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.
Optical tweezers are a versatile tool in the domain of cytology, enabling trapping and manipulation of individual cells. However, the incidence of laser light causes photodamage to biological matter, even when operating at low optical powers and over short periods of time. Here, we demonstrate stable trapping of single living Saccharomyces cerevisiae yeast cells in vitro using a dark optical trap operating in the repulsive regime of light-matter interactions. In contrast to standard tweezers, our dark optical trap confines cells for hours with negligible disruption to their morphology and reproduction cycle, opening up new possibilities for long duration experiments with living organisms such as the observation of cell reproduction under laser trapping.
This work explores the feasibility of inducing lasing action in a single dye molecule using an optical microcavity. A single-molecule light source is proposed, in which a microcavity-coupled dye molecule is pumped by multiple energy donors via an intermolecular resonance energy transfer mechanism. A quantitative model based on realistic parameters for microcavities and for organic dyes shows that stimulated emission may become dominant over spontaneous fluorescence under optimal yet technically reachable conditions, suggesting the likelihood of achieving a single-molecule lasing photon source with the proposed device. Lasing of a single dye molecule generates signals much brighter than spontaneous fluorescence, and may find applications in a wide range of fields from physics and chemistry to biology.