and well-established micromachining processes [ 10 , 11 ]. Furthermore, both the
materials can be chemically modified and functionalized to provide biocompatible
platforms for sensing and cell culture applications. However, since silicon is a
semiconductor, usually a dielectric SiO 2 layer is thermally grown on the surface of
silicon as an insulating layer to separate the electrode surface from the substrate of
most silicon-based sensors that require electrical isolation [ 12 ]. This is particularly
important for sensors that employ electrically-based detection methods since elec-
trical effects in the bulk silicon substrate could potentially interfere with detection
or provide stray noise in the sensor. The silicon’s surface chemistry, based on the
silanol group (─Si─OH) is well developed and modification can be easily accom-
plished via silanes [ 9 , 13 ]. For example, nonspecific adsorption can be reduced or
cellular growth improved through chemical modification of the surface.
Due to its intrinsic properties, silicon is transparent to electromagnetic wave-
lengths in the infrared spectrum but not to wavelengths in the visible light spectrum,
making typical fluorescence detection or fluid imaging challenging for embedded
structures. This issue can be overcome by having a transparent material (polymer or
glass) bound to silicon in a hybrid system. Such hybrid devices have led to a
renaissance in Si-based detectors for microfluidic systems [ 15 , 16 ]. For example,
ElastomerSilicon/GlassThermosetsHydrogelFabrication costResearch useCommercial useThermoplasticsPaperMicrofluidicsFig. 6.2 Schematic representation of different types of materials used for microfluidics design
148 P. Manickam et al.