Imaging Technology Enables Superresolution Inside Whole Cells

Purdue University researchers have developed a technology that enables 3D superresolution imaging inside whole-cell or tissue specimens. The technology allows scientists to locate the positions of biomolecules inside whole cells and tissues with a precision down to a few nanometers.

Although superresolution fluorescence microscopy can improve spatial resolution up to tenfold, resolution can be restricted when light signals, emitted from molecules inside a specimen, travel through different parts of cell or tissue structures at different speeds and cause aberrations in the lightwaves.

“Our technology allows us to measure wavefront distortions induced by the specimen, either a cell or a tissue, directly from the signals generated by single molecules — tiny light sources attached to the cellular structures of interest,” professor Fang Huang said. “By knowing the distortion induced, we can pinpoint the positions of individual molecules at high precision and accuracy. We obtain thousands to millions of coordinates of individual molecules within a cell or tissue volume and use these coordinates to reveal the nanoscale architectures of specimen constituents.”

This image shows a 3D superresolution reconstruction of dendrites in primary visual cortex. Purdue University innovators created an imaging tool that allows visualization of nanoscale structures inside whole cells and tissues. Courtesy of Fang Huang/Purdue University.

Researcher Fan Xu said that the team’s technology uses two steps: assignment and update, to iteratively retrieve the wavefront distortion and the 3D responses from the recorded single molecule data set containing emission patterns of molecules at arbitrary locations. “During three-dimensional superresolution imaging, we record thousands to millions of emission patterns of single fluorescent molecules,” Xu said. “These emission patterns can be regarded as random observations at various axial positions, sampled from the underlying 3D point-spread function (PSF) describing the shapes of these emission patterns at different depths, which we aim to retrieve.”

The researchers demonstrated their method, named in situ PSF retrieval (INSPR), across a range of cellular and tissue architectures, from mitochondrial networks and nuclear pores in mammalian cells to amyloid-β plaques and dendrites in brain tissues and elastic fibers in developing cartilage of mice.

“This advancement expands the routine applicability of superresolution microscopy from selected cellular targets near coverslips to intra- and extracellular targets deep inside tissues,” researcher Donghan Ma said. “This newfound capacity of visualization could allow for better understanding for neurodegenerative diseases such as Alzheimer’s, and many other diseases affecting the brain and various parts inside the body.” Professor Sarah Calve said the technology is a step forward in regenerative therapies to help promote repair within the body.

The researchers are looking for partners to commercialize their technology. For more information, contact Dipak Narula at the Purdue Research Foundation Office of Technology Commercialization at dnarula@prf.org.

The research was published in Nature Methods (www.doi.org/10.1038/s41592-020-0816-x).

Tool from Purdue researchers allows visualization of nanoscale structures inside whole cells and tissues. It could allow for better understanding for diseases affecting the brain and regenerative therapies. Courtesy of Purdue University.