MULTI-PGNAS · Multifunctional Photothermal Gold Nanoarrays for Cellular Manipulation

Multifunctional photothermal gold nanoarrays for cellular manipulation

The cell, as the smallest structural and functional unit of all living organisms uses specific transmembrane receptors, the integrins, to bind its environment, the Extracellular matrix (ECM), in order to mediate adhesion and intracellular signalling activities. Control over these binding-sites represents, on the one hand, a versatile way to tailor in vitro the internal cell machinery that regulates cell spreading and migration and on the other hand, a tool to trigger attachment / detachment for cell manipulation and transport in microfluidic channels and lab-on-chip systems. The fellow Dr J. Polleux mainly worked with nanosized gold, an ideal system to engineer devices with a wide range of potential biological applications. The ability of gold to strongly absorb laser radiations that get converted into heat, the so called photothermal effect, has proven to be a promising tool for the selective destruction of cancerous cells and for the molecular dissociation of DNA strands. To generate photothermal nanostructured surfaces, hexagonally-organised gold patterns made of 25 nm particles were prepared on transparent glass coverslips via micellar nanolithography and chemically modified for cell culture application upon PEG passivation of the glass and immobilisation of ECM-mimetics on gold. Because integrins exclusively bind to biofunctionalised nanogold, irradiating well-defined areas with a green laser beam appeared as an original strategy to generate heat nano-locally in order to prevent further cell attachment and to induce release of integrins and cells from these hotter zones. By simply adjusting the laser power, the released thermal energy can be tuned. With an increase of 11 degrees Celsius (or 40 mW/cm2) for 30 s, cell death occurred through partial retraction of the cell membrane followed by permanent rounding, whereas a raise of 8 degrees Celsius (30 mW/cm2) causes faster detachment of elongated adhesive sites (the filopodia) and retraction of broad ones (the lamellipodia) leading to temporary cell rounding without lethal effects. Importantly, cell spreading is instantly re-initiated when the laser is stopped. In collaboration with Dr G. Baffou (ICFO, Spain), it was found from simulations that a continuous wave laser generates a diffuse heat profile of gold nanopatterns, whereas a 10-15 s pulsed laser induces heat confinement at the nanoscale, which is a critical requirement for targeting single transmembrane receptor without disturbing the rest of the cell. During the last two years, the MULTI-PGNAs project grew up while integrating knowledge and savoir-faire from surface chemistry, photothermal physics, and cell biology. To strengthen the fellow's expertise in bioengineering, the establishment of collaborations with physicists and biologists within the EU was crucial to address several fundamental and experimental critical points. Because the organisation, release and transport of entities like cells or biomolecules are the central goals driving the development of lab-on-chip systems and high throughput biological devices, this project might not get a direct impact on the society, but it could find its place as a new tool for fundamental research. For instance, companies like Zeiss and Thermo Fisher Scientific offer new tools based on contact-free cell manipulation with commercially available products like the PALM microscope system and UpCellTM Surfaces, respectively. Furthermore, a better understanding in controlling the production of heat confined at the nanoscale can open new avenues for other fields of research like nanochemistry, nanocatalysis, drug release and microfluidics while stimulating new pluridisciplinary collaborative exchanges within the EU. A page on the Max Planck Institute's website is dedicated to the fellow's research activity with a section advertising the MULTI-PGNAs project. A logo was designed for this occasion and more information are available at http://www.mf.mpg.de/spatz/polleux.

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