Sensing: a unified perspective for integrated photonics Chemical detection Environmental monitoring Process control Warfighter protection Biological sensing Drug discovery Food safety Medical diagnosis
The team Prof. Kathleen Richardson Prof. Igor Luzinov Prof. Clara Dimas Prof. Kenneth Crozier Dr. Mark Allen Dr. Vishal Vaidya
From components to functions: multi-functional planar integration Photonic integration holds the promise to resolve the most challenging issues in chem-bio sensing
Optical resonators are extremely sensitive to complex refractive index variations Complex refractive index variations: Change of the index of refraction creates a resonant wavelength shift Index of refraction Absorption coefficient Introduction of optical absorption leads to extinction ratio change Information regarding index of refraction and absorption change can be simultaneously extracted Detection limit: 10-7 index change, 0.005 db/cm absorption
Material property requirements for chemical and biological sensing Chemical sensing IR absorption spectroscopy Biological sensing Resonator refractometry Very low infrared material attenuation (< 0.01 db/cm) Low scattering loss after thermal reflow High refractive index for compact design and on-chip coupling Si-backend-compatible processing for monolithic integration Chemical and biological stability & compatibility Mid-infrared transparency Near-infrared transparency Moderate positive thermooptic coefficient (~ 10-5 K -1 )
Chalcogenide glasses (ChG s): Amorphous compounds of chalcogens (S, Se and Te) covalently bonded to other metal or non-metal elements (Ge, Ga, As, Sb etc.)
Glass resonators are fabricated on silicon via a CMOS-backend compatible lift-off process Lift-off process flow Resist coating UV exposure on a 500 nm i-line stepper Development Glass thermal evaporation Lift-off Si-CMOS-compatible lift-off fabrication of low-loss planar chalcogenide waveguides, Opt. Express 15, 11798 (2007). Single-source evaporation Ge 23 Sb 7 S 70 /As 2 S 3 As 2 S 3 Microdisk Leverage on standard silicon- CMOS tools Non-composition specific Loaded cavity Q up to 5 10 5
Cavity-enhanced IR spectroscopy achieves high sensitivity and small footprint simultaneously Single-pass spectrophotometer* Cavity-enhanced spectroscopy Source Optical path length: L Lambert-beer s law: Trade-off resolved: small footprint & high sensitivity attained simultaneously! * Even in the case of ATR IR spectroscopy, the effective optical path length is still no more than the physical length of an ATR crystal
The optofluidic resonator features a 3-fold sensitivity improvement over a waveguide sensor, and the physical length is reduced 40x Ge-Sb-S waveguide sensor Detection limit: 0.005 cm -1 Corresponding to sub-ppm level sensitivity Optofluidic Ge-Sb-S resonator 40x smaller: significantly cheaper and 10x more sensitive! 2 cm Fabrication Cavity-enhanced and testing infrared of absorption planar chalcogenide in planar chalcogenide waveguide integrated glass resonators: microfluidic experiment sensor, Opt. & analysis, Express 15, IEEE 2307 J. Lightwave (2007). Technol. 27, 5240-5245 (2009).
Polymer coatings for chalcogenide glasses Objectives: Strategy: Enhance evanescent wave sensor respond to analyte of interest Approach: Create a polymer layer on top of glass resonators able to selectively bind analyte of interest Grafting of the polymer layer bearing chemical moieties able to react reversibly with the analyte Polymer grafting Analyte ChG waveguide Change of the enrichment layer thickness and refractive index
Responses from multiple coatings can be used to significantly enhance specificity Species 1 Coating 1 Coating 2 Coating 3 The characteristic fingerprint response can be used to distinguish likedstructured molecules
The strong photon-matter interaction in integrated high-q optical resonators make them ideal for biological sensing WGM resonance in 15 min Detection of refractive index change induced by surface binding of biological molecular species: proteins, nucleic acids, virus particles
We demonstrate chalcogenide glass resonators for sensitive biomarker detection at clinically relevant concentrations Prostate specific antigen (PSA) Clinically verified screening test for prostate cancer > 4 ng/ml in blood indicates elevated risk of cancer Typical ELISA limit of detection (LOD): 0.2 ng/ml Our demonstrated LOD (1 st generation): 0.05 ng/ml Sensitive prostate specific antigen detection using high-q chalcogenide glass resonators, to be submitted.
Integration enables multi-channel detection Laser Photodetectors Fluid flow
Integration enables multi-channel detection Laser Photodetectors Fluid flow
Photonic smart sensor chip The Holy Grail of ultrasensitive detection: Isolation of a single molecule at the active sensing volume
Cavity field enhancement for trapping: the solution to molecular trapping & detection QD s Viruses Molecules Resonant cavity trapping MEMS Free-space trapping Cells A. Rahmani et al., Opt. Express 14, 6353-6358 (2006). M. Barth et al., Appl. Phys. Lett. 89, 253114 (2006). S. Arnold et al., Opt. Express 17, 6230-6238 (2009). S. Lin et al., Opt. Lett. to be published. Evanescent optical trapping
One cavity too crowded for two molecules Selective trapping of a single bead from an ensemble of particles Single molecule detection Single quantum dot devices J. Hu et al., Optical trapping of nanoparticles in resonant cavities, submitted to Phys. Rev. Lett.
Optical trapping of particles on a micro-ring resonator Optically assisted molecular diffusion: rapid response, high sensitivity S. Lin et al., Optical trapping using planar ring resonators, FiO 2009 Postdeadline paper PDPC8
Detection techniques Components Functionalities Photonic integration will ultimately enable the paradigm-shifting scaling law towards higher sensitivity, better resolution, and improved selectivity for sensing.