Biomedical Engineering Reference
In-Depth Information
carried out incorporating specific proteins, DNA, and cellular systems into biosensors for
small molecule detection. Then in Section 1.3, we describe our most recent efforts to
understand the properties of some specific DNA systems using computational
approaches, with the ultimate aim of intelligent property prediction that can be used in the
design of both intelligent biosensors and biomaterials. In Section 1.4, we describe infor-
matics and data mining approaches and how these techniques can be applied to under-
stand complex nonlinear data systems. The idea here is to apply these techniques, where
appropriate, to help decipher the behavior of complex biosensors to create an optimal sig-
nal output and also to improve the design of biosensors by better understanding and
selecting optimal biological components. Finally, in Section 1.5, we describe future
prospects for the creation of newer and smaller biosensors with superior properties.
1.2
Creating Biosensors That Detect Small and Large Molecules Using
Different Signal Transduction Mechanisms
1.2.1
Optical-Based Biosensors
Some of the Center's initial research centered upon the creation of systems involving opti-
cal signal transduction. The optical elements were of two basic types. In one, the chro-
mophores were integral moieties of naturally occurring proteins. In the second, the
chromophore was an enzymatically activated chemiluminescent molecule that emitted a
visible photon. In the first type, the phycobiliproteins had the advantage of being proteins
that evolved to possess efficient optical absorption at low light levels and had high-fluo-
rescence quantum yields (6). These were studied in a number of immobilization formats.
We also studied the very stable membrane-bound protein bacteriorhodopsin (bR) (7) that
possesses a complex photocycle involving well-defined protein conformation-chro-
mophore states. In the case of the second type of optical element, we studied a particular
molecule that was developed to be capable of undergoing enzymatic cleavage to the
chemiluminescent product species by phosphatase enzymes such as alkaline phosphatase.
The alkaline phosphatase we used was primarily immobilized via conducting polymers to
sensitively detect low solution concentrations of organophosphate pesticides and certain
metal ions using a competition strategy. Examples of these biosensor systems are pre-
sented in the following subsections.
1.2.1.1 Chromophore-Containing Proteins in Biosensor Applications
1.2.1.1.1 The Phycobiliproteins
The phycobiliproteins represent an interesting class of photodynamic proteins that have
evolved to function with extremely high light collection efficiency in low-light-level envi-
ronments, such as deep underwater, where their host algae are often found in highly com-
petitive ecological niches. A closely related family of proteins, the phycobiliproteins—
phycoerythrin, phycocyanin, and allophycocyanin—in that order, are found in vivo in
supramolecular assemblies in an antennalike structure called the phycobilisome. Each
protein absorbs in their respective region in the visible spectrum and progressively trans-
fers the absorbed light energy with high efficiency (
90% quantum yield) via a Forster-
type transfer mechanism down the phycobilisome and into Photosystem II to drive
photosynthesis (8). The chromophores found in the individual subunits of the three
