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Resonant Photonic Biosensing

High-Q optical microresonators are excellent candidates for photonic sensing. These devices have been successfully used for detecting nanoparticles, biomolecules, gases, chemical compounds down to single nanoparticles and single molecules resolution. Three main mechanisms are used to detected particles and molecules that come into contact with microresonator: 1) Resonant frequency shift , 2) Quality factor degradation and 3) Resonant frequency splitting.
In our group we work on different aspects of resonant photonic biosensing using Whispering-Gallery and microring optical resonators. We study the theory of resonant photonic detection as well as fabrication of novel microresonator based sensors with new functionalities.

-A novel platform for high sensitivity photonic biosensing
With his colleagues Professor Ivory (Washington University) and Professor Han (UNM), Dr Hossein-Zadeh has developed a new integrated optofluidic
platfrom based on active nanochannels with resonant photonic sensors.  This patent pending technology combines nanofluidic amplification
and resonant photonic detection on a silicon platform compatible with CMOS technology. In 2012 this  technology has been lisceneced t
o Protomex
to develop a hand held biosesor unit for separating and detection of protein biomarkers in blood for the presence of heart, cancer and infectious diseases.

-Application of Dynamic Linenarrowing in Resonant Photonic Sensing 
We have proposed and demonstrated the dynamic operational mode and the resulting dynamic line-narrowing
as a method for enhancing the resolution and the detection limit of high-Q resonant optical sensors.Using silica
microtoroid as an experimental platform we demonstrate that dynamic line narrowing through thermo-optic effect
can significantly improve the detection limit in both resonant shift and resonance splitting operating modes.

*F. Liu, S. Lan and M. Hossein-Zadeh, "Application of dynamic line narrowing in resonant optical sensing”,
Optics Letters
, vol. 36, no. 22, pp. 4395-4397, Nov 2011.(Also appeared on Virtual Journal for Biomedical Optics (VJBO), vol. 7(1), Jan 2012)

-Mass sensing with optomechanical oscillator
We have demonstrated the application of optomechanical oscillator (OMO) as a high-resolution mass sensor.
The coupling between high-Q optical and mechanical modes of a single optical microcavity results in narrow
linewidth mechanical oscillation driven by the radiation pressure of the circulating optical power.The oscillation
frequency can be monitored upon detection of the modulated transmitted optical power;Therefore the optical wave
plays a dual role as the driving power and a sensitive probe. The narrow oscillation linewidth combined with sensitivity
of the mechanical resonance to mass changes, make OMO an excellent candidate for all-optical mass sensing.
Experimental results and theoretical analysis show that OMO can function as a compact, low-power mass sensor with sub-pg sensitivity.

*F. Liu, and M. Hossein-Zadeh, "Mass Sensing with Optomechanical Oscillation
,IEEE Sensors journal
, vol. 13, no. 1, pp. 146-147, Jan 2013.
*F. Liu, Seyedhamidreza Alaie, Zayd C. Leseman, and M. Hossein-Zadeh, "Sub-pg mass sensing and measurement with an optomechanical oscillator,
Optics Express, vol. 21,  no.17, pp. 19555-19567, Aug. 2013.

-Mid-IR WGM microresonators for breath monitoring
The unique characteristics of such WGM devices are particularly relevant for mid-IR (MIR) applications because of the stronger absorption of certain biomarkers in MIR  “molecular fingerprint” region. We have proposed and demonstrate a simple and reliable method for fabricating high-quality whispering-gallery mode (WGM) optical microresonators in “mid-IR relevant” low-loss ZrF4-BaF2-LaF3-AlF3-NaF (ZBLAN) glasses. Intrinsic quality factors of 10^7 have been demonstrated, providing great promise for WGM-based mid-IR (MIR) devices. Absorption-limited Q-factors of over 3 10^8 are anticipated over the 2.0 to 3.2 micron MIR wavelength range in ZBLAN microcavities in the foreseeable future.

*B. Way, R. K. Jain, and M. Hossein-Zadeh, "High-Q Microresonators for Mid-IR Light Sources and Molecular Sensors", Optics Letters, vol. 37, no. 21, pp. 4389-4391, 2012.

- Plasmonic enhancement of microring resonators
High quality factor (high-Q) optical microcavities detect the presence of molecules in the vicinity of the cavity surface through the evanescent field. When combined with an affinity based molecular recognition mechanism (such as antibody-antigen binding), this optical transduction mechanism can be used as label free biosensor with extremely low detection limit. The basic principle used in these biosensors is resonant wavelength shift (effective refractive index change) due to induced polarization of bound molecules (by evanescent optical field). The minimum detectable wavelength shift (MDWS) is inversely proportional to the optical quality factor while the magnitude of the shift is proportional to the induced molecular polarization. So the limit of detection is proportional to MDWS and wavelength shift. While significant effort has been spent on increasing MDWS by improving the Q-factor and noise reduction techniques, less attention has been paid to the magnitude of shift. Molecular polarization and therefore is proportional to the strength of the evanescent optical field so any mechanism that amplifies the field (confinement and amplification) will also increase wavelength shift. Based on this basic principle, recently few research groups have demonstrated that presence of metallic nanoparticles on the microcavity surface can enhance the sensitivity through plasmonic resonance. We work on novel microresonators designs that combine high-Q optical resonance and localized plasmonic resonance to improve the overall sensitivity.