Microlenses are a cutting-edge technology for imaging, detecting, and coupling light, but current fabrication methods require labor- and energy-intensive steps. The use of bacteria for the assembly of microlenses can combine high refractive indices, short focal lengths, and the aberration free nature of silica-based bioglass, while also being more tunable and patternable. The sea sponge enzyme silicatein can catalyze the polymerization of monomeric silica into polysilicate layers at physiological pH and temperature. We have engineered <i>Escherichia coli</i> to express silicatein fused to outer membrane protein OmpA at the surface of the bacteria, so that the silicatein enzyme can polymerize a layer of polysilicate surrounding the cell. Fluorescence confocal microscopy of silicatein-expressing bacterial cells stained with Rhodamine123, which binds polysilicate, revealed a highly stained cell boundary with little internal staining. This result indicates that the <i>E. coli</i> are encapsulated with polysilicate. To measure the light-focusing behavior of the polysilicate-coated bacterial cells, we illuminated them with total internal fluorescence microscopy and detected the pattern of light that was scattered into a fluorescent agarose pad. The bioglass-coated bacteria scattered light off their surface that illuminated a larger area with a brighter intensity compared to bacteria not expressing silicatein, indicating that the engineered bacteria can capture and focus light. Our bacterial microlenses are sustainably self-assembled and have wide-ranging applications in the optical and biomedical industries, such as compact image sensors, 3D displays, concentrators for photovoltaics, solar cell technologies, and more.

Self-assembled bacterial microlenses for optical applications

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