Immobilization of Fluorescent Aptamer Biosensors on Magnetic Microparticles and Its Potential Application for Ocean Sensing

Many important analytes are present in the ocean water and primary examples include various marine toxins. The unique marine environment possesses an extremely high ionic strength, posing a significant analytical challenge for biosensor design. Protein-based enzymes and antibodies are likely to denature under such non-physiological conditions. Aptamers are nucleic acid-based binding molecules that can be obtained using a combinatorial in vitro selection technique. Since such selections are carried out in the absence of living cells, it is possible to obtain aptamers that work optimally under high salt conditions. Similarly selections in low pH and high temperatures have already been carried out. The high salt concentration in marine samples may also cause significant fluorescence quenching, reducing the sensitivity of fluorescent aptamer sensors. We propose that this problem may be solved by immobilization of aptamer-based biosensors on magnetic microparticles, allowing spatial separation of the target binding and the fluorescence detection steps. In this chapter, we describe a protocol for the detection of adenosine and ATP in high salt buffers and in human blood serum. Compared to the non-immobilized sensor, more consistent results with reduced interference were achieved after immobilization. Future research directions of using such immobilized sensors for marine detection are also discussed.