Laser threshold magnetometry

High precision magnetometry is a vital tool for physical and biological sensing applications. In particular, magnetoencephalography (MEG), the sensing of minute magnetic fields generated in the brain, is a minimally invasive technique for monitoring deep brain activity in real time. MEG is opening new frontiers in understanding human cognition and is poised to become a new diagnostic technique for epilepsy and mild traumatic brain injury. We have discovered a new way to measure magnetic fields using nitrogen-vacancy colour centres in diamond, where we create a laser from the nitrogen-vacancy centres. This approach promises femto-tesla per root Hertz sensitivity at room temperature and ambient magnetic fields. This represents an unprecendented opportunity for portable brain scanning applications.

(a) Concept for a nitrogen-vacancy (NV−) laser system using laser threshold magnetometry (LTM). NV− is the laser gain medium, pumped in the green and lasing on the red three-phonon sideband. (b) The laser output over the pumping rate when the RF drive is off-resonant, Δ = 100MHz, or on-resonant, Δ = 0. The lasing threshold is dependent on the spin manifold. The operating point is chosen in between such that the laser turns on and off depending on the magnetic resonance of the spin manifolds and achieves maximal sensitivity. Setting the operating point to Λ = 1.06 MHz ensures the laser turns off at Δ = 0 and maximises the laser output at Δ = 100 MHz. The Rabi frequency is Ω = 3.67 MHz. (c) Reduced level structure for NV−, breaking the system into the manifolds for spin 0 and spin 1 and highlighting the state transitions. Mixing between the manifolds is only possible via the singlet pathway L57, which takes population from the spin 1 manifold to the spin 0 manifold, and via the RF drive, which in the incoherent limit tends to equalise populations. The green pump laser lifts population into a phonon-added state just above ∣2〉 and ∣5〉, followed by a very rapid decay into ∣2〉, ∣5〉. The ∣2〉 ↔ ∣3〉 and ∣5〉 ↔ ∣6〉 transitions emit into the cavity. Reproduced from Jeske et al. New Journal of Physics 18, 013015 (2016).


Potential Uses and Applications

  • High precision magnetometry
  • Magento-encephalography
  • Foetal magneto-cardiography
  • Mineral exploration


Prof Andrew Greentree:
Prof Brant Gibson:

Key publication

  1. Jeske, J. H. Cole, and A. D. Greentree, Laser threshold magnetometry, New Journal of Physics 18, 013015. J. Jeske, D. W. M. Lau, X. Vidal, L. P. McGuinness, P. Reineck, B. C. Johnson, M. W. Doherty, J. C. McCallum, S. Onoda, F. Jelezko, T. Ohshima, T. Volz, J. H. Cole, B. C. Gibson and A. D. Greentree, Stimulated emission from nitrogen-vacancy centres in diamond, Nature Communications 8:14000 (2017) DOI:10.1038/ncomms14000

Sensing of cytokines and other biomolecular targets

The CNBP biosensing program in has created a range technologies for ultrasensitive detection of key biological analytes including cytokines, but also analytes detectable by using antibodies and aptamers as well as nucleic acids. We have been able to increase the sensitivity of popular ELISA assays by three orders of magnitude and expand their linear range by several orders of magnitude. The detection limit of ~ 50 aM for important cytokine analytes has been demonstrated. We can detect nucleic acids at the same level of sensitivity as PCR but in a deployable format, without the need for instrumentation.

OnCELISA (courtesy Ewa Goldys)

Potential Uses and Applications

  • We developed unique technology platforms for in vivo sensing of cytokines including in the spinal cord1 and in the brain2, for cellular sensing3 and for point-of-care testing. Ultrasensitive detection of cytokines allows to probe very small clinical samples such as tears or the cerebrospinal fluid, also using standard ELISA detection systems (plate readers). Ultrahigh sensitivity also unlocks the possibility of environmental sensing


Prof Ewa Goldys:
Dr Guozhen Liu:

Key publications

  1. An optical fiber based immunosensor for localized detection of IL-1 in rat spinal cord, K. Zhang, A. Arman, A.G. Anwer, Mark R. Hutchinson and E. M. Goldys., Sensors and Actuators B: Chemical, Volume 282, 1, pp 122-129, (2019) DOI:1016/j.snb.2018.11.054
  2. A novel platform for in vivo detection of cytokine release within discrete brain regions, Kaixin Zhang, Michael V Baratta, Guozhen Liu, Matthew G Frank, Nathan R Leslie, Linda R Watkins, Steven F Maier, Mark R Hutchinson, Ewa M Goldys, Brain, behavior, and immunity, 71, 18-22, (2018) DOI:1016/j.bbi.2018.04.011
  3. A Nanoparticle-Based Affinity Sensor that Identifies and Selects Highly Cytokine-Secreting Cells, Liu, C. Bursill, S. Cartland, A. Anwer, L. Parker, K. Zhang, S. Feng, M. He, D. Inglis, M. Hutchinson, E. Goldys, iScience, Volume 20, P137-147, (2019) DOI:10.1016/j.isci.2019.09.019

Surface-enhanced Raman spectroscopy (SERS)

SERS assay for circulating tumor DNA (ctDNA) detection (courtesy: Yuling Wang)

Surface-enhanced Raman scattering (SERS) is an optical technique that uses metal nanoparticles (e.g. gold) to enhance the Raman signal of the molecules and generates a million-fold or even higher Raman signal. Due to the great advantages of SERS in sensitivity (down to a single molecule), highly multiplexed capability and photostability, SERS nanotags and SERS imaging have become a new class of labels and a new molecular imaging technique for the detection and imaging of low abundant analytes. With the development of a handheld Raman reader, SERS has been used as a deployable technique for on-site and point-of-need detection of target analytes.

Potential Uses and Applications

  • In vitro cancer biomarkers (e.g. soluble proteins) sensing
  • liquid biopsy for circulating tumor DNA (ctDNA), circulating tumor cells (CTC) and circulating extracellular vesicles detection
  • Cytokine sensing
  • Pathogen detection
  • In vivo imaging

    Lectin-SERS nanotags for cell surface glycan profiling (courtesy: Yuling Wang)


Dr Yuling Wang:

Key Publications

  1. Liu Y, Lyu N, Rajendran VK, Piper JA, Rodger A, Wang YL*, (2020) Sensitive and Direct DNA Mutation Detection by Surface-enhanced Raman Spectroscopy using Rational Designed and Tunable Plasmonic Nanostructures, Anal Chem. 92, 5708-5716. DOI:1021/acs.analchem.9b04183
  2. Zhang W, Jiang LM, Diefenbach RJ, Campbell DH, Walsh BJ, Packer NH, Wang YL*, (2020) Enabling Sensitive Phenotypic Profiling of Cancer-Derived Small Extracellular Vesicles Using Surface-Enhanced Raman Spectroscopy Nanotags, ACS Sensors, 5, 764-771. DOI: 1021/acssensors.9b02377