Microfludic Whole-Cell Biosensor

Whole-cell biosensors are a type of biosensor that incorporates living cells as a biorecognition element [1]. Conventionally, chemical or physical sensors, such as high-performance liquid chromatography (HPLC) or gas chromatography coupled with mass spectrometry (GC-MS), have been used for analyzing samples of interest (e.g., the composition and concentration of chemicals). Although they are highly accurate and results are reliable, such instrumentation is expensive and often requires special skills and facilities for analysis. An alternative approach in sensor technologies is sensors using biological components, such as enzymes and living cells. They are simpler and often singlepurpose devices, but can be easily produced (hence inexpensive). There are two different objectives in biosensor research: One objective is to develop biological counterparts of conventional chemical or physical sensors. Biological molecules (enzymes, antibodies, and nucleic acid fragments) are commonly used to develop such biosensors due to their substrate specificities [2]. Another objective is the toxicity assessment. While biomolecule-based biosensors are more accurate and give more detailed information about analytes, it is difficult to know the effect of the analyte on living organisms. Thus, a main application domain of biosensor using living cells or tissues is to obtain information about functional consequences of substrates being analyzed or the measurement of the total “bioavailability.” The bioavailable (or bioaccessible) compound is defined as “(a molecule that) is freely available to cross an organism’s cellular membrane from the medium the organism inhabits at a given time” [3], which would be useful for the understanding of, for example, the environmental effect of the compound. Potential applications of whole-cell biosensors could be the assessment of physiological effect of a pharmaceutical compound, checking if a substance is an agonist or an antagonist for a receptor, the cellular toxicity test, and the environmental pollution test [4]. As these types of information involve vital reactions