Live-cell imaging of cellular and tissue samples relies predominantly on optical modalities, such as fluorescence, confocal, and multiphoton microscopy, in which cellular information is encoded in emitted photons. Photons scatter and attenuate in biological samples, restricting depth resolution, while the excitation light required to produce them induces photodamage that perturbs the very biology under observation. Magnetic fields, by contrast, traverse biological samples without attenuation at cellular length scales, but the imaging modality that extracts the encoded information, magnetic resonance imaging, cannot resolve individual cells. Here we present Quantum Cell Monitoring (QCM), a widefield nitrogen-vacancy magnetometry platform that encodes single-cell information in stray magnetic fields rather than emitted photons and reads it out at subcellular resolution. Integrated with a specialized live-cell incubator, QCM tracks magnetically labeled living cancer for up to 72 h through their individual magnetic field signatures. It captures single-cell mitosis and morphological remodeling, as well as cell cluster formation, splitting, and migration even within dense regions where brightfield contrast collapses. By shifting the carrier of single-cell information from propagating optical photons to static magnetic stray fields, QCM decouples cell from cellular optical accessibility and auto-fluorescence, enabling sustained live-cell observation in regimes inaccessible to optical microscopy.
AI Summary
The paper asks whether widefield nitrogen-vacancy (NV) magnetometry can monitor magnetically labeled living cells over multiple days. Its Quantum Cell Monitoring platform combines a diamond NV ensemble, total-internal-reflection laser excitation, microwave readout, and a temperature-, humidity-, and CO$_2$-controlled incubation chamber. Antibody-linked superparamagnetic iron oxide nanoparticles label EpCAM on HT29 colorectal cancer cells seeded directly onto the diamond.
Three monolayer experiments span 48, 66, and 72 hours. Magnetic maps acquired every 8 hours resolve micrometer-scale structure in cellular stray-field signatures with amplitudes of a few $\mu\mathrm{T}$. Each acquisition takes 5 minutes at 25 mW excitation power; reported per-pixel sensitivity is approximately $2.5\,\mu\mathrm{T}/\sqrt{\mathrm{Hz}}$. Correlated brightfield imaging supports identification of division, morphological changes, migration, and cluster formation and splitting. A sparse nonnegative dipole-deconvolution procedure also recovers cell positions from one clustered magnetic map without optical input and estimates iron mass assuming fixed cell size and depth.
The demonstrated samples are surface-adherent monolayers, not optically inaccessible three-dimensional tissue. Most longitudinal identities are established using frequent brightfield images; magnetic-only localization is a proof of concept rather than a validated multi-day tracking pipeline. Standard viability assays were unavailable, so viability is assessed from migration, proliferation, and morphological activity. Five-minute acquisitions can blur moving cells, brightfield segmentation is insufficient for quantitative morphology, and the magnetic reconstruction approximates extended cells as point dipoles. Detection tens of micrometers above the sensor, and extensions beyond $100\,\mu\mathrm{m}$ using stronger labels, are extrapolations rather than demonstrated imaging depths.
Central claim may not hold: Magnetic-only longitudinal identity retention is not validated by the optical-derived tracking or single-map magnetic localization, and the short-delay subdiffusive MSD exponent cannot establish unique assignments across eight-hour intervals.
Sustained observation independently of cellular optical accessibility is not demonstrated by the near-surface monolayer experiments; tissue-depth performance remains extrapolated or contingent on improved labels.
Loss of brightfield contrast does not demonstrate failure of optical microscopy generally, and terminal mounting is not an inherent requirement of light-sheet microscopy.
Observed migration and proliferation support cell survival but do not establish normal kinetics or absence of measurement-induced stress without appropriate controls.
The projected tenfold-to-twentyfold signal improvement reduces a 300-second acquisition to 3–0.75 seconds, not uniformly below one second, through quadratic rather than exponential scaling.
Written by gpt-6.1-sol from the paper's full text. Automated: it can be wrong.
Live-cell imaging of cellular and tissue samples relies predominantly on optical modalities, such as fluorescence, confocal, and multiphoton microscopy, in which cellular information is encoded in emitted photons. Photons scatter and attenuate in biological samples, restricting depth resolution, while the excitation light required to produce them induces photodamage that perturbs the very biology under observation. Magnetic fields, by contrast, traverse biological samples without attenuation at cellular length scales, but the imaging modality that extracts the encoded information, magnetic resonance imaging, cannot resolve individual cells. Here we present Quantum Cell Monitoring (QCM), a widefield nitrogen-vacancy magnetometry platform that encodes single-cell information in stray magnetic fields rather than emitted photons and reads it out at subcellular resolution. Integrated with a specialized live-cell incubator, QCM tracks magnetically labeled living cancer for up to 72 h through their individual magnetic field signatures. It captures single-cell mitosis and morphological remodeling, as well as cell cluster formation, splitting, and migration even within dense regions where brightfield contrast collapses. By shifting the carrier of single-cell information from propagating optical photons to static magnetic stray fields, QCM decouples cell from cellular optical accessibility and auto-fluorescence, enabling sustained live-cell observation in regimes inaccessible to optical microscopy.
The paper asks whether widefield nitrogen-vacancy (NV) magnetometry can monitor magnetically labeled living cells over multiple days. Its Quantum Cell Monitoring platform combines a diamond NV ensemble, total-internal-reflection laser excitation, microwave readout, and a temperature-, humidity-, and CO2-controlled incubation chamber. Antibody-linked superparamagnetic iron oxide nanoparticles label EpCAM on HT29 colorectal cancer cells seeded directly onto the diamond.
Three monolayer experiments span 48, 66, and 72 hours. Magnetic maps acquired every 8 hours resolve micrometer-scale structure in cellular stray-field signatures with amplitudes of a few μT. Each acquisition takes 5 minutes at 25 mW excitation power; reported per-pixel sensitivity is approximately 2.5μT/Hz. Correlated brightfield imaging supports identification of division, morphological changes, migration, and cluster formation and splitting. A sparse nonnegative dipole-deconvolution procedure also recovers cell positions from one clustered magnetic map without optical input and estimates iron mass assuming fixed cell size and depth.
The demonstrated samples are surface-adherent monolayers, not optically inaccessible three-dimensional tissue. Most longitudinal identities are established using frequent brightfield images; magnetic-only localization is a proof of concept rather than a validated multi-day tracking pipeline. Standard viability assays were unavailable, so viability is assessed from migration, proliferation, and morphological activity. Five-minute acquisitions can blur moving cells, brightfield segmentation is insufficient for quantitative morphology, and the magnetic reconstruction approximates extended cells as point dipoles. Detection tens of micrometers above the sensor, and extensions beyond 100μm using stronger labels, are extrapolations rather than demonstrated imaging depths.
Combining optical tweezers with fluorescence microscopy is a powerful tool for single-cell analysis, playing a pivotal role in disease diagnosis, cell sorting, and the investigation of cellular dynamics. However, fluorescence detection faces challenges such as blinking, photobleaching and autofluorescence in biotissues. To address these limitations, we developed a magnetic detection strategy by integrating quantum magnetometry using nitrogen-vacancy centers into optical tweezers, demonstrating precise trapping and manipulation of individual cells in microfluidic environment. We detected a magnetic signal of 89 μT from a single cell labeled with magnetic nanoparticles, compared to a noise floor of 3.9 μT observed in unlabeled cells. This platform provides a promising approach for high-precision single-cell analysis and holds significant potential for probing cellular activities within biological microenvironments.
Nitrogen-vacancy (NV) centers in diamond provide a versatile quantum sensing platform for biological imaging through magnetic field detection, offering unlimited photostability and the ability to perform long-term observations without photobleaching or phototoxicity. However, conventional stage-top incubators are incompatible with the unique requirements for NV widefield magnetometry to study cellular dynamics. Here, we present a purpose-built compact incubation platform that maintains precise environmental control of temperature, CO2 atmosphere, and humidity while accommodating the complex constraints of NV widefield microscopy. The system employs a 3D-printed biocompatible chamber with integrated heating elements, temperature control, and humidified gas flow to create a stable physiological environment directly on the diamond sensing surface. We demonstrate sustained viability and proliferation of HT29 colorectal cancer cells over 90 hours of continuous incubation, with successful magnetic field imaging of immunomagnetically labeled cells after extended cultivation periods. This incubation platform enables long-term cultivation and real-time monitoring of biological samples on NV widefield magnetometry platforms, opening new possibilities for studying dynamic cellular processes using quantum sensing technologies.
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.
Direct monitoring the multifaceted intracellular microenvironment is fundamental for deciphering localized cellular behavior and function. However, performing nanoscale spatiotemporal sensing of the dynamic physiochemical environment within a live cell has remained challenging, mainly limited by the lack of robust, biocompatible method which satisfies the requirements for spatiotemporal resolution, sensitivity, multi-physical sensing capability and long-term viability. Here we present a super-resolution-based quantum biosensing approach, namely Super-resolution Multi-physical field Imaging with Deconvolution, implemented in our custom-built setup which integrates nitrogen vacancy center-based quantum sensing with structured illumination microscopy. This enables quantitative, super-resolved, and long-term tracking of intracellular physical fields, featuring spatial resolution of 136 nm, temporal resolution of 150 ms, and field of view of 180×180 μm2. We further perform super-resolution multimodal imaging in a live cell, revealing the spatially heterogeneous reactive oxygen species dynamics under external stimulation. Our work enables the dynamic assessment of localized physiochemical dynamics under super-resolution quantum biosensing. This work presents a super-resolution quantum biosensing approach by integrating nitrogen vacancy (NV) center-based quantum nanodiamond sensors with structured illumination microscopy, which achieves super-resolution multi-physical imaging within live cells.
Many spintronic, magnetic-memory, and neuromorphic devices rely on spatially varying magnetic fields. Quantitatively imaging these fields with full vector information over extended areas remains a major challenge. Existing probes either offer nanoscale resolution at the cost of slow scanning, or widefield imaging with limited vector sensitivity or material constraints. Quantum sensing with nitrogen-vacancy (NV) centers in diamond promises to bridge this gap, but a practical camera-based vector magnetometry implementation on relevant microstructures has not been demonstrated. Here we adapt a commercial widefield microscope to implement a camera-compatible pulsed optically detected magnetic resonance protocol to reconstruct stray-field vectors from microscale devices. By resolving the Zeeman shifts of the four NV orientations, we reconstruct the stray-field vector generated by microfabricated permalloy structures that host multiple stable remanent states. Our implementation achieves a spatial resolution of ≈0.52μm across an 83μm×83μm field of view and a peak sensitivity of $ (828 \pm 142)~\mathrm{nT\,Hz^{-1}}$, with acquisition times of only a few minutes. These results establish pulsed widefield NV magnetometry on standard microscopes as a practical and scalable tool for routine vector-resolved imaging of complex magnetic devices.
Two revolutions in quantum sensing are converging on the same microscope stage. Biological qubits have emerged as genetically encoded, optically addressable quantum systems inside live cells. Solid state spin based qubits have been entangled and used as nanoscale correlator magnetometers, delivering sensitivity and spatial-resolution gains that single-spin probes cannot reach. Here we report a pulsed quantum microscope that enables simultaneous quantum state manipulation of both qubit technologies in live cells. The platform combines nanosecond-gated optical excitation at 450 nm and 520 nm, three-dimensional diffraction-limited addressing by galvo beam scanning and piezo objective focus, rapidly switched static and radio-frequency magnetic fields, single-photon timing with picosecond resolution, and microwave control for frequencies from DC to 5 GHz, including the 2.87 GHz resonance of solid state spins, the 500 MHz to 800 MHz resonance of radical pairs in biological qubits, and any future qubit resonance in the GHz range. Live cell imaging with simultaneous biological and solid state nanoparticle qubits in the same cell demonstrates the power of this technique for multiplexed quantum sensing. We anticipate this approach will open new opportunities for researchers to explore quantum sensing in live cells, and, ultimately, entanglement between a solid-state qubit and a protein-hosted spin qubit.