Synthetic Metals 203 (2015) 54–58
Contents lists available at ScienceDirect
Synthetic Metals
journal homepage: www.elsevier.com/locate/synmet
Amplified electrochemical signal taking polyanline as sensing interface
compared to polyindole carboxylic acid
Jagriti Narang a, * , Kirti Rani Sharma b, **, Nidhi Chauhan a , Abhishek Mishra b
a
b
Amity Institute of Nanotechnology, Amity University Uttar Pradesh, Noida, Sec-125, Noida 201303, UP, India
Amity Institute of Biotechnology, Amity University Uttar Pradesh, Noida, Sec-125, Gautam Buddha Nagar, Noida 201303, UP, India
A R T I C L E I N F O
A B S T R A C T
Article history:
Received 11 October 2014
Received in revised form 17 January 2015
Accepted 14 February 2015
Available online xxx
In present work, nanocomposite of gold nanoparticles–polyaniline (AuNPs/PANI) produces amplified
electrochemical signal as compared to gold nanoparticles–polyindole carboxylic acid (AuNPs/Pin5COOH)
modified gold electrode (AuE). Present work also compares gold nanoparticles prepared by using green
(extracts of Elettaria cardamomum) and chemical synthesis. The characterization studies of the gold
nanoparticles prepared from both methods were performed using dynamic light scattering (DLS) and
UV–vis spectroscopy. The surface functionalization of modified electrodes was characterized by cyclic
voltammetry (CV) and scanning electron microscopy (SEM). Comparison of signal amplification was
performed using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS).
Voltammetric approach reveals that gold nanoparticles prepared from chemical synthesis resulted in
higher electrochemical signal than gold nanoparticles prepared from green technology. Comparisons
between two hybrid nanocomposites can prove to be a new avenue for making best sensing interface for
biosensor fabrication.
ã 2015 Elsevier B.V. All rights reserved.
Keywords:
Nanocomposite
Gold nanoparticles–polyaniline
Gold nanoparticles–polyindole carboxylic
acid
1. Introduction
Conductive polymers synthesized in the form of nanostructures
have unique morphology with high specific surface area usually
results in very exclusive advantages such as improved dispersion
[1] in organic and inorganic solvents, enhanced electronic
conductivity [2] and response to sensor applications [3,4]. Their
synthesis and chemical modification offer unlimited possibilities
unlike inorganic metals and semiconductors, which is an advantage with these polymers. There are various polymers which are
used as sensing interface like polyanilne (PANI) [5], polyindole
carboxylic acid (Pin5COOH) [6], polypyrrole (PPy) [4]. Among the
various conducting polymers, polyaniline (PANI) is one of the most
important polymers due to its environmental stability, high degree
of processability, facile synthesis, reversible control of electrical
properties by both charge-transfer doping and protonation and
interesting redox properties associated with its chain heteroatom,
PANI has been one of the most extensively studied electroactive
* Corresponding author. Tel.: +91 09811792572.
** Corresponding author. Tel.: +91 120 4392946/9990329492.
E-mail addresses: jags_biotech@yahoo.co.in (J. Narang), krsharma@amity.edu,
Kirtisharma2k@rediffmail.com (K.R. Sharma).
http://dx.doi.org/10.1016/j.synthmet.2015.02.019
0379-6779/ ã 2015 Elsevier B.V. All rights reserved.
(conductive) polymer [7,8]. The introduction of CNTs to PANI
composites enhances the electrical properties (the room temperature resistivity is decreased by one order of magnitude as
compared to PANI) by facilitating charge-transfer processes,
between the two components. The preparation of CNTs and PANI
composites by chemical or electrochemical method has been
reported recently [8,9]. While polyindole carboxylic acid (Pin5COOH) provides carboxylic group which make it best immobilization matrix for biomolecules [6]. The use of these composites in
construction of electrodes has been shown to enhance charge
density, electrical conductivity and electrocatalytic activity compared with pure conducting polymer materials. As both PANI and
Pin5COOH are excellent materials for the construction of
electrochemical sensors and biosensors, the combination of these
two materials is also expected to be an excellent platform for
electrochemical sensing applications [10,11]. Current work proved
that gold nanoparticles from chemical synthesis produces amplified signal as compared to green technology. In present work we
compare the use of PANI and Pin5COOH in combination with gold
nanoparticles from chemical synthesis and MWCNT for electrochemical sensing. Our results proved that PANI in synergistic effect
with MWCNT produces amplified signal in the form of current. So
PANI can be considered as better sensing interface for preparation
of working electrode as compared to Pin5COOH and MWCNT.
J. Narang et al. / Synthetic Metals 203 (2015) 54–58
55
Materials Pvt. Ltd., Panchkula (Haryana), India. Gold colloid
solution (20 nm) from GWENT Group, UK, aniline from Sigma
(Aldrich), indole-5-carboxylic acid from Sigma–Aldrich Co, St.
Louis USA were purchased. All the other chemicals were of
analytical reagent (AR) grade. Gold wire (1.5 0.05 cm2) (23 carat)
was purchased from local market. Double distilled water (DW) was
used throughout the experiment.
2.2. Apparatus
Cyclic voltammetry (CV) and electrochemical impedance
spectroscopy (EIS) measurements were performed in a potentiostat/galvanostat (Autolab, Eco Chemie, The Netherlands. Model:
AUT83785) with a three electrode system consisting of a Pt wire as
an auxiliary electrode, an Ag/AgCl electrode as reference electrode
and modified Pt wire as a working electrode. All the electrochemical experiments were performed at ambient temperature (25 C).
2.3. Preparation of gold nanoparticles using green technology
(gAuNPs)
Scheme 1. Graphical representations of the stepwise working electrode fabrication
process.
2. Experimental
2.1. Materials
Multiwalled carbon nanotubes (MWCNTs) (12 walls, length
15–30 mm, purity 90%, metal content: nil) from Intelligent
Gold nanoparticles were prepared according to the methods of
Pattanayak et al. [12] with slight modifications. Elettaria cardamomum seed (25 g) were procured from local market. Then seeds
were soaked overnight in distilled water. After soaking, seed coats
were removed and internal seeds were crushed with pestal and
mortar. The crushed internal seeds were boiled in a water bath at
80 C for 45 min. After boiling, centrifuge the crushed solution at
5000 rpm for 20 min. The supernatant obtained was filtered using
Fig. 1. A and B DLS spectra analysis of gold nanoparticles from green (A) and chemical synthesis (B).
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J. Narang et al. / Synthetic Metals 203 (2015) 54–58
Whatman’s filter paper and stored at 4 C. HAuCl4 (1.7 mg) was
dissolved in 5 ml of distilled water. E. cardamomum supernatant
(5 ml) was dissolved in HAuCl4 (1 ml) in it drop wise at magnetic
stirrer for 2 h. Store it at 4 C. Thus green gold nanoparticles were
prepared.
2.4. Preparation of gold nanoparticles using chemical synthesis
(cAuNPs)
Gold nanoparticles were prepared according to the methods of
Verma et al. [13] with slight modifications. HAuCl4 (2 ml) solution
was kept on a hot plate and heated to boil. Then prepared trisodium
citrate dehydrate (1%) was added drop wise. Thus chemical
synthesized gold nanoparticles were prepared. The characterization of gold nanoparticles prepared from both methods was carried
out by recording its UV and visible spectra in a UV–vis
spectrophotometer and diffraction light scattering.
as described. One milligram MWCNT was suspended in1 ml
mixture of concentrated H2SO4 and HNO3 in 3:1 ratio (v/v) and
ultrasonicated for 2 h to get a finally dispersed black colored
solution of MWCNTs. The MWCNT solution was washed with DW
thoroughly to remove acid. The PANI modified electrode was
dipped into the MWCNT solution for 24 h. MWCNTs bind with the
PANI layer by forming a —CO—NH— bond between its —COOH
group and free —NH2 group of PANI (at the end of its chain). The
resulting MWCNT/PANI/Au electrode was washed thoroughly
with DW to remove unbound matter and kept in a dry petri plate
at 4 C. After that the electrode was immersed in a colloidal gold
solution prepared from chemical synthesis for 12 h at 4 C [6].
Polyindole nanocomposite (AuNPs/Pin5COOH/MWCNT) was prepared by direct redox reaction between indole monomers and
HAuCl4. Typically, indole (0.01 ml) was mixed in 2 ml 0.5 M H2SO4
containing 10 mM CTAB. The Pin5COOH modified electrode was
dipped into the MWCNT solution for 24 h. MWCNTs gets physical
absorbed with the Pin5COOH. The resulting MWCNT/ Pin5COOH/
2.5. Preparation of cAuNPs/PANI/MWCNT and cAuNPs/Pin5COOH/
MWCNT modified working electrode
Before electrodeposition, the gold electrode was polished with
0.05 mM alumina slurry. Aniline (50 ml) was added to 10.0 ml of
1 N HCl and electro deposited onto Au electrode through cyclic
voltammetric technique using potentiostat/galvanostat. The
electro chemical polymerization of aniline onto Au electrode
(working electrode) was achieved immediately through cyclic
voltammetry by applying 10 polymerization cycles at 0.0 to +1.5 V
Fig. 2. A and B. U-V spectra analysis of gold nanoparticles from green (A) and
chemical synthesis (B).
Fig. 3. (A) SEM of AuNPs/PANi/Au and (B) AuNPs/Pin/Au.
J. Narang et al. / Synthetic Metals 203 (2015) 54–58
Au electrode was washed thoroughly with DW to remove
unbound matter and kept in a dry petri plate at 4 C. Then,
colloidal gold solution prepared from chemical synthesis was
added to it drop wise [10] (Scheme1).
2.6. Electrochemical characterization of cAuNPs/MWCNT/PANI/Au and
cAuNPs/Pin5C/MWCNT/Au electrodes
Cyclic voltammetry studies was carried out using a three
electrode system composed of AuNPs/Pin5COOH/MWCNT/Au and
57
AuNPs/MWCNT/PANI/Au as working electrodes, Ag/AgCl as
reference electrode and Pt wire as auxiliary electrode. For
comparison, role of individual components, cyclic voltammograms of AuNPs/Pin5COOH/MWCNT/Au and AuNPs/MWCNT/
PANI/Au electrodes was recorded in sodium phosphate buffer
(0.1 M, pH 7.0) containing 0.1 mM H2O2 at a scan rate of 0.0 to
+1.5 V at an interval of 50 mV s–1. The surface functionalization of
working electrodes was carried out by scanning electron
microscopy.
Fig. 4. (A) Cyclic voltammograms of (i) gold nanoparticles from green synthesis modified Au electrode and (ii) gold nanoparticles from chemical synthesis modified Au
electrode in a 2.5 mM K3Fe(CN)6/K4Fe(CN)6 solution and sodium phosphate buffer 0.05 M (pH 7.2) at a scan rate of 50 m Vs 1. (B) Cyclic voltammograms of (i) AuNPs/PANi/Au
and (ii) AuNPs/Pin/Au (C) EIS of AuNPs/PANi/Au and AuNPs/Pin/Au (c) in the background solution of phosphate buffer/KCl (0.1 M, pH 7.0). (For interpretation of the references
to color in this figure legend, the reader is referred to the web version of this article.)
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J. Narang et al. / Synthetic Metals 203 (2015) 54–58
3. Results and discussion
3.4. Storage stability and reusability
3.1. Characterization of gAuNPs and cAuNPs
The half life of the cAuNPs/MWCNT/PANI/AuE biosensor was 4
months, which is better than that of the cAuNPs/Pin5COOH/
MWCNT/AuE (3 months).
DLS utilizes temporal variations of fluctuations of the scattered
light to measure an average hydrodynamic diameter of particles
suspended in a liquid medium [14]. Fig. 1A and B shows DLS of
gAuNPs and cAuNPs, the results of dynamic light scattering
showed the size of the gAuNPs and cAuNPs to be 150 nm and
100 nm respectively. Fig. 2A and B presents the spectral region
between 200 and 600 nm The U-V spectra analysis of the gAuNPs
and cAuNPs was done and the maxima peak was observed at a
wavelength of 500 nm and 500 nm respectively.
3.2. Scanning electron microscopy (SEM)
4. Conclusion
The PANI/ Pin5COOH and nanoparticles (AuNPs/c-MWCNT) in
the construction of working electrode were used. The PANI
modified electrode showed better electrochemical signal than
the Pin5COOH modified Au electrode under same experimental
conditions. Results were confirmed through CV and EIS techniques.
Polyailine in combination with nanoparticle can prove to be
amplified sensing interface for fabrication of working electrodes.
Surface morphologies of MWCNT/PANI/Au and Pin5COOH/
MWCNT/Au electrodes were also investigated by SEM (Fig. 3). The
morphologies of MWCNT/PANI/Au and Pin5COOH/MWCNT/Au
were characterized by SEM studies. SEM of MWCNT/PANI/Au
depicts fine fiber-like structures which show the presence of PANI
on the Au electrode surfaces (Fig. 3A). However SEM of MWCNT/
Pin5COOH/Au depicts tubular network structures which show the
presence of Pin5COOH on the Au electrode surfaces. (Fig. 3B).
Acknowledgements
3.3. Comparisons of amplification signal through cyclic voltammetry
(CV) and electrochemical impedance studies (EIS)
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The cyclic voltammetry (CV) responses for different electrodes
in 50 mM pH 7.0 phosphate buffer solution containing 0.1 mM
H2O2 at a scan rate of 50 mV s 1 were recorded. Firstly, CV pattern
was taken by modifying gold electrode with gAuNPs and cAuNP.
The CV curve shows that at same experimental conditions cAuNPs/
Au electrode (0.160 mA) shows better amplifications signal as
compared to gAuNP/AuE (0.137 mA). In comparison, cAuNPs/AuE
and gAuNP/AuE exhibited a bigger peak-to-peak separation,
indicating high electron transfer in case of cAuNPs/AuE (Fig. 4A).
However, the electrodes coated cAuNPs/MWCNT/PANI/Au and
cAuNPs/MWCNT/Pin5COOH/Au electrodes were also investigated
through CV. CV curve reveals that cAuNPs/MWCNT/PANI/Au
(0.200 mA) shows better sensing signal in the form of current as
compared to Pin5COOH (0.100 mA) modified gold electrode under
same experimental conditions. This was due to the fact that
cAuNPs/MWCNT/PANI/Au have better conductivity than the
Pin5COOH modified gold electrode, and ease the electron transfer
(Fig. 4B). Fig. 4C shows electrochemical impedance spectra (EIS) of
cAuNPs/MWCNT/PANI/Au and cAuNPs/Pin5COOH/MWCNT/Au
electrodes. The Rct values for the cAuNPs/MWCNT/PANI/Au and
cAuNPs/Pin5COOH/MWCNT/Au electrode were obtained as
600 and 1500 V, respectively. Rct value of cAuNPs/MWCNT/
PANI/Au electrode was low as compared to cAuNPs/Pin5COOH/
MWCNT/Au. This means charge transfer resistance is low which
means electron transfer kinetics is more in case of PANI modified
electrode. Our results show that the cAuNPs/MWCNT/PANI/AuE
demonstrated a greater synergistic effect toward the oxidation of
H2O2 compared with the cAuNPs/Pin5COOH/MWCNT/AuE.
The present work was supported by SERB, Department of
Science and Technology (DST), India. Thanks to all scientists
referenced throughout the paper whose valuable work has guided
the way through to this research work.
References