06 October 2017 Plasmonic Antennas on the Realm of Biology

Photonic antenna arrays reveal nanodomains in biological membranes

Nanoscale dynamics on biological membranes resolved with photonic antennas in ACS Nano and Nano Letters Biological membranes are highly complex in terms of composition, organization and dynamics. Key mechanistic understanding of how biological membranes control the spatiotemporal organization of their molecular constituents depends on our ability to observe these events with spatial resolution on the molecular levels and temporal resolution in the micro-second range. Researchers Pamina Winkler and Raju Regmi working in the Single Molecule Biophotonics group led by ICREA Professor at ICFO Maria Garcia Parajo have exploited photonic antenna arrays to dynamically visualize biological membranes with 10 nm spatial resolution and microsecond time resolution. The work performed in collaboration with the Fresnel Institute and the EPFL has been recently published in ACS Nano and Nano Letters and carried out under the EU FP7 framework project NanoVista - Photonic Antennas for Biology.

Photonic nanoantennas can efficiently confine light into nanoscopic hotspots, enabling single-molecule detection sensitivity under biologically relevant conditions. However, most applications of photonic antennas have been restricted so far to the study of single molecules in solution since the extension of these approaches to live cell research has remained highly challenging. Researchers Pamina Winkler and Raju Regmi have now overcome current technological hurdles and succeeded in exploiting photonic antenna arrays to monitor the diffusion of individual lipids on mimetic biological membranes and intact living cells.

By using antennas of different gap sizes (down to 10nm in size) and in combination with fluorescence correlation spectroscopy, the researchers revealed the existence of nanoscopic domains of lipids and cholesterol on biological membranes. These domains are as small as 10nm in size, and highly transient, with characteristics lifetimes around 100 microseconds. The existence of such nanodomains in living cells, also known as lipid rafts, have been predicted theoretically and through stochastic simulations, but until now, never observed experimentally due to their small size and transient character.

Lipid rafts play a crucial role in many cellular processes that include signal transduction, protein and lipid sorting, and immune response among others. Understanding their formation, biophysical properties and relating their structure to their functional role are therefore of paramount interest. Importantly, these two papers underscore the high potential of photonic nanoantennas to interrogate the nanoscale heterogeneity of native biological membranes with ultrahigh spatiotemporal resolution.