Multilayer Coatings for Bloch Surface Wave Optical Biosensors

Sensors using surface plasmon resonance (SPR) are established as the method of choice in label-free optical biosensing. Their sensitivity for small refractive index changes at the surface originates from the enhanced evanescent field at the surface of a thin metal layer. However, the small number of well-suited metals (Ag, Au) with fixed optical constants limits a further refinement of the SPR performance in terms of dispersion and resonance width. An alternative can be found in Bloch surface waves (BSW) sustained at specially designed dielectric multilayer stacks with low absorption losses. Due to the low losses an enormous narrowing of the resonance is obtained, promising the reduction of the detection limit for such a label-free sensor. Furthermore, fluorescence enhancement caused by near field effects can also be exploited and, by engineering the BSW dispersion, both detection schemes can be combined. This paper illustrates the basic principles of BSW generation by designing thin dielectric multilayer stacks and the vacuum deposition of these coatings on disposable polymer biochips. In addition, the measurement and analysis of the Bloch resonance shift caused by the interaction of biomolecules at extremely small concentrations is presented.