Fluorescent Nanodiamonds Achieve Real-Time Monitoring of Ultra-Short-Lived Radicals

The challenge of detecting extremely short-lived radicals, existing for mere billionths of a second, has long hindered progress in fields requiring real-time monitoring of chemical processes. Jia Su, Zenghao Kong, and Fei Kong, from Advanced Special Steel at Shanghai University, alongside Xing Liu and Zhecheng Wang et al., now present a significant advance in this area, demonstrating a novel platform for both generating and sensing these elusive species. Their work centres on fluorescent nanodiamonds engineered with a unique double-layered silica structure, effectively shielding the nanodiamond’s sensitive quantum properties while simultaneously providing a scaffold for catalytic radical production. By embedding gadolinium catalysts within the porous outer layer, the team achieves sustained hydroxyl radical generation from water, bypassing the need for external light or chemical additives, and importantly, enables continuous, real-time monitoring of radical dynamics using the nanodiamond’s inherent quantum sensitivity. This breakthrough establishes a robust system for on-demand radical control and sensing, promising new capabilities for understanding and optimising complex chemical environments and paving the way for applications in intelligent manufacturing.

Fluorescent Nanodiamonds Detect Hydroxyl Radicals In Situ

Detecting and monitoring hydroxyl radicals (·OH) is crucial in biology, chemistry, and materials science because these highly reactive molecules participate in oxidative stress, signaling, and degradation processes. Traditional detection methods often lack real-time capabilities and sensitivity, so scientists developed fluorescent nanodiamonds (FNDs) with nitrogen-vacancy (NV) centers to monitor ·OH generation. These FNDs feature a double-layered silica coating, specifically mesoporous silica (MS-silica), which enhances biocompatibility, provides a platform for catalytic water splitting, and concentrates ·OH radicals near the NV center to increase sensitivity. The team synthesized core-shell MS-silica-FNDs with controlled size and morphology, then incorporated gadolinium (Gd) into the MS-silica layer to act as a catalyst for water splitting, even at extremely low concentrations.

Transmission Electron Microscopy (TEM) and Dynamic Light Scattering (DLS) characterized the nanoparticles, while Electron Paramagnetic Resonance (EPR) and time-resolved measurements assessed the NV center’s spin properties. The researchers then used these FNDs to catalyze water splitting and monitored changes in the NV center’s T1 relaxation time, which shortens in the presence of paramagnetic radicals like ·OH, indicating concentration. Conventional EPR spectroscopy with a spin trapping agent confirmed the generation of ·OH radicals. Results show the FNDs exhibit suitable spin relaxation properties for use as sensors and demonstrate a strong response to gadolinium catalysts, with the ability to detect ·OH at extremely low concentrations.

Density Functional Theory (DFT) calculations revealed that Gd doping lowers the energy barrier for water dissociation and increases the adsorption of water and ·OH radicals on the silica surface. Single-particle analysis confirmed a clear shift in T1 relaxation rates when exposed to low concentrations of the catalyst. This research provides a highly sensitive platform for detecting ·OH radicals, with potential applications in biochemistry, materials science, environmental monitoring, and metabolic tracking.

Real-Time Monitoring of Reactive Free Radicals

Scientists have created a new platform using fluorescent nanodiamonds (FNDs) to both generate and monitor ultra-short-lived reactive free radicals in real time, representing a significant advancement in controlling and analyzing these critical chemical species. The research focuses on nanodiamonds hosting nitrogen-vacancy (NV) centers and utilizes a double-layered silica modification strategy to enhance functionality, enabling sustained hydroxyl radical generation without external precursors. An inner dense silica layer protects the NV centers, while an outer porous silica layer facilitates the adsorption and stabilization of hydroxyl radicals and their precursors. The team achieved sustained, light-free generation of hydroxyl radicals through catalytic water splitting by doping the porous silica shell with gadolinium (III) catalysts, demonstrating stable and tunable radical fluxes.

They monitored this radical production in situ using spin-dependent T1 relaxometry of the NV centers, a technique measuring the time it takes for the NV center’s electron spin to return to equilibrium. Characterization revealed a silica shell thickness of approximately 9.4nm, with the overall diameter of the mesoporous silica-coated nanodiamonds reaching approximately 127.3nm. Experiments demonstrated measurable increases in NV center relaxation rates even at gadolinium (III) concentrations as low as 1 fM, indicating highly sensitive radical detection. Control experiments using radical quenchers and traditional electron paramagnetic resonance (EPR) spectroscopy confirmed the signals originated specifically from hydroxyl radicals generated through water splitting. This work establishes a robust platform for on-demand hydroxyl radical generation and sensing, opening new avenues for persistent, in-situ monitoring of transient species and redox dynamics in complex environments and integrating materials science with quantum technology.

Nanodiamonds Capture and Stabilize Reactive Molecules

This research represents a significant advance in quantum sensing and the monitoring of reactive species, achieved through the innovative integration of material design with the properties of nitrogen-vacancy centers in fluorescent nanodiamonds. Scientists successfully designed and synthesized a nanodiamond structure featuring a double-layered silica coating, simultaneously protecting the quantum sensor from external interference and creating a functional interface for capturing transient molecules. The dense inner silica layer shields the nanodiamond’s sensitive components, preserving their quantum characteristics, while the outer mesoporous silica layer efficiently captures and stabilizes short-lived hydroxyl radicals. A key innovation is the system’s ability to generate hydroxyl radicals without external energy sources or chemical additives, utilizing a light-free catalytic water splitting process facilitated by gadolinium doping within the porous silica shell.

Detailed analysis confirms that this doping lowers the energy required for water dissociation, enabling continuous and controlled radical production. Real-time monitoring, performed using the nanodiamond’s response to local radical concentrations via T1 relaxometry, demonstrates stable and tunable radical fluxes with concentrations adjustable across a wide range. While the system demonstrates robust performance in controlled conditions, further investigation is needed to fully understand its behavior in more complex environments. Future work may focus on expanding the application of this platform to biological systems, leveraging the biocompatibility of nanodiamonds and silica, and exploring its potential in intelligent manufacturing processes.