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Hybrid Nanosystems in phospholipid membranes

Final Report Summary - HYMEM (Hybrid Nanosystems in phospholipid membranes)

We have developed a versatile photonic toolbox to analyze and manipulate biophysical and biochemical processes on the nanoscale and have accomplished their implementation to cell membranes and the interior of living cells. In particular, we have been exploiting the variety of feats that arise from the unique optical properties of plasmonic nanoparticles such as heating, optical forces for guiding, printing and controlling plasmonic nanosystems, self-assembly of plasmonic nano-architectures, plasmonically enhanced electromagnetic fields, nanoparticle tracking as well as thermophoretic effects for nanoscale optical manipulation and spectroscopy.

Notably, we have developed the methodology to precisely print, rotate and guide gold nanoparticles of various size and shape by means of light. A broad range of applications for manipulation and nanofabrication arise from this new technique, which has been demonstrated in a series of experiments on both organic films and biological membranes. The combination of optical force and plasmonic heating, for example, allowed us to print functionalized gold nanoparticles on top of living cells, control membrane permeability on the nanoscale, and even to inject individual particles across the membrane barrier. This new plasmonic technology is now established and ready-to-use for drug delivery, gene transfection, and optical voltage control of cells.

Self-assembly of plasmonic nanosystems for enhancing optical interactions and thus spectroscopic signals has been achieved by exploiting the unique possibilities of DNA origami technology. By this approach, the realization of nanosystems for enhancing Raman signals and precisely controlling dye quenching due to energy transfer close to gold nanoparticles was realized. Moreover, we could demonstrate the first surface-enhanced Raman spectroscopy (SERS) experiments on supported lipid membranes and introduced a new tool to perform plasmonically enhanced spectroscopy on living cells.

By tracking a single gold nanoparticle within an optical trap a so-called "nano-ear" could be demonstrated, which is capable of locally detecting fluidic motion and even acoustic signals with high sensitivity. This concept has been used for various biological applications such as the spectral characterization of the flagellar rotation dynamics of an individual bacterium. Combining the nano-ear concept with the gold nanoparticle cell injection technology allowed us to locally sense forces inside a cell with fN accuracy and to derive local intracellular viscosities of the immediate particle environment on a nano- to micron length scale. This opens up a range of unprecedented possibilities for local sensing of biological processes within cells with high resolution.

A further highlight of this project is the first demonstration of optically controlled elevation of a single plasmonic ‘Janus’-particle within an optical trap ("optical nanoparticle elevator"). Asymmetric heating of the particle in a focused laser beam results in a temperature gradient that induces a thermophoretic force. This force can be harnessed to optically control the elevation of the particle along the laser beam axis. We could show that the elevation cannot only be controlled optically but also chemically. By changing ion strengths in the solution, thermo-osmotic as well as thermo-electric forces can be separately controlled. This new technology paves the way to in vivo force measurements without the need of immobilizing nanoparticles on a substrate.

In summary, this ERC project has demonstrated and developed a series of novel nanophotonic concepts for direct use in cell studies and with high potential for biomedical applications.