Silicon optical microring resonators (MRRs) are sensitive devices that can be used for biosensing. We present a novel biosensing platform based on the application of polyelectrolyte (PE) layers on such MRRs. The top PE layer was covalently labeled with biotin to ensure binding sites for antibodies via a streptavidin-biotin binding scheme. Monitoring the shift in the microring resonance wavelength allows real-time, highly sensitive detection of the biomolecular interaction.