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Single-molecule Scale Nuclear Magnetic Resonance Spectroscopy using a Robust Near-Infrared Spin Sensor

Yu Chen, Qi Zhang, Yuanhong Teng, Chihang Luo, Zhijie Li, Jinpeng Liu, Ya Wang, Fazhan Shi, Jiangfeng Du

TL;DR

The paper addresses nanoscale NMR of single molecules using robust, biocompatible spin sensors. It introduces shallow PL6 color centers in 4H-SiC that are addressable at near-infrared wavelengths ($\lambda \approx 1038~\text{nm}$) and remain stable within ~2 nm of the surface, enabling nanoscale detection of $^1H$ and $^{19}\mathrm{F}$ with a detection volume of $ (3~\text{nm})^3 $ and sensitivities approaching single-spin limits. The authors demonstrate multi-species NMR (both $^1H$ and $^{19}\mathrm{F}$) and quantify surface proton layers, achieving a measured sensitivity of around $3.07\times 10^2~\text{nT}/\sqrt{\text{Hz}}$ at $d=2$~nm and photostability over extended illumination. This work positions 4H-SiC PL6 sensors as a practical platform for nanoscale, potentially atomic-resolution NMR of biomolecules and interfacial chemistry, with clear pathways to further enhancements via advanced readout and nanostructuring.

Abstract

Nuclear magnetic resonance (NMR) at the single-molecule level with atomic resolution holds transformative potential for structural biology and surface chemistry. Near-surface solid-state spin sensors with optical readout ability offer a promising pathway toward this goal. However, their extreme proximity to target molecules demands exceptional robustness against surface-induced perturbations. Furthermore, life science applications require these sensors to operate in biocompatible spectral ranges that minimize photodamage. In this work, we demonstrate that the PL6 quantum defect in 4H silicon carbide (4H-SiC) can serve as a robust near-infrared spin sensor. This sensor operates at tissue-transparent wavelengths and exhibits exceptional near-surface stability even at depth of 2 nm. Using shallow PL6 centers, we achieve nanoscale NMR detection of proton ($\mathrm{^{1}H}$) spins in immersion oil and fluorine ($\mathrm{^{19}F}$) spins in Fomblin, attaining a detection volume of $\mathrm{(3~nm)^3}$ and a sensitivity reaching the requirement for single-proton spin detection. This work establishes 4H-SiC quantum sensors as a compelling platform for nanoscale magnetic resonance, with promising applications in probing low-dimensional water phases, protein folding dynamics, and molecular interactions.

Single-molecule Scale Nuclear Magnetic Resonance Spectroscopy using a Robust Near-Infrared Spin Sensor

TL;DR

The paper addresses nanoscale NMR of single molecules using robust, biocompatible spin sensors. It introduces shallow PL6 color centers in 4H-SiC that are addressable at near-infrared wavelengths () and remain stable within ~2 nm of the surface, enabling nanoscale detection of and with a detection volume of and sensitivities approaching single-spin limits. The authors demonstrate multi-species NMR (both and ) and quantify surface proton layers, achieving a measured sensitivity of around at ~nm and photostability over extended illumination. This work positions 4H-SiC PL6 sensors as a practical platform for nanoscale, potentially atomic-resolution NMR of biomolecules and interfacial chemistry, with clear pathways to further enhancements via advanced readout and nanostructuring.

Abstract

Nuclear magnetic resonance (NMR) at the single-molecule level with atomic resolution holds transformative potential for structural biology and surface chemistry. Near-surface solid-state spin sensors with optical readout ability offer a promising pathway toward this goal. However, their extreme proximity to target molecules demands exceptional robustness against surface-induced perturbations. Furthermore, life science applications require these sensors to operate in biocompatible spectral ranges that minimize photodamage. In this work, we demonstrate that the PL6 quantum defect in 4H silicon carbide (4H-SiC) can serve as a robust near-infrared spin sensor. This sensor operates at tissue-transparent wavelengths and exhibits exceptional near-surface stability even at depth of 2 nm. Using shallow PL6 centers, we achieve nanoscale NMR detection of proton () spins in immersion oil and fluorine () spins in Fomblin, attaining a detection volume of and a sensitivity reaching the requirement for single-proton spin detection. This work establishes 4H-SiC quantum sensors as a compelling platform for nanoscale magnetic resonance, with promising applications in probing low-dimensional water phases, protein folding dynamics, and molecular interactions.

Paper Structure

This paper contains 4 sections, 1 equation, 4 figures.

Table of Contents

  1. Introduction
  2. Results
  3. Discussion
  4. Methods

Figures (4)

  • Figure 1: PL6 color center for nanoscale NMR spectroscopy. a, Schematic of a shallow PL6 center in 4H-SiC detecting proton spins within immersion oil placed on the 4H-SiC surface. b, PL6 energy level diagram. c-d, Measured auto-correlation function $g^{(2)}(\tau)$ and saturation curve of a single PL6 emitter. e, Photostability of a shallow PL6 with laser power 2.2 times the saturation power $P_s$. The depth of the PL6 is calibrated with NMR technique 2016-NMRTechniqueDetermining-Pham-Phys.Rev.B. Insets show Rabi oscillations before (yellow) and after (red) illumination, demonstrating maintained optical spin readout contrast.
  • Figure 2: Nanoscale nuclear magnetic resonance with single shallow PL6 center.a, Schematic illustration of the XY8-$k$ dynamical decoupling pulse sequence employed for NMR detection. b, Measured $\mathrm{^1H}$ NMR spectra at various applied magnetic fields, exhibiting characteristic coherence dips. The solid curves represent theoretical fits to the expected NMR lineshape. c, Magnetic field dependence of the $\mathrm{^1H}$ resonance frequency, with a linear fit yielding a gyromagnetic ratio $\gamma_\mathrm{H} = 4.25(8)$ kHz/G. d, Proton NMR spectrum acquired at $B_0 = 235$ G with the optimal fit (red curve) indicating $d=~$2.00(4) nm depth, compared with theoretically predicted NMR spectra for shallower ($d = 1.5$ nm, golden curve) and deeper ($d = 2.5$ nm, blue curve) sensors. e, Proton NMR spectrum measured with varying dynamical decoupling orders at $B_0 = 216$ G. f, Corresponding coherence times extracted from data in panel (e).
  • Figure 3: Detection volume and sensitivity characterization.a-b, Simulated magnetic field contributions showing the detection volume of a 2 nm-deep PL6 sensor. c, Measured sensitivity of fourteen shallow PL6 centers (blue dots) compared with theoretical thresholds for single-spin detection, including the requirements for ENDOR detection of single proton spin (yellow line) and DEER detection of single electron spin (red line) at SNR = 1 with 1 second integration time.
  • Figure 4: Multi-species nanoscale NMR spectroscopy.a, Experimental schematic for detecting $\mathrm{^{19}F}$ in Fomblin and surface-adsorbed $\mathrm{^{1}H}$ on 4H-SiC surface. b, XY8 correlation spectroscopy pulse sequence. c, Correlation signal showing oscillations from both $\mathrm{^{1}H}$ (proton layer) and $\mathrm{^{19}F}$ (Fomblin) at $B_0 = 215.8$ G. The solid line represents a fit using double decaying cosine model, yielding $T^{(^1\mathrm{H})} _{\mathrm{coor}}=27(5) ~\mathrm{\mu s}$ and $T^{(^{19}\mathrm{F})} _{\mathrm{coor}}=55(10) ~\mathrm{\mu s}$.. d, Fourier transform of the correlation signal revealing distinct $\mathrm{^{1}H}$ and $\mathrm{^{19}F}$ peaks. Inset displays a magnified view with two-Lorentzian fitting (solid curve), yielding measured FWHM linewidths of $26(5)$ kHz for $\mathrm{^{1}H}$ and $10(4)$ kHz for $\mathrm{^{19}F}$. Vertical lines indicate the expected Larmor frequencies for both nuclear species at this magnetic field strength.