Hybrid supramolecular/plasmonic switches as luminescence sensors and watermarkers – SupraSwitch

First, we will explore a number of stimuli-responsive molecules, going from simple host/guest interactions to orthogonal oligopeptide scaffolds. Their comparison will allow us to assess the versatility of supramolecular interactions as a mean to tune nanoparticle/fluorophore distance and to identify the most efficient molecular scaffolds and stimuli. Second, we will use recent advances in nanofabrication to fabricate well-defined and tunable nanostructured surfaces. Third, we will master surface functionalization with a control over non-specific interactions and surface coverage, in order to maximize luminescence modulation. Fourth, the direct access to a toolbox of characterization techniques (fluorescence, electrochemistry, AFM, QCM-D), including their in situ coupling, will allow us to fully characterize nanoparticle/fluorophore interactions and to maximize the amount of studied stimuli (electrochemistry, light, temperature). Finally, our expertise in luminescence and microfluidics will allow us to assess the performance of the developed switches as surface-confined optical sensors.

The first promising results have been obtained for hybrid systems based on thermosensitive polymers such as pNIPAM. We have shown that the fluorescence can be reversibly modulated by changing the distance between the nanoparticle and the fluorophores.

Once our systems are characterized in solution, we will study the modulation of fluorescence at nanostructured surfaces. These results will allow us to demonstrate that the developed strategy is compatible with various plasmonic nanostructures (including planar surfaces) and can be adapted to different external stimuli. Finally, by proposing an example of application (sensor or optical nano-probe), we will demonstrate that this approach has an important potential for nanotechnologies, in particular for chemical and biological sensing where multifunctional detection of fluorescence is needed at the nanoscale.

The results obtained for the thermoresponsive system has been submitted to an international journal (Journal of Physical Chemistry C).

One of the current challenges of applied plasmonics is to control the molecular configuration around nanostructures as a promising route to drive their functionality. The goal of SupraSwitch is to couple metal nanoparticles (Me NPs) with fluorophores and to achieve distance control between them using stimuli-responsive molecules like ß-cyclodextrin/guest and poly(N-isopropylacrylamide). These switches are expected to present wide modulation of luminescence (up to several orders), because its quenching and enhancement depend supra-linearly on the NP/fluorophore distance. The proposed switches will feature i) multiple-stimuli responsiveness, ii) external control, iii) fast and reversible response, compatibility with iv) a wide array of fluorophores and v) surface confinement. These properties should extend current applications of dynamic plasmonics from solution-based bio-diagnostics to intelligent nanomaterials for surface-confined sensing or watermarking. To achieve this ambitious goal, we will use our complementary expertise in organic synthesis, supramolecular interactions, surface chemistry, nanofabrication and physico-chemical characterization and know-how in stimuli-responsive systems and luminescence. Building upon this unique ensemble of skills, our research program aims to achieve several crucial steps. First, we will explore a number of stimuli-responsive molecules, going from simple host/guest interactions to orthogonal oligopeptide scaffolds and branched polymers. Their comparison will allow us to assess the versatility of supramolecular interactions as a mean to tune NP/fluorophore distance and to identify the most efficient molecular scaffolds and input/output combinations. Second, we will use recent advances in bottom-up nanofabrication, such as block-polymer micelle nanolithography, to fabricate well-defined and tunable plasmonic surfaces at low cost and high throughput. Third, we will master surface functionalization with a control over non-specific interactions and surface coverage, in order to maximize luminescence modulation. Fourth, the direct access to a toolbox of characterization techniques (fluorescence, electrochemistry, AFM, ellipsometry), including their in situ coupling, will allow us to fully characterize NP/fluorophore interactions and to maximize the amount of studied inputs (electrochemistry, light, temperature). Finally, our expertise in luminescence and microfluidics will allow us to assess for the first time the performance of the supramolecular/plasmonic switches as surface-confined optical sensors and watermarkers. SupraSwitch thus represents a multidisciplinary research project, involving both fundamental and technical aspects, with a high degree of innovative applicative outcomes in the fields of materials sciences and nanotechnology.