Label-free optical biosensing at femtomolar detection limit

Detection of target biomolecules has attracted a great deal of interest lately particularly when label-free techniques are involved as they can be much faster than label needing ones. As yet state-of-the-art high throughput quantitative determinations are in the sub-picomolar regime. This study is focused on the development of a highly performing biosensor based on a biofunctionalized photonic crystal (PhC) immobilized on the tip of an UV-vis optical fiber. The PhC is easily realized by self-assembly of polystyrene nano-beads on the optical fiber tip. The device performance level has been evaluated using the highly stable streptavidin-biotin binding. To this end a convenient streptavidin physisorption immobilization strategy directly on the polystyrene beads surface is herein proposed. Eventually, real time detection of biotinylated Bovine Serum Albumin (bBSA) molecules has been achieved at limit of detection (LOD) as low as 1.5 fM. Functionalized PhCs are therefore proven to be a powerful tool for the detection of biological species, down to femtomolar detection limit.