Biology is a longstanding frontier for quantum metrology, where high optical intensities are frequently required to get sufficient signal, but lead to specimen damage . In this regime quantum-noise limited sensitivity allows higher signal to noise or reduced optical intensities. I will give an overview of efforts in the Queensland Quantum Optics Laboratory to apply nanofiber based quantum-noise limited biosensor to biological measurements and our recent progress in nanofiber characterization.
We demonstrate a quantum noise limited biosensor capable of detecting single unlabelled biomolecules with radii below 5 nm . The nanoparticles are illuminated through a microscope objective and the scattered light is collected by a nanofiber. The collected light is detected with a heterodyne detector and obtains a quantum-noise limited performance down to 5 Hz and particle tracking with 1 kHz bandwidth. This detection performance opens for observation of biomolecular movements avoiding large biomarkers.
We present a method for directly measuring the evanescent field of an optical nanofiber . Unlike SEM-based methods, this method is non-destructive and yields a full profile of the nanofiber within minutes of fabrication. We obtain the radius with a resolution of 0.7 nm in 10 milliseconds. The method allows quality control and calibration of optical nanofibers for precision experiments for example as in the above mentioned biosensor.
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Lars Madsen, "Nanofiber nanoscopy and quantum noise limited biosensing (Conference Presentation)," Proc. SPIE 10518, Laser Resonators, Microresonators, and Beam Control XX, 1051803 (Presented at SPIE LASE: January 29, 2018; Published: 14 March 2018); https://doi.org/10.1117/12.2287301.5751432981001.
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