Biomedical Engineering Reference
In-Depth Information
simple fabrication method, achieved excellent performance in terms of
sensitivity, stability, selectivity, reproducibility and anti-interference. h ese
nanoelectrode devices, which were successfully applied to the determina-
tion of intracellular Ca
2+
and Mg
2+
in two types of cells (human adipocytes
and frog oocytes) (see experimental setup in Figure 1.5), pave the way to
enable analytical measurements in single living cells and to sense other
biochemical species at the intracellular level.
Functionalized ZnONR-based potentiometric microsensors have been
developed to measure intracellular metal ions (Ca
2+
, Mg
2+
, K
+
and Na
+
) and
glucose [17]. ZnO nanorods, grown on the tip of borosilicate glass capillar-
ies (0.7 μm in diameter), and functionalized by using a metal-ion selective
plastic membrane or GOx showed high sensitivity and good biocompat-
ibility for intracellular environments and were capable of penetrating the
cell membrane. Human adipocytes and frog oocytes were used for deter-
minations of intracellular free metal ions and glucose concentrations. h e
performance of the ZnO nanostructure-based intracellular sensor could
be improved through engineering of morphology, ef ective surface area,
functionality, and adsorption/desorption capability.
A functionalized ZnONRs-based selective electrochemical sensor for
intracellular glucose measurements was developed by Asif
et al.
[28].
To adjust the sensor for intracellular glucose measurements, hexagonal
ZnONRs grown on the tip of a silver-covered borosilicate glass capillary
(0.7 μm diameter) were then coated with GOx. h e proposed intracellular
potentiometric biosensor showed a fast response with a time constant of
less than 1 s and showed quite a wide linear range from 0.5 to 1000 μM. It
was used to measure intracellular glucose concentration in human adipo-
cytes and
Xenopus laevis
oocytes and to demonstrate that insulin increased
the intracellular glucose concentration in both cells. h ese results dem-
onstrated the capability to perform biologically relevant measurements
of glucose within living cells. h e ZnONRs-based glucose electrode thus
holds promise for minimally invasive dynamic analyses of single cells. All
of these advantageous features can make the proposed nanoelectrode bio-
device applicable in medical, food or other areas. Moreover, the fabrica-
tion method is simple and can be extended to immobilize other enzymes
and other bioactive molecules with small IEPs for a variety of biosensor
designs.
Ali
et al.
[18] also developed a potentiometric nanosensor for glucose
based on functionalized highly-oriented single-crystal ZnONT arrays
(Figure 1.6). h e ZnONT arrays were prepared by a trimming of ZnONRs
along the c-axis on the gold coated glass substrate having a diameter
of 100-200 nm and a length of ~1 μm, using low temperature aqueous
