Biomedical Engineering Reference
In-Depth Information
(3)
Reimmerse in MPS sol-gel solution overnight to form a second silane layer.
(4)
Expose this gold electrode to the AuNPs and AgNPs for chemisorption on
to the thiol groups of the second silane layer.
(4)
Adsorb the diphtheria antibody (anti-Diph) on the surface of the NPs.
(5)
Characterize the modified gold electrode by CV.
For this particular study,
90
the detection was based on the change in the poten-
tiometric response before and after the antigen-antibody interaction. The
potentiometric response for the diphtheria antigen (Diph) was obtained as a
result of capture with the immobilized diphtheria antibody. Tang's group estab-
lished a potentiometric response that was rapid with a linear range from 22 to
800 ng/mL. This method established a detection limit of 3.7 ng/mL. The assay
was repeated up to 19 successive assay cycles without change in sensitivity for
probes that were regenerated with 0.2 mol/L Gly-HCl buffer solution. Stud-
ies using several serum samples were in agreement with those given by the
enzyme-linked immunosorbent assay (ELISA) method, implying a promising
alternative approach for detecting diphtheria antigen in clinical diagnosis.
4.5.2 Preparation of SAMs on Gold NMs for DNA Detection
A new method for development of a DNA sensor by means of self-assembling
compound NMs to thiolated DNA was reported.
51,91
The sensor used fluores-
cence detection to establish the number of thiol-derivatized single-stranded
ONTs bound to AuNPs as well as the extent of hybridization with comple-
mentary ONTs in solution. Their results indicated that ONT surface coverages
of hexanethiol 12-mer ONTs on AuNPs (34 ± 1 pmol/cm
2
) were significantly
higher than on planar gold thin films (18 ± 3 pmol/cm
2
), while the percentage
of hybridizable strands on the AuNPs (1.3 ± 0.3 pmol/cm
2
, 4%) was lower than
for gold thin films (6 ± 2 pmol/cm
2
, 33%). A gradual increase in electrolyte
concentration during the process of ONT deposition significantly increased sur-
face coverage that resulted in particle stability. Additionally, the ONT spacer
sequences improved the hybridization efficiency of ONT-modified NPs from
~4 to 44%. The surface coverage of recognition strands that can be tailored
using coadsorbed diluent ONTs provided a means of indirectly controlling the
average number of hybridized strands per NP. This study presented important
understanding of the interactions between modified ONTs and metal NPs, as
well as optimizing the sensitivity of AuNP-based ONT detection methods. In
this study, the following protocol was used to create the NMs with SAMs for
DNA sensor.
4.5.2.1 Chemicals
(1)
10 nM AuNP.
(2)
Fluorescein-alkanethiol ONTs, 3 µM.
