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Hindawi Journal of Analytical Methods in Chemistry Volume 2023, Article ID 7515979, 9 pages https://doi.org/10.1155/2023/7515979 Research Article Preparation of One-Emission Nitrogen-Fluorine-Doped Carbon Quantum Dots and Their Applications in Environmental Water Samples and Living Cells for ClO Detection and Imaging Qianchun Zhang , Haijiang Du , Siqi Xie , Fengling Tian , Xixi Long , Shan Liu , and Yun Wu School of Biology and Chemistry, Key Laboratory for Analytical Science of Food and Environment Pollution of Qian Xi Nan, Minzu Normal University of Xingyi, Xingyi 562400, China Correspondence should be addressed to Qianchun Zhang; email@example.com and Siqi Xie; firstname.lastname@example.org Received 2 June 2022; Revised 5 March 2023; Accepted 13 April 2023; Published 25 April 2023 Academic Editor: Idaira Pacheco-Ferna´ndez Copyright © 2023 Qianchun Zhang et al. Tis is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Hypochlorite (ClO ) has received extensive attention owing to its signifcant roles in the immune defense and pathogenesis of numerous diseases. However, excessive or misplaced production of ClO may pose certain diseases. Tus, to determine its biological functions in depth, ClO should be tested in biosystems. In this study, a facile, one-pot synthesis of nitrogen-fuorine- doped carbon quantum dots (N, F-CDs) was developed using ammonium citrate tribasic, L-alanine, and ammonium fuoride as raw materials under hydrothermal conditions. Te prepared N, F-CDs demonstrate not only strong blue fuorescence emission with a high fuorescence quantum yield (26.3%) but also a small particle size of approximately 2.9 nm, as well as excellent water solubility and biocompatibility. Meanwhile, the as-prepared N, F-CDs exhibit good performance in the highly selective and sensitive detection of ClO . Tus, a wide concentration response range of 0–600 μM with a low limit of detection (0.75 μM) was favorably obtained for the N, F-CDs. Based on the excellent fuorescence stability, excellent water solubility, and low cell toxicity, the practicality and viability of the fuorescent composites were also successfully verifed via detecting ClO in water samples and living RAW 264.7 cells. Te proposed probe is expected to provide a new approach for detecting ClO in other organelles. chemiluminescence , potentiometric , and colorimetric 1. Introduction methods . Although these methods ofer unique advan- −5 Sodium hypochlorite at concentrations between 10 and tages, they still possess several limitations, including special −2 10 mol/L is widely used as a household bleach and disin- equipment, tedious operation, complicated sample prepara- fectant [1, 2]. ClO is an important type of reactive oxygen tion, and long time. Compared with other analytical methods, species that is widely used in the antimicrobial immunity of fuorescent probes ofer inherent benefts due to their high living systems [3, 4]. It is extensively used in daily life as sensitivity , excellent specifcity , simple manipulation disinfectant and household cleaning agent for water treatment [13, 14], low cost, short analytical times , and deep bio- . However, an excessive level of reactive oxygen species imaging capacity , which beneft application strategies for may cause certain pathological problems such as tissue aging, in vitro assays and in vivo imaging studies. For example, chronic infammatory diseases, and bladder cancer [4, 6]. McCarroll  reported a pH-dependent probe to detect Terefore, an efective method detecting ClO in environ- HOCl. Furthermore, certain HOCl probes can monitor HOCl mental water samples and living cells should be established. in living cells. Duan et al.  proposed a hepatoma-specifc Currently, various approaches have been developed to probe for examining HOCl, and Yuan et al.  developed detect and quantify hypochlorite, such as coulometric , two-photon fuorescent probes for HOCl imaging in 2 Journal of Analytical Methods in Chemistry mitochondria and lysosomes. Although the precursors play 2.3. Preparation of N, F-CDs. Ammonium citrate tribasic a vital role in improving the quantum yield and property of (243 mg), L-alanine (445 mg), and ammonium fuoride CDs, the researchers reported many precursors and prepared (222 mg) as precursor were added to 10 mL of ultrapure diferent CDs to detect ClO and perform imaging in vitro and water. Te mixture was carefully mixed by ultrasonication vivo [18–20]. Methods for endogenous ClO detection and (10 min) and then transferred to a polytetrafuoro- measurement in RAW 264.7 cells using nitrogen-fuorine- ethylene-lined autoclave (50 mL) and reacted at 160 C doped carbon quantum dots (N, F-CDs) are few, and it is for 4 h in an oven. Subsequently, the resulting solution ° ° necessary to hunt for the precursors and develop the sensitive was naturally cooled to room temperature (25 C± 10 C) and efcient sensors. Terefore, designing efcient carbon and purifed using a 0.22 μm end remover flter to remove quantum dots for quantitative analysis of ClO and selective large particles. imaging of ClO in RAW 264.7 cells is of great signifcance. Here, N, F-CDs were simply prepared utilizing the novel 2.4. Probe Selectivity and Detection of Hypochlorite. Te precursor via one-pot hydrothermal strategy. Te as- selectivity of prepared composites was estimated through the prepared composites displayed excellent fuorescence + − addition of various ions and small molecules. Na , H PO , 2 4 properties, good water solubility, low toxicity, and bio- 3+ − − 2+ − 2+ − 2+ − Fe , ClO , Cl , Ca , NO , Mn , HCO , I, Cu , I , L 3 3 3 compatibility owing to nitrogen and fuorine doping. Ad- + 2+ 2+ 2+ − (+)-ascorbic acid, L-cysteine, K , Ba , Mg , Zn , ClO , ditionally, the N, F-CDs exhibited excellent selectivity and 2− 2− 2− − S O , H O , SO , Cr O , and MnO were added to 2 8 2 2 3 2 7 4 high sensitivity for ClO with efective fuorescence 1.96 mL of N, F-CD solution (0.094 mg/mL). Ten, the quenching based on their unique performance. Tus, we fuorescence spectrum was measured under an excitation successfully developed an efective strategy to quantitatively wavelength of 356 nm after 5 min. analyze ClO in real water. In addition, this probe was Te sensitivity of ClO was investigated in 1.96 mL seamlessly used for the imaging of living cells and sensitive of N, F-CD solution (0.094 mg/mL). In a typical assay, detection of endogenous ClO in living RAW 264.7 cells. the fuorescence data of N, F-CDs with diferent con- centrations of ClO (0.00, 1.00, 6.25, 12.5, 25.0, 50.0, 100, 2. Experimental and 600 μM) were investigated. Te emission spectrum of the above solution was recorded under excitation 2.1. Materials. L-Alanine and lipopolysaccharides (LPS) were wavelength of 356 nm. All measurements were repeated purchased from J&K Scientifc Co. Ltd. (Hebei, China). Am- fve times. monium citrate tribasic, sodium hydroxide, sodium chloride, barium chloride, sodium hypochlorite solution, and K Cr O 2 2 7 were supplied by Chongqing East Chuandong Chemical Co. 2.5.RealSampleAssays. Te feasibility and practicality of the Ltd. (Chongqing, China). Ammonium fuoride and potassium prepared N, F-CDs-based probe were tested by generalizing iodide were provided by Xilong Scientifc Co. Ltd. (Shantou, the detection of diferent water samples. Lake, tap, and China). Quinine sulfate, L(+)-ascorbic, cupric chloride, dibasic swimming pool water samples were collected from Wanfeng sodium phosphate, potassium dihydrogen phosphate, sodium Lake (Xingyi, China), Minzu Normal University of Xingyi bicarbonate, calcium chloride, manganese sulfate, potassium (Xingyi, China), and its gymnasium (Xingyi, China), re- chloride, L-cysteine, phorbol 12-myristate 13-acetate (PMA), spectively. All raw samples were fltered through a 0.22 μm hydrogen chloride (36.5%, w/w), BaCl ·2H O, MgCl , ZnCl , 2 2 2 2 end remover flter to remove the large particles. Te con- K S O , H O , K SO , and KMnO were sourced from Aladdin 2 2 8 2 2 2 3 4 centration of ClO in the water samples was detected using Chemistry Co. Ltd. (Shanghai, China). Ultrapure water was the developed probe method. In brief, 40 μL of the water used in all experiments. sample was added into the N, F-CD solution (0.094 mg/mL, 1.96 mL), fuorescence intensity was measured at excitation wavelength of 356 nm, and the reliability of the developed 2.2. Instrumentation and Characterization. A Shimadzu method was further assessed via the spiked recovery RF-6000 spectrometer (Tokyo, Japan) was used for fuo- approach. rescence intensity measurements. A UV-5500 spectropho- tometer (Shanghai Metash Instruments Co. Ltd., China) recorded the UV-vis absorption spectra at 20 C. Te particle 2.6. Cytotoxicity and Cellular Imaging. Before cellular im- size of N, F-CDs was accurately measured using Tecnai aging of RAW 264.7 cells, the MTT assay was used to G2F30 instrument (Termo Fisher Scientifc, USA). Te evaluate the potential cytotoxicity of N, F-CDs for RAW Fourier-transform infrared (FT-IR) spectra were measured 264.7 cells. Te details are as follows: RAW 264.7 cells were using an iS10 FT-IR spectrometer (Nicolet Corporation, incubated and treated with diferent concentrations USA). Atomic force microscopy (AFM) image was obtained (15.6–1000 μg/mL) of N, F-CDs at 37 C for 24 h. Afterwards, on Dimension Icon (Bruker, Germany). To investigate the the MTT reagent (20 μL, 5 mg/mL) was added to each hole, N- and F-doping status in N, F-CDs, X-ray photoelectron and the cells were incubated at 37 C for 4 h. Finally, 150 μL spectroscopy (XPS) was carried out using a 250 Xi in- dimethyl sulfoxide was added to each hole to dissolve and strument (Termo Fisher Scientifc). Confocal microscopic crystallize the precipitates. Cell survival rate was computed images were obtained using UltraVIEW VoX& IX81 as the ratio of cells in the solution treated with the probe to (Olympus, Japan) scanning. those in the control group. Journal of Analytical Methods in Chemistry 3 To explore the potential application of N, F-CDs, mouse peaks at 284.8, 401.0, 531.9, and 685.6 eV, which are ascribed macrophage-like cell line RAW 264.7 was cultured in to C1s, N1s, O1s, and F1s, respectively (Figure S2B). Te HyClone with fetal bovine serum (10%, w/w) at 37 C under elemental analysis results of N, F-CDs revealed the atomic 5% CO atmosphere. Ten, the cells were transferred to new ratios of C, O, N, and F to be 60.22%, 28.18%, 10.45%, and confocal dishes and divided into fve groups. Tree groups 1.15%, respectively. Tis fnding indicates considerable were incubated with multifarious concentrations (50, 100, doping percentages of F and N. and 200 μg/mL) of the N, F-CDs (3 h) and normal saline Te high-resolution spectrum of C1s (Figure 2(a)) signal (4 h) in each well. Meanwhile, the remaining two groups of exhibits three peaks at 284.8 (C–C/C–N), 285.8 (C–O), and cells were stimulated by PMA (2 μg/mL) and LPS (100 μg/ 288.9 eV (C–F). As depicted in Figure 2(b), the two peaks at mL) for 4 h; then, the cell groups were cultivated with N, F- 399.5 (C–N�C) and 401.6 eV (N–H) appeared in the high- CDs for 3 h to detect the endogenous ClO . Te group resolution N1s spectrum. Te O1s spectrum (Figure 2(c)) incubated with 200 μM N, F-CDs was added to each hole and demonstrates three ftted peaks at 531.7 eV, 532.4, and, cultivated for 3 h. Subsequently, NaOCl (50 μM) was added 533.9 eV, which are attributed to the C�O, C–O, and C–OH for another 4 h to detect the exogenous ClO . Ten, groups, respectively. Te F1s spectrum (Figure 2(d)) peaks at phosphate-bufered saline solution (pH � 7.4) was used to 685.7 and 686.7 eV correspond to the semi-ionic C–F and wash the cells for three times. Te fuorescence of stained covalent C–F bonds [24, 26], respectively. Te XPS results cells was observed, and the images were taken in blue are consistent with the FT-IR results. Hydrophilic functional channels (370 nm). groups such as –NH , C–OH, and O�C–OH on the surface of N, F-CDs impart excellent water solubility . 3. Results and Discussion 3.3. Optical Properties of N, F-CDs. Te N, F-CDs were 3.1. Optimization of Preparation Conditions for N, F-CDs. distilled with water (1.14 mg/mL), and then their optical Te preparation conditions including reaction time, reaction properties were explored. It is important to explore the temperature, and diluted concentration were studied excitation and emission wavelengths of N, F-CDs for their (Figure S1). As shown in Figure S1A, the fuorescence in- potential applications. Te excitation wavelength was ap- tensity increased with the reaction time from 2–4 h. After proximately 300–390 nm, and the emission band was con- 4 h, the fuorescence intensity of N, F-CDs gradually de- centrated at approximately 350–550 nm (Figure 3(a)). Te creased. In consequence, 4 h was selected as the optimal maximum excitation peak was observed at 356 nm, while the reaction time. Figure S1B demonstrates that the N, F-CDs maximum emission peak was observed at 440 nm. Tese illustrate the best fuorescence properties below 160 C. Fi- fndings revealed the typical fuorescence dependence of N, nally, Figure S1C shows the strongest fuorescence intensity F-CDs between the excitation and emission wavelengths. with a raw N, F-CD solution at 80-fold dilution (1.14 mg/ Te aqueous solution of N, F-CDs (Figure 3(b), left inset) mL). presented strong blue fuorescence emission (right) under 356 nm. Te UV-vis spectra of N, F-CDs show the char- acteristic peaks at 340 nm, which can be attributed to the 3.2. Characterization of N, F-CDs. Te morphology of N, F- n–π∗ transition of the N, F-CDs core due to the presence of CDs was characterized by transmission electron microscopy C�O, C-F, and N-H groups on their surfaces . (TEM) and AFM (Figure 1). Te TEM images display that Fluorescence stability plays a crucial role in quantitative the prepared N, F-CDs are spherical composites with an analysis. As shown in Figure S3A, the N, F-CD fuorescence average diameter of 2.9 nm and a narrow particle size dis- intensity did not change within 24 h, proving the excellent tribution of 2.3–3.5 nm (Figure 1(b)). Most particles are fuorescence stability of N, F-CDs. Te photoluminescence amorphous carbon, as can been seen in the high-resolution response of N, F-CDs was studied by adding NaOH and HCl TEM image. Te interplanar spacing of lattice fringes is to adjust the pH to diferent levels. As illustrated in 0.203 nm, corresponding to the (100) facets of graphitic Figure S3B, the fuorescence intensity of N, F-CDs was carbon . As shown in Figures 1(c) and 1(d), the AFM closely related to pH; when the pH was 1.0–4.0, the fuo- images are consistent with the TEM results, showing an rescence intensity increased gradually; within the wide average height of N, F-CDs of approximately 2.9 nm. pH range of 4.0–14.0, the fuorescence intensity did not To reveal the surface-functional groups of N, F-CDs, the change signifcantly, which meant that this range was FT-IR and XPS survey spectra were adopted. As shown in suitable for application. Moreover, quinine sulfate −1 Figure S2A, the wide absorption at 3107 cm is attributed to (QY = 54% in 0.1 M H SO at 360 nm) was used as the 2 4 the stretching vibrations of O–H . Moreover, the small standard sample to calculate the fuorescence quantum yield −1 peaks at 1593 and 1455 cm originate from the stretching (QY) of N, F-CDs. Te average QY of the N, F-CDs in vibration band of C�C and C–N groups , respectively. ° ° aqueous solution was 26.3% at 24 C± 4 C. −1 Te peaks at 1014 and 1255 cm are consistent with the bending vibrations of the C–O and C–F groups , re- −1 − spectively. Te characteristic peaks at 1408 and 744 cm are 3.4. Fluorescence Measurement of ClO . Tanks to the ex- attributed to C�N and –NH , respectively. Moreover, the cellent properties of N, F-CDs, their selectivity was explored XPS survey spectrum, which is further used to investigate the in the presence of diferent ions and small molecules in + − 3+ surface state and composition of N, F-CDs, displays the 100 μM solutions. Te species included Na , H PO , Fe , 2 4 4 Journal of Analytical Methods in Chemistry (B) 2.2 2.4 2.6 2.8 3.0 3.2 3.4 3.6 Particle size (nm) Relative count Gauss fit of relative count 7.9 nm (D) -1 -4.3 nm -2 0 50 100 150 200 250 0.0 Height 1.0 μm Diameter (nm) Figure 1: (A) High-resolution transmission electron microscopy (TEM) images of the N, F-CDs (inset). (B) Size distribution. (C) Atomic force microscopy (AFM) images of the nitrogen-fuorine-doped carbon quantum dots (N, F-CDs). (D) Height profle of N, F-CDs. − − 2+ − 2+ − 2+ − ClO , Cl , Ca , NO , Mn , HCO , I, Cu , I , L where F and F are the fuorescence intensities of N, F-CDs 3 3 3 0 + 2+ 2+ 2+ − − (+)-ascorbic acid, L-cysteine, K , Ba , Mg , Zn , ClO , at 356 nm in the absence and presence of ClO , respectively, 2− 2− 2− − − S O , H O , SO , Cr O , and MnO . Te comparison and C is the concentration of ClO . Te linear relationship 2 8 2 2 3 2 7 4 was confrmed based on the relative strength change of F /F, was 2.50–600 μM with a correlation coefcient R of 0.996. where F is the fuorescence intensity in the absence of the Te limit of detection was calculated to be (S/N = 3, n = 5) chaf interferent and F is that in the presence of the chaf 0.75 μM. Te developed probe method clearly demonstrated 2− − − interferent. For example, Cr O and MnO produced low that N, F-CDs can be used to detect trace ClO amounts and 2 7 4 quenching, with values that were 1.36, and 1.06 that of ClO , evidenced their promising applications in environmental respectively. Evidently, the ClO ion was quenched with and biomedical systems. other tested ions and small molecules, indicating that N, F- CDs are selective, highly sensitive, and strongly tolerant in 3.5. Detecting ClO in Water Samples. To explore the ClO detection (Figure 4(a)). Furthermore, the fuorescence practical applications of N, F-CDs, the developed method intensity gradually decreased with increasing concentration − was used to detect trace amounts of ClO in water samples of ClO from 2.5 μM to 600 μM (Figure 4(b)), and the obtained from Wanfeng Lake, tap, and a swimming pool. As quenched relationship could be quantifed using the linear shown in Table 1, the recovery ranged from 92.2% to 120%, correlation in the following equation: with relative standard deviations (RSDs) of less than 12%. Tese results indicate that the N, F-CDs-based probing Y � � 0.0174C + 0.917, (1) method was accurate and reliable. Moreover, the proposed method demonstrated that the probe can be used to detect ClO in diferent water samples. Height (nm) Relative Count (%) Journal of Analytical Methods in Chemistry 5 7.2 2.0 C1s N1s 6.0 1.6 4.8 3.6 1.2 2.4 0.8 1.2 0.0 0.4 292 290 288 286 284 282 406 404 402 400 398 396 Binding Energy (eV) Binding Energy (eV) C–C/C–N C–N=C C–O N–H C–F (a) (b) 10.0 2.0 F1s O1s 8.0 1.9 6.0 1.8 4.0 1.7 2.0 1.6 0.0 1.5 538 536 534 532 530 528 690 688 686 684 682 680 Binding Energy (eV) Binding Energy (eV) C=O semi-ionic C–F C–O covalent C–F C–OH (c) (d) Figure 2: Elemental analysis of N, F-CDs. (a) C1s, (b) N1s, (c) O1s, and (d) F1s high-resolution XPS spectrum. 400 3.5 8.0 EX=356 EM=440 7.0 3.0 6.0 2.5 Abs 5.0 2.0 4.0 1.5 3.0 1.0 2.0 1.0 0.5 0.0 0.0 -1.0 350 400 450 500 550 600 300 350 400 450 500 550 600 Emission Wavelength (nm) Wavelength (nm) (a) (b) Figure 3: (a) Excitation-emission matrix for the UV-vis absorption spectra of N, F-CDs. (b) UV-vis absorption, fuorescence excitation, and emission spectra of N, F-CDs. Inset shows images of the N, F-CDs under daylight (a) and UV irradiation (b). Abs, absorption; EM, emission; EX, excitation; FL, fuorescence. Excitation Wavelength (nm) 5 Counts (×10 ) Counts (×10 ) Absorbance 4 4 Counts (×10 ) Counts (×10 ) FL Intensity (a.u.) (×10 ) 6 Journal of Analytical Methods in Chemistry 3.0 1.8 12.0 Y=0.0174C+0.917 1.5 10.0 2.5 R =0.995 0 µM 1.2 8.0 2.0 C1O 0.9 6.0 1.5 0.6 4.0 1.0 600 µM 0.3 2.0 0.5 0.0 0.0 0 100 200 300 400 500 600 700 350 400 450 500 550 600 650 C1O (µM) Wavelength (nm) Medicines (a) (b) (c) Figure 4: (a) Fluorescence intensities of N, F-CDs alone and of those in the presence of 100 μM of various metal ions and common + − 3+ − − 2+ − 2+ − 2+ − molecules, including (A) Na ; (B) H PO ; (C) Fe ; (D) ClO ; (E) Cl ; (F) Ca ; (G) NO ; (H) Mn ; (I) HCO ; (J) I; (K) Cu ; (L) I ; (M) 2 4 3 3 3 + 2+ 2+ 2+ − 2− 2− 2− L (+)-ascorbic acid; (N) L-cysteine; (O) K ; (P) Ba ; (Q) Mg ; (R) Zn ; (S) ClO ; (T) S O ; (U) H O ; (V) SO ; (W) Cr O ; and (X) 2 8 2 2 3 2 7 − − − MnO . (b) Fluorescence intensity of ClO at diferent concentrations. (c) Dependence of F /F on the concentration of ClO . 4 0 Table 1: Determination of ClO in Wanfeng Lake, tap, and swimming pool water (n � 5). Spiked concentration Sample Concentration (μM) Found (μM) Recovery (%) RSD (%) (μM) 5.00 6.01 120 4.1 Wanfeng Lake — 50.0 56.5 113 5.5 100 117 117 2.6 5.00 11.2 115 11 Tap water 5.43± 0.59 10.0 15.1 96.7 3.9 5.00 6.00 120 12 Swimming pool water — 50.0 46.0 92.2 5.6 100 115 115 5.9 4.0 3.0 2.5 3.2 2.0 2.4 1.5 1.6 1.0 0.8 0.5 0.0 0.0 0 25 50 75 100 125 150 300 350 400 450 500 550 600 −1 Time (ns) Wavelength (cm ) N, F-CDs N, F-CDs N, F-CDs+ClO N, F-CDs+ClO (a) (b) Figure 5: (a) Fluorescence decay times of N, F-CDs and N, F-CDs + 100 μM ClO . (b) UV-vis absorption spectra of N, F-CDs and N, F- CDs + 100 μM ClO . − − 3.6. Possible Mechanism between N, F-CDs and ClO . Te 100 μM ClO were evaluated. Teir average lifetimes were possible quenching mechanism between ClO and N, F-CDs 8.2 and 7.5 ns, respectively (Figure 5(a)). Te lifetime of N, F- plays a vital role. For an in-depth exploration of the CDs+ 100 μM ClO evidently decreased compared to that of quenching mechanism of ClO toward N, F-CD fuores- N, F-CDs alone, exhibiting that a dynamic quenching model cence, the fuorescence lifetimes of N, F-CDs and N, F-CDs+ can be observed. Because static quenching does not shorten F /F (A) (B) (C) (D) (E) (F) Intensity (a.u.) (×10 ) (G) (H) (I) (J) (K) (L) (M) (N) (O) (P) (Q) (R) (S) (T) (U) (V) (W) (X) FL Intensity (a.u.) (×10 ) Absorbance F /F 0 Journal of Analytical Methods in Chemistry 7 50 µg/mL 100 µg/mL 200 µg/mL 200 µg/mL+LPS+PMA 200 µg/mL+NaOC1 Figure 6: Confocal microscope images of RAW 264.7 cells in N, F-CD solution at an excitation wavelength of 370 nm and emission wavelengths of 430–470 nm. the lifetime, fuorescence quenching can be attributed to the stability, low biotoxicity, water solubility, and bio- dynamic mode. Tese results were further verifed by the compatibility. Tus, the broad application prospects of N, F- UV-vis absorption spectra in Figure 5(b). After adding ClO CDs were demonstrated. First, N, F-CDs can function as to the N, F-CD solution, the absorption intensity markedly highly selective and sensitive fuorescent probes for ClO . decreased at 340 nm. Te decrease process revealed that Second, they can be used for quantitatively detecting ClO in ClO may selectively oxidate the amino N groups on the real water samples, ofering a low detection limit of 0.75 μM surface of N, F-CDs to form new substances with less π–π and broad linear range of 2.50–600 μM. Finally, owing to and n–π conjugate systems at 300–600 nm, thereby leading their low biotoxicity, water solubility, and biocompatibility, to the fuorescence quenching of N, F-CDs. Tese results N, F-CDs can be used in in vitro imaging. Te results show proved that a dynamic quenching mode occurred between that the probes can not only exhibit cell permeability but can − − N, F-CDs and ClO [29, 30]. also efectively detect endogenous/exogenous ClO in living RAW 264.7 cells. Tis probe is expected to provide a new approach for detecting ClO in other organelles. 3.7. Cytotoxicity Assays and Cell Imaging. To assess the cy- totoxicity of N, F-CDs and develop their potential appli- Data Availability cation in bioimaging, traditional MTTassays were employed to test their cytotoxicity in RAW 264.7. As expected, more Te data used to support the fndings of this study are than 83% of the RAW 264.7 cells were viable after exposure available from the corresponding author upon reasonable −1 at 500 μg·mL (Figure S4). Te results exhibit excellent request. properties of the N, F-CDs, such as low toxicity and excellent biocompatibility, indicating their potential use as Conflicts of Interest biomarkers. Te practicality and feasibility of N, F-CDs were further Te authors declare that they have no conficts of interest. evaluated in cell imaging. As shown in Figure 6, the obtained confocal image of RAW 264.7 cells became brighter with Acknowledgments increasing concentration of the probe. Te overlaid image reveals that N, F-CDs can easily penetrate cell membranes or Financial support was received from the National Natural translocate by endocytosis. Moreover, when the bright N, F- Science Foundation of China (21505115), the Top Scientifc CDs (200 μg/mL) were added with LPS (100 μg/mL) and and Technological Talents in Universities of Guizhou PMA (2 μg/mL) or NaOCl (50 μM), the intracellular fuo- Province (KY2018078), Guizhou Basic Research Project (ZK rescence confocal intensity of RAW 264.7 cells weakened 561), the Science and Technology for Youth Talent because of the intracellular presence of trace ClO . Tere- Growth Project of the Guizhou Provincial Education De- fore, these experimental results further prove that the N, F- partment (KY2020217), the Key Laboratory for Analytical CDs probes can track native ClO and the fuctuations of Science of Food and Environment Pollution of Qian Xi Nan endogenous/exogenous ClO levels in live RAW 264.7 cells. (2021-2-31), and the Projects of Xingyi Normal University for Nationalities (21XYZJ01 and 21XYXS06). 4. Conclusions Supplementary Materials Novel N, F-CDs (QY � 26.3%) were successfully synthesized using ammonium citrate tribasic, L-alanine, and ammonium Figure S1: optimization of preparation conditions—(A) fuoride via a facile, low-cost, ecofriendly hydrothermal reaction time, (B) reaction temperature, and (C) diluted approach. Te as-prepared N, F-CDs are nanometer-sized concentration. FL, fuorescence. 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Journal of Analytical Methods in Chemistry – Hindawi Publishing Corporation
Published: Apr 25, 2023
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