Fluorescent and bioluminescent cell-based sensors: Strategies for their preservation

Luminescent whole-cell biosensing systems have been developed for a variety of analytes of environmental, clinical, and biological interest. These analytical tools allow for sensitive, rapid, simple, and inexpensive quantitative detection of target analytes. Furthermore, they can be designed to be nonspecific, semispecific, or highly specific/selective. A notable feature of such sensing systems employing living cells is that they provide information on the analyte bioavailability and activity. These characteristics, along with their suitability to miniaturization, make cell-based sensors ideal for field applications. However, a major limitation to on-site use is their "shelf-life." To address this problem, various methods for preservation of sensing cells have been reported, including freeze-drying, immobilization in different types of matrices, and formation of spores. Among these, the use of spores emerged as a promising strategy for long-term storage of whole-cell sensing systems at room temperature as well as in extreme environmental conditions.