INTRODUCTION
Dendrimers are hyperbranched globular
macromolecules with well-defined, mono-
disperse, three dimensional spatial
conformations, and a wide spectrum of
chemical and physical properties (Tomalia et
al., 1985). These characteristics indicate
significant differences from the classical
polymeric molecules. Structurally, these
macromolecules are divided into three
architectural regions: the central core,
repetitive and radial branching units and the
terminal functional groups. To achieve a high
degree of precision and structural order,
dendrimers are synthesized in a stepwise
fashion. The number of repeat branching
molecules used during the synthesis refers to
the generation of dendrimers, which also
governs the shape and size of the dendrimers.
Generally, two different methods namely,
divergent and convergent, are adopted for the
Key words: Dendrimers, Biosensors, Polyamidoamine, Polypropylene imine, Bioreceptors, DNA sensor. *Corresponding Author: Dhirendra Bahadur, Department of Metallurgical Engineering and Material Science, Indian Institute of Technology Bombay, Powai, Mumbai, India. Email: [email protected]
Dendrimers based Electrochemical Biosensors
Electrochemical biosensors are portable devices that permit rapid detection and monitoring of biological,
chemical and toxic substances. In the electrochemical biosensors, the bioreceptor is incorporated into the
transducer surface; and when in contact with the analyte, generates measurable signals proportional to the
analyte concentration. Materials with high surface area, high reactivity, and easy dispersability, are most
suited for use in biosensors. Dendrimers are nanomaterial gaining importance for fabrication of
electrochemical biosensors. These are synthetic macromolecules with regularly branched tree-like and
globular structure. The potential applications of dendrimers as biosensors are explored due to their
geometric symmetrical structure, chemical stability, controlled shape and size, and varied surface
functionalities, with adequate functional groups for chemical fixation. The current review provides multi-
faceted use of dendrimers for developing effective, rapid, and versatile electrochemical sensors for
biomolecules. The redox centers in the dendrimers play an important role in the electron transfer process
during immobilization of biomolecules on the electrodes. This has led to an intensive use of dendrimer
based materials for fabrication of electrochemical sensors with improved analytical parameters. The review
emphasizes development of new methods and applications of electrochemical biosensors based on novel
nanomaterials.
1 2 1Saumya Nigam , Sudeshna Chandra , Dhirendra Bahadur *
1Department of Metallurgical Engineering and Material Science, Indian Institute of Technology Bombay, Powai,
Mumbai, India2Department of Chemical Sciences, School of Science, NMIMS (Deemed-to-be) University, Vile Parle (W), Mumbai,
India
Biomed Res J 2015;2(1):21-36
Review
synthesis of dendrimers, and classified into
different “generations”. It is the hyper-
branching of the molecule from the centre of
the dendrimer towards the periphery that
results in homostructural layers between the
focal points (branching points). The number of
focal points from the core towards the outer
surface is the generation number. Thus,
generation refers to the number of repeated
branching cycles performed during the
synthesis. The core part of the dendrimer is
denoted generation “zero” (G0). For example
if a dendrimer is made by convergent
synthesis, and the branching reactions are
performed onto the core molecule three times,
the resulting dendrimer is considered a third
generation dendrimer. Each successive
generation results in a dendrimer roughly
twice the molecular weight of the previous
generation.
The two synthetic methods have inherent
advantages and disadvantages. Using the
divergent synthesis method, the dendritic
molecule is formed from a central core which
then extends radially outwards through
addition of branching molecules. The main
advantage of the divergent method is that high
molecular nanoscaffold architecture is
attained with desired repetitive branching
monomers. Thus, the dendrimer can be tailor
made to achieve maximum functionalities and
properties. However, two major challenges are
encountered in divergent synthesis. First, the
number of reaction points increase in
geometric progression with every generation
followed by increase in molecular weight.
This compromises the reaction kinetics,
making it slower and synthesis of high
generation dendrimers becomes difficult,
further lowering the yield of desired product.
Addition of each branching unit requires care
and precision to prevent structural defects and
asymmetry in the dendrimer structure.
Secondly, the separation of desired dendrimer
from the by-products is hindered due to
molecular similarity exhibited by the by-
product as well as the desired dendrimer. On
the other hand, convergent method employs
synthesis of small dendrites from the exterior
and the reaction proceeds inwards to the
central core. The convergent procedure results
in lesser structural defects and easy
purification of dendrimers resulting in high
degree of monodispersity. Despite the
possibility of purer and flawless dendrimers,
the convergent method falls short in synthesis
of higher generation dendrimers. This choice
is limited due to the steric forces crowding the
dendrites around the central core molecule.
Despite the difficulties, these macro-
molecules have gained interest over classical
polymers due to the varied options presented
by dendritic macromolecules. The freedom of
choice of central core, branching monomeric
units and surface functional groups from the
vast pool of molecules gives rise to a
multivalent system. Ethylenediamine, 1,4-
diaminobutane, 1,12-diaminododecane,
Biomed Res J 2015;2(1):21-36
22 Dendrimers based electrochemical biosensors
cystamine, 1,6-diaminohexane and ammonia
are the most common core molecules. The
varied core and branching monomers affect
the internal chemical environment, three
dimensional structures and size of internal
cavities in the dendrimer. Due to the different
structural and chemical properties, these user-
customized dendrimers find applications in
the fields of drug delivery, gene delivery,
antimicrobials, magnetic resonance imaging,
immunosensing and biosensing.
Methyl acrylate alternating with ethylene
diamine forms the most widely synthesized,
studied and used class of polyamidoamine
(PAMAM) dendrimers (Esfand et al., 2002),
with the internal amide groups providing an
abundance of lone pairs of electrons. Another
popular class of amine terminated dendrimers
is the poly (propylene imine) (PPI)
synthesized by Michael's addition of primary
amines to acrylonitrile followed by
subsequent hydrogenation by Raney cobalt or
Raney nickel catalyst (de Brabander-van den
Berg et al., 2003). The interiors of PPI
dendrimers are the tertiary nitrogen atoms with
lone pairs of electron contributing to their
reactive cavities. Both the classes of
dendrimers have primary amine groups on the
surfaces governing the surface properties,
reactivity and surface charge. Thus, any kind
of detection response observed in these
dendrimers is attributed to the amine groups.
The surface of dendrimers is further modified
to enhance the reactivity/interaction and
Biomed Res J 2015;2(1):21-36
sensor response to be used in biosensing
applications. Various molecules like
ferrocene, polystyrene, polyaniline,
carbohydrates, etc. have been explored for
surface modification (Ashton et al., 1997;
Chen et al., 2014; Hung et al., 2013; Yoon et
al., 2000). The conductivity of the moieties
plays an important role in enhancing response
of the dendritic scaffold in sensing various
biomolecules. The most common modifying
molecule is ferrocene which exhibits multi-
electron transfer in various redox interactions.
Ferrocene has been exploited as central core,
branching monomer as well as for surface
groups in various dendritic systems (Mehmet
et al., 2013; Villalonga-Barber et al., 2013).
They behave as non-interacting redox
moieties undergoing redox processes without
decomposition while maintaining the desired
electrochemical reversibility (Sun et al.,
2014).
The molecular recognition of
biomolecules by dendrimers is primarily
governed by the three dimensional
conformation in higher generations. The
branches of lower generation dendrimers tend
to radiate out towards the periphery and exist
in open conformation. On the other hand, as
the number of generation is increased, the
branches tend to retract and adopt globular
conformations in a three dimensional space
with intramolecular hydrogen bonding
governing the structures. The generation
dependent conformational changes confirmed
Nigam et al. 23
by X-ray analysis, demonstrated that the
higher generations are more spherical as
compared to lower linear generations (Percec
et al., 1998). The globular conformations
closely resemble morphology of globular
proteins and are useful in several biosensing
applications associated with the biomimetic
macromolecular architecture. A vast variety of
biomolecular species have been detected using
dendrimer scaffolds. In the following sections,
details of the various sensors using different
types of dendrimers are discussed.
Dendrimers in electrochemical biosensing
By definition, a biosensor is an analytical
device that makes use of bioreceptor molecule
immobilized onto a transducer (recognition)
surface and produces measurable signals in the
presence of an analyte, due to the bio-
recognition event proportional to the
concentration of the analyte. Biosensors are
classified based on either the bioreceptor or
transduction method or both. Common
bioreceptors include enzymes, antibodies and
DNA, while transducers include electro-
chemical, piezoelectrical, optical techniques.
The transducer techniques using electro-
chemical biosensors have an edge over other
methods due to excellent selectivity and
sensitivity, and precise detection of the desired
species. These are relatively cheaper, faster
and more user friendly as compared to other
techniques. The exceptional features render
the electrochemical biosensors increasingly
applicable in several biomedical and
environmental analyses.
a) Peroxide sensor: Copolymers of pyrrole-
PAMAM dendrimer are used for
electrochemical sensing of hydrogen
peroxide. Different generations of
pyrrole-PAMAM with branched amine
periphery and focal pyrrole functionality
are synthesized by divergent method. The
conjugate is covalently attached to the
electrode surface and horseradish
peroxidase (HRP) immobilized on it to
form conducting films for H O sensing. 2 2
The steady state amperometric response is
measured as a function of H O 2 2
concentration at +0.35V vs. Ag/AgCl, and
demonstrated that the dendritic wedge
played an important role for
immobilization of the HRP enzyme
(Mehmet et al., 2012). Yang et al. (2014)
described a magnetic electrochemical
sensor comprising Fe O nanoparticles 3 4
with graphene oxide (GO) and subsequent
modification by PAMAM dendrimers.
The platform was employed for
modification of the gold electrode acting
as the working electrode and used for the
detection of H O in phosphate buffer 2 2
solution by the method of amperometric
i-t curve. The cyclic voltammograms of
Fe O /GO and Fe O /GO–PAMAM 3 4 3 4
showed an increase in current while
displaying steady redox peaks which
confirmed occurrence of a catalytic
Biomed Res J 2015;2(1):21-36
24 Dendrimers based electrochemical biosensors
reaction on the electrode interface. H O 2 2
was detected in a linear calibration range –5 –3of 2.0 × 10 –1.0 × 10 M with a
correlation coefficient of 0.9950 and -6detection limit of 2.0 × 10 M. The sensor
platform also displayed excellent recovery
ratios of 96.9–108.1% H O added to milk 2 2
and juice samples. Another amperometric
electro-chemical biosensor for H O was 2 2
developed by modifying gold bead
electrodes with starburst PAMAM
dendrimers of different generations of 2, 3
and 4, followed by absorption of Prussian
blue (PB). The covalently bonded
dendrimer/PB modified electrodes offered
enhanced sensitivity and lower detection
limits (Bustos et al., 2006). Metallic
(Rhodium) nanoparticles stabilized with
N, N-bis-succinamide-based dendrimer
were immobilized on glassy carbon
electrode (GCE) and electrocatalytic
activity towards hydrogen peroxide
reduction investigated using cyclic
voltammetry and chronoamperometry.
The dendrimer stabilized nanoparticles
showed excellent electrocatalytic activity
for H O reduction reactions and a steady-2 2
state cathodic current response was
observed at −0.3 V (vs. SCE) in phosphate
buffer (pH 7.0). The electrochemical
sensor displayed a linear response to H O 2 2
concentrations ranging from 8 to 30 μM
with a detection limit and sensitivity of 5 −6 −1
μM and 0.031 × 10 A μM , respectively
Biomed Res J 2015;2(1):21-36
(Chandra et al., 2009).
b) Glucose Sensor: A dendritic wedge based
on pyrrole-PAMAM dendrimer was used
to immobilize glucose oxidase (GOx) for
the construction of an amperometric
glucose sensor (Mehmet and Cevdet,
2012). Nanobiocomposite based glucose
biosensor was prepared by electro-
polymerization of pyrrole containing
PAMAM encapsulated Pt nanoparticles
(Pt-PAMAM), and GOx. The developed –1sensor had a sensitivity of 164 µA mM
–1cm and a detection limit of 10 nM within
a wide working range from 0.2−600 µM.
Pyrrole provided electrical conductivity,
stability and homogeneity to the thin film,
while PAMAM provided a favorable
microenvironment to maintain bioactivity
of GOx (Tang et al., 2007). Yoon and
colleagues used varying degrees of redox-
active ferrocenyl in combination with
PAMAM dendrimers (Fc-D) as
recognition unit for fabrication of a
glucose sensor (Yoon et al., 2000). GOx
was deposited layer-by-layer on Au-
surface to form an enzymatically active
GOx/Fc-D multilayered assembly. The
bio-electrocatalytic signals from the
multilayer were directly correlated to the
number of layers deposited, confirming
the tunable sensitivity of the electrode and
hence a potential microbiosensor. Cyclic
voltammetry and surface plasmon
resonance (SPR) was used to investigate
Nigam et al. 25
the redox-orientation changes of
ferrocene-tethered dendrimers and GOx.
SPR monitors change in the refractive
index of the medium next to the Au
sensing surface and are used to monitor
immobilization of GOx onto the Au
surface (Frasconi et al., 2009). Redox-
active dendrimer fabricated using
different generations of poly (propylene
imine) core with peripheral octamethyl
ferrocenyl units (Fig. 1) and deposited on
Pt electrodes for immobilizing GOx has
been used for detection of glucose
(Armada et al., 2006). The amperometric
response of all the dendritic mediators
towards glucose was determined at several
applied potentials. Glucose biosensor has
been developed based on bioactive
polyglycerol (PGLD) and chitosan
dendrimer (CHD). Both the dendrimers
were conjugated with GOx to form
PGLD-GOx and CHD-GOx and
entrapped in polyaniline nanotubes
(PANINT's) during template electro-
chemical polymerization of aniline. The
prepared PGLD-GOx/PANINT's and
CHD-GOx/PANINT's biosensors
exhibited strong amperometric response
to glucose concentrations in ranges
observed in human blood. PGLD-
GOx/PANINT's was more sensitive –1(10.41 nA.mM ) as compared to CHD-
–1GOx/PANINT's (7.04 nA.mM ), due to
specific organization of the GOx layer at
the surface of PGLD and distribution of
PANINT's (Santos et al., 2010).
Ferrocenyl dendrimer (PAMAM-Fc)
has also used for fabricating an
amperometric glucose biosensor. Series of
asymmetric PAMAM dendrimers
containing a single ferrocene unit located
in the focal point have been synthesized.
The transducer consisted of a gold
electrode covalently modified with 3-
mercaptopropionic acid, PAMAM-Fc
dendrimers and GOx enzyme. The
PAMAM-Fc/GOx biosensor showed
excellent performance for recognizing
glucose at +0.25 V with a high sensitivity
(6.54 μA/mM) and low response time
(~3s) in the concentration range of 1–22
mM (Mehmet et al., 2013).
Figure 1: Structures of varying generations of octamethyl
ferrocenyl dendrimers for use as electrode material for
determination of glucose (Armada et al., 2006).
Biomed Res J 2015;2(1):21-36
26 Dendrimers based electrochemical biosensors
c) DNA Sensor: Dendrimers were also
exploited for their possible use in
fabricating DNA sensors. An electro-
chemical DNA nanobiosensor was
developed by immobilization of 20-mer
thiolated probe ssDNA on electro-
deposited poly (propyleneimine)
dendrimer (PPI) of generation 4 (G4),
doped with gold nanoparticles (AuNP)
(Arotiba et al., 2008). Cyclic voltammetry
showed that the designed platform
(GCE/PPI-AuNP) exhibited reversible
electrochemical behavior in pH 7.2
phosphate buffer saline (PBS) solution
due to PPI. The redox chemistry of PPI
involves a two electron and one proton
process and is pH-dependent. PPI-AuNP
was able to amperometrically detect target
DNA concentrations at 0.05 nM in PBS.
Using electrochemical impedance
spectroscopy (EIS), the biosensor –12 –9exhibited a dynamic linearity of 10 –10
M for target DNA. The probe immobiliza-
tion effectiveness is apparently attributed
to the AuNP's ability to connect to the
thiolatedssDNA on the GCE surface via
Au-S linkages. Further, the electrostatic
interaction between the cationic platform
and the anionic DNA probe improved the
immobilization process. Proposed charge
transfer scheme between the electrolyte,
DNA and PPI-AuNP is shown in Fig. 2.
A DNA biosensor with probe DNA
sequence, immobilized on a multinuclear
Biomed Res J 2015;2(1):21-36
nickel (II) salicylaldimine metallo-
dendrimer on GCE has been reported
(Arotiba et al., 2007). The authors studied
electrochemical characterization on
immobilization layer of the PPI derivative
by impedimetric and amperometric
methods. The metallo-dendrimer was
electroactive with two reversible redox
centers and was a strong DNA adsorbant.
The sensor responded to 10 µL of 5 nM
target DNA with detection limit as low as –12 3.4 × 10 M. Gold electrode has been
modified with 3-mercaptopropionic acid
and reacted with amino-terminated
PAMAM G-4 dendrimer to obtain a thin
film (Li et al., 2009). Recognition layer of
single-stranded 3´-biotin-avidin combina-
tion was immobilized onto the thin film to
detect the complimentary target. Cyclic
voltammetry (CV), differential pulse
voltammetry (DPV) and electrochemical
impedance spectroscopy (EIS) has been
used to study immobilization and
hybridization of DNA. The dynamic
detection range of the sequence-specific –11 –14DNA was 1.4 × 10 –2.7×10 M with a
–14detection limit of 1.4 × 10 M. Sahoo et
al. (2013), demonstrated a label free
Figure 2: Proposed charge transfer scheme between
PBS, DNA and PPI-AuNP (Arotiba et al., 2008).
Nigam et al. 27
impedimetric DNA biosensor based on
third generation G3 PAMAM dendrimer
functionalized GaN nanowires (NWs).
The developed nanosystem provided large
docking sites to immobilize probe (p-)
DNA covalently. The biosensor was
ultrasensitive and showed detection limit
as low as attomolar (aM) concentration of
complementary target (t-) DNA.
Impedance spectroscopy revealed an
increase in the resistance polarization (R ) p
indicating efficient charge transfer due to
strong covalent binding on NWs surface.
Zhu et al. (2006) modified gold electrodes
with sub-monolayers of mercaptoacetic
acid (RSH) and reacted with G-4 PAMAM
dendrimers to obtain thin films of
PAMAM/RSH. DNA probe was then
immobilized onto the thin films to afford
stable recognition layers. DPV was used to
monitor DNA hybridization with
daunomycin (DNR) as indicator. The
PAMAM-modified Au electrodes without
ssDNA showed good electrochemical
response in DNR solution, while on
attachment with ssDNA the modified
electrode showed a decrease in the DPV
response of DNR. This is attributed to less
accessibility of DNR molecules to ssDNA
probe on the electrode surface. Besides
high generation dendrimers, low
generation dendrimers are also used to
develop DNA biosensor. A second
generation PAMAM (G2-PAMAM)
dendrimer was covalently functionalized
onto multi-walled carbon nanotube
(MWNT) and used as electronic
transducer and tether for surface
confinement of probe DNA. Impedance
spectroscopy revealed occurrence of
hybridization between surface confined
ssDNA probe with target DNA in solution
to form double stranded DNA (dsDNA).
The interfacial charge-transfer resistance
of the electrode towards the redox
electrolyte changed due to occurrence of
hybridization. The large number of amino
groups of the dendrimer enhanced the
surface binding of the probe DNA which
in turn resulted in increase in the
sensitivity of the impedimetric biosensor
for the target DNA. The interfacial charge-
transfer resistance responded linearly to
the logarithmic concentration of the target
DNA within a concentration range of
0.5–500 pM with a detection limit of 0.1
pM (S/N = 3) (Zhu et al., 2010). Single-
use electrochemical DNA biosensor has
been fabricated based on pencil graphite
electrode modified with succinamic acid
and G2 PAMAM dendrimer (G2-
PS/GCE). Calf thymus double stranded
DNA (ctDNA) and DNA oligonucleotide
(DNA ODN) immobilized on surface of
G2-PS/GCE under optimum conditions,
showed a detection limit of 4.2 µg/mL
(Congur et al., 2014). Besides dendrimers,
dendritic nanostructures have been used
Biomed Res J 2015;2(1):21-36
28 Dendrimers based electrochemical biosensors
dendrimer. Thrombin aptamer probe was
immobilized onto activated dendrimer
monolayer film and detection of thrombin
was investigated in the presence of the 3−/4−reversible [Fe(CN) ] redox couple 6
using impedance technique. The results
showed that the charge-transfer resistance
(R ) value had a linear relationship within ct
concentrations range of 1–50 nM
thrombin, and detection limit (S/N = 3) of
0.01 nM (Zhang et al., 2009).
Impedimetric aptasensor based on
succinamic acid-terminated PAMAM
dendrimer was developed for monitoring
interaction between DNA aptamer (DNA-
APT) and its cognate protein, human
as electrode material in biosensing
applications. Li et al. (2011) described
dendrimer-gold (Den-Au) nanostructure
modified electrode by directly placing the
electrode into 2.8 mM HAuCl and 0.1 M 4
H SO solution at –1.5 V. Scanning 2 4
electron microscopic images show growth
evolution of Den-Au at different time
period (Fig. 3). The Den-Au modified
electrode respond to 1 fM complimentary
target DNA within a wide detection range.
Aptamers, as single-stranded DNA or
RNA sequences that bind to specific target
molecules was determined by a label-free
highly sensitive impedimetric aptasensor
based on amino-terminated PAMAM
Figure 3: SEM images of Den-Au electrodes by electrodeposition in 2.8 mM HAuCl and 0.1 M H SO at different time 4 2 4
points (A) 20s, (B) 100s, (C) 300s and (D) 600s (Li et al. 2011).
Biomed Res J 2015;2(1):21-36
Nigam et al. 29
activated protein C (APC), a key enzyme
in the protein C pathway. The dendrimer
modified aptasensor showed detection
limits of 1.81 µg/mL in buffer solution and
0.02 µg/mL in diluted FBS (Erdem et al.,
2014).
d) Coenzyme Sensor: Hyperbranched
carbosilane polymers, polydiallyl methyl
silane (PDAMS) and polymethyl
diundecenyl silane (PMDUS) with
ferrocene moieties were used for
stabilization of Pt nanoparticles and as
electrode material for NADH oxidation.
The modified electrodes worked in wide
linear concentration ranges for NADH
with a detection limit of 4.78 µM for
PDAMS/PtNPs/Pt and 6.18 µM for
PMDUS/PtNPs/Pt. With regard to the
structure of the two carbosilane polymers
and their films, PDAMS with shorter
branches form rougher films and exhibit
higher rate constants (K ) and sensitivity obs
and smaller Michaelis constants (K' ), M
than PMDUS indicating better
electrocatalytic activity towards NADH
oxidation (Jiménez et al., 2014).
e) Other biomolecules: Tang et al. (2007)
reported enzyme based amperometric
biosensor for determination of glutamate.
A self-assembly of glutamate dehydro-
genase (GLDH) and PAMAM dendrimer
encapsulated Pt nanoparticles on carbon
nanotubes (GLDH/Pt-PAMAM) /CNT) n
were used as electroactive material (Fig.
4). The electrochemical activity was
reported to be attractive with large
determination range of glutamate (2–250
µM), short response time (< 3 s), high –1 2sensitivity (433 µA/mM cm ) and
stability.
Figure 4: Schematic showing the procedure of immobilizing Pt-PAMAM onto CNTs (a) layer-by-layer self-assembly of
GLDH and Pt-PAMAM onto CNTs (b) Pt-PAMAM/CNTs heterostructures were covalently attached via EDC (Tang et al.
2007).
Biomed Res J 2015;2(1):21-36
30 Dendrimers based electrochemical biosensors
Pt-PAMAM and GLDH were
alternately deposited until suitable layers
were obtained. PAMAM G-4 dendrimers
crosslinked with reduced graphene oxide
were tested for performance as electro-
chemical biosensors by immobilizing
enzyme tyrosinase (Araque et al., 2013).
The bioelectrode showed excellent
electrocatalytic behavior towards
determination of catechol with a response
time of about 6s, linear range of 10 nM to –122 µM, sensitivity of 424 mAM and a
low detection limit of 6 nM (Fig. 5).
PAMAM dendrimer encapsulated
AuNPs were first immobilized to a
conducting polymer with two amine
groups (3',4'-diamine-2,2',5',2''-terthio-
phene (PDATT) through covalent bonding
between –COOH group of PAMAM and
–NH group of PDATT. Laccase was 2
subsequently covalently bonded to the
–COOH of PAMAM dendrimers to form
PDATT/Den (AuNPs)/laccase probe
(Rahman et al., 2008). The modified
electrode displayed direct electron-
transfer (DET) process of laccase and a
catechin biosensor was fabricated based
on the electrocatalytic process of laccase.
The linear range and detection limit for
catechin sensing was 0.1–10 and 0.05 µM,
respectively. An electrochemical
biosensor based on PAMAM dendrimers
was developed for the detection of
fructose in food samples by immobilizing
fructose dehydrogenase (FDH) on
cysteamine and PAMAM dendrimers. The
concentration range of the enzymatic
biosensor was 0.25–5.0 mM fructose
(Damar et al., 2011). PAMAM dendrimers
were also used to enhance signal response
of a nanobiocomposite fabricated to
obtain an immunosensor for alpha-feto
protein (AFP) in human serum (Giannetto
et al., 2011). The binding of the dendrimer
with biologically active molecules like
antibodies can improve the activity and
Figure 5: (A) Amperometric response obtained with Tyr/PAMAM-Sil-rGO/GCE for different catechol concentrations at
E = –150 mV (B) FE-SEM image of Tyr/PAMAM-Sil-rGO (Araqueet al., 2013).app
Biomed Res J 2015;2(1):21-36
Nigam et al. 31
Biomed Res J 2015;2(1):21-36
sensitivity of the system. Response range
and precision were evaluated using cyclic
voltammetry (CV) and double step
chronoamperometry (DSCA) with limit of
detection of 3 ng/mL and limit of
quantification of 15 ng/mL. The enhanced
immunosensor could be useful for
monitoring prognosis of pregnancy and
occurrence of neoplastic diseases.
Recently, a redox-active silver-PAMAM
dendrimer nanostructure was synthesized
in situ by using wet chemistry (Xiaomei et
al., 2013), and functionalized with mono-
clonal mouse anti-human antibody for free
prostate specific antigen (fPSA). Using,
graphite as the working electrode, a layer
of gold nanoparticles modified with
prostate-specific antibody (mAb2). In
presence of the fPSA, specific immuno-
complex was formed on the functionalized
antibody modified electrode. The Ag-
mediated PAMAM dendrimer directly
catalyzed reduction of H O in the 2 2
detection solution. Thus, PSA was
detected primarily due to the antigen-
antibody immunocoupling. Under optimal
conditions, the developed immunoassay
could determine target fPSA in the
dynamic range of 0.005–5.0 ng/mL with a
detection limit (LOD) of 1.0 pg/mL (S/N =
3). In addition, the accuracy of the
electrochemical immunoassay evaluated
for detection of clinical serum specimens,
was in accordance with referenced
enzyme-linked immunosorbent assay
(ELISA) method.
A multi-analyte sensing device based
on PAMAM dendrimer for simultaneous
at-line monitoring of glucose, ethanol,
pO - and cell density was fabricated (Akin 2
et al., 2011). The device consisted of a
dual biosensor, a modified microscope
and a fiber optical pO -sensor integrated 2
into a flow analysis (FA) system. The
electrochemical transducer consisted of
self-assembly of cysteamine on gold
surface. Alcohol oxidase and pyranose
oxidase were immobilized onto the gold
surface by means of PAMAM (poly-
amidoamine) dendrimer via glutar-
aldehyde cross-linking. The responses for
glucose and ethanol were linear up to 0.5
mM. The biosensor was used for
simultaneous determination of ethanol
and glucose in yeast fermentation process.
A highly stable and sensitive ampero-
metric biosensor was developed by
immobilizing alcohol oxidase (AOX)
through PAMAM dendrimers on a
cysteamine-modified gold electrode
surface for determination of ethanol (Akin
et al., 2009). The optimized ethanol
biosensor showed a linearity from
0.025–1.0 mM with 100 s response time
and detection limit (LOD) of 0.016 mM.
The analytical characteristics of the
system were also evaluated for alcohol
determination in flow injection analysis
32 Dendrimers based electrochemical biosensors
(FIA) mode for analysis of ethanol in
various alcoholic beverage as well as
offline monitoring of alcohol production
through yeast cultivation (Yuksel et al.,
2012).
PAMAM dendrimer (generation G4)
stabilized with 1-hexadecanethiol was
used for immobilization of acetylcholin
esterase from electric eel, and choline
oxidase from Alcaligenes sp. was used as
electrode material for fabrication of an
amperometric sensor for pesticides
(Snejdarkova et al., 2004). On similar
lines, urea electrochemical biosensor was
developed based on an electro-co-
deposited zirconia-PPI dendrimer
modified screen printed carbon electrode.
Urease enzyme was immobilized onto
electrodes and an amperometric response
in urea concentration from 0.01 mM to
2.99 mM was obtained with sensitivity of –1 –23.89 µA mM cm (Shukla et al., 2014).
PPI dendrimers have also been used to
reduce HAuCl to form core-shell PPI-Au 4
nanoclusters with several PPI molecules
attached on the surface of one gold
nanoparticles (Zhang et al., 2007). PPI-Au
nanoclusters and myoglobin (Mb) were
alternately adsorbed on the surface of
pyrolytic graphite (PG) electrodes
forming {PPI-Au/Mb} layer-by-layer n
films. The multilayer film assembled with
the dendrimer stabilized Au nanoparticles,
provided a new approach to fabricate
biosensors and bioreactors based on direct
electrochemistry of proteins and enzymes.
CONCLUSIONS
Contemporary studies indicate that the most
elementary chemical reaction of electron
transfer is widely prevalent in several
biological systems and more importantly in
nanosystems with redox dendrimers. This is
possible by tailoring the nature and topology
of the dendrimers to precisely control location
of the redox sites within the macromolecule
and study its electron-transfer processes. The
increase in efforts to combine dendrimers with
other molecules like pyrrole, ferrocene,
enzymes, etc. is promising in biosensing
applications.
ACKNOWLEDGEMENTS
The authors acknowledge Department of
Science and Technology, Government of
India, New Delhi, for providing financial
support. The authors also acknowledge the
publishers for providing copyright
permissions for the figures.
CONFLICT OF INTEREST
The authors claim no conflict of interest.
Biomed Res J 2015;2(1):21-36
Nigam et al. 33
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