Molybdenum oxide/Platinum Modified Glassy Carbon Electrode: A Novel Electrocatalytic Platform for...

Accepted Manuscript

Title: Molybdenum oxide/Platinum Modified Glassy CarbonElectrode: A Novel Electrocatalytic Platform for theMonitoring of Electrochemical Reduction of Oxygen and ItsBiosensing Applications

Author: <ce:author id="aut0005" biographyid="vt0005">Irem Cakar<ce:author id="aut0010" biographyid="vt0010">K. Volkan Ozdokur<ce:author id="aut0015"biographyid="vt0015"> Bilal Demir<ce:author id="aut0020"biographyid="vt0020"> Elvin Yavuz<ce:author id="aut0025"biographyid="vt0025"> Dilek Odacı Demirkol<ce:authorid="aut0030" biographyid="vt0030"> SuleymanKocak<ce:author id="aut0035" biographyid="vt0035"> SunaTimur<ce:author id="aut0040" biographyid="vt0040"> FatmaNil Ertas

PII: S0925-4005(13)00547-9DOI: http://dx.doi.org/doi:10.1016/j.snb.2013.04.106Reference: SNB 15472

To appear in: Sensors and Actuators B

Received date: 31-12-2012Revised date: 20-4-2013Accepted date: 24-4-2013

Please cite this article as: I. Cakar, K.V. Ozdokur, B. Demir, E. Yavuz, D.O. Demirkol,S. Kocak, S. Timur, F.N. Ertas, Molybdenum oxide/Platinum Modified Glassy CarbonElectrode: A Novel Electrocatalytic Platform for the Monitoring of ElectrochemicalReduction of Oxygen and Its Biosensing Applications, Sensors and Actuators B:Chemical (2013), http://dx.doi.org/10.1016/j.snb.2013.04.106

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http://dx.doi.org/doi:10.1016/j.snb.2013.04.106

http://dx.doi.org/10.1016/j.snb.2013.04.106

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Molybdenum oxide/Platinum Modified Glassy Carbon Electrode: 1

A Novel Electrocatalytic Platform for the Monitoring of Electrochemical Reduction of 2

Oxygen and Its Biosensing Applications 3

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İrem Çakara, K. Volkan Özdokura, Bilal Demirb, Elvin Yavuza, Dilek Odacı Demirkolb, 5

Süleyman Koçakc, Suna Timurb, Fatma Nil Ertaşa*6

aDepartment of Chemistry, Faculty of Science, Ege University 35100 Bornova, Izmir, Turkey7

bDepartment of Biochemistry, Faculty of Science, Ege University 35100 Bornova, Izmir, Turkey8

cDepartment of Chemistry, Faculty of Science & Art, Celal Bayar University, 45030 Muradiye, Manisa, Turkey9

*[email protected]

Abstract11

The reduction of oxygen to water is one of the most important reactions in electrochemistry 12

with regards to the wide range of applications in electrocatalysis, metal corrosion, and fuel 13

cell and mostly in biosensor studies. Present study describes the use of a glassy carbon 14

electrode modified with platinum and molybdenum oxide (Pt-MoOx) in strongly acidic 15

solutions for electrocatalytic reduction of oxygen dissolved in buffer solution for the first 16

time. The dispersion of Pt nanoparticles on MoOx provides larger surface area and better 17

electrocatalytic activity for oxygen reduction and the best response towards dissolved oxygen 18

was obtained with a mole ratio of 1:90 Pt:Mo in deposition solution. The modified surface 19

was then used as a biosensing platform for the monitoring of oxygen consumption due to the 20

bio-catalytic action of glucose oxidase (GOx) as the model enzyme. After optimization of the 21

operational conditions, analytical characterization and application of the glucose oxidase GOx 22

biosensor to flow injection analysis mode have been successfully performed.23

Keywords: Molybdenum trioxide; platinum nanoparticle; oxygen reduction; glucose oxidase; 24

flow injection analysis.25

*Corresponding author. Tel.: +90 232 3112356; Fax: +90 232 311235026

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1. Introduction1

Transition metal oxides, molybdenum oxide in particular, have recently received much 2

attention owing to their remarkable electrical, optical and electrochromic properties [1-3]. The 3

properties of the oxide film mostly depend on the synthesis procedure. To date, these oxide 4

films have been prepared by various techniques such as thermal evaporation [4], liquid phase 5

deposition [5], sol–gel [6], sputtering and oxidation of metal and more recently 6

electrochemical deposition [7]. Among these methods, the electrodeposition is probably the 7

most economic and suitable technique for readily producing large uniform oxide thin films 8

[8]. Responses of the prepared molybdenum oxide thin films in different supporting 9

electrolytes were studied by cyclic voltammetry and acidity was shown to have a great effect 10

on the film morphology [8-10]. 11

A recent study carried out in this lab revealed that a mixed-valent molybdenum oxide 12

(MoOx) deposit was produced electrochemically on a glassy carbon (GCE) and ITO 13

electrodes from a solution containing molybdate ion in chloroacetic acid solution [11]. XPS 14

studies have revealed the mixed valent nature of molybdenum oxide deposit including Mo(V) 15

and Mo(VI). This deposit has exhibited unique catalytic activity towards nitrite oxidation and 16

it was also noted that the deposit displays a catalytic activity towards reduction of dissolved 17

oxygen. 18

Dissolved oxygen is usually consumed during the enzymatic reactions thus; its detection 19

is very interesting for the development of biosensors [12]. In addition, electrocatalytic oxygen 20

reduction in fuel cell cathodes has been the focus of attention due to its slow kinetics and 21

therefore, the reduction mechanism was studied at various electrode materials [13]. It has 22

been established that the reaction can proceed as two or four electroned process depending on 23

the cathode material and cell composition. Over the last decade, much attention was paid to 24

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the use of nanoparticles of noble metals such as Pt, Au and Pd as their electrocatalytic 1

activities differ from the bulk metal [14].2

Noble metal catalysts mixed with inorganic oxides are of considerable interest for 3

catalysis process [15]. A recent study with graphite electrode modified with platinum and 4

molybdenum oxide nanoparticles has revealed its electrocatalytic effect on the oxidation of 5

methanol [16]. The oxide deposit physically separates the catalytic particles avoiding them 6

from agglomeration. In addition, the oxide is assumed to modify the chemisorptive and 7

catalytic properties of Pt particles. 8

Alloys of Pt with other metals, mostly first row transition metals as Co, Ni, Cr, V and 9

Fe, were found to be more active for ORR than pure Pt. Carbon based electrodes modified 10

with molybdenum oxide including platinum nanoparticles have exhibited higher catalytic 11

activity for the oxygen reduction reaction than platinum deposited carbon electrodes. This 12

enhancement in catalytic activity was attributed to the synergetic effects due to formation of 13

an interface between the platinum and MoOx [17].14

This study reveals the catalytic activity of platinum and molybdenum trioxide 15

nanoparticles (Pt-MoOx) co-deposited on a glassy carbon electrode (GCE) towards oxygen 16

reduction reactions and their use in biosensing technology, i.e. glucose sensing. Since it was 17

proposed in 1962, a vast number of different approaches have been explored in the operation 18

of glucose enzyme electrodes toward the development of reliable devices for diabetes control 19

[12]. Yet, in spite of the remarkable advances in the design and use of glucose biosensors, 20

there are still major challenges in achieving clinically accurate and sensitive results in 21

continuous glycemic monitoring. 22

2. Experimental 23

2.1 Reagents and Apparatus24

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Glucose oxidase (GOx; EC 1.1.3.4, 50 units/mg), glutaraldehyde solution (%25, v/v) 1

and D-glucose were obtained from Sigma Aldrich (Dorset, UK). All other reagents used were 2

of analytical grade. The solutions were prepared with ultra pure water from a Millipore water 3

system. 0.1 M acetic acid/acetate buffer system was prepared at pH 5.0. Phosphate buffer was 4

prepared from sodium salt and the pH was set at 7.0 by addition of necessary amount of HCl 5

solution.6

Voltammetric measurements were carried out by PalmSens voltammetric analyzer. A 7

three electrode system consisted of the GCE as the working electrode, a platinum wire as the 8

auxiliary electrode and Ag/AgCl electrode was used as the reference electrode. Cyclic 9

voltammetry was used during the electroanalytical studies. All experiments were carried out 10

at ambient temperature and high purity nitrogen is used to de-aerate the solution if it is 11

required.12

Biosensor responses were measured chronoamperometrically in stirred working buffer 13

solutions by applying a potential of 0.25 V (vs Ag/AgCl). In the case of FIA, a peristaltic 14

pump (FIAtron, Oconomovoc, WI, USA) equipped with silicon tubing (0.89 mm inner 15

diameter), for carrying 0.9 mL buffer solution per minute, an eight-port injection valve 16

(FIAtron, Oconomovoc, WI) with a 100 µL sample injection loop, a computer system 17

connected PalmSens potentiostat for electrochemical measurements, and a cross-flow cell 18

with three electrodes were used. Flow cell configuration consists of GC electrode (3.0 mm 19

diameter and 1.0 mm electrode gap), an Ag/AgCl electrode and a Pt wire (CHI 130, Austin, 20

US) was used as a working, reference and counter electrode, respectively. 21

2.2 Preparation of Pt-MoOx modified GC electrode22

The GCE was polished on a piece of cloth with alumina and then rinsed with pure 23

water. It was placed into beaker containing deionized water in an ultrasonic bath for 5 min.24

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Cyclic voltammetric response of the bare electrode was monitored in pH 5.0 acetate 1

buffer for background recording. Then, the electrode was placed in 2.2 M H2SO4 solution 2

containing 2.2 mM H2PtCl6 and 0.2 M Na2MoO4 as given elsewhere [16]. The potential of the 3

modification step was applied from 1.05 V to -0.25 V with 20 mV/s scan rate. Afterwards, the 4

modified GC electrode was placed in pH 5.0 acetate buffer which is bubbled with N2 and then 5

O2 gas respectively, prior to each measurement. 6

2.3 Biosensor construction and measurements 7

The biosensor was prepared as follow; 1.0 mg GOx and 2.0 mg gelatin was mixed with 8

50 L of pH 7.0 sodium phosphate buffer solution and kept in water bath at 37oC for few min. 9

Afterwards, 25 L of this mixture were dropped onto the Pt-MoOx modified GCE surface and 10

kept in a refrigerator for one hour. The electrode was then dipped into the 100 L 11

glutaraldehyde (2.5%, v/v) in pH 7.0 sodium phosphate buffer solution and kept in 5 min. 12

3. Results and Discussion13

Initial studies deal with the characterization of the electrode surface modified with Pt-14

MoOx nanoparticles and its performance for dissolved oxygen. In pursuit of this study, the 15

results obtained for biosensor applications in which an oxidase enzyme (GOx) using oxygen 16

as the co-substrate were given.17

3.1 Characterization of Molybdenum trioxide/Platinum Modified GCE18

Cyclic voltammograms obtained for Pt-MoOx nanoparticles grown on GCE are given in 19

Fig. 1A. In the first scan, a steep reduction peak at -0.15 V and a broad oxidation peak around 20

0.8 V were observed. Another peak has appeared at 0.06 V on the second scan and increased 21

in height with scan number and a corresponding oxidation peak has appeared at 0.2 V. This 22

quasi-reversible reduction peak can also be related with molybdenum oxide species modified 23

with platinum particles in agreement with a former study [16]. For comparison, the cyclic 24

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voltammetric experiment was repeated in the absence of platinum ions by using the same 1

scale (Fig. 1B).2

< Insert Figure 1>3

Successive cycles of the potential from 1.05 V to -0.25 V has shown a decline in the 4

peak height at -0.15 while the peak around 0.8 V was increasing progressively (Fig. 1A). In 5

agreement with the literature, the former peak corresponds to the Pt reduction gradually 6

grown on GCE surface and hydrogen adsorption/desorption on the Pt particles. As pointed out 7

earlier, the latter peak could be related to the molybdenum species deposited on the electrode 8

surface, though the peak potential is more positive than the former study which can be 9

attributed to the use of different support materials for the coating. 10

After five successive cycles in the potential range studied, SEM images have revealed that 11

Pt nanoparticles with size of about 20-100 nm were deposited on the GCE and in the presence 12

of Mo(VI) (Fig. 2a) and larger particles were observed in a range of 40-200 nm and Pt 13

particles were dispersed on the MoOx grown on the surface (Fig. 2b). The element content of 14

the deposit on the GCE was analyzed with EDX (Fig. 2c) and the inset table shows the Pt/Mo 15

atomic ratio of the electrode surface.16

As it is known that activity of noble metal catalyst can be increased by addition of 17

inorganic oxides including MoO3 as they physically separate the catalytic particles preventing 18

agglomeration [15]. The oxide is also believed to modify the electronic nature of the metal 19

particles affecting their chemisorptive and catalytic properties. Therefore, high dispersion of 20

Pt particles on MoOx provides larger surface area and better electrocatalytic activity for 21

oxygen reduction. 22

< Insert Figure 2>23

In electrodeposition process carried out by cyclic voltammetry, the thickness of the 24

coating can be easily controlled by simply adjusting the scan number. Fig. 3 shows the cyclic 25

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voltammograms recorded in pH 5.0 acetate buffer saturated with oxygen at a GCE which was 1

modified in the solution specified above by using various cycle numbers from 1 to 10, 2

respectively and then transferred into the other cell. Clearly, the change in the surface 3

characteristics of the electrode reflects in the electrode response to dissolved oxygen. The 4

same GCE was employed for different deposition procedures and reproducible peak current 5

formation is governed by the reproducibility in the film thicknesses inherited from electrochemical 6

deposition. The reduction peak of dissolved oxygen can be seen at -0.04 V with a height about 7

24 A at a bare GCE (Fig. 3a). Upon cycling the potential in a range of 1.05 and -0.25 V with 8

20 mV/s scan rate, the peak potential has shifted about 0.2 V in the first scan while the peak 9

current has doubled. The shift was more obvious for further scans and the peak current has 10

progressively increased. Even though the highest peak currents were seemed to be obtained 11

with scan number of 10, the baseline was also high for this electrode (Fig. 3A-e) and 12

therefore, optimum cycle number was chosen as 5 for further studies (Fig. 3B).13


Another parameter to be optimized is the Pt:Mo mole ratio in the modification solution 15

onto the peak characteristics of oxygen reduction. The first modification was made with the 16

solution consisting of 2.2 mM H2PtCl6 and 2.2 M H2SO4. Then, the Na2MoO4 concentration 17

was changed to maintain the mole ratio of 1:30, 1:60, 1:90 Pt:Mo, respectively. The peak 18

characteristics obtained from the resulting voltammograms were summarized in Table 1. Best 19

response towards dissolved oxygen was obtained with a mole ratio of 1:90 Pt:Mo. 20

< Insert Table 1 >21

Clearly, the Pt-MoOx/GCE electrode with this composition displays the best catalytic 22

activity towards oxygen reduction. In order to elucidate the catalytic activity of the composite 23

electrode thoroughly, the electrode performance was tested by using Fe(CN)64−/Fe(CN)6

3− as 24

redox pairs which usually serve as a benchmark in investigating the electrochemical behavior 25

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of the such modified electrodes. Cyclic voltammetric experiments were performed with 5.0 1

mM Fe(CN)63- solution prepared in 0.1 M KCl. The scan rate was changed in a range of 5-200 2

mV/s and the peak currents were found to be correlated with square root of scan rate with a 3

deviation from linearity at faster scan rates (Fig. 4). The linearity designates that the 4

magnitude of the current is dominated by diffusive mass transport, although the deviation at 5

high scan rate indicates insufficient solute reaches to the electrode surface. The peak 6

potentials were also found to be dependent on the scan rate indicating a quasireversible 7

character of the electrode process. In the range of scan rates 5-250 mVs－1 used, the anodic peak 8

has shifted from -0.13 to -0.05 while the cathodic peak shifts from -0.24 to -0.29 V. 9

< Insert Figure 4 >10

3.2 Biosensor Applications of Enzyme immobilized Pt-MoO3/GCE11

The performance of the biosensor developed was tested by addition of glucose into the 12

cell to be 1.0 mM. Chronoamperometric response of the electrode was recorded and after 13

addition of substrate to the buffer solution, it was allowed to obtain a steady state about 1.5 14

A in 2 min. Upon addition of glucose standard to the solution, the oxygen consumed by the 15

enzymatic reaction at around the electrode surface has reflected as the decreased peak height 16

and resulting difference in the peak current was employed as the response signal. Following 17

that, the effect of parameters namely; amount of the immobilized enzyme, the operating pH 18

on the response of the glucose biosensor and the effect of interferences were investigated. 19

First study was dedicated to optimize the pH of the buffer system including 1.0 mM 20

glucose. The prepared glucose biosensor was studied at pH 3.5 and 4.0 citrate buffer and pH 21

3.7 - 5.5 acetate buffer solutions. The best results were obtained in pH 4.0 (data not shown) 22

and further experiments were carried out at pH 4.0 acetate buffer solutions.23

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The amount of enzyme is another parameter to be optimized. In the modification step, 1

the enzyme amount was varied in a range of 0.25 - 2.0 mg and the electrode response was 2

plotted against the glucose concentration which was changed between 0.01-2.5 mM. As can 3

be deduced from the Fig. 5, during working with 0.5, 1.0 and 2.0 mg enzyme amounts, similar 4

slope and correlation coefficients were obtained for the linear range from 0.01 to 1.0 mM 5

glucose. 6

In order to avoid needless consumption of chemicals, it was decided to continue the 7

studies with 0.5 mg of enzyme (which equals 48 U enzyme activity). For this calibration 8

curve, the limit of detection was calculated as 0.025 mM (S/N = 3).9


Optimization studies were completed by this means and effect of some interference that 11

is possible to be found in the sample matrix were also investigated. Equal concentrations (0.5 12

mM) of uric acid, ascorbic acid and phenol solutions were studied alone and no signal was 13

observed for any of these compounds. Upon addition of these compounds into the 14

measurement medium along with the glucose, a slight decrease in the signal was observed 15

being less than 5%.16

The current response of the biosensor was also investigated in FIA configuration, after 17

injecting standard glucose solutions to the carrier solution under optimized conditions. The 18

maximum steady-state response was achieved in ~70 s. As illustrated in Fig. 6, the calibration 19

plot was linear in the glucose concentration range from 0.05 to 0.5 mM. This linear range was 20

noticed to be narrower than the one obtained by batch system (from 0.01 to 1.0 mM).21


The reproducibility of the biosensor was studied by making 10 consecutive injections of 23

0.25 mM glucose. The calculated coefficient of variation was 1.17% for injections with a 24

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single biosensor. The limit of detection was calculated as 0.048 mM (S/N = 3). The 1

comparison of the sensitivity of the method with former studies can be followed from Table 2. 2

< Insert Table 2 >3

4. Conclusion4

Present study demonstrates the earliest results of platinum and molybdenum oxide 5

composite electrode for electrocatalytic reduction of oxygen dissolved in a buffer solution. Pt-6

MoO3 nanoparticles codeposited on a GCE deposited showed an increased current density 7

over a wider potential range for the oxygen reduction peak by shifting towards positive 8

direction. Besides other applications, the monitoring of oxygen consumed by the enzyme-9

catalyzed reaction constitutes the basis of most biosensing studies. Therefore, the possibility 10

to use composite electrode as a platform for biosensor applications was searched by 11

immobilizing GOx onto the modified surface. The electrode performance was found 12

comparable to the results of other biosensor studies with various modification nanomaterials, 13

including gold nanoparticles or carbon nanotubes as electrical connectors between the 14

electrode and the redox center of GOx. The method developed can also be adopted to flow 15

systems which constitutes a reliable and sensitive alternative for continuous glycemic 16

monitoring.17

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Acknowledgement19

This work was supported by the Research Funds of Ege University (BAP) Turkey with 20

2010FEN032 project number. 21

22

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Biographies1

Irem Çakar has received her M.S. degree in Ege University in 2012. Her current research 2

focuses on electrochemical sensor and biosensor.3

Kemal Volkan Özdokur has received his M.S. degree in Ege University in 2012. His current 4

research focuses on Electroanalytical chemistry, voltammetric techniques 5

Bilal Demir is now studying as M.S. student in Department of Biochemistry, Ege University. 6

His current research focuses on sensor and biosensor, FIA system.7

Elvin Yavuz is now studying as M.S. student in Department of Chemistry, Ege University. 8

Her current research focuses on voltammetric techniques.9

Dilek Odacı Demirkol received her PhD degree of Biochemistry in Ege University in 2010. 10

She is currently a associate professor at the Department of Biochemistry, Ege University. Her 11

current research focuses on electrochemical sensor and biosensor, Nano Biomaterial, Nano 12

medicine.13

Süleyman Koçak received his PhD in analytical chemistry from Ege University, Turkey in 14

2009. He is now working in Department of Chemistry Celal Bayar University as an assistant 15

professor. His current interests include Electroanalytical chemistry, voltammetric techniques, 16

fuel cell and heavy metal analysis.17

Suna Timur received her PhD degree of Biochemistry in Ege University in 2001. She is 18

currently a full-time professor at Department of Biochemistry, Ege University. Her current 19

research focuses on electrochemical sensor and biosensor, Nano Biomaterial, Nano medicine, 20

Drug Delivery.21

Fatma Nil Ertaş received her PhD in analytical chemistry from Loughborough University of 22

Technology, United Kingdom in 1993. She is now working in Department of Chemistry Ege 23

University as a full-time professor. Her current interests include Electroanalytical chemistry, 24

voltammetric techniques and chromatographic techniques.25

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Captions1

Figures2

3

Fig.1 The modification voltammograms of GCE by cycling the potential with a scan rate of 4

20 mV/s in the solution containing 2.2 mM H2PtCl6, 0.2 M Na2MoO4 (A) and 0.2 M 5

Na2MoO4 (B) in 2.2 M H2SO4 medium.6

Fig.2 The SEM images shows Pt and MoOx on GCE surface by cycling the potential with a 7

scan rate of 20 mV/s for five times in the range of 1.05 and -0.25 V in the solution containing 8

a) 2.2 mM H2PtCl6 in 2.2 M H2SO4 b) 2.2 mM H2PtCl6, 0.2 M Na2MoO4 in 2.2 M H2SO4, c) 9

EDX spectra and the element content of surface deposit on GCE obtained from solution of 2.2 10

mM H2PtCl6, 0.2 M Na2MoO4 in 2.2 M H2SO4.11

Fig. 3 The effect of the cycle number on the response of the Pt-MoO3-GCE in pH 5.0 acetate 12

buffer saturated with oxygen gas. The curves are the response of the a) bare GCE to dissolved 13

oxygen and after transferring the GCE modified with Pt-MoOx by cycling the potential from 14

1.05 and -0.25 V with a scan number of b) 1, c) 3, d) 5 and e) 10 at a scan rate of 20 mV/s. 15

The background voltammograms (A) and the cycle number versus current (B) are shown as 16

insets.17

Fig.4 The effect of scan rate on the cyclic voltammograms of a) bare GCE, b) Mo/GCE, c) 18

Pt/GCE, d) Pt-MoOx/GCE modified electrode in 5.0 mM Fe(CN)63- solution in 0.1 M KCl 19

and 50 mM pH 4.0 acetate buffer at scan rates 5-250 mVs−1. The graph shows the dependence 20

of anodic (a, b, c, d) and cathodic (aı, bı, cı, dı) peak currents versus the square root of 21

potential scan rate. 22

Fig.5 The effect of enzyme amount on the amperometric response of the biosensor and the 23

equations of the linear concentration range.24

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16

16

Fig.6 The reproducibility of the actual FIA peaks after injecting 0.4 mM glucose in the inset 1

and calibration plot for glucose in a concentration range studied.2

Tables3

Table 1 The peak characteristics obtained for dissolved oxygen reduction at a Pt-MoOx / GCE 4

modified in solution with different Pt : Mo mole ratios 5

Table 2 Comparison of performances of various glucose biosensors in literature6

7

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1

Figures

Potential (V)

-0,2 0,0 0,2 0,4 0,6 0,8 1,0

Cu

rren

t (

A)

-1400

-1200

-1000

-800

-600

-400

-200

0

200

400

5

1

1

5

5

1

Scanning direction

(A)

Potential (V)

-0,2 0,0 0,2 0,4 0,6 0,8 1,0

Cu

rren

t (

A)

-80

-60

-40

-20

0

20 1

5

1

5

Scanning direction

(B)

Fig. 1

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2

2

Fig.2

(a) (b)

(c)

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3

3

Potential (V)

-0,4 -0,2 0,0 0,2 0,4 0,6 0,8

Cu

rren

t (

A)

-150

-100

-50

0

50

100

150

a

b

c

de

Potential (V)-0,4 0,0 0,4 0,8

Cu

rren

t (

A)

-100

-50

0

50

Cycle number0 2 4 6 8 10

(A

)65

70

75

80

85(A) (B)

e

a

Fig. 3

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4

4

Fig. 4

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5

5

Concentration (mmol L-1)

0,0 0,5 1,0 1,5 2,0 2,5

Cu

rren

t R

esp

onse

(A

)

0,0

0,2

0,4

0,6

0,8

1,0

1,2

1,4

1,6

0.25 mg0.50 mg1.00 mg2.00 mg

Fig. 5

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6

6

Concentration (mmol L-1 )

0,0 0,1 0,2 0,3 0,4 0,5

Cur

rent

Res

pons

e (m

A)

0,0

0,1

0,2

0,3

0,4

Time (s)0 100 200 300 400 500 600 700

Cu

rren

t (

A)

-1,8

-1,6

-1,4

-1,2

-1,0

-0,8

y = 0.8790x - 0.0263

R2 = 0.9971

Fig. 6

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Graphical Abstract

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Table 1

Pt:Mo E (V) Ip (A)

1:0 -0.023 24.22

1:30 0.22 39.45

1:60 0.26 67.32

1:90 0.26 69.19

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Table 2

Electrode Configuration Linear Range LOD

Working

Potential

(vs. Ag/AgCl)

Reference

SNS-NH2 - CNT/AuNP/GOx 0.05 - 0.75 mM 2.1 μM -0.7 V [18]

Cyst/PAMAM/GOx 0.01 - 1.0 mM 11.84 μM -0.7 V [19]

PBDT/GOx

PESeE/GOx

0.05 - 2.0 mM

0.01 - 2.0 mM

0.05 mM

0.01 mM

-0.7 V [20]

DM-Mont/GOx

DM-Mont/GOx (FIA)

0.05–1.0 mM

1.0 – 10.0 mM

0.038 mM

0.47 mM

-0.7 V [21]

Pt-DENs /PANI/CNT/GOx 1.0 µM – 12 mM 0.5 μM 0.0 V [22]

CHIT-CNT/GOx 1.0 – 10 mM 21 μM 0.6 V [23]

CHIT–Fc/GOx 0.8 - 4.0 mM 0.565 mM 0.35 V [24]

AuNP/(FcSH+Cyst)/PAMAM/GOx 1.0 - 5.0 mM 0.6 mM 0.35 V [25]

Pt/MoO3/GCE/GOx

Pt/MoO3/GCE/GOx (FIA)

0.05 - 0.5 mM 0.025 mM

0.053 mM

0.25 V This work

SNS-NH2: 4-(2,5-di(thiophen-2-yl)-1H-pyrrole-1-l) benzenamine; CNT: Carbon Nanotube; AuNPs: Gold

Nanoparticles, Cyst: Cysteamine; PAMAM: Poly(amido amine).; PBDT: Poly(4,7-di(2,3)-dihydrothienol[3,4-

b][1,4]dioxin-5-yl-benzo[1,2,5]thiadiazole); PESeE: Poly(4,7-di(2,3)-dihydrothienol[3,4-b][1,4]dioxin-5-yl-

2,1,3-benzoselenadiazole; Pt-DENs: Dendrimer-encapsulated Pt Nanoparticles; FcSH: 6-(Ferrocenyl)

hexanethiol; PANI: Polyaniline; CHIT: Chitosan; Fc: Ferrocen, FIA: Flow injection analysis.

Molybdenum oxide/Platinum Modified Glassy Carbon Electrode: A Novel Electrocatalytic Platform for...

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