Zinn Labs leverages event sensors to bring gaze tracking to a new class of low-power smart frames and head-mounted displays. Gaze provides rich contextual data for AI systems that interact with users, enabling applications from understanding intent, or building a user interface, to optimizing display and lens systems. Zinn’s event-based gaze tracking system delivers fast and accurate performance for these applications, without the high computational cost or power of image-based approaches. This low-power, high-performance system brings a ubiquitous gaze signal to intelligent wearable devices that is enabling new applications like foveated rendering and context-aware virtual assistants that see what you see.
Nanometer-scale deformations of the neuron accompany the action potential. These displacements are measured using a fast quantitative phase microscope and averaged in synchrony with optogenetic stimulation of cultured neurons. The phase movie is further processed by leveraging the spatial and temporal distribution of the spiking signal to detect and segment the separate action potentials in individual cells. An accompanying confocal fluorescence microscopy provides the 3-D cell shape for calibration of the refractive index to calculate the mechanical displacements from the optical phase. Together, these results illuminate the underlying mechanism of the cellular deformations and techniques for achieving all-optical single spike detection.
We report the full-field imaging of the mechanical deformations accompanying the action potential in primary cortical neurons using ultrafast quantitative phase imaging (QPI) with a temporal resolution of 0.1 ms and a membrane displacement sensitivity of <0.2 nm per pixel. The average displacements were ~0.7 nm on cell somas and ~0.5 nm on neurites. Finite element modeling based on the 3D shape extracted from confocal imaging and on scaling of the surface tension with trans-membrane voltage yielded the deformation map during action potential, which matched the features of the experimental results, including the displacement amplitude, time course, and spatial distribution.
We developed a high-speed adaptive optics, line-scan spectral domain OCT and used it to characterize stimulus-induced optical path length changes in cones with high spatiotemporal resolution. We find that individual cone outer segments exhibit a biphasic light-induced response—a rapid axial shrinkage followed by a gradual increase in optical path length, both increasing in magnitude with the stimulus intensity. AO line-scan OCT thus offers high-speed volume acquisitions, high phase stability, sub-ms temporal resolution and cellular-scale spatial resolution, that together enable imaging retinal structure and function in health and disease.
Nanometer-scale movements of the cell membrane associated with changes in cell potential can reveal the underlying electrical activity. Using wide-field quantitative phase imaging, we observed deformations of up to 3 nm (0.9 mrad) during the action potential in spiking HEK cells, and about 0.3 nm in neurons. The time course of the optically-recorded action potential is similar to intracellular recordings based on patch clamp, while time derivative of the rising edge of the optical spike matches the timing and duration of the extracellular electrical recording. Sufficiently fast QPI may enable non-invasive and label-free monitoring of cellular physiology.
Imaging of the optical phase changes induced by transient heating provides a sensitive measure of material properties associated with refractive index dependence on temperature and thermal expansion. Using fast (50 kHz) QPI, we demonstrate the shot-noise limited sensitivity of about 3.4 mJ/cm2 in a single pulse. Phase-resolved OCT can detect energy deposition of 4.7 mJ/cm2 between two scattering interfaces producing signals with about 45 dB SNR. Integration of the phase changes along the beam path helps increase temperature sensitivity during perturbation. For example, temperature rise of about 0.8 C can be detected in a single cell layer, while hundred times lower heating produces the same phase change in 100-fold thicker tissue layer. Time course of thermal relaxation in QPI can reveal the size and shape of the hidden objects.
Methods based on fast phase imaging may enable multiple applications, ranging from temperature control in retinal laser therapy to subsurface characterization of semiconductor devices.
Movements of the cell membrane accompanying action potentials have been detected by various methods, including reflection of a laser beam, atomic force microscopy and even bright-field microscopy. However, imaging of the entire cell dynamics during action potential has not been achieved, and the mechanism behind this phenomenon is still actively debated. Here we report full-field interferometric imaging of cellular movements during action potential by simultaneous quantitative phase microscopy (QPM) and multi-electrode array (MEA) recordings. Using spike-triggered averaging of the movies synchronized to electrical recording, we demonstrate deformations of up to 3 nm (0.9 mrad) during the action potential in spiking HEK-293 cells, with a rise time of 4 ms. The time course of the optically-recorded action potential is very similar to intracellular potential recorded with a whole-cell patch clamp, while the time derivative of the rising edge of the optical spike matches the timing and duration of the extracellular electrical recording on MEA. In some cells, phase increases at the center and decreases along the cell boundaries, while in others it increases on one side and decreases on the other. These findings suggest that optical phase changes during an action potential are due to cellular deformation, likely associated with changes in the membrane tension, rather than refractive index change due to ion influx or cell swelling. High-speed QPM may enable all-optical, label-free, full-field imaging of electrical activity in mammalian cells.
Wide-field interferometric imaging systems can detect mechanical deformations of a cell during an action potential (AP), such as in quantitative phase microscopy, which is highly sensitive to the changing optical path length. This enables non-invasive optophysiology of spiking cells without exogeneous markers, but high-fidelity imaging of such deformations requires averaging of a large number of spikes synchronized by electrical recordings. We have developed new iterative methods for detecting single APs from quantitative phase microscopy of spiking cells, enabling an all-optical detection system with high accuracy and good temporal resolution. We demonstrate performance of the method across multiple preparations of spiking HEK-293 cells and compare the outcomes of the all-optical measurements with the ground truth detected on a multi-electrode array. We initially use a spike-triggered average, synchronized to an electrical recording, to measure deformations during the AP in spiking cells, which reach up to 3 nm (0.9 mrad) with a rise time of 4 ms and fall time of about 120 ms. Based on this knowledge of the AP dynamics, optical data analysis can provide reliable spike detection, within a standard deviation of 11.6 ms (9.7% of the length of the action potential) with an 8.5% false negative detection rate. The method is robust to natural variations between cells and can be modified to function without any prior knowledge of the AP dynamics. Such a system could achieve high-throughput measurements of network activity in culture and help identify the mechanisms linking cell deformations to the changes of transmembrane potential.
KEYWORDS: Target detection, Ultrasonography, Imaging systems, Dielectrics, Signal detection, Signal to noise ratio, Acoustics, Process control, Electronic filtering, Tissues
A microwave-induced thermoacoustic detection system for embedded targets in lossy media is presented. The system achieves reliable detection of 5 cm × 5 cm × 2 cm targets embedded in a large Agarose sample at a 20 cm acoustic standoff. Repeated measurements across different target and sample configurations confirm the system’s ability to distinguish between a target signal and a baseline control signal generated by the package without embedded targets. Post-processing techniques including filtering and baseline signal characterization further improve detection performance.
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