We report a unique approach in which living cells direct their integration into 3D solid-state nanostructures. Yeast cells deposited on a weakly condensed lipid/silica thin film mesophase actively reconstruct the surface to create a fully 3D bio/nano interface, composed of localized lipid bilayers enveloped by a lipid/silica mesophase, through a self-catalyzed silica condensation process. Remarkably, this integration process selects exclusively for living cells over the corresponding apoptotic cells (those undergoing programmed cell death), via the development of a pH gradient, which catalyzes silica deposition and the formation of a coherent interface between the cell and surrounding silica matrix. Added long-chain lipids or auxiliary nanocomponents are localized within the pH gradient, allowing the development of complex active and accessible bio/nano interfaces not achievable by other synthetic methods. Overall, this approach provides the first demonstration of active cell-directed integration into a nominally solid-state three-dimensional architecture. It promises a new means to integrate "bio" with "nano" into platforms useful to study and manipulate cellular behavior at the individual cell level and to interface living organisms with electronics, photonics, and fluidics.

This is the first report of a living cell-based environmental sensing device capable of generating orthogonal fluorescent, electrochemical, and colorimetric signals in response to a single target analyte in complex media. Orthogonality is enabled by use of cellular communities that are engineered to provide distinct signals in response to the model analyte. Coupling these three signal transduction methods provides additional and/or complementary data regarding the sample which may reduce the impact of interferants and increase confidence in the sensor's output. Long-term stability of the cells was addressed via 3D entrapment within a nanostructured matrix derived from glycerated silicate, which allows the device to be sealed and stored under dry, ambient conditions for months with significant retention in cellular activity and viability (40% viability after 60 days). Furthermore, the first co-entrapment of eukaryotic and bacterial cells in a silica matrix is reported, demonstrating multianalyte biodetection by mixing disparate cell lines at intimate proximities which remain viable and responsive. These advances in cell-based biosensing open intriguing opportunities for integrating living cells with nanomaterials and macroscale systems.

The remarkable impact encapsulation matrix chemistry can have on the bioactivity and viability of integrated living cells is reported. Two silica chemistries (aqueous silicate and alkoxysilane), and a functional component additive (glycerol), are employed to generate three distinct silica matrices. These matrices are used to encapsulate living E. coli cells engineered with a synthetic riboswitch for cell-based biosensing. Following encapsulation, membrane integrity, reproductive capability, and riboswitch-based protein expression levels and rates are measured over a 5 week period. Striking differences in E. coli bioactivity, viability, and biosensing performance are observed for cells encapsulated within the different matrices. E. coli cells encapsulated for 35 days in aqueous silicate-based (AqS) matrices showed relatively low membrane integrity, but high reproductive capability in comparison to cells encapsulated in glycerol containing sodium silicate-based (AqS + g) and alkoxysilane-based (PGS) gels. Further, cells in sodium silicate-based matrices showed increasing fluorescence output over time, resulting in a 1.8-fold higher fluorescence level, and a faster expression rate, over cells free in solution. This unusual and unique combination of biological properties demonstrates that careful design of the encapsulation matrix chemistry can improve functionality of the biocomposite material, and result in new and unexpected physiological states.

An inexpensive device housing communities of living cells is stabilized by C. J. Brinker, S. M. Brozik, and co‐workers within a silica matrix, for cell‐based environmental biosensing, as described . Disparate cell lines (eukaryotic and bacterial) are co‐entrapped, remaining viable and responsive even at intimate proximities. Furthermore, this platform is capable of fluorescent, electrochemical, and colorimetric detection of a single analyte in a complex solution. Coupling these methods may substantially reduce the impact of interferants, opening intriguing opportunities for integrating living cells with nanomaterials and macroscale systems.

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