Biomedical Engineering Reference
In-Depth Information
Fig. 5.4
Schematic illustration of the QDs (CdSe/ZnS) electrochemical aptasensor based on
3DOM gold film. Reproduced with permission from Ref. [
41
]. Copyright 2010, Elsevier
as shown in Fig.
5.4
. The 3DOM gold film endowed the active surface area of the
electrode up to 9.52 times larger than that of a classical bare flat one. The reaction
was monitored by electrochemical stripping analysis of dissolved QDs which were
bound to the residual cDNA through biotin-streptavidin system. The decrease in
peak current was proportional to the amount of ATP. The unique interconnected
structure in 3DOM gold film along with the “built-in” preconcentration remark-
ably improved the sensitivity down to 0.01 nM. This promised a novel model for
the detection of small molecules with higher sensitivity.
The multicomponent analysis could not only be used in the DNA analysis,
but also be employed in the field of aptasensor. As back in 2006, based on their
multielectrochemical coding technology for the simultaneous detection of multi-
ple DNA targets, Wang and cooperators described a simple method for preparing
a QD/aptamer-based ultrasensitive multianalyte electrochemical biosensor with
subpicomolar (attomole) detection limits [
44
]. The main strategy is accomplished
using a simple single-step displacement assay, which involved the coimmobiliza-
tion of several thiolated aptamers, along with binding of the corresponding QD-
tagged proteins on a gold surface. After the addition of the protein sample without
QD label, monitoring the displacement through electrochemical detection of the
remaining QDs could be achieved. Such electronic transduction of aptamer-
protein interactions is extremely attractive for meeting the low power, size, and
cost requirements of decentralized diagnostic systems. What is more, unlike two-
step sandwich assays, the new aptamer biosensor protocol relies on a single-step
displacement protocol.
Most recently, Yuan's group [
43
] developed a “signal on” and sensitive biosen-
sor for one-spot simultaneous detection of multiple small molecular analytes based
on electrochemically encoded barcode QD tags. In this route, the target analytes
of adenosine triphosphate (ATP) and cocaine are respectively sandwiched between
the corresponding set of surface-immobilized primary binding aptamers and the
secondary binding aptamer/QD bioconjugates. The captured QDs (CdS and PbS)
yield distinct electrochemical signals after acid dissolution. Due to the inherent
amplification feature of the QD labels and the “signal on” detection scheme, as
