Biocompatible Surface Functionalization Architecture for a Diamond Quantum Sensor

Diamond-based quantum metrology has enabled a new class of biophysical sensors and diagnostic devices that are being investigated as a platform for cancer screening and ultra-sensitive immunoassays. However, a broader application in the life sciences based on nanoscale nuclear magnetic resonance spectroscopy has been hampered by the need to interface highly sensitive quantum bit sensors with their biological targets. Here, we demonstrate a new approach that combines quantum engineering with single-molecule biophysics to immobilize individual proteins and DNA molecules on the surface of a bulk diamond crystal that hosts coherent nitrogen-vacancy qubit sensors. Our thin (sub-5 nm) functionalization architecture provides precise control over protein adsorption density and results in near-surface qubit coherence approaching 100 μs. The architecture remains chemically stable under physiological conditions for over five days, making our technique compatible with most biophysical and biomedical applications. This method should facilitate the realization of NV-based single-molecule electron paramagnetic resonance (EPR) or nuclear magnetic resonance (NMR) experiments on a variety of biomolecules to deepen our understanding of their biological functions.