Biology Reference
In-Depth Information
3.4.4 Electrochemical Genosensing Based on Magnetic
Beads and m-GEC Electrochemical Transducer
Oneof the mostpromising materials, whichhave been developed, is
biologically modified magnetic beads [86] based on the concept of
magnetic bioseparations. Magnetic beads offer some new attractive
possibilities in biomedicine and bioanalysis since their size is com-
parabletothoseofcells.Moreover,theycanbecoatedwithbiological
molecules and they can also be manipulated by an external mag-
netic field gradient. As such, the biomaterial, specific cells, proteins,
or DNA, can be selectively bound to the magnetic beads and then
separated from its biological matrix by using an external magnetic
field. Moreover, magnetic beads of a variety of materials and sizes,
and modified with a wide variety of surface functional groups, are
now commercially available. They have brought novel capabilities
to electrochemical immunosensing [87-89]. The magnetic beads
havealso been usedin novelelectrochemical genosensingprotocols
[90]. These approaches using magnetic beads for detection of DNA
hybridization have been combined with different strategies for the
electrochemical detection, such as label-free genosensing [91-93]
or different external labels, such as enzymes [90], electrochemical
indicators [94], or metal tags, for example, gold or silver NPs [95],
and using different electrochemical techniques, such as DPV, poten-
tiometric stripping analysis (PSA), or square wave voltammetry
(SWV).
Instead of the direct modification of the electrode surface, the
biological reactions (as immobilization, hybridization, enzymatic
labeling, or a nity reactions) and the washing steps can be suc-
cessfully performed on magnetic beads. After the modifications, the
magnetic beads can be easily captured by magnetic forces onto the
surface of GEC electrodes holding a small magnet inside (m-GEC).
Once immobilized on m-GEC, the hybridization performed on the
magnetic beads can be electrochemically revealed using different
strategies based on both enzymatic labeling and the intrinsic sig-
nal coming from the DNA oxidation [96] (as shown in Fig. 3.4).
In the case of using magnetic beads, a single-point immobilization
procedure based on streptavidin-biotin interaction is performed
(Fig.3.3C).BiotinylatedDNAcanbefirmlyattachedonstreptavidin-
modified magnetic beads in that way.
 
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