Authors: Mohammed A. Al-Qadasi, Samantha M. Grist, Matthew Mitchell, Karyn Newton, Stephen Kioussis, Sheri J. Chowdhury, Avineet Randhawa, Yifei Liu, Piramon Tisapramotkul, Karen C. Cheung, Lukas Chrostowski, and Sudip Shekhar
Abstract
Decentralized diagnostic testing that is accurate, portable, quantitative, and capable of making multiple simultaneous measurements of different biomarkers at the point-of-need remains an important unmet need in the post-pandemic world. Resonator-based biosensors using silicon photonic integrated circuits are a promising technology to meet this need, as they can leverage (1) semiconductor manufacturing economies of scale, (2) exquisite optical sensitivity, and (3) the ability to integrate tens to hundreds of sensors on a millimeter-scale photonic chip. However, their application to decentralized testing has historically been limited by the expensive, bulky tunable lasers and alignment optics required for their readout. In this work, we introduce a segmented sensor architecture that addresses this important challenge by facilitating resonance-tracking readout using a fixed-wavelength laser. The architecture incorporates an in-resonator phase shifter modulated by CMOS drivers to periodically sweep and acquire the resonance peak shifts as well as a distinct high-sensitivity sensing region, maintaining high performance at a fraction of the cost and size. We show, for the first time, that fixed-wavelength sensor readout can offer similar performance to traditional tunable laser readout, demonstrating a system limit of detection of 6.1 x 10-5 RIU as well as immunoassay-based detection of the SARS-CoV-2 spike protein. We anticipate that this sensor architecture will open the door to a new data-rich class of portable, accurate, multiplexed diagnostics for decentralized testing.
Fig. The novel segmented sensor architecture permits fixed-wavelength resonator readout. (A) (i) Sensor transmission spectrum shifts reproducibly with phase shifter voltage, as depicted by monitoring the resonance peak position at 0.1 V steps between 0 and 1 V, with 15 spectra measurements plotted for each voltage step. (ii) A spectrogram (each column of the image depicts a reading of the resonator’s transmission spectrum, measured using a TLS with optical intensity plotted on a colour scale), visualizing the resonance shift with voltage from an example voltage sweep. (iii) A quadratic fit to two replicate voltage sweeps (λ = 0.05097 V2 + 1310.091 nm, R2=0.9955), used to measure the sensor’s response to phase shifter voltage. The shaded region denotes the 95% confidence interval of the fit. (B) (i) The pulse density of the PDM driving signal used to modulate the sensor-tuning phase shifter, the corresponding analog voltage, and the raw transmission photocurrent waveform in response to the PDM-driven sensor tuning, depicting the raw data showing the (nonlinear with voltage) resonance peaks. (ii) Linearized readout waveform with regions of uncertainty and probability density function of the resonance peak shifts during an air-clad sensor measurement. (iii) Converting fixed-wavelength readout data to phase shift and equivalent resonance wavelength permits quantification of the resonator’s quality factor at 36,100 for this example spectrum and a mean and standard deviation of 37,200 ± 5900 across 4 replicate chips.
Selected Figure
Keywords: resonator biosensors; fixed-wavelength sensor; SARS-CoV2; bubble trap
arXiv 2024