Impedimetric sensors measure the changes in impedance when biomolecules
bind to the electrode hindering the electron transfer. Based on this, carbon elec-
trodes deposited with PBA-modified graphene oxide were reported for detection of
glycated haemoglobin (HbA1c) for diagnosis of diabetes [ 122 ].
Liu et al. reported a device for label-free electrical detection of DNA through
impedance measurement (Fig.2.35). Impedance vs. frequency characteristic was
extracted to detect the presence of DNA molecules in a nanomolar range for a
400 bp molecule [ 123 ]. Such electrochemical sensors have great potential for point-
of-care diagnostic devices, providing low-cost, high precision and portability.
6.2 Optical Sensing
In the recent decade optical biosensors have drawn extensive attention and have
rapidly developed changing the face of communication technologies. Due to its
advantages like high sensitivity, low-weight, high capacity to transfer information,
invulnerability to electromagnetic interference and low-cost, varied applications
are integrating these sensors [ 124 ]. The sensing mechanism works on the basis of
changes in optical properties such as UV–Vis absorption, bio or chemilumines-
cence, reflectance and fluorescence brought by the interaction of the biocatalyst
with the target analyte [ 125 ].
A SU8 based optical biosensor has been reported by Yardi et al. A novel
technique has been developed to tag standalone optical fibres to a substrate using
laser exposed SU8 micro-droplet (Fig.2.36). The stitched optical fibres show high
transmissibility for both aligned and misaligned configurations of the fibres [ 126 ].
RserabZdl Rsol ZdlCdlZparSolution with DNA3500+/-200A* SiO 2PDMS Well25 μm line/space
electrodesFig. 2.35 (a) Schematic of the sensing device (b) Equivalent circuit model of solution with DNA
molecules (Reproduced from Liu et al. [ 123 ] with permission from the American Institute of
Physics)
2 Microfluidics Overview 75