Biomedical Engineering Reference
In-Depth Information
the help of EIS [52] which demonstrates that the technique is sensitive to
the interfacial electrical changes that accompany DNA bio-recognition
event. A ratio of the applied voltage to its current response is given as
impedance in the EIS. It is found that there is usually a phase shit ϕ
in between current (or voltage) response and the voltage (or current)
applied. Faradaic impedance and the charge transfer resistance,
R
ct
, is
termed due to interfacial electrochemistry involves an electroactive spe-
cie and is mostly used as the reporting impedance element in biosensor.
On the other hand, if the interfacial electrochemistry does not involve
electro-active specie, it is called as non faradic impedance. h ere are two
ways that is (a) non faradic measurement of impedance or capacitance
at single frequency (b) faradic measurement of the charge transfer resis-
tance
R
ct
over a wide frequency range in the EIS measurement in EDB.
EIS as a characterised tool is used in few biosensor design at dif erent
stages but do not report the i nal DNA target responses [53, 54]. Such
biosensor can generally not be termed as impedimetric.
h e main and systematic types of immune-sensor detection devices
are as followed: optical, electrochemical (potentiometric, amperometric
or conductometric/capacitive) and microgravimetric. All such types can
either be described and emphasized as direct (non- labelled) or as indirect
(labelled) immune-sensors. h e direct sensors are capable of signii cantly
detecting the physical changes in the immune complex formation, but the
indirect sensors uses only signal-generating labels which allow more sensi-
tive and versatile detection modes when incorporated into the intervene
complex. h ere is a dif erent variety of identii ed labels which is applied
in indirect immune-sensors as such. h e most commonly enzyme labels
include enzymes such as catalase (EC1.11.1.6), peroxidase (EC 1.11.1.7),
alkaline phosphatase (aP), glucose oxidase (EC 1.1.3.4) or lucifarase (EC
1.13.12.7) which is generally due to their excellent stability and high turn-
over number. Electro-active compounds namely ferrocene or In
2+
salts, and
a series of l uorescent labels such Cy5, asrhodamine, ruthenium diamine
complexes, l uorescein and phosphorescent porpyhrin dyes have also been
used in the detection [55, 56].
A quantitative polypyrrole based and stable potentiometric immune-
sensor that is provided by broad-spectrum assay capability was designed
and estimated by Purvis
et al.
[57]. h e biosensor detected an enzyme
labelled by immuno-complexes were formed at the surface of a polypyrrole
is coated with screen printed with gold electrode. Such detection mode
was mediated by a secondary reaction that has produced charged products
at the end. A shit in potential was measured at the sensor surface, which
has been caused by local changes in properties such as pH, ionic strength,
