The aim of the CAFEMICRO project is to develop an ultra-sensitive fluorescence sensor using the enhancement of the fluorescence  in the gaps of a metallic nanostructure. This nanostructure will be created by the dielectrophoretic force produced using micro-electrodes in a microfluidic system, acting on anisotropic gold nanoparticles. The amplitude of the electric field between the electrodes, the shape and chemistry of the nano-particles are all issues to be monitored to obtain reproducible and effective structures. The analysis of the intrinsic luminescence of the gold particles by correlation spectroscopy and spectral measurements will allow  monitoring of the particle motion and nanoparticle pattern formation. Before trapping occurs, the analysis of single particle motion will bring information on the temperature distribution around the electrodes and on electrokinetics effects, with a submicronspatial resolution. Beyond addressing basic questions of interest for applications in microfluidics, we can illustrate the potential application of such a sensor by two examples: the highly sensitive detection of auto-fluorescent biological molecules and the ultra-sensitive detection of pollutants. By further exploiting the surface functionalization  of gold, the metallic structures can be transformed into controlled platforms for molecular recognition enlarging the scope for sensing in chemistry and biology. An originality of the CAFEMICRO sensor is the possibility to switch it on and off by controlling the trapping field, thus avoiding a permanent perturbation of the other functions of the microfluidic system.

The success of the project relies on the synergy of the three research fields: microfluidics including dielectrophoresis, synthesis of nanoparticles, and single particle spectroscopy. Each of the three laboratories masters one of the topics, with complementary competences for SATIE and LAC on some spectroscopic methods. Past studies performed by SATIE and LAC have already pioneered fruitful interactions. Let us mention the complementary studies of the scattering and luminescence properties of metallic particles such as bipyramids or nanostars led by SATIE and LAC, or the measurement of the quantum yields of luminescence of monomers and dimers involving the three partners, SATIE, PPSM and LAC. Despite the current degree of expertise of each team, a new step must be taken to progress in the project. Specifically, the design and fabrication of microfluidic circuits by SATIE must be adapted to make them compatible with the single particle spectroscopy methods used at LAC. It will be necessary to maintain an efficient scientific communication between PPSM and the two other partners to define and then take advantage of the best suitable particles. These particles play a key role in the efficiency of the sensor.