Molecular weight dependence of a whispering gallery mode biosensor
M. Noto, M. Khoshsima, D. Keng, I. Teraoka, V. Kolchenko, and S. Arnold
Appl. Phys. Lett. 87, 223901 (2005)

We report on molecular weight dependence measurements for an optical resonance biosensor. A
dielectric microparticle is evanescently coupled with an optical fiber for the resonance stimulation,
and a shift of the resonance wavelength is measured to monitor protein monolayer formation on the
microparticle surface. Wavelength shifts for proteins over two orders of magnitude in molecular
weight are measured. We show that the shift is proportional to molecular weight to the one-third
power. Our result demonstrates that the optical resonance biosensor provides protein size
information upon detection. This molecular weight dependency differentiates optical resonance
sensing from electrical detection using field-effect transistors.