Electrochemical Determination of Chrysophanol Based on the Enhancement Effect of Acetylene Black Nanoparticles
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Colloids and Surfaces B: Biointerfaces 103 (2013) 94–98 Contents lists available at SciVerse ScienceDirect Colloids and Surfaces B: Biointerfaces jou rnal homepage: www.elsevier.com/locate/colsurfb Electrochemical determination of chrysophanol based on the enhancement effect of acetylene black nanoparticles a a,c a,∗ b b b,∗ Yuanyuan Zhang , Yanying Wang , Kangbing Wu , Shichao Zhang , Yu Zhang , Chidan Wan a School of Chemistry and Chemical Engineering, Huazhong University of Science and Technology, Wuhan 430074, China b General Surgery, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan 430030, China c College of Chemistry and Materials Science, South-Central University for Nationalities, Wuhan 430074, China a r t i c l e i n f o a b s t r a c t Article history: Acetylene black (AB) nanoparticles were readily dispersed into water in the presence of dihexade- Received 6 August 2012 cyl hydrogen phosphate. After evaporation of water, the surface of glassy carbon electrode (GCE) was Received in revised form 2 October 2012 coated with AB nanoparticles as confirmed from the scanning electron microscopy measurements. The Accepted 9 October 2012 transmission electron microscopy images indicated that AB nanoparticles possessed porous structure. Available online xxx Electrochemical behavior of chrysophanol was studied, and a sensitive oxidation peak was observed in pH 3.6 acetate buffer solution. Compared with the bare GCE, the AB nanoparticles-modified GCE greatly Keywords: increased the oxidation peak current of chrysophanol, showing remarkable signal enhancement effect. Acetylene black Nanoparticles The influences of pH value, amount of AB, accumulation potential and time on the signal enhancement of chrysophanol were studied. As a result, a novel electrochemical method was developed for the deter- Surface enhancement −1 Chrysophanol mination of chrysophanol. The linear range was from 1.5 to 200 g L , and the detection limit was −1 −9 × Electrochemical detection 0.51 g L (2.01 10 M) after 2-min accumulation. Finally, this method was used in traditional Chi- nese medicines, and the results consisted with the values that obtained by high-performance liquid chromatography. © 2012 Elsevier B.V. All rights reserved. 1. Introduction 2-chlorophenol [9], kojic acid [10], erythromycin [11], topotecan [12] and 6-benzylaminopurine [13] were greatly increased by AB Chrysophanol (1,8-dihydroxy-3-methylanthraquinone) is a free nanoparticles. anthraquinone compound and a secondary metabolite of medici- The main objective of this work is to develop a simple and sen- nal plant rhubarb. Chrysophanol has been reported to have many sitive electrochemical method for the detection of chrysophanol pharmacological effects such as anti-inflammatory activity [1], utilizing the excellent properties of AB nanoparticles. Thus, insolu- anti-microbial activity [2] and anti-cancer action [3,4]. Therefore, ble AB nanoparticles were firstly dispersed into water and then used the detection of chrysophanol is quite important and interest- to modify the GCE surface, constructing a sensing film for chryso- ing. Until now, the widely used method for the detection of phanol. On the surface of AB nanoparticles-modified GCE (denoted chrysophanol is high-performance liquid chromatography (HPLC) as nano-AB/GCE), the oxidation signal of chrysophanol increased [5–8]. Although electrochemical detection possesses high sensitiv- remarkably. Undoubtedly, the sensitivity of chrysophanol detec- ity, short analysis time, low cost and handling convenience, the tion is greatly enhanced by AB nanoparticles. study regarding electrochemical determination of chrysophanol is very limited. 2. Experimental Acetylene black (AB), a special kind of carbon black, has attracted 2.1. Reagents much attention and been widely used in the field of electroanaly- sis because of extraordinary properties such as high accumulation All chemicals were of analytical grade and used as received. efficiency, excellent electric conductivity and large surface area. Chrysophanol (National Institute for the Control of Pharmaceu- For example, the response signal and detection sensitivity of tical and Biological Products, Beijing, China) was dissolved into −1 ethanol to prepare 0.1 g L standard solution, and stored in the ◦ fridge at 4 C. AB nanoparticles (purity >99.99%) was purchased ∗ from STREM Chemicals (USA). Dihexadecyl hydrogen phosphate Corresponding authors. Tel.: +86 27 87543632; fax: +86 27 87543632. (DHP) was obtained from Sigma. E-mail address: [email protected] (K. Wu). 0927-7765/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.colsurfb.2012.10.015 Y. Zhang et al. / Colloids and Surfaces B: Biointerfaces 103 (2013) 94–98 95 2.2. Instruments Electrochemical measurements were performed on a CHI 830C electrochemical workstation (Chenhua Instrument, Shanghai, China). A conventional three-electrode system, consisting of an AB-modified GC working electrode, a saturated calomel reference electrode (SCE) and a platinum wire auxiliary electrode, was employed. Scanning electron microscopy (SEM) characterization was conducted with a Quanta 200 microscope (FEI Company, Netherlands). Transmission electron microscopy (TEM) image was measured using a Tecnai G220 microscope (FEI Company, Netherlands). HPLC detection of chrysophanol was carried out with an Agi- lent 1100, coupled with a UV-VIS detector. The C18 analytical column (4.6 mm × 150 mm × 5 m) was used. The mobile phase was methanol–H2O (85:15, v/v), filtered through a 0.2-m Mil- −1 lipore filter prior to use. The flow rate was 1 mL min , and the sample injection volume was 20 L. The detection wavelength was 254 nm. 2.3. Preparation of nano-AB/GCE AB nanoparticles (10.0 mg) and DHP (10.0 mg) were added into doubly distilled water (10.0 mL), and then sonicated in a KQ-50B ultrasonicator for 1 h. Before modification, the GCE with diameter of 3 mm was polished with 0.05 m alumina slurry, and sonicated in doubly distilled water for 2 min. After that, the GCE surface was coated with 5 L AB suspension, and the water was evap- orated from the surface under an infrared lamp in air. The DHP film-modified GCE was prepared as the same procedure without addition of AB. 2.4. Sample preparation Four representative rhubarb samples were purchased from a local pharmacy, and then treated as follows. The sample was firstly pulverized, and 50 mg of the powder was accurately weighed and Fig. 1. TEM (A) and SEM (B) images of AB nanoparticles. added into 25 mL of ethanol. After 30-min ultrasonication and sub- sequent 6-min centrifugation at 8000 rpm, the clear liquid phase was collected. The extraction was repeated, and the extract solu- 3.2. Enhancement effect of AB nanoparticles tion was finally diluted to 50.0 mL for further measurement. Spiked samples were prepared by adding a known amount of chrysophanol The electrochemical responses of low concentration of chryso- standard to sample before extraction. phanol on different electrodes were compared using differential pulse voltammetry (DPV). Fig. 2 shows the DPV responses of 2.5. Analytical procedure Acetate buffer (0.1 M) at pH of 3.6 was used for the detec- tion of chrysophanol. After 2-min accumulation under open-circuit, the differential pulse voltammograms were recorded from −0.7 to − 0.2 V, and the oxidation peak current at −0.48 V was measured for chrysophanol. The pulse amplitude was 50 mV, the pulse width −1 was 40 ms and the scan rate was 40 mV s . 3. Results and discussion 3.1. Characterization of AB nanoparticles The inner structure of AB nanoparticles in suspension was char- acterized using TEM. As shown in Fig. 1A, the particle size was about 80 nm and porous structure was clearly observed. In addition, the surface morphology of AB film on GCE surface was studied via SEM −1 Fig. 2. DPV curves of 30 g L chrysophanol on GCE (a), DHP film-modified GCE (Fig. 1B). It was apparent that the GCE surface was coated with (b) and nano-AB/GCE (d). (c) DPV curve of nano-AB/GCE in pH 3.6 acetate buffer homogeneous AB nanoparticles. without chrysophanol. Accumulation was performed under open-circuit for 2 min. 96 Y. Zhang et al. / Colloids and Surfaces B: Biointerfaces 103 (2013) 94–98 −1 −1 Fig. 4. Variation of oxidation peak current of 30 g L chrysophanol with the Fig. 3. DPV curves of 50 g L chrysophanol on nano-AB/GCE in 0.1 M acetate buffer amount of AB suspension. Accumulation was performed under open-circuit for solutions with different pH values. Accumulation was performed under open-circuit 2 min. Error bar represents the standard deviation of triple measurements. for 2 min. −1 30 g L chrysophanol in pH 3.6 acetate buffer. After 2-min In order to discuss the effect of accumulation potential, the accumulation under open-circuit, an oxidation peak at −0.48 V oxidation peak currents of chrysophanol at different potentials was observed on GCE surface (curve (a)). On the surface of DHP were measured individually. The oxidation peak currents of film-modified GCE (curve (b)), the oxidation peak current of chryso- chrysophanol increased gradually when the accumulation poten- phanol decreased slightly. This is because that DHP, a surfactant − tials changed from 1 to −0.6 V. In addition, the oxidation peak with poor electric conductivity, forms a perfect film on GCE sur- currents of chrysophanol under open-circuit accumulation were face and blocks the electron transfer of chrysophanol. However, the also studied. It was found that the oxidation peak current under oxidation signal of chrysophanol greatly increased on the surface open-circuit accumulation was much higher, suggesting that the of nano-AB/GCE (curve (d)). The notable peak current enlargement accumulation of chrysophanol on AB nanoparticles surface is non- indicates that AB nanoparticles exhibit strong enhancement effect electrostatic. In order to achieve high sensitivity, accumulation toward the oxidation of chrysophanol.