Hybrid Biosensors: Detecting femto Molar protein concentration

31.10.2012, 14:22

Newsletter 5

Measuring proteins in real-time down to fM solution concentration levels, corresponding to only a few thousand of protein molecules, has been demonstrated for the first time using a hybrid photonic-plasmonic whispering gallery mode (WGM) biosensor. Its unprecedented sensitivity is due to optical trapping of proteins at highly sensitive plasmonic hotspots. WGM sensors derive their sensitivity from the use of high quality-factor (Q-factor) optical resonances to monitor wavelength shift signals upon binding of biomolecules or nanobeads to the resonator surface. Even a single virus can be detected. In collaboration with Melik Demirel (Penn State), the Vollmer group is now proposing an alternative concept overcoming these problems. The idea is to trap protein molecules optically at the sites of plasmonic field enhancements in a randomly nano-textured gold layer. The stable integration of the microsphere WGM biosensor with a wetted gold layer is critical for detecting with ultra-high sensitivity. The silica microsphere cavity remains fixed on the Au layer. The Q-factor of the microsphere drops slightly but is still in the range of 100. After adding microliter volumes of bovine serum albumin solution an unexpectedly large and significant wavelength shift was observed.


Contact: frank.vollmer(at)mpl.mpg(dot)de
Group: Biophotonics and Biosensing (MPRG)
Reference: J. Biophotonics 5, 629–638 (2012)