Hindawi Journal of Sensors Volume 2021, Article ID 8822558, 7 pages https://doi.org/10.1155/2021/8822558 Research Article Design and Synthesis of a Fluorescent Probe Based on Copper Complex for Selective Detection of Hydrogen Sulfide Guanglan Mao ,1 Chenxi Liu ,2 Nan Yang ,2 Linlin Yang ,2 and Guangjie He 2 1Department of Traditional Chinese Medicine, The Third Affiliated Hospital of Xinxiang Medical College, East Section of Hualan Avenue, Xinxiang, 453000 Henan Province, China 2Xinxiang Key Laboratory of Forensic Science Evidence, School of Forensic Medicine, Xinxiang Medical University, Jinsui Road No. 601, Xinxiang, 453003 Henan Province, China Correspondence should be addressed to Guangjie He; [email protected] Received 20 September 2020; Revised 29 January 2021; Accepted 2 February 2021; Published 16 February 2021 Academic Editor: Roberto Paolesse Copyright © 2021 Guanglan Mao et al. This 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. fl 2+ A novel uorescence probe NA-LCX was rationally designed and synthesized for the sequential recognition of Cu and H2S by the 2+ combination of hydroxyl-naphthalene and diformylphenol groups. The response properties of NA-LCX for Cu ions and H2S with “on-off-on” manner were investigated by fluorescence emission spectra. A highly selective and sensitive response of complex NA- 2+ μ LCX-Cu for H2S over other competing amino acids was observed with a limit of detection at 2.79 M. The stoichiometry of NA- LCX toward Cu2+ ions was determined to be 1 : 1 by the UV-Vis absorption spectrum, and the coordination configuration was calculated by density functional theory (DFT) calculations. Moreover, probe NA-LCX was applied successfully for the 2+ recognition of Cu ions and H2S in living cells. 1. Introduction chemical analysis [18, 19], liquid chromatography mass spec- trometry [20, 21], and fluorescence analysis [22–24]. Among fi fl Hydrogen sul de (H2S), the simplest biomercapto com- them, uorescence analysis is more desirable due to its simple pound, is not only a rotten egg smelling gas pollutant but also operation, high sensitivity, wide dynamic range, high fluores- the third gasotransmitter and cellular signaling molecule cence quantum yield, good biocompatibility, noninvasive- after CO and NO [1, 2]. The endogenous H2S could regulate ness, and ability of in situ real-time detection in living vascular smooth muscle tension and cardiac contractile func- systems [25]. In recent years, many fluorescent probes for fl ff tion, anti-in ammatory and antioxidative stress, neurotrans- H2S detection have been reported on account of di erent mitter transmission, and insulin signaling inhibition, which types of strategies such as reduction reactions [26, 27], nucle- plays an important role in the physiological and pathological ophilic addition reactions [28, 29], dinitrophenyl ether/sulfo- processes of the cardiovascular, nervous, immune, and diges- nyl ester cleavage [30, 31], and metal sulfide precipitation – – tive systems [3 7]. The concentrations of H2S in the normal reaction [32 40]. However, there are some limitations to metabolism often maintain dynamic equilibrium, while those reaction methods as well as the products obtained via abnormal changes of the H2S level could induce serious those reactions. For example, those reactions are insensitive, health problems, such as heart diseases [8, 9], chronic complex, and time-consuming; moreover, fluorescent probes obstructive pulmonary diseases [10, 11], cirrhosis [12, 13], prepared via those reactions are sometimes not biocompati- and Alzheimer [14, 15]. Hence, it is crucial to exploit a highly ble and sometimes unstable in the presence of biological sensitive and selective method for the detection of hydrogen thiols (glutathione, cysteine, etc.) [31]. The strategy by using sulfide in living systems. a metal displacement approach is in high demand for its fast fi Many conventional methods for H2S detection have been response and high sensitivity and selectivity. Sul de is known developed, including colorimetric method [16, 17], electro- to react with copper ion to form very stable CuS with a very 2 Journal of Sensors CH3 CH 3 H N 2 NH N N + HN NH O O O OH O O OH HO OH HO NA-LCX Scheme 1: Synthesis route of ligand NA-LCX. −36 low solubility product constant Ksp =6:3×10 (for cya- 2.3. Synthesis of the Probe NA-LCX. 3-Hydroxy-2-naphtho- −20 nide, Ksp =3:2×10 ). Thus, the utilization of the higher hydrazide (0.40 g, 2.0 mmol) and 2,6-diformyl-4-methylphe- affinity of Cu2+ towards sulfide for designing a specificCu2+ nol (0.164 g, 1.0 mmol) were dissolved in 30 mL of ethanol, respectively. Then, the solution was mixed dropwise and sensor to sequentially identify H2S has received considerable fl fi attention because it can effectively eliminate the interference re uxed for 6 hours. The obtained mixture was ltered, washed, and vacuum dried to afford ligand NA-LCX of other analytes in the system. 1 6 δ Naphthalene derivatives with an electron donor-π-accep- (Scheme 1). H NMR (400 MHz, d -DMSO), 8.76 (s, 2H), π 8.48 (s, 2H), 7.94 (d,J =8:2Hz, 2H), 7.78 (d,J =8:2Hz, 2H), tor (D- -A) structure have been widely used due to good J =7:6Hz J =14:7 optical properties, such as high fluorescence quantum yield, 7.61 (s, 2H), 7.53 (t, , 2H), 7.37 (dd, , 7.1 Hz, 4H), 2.36 (s, 3H). 13C NMR (101 MHz, d6-DMSO), good biocompatibility, and light stability. Herein, we synthe- δ sized a new fluorescent probe NA-LCX based on hydroxyl- 164.23, 155.37, 154.54, 147.20, 136.36, 130.95, 130.72, 129.15, 128.76, 127.24, 126.35, 124.31, 120.70, 120.33, and naphthalene and diformylphenol which have excellent coor- + dination ability to metal ions. The probe showed an obvious 111.02, 20.41. MS: calculated [(M+Na) ] 555.1644; found “on-off” fluorescence quenching response toward Cu2+, and 555.1638. the NA-LCX-Cu2+ complex showed an “off-on” fluorescence 2+ enhancement response toward H2S in a DMSO/HEPES (3 : 2 2.4. Synthesis of Complex NA-LCX-Cu . In a 50 mL round v/v, pH = 7:4). The photophysical capabilities of probe NA- bottom flask, ligand NA-LCX (0.053 g, 0.1 mmol) and 2+ 2+ · LCX for Cu and NA-LCX-Cu for H2S were studied in Cu(ClO4)2 6H2O (0.037 g, 0.1 mmol) were mixed in 15 mL details from fluorescence spectroscopy, absorption spectros- methanol. After being stirred for 30 minutes, the obtained copy, and fluorescence images in vivo. precipitate was filtered, washed, and dried to afford the NA-LCX-Cu2+ complex. 2. Experimental Section 2.5. General Method for Cell Imaging. Human liver cancer 2.1. Reagents and Materials. 2,6-Diformyl-4-methylphenol HepG-2 cells were cultured in a 12-well plate, and when the was purchased from Shanghai TCI Chemical Industry Devel- cell saturation exceeded 80%, ligand NA-LCX and probe opment Co. Ltd. 3-Hydroxy-2-naphthoyl hydrazide was pur- NA-LCX-Cu2+ solution were added. The mixture was then chased from Sinopharm Chemical Reagent Co. Ltd. All the incubated for 3 hours in a CO2 incubator and washed three other chemicals and reagents were commercially available times with precooled PBS, followed by the addition of 1 mL and were analytical grade. All solvents were purified by stan- PBS. The resulting mixture was observed under a Leica dard procedures. Aqueous solutions (2:0×10−2 M) of per- DMI8 inverted fluorescence microscope. chlorates of various metal ions (Al3+,K+,Na+,Mg2+,Ca2+, Cr3+,Mn2+,Fe2+,Fe3+,Co2+,Ni2+,Zn2+,Cd2+,Hg2+,Ag+, Pb2+, and Cu2+) and various amino acids (Asn, Glu, Cys, 3. Results and Discussion Phe, Pro, Gln, Arg, Trp, Asp, Tyr, Ile, Thr, His, Gly, Met, 3.1. UV-Vis Spectrum Recognition of Probe NA-LCX toward Leu, Ala, Val, Ser, Lys, Cys, GSH, Hcy, and NAC) were pre- Cu2+. UV-Vis absorption spectra of ligand NA-LCX (20 μM) pared before use. in the presence of Cu2+ ions in DMSO : HEPES (3 : 2, v/v, pH = 7:4) at various concentrations were performed in 2.2. Apparatus and Instruments. The following are the appa- Figure 1. Upon the addition of Cu2+ ions, the UV-Vis absorp- ratus and instruments used in the study: UV-Vis spectropho- tion intensities of ligand NA-LCX at 312 nm and 366 nm tometer (UV-2600, Shimadzu Corporation), fluorescence decreased gradually, while the intensities at 346 nm and spectrophotometer (FS5, Edinburgh, UK), nuclear magnetic 438 nm increased with a change in color from yellowish to resonance spectrometer (NMR) (Ascend™ 400, Bruker Co., orange. A plateau was reached for the 438 nm wavelength USA), precision pH meter (PHS-3E, Zhengzhou Tailai upon the addition of about 1.5 equivalents of Cu2+ ions. To Instruments Co., Ltd.), and inverted fluorescence microscope further determine the molar ratio of probe NA-LCX to Cu2+ (Leica DMI8, Leica Microsystems, Germany). ions, Job’splotfitting was performed and the molar ratio of Journal of Sensors 3 1.2 0.45 6 0.40 7 0.35 5 1.0 0.30 6 0 4 F 0.25 / F 3 0.20 5 0.8 Absorbance 0.15 2 0.10 1 0.05 4 0.6 0 F 0 5 10 15 20 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 / 2+ F 3 Equiv. of Cu Equiv. of Na2S Absorbance 0.4 2 0.2 1 0.0 0 300 400 500 600 450 500 550 600 650 700 750 800 Wavelength (nm) Wavelength (nm) Figure μ 1: UV-Vis spectrum of ligand NA-LCX (20 M) with the Figure 2+ 2+ v/v fi 3: Fluorescence spectra change of probe NA-LCX-Cu addition of Cu ions in DMSO : HEPES (3 : 2, ).