Chemistry Reference
In-Depth Information
CHO
CHO
CHO
NH
2
Fc
OHC
NH
2
NH
2
NH
2
NH
2
NH
2
NH
2
NH
2
NH
2
CHO
H
2
N
D
D
Fc
CHO
E
E
NH
2
D
OHC
E
CHO
CHO
Fc
Fc
CHO
H
2
N
Au
Au
Au
NH
2
Au
NH
2
CHO
OHC
E
E
D
NH
2
CHO
CHO
Fc
Fc
(2) Partial ferrocenyl-
tethered dendrimer (Fc-D)
CHO
(3) NaBH
3
CN,
ethanolamine
D
NH
(1) IO
4
-
-oxidized GOx
2
Cystamine
F
c
E
CHO
E
D
Fc
NH
2
CHO
SCHEME 8.13
Schematic organization of the multilayered GOx-Fc-D network on the Au
electrodes.
ordered way. The bioelectrocatalytic signals were shown to be amplified with
multilayer growth. This fact indicates that the electrode sensitivity is controllable
and the method would be applicable to the construction of sensitivity adjustable
biosensing devices. The stability of these sensors seems to be due to the integrity of
multilayered network with multiple covalent linkages and the rigidity of the den-
drimer building blocks (Scheme 8.13).
Using the same Fc-Ds dendrimers as building blocks of a sensing monolayer Yoon
et al. [125] have developed an affinity biosensor system based on avidin-biotin
interaction. On Au electrodes an amine self-assembled monolayer (SAM) was
prepared (3,3-dithiopropionic acid, N-hydroxysuccinimide ester), then amine groups
of dendrimers are used for immobilization in the SAMmonolayer and functionaliza-
tion with biotinyl groups. An electrochemical signal was generated by free glucose
oxidase, depending on the degree of coverage of the sensing surface with avidin. The
sensor signal decreased with increasing avidin concentration. From a kinetic analysis
the formation of a spatially ordered and compact protein layer on the electrode surface
was demonstrated.
A dendrimer Fc-D was also used as an electrocatalyst to enhance the DNA
detection as well as a building block to immobilize capture probes. Thus, a
sandwich-type enzyme-linked DNA sensor was developed by Kim and cowor-
kers [126]. Fc-Ds have been immobilized on a carboxylic acid-terminated SAM.
The target DNA was hybridized with the capture probe and an extension in the
DNA was then hybridized with a biotinylated detection probe. The bioterminated
layer is detected using avidin-conjugated alkaline phosphatase (Av-ALP), which
generates p-aminophenol (pAP) from p-aminophenyl phosphate (pAPP); pAP is
electrochemically oxidized with the mediation of Fc in the layer. The combination of
electrocatalysis using Fc-Ds and biochemical amplification enabled the sequence-
selective detection of various targets, including single-based mismatched oligonu-
cleotide allowing highly sensitive amperometric measurements.
It has been reported [127] a highly sensitive electrochemical DNA sensor that uses
Au nanoparticles (AuNPs), magnetic beads (MBs), and an ITO electrode modified
with partially functionalized Fc dendrimers (Fc-Ds) [123,124]. AuNPs are employed
as catalytic labels, MBs to permit lownonspecific binding of DNA-conjugatedAuNPs
and to take advantage of easy magnetic separation. Fc-D-modified ITO electrodes
are used to obtain a low background current and easy electron oxidation of pAP.
