The nitrogen-vacancy (NV) defect in diamond is an optically-active colour centre that shows much promise for all-optical sensing. Its ground state is a spin-triplet that has been investigated as a potential qubit. The interaction of the system with the environment also allows detection of magnetic fields and, through the frequency shift of a microwave-frequency spin-resonance, temperature. Current measurements use pulsed control of the spin state of the NV centre to enact rephasing of the spin, allowing decoupling of the system from environmental noise while retaining sensitivity to the parameters being measured.
In addition, even when embedded in nanodiamond (typically diamond particles smaller than a few hundred nanometres), the NV centre retains the ability to be used as an effective sensor. Diamond is biologically inert, yet can be functionalised through surface chemistry modifications to target structures of interest within cells. Nanodiamond therefore offers an exciting route to all-optical, sub-cellular detection of biological activity.
Many biological processes of interest to a wide range of researchers involve local thermal effects (both endothermic and exothermic); sub-cellular temperature sensing offers a powerful way to infer the activity of cells undergoing numerous processes. However, measurement of cell temperature with the required accuracy to monitor dynamic cellular processes in living cells is an unsolved problem; NV centres offer themselves as a uniquely promising technology solution to this problem. Furthermore, when performing thermometry with NV centres, there are effective ways to decouple the sensor from sources of noise within the system of interest. Excitingly, this approach also enables correlated thermometry / magnetometry with the same setup and samples.
While NV centres are perhaps better known for magnetometry applications, sensitivity to noise-generating processes within cells poses significant engineering challenges. Initial results demonstrate that passivation of the external surface of the ND, with long chain organic molecules or a silica coating, offers a way to retain sensitivity while also reducing local noise effects.
We feel that specialising on sub-cellular thermometry will offer a significant benefit to the training of the students in this project – they can quickly apply and develop quantum sensing techniques to biologically relevant questions. This also allows the student to come from a wider range of scientific backgrounds.
With this project, we propose to build on our existing expertise with NV sensing to further develop the use of nanodiamond as a sub-cellular thermometer for applications in biological imaging.
The student will initially implement existing passivation approaches, allowing them to gain key skills in nanodiamond surface modification and, by validating the passivation, in quantum-enhanced sensing. Having gained these skills, a student-led approach will further develop surface functionalization with the aims of targeting specific sub-cellular structures and/or using active surface chemistry to modify the nanodiamond sensitivity to local chemical environment. Both approaches will open new routes to quantum-enhanced sensing in biology.
An existing, low-cost widefield NV sensing system will be expanded to allow investigation of biological systems while incorporating state of the art pulsed microwave techniques to improve sensitivity and reject noise. Anticipated systems of interest include mitochondrial activity within cells and the impact of photosynthesis on the local thermal environment within a cell.