Single-Molecule Paramagnetic Resonance Spectroscopy Based On Nitrogen-Vacancy Center In Diamond

Electron paramagnetic resonance(EPR)technology is one of the most significant contemporary tools for the detection and analysis of substances.From in situ imag-ing to structural analysis of spin-labeled macromolecules,EPR has encompassed many disciplines including biology,medicine and materials.An ultimate goal of EPR is to achieve in situ single-molecule detection and to extract unique information from it.This requires extremely high detection sensitivity and spectral resolution.However,the de-tection principle of conventional EPR techniques is based on Faraday electromagnetic induction,which detects the interaction of spin and microwave resonant cavities.This detection method is limited by the geometry of the resonator itself resulting in low sen-sitivity and often requires accumulating billions of spin signals.A number of related techniques have been developed to achieve EPR at the single-molecule level,but most of these techniques require harsh environments such as vacuum and low temperature.NV color centers in diamond,a highly sensitive quantum sensor,was the first to achieve single-molecule level paramagnetic resonance detection under ambient conditions in 2015,and is one of the most promising candiadates to further advance it to in situ mea-surement of single molecules.In this PhD thesis,I will present single-molecule detection technique in a solution environment based on NV color centers in diamond and a zero-field EPR technique developed to enhance the spectral resolution.The work is divided into three main areas as follows.1.single-molecule EPR detection in a solution environment is achieved.In or-der to further practicalize the previously available NV-based single-molecule detection technique,we developed a set of EPR techniques for detecting single molecules in an aqueous solution environment.We successfully detected the EPR spectra of single DNA molecules in solution labeled with nitroxide radicals.And by analyzing the spectral line broadening and hyperfine interactions,we obtained more information about the local environment of DNA molecules.2.Zero-field EPR is an effective way to solve the inhomogeneous broadening of spectral lines and analyze the intrinsic spin interactions.However,conventional EPR is limited by the detection sensitivity and has not spread this technique.We have de-veloped a set of nanoscale paramagnetic resonance techniques applicable to zero-field by taking advantage of the high sensitivity of NV color centers in diamond.The exper-iments have successfully achieved zero-field EPR detection at nanoscale with nitrogen defects in diamond as the demonstration target.It provides a new way for the practical-ization of zero-field EPR.3.The current spectral resolution of single-spin paramagnetic resonance is mostly at the megahertz level,which is mainly limited by the short dephasing time of electron spins.We have designed a set of paramagnetic resonance correlation spectral sequence applicable to zero field by exploiting the property that some special spin states of the electron spin system are insensitive to the magnetic field,and detected the paramag-netic resonance spectrum of a single 15N defect in diamond.The spectral resolution is improved by nearly 30 times to the kilohertz level.