Proceedings of the 4th International Conference on Nanostructures (ICNS4) 12-14 March, 2012, Kish Island, I.R. Iran

Nanodiamond–graphite decorated with Silver nanoparticles for determination of Thioridazine N. Hosseini Nassab a, S. Shahrokhian a Department of Chemistry, Sharif University of Technology, Tehran 11155-9516, Iran [email protected]

Abstract: In this work, nanodiamonds–graphite decorated with silver nanoparticles (AgNPs/NDG) was used as an effective and new modifier for electrode surface modification. The decoration of NDG with AgNPs improved colloidal dispersion of the decorated NDG in water, affording uniform and stable thin films for improving the surface properties of the working electrode. The resulting modified electrode was used for sensitive voltammetric determination of Thioridazine (TR). Because of enchantment of surface area peak current for TR increased significantly. The effect of different experimental parameters, such as deposited amount of the modifier suspension, pH, accumulation time, and scan rate on the voltammetric response of TR was investigated using cyclic voltammetry. Under optimal conditions, the modified electrode showed a wide linear response to the concentration of TR in the range of 0.08–100 μM with a detection limit of 10 nM. The proposed method was successfully applied in determination of TR in biological samples with satisfactory results. The modified electrode showed excellent sensitivity, selectivity, long-term stability and remarkable reproducibility.

Keywords: Thioridazine; Nanodiamond; Ag Nanoparticles; Modified Electrode; Cyclic Voltammetry 1.Introduction Nowadays, various carbon-based nanomaterials have attracted enormous interest due to their excellent electrical, chemical and mechanical properties, which make them suitable for developing nano-electronics and electrochemical sensors [1-3]. Recently, nano-crystalline diamond (also called nanodiamond, ND) as a novel carbon material, base on its special properties such as high surface area, biocompatibility and non- toxicity, can be used in fabrication of electrochemical sensors [4-5]. In this region, metal nanoparticles have attracted much attention as well. Due to this fact, interesting classes of carbon nanostructures derivatives were formed by deposition of metallic nanoclusters on their surfaces. Furthermore, uniform dispersion of metallic nanoparticles decorated on their surfaces can yield ideal nanocatalysts for application in chemically modified electrodes [6-7]. 2.Experimental 2.1. Chemicals and reagents TR, in the form of thioridazie (1:1) (>99.0% purity), was purchased from Natco India. All other chemicals were of analytical reagent grade from Merck. All aqueous solutions were prepared with doubly distilled deionized water. 2.2. Apparatus Voltammetric experiments were performed using a Metrohm potentiostat/galvanostat model 797VA. A conventional three electrode system was used with a basal plane pyrolytic graphite working electrode (BPPGE, unmodified or modified, d=3mm), a saturated Ag/AgCl reference electrode and a Pt wire counter electrode. A BPPGE, or an EPPGE (4.9mm diameter, Le Carbone,

Ltd., Sussex, U.K.) was used as the working electrode. A digital pH/mV/Ion meter (CyberScan model 2500)was used for the preparation of the buffer solutions. 2.3. Preparation of nanosilver decorated Diamond nanoprticles Simple process was used to synthesis the AgNPs/DNG. Briefly, DNG was mixed with mixture solution of 38% formaldehyde, absolute ethyl alcohol and double distilled water. Then, mixture solution of 35 g L−1 silver nitrate (AgNO3) solution and 25% ammonia solution were dropped one by one into the mixture of DNPs– formaldehyde–alcohol–water solution, while; the pH value was kept about 8–9. After completing the reaction, the product was centrifuged and washed by doubly distilled water several times then dried in vacuum oven at 60 ◦C. 2.4. Preparation of modified PGE Before modification, the PGE was polished with 0.05μm alumina slurry on a polishing cloth, rinsed thoroughly with doubly distilled water, an. The modifier suspension was prepared by dispersing 1mg of the AgNPs/DNG in 1.0 ml of doubly distilled water under sonication for 30min. The AgNPs/DNG modified PGE was prepared by casting 10μL of the mentioned black suspension on the PG electrode surface using a micropipette and left to dry at room temperature. Before the voltammetric measurements, the modified electrode was cycled between -0.2 and 1V (scan rate 100mVs−1) in 0.01mol L−1 Phosphat buffer solution pH 7 for several times until acquiring the reproducible responses.

3.Results and Discussion 3.1. Characterization of the AgNPs/ DNG

Proceedings of the 4th International Conference on Nanostructures (ICNS4) 12-14 March, 2012, Kish Island, I.R. Iran

A

300

Current(A)

The microscopic structure of AgNPs/DNG was characterized using SEM images. Fig. 1.A shows the well dispersed/deposited Ag nanoparticles on the surface of DNG. From the SEM images, the size of Ag nanoparticles was estimated to be less than 20–25 nm. The electrochemical response of the AgNPs/ NDG/ PG electrode in purged N2 phosphat buffer solution (0.01mol L−1, pH 7) is presented in Fig.1.B. A pair of redox peak was observed on the surface of the modified PGE at 0.28 and −0.05 V. It can be suggested that the observed redox peak is corresponding to the redox behavior of the AgNPs on the surface of the modified electrode, which proves that NDs were decorated with AgNPs.

200 B

100 3.2. Electrochemical characterization of TR on the surface of various electrodes Fig. 2 depicts the cyclic voltammetric responses of TR at the different modified electrodes in a 0.1M phosphate buffer solution of pH 7.0, recorded at a scan rate of 100mVs−1. There is a very small anodic peak for TR on the surface of the bare PGE. In these voltammograms, the peak current was enhanced considerably at the DNG/PGE and AgNPs/DNG/PGE compared to the bare PGE.

0 0.4

0.7

0.8

0.9

1.0

260

170

80

-10 0.4

0.7 0.8 0.9 E (V) Fig 3. CVs for various concentrations of TR in 0.1 M PBS

300 200 I(A)

0.6

350

400

100

0.5

0.6

300 y = 3.3169x + 5.0418 R² = 0.9959

0 -100

200 -0.4

-0.2

0.0

0.2

0.4

0.6

0.8

E (V)

Fig.1(A)CV of the AgNPs/NDG/ PGE in the posphat buffer ph=7 (B)SEM image of AgNPs/ NDG

I( μA)

-200 -0.6

0.5

Fig2.Cyclic voltammogram recorded for the A) AgNPs/ NDG/ PGE B) NDs/ PGE C) Bare electrode E (mV) in the TR 10 μM solution of pH= 7

I( μA)

3.3 Calibration curve The cyclic voltammograms for various concentrations of TR were obtained under the optimized experimental conditions (data not reported here) on the surface of the AgNPs/DNG/PGE (Fig3). After each determination, the modified electrode was refreshed by successive cyclic voltammetric sweeps between −0.2 and −1.0V in a buffer solution for 5cycles. Calibration curve is shown in the Fig4.

C

100

0 0

Conclusions

50 C( μM )

Fig4.Calibration curve

100

Proceedings of the 4th International Conference on Nanostructures (ICNS4) 12-14 March, 2012, Kish Island, I.R. Iran

Conclusions In this work, it was demonstrated that modification of PGE with DNG decorated with silver nanoparticles is a new and effective method for obtaining highly sensitive electrodes for electrochemical measurements. The procedure enables preparation of highly stable and reproducible uniform modifier films, which leads to a considerable enhancement in repeatability and reproducibility in the voltammetric measurements. Moreover, this modified electrode is capable to measure the TR in the real samples.

References [1] M. Musameh, J. Wang, A. Merkoci, Y. Lin, Electrochem. Commun. 4 (2002) 743. [2] J. Wang, M. Li, Z. Shi, N. Li, Z. Gu, Electrochim. Acta 47 (2001) 651. [3] I. Streeter, G.G. Wildgoose, L. Shao, R.G. Compton, Sens. Actuators B 133 (2008) 462. [4] W. Zhao, J.J. Xu, Q.Q. Qiu, H.Y. Chen, Biosens. Bioelectron. 22 (2006) 649. [5] N. Gibson, O. Shenderova, T.J.M. Luo, S. Moseenkov, V. Bondar, A. Puzyr, K.Purtov, Z.Fitzgerald, D.W. Brenner, Diamond Relat. Mater. 18 (2009) 620. [6] Huang, J., Liu, Y., Hou, H., You, T., Biosens. Bioelectron. 24 (2008) 632–637. [7] Tzitzios, V., Georgakilas, V., Oikonomou, E., Karakassides, M., Petridis, D., Carbon 44 (2006) 848–853.

1955