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PhotoSmart Résumé de rapport

Project ID: 307800
Financé au titre de: FP7-IDEAS-ERC
Pays: Germany

Mid-Term Report Summary - PHOTOSMART (Photo-switching of smart surfaces for integrated biosensors)

The project PhotoSmart aims to master the first steps towards integrated biosensors with photo-switchable smart surfaces. The idea is to integrate an array of organic light emitting diodes (OLEDs) with a surface of immobilized molecular motor molecules. Such a surface is termed a “smart” surface as the surface properties may be adjusted automatically during operation. In order to demonstrate molecular switching with relatively low intensity OLEDs, losses at the surface need to be minimized and the intensity delivered to the surface needs to be maximized.

We employ azobenzene molecules as molecular motors as they may be switched with light reversibly between the trans and cis isomer. These two isomers differ markedly in their molecular geometries and electronic properties. In the first half of the project we implemented and compared three different immobilization methods for azobenzene molecules on dielectric surfaces (click chemistry, crosslinker applications, mussel-inspired adhesion methods with polydopamine). Dielectric surfaces were chosen as they have significantly lower absorption losses than metal surfaces. All three types of functionalization processes were tested on different types of dielectric surfaces (glass, PDMS, SiO2, ZnO, TiO2) as well as on nanostructured surfaces. The polydopamine-based process was found to be most suitable for application as it is a facile process that does not damage an underlying nanostructure.

An on-chip light source for molecular switching was realized employing blue OLEDs based on the fluorescent emitter DPvBi:BCzVBi. Switching from the cis to the trans state within 5 minutes was demonstrated for self-assembled monolayers (SAMs) of azobenzene molecules on a flat glass substrates. Light concentration at the surface was demonstrated using a periodically nanostructured surface (photonic crystal slab). For resonant excitation in both switching directions of the azobenzene we proposed and designed a compound grating structure with two superimposed grating periods of 180 nm and 220 nm. Using this approach we expect a further significant reduction of the switching time. The successful switching of the azobenzene-functionalized surfaces with OLEDs is the basis for the remainder of the project.

In the second half of the project switching demonstration of two types of smart surfaces for integrated biosensors is targeted. Firstly, the reversible switching of wettability between hydrophilic and hydrophobic in an integrated sensor will be investigated. Recently, we demonstrated for nanoporous hybrid-layer surfaces cast with polydopamine-assisted azobenzene-SiO2-nanoparticles a reversible change of contact angle by more than 40°. Next we target the controlled movement of droplets by local switching of the surface wettability using the integrated OLED light source. This system potentially allows for a microfluidic system that is completely programmable and does not rely on predefined channels.

Switchable surface adsorption of biomaterials excited with on-chip light sources is the second objective of the second half of the project. In the first half of the project we developed a compact readout system for imaging readout of biomolecular binding to dielectric surfaces. The overall system response was designed such that a change in the spectral resonance is converted into an intensity change that may be detected with a simple camera. Using this setup we measured the binding kinetics of several biomarkers to locally spotted functionalization sites. This approach has the particular advantage that the complete surface is captured simultaneously allowing for dynamic background subtraction.

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