination of AZM in biological fluids and sulfide in environmental water samples with high selectivity. This work presents the first fluorometric method for the detection of AZM in biological fluids.