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

Abstract A silicon microphotonic chip with ten monolithically integrated interferometers and an equal number of light sources is employed for the label-free and multiplexed detection of two proteins of the cytokine family. The chip implements broad-band Mach-Zehnder interferometry and is used for the detection of the IL-6 and IL-8 interleukins. The silicon transducer is made through mainstream silicon technology and integrates avalanche diode based white light LEDs and monomodal waveguides forming Mach-Zehnder interferometers. The light spectrum is modulated through the interferometer and the spectrally resolved interference fringes are monitored by a digital spectrometer. Biomolecular built-up on the sensing arm causes pattern shifts that are evaluated through Fourier Transform. The microsystem level set-up includes microfluidic components, direct contacting of the chip contact pads through spring loaded pins and alignment guides and a spectrometer. The dual polarization optics allows the simultaneous derivation of the TE and TM sensitivity plots and the calculation of the refractive indices of either protein.