In-Solution Quantum Sensing Using Nanodiamond Ensembles

Nanodiamonds containing the nitrogen-vacancy (NV) colour centre represent an emerging class of materials suited to a range of sensing and imaging applications. Their photostability, surface functionality and range of particle sizes are particularly useful for biological sensing¹. However, to date, the majority of magnetic², temperature, pH⁴, and free radical⁵ sensor demonstrations have been performed using single nanodiamonds. Such approaches are generally time-consuming and limit measurement statistics. In this work, we develop a measurement platform that can report the spin-lattice relaxation time (T₁) for an ensemble of NV-containing nanodiamonds in solution. We have applied this new sensing modality to detect concentrations of biologically relevant metal ions and metalloproteins, as well as establishing the effect of pH on nanodiamonds. This sensing modality is advantageous because it provides ensemble averaging which enables low-noise measurements of high contrast, fast throughput, and high reproducibility.<br/><b>References:</b><br/>1. Miller, B. S. <i>et al.</i> Spin-enhanced nanodiamond biosensing for ultrasensitive diagnostics. <i>Nature</i> <b>587</b>, 588–593 (2020).<br/>2. Kaufmanna, S. <i>et al.</i> Detection of atomic spin labels in a lipid bilayer using a single-spin nanodiamond probe. <i>Proc. Natl. Acad. Sci. U. S. A.</i> <b>110</b>, 10894–10898 (2013).<br/>3. Simpson, D. A. <i>et al.</i> Non-Neurotoxic Nanodiamond Probes for Intraneuronal Temperature Mapping. <i>ACS Nano</i> <b>11</b>, 12077–12086 (2017).<br/>4. Fujisaku, T. <i>et al.</i> PH Nanosensor Using Electronic Spins in Diamond. <i>ACS Nano</i> <b>13</b>, 11726–11732 (2019).<br/>5. Barton, J. <i>et al.</i> Nanoscale Dynamic Readout of a Chemical Redox Process Using Radicals Coupled with Nitrogen-Vacancy Centers in Nanodiamonds. <i>ACS Nano</i> <b>14</b>, 12938–12950 (2020).