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Sensors and Actuators B 129 (2008) 372–379

An electrochemical impedance biosensor with aptamer-modifiedpyrolyzed carbon electrode for label-free protein detection

Jung A Lee a, Seongpil Hwang b, Juhyoun Kwak b, Se Il Park c,Seung S. Lee a, Kwang-Cheol Lee c,∗

a Department of Mechanical Engineering, Korea Advanced Institute of Science and Technology,373-1 Guseong-dong Yuseong-gu, Daejeon 305-701, Republic of Korea

b Department of Chemistry, Korea Advanced Institute of Science and Technology, 373-1 Guseong-dongYuseong-gu, Daejeon 305-701, Republic of Korea

c Leading-Edge Technology Group, Korea Research Institute of Standards and Science (KRISS),1 Doryong-dong Yuseong-gu, Daejeon 305-340, Republic of Korea

Received 13 June 2007; accepted 17 August 2007Available online 24 August 2007

bstract

We present an electrochemical impedance biosensor utilizing pyrolyzed carbon film as a working electrode material for aptamer-based thrombinetection. Batch-fabricated, smooth thin film carbon electrodes, which are fabricated by photolithography and photoresist thermal decompositiont high temperatures in inert ambient, are obtained for integrated electrochemical biosensors. To confirm the suitability of pyrolyzed carbon forse in an electrochemical biosensor, physical and electrical properties of carbon film pyrolyzed with a positive photoresist, AZ9260, were studied.ilm thickness after pyrolysis was between 19% and 15% relative to the initial photoresist thickness and the cross-section was changed fromectangular to round shape due to the photoresist reflow characteristics. Resistivity of carbon thin film pyrolyzed at 1000 ◦C was 3 m� cm, whichs comparable to that of highly boron-doped polysilicon. The pyrolysis temperature of 1000 ◦C was chosen in order to obtain carbon film withigh conductivity for use as a working electrode. Thrombin aptamer was grafted onto the pyrolyzed carbon surface using carbodiimide-mediatedhemistry, followed by Triton-X 100 and BSA treatment to reduce non-specific binding of thrombin. Electron-transfer resistance changes due to

hrombin binding onto the carbon surface were measured using electrochemical impedance spectroscopy techniques. Thrombin concentrationsetween 0.5 nM and 500 nM were detected by electrochemical measurement. Pyrolyzed carbon can provide a new approach for miniaturization,ntegration, and low-cost fabrication in electrochemical biosensors.

2007 Elsevier B.V. All rights reserved.

MS;

tmfates

eywords: Aptamer; Biosensor; Electrochemical impedance spectroscopy; ME

. Introduction

Aptamers, artificial nucleic acid with specific binding affin-ty and selectivity for amino acids, drugs, proteins, and othermall molecules, have potential applications as a recognitionlement in analytical and diagnostic assays [1,2]. With respecto biosensors, aptamers are getting more attention as more robust

apture molecules compared to current sensitive antibodies ornzymes, because features of aptamer such as long-term, thermaltability can be very useful for realizing easy-to-stock, easy-

∗ Corresponding author.E-mail address: kclee@kriss.re.kr (K.-C. Lee).

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925-4005/$ – see front matter © 2007 Elsevier B.V. All rights reserved.oi:10.1016/j.snb.2007.08.034

Pyrolyzed carbon; Thrombin

o-use biosensors. Aptamer-based biosensors utilizing variousethods such as quartz crystal microbalance (QCM), atomic

orce microscopy, surface plasmon resonance (SPR), and opticalnd electrochemical techniques have been reported [3–6]. Elec-rochemical methods for detection of chemical and biologicallements are also receiving attention as they offer advantagesuch as rapid response, miniaturization, and low-cost. Espe-ially, electrochemical impedance spectroscopy (EIS) is anttractive tool for the analysis of interfacial changes inducedrom biomolecular interactions at electrode surfaces.

Among various electrochemical biosensors, several aptamer-ased electrochemical biosensors have been reported, wherehe intercalation of methylene blue is utilized as an electro-hemical marker and the amplification is accomplished by

Actuators B 129 (2008) 372–379 373

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J.A. Lee et al. / Sensors and

old-colloid labeling [7,8]. Generally, these previous studiessed gold films as working electrodes in the electrochemicaliosensors. Although the use of glassy carbon or a carbon filmesistor as working electrodes has been reported, cheap carbonaterial is not widely used in biosensors [9–13].Carbon is one of the most popular materials in electrochem-

cal sensors due to properties such as wide electrochemicalindow, low non-specific adsorption of biomolecules, and

xcellent biocompatibility. Though commercially availablecreen-printed-electrode (SPE) is widely used in sensors, SPElso has a limitation with regard to the miniaturization ofensors. Pyrolyzed carbon provides a new approach for minia-urization and integration of electrochemical sensors. Pyrolyzedarbon, which is fabricated by photolithography and pho-oresist thermal decomposition at high temperatures in inertmbient, has many advantages such as batch fabrication, fineesolution, and reproducibility. Various applications such asicrobatteries, image sensors, and biochemical sensors utiliz-

ng pyrolyzed carbon have been reported [14–18,26]. It exhibitslectrochemical behaviors similar to those of glassy carbonlectrodes and has lower capacitance, background current, andxygen/carbon atomic (O/C) ratio compared to glassy carbonlectrodes [19–22].

In this paper, we describe an electrochemical impedanceiosensor utilizing aptamer-modified pyrolyzed carbon elec-rode for label-free protein detection. Batch-fabricated, smooth,hin film carbon electrodes, which are lithographically defined,re obtained for integrated electrochemical biosensors. Physicalnd electrical properties of pyrolyzed carbon derived from a pho-oresist (AZ9260), device fabrication, and aptamer-based throm-in detection using electrochemical impedance measurementsased on the electrostatic interaction between negatively chargedhrombin and negatively charged ferricyanide are described.

. Principle

Fig. 1 shows a schematic view of the proposed electrochem-cal biosensor utilizing a carbon electrode pyrolyzed from ahotoresist for aptamer-based thrombin detection. We studiedhrombin, a critical enzyme in blood clotting with a well-stablished aptamer structure, as a model system for ourlectrochemical biosensor. A circular working electrode, uti-izing carbon thin film pyrolyzed with AZ9260, is covered withhrombin aptamer via EDC (1-ethyl-3-(3-dimethylaminopropyl)arbodiimide hydrochloride) mediated carbodiimide chemistry.erricyanide serves as an electroactive probe molecule, ashown in Fig. 1(b). When thrombin is tethered on the aptamer-mmobilized electrode surface, the negatively charged thrombinpI: 7.0–7.6) in a solution of pH 8 acts as an electrostatic bar-ier that repels ferricyanide and hinders electron-transfer [23].harge-transfer resistance of electrochemical impedance spec-

roscopy (EIS) provides the degree of electrostatic interactionetween thrombin and ferricyanide, i.e. the number of surface-

mmobilized thrombin, without any labeling procedure. Theespective semicircle diameters correspond to the interfaciallectron-transfer resistance (Ret), of which values are calculatedrom the non-linear least-squares (NLLS) fitting program of a

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yrolyzed carbon for aptamer-based thrombin detection and (b) electrochemicalmpedance change due to hindrance of electron-transfer by negatively chargedhrombin binding onto the pyrolyzed carbon surface.

requency response analyzer (FRA). The impedance spectra aretted to a modified Randles equivalent electrical circuit includ-

ng a solution resistance, Rs, a constant phase element, CPE,n electron-transfer resistance, Ret, and a Warburg impedance,W, as shown in Fig. 2. Instead of an ideal capacitor, the CPE

s used to compromise errors due to microscopic roughness andtomic scale inhomogeneity in surfaces. From the regression,he electron-transfer resistance (Ret) is obtained as shown inig. 2(b).

. Materials and methods

.1. Materials

Phosphate buffered saline solution (PBS, pH 7.4, Bioneero., Korea), potassium phosphate (Sigma), potassium ferri-yanide (Mallinckrodt), thrombin from human plasma (Sigma),

riton-X 100 (Sigma), bovine serum albumin (BSA, Pierce), and-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochlo-ide (EDC, Aldrich) were used in this experiment. The 15-basehrombin aptamer-modified at the 3′ end with amine linker, 5′-

374 J.A. Lee et al. / Sensors and Actuators B 129 (2008) 372–379

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ig. 2. Schematic views of the equivalent circuit to fit impedance spectra andlectrochemical impedance changes due to thrombin binding onto the pyrolyzedarbon surface.

GT TGG TGT GGT TGG-(CH2)6-NH2-3′, was provided byioneer Co. (Korea).

.2. Device fabrication

Fig. 3 shows the fabrication processes of the electrochemicalmpedance biosensor for thrombin detection. Fabrication pro-

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Fig. 4. Schematic view and images of the fabricat

ig. 3. Fabrication processes of the electrochemical impedance biosensor uti-izing carbon thin film pyrolyzed with a photoresist.

esses start with P (100) Si wafer. A 0.8 �m thick SiO2 layer forlectrical isolation was grown by thermal oxidation in wet ambi-nt at 1050 ◦C for 240 min (Fig. 3(a)). An AZ9260 photoresistas spin-coated onto the wafer at 5000 rpm for 35 s and devel-

ped after baking on a hotplate at 110 ◦C for 160 s. A 0.76 �mhick circular carbon working electrode with a radius of 450 �mas fabricated by pyrolysis of 5 �m thick AZ9260 photoresist

ed device for electrochemical experiments.

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Fig. 6 shows the relative thickness, surface roughness, andresistivity of the pyrolyzed carbon film as a function of pyrolysistemperature. After the pyrolysis processes, pyrolyzed AZ9260thickness was decreased and its cross-sectional shape was

J.A. Lee et al. / Sensors and

t 1000 ◦C for 30 min (Fig. 3(b)). A pyrolysis temperature of000 ◦C was chosen so as to obtain carbon films with high con-uctivity. The electrochemical experiments were difficult forow conductive carbon films pyrolyzed at low temperatures.00/15 nm thick Au/Cr metal layer was patterned by electroneam evaporation and lift-off technique for a 300 �m wide annu-ar counter electrode and metal interconnections (Fig. 3(c)). Theevice was covered with a 5 �m thick negative photoresist, SU8,or passivation from electrolytic solution, except the workingnd counter electrodes for the electrolytic cell and metal padsFig. 3(d)). The exposed area of the counter electrode in theolution was approximately 2.6 mm2, a factor of 4 larger thanhat (0.6 mm2) of the carbon working electrode.

Before the electrochemical experiments, the device was O2lasma treated at 150 mTorr and 50 W for 30 s to increase theensity of oxygen containing functional groups on the pyrolyzedarbon working electrode surfaces. A reservoir for an elec-rolytic cell was formed using a silicone tube with an inneriameter of 3 mm. By curing 10:1 mixture of PDMS (Syl-ard 184, Dow Corning) at 60 ◦C for 8 h as glue, the siliconeube was sealed to the device chip. Fig. 4 shows a schematiciew and fabricated device images with a silicone tube reser-oir and a close-up SEM photomicrograph of pyrolyzed carbonorking and Au/Cr counter electrodes and the SU8 passivation

ayer.

.3. Aptamer immobilization

For immobilization of thrombin aptamer onto the pyrolyzedarbon working electrode, the device was incubated overnightn 10 mM PBS (pH 7.4) containing 50 mM EDC and 1 �Mmine terminated thrombin aptamer. The carboxyl (COOH)roups on the pyrolyzed carbon surface are transformed usingDC into intermediates that readily react with the NH2 groupsn the thrombin aptamer. The thrombin aptamer immobilizesnto the pyrolyzed carbon surface with an amide bond. Theptamer-grafted electrode was immersed in 10 mM PBS (pH.4) with 10% Triton X-100 for 1 h to block unreacted functionalroups on the pyrolyzed carbon surface. The device was furthermmersed in 10 mM PBS (pH 7.4) with 1% BSA for 10 min toeduce non-specific binding of thrombin onto the pyrolyzed car-on surface. After each step, the device was rinsed thoroughlyith 10 mM PBS (pH 7.4).

.4. Electrochemical measurements

Electrochemical measurements including cyclic voltamme-ry and electrochemical impedance spectroscopy (EIS) wereonducted at room temperature using an Autolab 10 modelGSTAT potentiostat/galvanostat (Eco Chemie, The Nether-

ands), controlled by GPES4.9 and FRA4.9 software. Theeasurements were performed in a three-electrode system with

pyrolyzed carbon working electrode and an Au counter elec-

rode fabricated on a silicon chip and an Ag wire (quasi)referencelectrode in the solution containing chloride ion, as shown inig. 4(a).

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tors B 129 (2008) 372–379 375

The cyclic voltammetry measurements were carried outn a potential interval of −0.8 V to 0.8 V at a scan rate of0 mV s−1 for electrochemical characterization of pyrolyzedarbon electrodes. For analysis of the thrombin-binding event,lectrochemical impedance experiments were performed at aotential of 111 mV and an alternating potential with amplitudef 10 mV at a frequency range from 2 kHz to 50 mHz. Nyquistlots (−Zre vs. Zim) were drawn to analyze the impedanceesults. The buffer solution for all impedance measurementsas 100 �l of 10 mM PBS (pH 8) containing 10 mM KCl and0 mM K3Fe(CN)6. Experiments were carried out in the fol-owing sequence. Impedance spectra of the aptamer-graftedyrolyzed carbon electrode were measured to assess the effec-iveness of the surface treatment. After rinsing with PBS (pH), 50 �l of thrombin solution was added into the reservoir vian Eppendorf pipette. The device was incubated for 15 min atoom temperature, followed by rinsing with PBS (pH 8). Afterhrombin immobilization, impedance spectra were measurednd the difference of the electron-transfer resistance (�Ret) wasnalyzed.

. Results and discussion

.1. Pyrolyzed carbon properties

To verify the suitability of pyrolyzed carbon film for ourlectrochemical biosensor, various properties such as thick-ess, surface roughness, and resistivity according to pyrolysisemperature were studied. To determine thickness variations ver-us pyrolysis temperature, we used 100 �m wide and 1.5 mmong photoresist patterns and a stylus profiler (TENCOR® P-

long scan profiler, Tencor Instruments). Surface roughnessf pyrolyzed carbon film was measured using an atomic forceicroscope (AFM, DimensionTM 3100, Digital Instruments)

ver an area of 4 �m × 4 �m. Sheet resistance of the pyrolyzedarbon film was determined by the van der Pauw method using areek cross-test pattern, as shown in Fig. 5. Eight dc resistanceeasurements were carried out for four ohmic contact terminals

sing a semiconductor parameter analyzer (HP4156A).

ig. 5. Schematic view of Greek cross-test pattern connected to a semiconductorarameter analyzer (HP 4156A) for electrical property measurements.

376 J.A. Lee et al. / Sensors and Actua

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rvcpt(aTworiented pyrolytic graphic (HOPG) [24]. This poor electron-transfer was enhanced by surface modification of the pyrolyzedcarbon. For aptamer-immobilized pyrolyzed carbon electrodes,a fast electron-transfer kinetics (�Ep = 234 mV) compared to the

ig. 6. (a) Relative thickness, (b) surface roughness, and (c) resistivity of

yrolyzed carbon film vs. pyrolysis temperature.

hanged due to photoresist reflow characteristics and outgassingf gaseous byproduct during high temperature treatment. Pyrol-sis experiments of the photoresist were carried out between00 ◦C and 1000 ◦C. Thickness of the carbon pyrolyzed between00 ◦C and 1000 ◦C was between 19% and 15% of the initialhotoresist thickness (T0) of 5 �m. It shows that a major thick-ess change of the pyrolyzed carbon occurs at temperatureselow 600 ◦C. The root mean square (rms) roughness of car-on film pyrolyzed between 600 ◦C and 1000 ◦C was between.9 nm and 0.4 nm and slightly decreased as the pyrolysis tem-erature increased. The color of pyrolyzed carbon film is blacknd opaque whereas the initial photoresist film is transparent

nd yellowish. The pyrolyzed carbon film appears shiny andmooth when viewed with the naked eye. The top and bottomurface of free-standing pyrolyzed carbon film detached fromhe supporting substrate was indistinguishable using the naked

F(is

tors B 129 (2008) 372–379

ye or a scanning electron microscope (SEM). Uniformity andmoothness of the pyrolyzed carbon film are attributed to theolished silicon surface and an annealing effect during the highemperature thermal processes.

The measured resistivity was 3 m� cm for carbon filmyrolyzed at 1000 ◦C, seven orders of magnitude less than theesistivity of 13.3 k� cm for films pyrolyzed at 600 ◦C. The filmesistivity decreases exponentially as the pyrolysis temperaturencreases and begins to saturate at higher pyrolysis temperatures.he limiting value of pyrolyzed carbon resistivity is considered

o be a result of the grain boundary effect. Compared to graphiteesistivity, the carbon film resistivity pyrolyzed at 1000 ◦C is inhe mid-range of c-axis resistivity (1 � cm) and in-plane resis-ivity (50 �� cm). The lower bound resistivity of highly dopedolysilicon, widely used in semiconductor processes as gatelectrodes, resistors, and interconnections, is about 2 m� cm forrsenic- and boron-doped films and 0.4 m� cm for phosphorous-oping. The carbon film pyrolyzed at 1000 ◦C shows similaresistivity to that of highly doped polysilicon. By varying theyrolysis temperatures, we can tailor the carbon film resistivityor various applications such as insulators, high value resistors,nd conductors.

.2. Electrochemical measurements

To evaluate the performance of the pyrolyzed carbon mate-ial as a working electrode in terms of electrochemistry, cyclicoltammetry was performed in PBS solution containing ferri-yanide. Fig. 7 shows cyclic voltammograms (CVs) of (a) a bareyrolyzed carbon (PC) electrode, (b) a pyrolyzed carbon elec-rode treated with Triton-X 100 and BSA (Triton/BSA/PC), andc) a pyrolyzed carbon electrode after aptamer immobilizationnd Triton-X 100 and BSA treatment (aptamer/Triton/BSA/PC).he separation of peak potential of pyrolyzed carbon is 782 mV,hich is similar to the previously reported value for highly

ig. 7. Cyclic voltammograms (CVs) for (a) bare pyrolyzed carbon (PC),b) Triton-X 100 and BSA treated carbon (Triton/BSA/PC), and (c) aptamer-mmobilized carbon electrode (Aptamer/Triton/BSA/PC) in a phosphate bufferolution containing 10 mM ferricyanide and 10 mM KCl (pH 8).

J.A. Lee et al. / Sensors and Actuators B 129 (2008) 372–379 377

Fig. 8. (A) Impedance measurements (−Zim vs. Zre) for (a) aptamer-treatedpyrolyzed carbon electrode (aptamer/Triton/BSA/PC) and (b) after exposure ofama

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ptamer/Triton/BSA/PC electrode to 500 nM thrombin. (B) Impedance measure-ents for (c) Triton-X 100 and BSA treated carbon electrode (Triton/BSA/PC)

nd (d) after exposure of Triton/BSA/PC electrode to 500 nM thrombin.

riton/BSA/PC and bare PC electrode was observed. Althoughhe microstructure of carbon, surface roughness, surface clean-iness, and surface functional group were suggested as being

actors affecting the electron-transfer kinetics, the mechanisms still controversial [25]. The present authors, however, believehat the surface functional group (thrombin aptamer in ourystem) may cause this increase in the kinetics, because the

ig. 9. Electron-transfer resistance changes (�Ret) after exposure of aptamer-reated pyrolyzed carbon (aptamer/Triton/BSA/PC) electrode to thrombin0.5 nM–500 nM).

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ig. 10. Electron-transfer resistance changes (�Ret) after exposure ofptamer/Triton/BSA/PC electrode to avidin (5 �M) and thrombin (0.5 nM).

icrostructure and roughness of pyrolyzed carbon are theame before and after the immobilization of thrombin aptamer.lthough the mechanism for enhancement is not clear, theseVs demonstrate that the aptamer-immobilized carbon elec-

rode has suitable electron-transfer kinetics for electrochemicalxperiments.

Electrochemical impedance spectroscopy (EIS) was per-ormed on these aptamer-immobilized carbon electrodes toerify the different electron-transfer kinetics before and afterinding of thrombin. As shown in Fig. 7, electron-transfer isairly rapid on the aptamer-modified carbon electrode beforeinding of thrombin. After thrombin aptamer–thrombin com-lexes are formed; the negatively charged thrombin (pI: 7.0–7.6)n the PBS solution of pH 8 repels ferricyanide, resulting inn increase of the electron-transfer resistance (Ret). Fig. 8(a)hows complex plane impedance spectra for the aptamer-reated pyrolyzed carbon (aptamer/Triton/BSA/PC) electrodeompared to the aptamer/Triton/BSA/PC electrode after incuba-ion with 500 nM thrombin solution for 15 min. Electron-transferesistance increases because thrombin inhibits charge transferetween ferricyanide in the electrolyte and the pyrolyzed carbonlectrode. We measured the electrochemical impedance changesrom the thrombin-treated Triton/BSA/PC to Triton/BSA/PClectrodes to assess the non-specific binding of thrombin inur system, as shown in Fig. 8(b). The electron-transfer resis-ance of Triton/BSA/PC electrode was about 39 k�, and slightlyecreased after thrombin treatment. These results show thathrombin binds to the aptamer on the electrode not by non-pecific interaction but by specific interaction, and that EISuccessfully detects this binding event.

In order to assess the sensitivity and the selectivity ofur thrombin sensor, calibration experiments and experi-ent with other protein were performed. Fig. 9 shows

lectron-transfer resistance changes (�Ret), extracted from cor-esponding Nyquist diagrams, after thrombin treatment withifferent concentrations onto aptamer/Triton/BSA/PC elec-rodes. We incubated the aptamer/Triton/BSA/PC electrode with

hrombin of concentrations between 0.5 nM and 500 nM in auffer solution (pH 8) for 15 min. As thrombin concentrationncreases from 0.5 nM to 500 nM, the electron-transfer resis-

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78 J.A. Lee et al. / Sensors and

ance change (�Ret) increases from 1.6 k� and 5.2 k� due tohe charge of the immobilized thrombin on the electrode. Theetection limit is comparable with that previously reported forptamer-based biosensors with Au electrode [6,9]. To check thepecificity, the aptamer/Triton/BSA/PC electrode was incubatedith 5 �M avidin in a buffer solution for 15 min. Electron-

ransfer resistance change (�Ret) due to avidin binding for thelectrode treated with 5 �M avidin solution was 1.84 k�, whichs similar to that for the electrode treated with 0.5 nM thrombinolution, as shown in Fig. 10. This discrimination in the pres-nce of unwanted protein exhibits minimal non-specific bindingue to successful prohibition of triton and BSA for non-specificinding. The high selectivity and sensitivity for thrombin detec-ion demonstrates that the pyrolyzed carbon electrode can beery useful in electrochemical biosensors.

. Conclusions

We presented an electrochemical impedance biosensor uti-izing carbon thin film as a working electrode for aptamer-basedhrombin detection. Because the pyrolyzed carbon electrode isabricated by photolithography and thermal treatment of a pho-oresist in inert ambient, we can obtain batch-fabricated carboniosensors.

Physical and electrical properties of carbon film pyrolyzedith AZ9260 photoresist at temperatures between 600 ◦C and000 ◦C were studied in order to assess the potential of usingyrolyzed carbon film as an electrode in our electrochemicaliosensors. Thickness of the pyrolyzed carbon film was between9% and 15% of the initial photoresist thickness. Very smooth,lack, opaque carbon film with root mean square (rms) rough-ess less than 1 nm was obtained. The carbon film resistivityaried seven orders of magnitude as a function of pyrolysisemperature. The resistivity of carbon film pyrolyzed at a tem-erature of 1000 ◦C was 3 m� cm, which is comparable to highlyoron-doped polysilicon resistivity of 2 m� cm. By varying theyrolysis temperature and photoresist, we can obtain insulatinglms, high-value resistors, and conductors. We used a 0.76 �m

hick carbon film pyrolyzed at 1000 ◦C as a working electrodeor our electrochemical biosensor.

To increase the density of oxygen containing functionalroups on the pyrolyzed carbon working electrode surfaces,he device was O2 plasma treated at 150 mTorr and 50 W for0 s. Thrombin aptamer was grafted onto the carbon electrodesing the carbodiimide-mediated amide bond between carboxylCOOH) groups on the pyrolyzed carbon surface and the amineNH2) group on the aptamer. Triton-X 100 and BSA were usedo reduce non-specific binding of thrombin onto the pyrolyzedarbon surface.

To evaluate the performance of the pyrolyzed carbon mate-ial as a working electrode in terms of electrochemistry, cyclicoltammetry was performed in a phosphate buffer solutionontaining ferricyanide. The results indicated that the apatamer-

odified carbon electrode has suitable electron-transfer kinetics

or electrochemical experiments. Electrochemical impedancepectroscopy (EIS) was carried out on aptamer-modified elec-rodes to verify the different electron-transfer kinetics before and

[

tors B 129 (2008) 372–379

fter binding of thrombin with different concentrations between.5 nM and 500 nM. The experiment results in the presence ofnwanted protein showed that exhibited minimal non-specificinding due to successful prohibition of triton and BSA for non-pecific binding. The high selectivity and sensitivity of our sen-or for thrombin detection demonstrates that the pyrolyzed car-on electrode can be very useful in electrochemical biosensors.

cknowledgement

This work was supported by the Brain Korea 21 program andhe National Nano Program for Applications (KOSEF 2006-4921).

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iographies

ung A Lee received her PhD degree in mechanical engineering from Koreadvanced Institute of Science and Technology (KAIST), Korea, in 2007. She

s currently working at Korea Research Institute of Standards and Science

KRISS), Korea, as a postdoctoral research associate. She studied in the areaf M/NEMS and bioMEMS such as carbon and silicon nanoelectromechanicalevices, microcantilever, electrical, and electrochemical biosensors. She is cur-ently working toward biomimetics and biosensors based on silicon and carbonanomechanical structures.

(mSim

tors B 129 (2008) 372–379 379

eongpil Hwang earned his BS, MS, and PhD degrees in chemistry from Koreadvanced Institute of Science and Technology (KAIST) in 1999, 2001, and005, respectively. Under the guidance of professor Juhyoun Kwak, he stud-ed surface electrochemisty using EC-STM(electrochemical scanning tunneling

icroscopy), Electrochemical DNA sensors, and self-assembled monolayerSAM). From 2005 to 2006, he continued to work as a postdoctoral associate athe same group. In 2006, he began postdoctoral studies as a member of professor

irkin’s group at Northwestern University.

uhyoun Kwak received the BS and MS degrees in chemistry from Seoulational University in 1978 and 1980, respectively, and PhD degree in chem-

stry from the University of Texas at Austin in 1989. From 1989 to 1991, heorked as a Postdoctoral in the Department of Chemistry and Chemical Engi-eering at California Institute of Technology. Since 1991, he is a faculty membern the Department of Chemistry at Korea Advanced Institute of Science andechnology (KAIST). His present research interests are in electrochemistry,lectroanalytical chemistry, and EC-STM.

e Il Park received the PhD degree in physics from Korea Advanced Institute ofcience and Technology (KAIST), Korea. Currently, he is a principal researchcientist at Korea Research Institute of Standards and Science (KRISS), Korea.is research interests include high sensitive mass and biomolecule detectionsing nanoelectromechanical devices and bioMEMS.

eung S. Lee received the BS degree from Seoul National University, Korea, in984, and the MS and PhD degrees in mechanical engineering from Universityf California at Berkeley in 1989 and 1995, respectively. After one year atamsung Advanced Institute of Technology in Kiheung, Korea, he joined theaculty of the Department of Mechanical Engineering in Pohang University ofcience and Technology, Korea, in 1997. In 2003, he joined the faculty of theepartment of Mechanical Engineering in Korea Advanced Institute of Science

nd Technology (KAIST). His research interests include all aspects of design,abrication, and analysis of MEMS, bioMEMS, and piezoMEMS.

wang-Cheol Lee received the MS degree in physics and the PhD degree inechanical engineering from Pohang University of Science and Technology

POSTECH), Korea. Currently, he is a principal research scientist in the Depart-ent of Advanced Technology at Korea Research Institute of Standards andcience (KRISS), Korea. His research interests include bioMEMS, biomimet-

cs, nanoelectromechanical devices for high sensitive sensors, and quantumeasurements.