Biology is a longstanding frontier for quantum metrology, where high optical intensities are frequently required to get sufficient signal, but lead to specimen damage [1]. 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 [2]. 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 [3]. 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.
References
[1] K. C. Neuman et al. Biophysics Journal 77, 2856-2863 (1999).
[2] N. Mauranyapin, L. Madsen et al. Nature Photonics, in press July (2017)
[3] L. Madsen, et al. Nano Letters, 16, 7333−7337 (2016)
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