Maximum Excitation Wavelengths Research Articles

Smartphone-based non-invasive detection of salivary uric acid based on the fluorescence quenching of gleditsia sinensis carbon dots.

Asmartphone-based non-invasive method was developedfor salivary uric acid detection using Gleditsia Sinensis carbon dots (GS-CDs). The GS-CDs synthesized by the one-pot hydrothermal method emitted blue fluorescence at a maximum excitation wavelength of 350nm and had good fluorescence stability in the presence of different ions, while showing selectivity to uric acid solution. The ability of uric acid(UA) to quench the fluorescent substances present in the GS-CDs, was confirmed through HPLC-FLD and LC-MS, FTIR and XPS. The results showed that UA reacted with GS-CDs, with a decrease in hydroxyl groups and the formation of carboxyl groups. The fluorescence quenching suggested a possible dynamic quenching mechanism. In addition, a smartphone-based non-invasive detection method was developed for the detection of salivary UA levels, which reflects blood UA levels. This study provides a new perspective on the utilization of GS shells and advances the development of non-invasive testing for UA.

Quantitative determination of Penicillamine in pharmaceutical samples by Copper-Modified Drug-Based carbon dots utilizing a turn ON-OFF-ON strategy

In the present work, a sensitive and simple method is developed for sensing and quantifying Penicillamine (PA) in pharmaceutical samples utilizing a copper-conjugated carbon dots probe. The proposed method employed a turn ON-OFF-ON strategy with carbon dots fluorescence quenching by addition of copper and fluorescence recovery of up to 91 % by addition of PA. Expired moxifloxacin tablet powder was used as a novel carbon precursor during the synthesis of the carbon dots (MOX–CDs) which involved a single-step solvothermal procedure. The prepared MOX–CDs demonstrated excitation independent yellowish green fluorescence emission (Quantum yield ≈ 51 %) with the maximum excitation and emission wavelengths being observed at 410 nm and 510 nm respectively. The suggested strategy for assaying PA offered a detection limit of 0.14 µM (S/N = 3) and a linear response from 2.5 µM to 50 µM (R2 = 0.9987). In addition to offering merits like accuracy and sensitivity, the proposed probe also provides a method for solid waste treatment by reprocessing expired moxifloxacin powder.

Green and sustainable synthesis of fluorescent carbon dots from crown daisy for information encryption application

Herein, we report a sustainable and eco-friendly synthesis of green fluorescent carbon dots (G-CDs) from crown daisy, a common vegetable, and o-phenylenediamine via a hydrothermal method. The synthesized G-CDs were comprehensively characterized using various spectroscopic techniques, revealing a maximum excitation wavelength of 436 nm and emission at 539 nm with a quantum yield of up to 14.5 % in ethanol. The optical properties was systematically investigated, demonstrating the excellent salt tolerance, pH stability, and photostability of the G-CDs. Notably, the G-CDs exhibited excitation-independent emissions behavior, indicating a single type of fluorescent emission center. The practical application of G-CDs as anti-counterfeiting ink was demonstrated by generating a clear QR code pattern under UV illumination, showcasing their potential for information encryption and anti-counterfeiting applications. This work not only provides a sustainable and cost-effective approach for G-CD synthesis but also highlights their promising prospects in optical anti-counterfeiting and information encryption domains.

Developing a Photoacoustic Probe for in vivo Tumor pH Detection by Gaussian calculation

pH dysregulation is a major feature of cancer, and the development of advanced photoacoustic probes capable of monitoring pH is important for both diagnosis and treatment of cancer. Previous work (done by Tijana Jokic’s group) found that aza-BODIPY molecule has better photoacoustic properties and this was investigated in depth, leading to the development of new pH probes, but the functionality of the molecule can be upgraded again if the photoacoustic properties of the molecule can be further expanded, while the maximum wavelength of the molecule can be further extended to fit the commercial range. This study optimized the previous molecule based on the Gaussian program, and the new molecule with NO2 attached to R4 showed the best properties in which the maximum excitation wavelength reached 770.85 nm.

A Water‐Soluble Fluorescent Probe Derived from Pyridine‐2,6‐Dicarboxylic Acid: Synthesis, Interaction with Ions, and Two‐Photon Microscopy

AbstractTwo‐photon excited fluorescence is a process in which the excited fluorophore relaxes and emits fluorescence after two‐photon absorption. Combined with appropriate two‐photon fluorescent probes, two‐photon microscopy enables observation deep inside tissue without damage. Former reports showed that the two‐photon absorption cross sections of donor–acceptor (D–A) dipoles, as well as D‐π‐D and D–A–D quadrupoles can be strengthened by using strong D–A groups. In this study, a novel water‐soluble fluorescent probe with D‐π‐A structure containing pyridine‐2,6‐dicarboxylic acid unit was synthesized. The maximum excitation wavelength and emission wavelength of the probe in aqueous solution were 328 nm and 471 nm, respectively. The fluorescence emitted by the probe can be quenched by various metal cations. The pyridyl N and carboxyl O in the probe formed chelates with Cu2+, which resulted in a fluorescence quenching response, and showed a linear relationship between fluorescent intensity and Cu2+ concentration with wide linear range and low limit of detection. CCK‐8 tests showed the probe had no obvious toxicity to 4T1 cells in the range of 0.4–50 μmol L−1, and the cell survival rate was above 86 %. The probe had a large two‐photon absorption cross section ranging from 680 nm to 820 nm. The two‐photon absorption cross section reached 100 GM at 760 nm of excitation wavelength. By means of microscopic imaging of 4T1 cells stained with the probe, one‐photon fluorescence represented blue emission, while two‐photon fluorescence represented bright green emission. The probe was proved to have good cell permeability, and preferred to target nucleus, showing application potential in two‐photon fluorescence imaging technology.

Green synthesis of carbon dots from Hakka yellow wine lees: Characterization and applications for Fe3+ and NaFeEDTA sensing

In this study, Hakka yellow wine lees carbon dots (HYWL-CDs) with an average diameter of 1.75 nm are synthesized from Hakka yellow wine lees (HYWL) via a one-pot hydrothermal method. Results of X-ray photoelectron spectroscopy and FTIR reveal the presence of C=C and –OH in the HYWL-CDs. Additionally, the HYWL-CDs present excitation-wavelength dependence, with maximum excitation and emission wavelengths of 360 and 440 nm, respectively. The fluorescence of the HYWL-CDs can be quenched by Fe3+. The Fe3+ concentration is correlated linearly with the quenching rate over a linear range of 0.6–1.1 mg/mL, and the limit of detection is 0.18 μg/mL. And phenols have been shown to be present in HYWL-CDs, and the color reaction between phenols and FeCl3 is most likely the mechanism by which FeCl3 causes fluorescence burst in HYWL-CDs. Moreover, the HYWL-CDs demonstrate significant potential for detecting NaFeEDTA in iron-fortified soy sauces, the linear-fit equation was y = 185.38x + 1024.6 (R2 = 0.9995) The HYWL-CDs are loaded onto paper strips, iron-fortified straw mushroom dark soy sauce showed noticeable color changes, which allows one to differentiate normal soy sauce from iron-fortified soy sauce more conveniently and provides a new perspective for the high-value utilization of yellow wine lees.

Partially Bio-Based Benzoxazine Monomers Derived from Thymol: Photoluminescent Properties, Polymerization Characteristics, Hydrophobic Coating Investigations, and Anticorrosion Studies.

In this work, four thymol-based benzoxazines were synthesized using four primary amines with different chain lengths, namely methylamine, ethylamine, 1-propylamine, and 1-butylamine, which are then named T-m, T-e, T-p, and T-b, respectively. The optical properties of the synthesized thymol-based benzoxazines were examined via the photoluminescent study of their solutions in acetone. The results show that all the prepared benzoxazines emitted blue light with the maximum wavelengths from 425 to 450 nm when irradiated by the excitation wavelengths from 275 to 315 nm. The maximum excitation wavelengths are found to be 275 nm. The polymerization of the thymol-based benzoxazines is triggered by heat treatments with different conditions (160, 180, and 200 °C for 1 h). According to the FTIR results, the heat-curing process introduces a presence of the OH peak, of which intensity increases as the curing temperature increases. Thermal decompositions of thymol-based benzoxazines regarding TGA analyses reveal the enhancement of thermal stability of the benzoxazines with respect to the N-substituent chain length, as significantly observed the change in the first thermal decomposition at temperature ranged from 253 to 260 °C. Synthesized benzoxazine derivatives are further employed to coat the substrate, e.g., the glass slides. The investigation of the water contact angle shows that the coating of the benzoxazines onto the surface improves the hydrophobicity of the substrate, resulting in the enlargement of the contact angle from 25.5° to 93.3°. Moreover, the anticorrosion performance of the polybenzoxazine coatings is examined using potentiodynamic polarization techniques. The results illustrate the anticorrosion efficiency of the thymol-based polybenzoxazine up to 99.99%. Both hydrophobic and electrochemical studies suggest the feasibility for employing benzoxazines in anticorrosion coating applications.

Photoactivatable Blue Fluorescent Protein.

Photoactivatable and photoswitchable fluorescent proteins (FPs) are sophisticated molecular tools that in combination with super-resolution microscopy are helping to elucidate many biological processes. Through the Y66H mutation in the chromophore of the violet fluorescent protein SumireF, we created the first photoactivatable blue fluorescent protein (PA-BFP). This protein is rapidly activated over ordinary UV transilluminators at 302 or 365 nm in irreversible mode and by direct exposition to sunlight. The maximum excitation and emission wavelengths of this protein, centered at 358 and 445 nm, respectively, resemble the values of DAPI-the blue stain widely used in fluorescence microscopy to visualize nucleic acids in cells. Therefore, the immediate use of PA-BFP in cellular biology is clear because the technology required to follow this new genetically encoded reporter at the microscopic level has already been established. PA-BFP can potentially be used together with other photoactivatable fluorescent proteins of different colors to label multiple proteins, which can be simultaneously tracked by advanced microscopic techniques.

Bioinspired Carbon Dots-Based Fluorescent Sensor for the Selective Determination of a Potent Anti-Inflammatory Drug in the Presence of Its Photodegradation Products.

Herein, we synthesized biogenic carbon dots (CDs) with blue-shifted maximum excitation (λex/λem of 320/404 nm) from largely wasted tangerine seeds for the first time via a one-step hydrothermal method. The biogenic CDs exhibit a maximum excitation wavelength that overlaps with the absorption spectrum of ketorolac tromethamine (KETO) at 320 nm. The developed CDs serve as a turn-off fluorescent probe via an inner filter effect (IFE) quenching mechanism. The resulting CDs have high quantum yield (QY) (39% ± 2.89%, n = 5) and exhibited great performance toward KETO over a concentration range of 0.50-16.00 μg/mL with a limit of detection (LOD) = 0.17 μg/mL. The nanoprobe achieved a high % recovery in assaying KETO in tablet dosage form and had not been significantly affected by various interferents including co-formulated and co-administered drugs. The nanoprobe shows selectivity toward KETO, even in the presence of its photocatalytic degradation products. It can effectively investigate the elimination of KETO from aquatic systems and test its stability in pharmaceutical preparations. The developed nanoprobe underwent a comprehensive evaluation of its environmental impact using analytical eco-scale (AES), complex green analytical procedure index (Complex GAPI), and the Analytical GREEnness calculator (AGREE). The sustainability of the developed nano sensor was assessed and compared to the reported metal-based quantum dots probe for KETO using the innovative RGB 12 model, considering 12 white analytical chemistry (WAC) perspectives.

Screening method for the analysis of Rhodamine B in chili powder

Rhodamine B is a synthetic dye known to enhance the visual appearance of chili powder. Due to its toxicity and carcinogenicity, chromatographic methods have been developed to monitor its presence in adulterated chili powder, but their assays are laborious, time consuming and expensive for screening purposes. The present studies propose an alternative for screening Rhodamine B in chili powder samples. The method combines thin layer chromatography (TLC) to solid surface room-temperature fluorescence spectroscopy. The scrape-dissolution procedure common to the instrumental analysis of TLC procedures was replaced with a fiber optic probe coupled to a commercial spectrofluorometer. The determination of Rhodamine B on the chromatographic plate is based on its retardation factor and maximum excitation and emission wavelengths. The limit of detection (1.9 ng.mL−1) and the limit of quantitation (5.2 ng.mL−1) are well below the usual contamination of Rhodamine B in adulterated foods.

Determination of Trace Nickel(ΙΙ) Using a Kinetic Fluorescence Method with a Morin-Hydrogen Peroxide System

Nickel (Ni[Ⅱ]) was used to catalyze the hydrogen peroxide oxidation of morin to weaken its fluorescence. In Na2B4O7-NaOH buffer solution at pH 10.10, Ni(Ⅱ) has an obvious catalytic effect on the oxidation of morin by H2O2 solution. At the maximum excitation and emission wavelengths (λex = 440 nm and λem = 530 nm), the fluorescence intensity of the system is linearly correlated with the concentration of Ni(II) within a certain range. The linear equation is ΔF = 11463ρ (μg/mL) − 34.70, and the R2 = 0.9992. The linear range is 1.6 × 10-2 − 9.6 × 10-2 μg/mL, and the detection limit was 2.9 × 10-4 μg/mL. Finally, the samples of tap water, Yellow River water and tea were analyzed, with the recoveries being 99.6%, 107.3%, and 104.6%, respectively. This method is suitable for the determination of trace Ni(II) in water samples.

Synthesis and characterization of a europium coordination polymer as a fluorescent sensor for the selective detection of PO43−, DTZ, and NFT

A new europium coordination polymer [Eu(2,3′-oba)(2,3′-Hoba)(IP)]n (Eu-CP) has been synthesized by hydrothermal reaction using 2,3′-oxbis (benzoic acid) (2,3′-H2oba) and 1H-imidazole [4,5-f] [1,10]-phenanthroline (IP). The semi-rigid ligand 2,3′-H2oba and large rigid ligand IP form a 1D chain structure of the Eu-CP, which is further stacked into a 3D supramolecular architecture through C–H⋯O and O–H⋯N hydrogen bonding. Below 400 °C, the Eu-CP does not decompose. It shows good chemical stability in common solvents and aqueous solutions with pH in the range of 3–12. The Eu-CP emits strong red luminescence, attributed to the 5D0→7FJ (J = 0–4) transitions of the Eu3+ ion. The luminescence quantum yield and lifetime are 61% and 0.94 ms, respectively. The Eu-CP has a broad absorption in the range of 200–400 nm, with a maximum excitation wavelength of 365 nm. Furthermore, Eu-CP is used as a sensor for the detection of PO43−, dimetridazole (DTZ), and nitrofurantoin (NFT) in aqueous systems, and NFT in biological samples (calf serum) based on the luminescence quenching effect. Notably, luminescent Eu-CP@film was prepared for sensing PO43−, NFT, and DTZ, which can be reused more than 20 times, facilitating a visually simple and rapid online detection platform. In addition, we also studied the luminescence quenching mechanism of Eu-CP by analytes.

RP-HPLC Separation and 1H NMR Identification of a Yellow Fluorescent Compound-Riboflavin (Vitamin B2)-Produced by the Yeast Hyphopichia wangnamkhiaoensis.

The yeast Hyphopichia wangnamkhiaoensis excretes a brilliant yellow fluorescent compound into its growth culture. In this study, we isolated and identified this compound using reverse-phase high-performance liquid chromatography-diode array detector (RP-HPLC-DAD) as well as 1H NMR and UV-Vis spectroscopy. Two of the three RP-HPLC-DAD methods used successfully separated the fluorescent compound and involved (1) a double separation step with isocratic flow elution, first on a C18 column and later on a cyano column, and (2) a separation with a linear gradient elution on a phenyl column. The wavelengths of maximum absorption of the fluorescent compound-containing HPLC fractions (~224, 268, 372, and 446 nm) are in good agreement with those exhibited by flavins. The 1H NMR spectra revealed methyl (δ 2.30 and 2.40) and aromatic proton (δ 7.79 and 7.77) signals of riboflavin. The 1H NMR spectra of the samples spiked with riboflavin confirmed that the brilliant yellow fluorescent compound is riboflavin. The maximum excitation and emission wavelengths of the fluorescent compound were 448 and 528 nm, respectively, which are identical to those of riboflavin.

Live synthesis of selective carbon dots as fluorescent probes for cobalt determination in water with an automatic microanalyzer

A new strategy integrating the straight synthesis of carbon dots (CDs) and their direct use for the determination of heavy metals by means of fluorescence quenching is presented. The proposal consists of a modular analyzer, which includes a low temperature co-fired ceramics (LTCC) microreactor for the synthesis of CDs and a cyclic olefin copolymer (COC) microfluidic platform, which automatically performs a reverse flow injection analysis (rFIA) protocol for the determination of heavy metal ions in water by CD fluorescence quenching. As a proof of concept, nitrogen-doped CDs were synthesized from acrylic acid and ethylenediamine (ED) with quantum yields (QYs) of up to 44%, which are selective to cobalt. With the described system, we synthesized homogeneous CDs without the need for further purification and with the minimum consumption of reagents, and optimized fluorescence measurements can be performed with freshly obtained luminescent nanomaterials that have not undergone decomposition processes. They have an average hydrodynamic diameter of 4.2 ± 0.9 nm and maximum excitation and emission wavelengths at 358 nm and 452 nm, respectively. The system allows the automatic dilution and buffering of the synthesized CDs and the sample prior to the determination of cobalt. The concentration of cobalt was determined with good sensitivity and a limit of detection of 7 μg·L−1 with a linear range of 0.02–1 mg·L−1 of Co2+. Spiked tap water and river water samples were analyzed, obtaining recovery from 98 to 104%. This demonstrates the potential of the equipment as an efficient on-site control system for heavy metal monitoring in water.Graphical abstract

Carbon dots enhanced ultra‐low‐density fluorescence proppants with both high‐compressive strength and anti‐deformation ability

AbstractThe polymer ultra‐low‐density proppants are critical to the development of slick‐water fracture technology, but which were prone to obvious deformation under high pressure in the fractures. To increase the stiffness of the styrene‐divinylbenzene copolymer (SDB) and obtain desired ultra‐low‐density (ULD) proppants, carbon dots (CDs) were introduced in‐situ considering their characteristics as the zero‐dimensional carbon nanomaterial. Taking the compressive strength and axial deflection, and so forth into consideration, the synthesis conditions of CDs modified SDB microspheres (CDs‐SDBs) were optimized. Taking the graphite modified SDBs (MG‐SDBs) as a reference, the density of CDs‐SDBs did keep almost constant at about 1.1800 ~ 1.1899 g·cm−3 with the increase of CDs amount. The CDs‐SDBs not only possess high‐peak pressure (41.5 N) but also minute axial deflection (0.090 mm). The advantages of CDs‐SDBs over MG‐SDBs become even more pronounced under higher pressure, which can withstand closure pressure of 80 MPa with a small crush ratio of 4.47%. CDs‐SDBs exhibit significant photoluminescence performances with maximum excitation and emission wavelengths of 634 nm and 554 nm.Highlights CDs‐SDBs as ULD proppants with high strength and anti‐deformation were developed. Advantages of CDs‐SDBs become more pronounced under high‐closure pressure. With increasing of CDs amount, apparent density of CDs‐SDBs keep almost constant. Axial deflection of CDs‐SDBs is only 0.09 mm under 41.5 N. The crush ratio is only 4.47% under 80 MPa closure pressure.

Development of turn-on fluorescent sensor based on green emissive carnosine-modified tannic acid carbon dots for the selective detection of ascorbic acid

Ascorbic acid (AA) is an indispensable biological antioxidant with anti-aging potential in neurological disorders such as Parkinson’s and Alzheimer’s. Its abnormal concentrations in physiological fluids like human serum can lead to neurological complications. In this study, a turn-on fluorescent sensor was developed using dipeptide (i.e., carnosine) modification of the polyphenolic tannic acid (TA) carbon dots (CDs) (TATA-CDs) for AA detection. Blue-fluorescent TATA-CDs were synthesized using the hydrothermal treatment of the TA and ethylene glycol-bis(β-aminoethyl ether)-N,N,N′,N′-tetraacetic acid (EGTA) as a nitrogen (N) dopant. TATA-CDs were functionalized with carnosine (TATA-Car CDs) using a facile stirring reaction. Their morphological and optical properties were studied via TEM, XRD, UV–Vis, and fluorescence spectroscopy. TATA-Car CDs displayed green fluorescence with excitation and emission wavelength maxima of 400 and 509 nm, respectively. These novel CDs are responsible for the selective turn-on fluorescence sensing of AA (0 to 15 nM) when mixed with copper (Cu2+) ions and deliver a low detection limit of 1.34 nM. The practicality and feasibility of TATA-Car CDs were investigated in human serum samples. From this perspective, the proposed fluorescent sensor is more suitable for the real-time monitoring of AA in different neurological disorders.

Dihydroxanthene-derived fluorescent probe with near-infrared excitation and emission maxima for detecting human carboxylesterase-2 and bioimaging

Carboxylesterases in human body play pivotal roles for catalyzing the hydrolysis of endogenous and exogenous substances such as lipids, thioesters and amides. Carboxylesterase-2 (CES2) as a major isoform of carboxylesterases is highly expressed in human digestive tract, and usually serves as an important mediator for pharmacokinetics and pharmacodynamics of ester medications or ester prodrugs. Therefore, developing effective strategies to detect and track CES2 in cells or tissues is of great significance for understanding its physiological and pharmacological effects on various diseases and therapeutic outcomes. In this study, we synthesized a fluorescent probe (CHQ-E) with near-infrared (NIR) excitation and emission maxima based on dihydroxanthene fluorophore for highly selective and sensitive detection of CES2. This probe exhibited rapid response (3 min), excellent sensitivity (detection limit = 0.35 ng/mL) and high binding affinity (Km = 9.4 μM) towards CES2, as well as low cytotoxicity towards living biosamples. Significantly, the maximum fluorescence excitation and emission wavelengths led to excellent optical properties of this probe including less photodamage, few autofluorescence and superior tissue penetration depth (180 µm). Moreover, CHQ-E has been applied to monitoring CES2 activity in drug-induced liver injury and its remediation models. Results of fluorescence imaging in vivo indicate the broad potential of CHQ-E for clinical diagnosis and evaluation of pharmaceuticals.

A Turn-On Fluorescence Sensor Based on Nitrogen-Doped Carbon Dots and Cu2+ for Sensitively and Selectively Sensing Glyphosate

Glyphosate has excellent herbicidal activity, and its extensive use may induce residue in the environment and enter into humans living through the food chain, causing negative impact. Here, water-soluble 1.55 nm size nitrogen-doped carbon quantum dots (NCDs) with strong blue fluorescence were synthesized using sodium citrate and adenine. The maximum excitation and emission wavelengths of NCDs were 380 nm and 440 nm, respectively. The above synthesized NCDs were first used for the construction of a fluorescence sensor for glyphosate detection. It was found that Cu2+ could quench the fluorescence of NCDs effectively through the photoinduced electron transfer (PET) process, which was confirmed using fluorescence lifetime measurements. Additionally, the fluorescence was restored with the addition of glyphosate. Hence, a sensitive turn-on fluorescence sensor based on NCDs/Cu2+ for glyphosate analysis was developed. The LODs of glyphosate for water and rice samples were recorded as 0.021 μg/mL and 0.049 μg/mL, respectively. The sensor was applied successfully for ultrasensitive and selective detection of glyphosate in environmental water and rice samples with satisfied recoveries from 82.1% to 113.0% using a simple sample pretreatment technique. The proposed strategy can provide a significant potential for monitoring glyphosate residue in water and agricultural product samples.

Rapid Analysis of Estrogens in Meat Samples by High Performance Liquid Chromatography with Fluorescence Detection.

A novel reagent named 4-(N-methyl-1,3-dioxo-benzoisoquinolin-6-yl-oxy)benzene sulfonyl chloride (MBIOBS-Cl) for the determination of estrogens in food samples by high-performance liquid chromatography (HPLC) with fluorescence detection has been developed. Estrogens could be easily labeled by MBIOBS-Cl in Na2CO3-NaHCO3 buffer solution at pH 10.0. The complete labeling reaction for estrogens could be accomplished within five minutes, the corresponding derivatives exhibited strong fluorescence with the maximum excitation and emission wavelengths at 249nm and 443nm, respectively. The derivatization conditions, such as the molar ratio of reagent to estrogens, derivatization time, pH, temperature, and buffers were optimized. Derivatives were sufficiently stable to be efficiently analyzed by HPLC with a reversed-phase Agilent ZORBAX 300SB-C18 column with a good baseline resolution. Excellent linear correlations were obtained for all estrogen derivatives with correlation coefficients greater than 0.9998. Ultrasonic-Assisted extraction was used to optimize the extraction of estrogens from meat samples with a recovery higher than 82%. The detection limits (LOD, S/N = 3) of the method ranged from 0.95 to 3.3μg· kg-1. The established method, which is fast, simple, inexpensive, and environment friendly, can be successfully applied for the detection of four steroidal estrogens from meat samples with little matrix interference.

Rapid and sensitive fluorescence determination of oxytocin using nitrogen-doped carbon dots as fluorophores

In this work, a novel nitrogen (N)-doped carbon dots (N-CDs) was prepared with quercetin as the carbon source and o-phenylenediamine as the nitrogen source by hydrothermal synthesis, and their application as fluorophores for selective and sensitive determination of oxytocin were reported. The fluorescence quantum yield of the as-prepared N-CDs, which exhibited good water solubility and photostability, was about 6.45 % using rhodamine 6 G as reference substance, and the maximum excitation (Ex) and emission (Em) wavelength were 460 nm and 542 nm, respectively. The results illustrated that the direct fluorescence quenching of N-CDs fluorophore for the detection of oxytocin achieved good linearity in the range of 0.2–5.0 IU/mL and 5.0–10.0 IU/mL, the correlation coefficients were 0.9954 and 0.9909, respectively, and the detection limit was 0.0196 IU/mL (S/N = 3). The recovery rates were 98.8∼103.8 % with RSD= 0.93 %. The interference experiments showed that common metal ions, possible impurities introduced in production and coexisting excipients in the preparation had little adverse influence on selective detection of oxytocin by the developed N-CDs based fluorescent detection method. The mechanism study on the fluorescence quenching of N-CDs by oxytocin concentrations under the given experimental conditions demonstrated that there were internal filtration effect and static quenching in the system. The developed fluorescence analysis platform for the detection of oxytocin had been proved to be rapid, sensitive, specific and accurate, and to be used for the quality inspection of oxytocin.