Biology Reference
In-Depth Information
It is obvious that the immobilization protocol depends on the
transducer characteristics, nevertheless itispreferred to userobust
immobilizationmethodsinordertoavoidtheprobedesorptionfrom
the sensor [57]. Thus, the retention in polymeric matrix, covalent
bonds on a functionalized surface, SAMs, and immobilization
through a
nity reactions are the most successful methods at the
moment, because these strategies give place to an immobilization
across the ends of the probes in a tidy and orientated way.
In addition, these strategies allow to control the conformational
freedom of the probes and the space between chains by means
of the control of the superficial covering obtaining hybridization
e
ciencies up to 100%.
The most of screen-printed electrodes employed as transducers
of genosensors are made of carbon or gold inks. Further sections
detail the most used probe immobilization strategies in these types
of electrodes.
9.3.2.1 Immobilization of ssDNA over carbon electrodes
Several strategies of DNA immobilization have been described onto
screen-printed carbon electrodes (SPCEs).
Althoughitisfrequentlyused[58,59],directssDNAimmobiliza-
tion over bare carbon surface happens in a random and untidy way
duetothemultipleinteractionsbetweenthecarbonsurfaceandthe
phosphate structure of DNA. DNA strands immobilized by physical
adsorption are not orientated and present a limited mobility, so the
hybridizationreaction ishampered by stearic impediments Fig. 9.6.
Adsorption at controlled potential is generally carried out on
pretreated SPCEs [13, 15, 60, 61]. Nevertheless, in these cases the
probe strands are not totally accessible for their hybridization,
diminishingthe genosensore
ciency.
Avidin [24], neutravidin [51], and streptavidin [54] have been
usedtoimmobilizebiotinylatedDNAstrandsontocarbonelectrodes
Fig. 9.7, but before immobilizing the probe the surface must be
blocked to avoid unspecific adsorptions like that of the components
of the genosensor.
Other strategies are based on the formation of a polymer, by
means of the electropolymerization of the probe modified with the
