Limits...
Silicon coupled-resonator optical-waveguide-based biosensors using light-scattering pattern recognition with pixelized mode-field-intensity distributions.

Wang J, Yao Z, Lei T, Poon AW - Sci Rep (2014)

Bottom Line: The sensing scheme is based on measurements in the spatial domain, and only requires exciting the CROW at a fixed wavelength and imaging the out-of-plane elastic light-scattering intensity patterns of the CROW.Based on correlating the light-scattering intensity pattern at a probe wavelength with the light-scattering intensity patterns at the CROW eigenstates, we devise a pattern-recognition algorithm that enables the extraction of a refractive index change, Δn, applied upon the CROW upper-cladding from a calibrated set of correlation coefficients.Our experiments using an 8-microring CROW covered by NaCl solutions of different concentrations reveal a Δn of ~1.5 × 10(-4) refractive index unit (RIU) and a sensitivity of ~752 RIU(-1), with a noise-equivalent detection limit of ~6 × 10(-6) RIU.

View Article: PubMed Central - PubMed

Affiliation: Photonic Device Laboratory, Department of Electronic and Computer Engineering, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong.

ABSTRACT
Chip-scale, optical microcavity-based biosensors typically employ an ultra-high-quality microcavity and require a precision wavelength-tunable laser for exciting the cavity resonance. For point-of-care applications, however, such a system based on measurements in the spectral domain is prone to equipment noise and not portable. An alternative microcavity-based biosensor that enables a high sensitivity in an equipment-noise-tolerant and potentially portable system is desirable. Here, we demonstrate the proof-of-concept of such a biosensor using a coupled-resonator optical-waveguide (CROW) on a silicon-on-insulator chip. The sensing scheme is based on measurements in the spatial domain, and only requires exciting the CROW at a fixed wavelength and imaging the out-of-plane elastic light-scattering intensity patterns of the CROW. Based on correlating the light-scattering intensity pattern at a probe wavelength with the light-scattering intensity patterns at the CROW eigenstates, we devise a pattern-recognition algorithm that enables the extraction of a refractive index change, Δn, applied upon the CROW upper-cladding from a calibrated set of correlation coefficients. Our experiments using an 8-microring CROW covered by NaCl solutions of different concentrations reveal a Δn of ~1.5 × 10(-4) refractive index unit (RIU) and a sensitivity of ~752 RIU(-1), with a noise-equivalent detection limit of ~6 × 10(-6) RIU.

Show MeSH
(a) Scanning-electron microscope image of the fabricated eight-element microring-based CROW. (b) Zoom-in-view image of an inter-cavity coupling region. (c) Schematic of the cross-sectional view of the optofluidic chip. (d) Schematic of the experimental setup. EDFA: erbium-doped fiber amplifier, PC: polarization controller, PBS: polarized beam splitter, LWD OB: long-working-distance objective lens, OB: objective lens, PD: photodetector.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4269880&req=5

f4: (a) Scanning-electron microscope image of the fabricated eight-element microring-based CROW. (b) Zoom-in-view image of an inter-cavity coupling region. (c) Schematic of the cross-sectional view of the optofluidic chip. (d) Schematic of the experimental setup. EDFA: erbium-doped fiber amplifier, PC: polarization controller, PBS: polarized beam splitter, LWD OB: long-working-distance objective lens, OB: objective lens, PD: photodetector.

Mentions: Fig. 4(a) shows the scanning-electron microscope (SEM) picture of the fabricated 8-element microring-based CROW. The racetrack microring comprises two half circles with a radius of 6.5 μm and two straight waveguides with an interaction length of 3.5 μm and a designed coupling gap spacing of 100 nm. We design the inter-cavity coupling in the strong-coupling regime in order to obtain a wide inhomogeneously broadened transmission band. This enables a large sensing dynamic range Δnd and a wide spectral range for choosing an arbitrary probe wavelength. Fig. 4(b) shows a representative zoom-in-view image of the inter-cavity coupling region.


Silicon coupled-resonator optical-waveguide-based biosensors using light-scattering pattern recognition with pixelized mode-field-intensity distributions.

Wang J, Yao Z, Lei T, Poon AW - Sci Rep (2014)

(a) Scanning-electron microscope image of the fabricated eight-element microring-based CROW. (b) Zoom-in-view image of an inter-cavity coupling region. (c) Schematic of the cross-sectional view of the optofluidic chip. (d) Schematic of the experimental setup. EDFA: erbium-doped fiber amplifier, PC: polarization controller, PBS: polarized beam splitter, LWD OB: long-working-distance objective lens, OB: objective lens, PD: photodetector.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4269880&req=5

f4: (a) Scanning-electron microscope image of the fabricated eight-element microring-based CROW. (b) Zoom-in-view image of an inter-cavity coupling region. (c) Schematic of the cross-sectional view of the optofluidic chip. (d) Schematic of the experimental setup. EDFA: erbium-doped fiber amplifier, PC: polarization controller, PBS: polarized beam splitter, LWD OB: long-working-distance objective lens, OB: objective lens, PD: photodetector.
Mentions: Fig. 4(a) shows the scanning-electron microscope (SEM) picture of the fabricated 8-element microring-based CROW. The racetrack microring comprises two half circles with a radius of 6.5 μm and two straight waveguides with an interaction length of 3.5 μm and a designed coupling gap spacing of 100 nm. We design the inter-cavity coupling in the strong-coupling regime in order to obtain a wide inhomogeneously broadened transmission band. This enables a large sensing dynamic range Δnd and a wide spectral range for choosing an arbitrary probe wavelength. Fig. 4(b) shows a representative zoom-in-view image of the inter-cavity coupling region.

Bottom Line: The sensing scheme is based on measurements in the spatial domain, and only requires exciting the CROW at a fixed wavelength and imaging the out-of-plane elastic light-scattering intensity patterns of the CROW.Based on correlating the light-scattering intensity pattern at a probe wavelength with the light-scattering intensity patterns at the CROW eigenstates, we devise a pattern-recognition algorithm that enables the extraction of a refractive index change, Δn, applied upon the CROW upper-cladding from a calibrated set of correlation coefficients.Our experiments using an 8-microring CROW covered by NaCl solutions of different concentrations reveal a Δn of ~1.5 × 10(-4) refractive index unit (RIU) and a sensitivity of ~752 RIU(-1), with a noise-equivalent detection limit of ~6 × 10(-6) RIU.

View Article: PubMed Central - PubMed

Affiliation: Photonic Device Laboratory, Department of Electronic and Computer Engineering, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong.

ABSTRACT
Chip-scale, optical microcavity-based biosensors typically employ an ultra-high-quality microcavity and require a precision wavelength-tunable laser for exciting the cavity resonance. For point-of-care applications, however, such a system based on measurements in the spectral domain is prone to equipment noise and not portable. An alternative microcavity-based biosensor that enables a high sensitivity in an equipment-noise-tolerant and potentially portable system is desirable. Here, we demonstrate the proof-of-concept of such a biosensor using a coupled-resonator optical-waveguide (CROW) on a silicon-on-insulator chip. The sensing scheme is based on measurements in the spatial domain, and only requires exciting the CROW at a fixed wavelength and imaging the out-of-plane elastic light-scattering intensity patterns of the CROW. Based on correlating the light-scattering intensity pattern at a probe wavelength with the light-scattering intensity patterns at the CROW eigenstates, we devise a pattern-recognition algorithm that enables the extraction of a refractive index change, Δn, applied upon the CROW upper-cladding from a calibrated set of correlation coefficients. Our experiments using an 8-microring CROW covered by NaCl solutions of different concentrations reveal a Δn of ~1.5 × 10(-4) refractive index unit (RIU) and a sensitivity of ~752 RIU(-1), with a noise-equivalent detection limit of ~6 × 10(-6) RIU.

Show MeSH