FRET between NV centers in diamond and chlorophyll molecules: a novel resource for multimodal sensing and imaging in plant cells

TL;DR

The study demonstrates efficient hetero-FRET between shallow NV centers in single-crystal diamond and a chlorophyll A+B layer, with NV lifetimes quenched from ~14 ns to under 4 ns and recoverable upon chlorophyll bleaching. By modeling a 2D acceptor plane and incorporating NV depth distributions, the work links spectral overlap and ensemble-scale quenching to an effective coupling parameter $R$ in the range of ~13–17 nm for shallow NVs, while deeper NVs remain unaffected, confirming the short-range nature of the interaction. Crucially, NV spin readout via optically detected magnetic resonance persists during FRET, though ODMR contrast is reduced by chlorophyll background and recovers after bleaching, indicating the feasibility of integrating FRET-based distance sensing with quantum sensing. This proof-of-principle platform opens avenues for multimodal intracellular sensing in plant cells, combining nanoscale distance measurements with spin-based detection of paramagnetic species or radicals.

Abstract

This work demonstrates efficient Forster resonance energy transfer (FRET) between ensembles of shallow nitrogen-vacancy (NV) centers located 7 nm and 9 nm below a single-crystal diamond surface and a naturally occurring fluorophore, namely a mixture of chlorophyll a and b molecules extracted from Arabidopsis thaliana. The broad fluorescence band of NV centers spectrally overlaps with the absorption of chlorophyll molecules, enabling FRET. As a result, depositing a chlorophyll layer on the diamond surface reduces the NV fluorescence lifetime from approximately 14 ns to below 4 ns, indicating efficient energy transfer. Laser-induced photobleaching of chlorophyll restores the unquenched NV lifetime. In contrast, NV centers located deeper within the diamond at depths of 40 nm and 72 nm remain unaffected, confirming that the observed quenching originates from a short-range FRET mechanism. The NV ensembles retain their optically detected magnetic resonance contrast while FRET is observed, demonstrating preservation of their spin properties. These proof-of-principle experiments establish the feasibility of combining FRET-based distance measurements with magnetic sensing using optically readable spins.

Figures (4)

• Figure 1: a) Spectral overlap between the NV center emission and the absorption spectrum of the chlorophyll sample. Both spectra were measured experimentally. b) Simulated effective NV ensemble lifetime $\tau_\text{NV}^\text{eff}$ as a function of the effective coupling parameter $R$, calculated using the FRET model described in Eq.\ref{['DecyI_Ensemble']}.
• Figure 2: Time-resolved fluorescence measurement of the NV–chlorophyll system. The data correspondsto an NV ensemble located at a depth of $9 \pm 4\,\text{nm}$, excited with pulsed laser light ($\lambda = 520\,\text{nm}$, pulse length $\approx 50\,\text{ps}$). Bleaching of the chlorophyll layer leads to a recovery of the NV lifetime from $4.36 \pm 0.03\,\text{ns}$ to $11.01 \pm 0.05\,\text{ns}$.
• Figure 3: NV fluorescence lifetimes before and after bleaching of the chlorophyll layer. The dashed lines indicate the mean NV lifetimes, and the shaded regions represent one standard deviation ($\pm 1\sigma$). a) NV ensemble with a depth distribution of $7 \pm 3\,\text{nm}$, showing an average NV lifetime of $\tau_\text{NV, before} = 3.3 \pm 0.5\,\text{ns}$ before bleaching and $\tau_\text{NV, after} = 9.3 \pm 0.5\,\text{ns}$ after bleaching of the chlorophyll layer. b) NV ensemble with a depth distribution of $9 \pm 4\,\text{nm}$, showing an increase in the average NV lifetime from $\tau_\text{NV, before} = 3.8 \pm 0.6\,\text{ns}$ to $\tau_\text{NV, after} = 10.8 \pm 0.6\,\text{ns}$ following chlorophyll bleaching. In both shallow NV ensembles, chlorophyll efficiently quenches the NV fluorescence, while bleaching restores the original NV lifetime.
• Figure 4: Optically detected magnetic resonance spectrum of the quenched NV ensemble (depth: $9 \pm 4\,\text{nm}$) under the chlorophyll layer in the absence of an external magnetic field. The measurement demonstrates that NV centers maintain their spin-dependent fluorescence contrast even in the presence of efficient energy transfer, highlighting their potential as multifunctional quantum sensors.