Supporting Information

Effective Seed-assisted Synthesis of Gold Nanoparticles Anchored Nitrogen-

doped Graphene for Electrochemical Detection of Glucose and Dopamine

Tran Duy Thanh,a Jayaraman Balamurugan,a Seung Hee Lee,a,b Nam Hoon Kim,a Joong Hee

Leea,b*

aAdvanced Materials Institute of BIN Technology (BK21 plus Global) & Dept. of BIN

Convergence Technology, Chonbuk National University, Jeonju, Jeonbuk 561-756, Republic of

Korea.bCarbon Composite Research Centre, Department of Polymer & Nanoscience and Technology,

Chonbuk National University Jeonju, Jeonbuk 561-756, Republic of Korea

*Corresponding authors: E-Mail: jhl@jbnu.ac.kr (Joong Hee Lee)

Fax: +82 832702341; Tel: +82 832702342

Fourier transform infrared spectroscopy (FT-IR) of HNO3-treated graphene included the

vibration modes of the C-O-C stretch (1192 cm−1 and 1447 cm−1), sp2-hybridized aromatic C=C

stretch and OH bending (1629 cm−1), C–OH (1,080 cm−1), C=O stretch (1,704 cm−1), CO2 stretch

(2349 cm−1), and hydroxyl stretch (3,050–3,800 cm−1, with all vibrations from C-OH, COOH,

and H2O). Regions of spectral overlap involving mostly C–O and C=O contributions (850–1,500

cm−1) are broken down into three regions: the α-region (900-1,100 cm−1), β-region (1,100–1,280

cm−1), and γ-region (1,280-1,500 cm−1) (Acik et al., 2010; Pham et al., 2011). The red dashed line

is the baseline. Furthermore, the Raman spectrum shows a higher value of ID/IG (ID/IG = 0.3) after

acid treatment compared to that of pristine graphene (ID/IG= 0.04), indicating a significant

increase in defects on the graphene surface. This result is consistent with the IR analysis.

1

Fig. S1. a) IR and b) Raman spectra of pristine graphene (PG) and HNO3-treated PG

2

Fig. S2 a) AuNP/NG modified ITO electrode; b) Connection between AuNP/NG modified ITO

electrode and electrochemical workstation; c) a three-electrode system with Ag/AgCl, Pt wire,

and AuNP/NG modified ITO electrode as reference and counter electrodes, and working

electrode, respectively; and d) CV measurement of CH Instruments.

3

Fig. S3 a) TEM; b) and c) HR-TEM images of PG.

4

Fig. S4 FE-SEM images of a) AuNP/ITO and b) AuNP/PG/ITO with a deposition time of 1 h.

5

Fig. S5 FE-SEM images of AuNP/NG with a deposition time of a) 0.5 h and b) 2 h. Inset:

Distribution of AuNPs on the NG surface

6

Fig. S6 a) C1s spectra of PG; b) C1s spectra of NG; and c) N1s spectra of NG

7

Contact angle

The hydrophilicity of the materials was quantitatively measured using water contact angle

technique. In general, a lower contact angle is associated with an improvement in wettability and

surface area, which facilitate the electrochemical reactivity of materials (Leszczak et al., 2014; Li

et al., 2012; Zhou et al., 2014). The contact angle of NG (61o) was significantly lower than that

of PG (101o) (Fig. S7), suggesting that NG is fairly hydrophilic due to the formation of nitrogen

functional groups attached to the graphene surface, leading to an increase in polarity of the

graphene surface. In the nanohybrids, the contact angle was low compared to that of NG, which

is due to the AuNPs immobilized on the NG nanosheet surface. The contact angle of the

AuNP/NG was 49o, which represents the increase of hydrophilicity as well as surface area. The

AuNPs/NG nanohybrid surface roughness increased due to the presence of highly active AuNPs

(Yang et al., 2013) in the NG matrix, which is shown in Fig. 2.

Fig. S7 Contact angle of ITO modified with a) PG; b) NG; and c) AuNP/NG.

8

Raman studies

Raman spectroscopy is a powerful non-destructive technique used to characterize the

ordered/disordered crystal structures of carbon materials. The structural features of PG, NG, and

AuNP/NG nanohybrids were examined using Raman spectroscopy (Fig. S8). The Raman spectra

of PG showed three specific characteristic D, G, and 2D bands at 1352 cm–1, 1583 cm−1 and 2695

cm−1, respectively. The intensity ratio of the D band to G band (ID/IG) and 2D band to G band

(I2D/IG) was 0.05 and 1.1, respectively, confirming the growth of 3-4 layers with a high degree

of crystallinity in PG (Graf et al., 2007). In contrast, NG presented a stronger D band (ID/IG =

0.92) and weaker 2D band (I2D/IG = 0.37) compared with those of PG. These results indicate that

the graphene structure was activated by defects due to the in-plane substitution of nitrogen

dopants (Park et al., 2014). Also, the G band of NG shifted to a 2 cm -1 higher frequency with

respect to that of PG, which is in agreement with the previous observations of nitrogen-doped

graphene (Park et al., 2014; Panchakarla et al., 2009). In the case of the AuNP/NG nanohybrids,

the ID/IG ratio of 0.95 and I2D/IG ratio of 0.31 changed only slightly compared to those of NG

due to the presence of the AuNPs embedded within the NG structures (Biroju et al., 2014).

9

Fig. S8 Raman spectra of PG, NG, and AuNP/NG nanohybrids.

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Electrochemical behavior

The electrochemical properties of the materials were evaluated using EIS analysis, which is a

powerful technique to identify the electrocatalytic activity of electrode materials. The EIS

method analyzes a semicircular portion at higher frequencies and a linear portion at lower

frequencies, which correspond to electron-transfer resistance (Rct) and the diffusion process,

respectively (Hu et al., 2012). A bigger semicircle at high frequency region reflects a higher

charge transfer resistance. The EIS of the as-synthesized PG, HNO3 treated graphene, NG,

and AuNP/NG nanohybrids are shown in Fig. S9. The PG displayed a large semicircle at high

frequencies consistent with Rct = 1789 , which refers to the weak charge transfer of PG due

to the electrochemical inert properties of the sp2 carbon layer on the electrode surface (Kibena

et al., 2013). In the case of the HNO3 treated graphene, the Rct value of 891 was measured

lower than that of the PG because of the attachment of certain electrochemical sensitive

groups, which promotes ion diffusion (Prathish et al., 2013). Meanwhile, the semicircle

diameter consistent with Rct = 582 was shown at NG, indicating the fact that nitrogen

doping increased the conductivity of the graphene networks and improved the electrocatalytic

activity of the graphene toward the redox system. Remarkably, the Rct value of 348

measured from the AuNP/NG nanohybrids was further decreased as compared with that of the

PG, functionalized graphene and NG. This is due to the synergistic effect of the AuNPs and

NG, which in turn accelerates the electron transfer rate in the nanohybrids [Borowiec et al.,

2013].

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Fig. S9 The EIS results of PG, HNO3-treated PG, NG, and AuNP/NG nanohybrids on the ITO

electrode.

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Table S1. The detection limits and linear ranges of AuNP/NG/ITO compared to different

modified electrodes for nonenzymatic glucose sensing.

Electrode materials LOD (M) Linear range (mM) Reference

Cu-MWCNTs 2 0.5-7.5 Zhao et al., 2013

Cu2O/graphene 3.3 0.3-3.3 Liu et al., 2013

PtRu(1:1)/MWNT–IL 50 Up to 15 Xiao et al., 2009

Gold nanowire array 30 Up to 10 Cherevko et al., 2009

Macroporous Au-Pt 25 1-20 Lee et al., 2011

Pt-Au/MWCNT 10 0.04-24.4 Wua et al., 2013

GO Nanoribbon/AuNPs 5 0.005-10 Ismail et al., 2014

AuNP/NG/ITO 12 0.04-16.1 Present work

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Table S2. Determination of glucose concentration in alkalized human serum samples using the

AuNP/NG-modified ITO electrode.

Sample Analyte Commercial sensor

(mM)

Our sensor

(mM)

Recovery

(%)

RSD (%)

(n = 3)

Serum 1 Glucose 3.52 3.28 93.2 3.1

Serum 2 Glucose 6.94 6.45 93.1 1.32

Serum 3 Glucose 10.47 9.9 94.6 1.27

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Table S3. The detection limits and linear ranges of different modified electrodes for the

detection of DA.

Electrode materials LOD (nM) Linear range (μM) Reference

rGO/MWCNTs/AuNPs 67 0.2-70 Yuan et al., 2014

AuNPs-β-CD–Graphene/GCE 150 0.5-150 Tian et al., 2012

RGO/PdNPs 233 1-150 Palanisamyetal., 2013

Graphene/Pt 30 30-8.13 Sun et al., 2011

GO nanoribbons /GCE 80 0.15-12.15 Sun et al., 2011

3D graphene foam 25 Up to 25 Dong et al., 2012

NG 250 0.5-170 Sheng et al., 2012

AuNP/NG/ITO 10 0.03-48 Present work

15

Table S4. Determination of DA concentration in spiked human serum samples using the

AuNP/NG-modified ITO electrode.

Sample Analyte Detected

(M)

Added

(M)

Founded

(M)

Recovery

(%)

RSD (%)

(n = 3)

Serum 1 DA - 10 9.52 95.2 4.5

Serum 2 DA - 20 18.96 94.8 3.2

Serum 3 DA - 40 39.48 98.7 1.6

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