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Data processing and applications of fluorescent nanodiamonds for bio-technology

Thea Vedelaar

Published Jan 17, 2023• 0 citations
Publisher

Abstract

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.

DOI
10.33612/diss.559755626

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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.
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.
Quantum sensing using nitrogen-vacancy (NV) centers in diamond has emerged as a powerful platform for detecting ultra-low magnetic fields under ambient conditions. Owing to their long spin coherence times, optical addressability, and compatibility with aqueous environments, it has found widespread applications in biosensing and bio-imaging. This review presents the fundamental principles and recent advances in NV-based quantum magnetometry for biosensing applications, with a particular focus on measurements in aqueous medium and at cellular and molecular length scales. We discuss the underlying spin physics of NV centers and highlight two primary detection modalities: optically detected magnetic resonance (ODMR) and T1 relaxometry-based sensing and how these approaches aids in the detection of both static magnetic fields and dynamic magnetic noise arising from biological processes. The review explores key application areas, including nanoscale nuclear magnetic resonance (NMR), monitoring of neural activity, detection of abnormal or rogue cells using NV-based platforms etc. In addition, strategies for enhancing sensitivity, such as surface functionalization of nanodiamonds, femtosecond (fs) laser-written photonic structures, and integration with microfluidic and lab-on-chip systems have also been discussed in depth. We also address the critical challenges, including surface-induced decoherence, charge-state instability, and signal-to-noise limitations in biofluids associated with NV-based biosensing applications. Finally, we outline future prospects, highlighting how NV-based magnetic biosensing provides a promising pathway for translating quantum sensing technologies into practical biomedical applications.
Nanodiamonds containing nitrogen-vacancy (NV) centers offer a versatile platform for sensing applications spanning from nanomagnetism to in vivo monitoring of cellular processes. In many cases, however, weak optical signals and poor contrast demand long acquisition times that prevent the measurement of environmental dynamics. Here, we demonstrate the ability to perform fast, high-contrast optical measurements of charge distributions in ensembles of NV centers in nanodiamonds and use the technique to improve the spin-readout signal-to-noise ratio through spin-to-charge conversion. A study of 38 nanodiamonds with sizes ranging between 20 and 70 nm, each hosting a small ensemble of NV centers, uncovers complex, multiple time scale dynamics due to radiative and nonradiative ionization and recombination processes. Nonetheless, the NV-containing nanodiamonds universally exhibit charge-dependent photoluminescence contrasts and the potential for enhanced spin readout using spin-to-charge conversion. We use the technique to speed up a T 1 relaxometry measurement by a factor of 5.
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 T1T_1T1​. Conventional pulsed protocols, however, probe T1T_1T1​ 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 T1T_1T1​ from the characteristic response time of the spin system. The method enables efficient T1T_1T1​ measurements spanning more than three orders of magnitude -- directly demonstrated from 60 μμμs 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 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.
Fluorescent nanodiamonds (FNDs) containing negatively charged nitrogen-vacancy (NV-) centers are vital for many emerging quantum sensing applications from magnetometry to intracellular sensing in biology. However, developing a scalable fabrication method for FNDs hosting color centers with consistent bulk-like photoluminescence (PL) and spin coherence properties remains a highly desired but unrealized goal. Here, we investigate optimized ball milling of single-crystal diamonds produced via chemical vapor deposition (CVD) and containing 2 ppm of substitutional nitrogen and 0.3 ppm of NV- to achieve this goal. The NV charge state, PL lifetime, and spin properties of bulk CVD diamond samples are directly compared to milled CVD FNDs and commercial high-pressure high-temperature (HPHT) FNDs. We find that on average, the relative contribution of the NV- charge state to the total NV PL is lower and the NV PL lifetime is longer in CVD FNDs compared to HPHT FNDs, both likely due to the lower Ns0 concentration in CVD FNDs. The CVD bulk and CVD FNDs on average show similar average T1 spin relaxation times of 3.2 ±\pm± 0.7 ms and 4.7 ±\pm± 1.6 ms, respectively, compared to 0.17 ±\pm± 0.01 ms for commercial HPHT FNDs. Our results demonstrate that ball milling of CVD diamonds enables the large-scale fabrication of NV ensembles in FNDs with bulk-like T1 spin relaxation properties.