Glass-Coated Bacteria Form Living Microlenses for Advanced Imaging

Microlenses, micrometer-sized lenses that capture and focus light into intense beams at a microscopic scale, typically require complex, expensive machinery and extreme temperatures or pressures to produce. A bioinspired approach to making microlenses, based on the enzymes secreted by sea sponges, could offer a way to create inexpensive, durable, advanced microlenses for use in medicine, biology, and materials science.

Sea sponges grow glass skeletons made of silica (also called bioglass). This silica skeleton is both lightweight and resilient, allowing the sea sponge to withstand harsh marine environments.

Graduate student Lynn Sidor prepares bacteria cells that will self-assemble their own glass coating by using enzymes from sea sponges. Sidor is working with biologist Anne Meyer and colleagues in optics and physics to create tiny, bacteria-based microlenses for advanced imaging. Courtesy of University of Rochester/J. Adam Fenster.

By using the principles of synthetic biology, an international research team replicated the material that comprises the natural bioglass shell of the sea sponge to create a living optical lens. The University of Rochester (UR)-led team included researchers from the University of Colorado Boulder (CU Boulder), Delft University of Technology, and Leiden University.

The researchers fused the bioglass-creating enzyme produced by sea sponges to the surface of bacteria cells. The modified cells self-assembled a layer of bioglass at their surface. The bioglass shell transformed the bacteria cells into engineered optical devices that could scatter high-intensity, focused light.

“By engineering microbes to display these same enzymes, our collaborators were able to form glass on the cell surface, which turned the cells into living microlenses,” CU Boulder professor Wil Srubar said. “This is a terrific example of how learning and applying nature’s design principles can enable the production of advanced materials.”

In addition to engineering the bacterial cells to express the silicatein enzyme made by sea sponges, the UR team, led by professor Anne Meyer, developed a microscopy technique to measure the optical properties of the cells. Working with material scientists at CU Boulder, the UR researchers examined the bacteria’s chemical properties to ensure that silica was present on the engineered cells.

The researchers designed and built a specialized microscope that illuminates samples from a wide range of angles. They also developed an innovative microscopy technique to measure the optical properties of the glass-coated bacteria cells, allowing them to visualize how the bacteria focus light. Courtesy of University of Rochester/J. Adam Fenster.

The CU Boulder researchers analyzed the silica displayed by the bacteria and quantified the amount surrounding different bacterial strains by using imaging and X-ray techniques. They demonstrated that bacteria engineered to form bioglass spheres contained significantly higher silica levels than nonengineered strains.

In collaboration with UR’s Institute of Optics, the researchers created mathematical models that predicted the optical properties of the glass-coated bacterial cells. The combined results of the research teams confirmed that bacteria could be bioengineered to create bioglass microlenses with excellent light-focusing properties.

The silica-encapsulated bacteria were able to focus light into intense nanojets that were nearly an order of magnitude brighter than unmodified bacteria. The researchers observed that silica-encapsulated bacteria are metabolically active for up to 4 months — long enough to allow the bacteria to sense and respond to stimuli over time.

Because the microlenses are created by bacterial cell “factories,” they are inexpensive and easy to grow. The bacteria can self-assemble the glass coating at standard temperatures and pressures. “These properties make them well-suited for a unique range of applications,” Meyer said. “The ease of producing these microlenses could make them a good way to fabricate optics in locations with less access to nanofabrication tools, including outer space.”

The glass-coated bacteria cells focus light into very bright beams, paving the way for advanced imaging technologies. These microlenses could enable higher-resolution image sensors and enhance conventional microscopy. Courtesy of University of Rochester/The Meyer Lab.

The bacterial microlenses are smaller than conventionally-produced microlenses. Their small size could make them useful for creating high-resolution image sensors for biomedical imaging, allowing sharper visualization of subcellular features like protein complexes.

In the field of materials science, the microlenses could be used to capture detailed images of nanoscale materials and structures. They could be used in clinical diagnostics to enhance the imaging of microscopic pathogens, enabling more accurate identification and analysis. Because the glass-coated bacteria focus light into very bright beams, they have the potential to image objects that are currently too small to be visualized.

Meyer and colleagues recently received a grant from the U.S. Air Force Office of Scientific Research to study the biosynthesized microlenses in low-gravity environments.

“This research is the first to engineer light-focusing properties into bacteria cells, and I am excited to explore the different possibilities that our work has opened up,” Meyer said.

The research was published in the Proceedings of the National Academy of Sciences (www.doi.org/10.1073/pnas.240933512).