1968 Bull. Koren Chem. Soc. 1, Vol. 31, No. 7 Mnln To et l. DOI 1.51/bkcs.1.31.7.1968 Amperometric Morphine Detection Using Pt-Co Alloy Nnowire Arry-modified Electrode Mnln To, Feng Xu, Yueting Li, Qunqing Xu, Ynbing Chng, Zisheng Wu, nd Yunhui Yng * College of Chemistry nd Chemicl Engineering, Yunnn Norml University, Kunming 659, P. R. Chin * E-mil: yyhui@yhoo.com.cn Stte Key Lbortory of Chemo/Biosensing nd Chemometrics, Hunn University, Chngsh 418, P. R. Chin Received November 5, 9, Accepted My 19, 1 Pt-Co lloy nnowire rry ws directly synthesized by electrochemicl deposition with polycrbonte templte t 1.V nd subsequent chemicl etching of the templte. The use of Pt-Co lloy nnowire rry-modified electrode (Pt- Co NAE) for the determintion of morphine (MO) is described. The morphology of the Pt-Co lloy nnowire rry hs been investigted by scnning electron microscopy (SEM) nd energy disperse X-ry spectroscopy (EDS) nlysis), respectively. The resulting Pt-Co NAE offered liner mperometric response for morphine rnging from.35 1 5 to.39 1 3 M with detection limit of 7.83 1 6 M t optimum conditions. This sensor displyed high sensitivity nd long-term stbility. Key Words: Morphine, Pt-Co lloy, Nnowire rry, Amperometric, Electrode Introduction Morphine, well-known potent nrcotic nlgesic nd the ctive metbolite derived from heroin (3,6-dicetylmorphine), hs been reported to influence vrious immune functions nd cuse disruption in the centrl nervous system. It is frequently used to relieve severe pin in ptients, especilly those undergoing surgicl procedure. However, morphine presents toxic symptoms when used to excess or bused. Morphine is extensively metbolized to its morphine-3-glucuronide (M3G), with normorphine (NM) nd morphine-6-glucuronide (M6G) s minor metbolites, irrespective of the species or dministrtion route. 1, Vrious nlyticl methods hve been developed for the determintion of morphine including gs chromtogrphy/ mss spectrometry, 3 liquid chromtogrphy 4 nd liquid chromtogrphy-mss spectrometry. 5,6 However, those methods re time-consuming nd very costly. Compred to other options, electro-nlysis hs the dvntges of simplicity nd high sensitivity,but the use of bre electrodes for electrochemicl mesurements hs number of limittions, such s slow electron trnsfer rection nd electrode fouling problems. Jin et l. hve prepred coblt hexcynoferrte (CoHCF) chemiclly modified electrode (CME) for mperometric determintion of morphine. 7 Ho et l. hve used Prussin blue modified- indium tin oxide electrode to determine MO. 8 Yeh nd Ho hve reported n mperometric MO sensor bsed on moleculrly imprinted electrode. 9 Pournghi-Azr nd Sdtird hve reported the use of prussin blue film modified-plldized luminum electrode (PB/Pd-Al) prepred by simple nd rpid electroless method for the determintion of codeine (CO) nd morphine (MO) simultneously. 1 Fst, sensitive, simple, inexpensive, nd specific method for the quntittive determintion of MO is still highly required. Recently, nnomterils hve become the focus of scientific reserchers becuse of their unique electronic, opticl, nd ctlytic properties. 11-14 Especilly, metllic lloys nnowires hve been of considerble interest in the field of ctlysis nd sensors becuse they often exhibit better ctlytic properties thn monometllic counterprts. 15,16 Sun et l. 16 hve reported Pt-Pb nnowire rry electrode for enzyme-free glucose detection. S. Frnz et l. 17 hve mde Pt-Co lloys with microelectrodeposition for micromgnetic pplictions. In this pper, the Pt-Co lloy nnowire rry ws synthesized in polycrbonte (PC) templte by mens of direct electrodeposition technique t 1.V. Furthermore, considering its good ctlysis to MO, the Pt-Co lloy nnowire rry-modified electrode (Pt-Co NAE) ws used for the determintion of MO with chronomperometry. The mjor dvntges of Pt-Co NAE re the simplicity, rpidity nd minituriztion in preprtion, high stbility of the Pt-Co lloy surfce nd its effective ctlytic ctivity for the electro-oxidtion of MO. Experimentl Chemicls. Nuclepore trck-etch polycrbonte (PC) templtes (. µm) were provided by Whtmn (Anodisc 5 mm). Co (NH SO 3 ) ws supplied by Jingxi Domestic cpitl chemicl Co., Ltd (Jingxi, Chin). Pt (NH 3) (NO ) ws purchsed from Shnghi Jiuyue chemicl Co., Ltd (Shnghi, Chin). Morphine hydrochloride (MO hydrochloride) ws from the mteril evidence identifiction center of Ministry of Public Security (Beijing, Chin). A. M phosphte buffer (PB) solution ws prepred using N HPO 4 nd NH PO 4 nd djusted to ph 6.5. All of the other chemicls were of nlyticl grde nd used s received. All solutions were prepred with doubly distilled wter. Instrumenttion. Cyclic voltmmetric nd chronomperometry mesurements were crried out on XJP-81(C) polrogrph (Jingsu, Chin). Scnning electron microscopy (SEM) ws performed on XL3ESEM-TMP microscope (Philips, Holnd). Energy dispersive X-ry spectroscopy (EDS) ws performed using n energy dispersive nlysis system of X-ry
Morphine Detection using Pt-Co Alloy Nnowire Arry Bull. Koren Chem. Soc. 1, Vol. 31, No. 7 1969 (EDAX, USA). A three-electrode cell (1 ml) with the Pt-Co lloy nnowire rry-modified electrode s the working electrode, sturted clomel electrode (SCE) s reference electrode nd pltinum foil electrode s counter electrode ws used. All potentils were mesured nd reported versus the SCE. The mesurements were crried out t 5 ± 1 o C. Synthesis of Pt-Co lloy nnowire. To mke the templte conductive, thin film of Au (~3 nm) ws first sputtered onto one surfce of the PC membrne using the pumped vcuum spry gold device of SEM. The PC templte sputtered with thin gold film ws connected with copper wire (5 cm) using grphite conductive dhesive. The preprtion of PC templte ws completed fter the conductive dhesive dried t room temperture. Before the deposition, the PC templte ws first plced in the electroplting solution for 1 min in order to llow the solution to penetrte throughout the templte. According to the report of S. Frnz et l., 17 electrodeposition ws crried out in complex solution contining.1 M coblt sulphmte,.1 M Pt (NH 3) (NO ),.1 M mmonium citrte, nd.1 M glycine by pplying certin potentil of 1. V. The electrolyte ph ws mintined t 8 by ddition of either sodium hydroxide or sulphmic cid if necessry. After deposition of 3 min, the synthesis of Pt-Co lloy nnowire ws completed. In contrst, Pt nnowires were prepred in.1 M KCl solution contining mm H PtCl 6 t 1. V. Fbriction of Pt-Co lloy nnowire rry-modified electrode. Glssy crbon electrode (GCE) (3 mm dimeter) ws used s the substrte electrode. Before use, it ws first polished with 1.,.3 nd.5 µm lumin slurry nd rinsed thoroughly with bsolute lcohol nd distilled wter in ultrsonic bth, nd dried in ir t room temperture. A piece of the deposited PC templte ws plced gold-side down onto the surfce of the GCE. Then, chloroform ws dropped onto PC membrne for severl times to dissolve PC membrne nd relese Pt-Co lloy nnowire. After the voltilizing of the chloroform, the film of Pt-Co lloy nnowire were kept onto the surfce of the GCE with good stbility nd conductivity. The electrode ws wshed successively with ethnol nd wter. For comprison, Pt nnowires rry-modified electrode ws prepred using sme process. Conventionl bre Pt electrode ws lso used s comprison fter physiclly polishing with lumin slurry of different size. Electrochemicl mesurements. The cyclic voltmmetric behviors of the modified electrode in. M PB solution (ph 6.5) before nd fter dding morphine were investigted t room temperture from V to +1.V (versus SCE). Amperometric mesurements were crried out t.7 V in stirred solution with stedy-stte bckground current first recorded before stock morphine hydrochloride stndrd solution ws dded into the buffer solution. Results nd Discussion Chrcteristics of Pt-Co lloy nnowire rry. The morphology of the nnowires rry ws chrcterized by SEM (Fig. 1A).The verge dimeter of nnowire is bout 5 nm, which corresponds to the size of the nnopore in the templte. The verge length of the nnowires is bout 5 µm. It cn lso be seen (A) (B) KCnt 1.8 1.4 1.1.7.4. Co Cu Pt Co D:\EDS-user\9-EDS\June9-EDS\1-1.spc 3-Jun-9 17:53:46 LSecs:4 Pt Cu. 4. 6. 8. 1. 1. 14. 16. 18.. Energy (KeV) Figure 1. SEM imge of the Pt -Co lloy nnowire rry fter PC templte ws dissolved for 15 min (A) nd EDS of the Pt -Co lloy nnowire rry (B). Figure. SEM imges of the pltinum nnowire rry fter PC templte ws dissolved for 15 min. from the imge tht ech nnowire is verticlly, mking ech nnowire work s n individul nnoelectrode. EDS nlysis lso confirmed the formtion of Pt-Co lloys (Fig. 1B). The morphology of the pltinum nnowire rry ws lso chrcterized by SEM (Fig. ). The verge dimeter of the nnowires ws bout 5 nm with the length of bout.5 ~ 3 µm. Fig. 3 shows the SEM imges of the Pt-Co lloy nnowire rry with different dissolved time by chloroform. As it cn be
197 Bull. Koren Chem. Soc. 1, Vol. 31, No. 7 Mnln To et l. (A) (B) (C) Acc.V Mgn Det WD 5 µm 3. kv 1x BSE 5.8 1# Mt Key Lb of KMUST min 15 min Acc.V Mgn Det WD µm 3. kv x BSE 5.8 1# Mt Key Lb of KMUST Acc.V Mgn Det WD µm 3. kv x SE 7.5 Pt Mt Key Lb of KMUST Figure 3. SEM imges of the Pt -Co lloy nnowire rry on PC templte with different dissolving time. A: min B: 15 min C: 3 min..3..1..1. b 15 1 5 5 1 6 4 4 6 4 5 6 7 8 9 1 11 e.3...4.6.8 1. 1. 1.4 Potentil (V vs. SCE) 15 V 1/...4.6.8 1. 1. 1.4 Potentil (V vs. SCE) Figure 4. Cyclic voltmmogrms of the Pt-Co NAE in buffer solution before (b) nd fter () dding.6 mm morphine (scn rte: 1 mv s 1 ). seen, when PC templte ws not dissolved, Pt -Co lloy nnowire rry cn not be relesed (Fig. 3A). When dissolved time ws 15 min (Fig. 3B), the Pt -Co nnowire stnds verticlly on the substrte surfce, nd the dimeter is rther uniformly distributed round (3 ± nm). As expected, these nnowires ssume the shpe nd dimensions of the pores. Furthermore, there re pprently no mcroscopic defects in the nnowire. However, when dissolved time ws too long (3 min), PC membrne ws dissolved so completely tht Pt -Co nnowire relesed from PC membrne were not verticlly oriented, nd the nnowire rry ws destroyed (Fig. 3C). Therefore, the dissolved time of 15 min ws dopted in the subsequent work. Electrochemicl properties of Pt-Co NAE. Voltmmetric experiments were used to evlute the electrochemistry of the Pt-Co NAE. Fig. 4 shows the cyclic voltmmogrms (CV) obtined with the Pt-Co NAE in unstirring. MPB (ph 6.5) solution without (b) nd with ().6 mm morphine. Only bckground current could be observed in Fig. 4 (b). In the presence of.6 mm morphine (Fig. 4 ()), the nodic pek current incresed t.543v, indicting tht Pt-Co NAE exhibits electroctlytic ctivity towrd morphine. Due to the higher bckground, the CV curves of Pt-Co NAE seem to hve wek redox peks compred with the CV curves of Prussin blue-modified indium tin oxide electrode 8 nd moleculrly imprinted polymer- Figure 5. Cyclic voltmmogrms of the Pt-Co NAE t different scn rte of : 1, b: 8, c: 5, d: 4 nd e: mv s 1 Inset: plots of oxidtion pek current versus v 1/. modified electrode. 9 Fig. 5 shows CV of the Pt-Co NAE in.m PB (ph 6.5) contining.6 mm morphine t different scn rtes. A liner reltionship between the redox pek currents nd the squre root of scn rte (v 1/ ) (see the inset of Fig. 5) indictes tht the pek current is diffusion-controlled. To discern the role of individul components nd possible synergy between Pt nd Co, four electrodes were investigted by chronomperometry with successive ddition of the sme mounts (.6 mm) of morphine in PB (ph 6.5) (Fig. 6: bre GCE; b: conventionl Pt electrode; c: Pt NWEs; d: Pt-Co NAE). Noticebly, the sensitivity of Pt-Co NAE ws the lrgest mong tht of four electrodes, indicting tht the Pt- Co lloy cn enhnce the response. The results prove tht Pt- Co lloy exhibit better ctlytic properties thn monometllic counterprts. 16 Optimiztion of mperometric detection conditions. The effect of pplied potentil on the response of Pt-Co NAE ws investigted in the presence of.6 mm morphine nd ws shown in Fig. 7 With the incresing of potentil from.46v to.88 V, the sensitivity of the electrode incresed significntly nd reched plt t.68 to.81 V. The inset of Fig. 7 showed bckground current in.m PB t ech potentil. To obtin high signl-tonoise (S/N) rtio, potentil of.7 V (vs. SCE) ws selected s the pplied potentil for mperometric mesurements.
Morphine Detection using Pt-Co Alloy Nnowire Arry Bull. Koren Chem. Soc. 1, Vol. 31, No. 7 1971 1.4 1 d. 8 6 4 c b. 1.8 1.6 1.4 1. 4 6 8 1 1 14 16 time (s) 1. 5.5 6. 6.5 7. 7.5 8. 8.5 9. ph Figure 6. Dynmic responses of different electrodes (() bre GCE; (b) bre Pt; (c) Pt NAE; (d) Pt-Co NAE) for successive ddition of the sme mount (.6 mm) morphine in. M phosphte buffer solution (ph 6.5). Figure 8. Effect of ph on the response of the Pt-Co NAE. 1. 1 1. 1.8 8.6.4...19 18 17 16 6 4. 15.4.5.6.7.8.9 potentil (V vs. SCE).4.5.6.7.8.9 Potentil (V vs. SCE) Figure 7. Effect of pplied potentil on the response of the Pt-Co NAE in. M phosphte buffer solution (ph 6.5) contining.6 mm morphine. Inset: plots of bckground current versus potentil..5.5 1. 1.5..5 3. c (mm) Figure 9. The clibrtion of Pt-Co NAE towrd morphine. The influence of the ph of the ssy solution over the rnge 5.9-8.64 on the chronomperometry response of the Pt-Co NAE to morphine t fixed concentrtion of. M in PB solution ws lso investigted. Fig.8 showed tht the optimum ph ws 6.5. According to the report of Pournghi-Azr. 1 the electro-ctlyticl oxidiztion pthwy of MO t neutrl medi cn be shown s follows: MO MO + e + H + (1) MO PMO () HO CH 3 N HO O OH O HO N-CH 3 N CH 3 HO O OH + e + H + Low ph is not beneficil to the rection. Therefore, ph 6.5 ws fixed for the rest of the experiments. Morphine detection performnce. The Pt-Co NAE exhibited rpid nd sensitive response to the chnge of morphine concentrtion. This indicted the nice electroctlytic behvior of the Pt-Co NAE. The clibrtion curve for morphine ws shown in Fig. 9. The liner rnge is from.35 1 5 to.39 1 3 M with correltion coefficient of.987, the regression eqution ws I (µa) =.9 + 4. C (mm), where I ws response current, nd C ws morphine concentrtion. The detection limit ws 7.83 1 6 M t signl-to-noise (S/N) rtio 3. The liner rnge is wider thn the report of Ho et l. 8 nd Pournghi-Azr et l. 1 The detection limit is lower thn Yeh nd Ho s report using moleculrly imprinted polymer-modified electrode. 9 The reltive low detection limit ws due to the Pt-Co NAE. It hs been reported tht the use of microelectrode rrys insted of conventionl ones could improve the rtio of signl-to-noise (S/N) rtio nd decrese the detection limit. 18
197 Bull. Koren Chem. Soc. 1, Vol. 31, No. 7 Mnln To et l. Tble 1. Possible interferences tested with the Pt-Co NAE Interferents C interferences/c morphine i interferences/i morphine scorbic cid 1.88 3.157 glucose 9.49.76 cocine 1.88.5 uric cid 7.97. Tble. Determintion of morphine recovery dded concentrtion (mm) found concentrtion (mm) recovery (%).1.17 18..57.68 14.3.53.59 99.6 The selectivity of the sensor ws lso ssessed by determintion of four possible interferences infection for the electrode. Tble 1 showed tht only scorbic cid interferes with the determintion of morphine becuse it lso cn be oxidized t this pplied potentil. The repetbility of the response current of the Pt-Co NAE ws investigted t morphine concentrtion of.6 mm. The vrition coefficient ws 3.5% for five successive ssys. The stbility nd lifetime of the electrode were investigted by mesuring the electrode response with.6 mm of morphine every six dys. The response current of the Pt-Co NAE decresed to 87.1% fter 1 dys. It suggests tht the stbility of the electrode ws good. When not in use, the electrode ws stored dry t room temperture. A preliminry evlution of the vlidity of the proposed Pt-Co NAE ws performed in the rel serum smples. Different mount morphine were dded into serum smples nd determined with proposed Pt-Co NAE. The results were shown in Tble. The recoveries were stisfctory. This result showed the proposed method my provide fesible lterntive tool for determining morphine in humn serum. Conclusions In this pper, Pt-Co lloy nnowire rry ws synthesized by electrodeposition with polycrbonte templte nd subsequent chemicl etching of the templte. Bsed on the electrochemistry oxidtion of morphine t.7 V, the Pt-Co lloy nnowire rry- modified electrode ws used to determine morphine. The Pt-Co lloy nnowire rry improves nlyticl performnces of the corresponding electrode compred to Pt nnowire rry-modified electrode nd the conventionl Pt electrodes, specificlly. The other possible interferents such s cocine, glucose hve no significnt interference. The determintion of morphine in rel serum smples ws stisfctory. The Pt-Co NAE displyed high sensitivity, quick response to morphine, good stbility, wide liner rnge, better detection limit. The simple nd fst fbriction of the electrode mkes it superior to other techniques. Acknowledgments. This work ws supported by the Ntionl Nturl Science Foundtion of Chin (Grnts No. 8656), the Foundtion of Science Commission of Yunnn Province (No.6B8M) nd the Foundtion of Deprtment of Eduction of Yunnn Province (No.7Z187). References 1. Milne, R. W.; Ntion, R. L.; Somogyi, A. A.; Crugten J. T. B: Biomed. Appl. 1991, 565, 457.. Yeh, S. Y.; Gorodetzky, C. W. J. Phrm Sci. 1977, 66, 188. 3. Pötsch, L.; Skoppb, G. Forensic Sci. Int. 1996, 81, 95. 4. Hr, S.; Moching, S.; Fukuzw, M.; Ono, N.; Kurod, T. Anl. Chim. Act 1999, 387, 11. 5. Sooyeun, L.; Ros, C.; Sue, P. Forensic Sci. Int. 9, 183, 74. 6. Schnzle, G.; Li, S.; Mikus, G.; Hofmnn, U. B: Biomed. Appl. 1999, 71, 55. 7. Xu, F.; Go, M.; Wng, L.; Zhou T.; Jin, L.; Jin, J. Tlnt, 58, 47. 8. Ho, K. C.; Chen, C. Y.; Hsu, H. C.; Chen, L. C.; Shiesh, S. C.; Lin, X. Z. Biosens. Bioelectron. 4,, 3. 9. Yeh, W. M.; Ho, K. C. Anl. Chim. Act 5, 54, 76. 1. Pournghi-Azr, M. H.; Sdtird, A. J. Electronl. Chem. 8, 6, 93. 11. Yng, G. M.; Tn, L.; Shi, Y.; Wng, S. P.; Lu, X. X.; Bi, H. P.; Yng, Y. H. Bull. Koren Chem. Soc. 9, 3, 454. 1. Xue, F. H.; Fei, G. T.; Wu, B.; Cui, P.; Zhng, L. D. J. Am. Chem. Soc. 5, 17, 15348. 13. Wen, D.; Liu, Y.; Yng, G. C.; Dong, S. J. Electrochimic Act 7, 5, 531. 14. M, H. X.; Yng, G. B.; Yu, L. G.; Zhng, P. Y. Surf. Cot. Technol. 8,, 5799. 15. Luo, J.; Njoki, N.; Lin, Y.; Wng, L.; Zhong, C. Lngmuir 6,, 89. 16. Bi, Y.; Sun, Y. Y.; Sun, C. Q. Biosens. Bioelectron. 8, 4, 579. 17. Cvllotti, P. L.; Bestetti, M.; Frnz, S. Electrochim. Act 3, 48, 313. 18. Pugnov, E. A.; Krykin, A. A. Sens. Actutors, B: Chemicl. 5, 19, 167.