Biomedical Engineering Reference
In-Depth Information
In a more recent work, AuNPs were simultaneously employed as the
immobilization platform and the signal amplii er. Initially, 4-aminothio-
phenol was self-assembled on electrodeposited AuNPs-modii ed electrode
to anchor capture ssDNA sequences and secondary AuNPs labeled with
reporter ssDNA sequences were employed for signaling [145].
4.5
Quantum Dots for Impedimetric Genosensing
Quantum dots (QDs) are nanometric-scale semiconductor crystals
(mainly sulphides, selenides, or tellurides of heavy metals Cd, In, Zn or Tl)
with unique properties originated in the quantum coni nement ef ect, that
are advantageous for the development of novel bioassays, chemical sensors
and biosensors [146]. h eir exceptional physical and chemical properties,
together with their capability to easily bind to biomolecules have attracted
signii cant interest in the biodiagnostic i eld [147]. Quantum dots are suc-
cessfully used to label biomolecules in order to either obtain an analytical
signal, as for colorimetry [148] or electrochemical detection [149, 150], or
to enhance the response in impedimetric genosensing [151].
Travas-Sejdic [152] and coworkers employed cadmium sulphide (CdS)
nanoparticles to amplify the electrochemical signal at er the detection
of specii c oligonucleotide sequences. h e sensor platform was based on
electropolymerization of a conducting polymer (polypyrrole) in the pres-
ence of the probe oligonucleotide. h e hybridization was then performed
with a CdS-labeled complementary target. A signii cant improvement in
sensor sensitivity was observed, comparing this system with the label-free
detection.
Kjallman
et al.
[153] used CdTe nanoparticles for the modii cation of a
hairpin DNA probe. h e stem-loop shaped probes were then self-assembled
on the gold electrode through Au-SH bonding. Impedance spectra were
recorded at the modii ed gold electrode surface before and at er hybridiza-
tion with the target DNA. h e sensor showed reliable and sensitive detection
of 4.7 fM of target sequences.
Xu
et al.
[151] immobilized DNA probes onto a self-assembled mer-
captoacetic acid monolayer modii ed gold electrode by the formation of
a covalent bond. Hybridization was then performed with ssDNA-CdS
nanoconjugate target. An increased R
ct
value was observed only when
complementary DNA sequence was used in comparison with a three-base
mismatched or non-completely matched sequences. h e sensitivity of the
assay using CdS nanoparticle labels was improved by two orders of magni-
tude when compared with non-labeled DNA sequences.
