consisting of two interdigitated Ag electrodes [173] to determine human serum albumin (HSA). During the sensing action, a sandwich type complex consisting of
the analyte, the immobilized antibody and the conjugate is formed at the electrode
surface, generating a conductimetric signal. Electrochemical immunoassay of immunoglobulin G (IgG) has also been demonstrated using colloidal gold label [174].
This method involves an interaction of IgG with an immobilized antibody and a
gold labeled antibody to form a sandwich type complex. The ASV of gold metal
leads to a low detection limit of pM concentration. The electrochemical detection of
DNA for the quantification of the human cytomegalovirus DNA sequence has been
reported by Limoges and co-workers [178]. The assay is carried out in microwells
where the single stranded (ss) target DNA is immobilized then undergoes hybridization with the corresponding oligonucleotide-modified Au particle. Gold is then
electrochemically quantified using the ASV. Similar studies for the detection of
DNA segments related to the breast cancer BRCA1 gene have also been reported
[179]. Recently, Wang reported on a novel detection method for DNA based on a
combination of magnetic separation and the already known concept of gold stripping analysis [180]. Very low detection limits of femtomoles (fM) have been
achieved by this method.
Cai and co-workers used colloidal gold attached to a macroelectrode to increase
the concentration of ss-DNA and consequently improving the sensitivity of DNA
detection [181]. Hybridization of the DNA strand attached to the gold particles
with a ferrocenecarboxaldehyde-labeled complementary strand from the bulk of
the solution leads to a detection limit of the order of 10
À10 mol, as observed by
DPV studies. The same authors demonstrated an electrochemical method for sitespecific DNA analysis, based on the stripping of silver formed on gold nanoparticles [182]. This method involves the electrochemical stripping of catalytically
formed Ag nanoparticles on Au to quantify the analyte. Even a single base pair
mismatch is possible to detect by this method (Figure 20.14). Ye and co-workers
[183] have recently reported the preparation of supported bilayer lipid membrane
(BLM)–metal nanoparticle composites for designing biosensors. The deposition
of Pt nanoparticles through non-conducting BLM is reported to be active for the
electrocatalyzed reduction of oxygen. The nanoparticle array is a novel way of
preparing electrodes similar to the NEEs reported by Martin and co-workers [5].
Direct electron transfer between hemoglobin and GCE has been demonstrated using synthetic lipid (didodecyldimethylammonium bromide, DDAB)-protected gold
nanoparticles of size around 6 nm [184].
20.6.2
Chemical Sensors
The use of nanoparticle arrays to generate surface-confined architectures has been
extensively studied by Willner and co-workers [6]. The structural motif involves
the sequential electrostatic assembly of nanoparticles and the desired molecules
on planar electrodes. An ITO substrate is functionalized using an aminosilane
molecule to yield a charged surface. Negatively charged citrate-stabilized gold
20 Electrochemistry with Nanoparticles
674
the analyte, the immobilized antibody and the conjugate is formed at the electrode
surface, generating a conductimetric signal. Electrochemical immunoassay of immunoglobulin G (IgG) has also been demonstrated using colloidal gold label [174].
This method involves an interaction of IgG with an immobilized antibody and a
gold labeled antibody to form a sandwich type complex. The ASV of gold metal
leads to a low detection limit of pM concentration. The electrochemical detection of
DNA for the quantification of the human cytomegalovirus DNA sequence has been
reported by Limoges and co-workers [178]. The assay is carried out in microwells
where the single stranded (ss) target DNA is immobilized then undergoes hybridization with the corresponding oligonucleotide-modified Au particle. Gold is then
electrochemically quantified using the ASV. Similar studies for the detection of
DNA segments related to the breast cancer BRCA1 gene have also been reported
[179]. Recently, Wang reported on a novel detection method for DNA based on a
combination of magnetic separation and the already known concept of gold stripping analysis [180]. Very low detection limits of femtomoles (fM) have been
achieved by this method.
Cai and co-workers used colloidal gold attached to a macroelectrode to increase
the concentration of ss-DNA and consequently improving the sensitivity of DNA
detection [181]. Hybridization of the DNA strand attached to the gold particles
with a ferrocenecarboxaldehyde-labeled complementary strand from the bulk of
the solution leads to a detection limit of the order of 10
À10 mol, as observed by
DPV studies. The same authors demonstrated an electrochemical method for sitespecific DNA analysis, based on the stripping of silver formed on gold nanoparticles [182]. This method involves the electrochemical stripping of catalytically
formed Ag nanoparticles on Au to quantify the analyte. Even a single base pair
mismatch is possible to detect by this method (Figure 20.14). Ye and co-workers
[183] have recently reported the preparation of supported bilayer lipid membrane
(BLM)–metal nanoparticle composites for designing biosensors. The deposition
of Pt nanoparticles through non-conducting BLM is reported to be active for the
electrocatalyzed reduction of oxygen. The nanoparticle array is a novel way of
preparing electrodes similar to the NEEs reported by Martin and co-workers [5].
Direct electron transfer between hemoglobin and GCE has been demonstrated using synthetic lipid (didodecyldimethylammonium bromide, DDAB)-protected gold
nanoparticles of size around 6 nm [184].
20.6.2
Chemical Sensors
The use of nanoparticle arrays to generate surface-confined architectures has been
extensively studied by Willner and co-workers [6]. The structural motif involves
the sequential electrostatic assembly of nanoparticles and the desired molecules
on planar electrodes. An ITO substrate is functionalized using an aminosilane
molecule to yield a charged surface. Negatively charged citrate-stabilized gold
20 Electrochemistry with Nanoparticles
674