Microwave transmission line dielectric probe to detect biomolecular surface interactions

A probe was developed to detect biomolecular binding events at a liquid-solid interface in the microwave regime in real time and without using fluorescence labels. The probe consists of a coplanar transmission line (CTL) fabricated on a glass slide that can detect dielectric changes in close proximity of the interface. The CTL geometry concentrates the electric flux density in the gap region between the signal and ground electrodes and makes it very sensitive to permittivity changes at the liquid-solid interface. The probe operation was demonstrated by immobilizing protein A on the glass surface and detecting rabbit IgG molecules in a flow channel. The sensitivity was conservatively estimated to be 100 pg/mm².