Microfluidics for Biologists Fundamentals and Applications

(National Geographic (Little) Kids) #1

developed a unique conductometric sensor which is a combination of interdigital
electrode structures with imprinted polymers for engine’s lubricating oil moni-
toring [ 113 ]. Using a sol–gel process, titania andsilicaareimprintedandusedas
sensitive coatings. The change of conductance in these layers is measured as
they are exposed to varying concentrationsof the oil. Conductometric biosensors
are extensively used for environmental monitoring as well. They are used for
detection of several pollutants, organophosphorous pesticide [ 114 ], heavy metal
ions [ 115 ], formaldehyde [ 116 ], 4-chlorophenol [ 117 ] and nitrate [ 118 ]. In spite
of being a novel field, arrays of such sensors can be used for various applications
in environmental modeling providing the advantage of improved accuracy and
low costs.
Potentiometric sensors work on a principle where an ion-selective or gas sensing
electrode is monitored for changes in potential with respect to a reference electrode.
When biological molecules bind to the sensing electrode the potential changes due
to consumption of the electrolyte by it. Gold coated silicon electrode with
alkanethiol molecules immobilized on it is used as a sensing element for detection
of cancer and proteins [ 119 ]. Real-time wearable sensors are paving their way in
owing to their self-tracking nature. From tracking heart rate to monitoring one’s
mood these sensors help the person quantify their health and make improvements
accordingly. A unique tattoo based epidermal pH ion-selective sensor has been
developed [ 120 ]. It is a flexible wearable sensor which can be an asset for physi-
ological monitoring purposes. Potentiometric sensors are targeting ultra-low cost
and robust sensors, which has led to development of paper based potentiometric
sensors. Bendable electronics and carbon nanotubes have been combined to
develop a novel low-cost sensor for diagnostic purposes which entails advantages
like excellent electrical properties, better conductivity and higher surface area
contact with the sample [ 121 ].


Fig. 2.34 Photomicrographs depicting cells targeted to docking sites (Reproduced from Gao
et al. [ 111 ] with permission from the Royal Society of Chemistry)


74 G. Bhatt et al.


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