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Sensors and Actuators B 192 (2014) 234– 238

Contents lists available at ScienceDirect

Sensors and Actuators B: Chemical

journa l h om epage: www.elsev ier .com/ locate /snb

lectrochemical sensing of the genotoxicity of the micron LiFePO4 riceranule using a guanine biosensor based on LiFePO4/HCl/K2S2O8

ystem

ong Chena, Xueliang Wangb,∗∗, Zhangyu Yua,b,∗

Department of Chemistry and Chemical Engineering, Qufu Normal University, Qufu, 273165, People’s Republic of ChinaDepartment of Chemistry and Chemical Engineering, Heze University, Heze, 274015, People’s Republic of China

r t i c l e i n f o

rticle history:eceived 23 July 2013eceived in revised form 21 October 2013ccepted 23 October 2013

a b s t r a c t

In order to investigate the genotoxicity of the micron LiFePO4 rice granule, an electrochemical biosensorbased on determination of guanine (G) oxidative damage induced by the LiFePO4/HCl/K2S2O8 system wasdeveloped. In the LiFePO4/HCl/K2S2O8 system, the reaction of the micron LiFePO4 rice granule with HClproduced Fe2+, and the produced Fe2+ would further react with S2O8

2−, generating sulfate radical (SO4•−)

vailable online 1 November 2013

eywords:uanine damageicron LiFePO4 rice granule

which could severely damage the guanine bases that was immobilized on a glassy carbon electrode (GCE)surface by electro-deposition. The square wave voltammetry (SWV) signal change of the guanine baseswas used to monitor the guanine damage. The present work provided a simple electrochemical approachfor screening the potential genotoxicity of particulate matters and chemicals in vitro, and it also hadpotential application in investigating some chemicals anti-oxidation property.

enotoxicity

ulfate radical (SO4•−)

. Introduction

With the rapid development of industry and transportation, aarge number of particulate matters are inevitably emitted intohe environment. Researchers have argued that the major pollu-ion factors include inhalable particulate matter PM10 (particulate

atter with aerodynamic diameter equal to or less than 10 �m)nd fine particulate matter PM2.5 (particulate matter with aerody-amic diameter equal to or less than 2.5 �m) [1,2]. Fine particulateatter has long residence time in the atmosphere and can pene-

rate deeply into the lung, thus, the toxicity of the fine particulateatter is higher than that of coarse airborne particles [3].It is known to all of us that exposing to airborne partic-

late matter usually associate with variously adverse healthutcomes, including cardiovascular disease, respiratory disease,nd an increased risk of developing lung cancer [4–8]. Therefore,ore and more people is concerning about the possible hazardous

ffects of particulate matter on public health and ecosystems. The

ey to understand the toxicity of particulate matter is whether itsize is 10 �m in diameter or smaller, allows it to pass through thehroat and nose and enter the lung, disrupt their normal functions.

∗ Corresponding author at: Department of Chemistry and Chemical Engineering,eze University, Heze, 274015, People’s Republic of China. Tel.: +86 530 5668162;

ax: +86 530 5668162.∗∗ Corresponding author.

E-mail addresses: qust-1977wxl@163.com (X. Wang), yuzywxl@163.com (Z. Yu).

925-4005/$ – see front matter © 2013 Elsevier B.V. All rights reserved.ttp://dx.doi.org/10.1016/j.snb.2013.10.105

© 2013 Elsevier B.V. All rights reserved.

So it is very necessary to evaluate the potential genotoxicity ofparticulate matter.

In recent years, to study the particulate matters is aninteresting discipline research region focusing on determiningstructure/function relationships between particulate matter andtoxicity, and characterizing the adverse effects caused by par-ticulate matters [9]. Some literatures have reported that manyparticulate matters are genotoxic. They can induce chromosomalaberrations, DNA strand breaks, DNA oxidative damage, and muta-tions [10–14]. For example, Knaapen et al. [15] investigated themechanism of PM-induced DNA damage using electron spin reso-nance (ESR). The results showed that metal PM suspensions as wellas their particle-free, water-soluble fractions can generate hydroxylradicals (•OH) in the presence of hydrogen peroxide (H2O2).

Hydroxyl radicals (•OH), superoxide radicals (O2•−) and H2O2,

are well known as reactive oxygen species (ROS), which have beenusually considered to be linked with a series of diseases, such ascancer, inflammation, cardiovascular and neurodegenerative dis-eases [16–20]. When ROS attack DNA, the guanine bases prior toundergo oxidative damage due to their low oxidation potential andtheir ability to bind to transition-metal ions which can catalyzeoxidative processes [21,22]. The guanine electrochemical biosen-sor has been used to study the total antioxidant capacity of flavoredwater [23,24].

Recently, LiFePO4 has been selected for a wide range of applica-tion in electronics fields (especially lithium ion batteries [25–28])due to its intrinsic properties, such as excellent thermal stability,low cost of precursors and high reversibility of Li+ insertion [29,30].

R. Chen et al. / Sensors and Actuators B 192 (2014) 234– 238 235

S methr system

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t

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cheme 1. Electro-immobilization of the guanine on GCE surface and the detectionespectively, before and after the sensor was treated with the LiFePO4/HCl/K2S2O8

n this work, the micron LiFePO4 rice granule was synthesized andts genotoxicity was studied in vitro using a guanine electrochem-cal biosensor. The biosensor was fabricated by electro-depositionf guanine molecules onto a glassy carbon electrode (GCE) first, andhen the guanines were damaged by incubating a guanine modifiedlectrode in the LiFePO4/HCl/K2S2O8 mixture solution. The SO4

•−

as produced through a series of reactions and induced the guaninexidative damage on the surface of the guanine modified GCE. Theuanine damage was detected by the square-wave voltammetrySWV) technique in pH 3.5 PBS solution.

. Experimental

.1. Materials and apparatuses

Guanine was acquired from Sigma. The 1.0 g L−1 guanine stockolution was prepared by dissolving guanine with 0.1 mol L−1 NaOHnd diluting with 0.1 mol L−1 phosphate buffered saline (PBS) of pH.5 to desired concentration. Potassium persulfate was purchasedrom Xilong Chemical Co., Ltd. (Guangdong, China). Hydrochloriccid and sulfuric acid were purchased from Laiyang Shuang Shuanghemical Co., Ltd. (Shandong, China). Micron LiFePO4 was pro-ided by laboratory of applied chemistry, Qingdao University ofcience and Technology. The scanning electron microscopy (SEM)mages of the micron LiFePO4 was showed in the supplementary

aterial (Fig. S1). 0.1 mol L−1 phosphate buffer solution (pH 3.5)as obtained by mixing with 0.1 mol L−1 NaH2PO4 and 0.1 mol L−1

a2HPO4 and adjusted with 0.1 mol L−1 H3PO4 or 0.1 mol L−1 NaOHo the pH. NaH2PO4, Na2HPO4, H3PO4 and NaOH were all purchasedrom Tianjin Chemical Co., Ltd. (Tianjin, China). All other chemicalsere of analytical grade and ultrapure water was used in all the

xperiments.Supplementary material related to this article can be found, in

he online version, at http://dx.doi.org/10.1016/j.snb.2013.10.105.

All electrochemical experiments were performed on a CHI 660 C

lectrochemical workstation (Shanghai CH Instruments Co., Ltd.,hina) with a standard three-electrode system of a GCE ( = 3 mm)r modified GCE electrode working electrode, a saturated calomel

od for guanine damage. Curve a and curve b are the SWV signals of the biosensor,. SWV: Square wave voltammetry.

reference electrode (SCE) and a platinum wire counter electrode.The square wave voltammetry (SWV) signal was recorded in thepotential range from 0.4 to 1.4 V with frequency of 15 Hz, steppotential of 4.0 mV and amplitude of 25 mV. The pH value of allsolutions was measured by a model pHS-25 digital acidometer(Shanghai Leici Factory, China).

2.2. The buildup processes of the sensor and detection

First, GCE was pretreated as previous report [31], then thepretreated GCE was put into 0.5 mol L−1 H2SO4 solution andcyclic voltammograms were recorded in a potential range of −0.5to 1.80 V until a constant signal was obtained to increase thehydrophilic properties of the electrode surface. This procedure wascalled electrode activation [22]. After that, the activated GCE wasimmersed in a 0.1 mol L−1 PBS of pH 3.5 containing 4 mg L−1 ofguanine, and an adsorption step was conducted at a constant pos-itive potential of +0.4 V for 180 s under constant stirring [23]. Theguanine damage was performed by immersing the guanine mod-ified electrode into the aqueous solution of 1.0 mg mL−1 LiFePO4,1.0 × 10−3 mol L−1 HCl and 2.0 × 10−5 mol L−1 K2S2O8 at 37 ◦C withstirring for a certain time. The guanine damage induced by sul-fate radicals (SO4

•−) was monitored by square wave voltammetry(SWV) in pH 3.5 of PBS. All measurements were made at least threetime and the results were expressed as mean ± standard deviation.

The buildup processes of the sensor and the detection methodare shown in Scheme 1. The generation mechanism of the SO4

•−

in the LiFePO4/HCl/K2S2O8 system is described as the Eqs. (1) and(2). When pH values are more than 7.0, the sulfate radicals (SO4

•−)change into hydroxyl radicals (HO•) according to the chemical reac-tions represented in Eqs. (3) and (4) [32,33]. If the Fe2+ is excess,the radical can be destroyed and producing the sulfate ions Eq. (5)[34].

LiFePO4 + H+ → Li+ + Fe2+ + PO43− (1)

Fe2+ + S2O82− → Fe3+ + SO4

2− + SO4•− (2)

236 R. Chen et al. / Sensors and Actuators B 192 (2014) 234– 238

1.5 2.0 2.5 3. 0 3. 5 4. 0 4.5 5. 01.2

1.4

1.6

1.8

2.0

2.2

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10

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pH

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S

F

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1 2 3 4 51.50

1.55

1.60

1.65

1.70

1.75

1.80

1.85

1.90

1.95

2.00

i / 1

10

-5A

CG/mg L

-1

Fig. 2. Influence of the guanine base concentration on the electrochemical current.

ig. 1. The influence of pH values of the detection solution on the SWV signals ofuanine.

O4•− + H2O → •OH + HSO4

− (3)

O4•− + HO− → •OH + SO4

2− (4)

e2+ + SO4•− → Fe3+ + SO4

2− (5)

. Results and discussion

.1. Optimizing the guanine bases damage conditions

The optimal pH value of the detection solution was investigatedy recording the SWV response of the guanine modified GCE inifferent pH values of PBS and the results were showed in Fig. 1. Thexperiments indicated that the SWV current of guanine increasedith the pH values at first and then declined in the pH range from

.0 to 4.5, and the biggest value of i was obtained at about pH 3.5.his may be due to guanine is an alkaline compound and the pH 3.5alue is more advantageous to the alkaline guanine immobilizedn the activated electrode surface. Therefore, pH 3.5 was used forhe further experiments.

Furthermore, the oxidation potentials of guanine shifted nega-ively with the increase of pH values, manifesting that the protonsave taken part in the electrode reaction processes. The oxida-ion peak potentials (Ep) of guanine and pH obey the equations:p = −0.05691pH + 1.0763 (R = 1.00). The EP with pH change rateEp/∂pH value is −0.05691 (V/pH), which implied that the elec-ron transfer was accompanied by an equal number of protons inhe electrode reaction process. These conclusions are in accordanceith the mechanisms of the reference [35].

For a guanine biosensor, the mount of the guanine immobi-ized on the electrode surface is one of the most important factorsnfluencing sensitivity and reproducibility. The guanine base wasmmobilized onto the activated GCE surface by an adsorption step,

hich involved the application of a positive electrode potentialo achieve the electrostatic binding with the negatively chargeduanine. The concentration of the guanine in adsorption step wasptimized by detection the SWV signal of guanine in pH 3.5 of PBS ashe adsorption time was 180 s (Fig. 2). The results showed that theWV signal of the guanine increased with the concentration of gua-ine and leveled off at 4.0 mg L−1, which suggested that the guanine

eached saturation adsorption on the electrode. The concentrationf 4.0 mg L−1 was used for further experiments.

In order to investigate the adsorption of guanine on the elec-rode surface, the influence of scan rate (�) on the oxidation peak

Inset: Square-wave voltammogram of guanine (4 mg L−1). Conditions: potentialrange from +0.2 V to +1.4 V, frequency = 15 Hz, step potential = 4.0 mV and ampli-tude = 25 mV.

current and potential of guanine were also studied by cyclic voltam-metry. The results showed that the Ep shifted positively withthe increase of � (10–200 mV s−1). Meanwhile, the electrode pro-cesses were totally irreversible as confirmed by the fact that therewas no reduction peak appeared in the cyclic voltammograms.The number of the transferred electrons (n) in the oxidation ofguanine was calculated to be 2.12 ≈ 2 from the equation: Ep

(V) = 0.7988 + 0.02421 ln v (mV s−1) (R = 0.9923) according to Lavi-ron [36].

The peak current (ip) was proportional to � and the equationwas ip = 0.2791v + 1.5497 (R = 0.9964), indicating that the oxidationof guanine on the GCE was an adsorption process and the sur-face concentration of guanine (� ) on the GCE was calculated to be1.05 × 10−9 mol cm−2 based on the equation of ip = n2F2v� A/4RTand ∂ip/∂v = 0.2791 (�A/mV). F is the Faraday constant. A is theapparent electrode area.

In the LiFePO4/HCl/K2S2O8 system, the persulfate (S2O82−) con-

centration has powerful effect on the generation of SO4•−. As the

concentration of LiFePO4 and HCl was fixed as 1.0 mg mL−1 and1.0 × 10−3 mol L−1 in the system, respectively, the concentrationof S2O8

2− was optimized by investigating the difference of theSWV peak current (�ip) of guanine in pH 3.5 of PBS before andafter the biosensor was incubated in the system containing differ-ent concentration of S2O8

2− for 8 min. The change of �ip with theconcentration of S2O8

2− was showed in Fig. 3. The experimentsindicated that the �ip increased with the increase of the concen-tration of S2O8

2− in the range of 2.0 × 10−5 and 1.0 × 10−4 mol L−1.However, because the S2O8

2− anion caused some electronics prob-lems on the GCE surface during the next optimization step [24],2.0 × 10−5 mol L−1 S2O8

2− was chosen for the further experiments.The volume of 1.0 mg mL−1 LiFePO4 was investigated by vary-

ing the volume from 5 to 25 �L. The volume change aroused theconcentration change of (S2O8

2− 2.0 × 10−5 mol L−1) was ignorable.The results showed that the �ip increased with the volume increaseof the LiFePO4 at first and then declined (Fig. 4). As showed in the Eq.(5), the excess Fe2+ can destroy the radical and produce the sulfateions [34]. So the optimal volume of LiFePO4 was 10 �L.

3.2. Electrochemical detection of guanine damage

The SWV signals of guanine in pH 3.5 of PBS decreased withthe prolonging of the incubation time of the biosensor in the

R. Chen et al. / Sensors and Actuators B 192 (2014) 234– 238 237

2 4 6 8 101.20

1.25

1.30

1.35

1.40

1.45

1.50

1.55

1.60

Fig. 3. Effect of the concentration of persulfate on the electrochemical currentof guanine immobilized on the GCE. �ip was the difference of the SWV peakcurrents of the sensor in pH 3.5 of PBS before and after it was treated with theLiFePO4/HCl/K2S2O8 system for 8 min.

Lro(

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E/ V

a

e

Fig. 5. Square wave voltammograms of the biosensor in LiFePO4/HCl/K2S2O8 systemfor different incubation time: (a) 0 min, (b) 2 min, (c) 4 min, (d) 6 min and (e) 8 min.Inset: relationship between ip and the incubation time.

Fig. 6. SWV oxidation peak current �ip for the films after incubation in differ-ent solutions for 8 min: (a) blank, (b) S2O8

2− , (c) HCl, (d) LiFePO4 + S2O82− , (e)

LiFePO4 + HCl, (f) HCl + K2S2O8 and (g) LiFePO4 + HCl + S2O82− . �ip is the same as

in Fig. 3.

iFePO4/HCl/K2S2O8 system. In this study, the incubation time wereanged from 0 to 8 min. A 60% decrease of the biggest ip wasbserved after the biosensor was treated with the system for 8 minFig. 5), indicating that most guanine has been damaged.

To verify whether the sulfate radical was generated by theiFePO4/HCl/K2S2O8 system and exhibited the ability to inducexidative damage on guanine bases immobilized on the GCE, theiosensor was incubated in different types of solutions for 8 mint 37 ◦C and the �ip was recorded. The results were displayed inig. 6. The results showed that among of these columns, the col-mn g was the highest, and the height of column b, c, d, e and fad no significant difference in comparison with that of column ablank solution). These results confirmed that all three componentsn micron LiFePO4 rice granule + HCl + S2O8

2− system are abso-utely necessary for guanine oxidative damage. Thus, this approach

as very suitable to investigate the genotoxicity mechanisms ofarticulate matters.

5 10 15 20 250.0

0.2

0.4

0.6

0.8

1.0

1.2

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10-5

A

VLiFePO4

/ µL

ig. 4. Effect of the volume of LiFePO4 on the electrochemical current of the biosen-or in pH 3.5 of PBS. �ip is the same as in Fig. 3.

Table 1The SWV peak current of guanine of a new fabricated biosensor and after it wasstored in 4 ◦C for 2 days in the air.

Biosensor SWV current (× 10−5 A)

New biosensor 2.073 2.071 2.041 2.028 1.972Stored biosensor 2.039 2.033 2.016 1.987 1.951

3.3. Repeatability and stability of the biosensor

The repeatability of the biosensor was investigated by mea-suring the SWV peak current of guanine before and after treatingwith LiFePO4/HCl/K2S2O8 system (�ip). For a batch of six biosen-sors fabricated in the same way after and before they weretreated with LiFePO4/HCl/K2S2O8 system for 8 min, the rela-tive standard deviation (RSD) of �ip was 5.10%, suggesting thatrepeatability of the sensor was good. The storage stability of thebiosensor was evaluated the SWV peak current of guanine of anew fabricated biosensor and after it was stored under 4 ◦C in

the air for 2 days. The results were listed Table 1. The resultsshowed that the stability of guanine modified electrode wasgood.

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38 R. Chen et al. / Sensors and A

. Conclusions

In summary, the rapid and sensitive detection of guaninexidative damage induced by the LiFePO4/HCl/S2O8

2− system wasealized for the first time by electro-immobilization step and SWVechniques, which provides an in vitro model to mimic the path-ay of guanine oxidative damage in real living systems. This model

ystem may help us to better understand the mechanism of purineamage in vivo, and the methodology also it is promising for the

n vitro screening of toxicity of new particulate matters and chemi-als. In addition, the experiment procedure exhibited good stabilitynd reproducibility.

cknowledgments

The work was supported by the National Natural Science Foun-ation of China (No. 21105023) and the Natural Science Foundationommittee of Shandong Province, China (Nos. BS2013HZ027 andR2009BM003).

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Biographies

Rong Chen, a master major in the analytical chemistry, now studying in the Collegeof Chemistry and Chemical Engineering, Qufu Normal University, Qufu, China.

Xueliang Wang, a doctor of engineering major in applied chemistry. Now he worksin the Department of Chemistry and Engineering as an associate professor, HezeUniversity, Heze, China. His research interests include electroanalytical chemistry,biosensors, nanotechnology, immunoassay and detection of the transgenic plantproducts.

Zhangyu Yu, a professor and a Ph.D. supervisor of Shandong University. Now heworks as president of Heze University, Heze, China. His research work focuseson bio-electrochemistry, electro-analytical chemistry, quantum chemistry andsupramolecular chemistry.