Label-free detection of the IL-6 and IL-8 interleukines through monolithic silicon photonic chips and simultaneous dual polarization optics

•A Si microphotonic chip with ten monolithically integrated broad-band Mach-Zehnder interferometers and an equal number of light sources.•The Si microphotonic chip is employed for the label-free and multiplexed detection of biomarkers.•The concentration of two proteins of the cytokine family, the IL-6 and the IL-8 interleukins, was determined.•The refractive index of the two interleukins is measured to be 1.38±0.01 by employing the dual polarization feature of the microphotonic chip.