Self-Assembled Nanodiamond Layers Enable Scalable Magnetic Imaging with NV Centers

Diamond’s potential as a revolutionary imaging technology hinges on its ability to detect incredibly faint magnetic and electric signals, but current methods rely on expensive, bulky materials. Katherine Chea, Erin Grant, and Kevin Rietwyk, all from RMIT University, alongside colleagues, now present a scalable technique for creating dense, uniform layers of fluorescent nanodiamonds through self-assembly. This innovative approach overcomes limitations of traditional diamond substrates, offering a cost-effective pathway to widespread application of this powerful technology. The team demonstrates successful microscale magnetic imaging using these nanodiamond layers, paving the way for on-demand sensing and imaging across diverse surfaces and potentially transforming fields from materials science to biomedicine.

The nitrogen-vacancy (NV) center in diamond is emerging as a powerful tool for imaging magnetic and electric signals at the microscale and below. Current imaging techniques largely rely on costly, millimeter-sized bulk diamond substrates, which present challenges for widespread use and integration with other materials. This research presents a scalable method for fabricating dense and homogenous layers of fluorescent nanodiamonds (FNDs) containing NV centers through electrostatic self-assembly, and demonstrates the utility of these layers for magnetic imaging. The investigation carefully examines how factors like nanodiamond concentration, immersion time, and solution pH affect the resulting density of FNDs on a substrate.

FND Layer Growth and Density Control

Researchers have extensively studied the formation and characteristics of self-assembled fluorescent nanodiamond (FND) layers to optimise their performance in quantum imaging. Data reveals that FND layer density strongly correlates with the initial concentration of nanodiamonds in suspension; higher concentrations consistently produce denser layers. Immersion time also plays a crucial role, with the number of deposited nanodiamonds increasing proportionally to the square root of the time, suggesting a diffusion-limited adsorption process. Furthermore, the addition of salt influences electrostatic interactions and deposition, altering the zeta potential of the FND suspension.

Analysis combining atomic force microscopy (AFM) and photoluminescence (PL) imaging demonstrates that PL coverage is significantly higher than AFM-determined coverage, indicating that many FNDs are closely spaced or stacked while still emitting light. Particle size distribution analysis shows the FNDs peak at 120nm, and AFM helps distinguish between individual nanodiamonds and aggregates based on height. Detailed analysis of the deposition process confirms the diffusion-limited adsorption model and provides calculations for the average surface-to-surface distance between FNDs. The researchers also investigated the impact of pH on the stability and behaviour of FND suspensions.

Uniform Nanodiamond Layers for Quantum Sensing

Researchers have developed a new method for creating dense layers of fluorescent nanodiamonds (FNDs) containing nitrogen-vacancy (NV) centers, paving the way for more affordable and versatile quantum sensing and imaging technologies. Existing techniques often rely on expensive, bulk diamond substrates, limiting their scalability and integration into diverse applications. This new approach utilizes commercially available FNDs and a simple electrostatic assembly process to create functional coatings on various surfaces. The process involves depositing negatively charged nanodiamonds onto positively charged substrates, resulting in remarkably uniform layers exhibiting fluorescence across millimeter scales.

The team meticulously investigated the factors influencing FND layer density, including nanodiamond concentration, solution pH, and immersion time, identifying optimal conditions to maximize particle distribution while minimizing unwanted aggregation. This level of control is crucial for achieving high spatial resolution in quantum imaging, as denser, more homogenous layers yield stronger signals and clearer images. The resulting FND layers demonstrate significant potential for applications where bulk diamond is impractical or too costly, such as creating sensitive sensing chips for diagnostic devices or even integrating quantum sensors into biomedical implants. To demonstrate the capabilities of these FND layers, researchers successfully imaged the magnetic properties of iron oxide particles deposited on the surface.

Utilizing NV center-based techniques, including optically detected magnetic resonance and T1 relaxometry, they were able to map the magnetic field distribution with microscale resolution. This achievement highlights the potential of this new approach to provide a cost-effective and scalable platform for a wide range of quantum sensing and imaging applications, opening doors for advancements in fields ranging from materials science to biomedicine. The ability to create these functional coatings on diverse substrates represents a significant step towards widespread adoption of diamond-based quantum technologies.

Scalable Nanodiamond Layers for Magnetic Imaging

This research demonstrates a scalable method for fabricating layers of fluorescent nanodiamonds (FNDs) containing nitrogen-vacancy (NV) centers, and validates their use for magnetic imaging. The team successfully assembled these FND layers using electrostatic self-assembly, optimising factors like nanodiamond concentration and immersion time to maximise density while minimising particle clumping. This approach offers a cost-effective alternative to traditional, bulky diamond substrates currently used in quantum sensing and imaging applications. The resulting FND layers enable high-resolution magnetic field and magnetic noise imaging at the microscale, utilising NV optically detected magnetic resonance and spin relaxometry techniques.

Importantly, the method allows for the clear distinction between static magnetic fields and magnetic noise, enhancing the precision of measurements. The researchers highlight the potential for mass-producing disposable quantum sensors based on these nanodiamond layers, broadening the scope of applications for NV-based quantum technology. The authors acknowledge that longer immersion times in the FND suspension can increase overall particle density, but may also lead to increased aggregation. Future work will likely focus on further refining the self-assembly process to balance density and uniformity. This research provides a pathway towards functional FND layers and coatings, enabling on-demand quantum sensing and imaging across a wider range of surfaces and applications.