A double fluorescent nanoprobe based on phosphorus/nitrogen co-doped carbon dots for detecting dichromate ions and dopamine

An “on–off–on” fluorescent phosphorus/nitrogen co-doped carbon dot (PNCD) probe was explored for the determination of Cr(vi) and dopamine resulting from the inner filter effect (IFE). The blue-emitting carbon dots with high quantum yields of 25.47% as well as a narrow size distribution were synthesized by a rapid, convenient route using H₃PO₄ and ethylenediamine as the precursors without any surface passivation. A wide linear region in the range of 7–70 μM with a detection limit of 0.71 μM was achieved for Cr(vi). Moreover, the proper reductants can weaken the inner filter effect to recover the PNCD fluorescence by converting Cr(vi) into Cr(iii). Therefore, the PNCDs/Cr(vi) hybrid could also be used as an “off–on” fluorescent probe for detecting dopamine (DA) with a detection limit of 0.49 μM. Consequently, the PNCDs could serve as a powerful fluorescent bi-sensor for detection of both Cr(vi) and DA in practical applications.

An “on–off–on” fluorescent phosphorus/nitrogen co-doped carbon dot (PNCD) probe was explored for the determination of Cr(vi) and dopamine resulting from the inner filter effect (IFE).     

Multi-shelled ZnO decorated with nitrogen and phosphorus co-doped carbon quantum dots: synthesis and enhanced photodegradation activity of methylene blue in aqueous solutions

The presence of organic dyes in wastewater has posed a huge threat to aquatic life and human health. In this study, nitrogen and phosphorus co-doped carbon quantum dot (CQD)-decorated multi-shelled ZnO microsphere photocatalysts (NPCQD/ZnO) were obtained via a simple absorption process; ZnO was prepared by calcining carbon microspheres as the sacrificial template. The as-prepared NPCQD/ZnO showed an obvious multi-shelled structure with the nitrogen and phosphorus co-doped CQDs homogeneously attached onto the inner and outer shells of ZnO. According to the UV-Vis DRS results, all the co-doped, single-doped and undoped carbon quantum dots could enhance the efficiency of absorption of visible light and reduce the optical band gap. Furthermore, the PL characterization results showed that the NPCQD/ZnO composites had lowest fluorescence intensity because the decoration of ZnO with NPCQDs could effectively reduce the recombination rate of photogenerated electron–hole pairs in the ZnO semiconductor photocatalyst. Importantly, 2 g-NPCQD/ZnO composites exhibited higher photodegradation performance towards methylene blue (MB) than pure ZnO and even the newly reported series of ZnO catalysts under the same conditions. Moreover, the degradation obeyed the pseudo-first-order and Langmuir–Hinshelwood kinetics models with a reaction constant of 0.0725 min⁻¹, which was 1.05 times that of pure ZnO (0.0353 min⁻¹). The NPCQD/ZnO composites not only showed good photocatalytic performance, but also had excellent stability since the photocatalytic activity did not significantly decrease after five cycling tests. In addition, compared with single-doped and undoped carbon quantum dots, N and P co-doped carbon quantum dots have more significant efficiency for the modification of semiconductor photocatalysts. The present study shows that the CQD-decorated multi-shelled ZnO can be regarded as an excellent photocatalyst candidate in the field of water treatment. Moreover, this new concept is helpful in the controllable construction of other multi-shelled metal oxides decorated with co-doped carbon quantum dots with enhanced photocatalytic properties.

The presence of organic dyes in wastewater has posed a huge threat to aquatic life and human health.     

Electro-spinning fabrication of nitrogen,phosphorus co-doped porous carbon nanofiber as an electro-chemiluminescent sensor for the determination of cyproheptadine

Nitrogen, phosphorus co-doped porous carbon nanofiber (N, P-PCNF) is prepared by electrospinning the mixed solution of polyacrylonitrile (PAN), polyvinylpyrrolidone (PVP) and phosphoric acid followed by carbonization. The N, P-PCNF as a modified electrode material is directly used to fabricate an electro-chemiluminescent sensor for determination of cyproheptadine, and owing to the large specific area, more active sites and promotion of electron transfer, the sensor exhibits high electro-catalytic activity, high sensitivity, a good linear relationship ranging from 1.0 × 10⁻⁷ to 1.0 × 10⁻⁵ mol L⁻¹ and a low detection limit (2.89 × 10⁻⁸ mol L⁻¹). In addition, the good recoveries indicate that the sensor is a promising device for the detection of cyproheptadine in real samples.

Nitrogen, phosphorus co-doped porous carbon nanofiber is as electrode modified material to fabricate an electro-chemiluminescent sensor for detecting cyproheptadine.     

Selective and sensitive detection of cinnamaldehyde by nitrogen and sulphur co-doped carbon dots: a detailed systematic study

Nitrogen and sulfur co-doped carbon dots (NSCDs) synthesized through one-pot microwave-assisted pyrolysis of tartaric acid and thioacetamide have been used as a fluorescent probe for the sensitive and selective detection of clinically important organic aldehyde cinnamaldehyde. The as-prepared NSCDs displayed blue fluorescence (∼12% quantum yield), excellent aqueous solubility along with pH and excitation wavelength dependent emission behavior. In comparison to other aldehydes (formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde, valeraldehyde, hexanal, crotonaldehyde and benzaldehyde) the fluorescence intensity of NSCDs was significantly quenched in the presence of cinnamaldehyde and the reduced intensity was linearly proportional to the concentration of cinnamaldehyde in the range of 0–15 mM with a detection limit of 99.0 μM. The fluorescence quenching of NSCDs was mainly attributed to the photo-excited electron transfer between NSCDs and aldehydes which was confirmed by measuring the life-time through time-resolved luminescence spectroscopy, energy levels of NSCDs through cyclic voltammetry (CV) and energy levels of aldehydes by density functional theory (DFT) based analyses. MTT assay of the NSCDs also proved their good biocompatibility and low toxicity towards human fibroblast cells thereby validating their suitability as a biologically relevant fluorescent probe for sensing cinnamaldehyde.

Nitrogen and sulfur co-doped carbon dots (NSCDs) have been used as a fluorescent probe for the sensitive and selective detection of clinically important organic aldehyde cinnamaldehyde.     

Nitrogen and phosphorus co-doped carbon modified activated carbon as an efficient oxygen reduction catalyst for microbial fuel cells

Activated carbon (AC) is an environmentally sustainable oxygen reduction reaction (ORR) catalyst and widely used in MFCs due to its intrinsic high specific surface area and mesoporous characteristics, but it shows relatively high ORR over-potential thus low electrocatalytic activity. In this study, a method of doped carbon modification was employed to decrease the over-potential and improve the ORR electrocatalytic activity of the AC catalyst. Nitrogen and phosphorus co-doped carbon modified AC (NPC@AC) was prepared by coating phytic acid doped polyaniline onto AC through in situ oxidative polymerization and subsequent high-temperature pyrolysis. The as-prepared NPC@AC possessed a large surface area of ∼649.3 m² g⁻¹ inherited from AC and a low ORR over-potential with a highly positive onset potential of +0.22 V vs. Ag/AgCl from NPC, thus showing an enhanced ORR electrocatalytic activity in neutral solution compared to the pristine AC, and even better than the pure NPC. The air-cathode MFC using the NPC@AC catalyst generated a much higher open circuit voltage of 0.753 V and two times higher power density of 1223 mW m⁻² than that using the pristine AC catalyst of about 0.432 V and 595 mW m⁻², respectively.

Nitrogen and phosphorus co-doped carbon modified activated carbon shows decreased ORR over-potential, thus enhanced ORR electrocatalytic activity in the air-cathode of microbial fuel cells compared to pristine AC.     

A facile green and one-pot synthesis of grape seed-derived carbon quantum dots as a fluorescence probe for Cu(ii) and ascorbic acid

In this study, an on–off–on fluorescence probe for the detection of trace Cu(ii) and ascorbic acid (AA) based on biomass-derived sulfur and nitrogen double heteroatom-doped carbon dots (N,S-CDs) was designed. For the first time, the probe (N,S-CDs) was prepared from grape seeds and thiourea as the precursor. Cu(ii) was added to the carbon point solution, the fluorescence intensity (FL) of N,S-CDs was strongly quenched (switch OFF) and the fluorescence probe turned to “ON” (switch ON) with the addition of AA. Under the optimal conditions, the as-synthesized N,S-CDs had a good detection performance for Cu(ii) and AA assay with the linearity ranges from 150–500 μg mL⁻¹ and 0.1–400 μg mL⁻¹, and the LODs were 0.048 mg L⁻¹ and 0.036 mg L⁻¹, respectively. The as-prepared N,S-CDs exhibited a low cytotoxicity and a good biocompatibility, which show their potential for application in the biological imaging of living cells.

In this study, an on–off–on fluorescence probe for the detection of trace Cu(ii) and ascorbic acid (AA) based on biomass-derived sulfur and nitrogen double heteroatom-doped carbon dots (N,S-CDs) was designed.     

Switch on fluorescence mode for determination of l-cysteine with carbon quantum dots and Au nanoparticles as a probe

Citric acid and urea were used as precursors for the preparation of carbon quantum dots (CQDs) which exhibited a maximum emission wavelength at 515 nm when excited at 410 nm. Upon addition of citrate-stabilized Au nanoparticles (AuNPs) with the maximum absorption wavelength at 520 nm, the fluorescence of the CQDs could be efficiently quenched, attributed to the energy transfer between CQDs and AuNPs. However, the further introduction of l-cysteine (Cys) could cause the aggregation of AuNPs along with a drop in absorption at 520 nm, resulting in the fluorescence recovery of the CQDs–AuNPs system. Therefore, a simple and reliable switch on fluorescence sensing platform for determination of Cys was constructed. The significant factors, such as pH and incubation time, that affected the detection of Cys were optimized with the AuNP concentration set as 2.50 nM at room temperature. Under the optimized conditions, the fluorescence recoveries (ΔF) were strongly correlated with Cys concentration in the 0.20 to 4.0 μM range, and the detection limit is 0.012 μM. More importantly, our CQD-based sensing platform was successfully used for the detection of Cys in milk samples with high precision and accuracy, indicating the potential of the probe in practical applications.

We demonstrated a fluorescence probe composed of CQDs and AuNPs for switch on detection of Cys, where CQDs as fluorescence reporters and AuNPs as fluorescence quenchers were chosen.     

Sulfhydryl functionalized carbon quantum dots as a turn-off fluorescent probe for sensitive detection of Hg2+

Mercury ion (Hg²⁺) is one of the most toxic heavy metal ions and lowering the detection limit of Hg²⁺ is always a challenge in analytical chemistry and environmental analysis. In this work, sulfhydryl functionalized carbon quantum dots (HS-CQDs) were synthesized through a one-pot hydrothermal method. The obtained HS-CQDs were able to detect mercury ions Hg²⁺ rapidly and sensitively through fluorescence quenching, which may be ascribed to the formation of nonfluorescent ground-state complexes and electron transfer reaction between HS-CQDs and Hg²⁺. A modification of the HS-CQD surface by –SH was confirmed using Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The HS-CQDs sensing system obtained a good linear relationship over a Hg²⁺ concentration ranging from 0.45 μM to 2.1 μM with a detection limit of 12 nM. Delightfully, the sensor has been successfully used to detect Hg²⁺ in real samples with satisfactory results. This means that the sensor has the potential to be used for testing actual samples.

Schematic presentation of the synthesis of HS-CQDs and the application as a “turn-off” fluorescent probe for Hg²⁺ detection.     

One-step synthesis of fluorescent graphene quantum dots as an effective fluorescence probe for vanillin detection

This study proposes an easy bottom-up method for the synthesis of photoluminescent (PL) graphene quantum dots (GQDs) using citric acid as the carbon source. The obtained GQDs were characterized by high-resolution transmission electron microscopy (HRTEM), UV-vis absorption spectroscopy, fluorescence spectroscopy, and Fourier transform infrared spectroscopy (FT-IR). The synthesised GQDs have an average diameter of 4.76 ± 0.96 nm, with a lattice spacing of 0.24 nm. The GQDs exhibit excitation-independent PL emission. The surface of the GQDs has a variety of functional groups (hydroxyl, carboxyl, and ether groups etc.) to enhance its stability and water solubility. In this study, a fluorescent “on–off” sensor is developed for the selective detection of vanillin in chocolates using GQDs as a fluorescent probe. Under optimal conditions, fluorescence intensity of the GQDs has a good linear relationship with the vanillin concentration (0.0–2.1 × 10⁻⁵ mol L⁻¹), with a limit of detection of 2.5 × 10⁻⁸ mol L⁻¹. For detection in real samples, the percent recovery of vanillin and the relative standard deviation were 88.0–108.9% and 0.90–5.4%, respectively. Thus, this GQDs-based method has good accuracy and precision and can be used for vanillin detection in practical applications.

This study proposes an easy bottom-up method for the synthesis of photoluminescent (PL) graphene quantum dots (GQDs) using citric acid as the carbon source.     

A highly selective and sensitive “on–off” fluorescent probe for detecting cadmium ions and l-cysteine based on nitrogen and boron co-doped carbon quantum dots

Cadmium ions (Cd²⁺) have caused relatively serious pollution, threatening human health and ecosystems. l-Cysteine (l-Cys) is an essential amino acid in living organisms and concentration of l-Cys is closely related to some human diseases. In this work, we first introduced 2-amino-3-hydroxypyridine and sodium borohydride as the nitrogen source and boron source to fabricate boron and nitrogen co-doped carbon quantum dots (N,B-CQDs) with high fluorescence quantum yield (21.2%), which were synthesized through a simple, low-consumption and pollution-free one-pot hydrothermal method. The obtained N,B-CQDs are able to detect Cd²⁺ rapidly and sensitively through fluorescence enhancement, which may be ascribed to chelation enhanced fluorescence that is induced by the formation of the N,B-CQDs/Cd²⁺ complex. Simultaneously, N,B-CQDs can be used to detect l-cysteine because significant fluorescence quenching was observed when l-Cys was added into the N,B-CQDs/Cd²⁺ system. In the two fluorescence “turn-on” and “turn-off” processes, this fluorescent probe obtained a good linear relationship over Cd²⁺ concentration ranging from 2.5 µM to 22.5 µM with a detection limit of 0.45 µM, while the concentration of l-cysteine showed a linear relationship in the range of 2.5–17.5 µM with a detection limit of 0.28 µM. The sensor has been successfully used to detect Cd²⁺ and l-cysteine in real samples with satisfying results.

Schematic presentation of the synthesis of N,B-CQDs and their application as an “on–off” fluorescent probe for Cd²⁺ and l-Cys detection.     

Solvent-controlled synthesis of multicolor photoluminescent carbon dots for bioimaging

Multicolor fluorescent carbon dots (CDs) have potential applications in multichannel detection and multicolor imaging. In this study, multicolor fluorescent CDs were synthesized by changing the solvent type and adjusting the reactant ratio. The four prepared CDs emitted bright and stable blue (B-), green (G-), yellow (Y-), and red (R-) fluorescence under a single UV light (λ_ex = 365 nm). The photoluminescence (PL) emission wavelengths changed from 445 nm for B-CDs to 620 nm for R-CDs, and therefore covered the entire visible spectrum. The absolute quantum yields for the B-, G-, Y-, and R-CDs were 27.3%, 31.1%, 22.9%, and 8.8%, respectively. Characterization of the CDs showed that the differences among the optical features of the four prepared CDs arise from the differences among the surface states and nitrogen-derived structures in the carbon core. The four prepared CDs all showed low toxicity and steady PL, and therefore have potential applications in both in vitro and in vivo imaging.

The synthesis and bioimaging of multicolor carbon dots from citric acid and urea.     

Novel N,Cl-doped deep eutectic solvents-based carbon dots as a selective fluorescent probe for determination of morphine in food

In the present study, new N,Cl co-doped carbon dots (N,Cl-CDs) based on deep eutectic solvent (DES) were fabricated by a facile hydrothermal process. This fluorescent probe exhibited a good quantum yield of 14% and was applied for the sensitive and selective quantification of morphine in foods. In addition, the influence of solution pH, interaction time, system temperature, interfering substances and analogues on the determination was also investigated. Under the optimized conditions, the luminescence intensity of carbon dots increased linearly with the addition of morphine in the concentration range of (0.15–280.25) μg mL⁻¹ (R² > 0.9969) and the limit of detection (LOD) of 46.5 ng mL⁻¹. Based on these results, it is suggested that N,Cl-CDs is a promising fluorescent probe for sensitive and selective quantification of morphine in foods.

A schematic illustrating the synthesis and morphine detection of N,Cl-CDs.     

Synthesis of green-emitting carbon quantum dots with double carbon sources and their application as a fluorescent probe for selective detection of Cu2+ ions

Green-emitting carbon quantum dots (G-CQDs) were prepared using tartaric acid and bran by one-pot solvothermal treatment and had photoluminescence quantum yields (PL QY) as high as 46%. The morphology of the G-CQDs is characterized by TEM, which shows the average diameter of G-CQDs is approximately ∼4.85 nm. The FT-IR spectra display the presence of –OH, C–N, N–H and –COOH on the surface of the G-CQDs. The emission wavelength of the G-CQDs was ∼539 nm in the case of ∼450 nm excitation wavelength, which corresponds to the green fluorescence. Furthermore, the G-CQDs were used as a fluorescent probe for detection Cu²⁺ ions, and demonstrated a linear distribution between ln(F/F₀) and the Cu²⁺ ions concentration. Specifically, the Cu²⁺ ion concentration should fall in the G-CQD concentration range of 0–0.5 mM and the detection limit is 0.0507 μM. Thus, due to the excellent chemical stability and good luminescence performance, these G-CQDs could be excellent probes widely used in detection fields.

Green-emitting carbon quantum dots (G-CQDs) were prepared using tartaric acid and bran by one-pot solvothermal treatment and had photoluminescence quantum yields (PL QY) as high as 46%.     

Facile synthesis of dual-emission fluorescent carbon nanodots for a multifunctional probe

In this study, we developed a facile method for synthesizing dual-emission carbon nanodots (CDs) through trimesic acid and o-phenylenediamine through electrolysis for 2 h. The synthesized CDs were mainly 3–7 nm in size, with an average size of 5.17 nm. The dual-emission fluorescent property of these CDs could be observed under two different excitation wavelengths. The green emission of the CDs could be quenched after the addition of mercury ions or copper ions, and the blue emission of the CDs could be inhibited using hydroxychloroquine (HCQ). Furthermore, the quenched fluorescence of CDs/Cu²⁺ could be recovered through the addition of glyphosate. We developed a multifunctional chemical sensor by using these special fluorescence materials. Under optimal conditions, the detection limits of mercury ions, glyphosate, and HCQ were 0.42 μM, 1.1 mg L⁻¹, and 0.14 μM, respectively. Moreover, this method can be used to detect mercury ions, glyphosate, and HCQ in environmental water, cereals, and urine samples, respectively.

The synthetic procedure and the applications of CDs.     

Facile synthesis of carbon nitride quantum dots as a highly selective and sensitive fluorescent sensor for the tetracycline detection

Enhanced blue fluorescent carbon nitride quantum dots (g-C₃N₄QDs) were synthesized by a simple solvothermal “tailoring” process from bulk g-C₃N₄ and analyzed by various characterization methods. The as-obtained g-C₃N₄QDs were successfully applied in the determination of tetracycline (TC) with a good linear relationship in the range of 0.23–202.70 μM. The proposed fluorescent sensor shows excellent stability, good repeatability, high selectivity and outstanding sensitivity to TC with a low detection limit of 0.19 μM. The fluorescence quenching mechanism of g-C₃N₄QDs with TC was mainly governed by static quenching and the inner filter effect. The method was successfully applied to monitor TC in tap water and milk powder samples.

The g-C₃N₄QDs were synthesized by a simple solvothermal “tailoring” process from bulk g-C₃N₄ which have a “strong quenching” behaviour in the presence of TC. The proposed fluorescent sensor has been successfully applied to detect TC in actual samples.     

Synthesis of multicolor-emitting nitrogen–sulfur co-doped carbon dots and their photochemical studies for sensing applications

Photoluminescent carbon dots (CDs) possess several advantages, which include high stability and a non-toxicity that are essential in different applications such as catalysis, drug delivery, and sensors. The presence of heteroatoms modifies their physicochemical characteristics. In this work, a combination of CDs is manufactured utilizing a solvothermal technique using citric acid and thiourea. After separating each section using column chromatography, green and yellow CDs with average diameters of 8.3 and 7.0 nm, respectively, are generated. Next, optical and structural characterizations indicated that the variation in the emission color was caused by differences in surface functional groups rather than particle size. The photoelectrochemical properties are explored by including quinone derivatives and metal ions, which are quenchers for the CDs. The photoluminescence quenching results showed the presence of anionic functional groups on the surface of the CDs. Furthermore, these functional groups interacted strongly with particular types of metal ions, indicating that they may be employed as metal ion sensors.

Luminescent carbon dots (CDs) have been synthesized by a solvothermal approach and their photochemical properties are evaluated. Responses to specific metal ions are observed, and the relationship with surface functional groups is discussed.     

Green synthesis of surface-passivated carbon dots from the prickly pear cactus as a fluorescent probe for the dual detection of arsenic(iii) and hypochlorite ions from drinking water

Efforts were made to develop a simple new approach for the green synthesis of surface-passivated carbon dots from edible prickly pear cactus fruit as the carbon source by a one-pot hydrothermal route. Glutathione (GSH) was passivated on the surface of the CDs to form a sensor probe, which exhibited excellent optical properties and water solubility. The prepared sensor was successfully characterized by UV-visible spectrophotometry, fluorescence spectrophotometry, Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The simple sensing platform developed by the GSH-CDs was highly sensitive and selective with a “turn-off” fluorescence response for the dual detection of As³⁺ and ClO⁻ ions in drinking water. This sensing system exhibited effective quenching in the presence of As³⁺ and ClO⁻ ions to display the formation of metal complexes and surface interaction with an oxygen functional group. The oxygen-rich GSH-CDs afforded a better selectivity for As³⁺/ClO⁻ ions over other competitive ions. The fluorescence quenching measurement quantified the concentration range as 2–12 nM and 10–90 μM with the lower detection limit of 2.3 nM and 0.016 μM for the detection of As³⁺ and ClO⁻ ions, respectively. Further, we explored the potential applications of this simple, reliable, and cost-effective sensor for the detection of As³⁺/ClO⁻ ions in environmental samples for practical analysis.

Efforts were made to develop a simple new approach for the green synthesis of surface-passivated carbon dots from edible prickly pear cactus fruit as the carbon source by a one-pot hydrothermal route.     

Thiosemicarbazide functionalized carbon quantum dots as a fluorescent probe for the determination of some oxicams: application to dosage forms and biological fluids

In this study, highly fluorescent water-soluble nitrogen and sulfur doped carbon quantum dots (N, S-CQDs) were synthesized via a one-step hydrothermal process utilizing citric acid as a carbon source and thiosemicarbazide as a sulfur and nitrogen source. The obtained N, S-CQDs exhibited an intense emission band at 415 nm (λ_ex = 345 nm). In the presence of either piroxicam, tenoxicam or lornoxicam, the emission band at 415 nm was significantly quenched which might be triggered due to destruction of the surface passivation layer of the N, S-CQDs. A linear correlation was found between the reduction in the fluorescence intensity of N, S-CQDs and the concentration of each drug in the ranges of 2.0–25.0 μM, 10.0–100.0 μM and 20.0–200.0 μM with correlation coefficients of more than 0.999 for all drugs. The detection limits were 0.49 μM, 1.58 μM and 4.63 μM for piroxicam, tenoxicam and lornoxicam, respectively. The effect of experimental parameters affecting the performance of the method was investigated and optimized. The developed sensor has the advantages of simplicity, time-saving, convenience and satisfactory selectivity for determination of the studied drugs in dosage forms with high % recoveries (98.86–101.69%). The method was extended for determination of piroxicam in spiked plasma with % recoveries ranging from 97.95–101.36%. The method was validated in accordance with International Council of Harmonization (ICH) standards, and the results obtained were compared statistically to those given by reported methods, indicating no significant differences in the level of accuracy and precision. The mechanism of the quenching process was studied and elucidated. The structure–activity relationship between the three drugs and the quenching efficiency was also studied and discussed.

Highly fluorescent nitrogen and sulfur doped carbon quantum dots were synthesized via hydrothermal process using citric acid and thiosemicarbazide. The dots had an emission band at 415 nm (λ_ex = 345 nm). The polarity of the studied drugs affects the method’s sensitivity.     

Fluorescent probe based on N-doped carbon dots for the detection of intracellular pH and glutathione

Carbon dots (CDs) as fluorescent probes have been widely exploited to detect biomarkers, however, tedious surface modification of CDs is generally required to achieve a relatively good detection ability. Here, we synthesized N-doped carbon dots (N-CDs) from triethylenetetramine (TETA) and m-phenylenediamine (m-PD) using a one-step hydrothermal method. When the pH increases from 3 to 11, the fluorescence intensity of the N-CDs gradually decreases. Furthermore, it displays a linear response to the physiological pH range of 5–8. Au³⁺ is reduced by amino groups on the surface of N-CDs to generate gold nanoparticles (AuNPs), causing fluorescence quenching of the N-CDs. If glutathione (GSH) is then added, the fluorescence of the N-CDs is recovered. The fluorescence intensity of the N-CDs is linearly correlated with the GSH concentration in the range of 50–400 μM with a limit of detection (LOD) of 7.83 μM. The fluorescence probe was used to distinguish cancer cells from normal cells using pH and to evaluate intracellular GSH. This work expands the application of CDs in multicomponent detection and provides a facile fluorescent probe for the detection of intracellular pH and GSH.

N-doped carbon dots used as a fluorescence probe can distinguish cancer cells from normal cells by pH and evaluate intracellular GSH.