Environmental Engineering Reference
In-Depth Information
While returning back to the ground state, they emit light with a different wavelength
than the exposed light. Fluorescein isothiocyanate, tris (2'2-bipyridyl)
dichlororuthenium (II) (Rubpy), 6-carboxyl-X-rhodamine are some of the commonly
used markers in bioassays. In order to improve the sensitivity and photostability of
organic fluorophores, dye doped silica nanoparticles have also been used (Yan et al.,
2007). Using the cage structure of a nanoparticle, a high number of organic fluorophores
(hundreds to thousands) can be incorporated inside a single silica particle. Labeling of
biomolecules, however, may be a time-consuming process. Alternatives like surface
plasmon resonance (SPR) permit the detection of label free molecular interactions and
shows improved specificity, sensitivity, and reproducibility and allows portability
(Chinowsky et al., 2007).
Fabrication of micro- and nano-sensors is accomplished using techniques already
developed in the integrated circuit manufacturing technology. It consists of four steps: i)
thin film growth/deposition, ii) photolithographic patterning, iii) etching, and iv) surface
and bulk micromachining. Earlier, photolithography had some limitations because the
then available 157-nm wavelength could produce features as small as 75 nm (Service,
2001). However, recent advances using deep ultraviolet light can generate 40 nm sized
features (Totzeck et al., 2007). The fabrication of more complex structures (~nm sized)
is also possible by the advancements in e-beam and X-ray lithography techniques. The
integrated circuit manufacturing technology, originally limited to silicon based materials
(e.g., silicon, silicon dioxide, and silicon nitride) is also now routinely used for the
fabrication of complex devices made out of glass, plastic, and quartz, and other novel
materials. These materials have specific electrical, mechanical, and thermal properties
enabling cost effective and tailored characteristics by combining two or more materials
Microcantilever-based sensors show high potential to detect biological molecules
with extraordinary accuracy. A number of commercial entities like Concentris
(www.concentris.ch),
Cantion (
www.cantion.com),
Veeco (
www.veeco.com)
now
produce micro-cantilevers with typical lengths of 10 to 500 μm and thickness of a few
nm. These cantilevers are batch fabricated by thin film processing technology from
silicon-based materials. High throughput platforms using arrays of cantilevers can be
used as an alternative to microarrays. For example, the VeriScan 3000 system from
Protiveris
(www.protiveris.com)
uses 64 cantilevers to detect biomolecular interaction
events in real time. Recently a company originating out of the work done at the
University of California, Berkley named Kalinex Inc. (
http://otl.berkeley.edu)
demonstrated the high throughput detection of 100 to 200 compounds by employing
1000 micro-cantilevers on a chip (Carrascosa et al., 2006). In recent years, considerable
effort has been devoted to the nano-patterning of biomolecules on surfaces. These are
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