Magnetic Signals from Single Cells Reveal 89 μT Detection Using Quantum Sensors
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A new approach to single-cell analysis combines optical tweezers with quantum magnetometry. Jun Yin and colleagues at University of Science and Technology of China demonstrate a magnetic detection strategy utilising nitrogen-vacancy centres to both trap and measure individual cells within a microfluidic channel. The method circumvents limitations inherent in fluorescence detection, such as blinking and photobleaching, and successfully detected a magnetic signal from a single cell labelled with magnetic nanoparticles. This platform represents a key advancement towards high-precision, non-optical single-cell analysis and offers a promising avenue for investigating cellular activities in complex biological environments. Single-cell magnetic field detection via integrated optical tweezers and quantum magnetometry A magnetic signal of 89 μT was detected from a single cell, exceeding the 3.9 μT noise floor of unlabeled cells. This represents a key improvement in magnetic sensitivity previously unattainable with single-cell manipulation, offering a substantial leap forward in the field of biophysics. Traditional methods for analysing single cells often rely on optical techniques, but these are hampered by the inherent limitations of fluorescence, including signal degradation due to photobleaching, the irreversible destruction of fluorescent molecules, and autofluorescence, the emission of light from cellular components themselves which obscures the desired signal. These effects limit the duration and accuracy of observations, particularly in complex biological samples. The integration of optical tweezers with nitrogen-vacancy (NV) centre quantum magnetometry provides a novel solution by enabling spin-based magnetic sensing, effectively bypassing these optical constraints. The ability to detect such a small magnetic field, originating from a single cell, opens up possibilities for studying subtle changes in cellular behaviour and identifying rare cell populations with unique magnetic signatures. This is particularly relevant in areas such as early disease detection, where identifying minute differences in cellular magnetic properties could indicate the onset of pathology. The new platform integrates optical tweezers with nitrogen-vacancy centre quantum magnetometry, enabling spin-based magnetic sensing and bypassing limitations of fluorescence techniques such as photobleaching and autofluorescence. Demonstrated within a microfluidic environment, the system allows for precise cell positioning and measurement of magnetic variations; a 2.48MHz resonance peak shift correlated to the 89 μT magnetic field change between different cell configurations. Real-time monitoring of cellular deformation and examination of cell-cell interactions are now possible without the damaging effects of light exposure. Control experiments utilising unlabeled cells exhibited no spectral shift, recording a minimal variation of 0.11MHz over 50 minutes, thus confirming the magnetic signal originated specifically within the labelled cells. Optically trapped cells experienced drift rates of up to 0.3MHz per minute, significantly higher than the 0.03MHz per minute observed in adhered cells, indicating sensitivity to cellular deformation. The absence of a significant resonant frequency shift when the laser was switched off ruled out substantial heating effects, ensuring the observed magnetic signals were not artefacts of the measurement technique. The microfluidic environment is crucial as it provides a controlled and stable platform for cell manipulation and measurement, minimising external disturbances and ensuring accurate data acquisition. The observed correlation between the resonance peak shift and the magnetic field change validates the system’s ability to accurately translate magnetic signals into measurable frequency shifts. Optical Tweezers and Nitrogen-Vacancy Centres Enable Nanoparticle Detection within Single Cells The technique hinged on integrating optical tweezers, tiny tractor beams of light used to hold and move microscopic objects like cells without physical contact, with quantum magnetometry utilising nitrogen-vacancy centres. These microscopic defects in diamond act as incredibly sensitive compass needles, detecting tiny changes in magnetic fields and forming the core of the magnetic sensing system. Nitrogen-vacancy centres are point defects in the diamond lattice, created by replacing a carbon atom with a nitrogen atom and leaving a vacancy next to it. These defects possess unique spin properties that are highly sensitive to external magnetic fields, making them ideal for use in quantum magnetometry. The sensitivity arises from the interaction between the electron spin of the NV centre and the surrounding magnetic field, which causes a shift in the energy levels of the NV centre, detectable through optical spectroscopy. At [Institution], Dr. [Name] carefully aligned a strong static magnetic field to polarise the NV centres and align magnetic nanoparticles within the cells. Single J774.1 murine macrophage cells, labelled with approximately 4.5x 10 5 magnetic nanoparticles, each with a magnetic moment of 8.6x 10 -16 emu and internalised via endocytosis, concentrating within endosomes and lysosomes, generated a magnetic signal of 89 microteslas. The process of endocytosis, where cells internalise external material, ensures that the nanoparticles are brought into proximity to the cell’s internal structures, maximising the magnetic signal. The concentration within endosomes and lysosomes further enhances the signal by increasing the local density of magnetic nanoparticles. The system achieved a magnetic sensitivity of 3 microteslas per root Hertz, with a T2* coherence time of 2 microseconds, obtained by optimising microwave power and employing an alternating 1064nm laser to maintain stable cell confinement. The T2* coherence time represents the duration for which the NV centre’s spin coherence is maintained, a critical parameter for the sensitivity and accuracy of the magnetic measurements. Optimising the microwave power and laser parameters is essential for maximising the T2* coherence time and achieving optimal performance. Quantum magnetometry bypasses fluorescence limitations for improved single-cell analysis Researchers are increasingly focused on understanding single cells, which is vital for progress in areas like disease diagnosis and personalised medicine. This new technique offers a potential route beyond established, yet imperfect, fluorescence microscopy. The ability to analyse individual cells, rather than relying on population averages, provides a more nuanced understanding of cellular heterogeneity and allows for the identification of rare cell types or subtle changes in cellular behaviour. Magnetic nanoparticle labels, while necessary to generate a detectable signal, could alter cellular behaviour, potentially undermining the precision the method seeks to achieve. Thorough investigations into the biocompatibility and potential effects of these nanoparticles on cellular function are crucial for ensuring the reliability of the results. Nevertheless, this advance remains significant as it establishes a fundamentally new detection pathway. The development of alternative labelling strategies, or the use of intrinsic magnetic properties of cells, could further enhance the technique and minimise potential artefacts. Current single-cell analysis heavily relies on fluorescence, a technique prone to interference from biological samples. Quantum magnetometry offers a distinct signal, potentially revealing details obscured by these limitations. This work successfully merges microscopic tools for manipulating cells with the sensitivity of quantum magnetometry utilising nitrogen-vacancy centres, microscopic defects within diamonds sensitive to magnetic fields. Detecting a magnetic signal of 89 μT from a single, magnetically labelled cell demonstrates a key improvement over traditional fluorescence techniques prone to interference, opening avenues for real-time observation of cellular processes and interactions without damaging light exposure. The potential applications of this technology extend beyond basic research, encompassing areas such as drug screening, where the response of individual cells to different compounds can be monitored, and the development of new diagnostic tools for detecting diseases at an early stage. Further research will focus on improving the sensitivity and resolution of the system, as well as exploring its applicability to a wider range of cell types and biological systems. The researchers successfully detected a magnetic signal of 89 μT from a single cell labelled with magnetic nanoparticles using a new platform combining optical tweezers and quantum magnetometry. This offers a potential alternative to fluorescence-based single-cell analysis, which can be affected by interference from biological tissues. The technique allows for precise cell manipulation and detection within a microfluidic environment, providing a more detailed understanding of cellular behaviour. The authors intend to improve the system’s sensitivity and explore its use with different cell types. 👉 More information 🗞 Spin-based magnetic detection of optically trapped single cell in microfluidic channel 🧠 DOI: https://doi.org/10.1088/1674-1056/adde38 Tags: