Microchemical Journal 103 (2012) 125–130

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Microchemical Journal

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Electrochemical immunoassay based on gold nanoparticles and reduced grapheneoxide functionalized carbon ionic liquid electrode

Sheng Yu a,⁎, Xiaoyu Cao b, Meng Yu a

a College of Chemistry and Chemical Engineering, Xinyang Normal University, Xinyang 464000, Chinab School of Chemistry and Chemical Engineering, Henan University of Technology, Zhengzhou 450001, China

⁎ Corresponding author. Tel.: +86 376 6390702.E-mail address: yusheng3156@163.com (S. Yu).

0026-265X/$ – see front matter © 2012 Elsevier B.V. Aldoi:10.1016/j.microc.2012.02.002

a b s t r a c t

a r t i c l e i n f o

Article history:Received 13 December 2011Received in revised form 7 February 2012Accepted 7 February 2012Available online 13 February 2012

Keywords:Carcinoembryonic antigenGold nanoparticlesReduced graphene oxideImmunosensorCarbon ionic liquid electrode

In this paper, a gold nanoparticle, reduced graphene oxide (R-GO) and poly(L-Arginine) composite materialmodified carbon ionic liquid electrode (CILE) was used as the platform for the construction of a new electro-chemical carcinoembryonic antigen (CEA) immunosensor. The poly(L-Arginine)/R-GO composite film wasused to modify CILE to fabricate Arg/R-GO/CILE through electropolymerization of L-Arginine on R-GO/CILE.Gold nanoparticles (AuNPs) were adsorbed on the modified electrode to immobilize the CEA antibody andto construct the immunosensor. The stepwise assembly process of the immunosensor was characterized bycyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). By combining the specific prop-erties such as the biocompatibility and big surface area of AuNPs, and the excellent electron transfer ability ofR-GO and the high conductivity of CILE, the synergistic effects of composite increased the amounts of CEA an-tibody adsorbed on the electrode surface and then resulted in the great increase of the electrochemical re-sponses. Under the optimal conditions, differential pulse voltammetric responses of [Fe(CN)6]

3−/4− wereproportional to CEA concentration in the range from 0.5 to 200 ng mL−1 with the detection limit as0.03 ng mL−1 (S/N=3). The proposed immunosensor showed good reproducibility, selectivity, and accept-able stability.

© 2012 Elsevier B.V. All rights reserved.

1. Introduction

Increasing attention has been focused on the development of im-munoassay because it has become a major analytical tool in clinicaldiagnosis [1]. In immunoassay, the determination of cancer markersassociated with certain tumors in patients plays an important rolein diagnosing cancer diseases. Carcinoembryonic antigen (CEA), anacidic glycoprotein with a molecular weight of about 200 kDa, isone of the most extensively used tumor markers. The normal rangefor CEA in an adult non-smoker is b2.5 ng/mL and for a smoker isb5.0 ng/mL. An elevated CEA level in serum may be an early indica-tion of lung cancer, ovarian carcinoma, colon cancer, breast cancerand cystadenocarcinoma [2]. Hence, developing rapid, simple andsensitive immunoassay methods for measuring serum CEA concen-tration has great clinical significance in the diagnosis of cancer. How-ever, sensitive detection of protein biomarkers remains a greatchallenge as CEA present at ultralow levels in the early state of dis-eases. It is very important to explore a new method for signal ampli-fication in order to increase the sensitivity of the detection. Differentmethods for signal enhancement have been investigated, such as

l rights reserved.

enzyme labeling [3], rolling circle amplification [4] and nanomateriallabeling [5]. Among these methods, nanomaterial labeling has gainedgrowing interest due to the intrinsic advantages of nanomaterials,such as low cost, good thermal stability and large surface area [6,7].

Reduced graphene oxide (R-GO) is a sheet of sp2 bonded two-dimensional carbon atoms that are arranged into a honeycomb struc-ture, which has attracted considerable attentions due to its uniqueand excellent properties, such as extremely high thermal conductivi-ty, good mechanical strength, high mobility of charge carriers, highspecific surface area, quantum hall effect and upstanding electric con-ductivity [8–10]. As electrode materials, R-GO can be used for pro-moting electron transfer between the electroactive species and theelectrode and provide a novel method for fabricating chemical sen-sors or biosensors [11–13]. Recently, the composite materials com-bining R-GO and polymer have received increased attention due tothe synergistic contribution of two or more functional componentsand the many potential applications [14,15]. On the other hand,gold nanoparticles (AuNPs) have been widely used for the construc-tion of electrochemical immunosensors [16,17] due to the fact thatthey can increase the amount of the biomolecules loaded and thenamplify the response.

Ionic liquids (ILs), which are composed of organic cations and var-ious anions, have been widely used in the fields of chemistry due tothe unique advantages such as high chemical and thermal stability,

126 S. Yu et al. / Microchemical Journal 103 (2012) 125–130

negligible vapor pressure, high ionic conductivity, wide electrochem-ical windows and low toxicity [18]. Carbon ionic liquid electrode(CILE) has showed the advantages including high electronic conduc-tivity, remarkable electrocatalytic activity, inexpensive reagents andeasy fabrication. For example, Sun et al. applied the CILE as thebasal electrode for the redox protein electrochemistry with differentnanoparticles such as CaCO3 nanoparticles [19] and CdS nanorods[20].

In this work, we proposed a novel electrochemical immunosensorfor CEA based on the advantages of R-GO, AuNPs and poly(L-Arginine).A CILE was fabricated by the addition of 1-butylpyridinium hexafluor-ophosphate (BPPF6) in carbon paste as binder and modifier, andfurther used as the basal electrode for the electrochemical CEA immu-nosensor. The AuNPs prepared by one-step direct chemical reductionwere used to immobilize the CEA antibody (anti-CEA). The interactionbetween anti-CEA and antigen was investigated by the electrochemi-cal probe of ferricyanide. Enhanced sensitivity was achieved by usingthe large specific surface area of AuNPs to increase anti-CEA loading,the high conductivity of R-GO, CILE and Au nanoparticles to promoteelectron transfer among probe and the electrode, which resulted inthe high sensitivity of the immunosensor. Based on signal amplifica-tion strategy of R-GO and CILE, the fabricated immunosensors usingAuNPs as labels showed a linear response within the wide range of0.5–200 ng mL−1 of CEA, low detection limit, good reproducibilityand selectivity, as well as acceptable stability.

2. Experimental

2.1. Materials

1-Butylpyridinium hexafluorophosphate (BPPF6, >99%, LanzhouGreenchem ILS, LICP, CAS, China), graphite powder was obtainedfrom Shanghai Chemical Reagent Corporation (Shanghai, China).HAuCl4·4H2O was bought from Sinopharm Chemical Reagent Co.,Ltd. (Shanghai, China). Sodium citrate was purchased from BeijingChemical Reagent Company (Beijing, China). L-Arg was purchasedfrom ZhongBei LinGe Biotechnology Ltd. (Beijing, China). Bovineserum albumin (BSA), prostate-specific antigen (PSA), low density li-poprotein (LDL) and human immunoglobulin (HIgG) were obtainedfrom Sigma (Saint Louis, MO, USA). CEA and anti-CEA were purchasedfrom Biocell (Zhengzhou, China). Phosphate-buffered saline (PBS,0.01 M) with various pH values was prepared with stock standard so-lution of Na2HPO4, NaH2PO4 and 0.1 M KCl. All other reagents wereused without any further purification. All the solutions were preparedwith doubly-distilled water.

2.2. Instruments

All the voltammetric measurements were performed on a CHI660D electrochemical workstation (Shanghai CH Instrument, China).A three-electrode system was employed for the electrochemical de-tection, which was composed of a modified CILE as working electrode,a Pt wire as auxiliary electrode and a saturated calomel electrode(SCE) as reference electrode. The pH measurements were madewith a pH meter (MP 230, Mettler-Toledo, Greiffensee, Switzerland).The images of scanning electron microscope (SEM) were obtained atHitachi S-4800 (Japan).

2.3. Preparation of R-GO nanocomposite

Graphene oxide was firstly synthesized from graphite according tothe Hummers and Offeman method [21]. Then the graphene oxidewas reduced and followed a typical procedure: the resulting gra-phene oxide dispersion (100 mL) was mixed with 70 μL of hydrazinesolution (50 wt.% in water) and 0.7 mL of ammonia solution (28 wt.%in water). The mixture was stirred for 1 h at the temperature of 95 °C.

Finally, black hydrophobic R-GO sheets were obtained by filtrationand dried in vacuum.

2.4. Preparation of AuNPs

AuNPs were prepared by a trisodium citrate reduction method asreported before [22]. Briefly, trisodium citrate (5 mL, 38.8 mM) wasrapidly added to a boiling solution of HAuCl4 (50 mL, 1 mM), andthe solution was kept continually boiling for another 30 min to givea wine-red solution. After filtering the solution through a 0.45-μmMillipore syringe to remove the precipitate, the filtrate was storedin a refrigerator at 4 °C.

2.5. Fabrication of the immunosensor

Carbon ionic liquid electrode (CILE) was fabricated based on thereported procedure [23]. 3.0 g of graphite powder and 1.0 g of BPPF6were mixed thoroughly in a mortar and further heated at 80 °C toform a homogeneous carbon paste. A portion of the carbon pastewas filled into one end of a glass tube (Ф=3 mm) and a copperwire was inserted through the opposite end to establish an electricalcontact. The CILE surface was smoothed on a piece of weighing paperjust before use.

0.1 mg R-GO was dispersed into 1 mL DMF to form 0.1 mg mL−1

R-GO dispersion. Then 10 μL R-GO dispersion was dropped onto thesurface of the CILE, dried under the infrared lamp, and finally rinsedwith water to remove loosely adsorbed R-GO. Thus, the R-GO/CILEelectrode was obtained.

The poly(L-Arg) film was electropolymerized on R-GO/CILE bydipping the R-GO/CILE into PBS (pH 6.0) containing 2.0 mM L-Argwith cyclic voltammetric sweeps in the potential range from −2.0to 2.5 V at 100 mV s−1 for 10 cycles [24]. Then poly(L-Arg) filmscould be obtained at the surface of R-GO/CILE. The prepared Arg/R-GO/CILE was cleaned with water and dried under a stream ofnitrogen.

The AuNPs/Arg/R-GO/CILE was prepared by immersing the Arg/R-GO/CILE into the AuNP solution for 6 h and then cleaned with waterand dried under a stream of nitrogen. The AuNPs were adsorbedonto the Arg/R-GO/CILE by chemisorption type interactions betweenthe NH2 group and AuNPs [25]. Then the modified electrode(AuNPs/Arg/R-GO/CILE) was immersed in the anti-CEA solution at4 °C overnight. At last the resulting electrode was incubated in BSAsolution (0.25%, w/w) for about 1 h in order to block possible remain-ing active sites and avoid the non-specific adsorption. The finishedimmunosensor (anti-CEA/AuNPs/Arg/R-GO/CILE) was stored at 4 °Cwhen not in use.

2.6. Experimental measurements

The electrochemical characteristics of the electrode were charac-terized by cyclic voltammetry. After the immunoreaction was per-formed by immersing the immunosensor in 0.01 M PBS (pH 7.0)containing various concentrations of CEA for 15 min at 30 °C andthen washed carefully with double distilled water, the electrochemi-cal measures were performed in an unstirred electrochemical cell.The CV measurements were taken from 0 to 0.7 V (vs. SCE) at50 mV s−1 in 10 mL 0.01 M PBS (pH=7.0). Electrochemical imped-ance spectroscopy measurements were carried out in the presenceof a 5.0 mM K3[Fe(CN)6]/K4[Fe(CN)6] (1:1) mixture as a redoxprobe in 0.01 M PBS (containing 0.1 M KCl, pH 7.0). The alternativevoltage is 5 mV and the frequency range is 0.1 to 100,000 Hz. The de-tection is based on the oxidation peak current response decreasingafter antigen–antibody reaction.

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3. Results and discussion

3.1. Characteristics of Gr

Fig. 1 shows the SEM image of R-GO, revealing the typical crum-pled and wrinkled R-GO sheet structure.

Fig. 2. Cyclic voltammograms of different modified electrodes in pH 7.0 PBS at50 mV s−1. (a) CILE; (b) R-GO/CILE; (c) Arg/R-GO/CILE; (d) AuNPs/Arg/R-GO/CILE;(e) anti-CEA/AuNPs/Arg/R-GO/CILE; (f) BSA/anti-CEA/AuNPs/Arg/R-GO/CILE; (g) CEA/BSA/anti-CEA/AuNPs/Arg/R-GO/CILE.

3.2. Electrochemical properties of different electrodes

CV and electrochemical impedance spectroscopy (EIS) are two ef-fective techniques in probing the interface properties of surface-modified electrodes. CVs of [Fe(CN)6]3−/4− on the different modifiedelectrodes were shown in Fig. 2. A couple of well-defined redox peakswas observed on CILE (curve a), which was due to the high ionic con-ductivity of IL present in the carbon paste. After the pretreated CILEwas modified with R-GO, the peak current increased greatly, indicat-ing that the introduction of the R-GO played a role in the increase ofthe electroactive surface area and provided the conducting bridgesfor the electron-transfer of [Fe(CN)6]3−/4− (curve b). When the sur-face of the R-GO/CILE was further coated with the poly(L-Arg) film(curve c), the peak currents increased in the presence of poly(L-Arg)due to the positive charges of the poly(L-Arg), which facilitated theelectrochemical reaction of [Fe(CN)6]3−/4− at the Arg/R-GO/CILE.When AuNPs were adsorbed onto the Arg/R-GO/CILE, the peak cur-rents decreased (curve d). This might be attributed to the followingreasons: the surface of AuNPs obtained by the citrate thermal reduc-tion method was capped by citrate ions. Thus AuNPs were negativelycharged. Therefore, the expelling interaction between negativelycharged AuNPs and [Fe(CN)6]3−/4− resulted in decreased peak cur-rents, yet the peak currents of the AuNPs/Arg/R-GO/CILE were stilllarger than those of the R-GO/GCE. After anti-CEA was immobilizedon the electrode surface, the peak currents decreased obviously(curve e), which suggested that the protein anti-CEA severely re-duced effective area and active sites for electron transfer. The peakcurrents decreased in the same way (curve f) after BSA was used toblock non-specific sites. Lastly, the peak current decreased againafter the immunosensor was incubated with CEA. The reason forthis was that the immunocomplex blocked the tunnel for mass andelectron transfer.

A typical EIS plot includes a semicircle region and a straight line.The semicircle part, which can be observed at higher frequency, cor-responds to the electron-transfer-limited process, whereas the linearpart at the lower frequency range represents the diffusional-limitedelectron-transfer process. The semicircle diameter equals the electron

Fig. 1. SEM images of R-GO.

transfer resistance (Ret). As shown in Fig. 3, the electron transfer re-sistance of CILE was small (curve a), which was in accordance withthe enhancement for electron transfer of CILE. After R-GO (curve b)and poly(L-Arg) (curve c) modification to the CILE, it can be seenthat EIS displayed almost a straight line in the Nyquist plot of imped-ance spectroscopy, characteristic of a diffusion-limited electron-transfer process, indicating that R-GO and poly(L-Arg) film acted asa good electron relay for shuttling electrons between the electro-chemical probe and the electrode. When electrode was coated withAuNPs, the semicircle increased obviously (curve d), which indicatesthat the deposition of AuNPs make interfacial electron transfer moredifficult. Subsequently, when the anti-CEA antibodies were adsorbedon the surface of AuNPs, Ret further increased (curve e). The resultwas consistent with the fact that the hydrophobic layer of protein fur-ther hindered the interfacial electron transfer. The Ret increased in asimilar way after BSA was used to block non-specific sites (curve f).After the resulting immunosensor was incubated in CEA solution,Ret increases dramatically (curve g), which indicates the formationof hydrophobic immunocomplex layer embarrassing the electrontransfer.

Fig. 4 shows the CVs of the proposed immunosensor at differentscan rates. The potential and peak currents are dependent on the

Fig. 3. EIS of different electrodes in 5 mM Fe(CN)63–/4– solution containing 0.1 M KCl:(a) CILE; (b) R-GO/CILE; (c) Arg/R-GO/CILE; (d) AuNPs/Arg/R-GO/CILE; (e) anti-CEA/AuNPs/Arg/R-GO/CILE; (f) BSA/anti-CEA/AuNPs/Arg/R-GO/CILE; (g) CEA/BSA/anti-CEA/AuNPs/Arg/R-GO/CILE.

Fig. 4. CVs of the immunosensor in pH 7.0 PBS at different scan rates of (from inner toouter): 20, 50, 80, 100, 150, 200, 250, 300, 400, and 500 mV s−1. The inset shows thelinear relationship between the peak currents and the square root of scan rate.

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scan rate, it was found that the redox peak current was proportionalto the square root of scan rate from 20 to 500 mV s−1, as shown inthe inset of Fig. 4, suggesting that the reaction was a diffusion-controlled process.

Fig. 5. Influence of incubation time (A) and incubation temperature (B) on the re-sponse signals.

3.3. Optimizing conditions for immunoassay

The influence of the immunochemical incubation time on re-sponse signals was studied. When the analyte antigens reach theantibodies on immunosensor surface, it took some time for the con-tacting species to form immunocomplex. Fig. 5A displayed that thecurrent response decreased with the increment of incubation timeand close to leveled off after 15 min in the incubation solution ofCEA, which implied that the building of immunocomplex reached sat-uration. Therefore, 15 min was chosen as the incubation time for thedetermination of CEA.

The effect of incubation temperature on the immunosensor wasstudied in the range from 10 to 50 °C as shown in Fig. 5B. When theincubation temperature increased from 10 to 30 °C, the current re-sponse of the immunosensor decreased obviously. When the temper-ature was over 30 °C, the current response increased. The reason wasthat the high temperature might cause an irreversible denaturation ofproteins in the process. So 30 °C was selected as incubation tempera-ture for the whole assays.

The effect of pH on the analytical response of the immunosensorwas investigated in the range from 5.5 to 8.0. The test results showedthat the maximum current response occurred at pH 7.0. So pH 7.0 ofthe working buffer was used.

3.4. Analytical performance of immunosensor

Under the optimal experimental conditions, DPVs for CEA detec-tion were obtained. Fig. 6 showed that the peak currents decreasedwith the increased concentrations of CEA. The oxidation peak currentof the immunosensor was found to be proportional to the CEAconcentration in the range from 0.5 to 200 ng mL−1 with a linearcoefficiency of 0.995. The linear regression equation was as following:Ipa (μA)=168.96–39.687 logC (ng mL−1), and a detection limit of0.01 ng mL−1 could be obtained (S/N=3).

To further find the performance of the proposed method, a com-parison of the detectionmethods was shown in Table 1, which includ-ed the limit of detection and the linear range. Table 1 indicated thatthe proposed immunosensor (BSA/anti-CEA/AuNPs/Arg/R-GO/CILE)exhibited lower detection limit and wider measurement range. Thereason might be as follows: firstly, the excellent electrical conductiv-ity of CILE and R-GO enhanced the charge transport; secondly, theformation of the poly(L-Arg) film increased the immobilizationamount of AuNPs. The unique physical and chemical features couldincrease the surface loading amount of the anti-CEA.

Fig. 6. Calibration plot of the immunosensor for detection of CEA. The amperometrymeasurement was carried out by DPV in 10 mL 0.01 M PBS (pH=7.0).

Table 1Comparison of different electrochemical immunosensors for the determination of CEA.

Modified electrode Linear range(ng mL−1)

Detectionlimit (ng mL−1)

Reference

Anti-CEA/AuNPs/poly-o-aminophenol 0.5–20 0.1 [26]Anti-CEA/AuNPs 0.50–25 0.25 [27]Anti-CEA/AuNPs/poly-sulfanilic acid/HRP 0.5–5.0 – [17]Anti-CEA/core–shell Fe3O4/SiO2 1.6–60 0.5 [28]Anti-CEA/Thi/HRP 0.6–200 0.2 [29]Anti-CEA/HRP/sol–gel 0.5–120 0.4 [30]Anti-CEA/AuNPs/(3-mercaptopropyl)trimethoxysilane/Fe3O4 1.0–55 0.13 [31]Anti-CEA/3-aminophenylboronic,11-mercaptoundecanoic acid/HRP/ 2.0–40.0 1.1 [32]Anti-CEA/AuNPs/Chit/NG 0.2–120.0 0.06 [33]Anti-CEA/AuNPs/Arg/R-GO/CILE 0.5–200 0.01 This work

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3.5. Selectivity of the immunosensor

Selective determination of target analytes plays an important role inanalyzing biological samples in situ without separation. The effect ofsubstances that might interfere with the response of immunosensorwas investigated. The evaluation selectivity of the immunosensor wascarried out by incubating the immunosensor in 20.0 ng mL−1 CEA con-taining some potential co-existed species with CEA, such as PSA, AFP,HIgG, LDL and BSA, ascorbic acid, dopamine, L-glucose, tryptophan,and tyrosine. The degree of interference from substances describedabove can be judged from the value of the current ratio. Herein, thecurrent ratios can be obtained from the current reading of the immuno-sensor incubated in 20.0 ng mL−1 CEA and 20.0 ng mL−1 interferingsubstances versus the current readingwith the immunosensor incubat-ed in 20.0 ng mL−1 CEA. The results were listed in Table 2. The resultssuggested that the substance selected did not interfere remarkably.Moreover, these non-specific species did not lead to a significant cur-rent shift or current change. So, the immunosensor had a good selectiv-ity to CEA.

3.6. Stability, reproducibility and regeneration of the immunosensor

The long-time stability of the immunosensor was studied on a 30-day period. After keeping it in a refrigerator for 2 weeks, the immuno-sensor was used to detect the same CEA concentration (20.0 ng mL−1).The current response maintained about 97.2%, 95.3%, and 84.1% ofthe original value after the storage periods of 10 days, 20 days, and30 days, respectively. The good stability may be ascribed to the factthat the anti-CEA molecules were absorbed firmly on the surface ofAuNPs/Arg/R-GO composite film which provided a good biocompatiblemicroenvironment.

The reproducibility of the immunosensor was examined by deter-mining 20.0 ng mL−1 of CEA with ten detections. The relative stan-dard deviation was 0.45% for 10 independent determinations. Theexperimental results indicated good reproducibility of the fabricationprotocol.

Regeneration of the immunosensor was a key factor for developinga practical and advantageous immunosensor. In this experiment, afterthe immunosensor was incubated in 20.0 ng mL−1 CEA sample for15 min, it was dipped into a stirred 0.2 M glycine–hydrochloric acidsolution (pH=2.8) and a 4 M urea solution for 5 min, respectively.

Table 2Interference studies with the immunosensor (n=6).

Interferences Current ratio Interferences Current ratio

PSA 0.95±0.05 Ascorbic acid 1.06±0.03AFP 0.91±0.03 Dopamine 0.92±0.04HIgG 0.93±0.04 Glucose 0.97±0.06BSA 1.02±0.02 Tryptophan 0.94±0.03LDL 0.94±0.05 Tyrosine 0.96±0.06

Consecutive measurements were repeated for five times and the rela-tive standard deviation was found to be 6.8% (n=6).

3.7. Preliminary application of the immunosensor

In order to further evaluate the practical application of theimmunosensor, six serum specimens supplied by the People's Hos-pital of Xinyang, China, were determined by both the proposed elec-trochemical immunosensor and the enzyme-linked immunosorbentassay (ELISA) methods, respectively. These serum samples were di-luted to different concentrations with 0.01 M PBS of pH 7.0, and in-cubated in the incubation solution at 30 °C for 15 min. After asimple washing step with doubly distilled water, the measurementswere carried out in 0.01 M pH 7.0 PBS. Table 3 showed the results ofthe two methods studied. It can be seen that the relative errorbetween the two methods was from −7.7% to 6.0%, suggesting anacceptable agreement. Thus, the presented method could be satis-factorily applied to the clinical determination of CEA antigen inhuman serum.

4. Conclusions

In this paper, a novel strategy of an amperometric immunosensorfor CEAwas developed based on the anti-CEA adsorbed in AuNPs/Arg/R-GO/CILE. The advantages of the immunosensor are as follows: theproposed strategy offered a simple and convenient methodology forthe preparation of stable structured poly(L-Arg)–R-GO compositeto increase the adsorption amount of AuNPs; AuNPs doped withpoly(L-Arg)–R-GO composite increased the conductibility, biocom-patibility and the immobilization amount of anti-CEA; the appearanceof R-GO and ionic liquid with high conductivity and prominent bio-compatibility greatly promoted the direct electron transfer between[Fe(CN)6]3−/4− and the underlying electrode. On the basis of theabove reasons, the prepared immunosensor exhibited high stabilityand a low detection limit. The simplicity in fabrication procedures,ease of the detection step and good reproducibility of the proposedmethod opened up an increasing possibility for the future develop-ment of practical devices for determination of CEA.

Table 3Experimental results of two methods obtained in serum samples.

Samples 1 2 3 4 5

ELISA (ng mL−1) 8.2±0.5 23.3±0.4 45.6±0.5 60.3±0.8 83.1±0.6This method(ng mL−1)

8.6±0.3 22.1±0.5 42.1±0.4 63.9±0.3 85.4±0.6

Relative deviation(%)

4.9 −5.2 −7.7 6.0 2.8

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