Biomedical Engineering Reference
In-Depth Information
4.7.2.1 Electromechanical Detection
One of the applications of NMs in nanobiosensors that are based on their
electronic properties is microgravimetric quartz crystal microbalance that is
used to transduce the NM-mediated biosensing reactions on the piezoelectric
crystals. The amplification of DNA sensors and detection of single-base mis-
matches used deposition of gold on a 10-nm Au colloid/avidin conjugate label
that served as a seed catalyst. The amplification of microgravimetric analy-
sis through the catalytic deposition of Au on an Au-avidin conjugate was
achieved.
129
DNA detection all the way down to a detection limit of 1 × 10
−15
M
was achieved.
4.7.2.2 Conductivity
Changes in conductivity resulting from NMs mediated DNA hybridization or
immunosensing have been reported. A DNA detection in an array involving the
binding of ONTs that were functionalized with AuNOs resulted in conductiv-
ity changes associated with the binding of the target probe that localized the
AuNPs in an electrode gap. The deposition of AgNPs bridged the gap that led
to measurable conductivity changes for DNA detection at concentrations as low
as 500 fM.
130
Using conventional microelectrodes, this system can be used for
massive multiplexing through the use of larger arrays of electrode pairs.
A nanoarray for electrical detection of hybridization events has been
reported.
131
The nanoarray sensor was used for DNA sequencing with targets
that were conjugated to AuNPs. During target and capture probe-binding events,
a conductive bridge is formed between the two electrodes resulting in change
in conductivity that enabled detection of a few (down to single) hybridization
events. This system can be potentially applied to other binding events such as
the specific interactions between proteins, antibodies, ligands, and receptors
eliminating the need for PCR target amplification techniques.
Direct electrical detection of autometallographically enhanced Au-labeled
analytes for DNA diagnostics was reported.
132-134
An online DNA diagnos-
tics at the point-of-care uses online DC resistance monitoring during the auto-
metallographic enhancement process. The system eliminates washing, drying,
and measurement cycles by taking the direct electrical detection method. The
method is applied in a simple DNA hybridization assay and the analysis of an
SNP using allele-specific hybridization that resulted in unequivocal discrimina-
tion of all possible base-pairing combinations in the SNP assay. Direct electric
conductivity readout resulted from secondary tagging with AuNPs and signal
was enhanced with AgNPs.
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4.7.2.3 Stripping Analysis
A multitarget detection capability has been made possible as a result of the cou-
pling of the amplification feature of stripping voltammetry when QDs are used
as labels for DNA hybridization. This is shown to be a promising alternative for
