Abstract
Protein detection and characterization based on Broad-band Mach-Zehnder Interferometry is analytically outlined and demonstrated through a monolithic silicon microphotonic transducer. Arrays of silicon light emitting diodes and monomodal silicon nitride waveguides forming Mach-Zehnder interferometers were integrated on a silicon chip. Broad-band light enters the interferometers and exits sinusoidally modulated with two distinct spectral frequencies characteristic of the two polarizations. Deconvolution in the Fourier transform domain makes possible the separation of the two polarizations and the simultaneous monitoring of the TE and the TM signals. The dual polarization analysis over a broad spectral band makes possible the refractive index calculation of the binding adlayers as well as the distinction of effective medium changes into cover medium or adlayer ones. At the same time, multi-analyte detection at concentrations in the pM range is demonstrated.
Highlights
Chip active optical components along with the interferometric sensing elements has so far hindered the proliferation of such devices
The light emitting devices (LEDs) are coupled to co-integrated monomodal waveguides that are shaped as Mach-Zehnder interferometers (MZIs) through mainstream silicon technology
By recording the entire spectrum emitted by the chip, wavelength interrogation is possible over a broad spectral range with substantial benefits in simultaneous dual polarization analysis and, in the limit of detection
Summary
The lower detection limit for TE despite the worse performance in terms of the δNs /λ ratio compared to TM is a result of the higher signal (A) and sharper resonance peak (δΜ) in the Fourier transform domain. The detection limits of the assay calculated as the concentration corresponding to + 3SD of the blank sensors values (sensors coated with BSA) is 32 pM when the TE phase shifts are used for the preparation of calibration curve and 40 pM when the TM phase shifts are taken into account This was due to higher variation of TM phase shifts obtained for the blank sensors as compared to respective TE phase shifts variations. The coefficient of variation (CV) of the values obtained from the different interferometers of the same chip was less than 10%, whereas the CVs of the responses obtained from different chips run in the same day or in different days did not exceed 12 and 15%, respectively
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