Abstract The nitrogen‐vacancy (NV) center in diamond is a powerful and versatile quantum sensor for diverse quantities. In particular, relaxometry (or T1), can be used to detect magnetic noise at the nanoscale. For experiments with single NV centers the analysis of the data is well established. However, due to relatively low brightness and reproducibility it is beneficial for biological experiments to use ensembles. While increasing the number of NV centers in a nanodiamond leads to more signal, a standardized method to extract information from relaxometry experiments is still missing. This article uses T1 relaxation curves acquired at different concentrations of gadolinium ions to calibrate and optimize the entire data processing flow, from the acquired raw data to the extracted T1. In particular, a bootstrap is used to derive a signal to noise ratio (SNR) that can be quantitatively compared from one method to another. At first, T1 curves are extracted from photoluminescence pulses. This work compares integrating their signal through an optimized window as performed conventionally, to fitting a known function on it. Fitting the decaying T1 curves leads to the relevant T1 value. This work compares here the three most commonly used fit models that are, single, bi, and stretched exponential. This work finally investigates the effect of the bootstrap itself on the precision of the result as well as the use of a rolling window to increase time resolution.
Abstract The nitrogen‐vacancy (NV) center in diamond is a powerful and versatile quantum sensor for diverse quantities. In particular, relaxometry (or T1), can be used to detect magnetic noise at the nanoscale. For experiments with single NV centers the analysis of the data is well established. However, due to relatively low brightness and reproducibility it is beneficial for biological experiments to use ensembles. While increasing the number of NV centers in a nanodiamond leads to more signal, a standardized method to extract information from relaxometry experiments is still missing. This article uses T1 relaxation curves acquired at different concentrations of gadolinium ions to calibrate and optimize the entire data processing flow, from the acquired raw data to the extracted T1. In particular, a bootstrap is used to derive a signal to noise ratio (SNR) that can be quantitatively compared from one method to another. At first, T1 curves are extracted from photoluminescence pulses. This work compares integrating their signal through an optimized window as performed conventionally, to fitting a known function on it. Fitting the decaying T1 curves leads to the relevant T1 value. This work compares here the three most commonly used fit models that are, single, bi, and stretched exponential. This work finally investigates the effect of the bootstrap itself on the precision of the result as well as the use of a rolling window to increase time resolution.
The negatively charged nitrogen-vacancy (NV) center in diamond has emerged as a powerful and versatile quantum sensor for diverse quantities.In particular, all-optical diamond based relaxometry (or T1), which consists of monitoring the NV centers' photoluminescence submitted to a train of green laser pulses, allows to detect magnetic noise and its origin.When applied on diamond nanoparticles, it allows nanoscale resolution and has many applications in biology, for monitoring chemical reactions metabolic activity or diagnostic markers.While increasing the number of NV centers in a nanodiamond allows to collect more signal, a standardized method to extract information from relaxometry experiments of such NV ensembles is still missing.In this article, we use a set of T1 relaxation curves acquired at different concentrations of gadolinium ions to calibrate and optimize the entire data processing flow, from the acquired raw data to the extracted T1.In particular, we use a bootstrap to derive a signal to noise ratio that can be quantitatively compared from one method to another.At first, T1 curves are extracted from photoluminescence pulses.We compare integrating their signal through an optimized window as performed conventionally, to fitting a known function on it.Fitting the decaying T1 curves allows to obtain the relevant T1 value.We compared here the three most commonly used fit models that are, single, bi, and stretched-exponential.We finally investigated the effect of the bootstrap itself on the precision of the result as well as the use of a rolling window to allows time-resolution.
Quantum relaxometry is one of the most successful applications of nitrogen-vacancy (NV) centers in diamond and, more broadly, solid-state spin qubits, enabling ultrasensitive detection of magnetic noise and paramagnetic species via measurements of the spin-lattice relaxation time T1. Conventional pulsed protocols, however, probe T1 efficiently only over a limited temporal range, which restricts the scope and throughput of the technique. Here we introduce a continuous-wave quantum relaxometry protocol that operates in the frequency domain. By measuring the frequency response of the optically detected magnetic resonance signal under low-frequency microwave amplitude modulation, we extract T1 from the characteristic response time of the spin system. The method enables efficient T1 measurements spanning more than three orders of magnitude -- directly demonstrated from 60 μs to 200 ms in our experiments -- across a broad temperature range and under substantial ensemble inhomogeneity. We further show that this protocol enables quantitative relaxometry-based sensing in nanodiamonds, achieving a substantial speed-up over the pulsed methods and offering a practical approach to optimizing nanodiamond size for enhanced sensitivity.
The longitudinal relaxation time (termed as T 1 ) of nitrogen-vacancy (NV) centers in nanodiamonds can be affected by surface electric or magnetic noise, which has been exploited to develop cutting-edge quantum relaxometry for biochemical sensing. In this work, a tiny all-fiber quantum probe based on longitudinal relaxometry was developed by chemically-anchoring nanodiamonds on the surface of a cone fiber tip. The dependences of T 1 on surface electric and magnetic noise were discussed in theories first and then experimentally demonstrated in varied pH and Gd 3+ concentration solutions, respectively. Because of NV centers being subject to enhanced coupling from surface noise, T 1 reduced from 290 to 245 µs when pH changed from 3 to 9 and reduced to 220 µs when Gd 3+ concentration increased to 10 mM, agreeing well with theoretical results. Based on these, the Gd 3+ -tagged-biotin and streptavidin model was designed and implemented on the all-fiber probe, and results demonstrated the detection of biotin with a limit of 168 nM and good specificity. This paper opens a new way to develop an all-fiber quantum probe by exploiting the unique electrical spin properties of NV centers, and the probe shows great potential for biological detection with high sensitivity and specificity.
The investigation of biomolecular interactions at the single-molecule level has emerged as a pivotal research area in life science, particularly through optical, mechanical, and electrochemical approaches. Spins existing widely in biological systems, offer a unique degree of freedom for detecting such interactions. However, most previous studies have been largely confined to ensemble-level detection in the spin degree. Here, we developed a molecular interaction analysis method approaching single-molecule level based on relaxometry using the quantum sensor, nitrogen-vacancy (NV) center in diamond. Experiments utilized an optimized diamond surface functionalized with a polyethylenimine nanogel layer, achieving $\sim$10 nm average protein distance and mitigating interfacial steric hindrance. Then we measured the strong interaction between streptavidin and spin-labeled biotin complexes, as well as the weak interaction between bovine serum albumin and biotin complexes, at both the micrometer scale and nanoscale. For the micrometer-scale measurements using ensemble NV centers, we re-examined the often-neglected fast relaxation component and proposed a relaxation rate evaluation method, substantially enhancing the measurement sensitivity. Furthermore, we achieved nanoscale detection approaching single-molecule level using single NV centers. This methodology holds promise for applications in molecular screening, identification and kinetic studies at the single-molecule level, offering critical insights into molecular function and activity mechanisms.
The use of optical tweezers as a tool to facilitate nondestructive nanoscale sensing has been a growing area of research, particularly in the biological sciences. The nitrogen-vacancy (NV) center in diamond has attracted significant interest in this area due to the array of sensing modalities available and the biocompatibility of the material itself. Many of the diamond sensing modalities rely on the measurement and characterization of the NV spin. Recent work has demonstrated the utility of the spin–lattice relaxation time ( T 1 ) of NV centers in nanodiamond for nanoscale magnetic sensing and spectroscopy. Here, we demonstrate spin relaxometry with optically trapped nanodiamonds. The all-optical sensing protocol we developed eliminates the spin decoherence effects of the trapping laser and can determine spin–lattice relaxation times on the order of ms. Moreover, the protocol requires relatively low trapping powers <50 mW, making it particularly applicable to biological systems.
The nitrogen-vacancy (NV) centre in diamond gained popularity as a probe for nanoscale sensing applications in research thanks to the array of sensing modalities available and the bio-compatibility of the material itself, however the utility of NV sensing is limited by the lack of suitable strategies to control them spatially. By confining single nanodiamonds using an optical tweezers (OT) we are able to combine the sensing opportunities of the NV centre with the precision control of position and orientation afforded by OT. This work is an investigation of the interaction of the trapping laser with the spin-based photoluminescence of the NV centre, further it is a demonstration of an all-optical sensing protocol which eliminates the spin depolarisation effects of the trapping laser and allows for NV spin relaxometry in an optically trapped nanodiamond. This relaxometry protocol can determine spin lattice relaxation times on the order of ms and requires relatively low trapping powers < 50 mW, making it particularly applicable to biological systems.