Biosensor for the nonspecific determination of ionic surfactants

We report the analytical figures of merit for the first biosensor for ionic surfactant quantification. The biosensor consists of a silanized silica optical fiber, onto which acrylodan-labeled bovine serum albumin (BSA-Ac) is immobilized. Recent work from our laboratory on native BSA-Ac (Lundgren, J. S.; Bright, F. V. J. Phys. Chem. 1996, 100, 8580-8586) has shown that ionic surfactants dehydrate the local environment surrounding the lone acrylodan residue, open up the pocket hosting the acrylodan reporter group, and dramatically increase the segmental mobility of domain I in BSA. In the current work, we use BSA-Ac as an actual biorecognition element for surfactant detection and quantification. We also compare several BSA-Ac immobilization strategies and determine the analytical figures of merit for the BSA-Ac-based biosensor to a prototypical analyte, cetyltrimethylammonium bromide (CTAB). The biosensor linear dynamic range extends from 5 to 60 μM, and the t(90) response time (90% of the total response) is less than 30 s. Biosensor response precision (relative standard deviation) during 34 sensing cycles is 2.5%. On the down side, biosensor performance decreases 38% after 25 days of storage; however, this drift can be compensated. This work also demonstrates the utility of BSA-Ac as a model biorecognition element-reporter group system for grading the suitability of different surface immobilization strategies.