Microlithographically fabricated interdigitated microsensor electrodes (IMEs) were cleaned, surface activated, chemically functionalized (amine) and derivatized with an Acrloyl-PEG-NHS to receive a spun-applied monomer cocktail of UV polymerizable monomer. IMEs were 2050.5, 1550.5, 1050.5 and 0550.5 possessing lines and spaces that were 20, 15, 10, and 5 μm respectively; 5 mm line lengths and were 50 lines on each opposing bus. Bioactive hydrogels were synthesized from spun-applied and UV-crosslinked tetraethyleneglycol diacrylate (TEGDA) (crosslinker), 2-hydroxyethylmethacrylate (HEMA), polyethyleneglycol(200) monomethacrylate (PEGMA), N-[tris(hydroxymethyl)methyl]-acrylamide (HMMA) and poly(HEMA) (MW 60,000) (viscosity modifier) and 2,2-dimethoxy-2-phenylacetophenone (DMPA) (photoinitiator) to produce a 5 μm thick p(HEMA-co-PEGMA-co-HMMA) hydrogel membrane on the IMEs. Unmodified and hydrogel coated IMEs where characterized by AC electrical impedance spectroscopy using 50 mV p-t-p over the frequency range from 10 Hz to 100 kHz in aqueous PBS 7.4 buffer and in buffer containing 50 mM [Fe(CN)(6)](3-/4- ) solution at RT. Impedimetric responses were found to scale with the device geometric parameters. Equivalent circuit modeling revealed deviations from ideality at lower device dimensions suggesting an implication of the substrate surface charge on the double layer capacitance of the electrodes. Diffusion coefficients derived from the Warburg component are in accord with literature values.

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This chapter looks at the use of microlithographically fabricated biochip platforms for DNA diagnostics and prognostics, although protein and RNA biochips are also briefly considered. Biodetection methods such as ion-selective electrodes (ISEs), microelectromechanical systems (MEMS) devices such as microcantilevers, optical, piezoelectric-based acoustic wave, and mass spectrometry are briefly discussed. Emphasis is given to label-free electrochemical (impedimetric, voltammetric, and amperometric) detection. The production of DNA biochips is highlighted as are the operation and design of the experiments to reveal gene expression and SNP data. Applications discussed include the monitoring of microbes, cancer classification studies, and patient stratification in drug development. Finally, challenges and issues facing the development of diagnostic and prognostic biochips are discussed in detail.