Nanoplasmonic imaging reveals real-time protein secretion


April 11, 2023

(Nanowerk News) Cell secretions such as proteins, antibodies, and neurotransmitters play an important role in immune response, metabolism, and communication between cells. Understanding cell secretions is key to developing disease treatments, but current methods can only report the amount of secretions, without detailing when and where they were produced.

Now, researchers at the Bionophotonic Systems Laboratory (BIOS) in the School of Engineering and at the University of Geneva have developed a new optical imaging approach that provides a four-dimensional view of cell secretions in both space and time. By placing individual cells into microscopic wells in the nanostructured gold-plated chip, and then inducing a phenomenon called plasmonic resonance on the surface of the chip, they were able to map secretions as they are produced, while observing the shape and movement of cells.

Because it provides an unprecedentedly detailed view of how cells function and communicate, scientists trust their method, which was recently published in Natural Biomedical Engineering (“High throughput spatiotemporal monitoring of single cell secretions via plasmonic microwell arrays”), has “tremendous” potential for pharmaceutical development as well as fundamental research. Single cell microwell array Single cell microwell array. (Image: EPFL BIOS)

“A key aspect of our work is that it allows us to screen cells individually in a high-throughput manner. The collective measurement of the average response of many cells does not reflect their heterogeneity… and in biology, everything is heterogeneous, from immune responses to cancer cells. This is why cancer is so difficult to treat,” said BIOS head Hatice Altug.

One million sensing elements

The essence of the method of scientists is 1 cm2 a nanoplasmonic chip is made up of millions of pinholes, and hundreds of spaces for individual cells. The chip is made of a gold nanostructured substrate covered with a thin polymer mesh. Each chamber is filled with cell media to keep cells alive and healthy during imaging.

Cell secretions are like cell words: they spread dynamically in space and time to connect with other cells. Our technology captures major heterogeneity in terms of where and how far these ‘words’ travel,” said BIOS PhD student and first author Saeid Ansaryan.

The nanoplasmonics part comes thanks to a beam, which causes the gold electrons to oscillate. Nanostructures are engineered so that only certain wavelengths can penetrate them. When something – such as protein secretion – occurs on the surface of the chip to change the light that passes through it, the spectrum shifts. The CMOS (Complementary Metal Oxide Semiconductor) image sensor and LED translate this shift into intensity variations in the CMOS pixels.

“The beauty of our equipment is that the nano-holes scattered across the surface turn every dot into a sensing element. This allowed us to observe the spatial patterns of the proteins released regardless of cell position,” said Ansaryan.

This method has allowed scientists to glimpse two important cellular processes – cell division and cell death – and to study human donor B cells that secrete antibodies.

“We saw cell contents released during two forms of cell death, apoptosis and necroptosis. In the latter, content is released in asymmetric bursts, resulting in image marks or fingerprints. This has never been shown at the single cell level,” said Altug. Single cell on a chip Single cell on a chip. (Image: EPFL BIOS)

Screening for cell fitness

Because the method bathes cells in a nourishing cell medium, and does not require the toxic fluorescent labels used by other imaging technologies, the cells studied can be easily recovered. This provides great potential for use in the development of pharmaceutical drugs, vaccines, and other treatments; for example, to help researchers understand how cells respond to various therapies at the individual level.

“Since the amount and pattern of secretions produced by cells are proxies for determining their overall effectiveness, we can also envision an application of immunotherapy where you screen a patient’s immune cells to identify which are the most effective, and then colonize those cells, said Anshari.


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