Sol-gel Encapsulation of a Bioluminescent Bioreporter

Genetic engineering has allowed for the development of a number of whole-cell bacterial bioreporters. In order for these cells to be used in certain devices and field applications, they must be maintained, and protected, but exposed to environmental conditions. One approach used to accomplish this goal is cellular encapsulation. The recent development of techniques to form inorganic matrices, in particular through the sol-gel process, displays promise as a system of encapsulation. The silica sol-gel process was originally designed for the fabrication of glass, and given that reactions are performed in standard lab conditions and room temperature, the process can be adapted for encapsulation of organic compounds, enzymes, and even whole cells. When mixed with sol, cells become enmeshed within the matrix of silica, forming a gel. The qualities that make silica glass strong, stable, and optically transparent are what also make this method useful for encapsulation of bacterial bioreporters. The nature of the silica matrix allows it to remain stable yet permeable to target analytes, nutrients, and oxygen. In addition, because they are arranged in a matrix, the encapsulated cells are sustained as a system allowing for direct placement of the reporter strain onto a signal processor. The increased understanding of sol-gel chemistry has allowed for the development of techniques that maintain viability of cells while encapsulating them in an inorganic matrix that should be able to withstand conditions in the field or in a sensor device.

In this project, cells of a bioluminescent bioreporter Pseudomonas fluorescens 5RL (5RL) were encapsulated in a silica sol-gel matrix. Electron microscopy, bioluminescence, oxygen uptake, protein concentration, and carbon utilization assays were designed and implemented to investigate the physiological state of encapsulated cells as compared to cells in suspension. Overall, results suggest that cells are not significantly affected by encapsulation. Furthermore, there do not appear to be additional significant mass transfer issues faced by cells inside the gel. Results are promising for the potential field applications of this process towards environmental monitoring, medical diagnostics, agricultural biotechnology, and biocomputing.