Ongoing efforts to scale neuroimaging towards direct visualization of mammalian brain-wide neural activity face major challenges, and a large gap still exists between localized optical microscopy looking at rapid cellular-resolved neuronal activities and whole-brain observations of slow hemodynamics and metabolism provided by macroscopic imaging modalities. Optoacoustic imaging holds inherent advantages for deep tissue observations, but to date has not been applied towards direct activity observation in the mammalian brain. Here we demonstrate in vitro and in vivo functional optoacoustic neuroimaging from mice expressing the genetically encoded calcium indicators GCaMP6, effectively bridging the gap between functional microscopy and whole-brain macroscopic neuroimaging. We yielded instantaneous high-resolution 3D snapshots of whole-brain activity maps with single optoacoustic excitations and enabled non-invasive detection of fast neural responses to sensory stimuli in the presence of strong hemoglobin background absorption. These results demonstrate a new enabling technique towards scalable direct neuroimaging at unprecedented penetration depths and spatio-temporal resolutions.

Mobile microrobots hold remarkable potential to revolutionize health care by enabling unprecedented active medical interventions and theranostics, such as active cargo delivery and microsurgical manipulations in hard-to-reach body sites. High-resolution imaging and control of cell-sized microrobots in the in vivo vascular system remains an unsolved challenge toward their clinical use. To overcome this limitation, we propose noninvasive real-time detection and tracking of circulating microrobots using optoacoustic imaging. We devised cell-sized nickel-based spherical Janus magnetic microrobots whose near-infrared optoacoustic signature is enhanced via gold conjugation. The 5-, 10-, and 20-μm-diameter microrobots are detected volumetrically both in bloodless ex vivo tissues and under real-life conditions with a strongly light-absorbing blood background. We further demonstrate real-time three-dimensional tracking and magnetic manipulation of the microrobots circulating in murine cerebral vasculature, thus paving the way toward effective and safe operation of cell-sized microrobots in challenging and clinically relevant intravascular environments.

Widespread metastasis is the major cause of death from melanoma and other types of cancer. At present, the dynamic aspects of the metastatic cascade remain enigmatic. The feasibility to track circulating melanoma cells deep within living intact organisms can greatly impact our knowledge on tumor metastasis, but existing imaging approaches lack the sensitivity, spatio-temporal resolution or penetration depth to capture flowing tumor cells over large fields of view within optically-opaque biological tissues. Vast progress with the development of optoacoustic tomography technologies has recently enabled two- and three-dimensional imaging at unprecedented frame rates in the order of hundreds of Hertz, effectively mapping up to a million image voxels within a single volumetric snapshot. Herein, we employ volumetric optoacoustic tomography for real-time visualization of passage and trapping of individual B16 melanoma cells in the whole mouse brain. Detection of individual circulating melanoma cells was facilitated by substituting blood with an artificial cerebrospinal fluid that removes the strong absorption background in the optoacoustic images. The approach can provide new opportunities for studying trafficking and accumulation of metastatic melanoma cells in different organs.