FONA International (Canada)

A biosensor is a device that physically combines a biologically active material to a transducer to convert a selective biochemical interaction into a measurable analytical signal The advantages ideally offered by biosensors over other forms of analysis include ease of use (by nonexpert personnel), rapid response, low cost, ease of fabrication, small size, ruggedness, facile interfacing with computers, low detection limits, high sensitivity, selectivity, and reusability of the devices. Biosensors have been used to selectively detect cells, viruses, other biologically significant materials, biochemical reactions, and immunological reactions by using detection strategies that involve immobilization of enzymes, antibodies, or other selective proteins onto piezoelectric, optical, electrochemical, and surface plasmon resonance sensors (see Table 9.1). Biosensors are not widely available from commercial sources due to problems associated with the long-term stability of the selective recognition elements when immobilized onto solid surfaces, but some have already made significant impact in certain areas of analysis such as blood glucose determination. An approach that may potentially be used to create biosensors with long-term chemical stability takes advantage of the stability of DNA. With the advent of DNA probe technology, a number of selective oligomers which interact with the DNA of important biological species have been identified These have been used to provide a new type of biorecognition element which is highly selective, stable, and can be easily synthesized in the laboratory. 12–14

The immobilization of oligonucleotides to solid surfaces can provide a platform of chemistry that is suitable for the development of biosensor and microarray technologies. Experiments were performed using a fiber optic nucleic acid biosensor based on total internal reflection fluorescence to examine the effects of the presence of non-complementary DNA on the detection of hybridization of complementary target DNA. The work has focused on the rates and extent of hybridization in the presence and absence of non-selective adsorption using fluorescein-labeled DNA. A stop-flow system of 137 microL volume permitted rapid introduction and mixing of each sample. Response times measured were on the order of seconds to minutes. Non-selective adsorption of non-complementary oligonucleotides (ncDNA) was found to occur at a significantly faster rate than hybridization of complementary oligomers (cDNA) in all cases. The presence of ncDNA oligonucleotides did not inhibit selective interactions between immobilized DNA and cDNA in solution. The presence of high concentrations of non-complementary genomic DNA had little effect on the extent of hybridization of complementary oligonucleotides, but actually reduced the response times of sensors to cDNA oligonucleotides.