A chemical platform for gentle diamond surface functionalization enabling quantum sensing and biomolecule attachment

Background

Diamond, particularly single-crystal diamond, has emerged as a critical material in the field of quantum sensing due to its exceptional physical properties and the unique quantum behavior of nitrogen vacancy (NV) centers embedded within its lattice. NV centers are atomic-scale defects that can be used as highly sensitive probes for magnetic and electric fields, enabling applications such as single-molecule nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) at the nanoscale. To harness the full potential of these quantum sensors, it is essential to functionalize the diamond surface with chemical groups or biomolecules that can interact with target analytes, all while maintaining the pristine nature and quantum coherence of the NV centers. This requirement has driven significant research into developing surface modification techniques that are compatible with both the chemical versatility needed for sensor applications and the delicate quantum properties of shallow NV centers.

Current approaches to diamond surface functionalization, however, present significant challenges. Traditional methods often rely on aggressive plasma treatments or high-pressure, high-temperature reactions to introduce functional groups onto the diamond surface. While effective at modifying surface chemistry, these harsh conditions can damage the diamond lattice and degrade the spin coherence of NV centers, especially those located within a few nanometers of the surface—precisely where high sensitivity is required for quantum sensing. Some milder wet chemical approaches have been developed, but they are typically limited to nanodiamonds and are not suitable for high-quality single-crystal diamond substrates. Furthermore, existing techniques often lack the ability to introduce a diverse array of functional handles or to achieve high coverage and stability of surface modifications, which are necessary for robust and versatile sensor platforms. As a result, there remains a critical need for gentle, versatile, and effective methods to functionalize single-crystal diamond surfaces without compromising the performance of near-surface NV centers.

Technology

This technology is a gentle, visible-light-driven chemical method for functionalizing single-crystal diamond surfaces, specifically designed to preserve the delicate quantum properties of near-surface nitrogen vacancy (NV) centers. The process begins with hydrogen-terminated diamond, from which hydrogen atoms are abstracted using N-fluorobenzenesulfonimide under visible-light photoredox conditions at room temperature and ambient pressure. The resulting surface carbon radicals are then intercepted by fluorinating agents or electron-deficient alkenes, creating covalent C–F or C–C bonds. This yields a mixed surface termination featuring both halide atoms and functional group handles, such as alkynes or alkenes, which can be further derivatized through click chemistry or cross metathesis to attach biomolecules, fluorophores, or other sensing elements. The method is validated through rigorous surface analysis techniques, including AFM, XPS, and NEXAFS, ensuring robust covalent attachment and pristine surface morphology.

What differentiates this technology is its ability to achieve high-coverage, versatile surface functionalization of single-crystal diamond under exceptionally mild conditions, thereby avoiding the damage and loss of NV center coherence associated with traditional plasma or high-pressure treatments. This compatibility with shallow NV centers—critical for quantum sensing applications—enables the precise positioning of biomolecules or sensors within nanometers of the quantum sensor, facilitating single-molecule NMR, MRI, and biosensing at the nanoscale. The approach’s modularity, allowing for various surface terminations and subsequent functionalizations, opens the door to a wide range of applications in quantum sensing, biointerfaces, and advanced electronics, setting a new standard for diamond surface chemistry in both research and industry.

Benefits

• Preserves the integrity and spin coherence of nitrogen vacancy (NV) centers near the diamond surface by using gentle, room-temperature visible-light photoredox chemistry instead of aggressive plasma or high-pressure treatments.
• Enables versatile mixed surface termination with halides and functional handles (e.g., alkyne or alkene groups) for subsequent attachment of biomolecules or sensors via click chemistry or cross metathesis.
• Allows covalent and stable functionalization of single-crystal diamond surfaces, ensuring robust chemical modification confirmed by multiple surface analysis techniques.
• Facilitates nanoscale quantum sensing and molecular imaging applications by positioning functional molecules within nanometers of NV centers.
• Supports attachment of a wide variety of biomolecules and sensing targets under mild, ambient conditions, expanding applications in biosensing and single-molecule NMR/MRI.
• Maintains pristine diamond surface morphology and NV center performance (e.g., photoluminescence and spin coherence) after functionalization.
• Offers a scalable and industry-relevant platform compatible with advanced quantum sensing technologies pursued by leading companies and research institutions.

Applications

• Single-molecule quantum biosensing
• Nanoscale magnetic resonance imaging
• Surface-tethered quantum sensors
• Diamond-based biointerfaces

Additional info

This photochemical method employs visible-light photoredox chemistry to functionalize single-crystal diamond surfaces under ambient conditions. Using hydrogen atom transfer reagents, it generates surface carbon radicals that form covalent C-F or C-C bonds with fluorinating agents or alkenes. This creates mixed terminations with functional handles for biomolecule attachment. Crucially, the process preserves the spin coherence of shallow nitrogen vacancy centers, enabling high-resolution nanoscale quantum sensing and molecular imaging.