08 May 2015 Thousands of nanoantennas to enlighten living cells

Antenna arrays fully compatible with live cell research at the nanometer scale

Large-scale arrays of photonic antennas for nanoscale dynamics in living cell membranes. A recent study carried out in collaboration with researchers of the EPFL and Thomas van Zanten, Mathieu Mivelle, and Carlo Manzo in the Single Molecule Biophotonics group led by ICREA Professor at ICFO Maria Garcia-Parajo, has succeeded in fabricating hundreds of thousands of photonic antennas to measure for the first time the nanoscale dynamics of individual molecules in living cells. This work constitutes a major breakthrough in our ability to study biological processes in living cells at the truly nanometer scale and in real-time. The work, supported by EU project NanoVista, was published in Nano Letters.

Photonic antennas amplify and confine optical fields at the nanoscale. As such, they break the sample concentration limit by overcoming diffraction, allowing the detection of individual molecules in solution at physiologically relevant concentrations (μM range). Unfortunately, extending this technology to live cell research is challenged by the difficulty of working with living cells and their inherent variability, requiring the development of large-scale antenna arrays while maintaining nanoscale control of their geometries. Now, EPFL researchers have developed a novel blurring-free stencil lithography-based patterning technique that relies on localized reactive ion etching to fabricate large arrays of nanoaperture-based antennas. The work demonstrates the reproducible fabrication of chips containing 12-antenna arrays for a total of over 400 000 antennas, with features controlled down to 20 nm. To validate their applicability on living cells, ICFO researchers used the antenna substrates as hotspots of localized illumination to excite fluorescently labeled lipids on living cell membranes. The high signal-to-background afforded by the antenna arrays allowed for the first time, the recording of single fluorescent bursts corresponding to the passage of freely diffusing individual lipids through hotspot excitation regions as small as 20 nm. Statistical analysis of burst length and intensity together with simulations demonstrate that the measured signals arise from the ultraconfined excitation region of the antennas.

The results of this joined collaboration establish that thru-stencil etching of metal nanostructures represents a cost-effective and scalable alternative for the fabrication of large arrays of photonic antennas fully compatible with life science applications. We foresee that these engineered substrates would become inexpensive, powerful tools to investigate the plasma membrane of living cells with nanoscale resolution at endogenous expression levels.

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