System and method for investigating a cell

Abstract

A system and method for investigating a cell is provided. In some aspects, the method includes directing a first beam of polarized light to a sample comprising a cell on a sample holder, and receiving a second beam of polarized light from the sample, wherein the second beam of polarized light is rotated relative to the first beam of polarized light by a rotation angle. The method also includes characterizing the second beam of polarized light using a detector, and determining a magnetic field about the sample based on characterization of the second beam of polarized light.

Description

Atorney Docket No. 065472-000982WOPTSYSTEM AND METHOD FOR INVESTIGATING A CELLCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of, and priority to, U.S. Provisional Patent Application No. 63 / 716,139 filed on November 4, 2024, and U.S. Provisional Patent Application No. 63 / 716,155 filed on November 4, 2024, each of which is hereby incorporated by reference herein in its entirety.BACKGROUND

[0002] Understanding biochemical and electrical signaling processes that underlie dynamic neural activity in a mammalian brain can have important impacts on research and therapeutic endeavors. For instance, understanding magnetic field dynamics can be useful in revealing neural coding and brain function. Also, decoding activity-dependent magnetic field dynamics in cellular and subcellular structures is vital for the development of next-generation non- invasive neuromodulatory technology.

[0003] Thus far, however, causes and consequences of magnetic fields generated by activity of individual neurons remain elusive. In part, this may be because conventional techniques used to perturb and measure magnetic fields in a brain are limited. For example, magnetoencephalography, and other techniques, can detect only macroscopic magnetic fields, thereby reflecting aggregate activity of many neurons across large regions of the brain.

[0004] Therefore, there is a need for an improved technologies for investigating cells.SUMMARY

[0005] In one aspects of the present disclosure, a system for investigating a cell is provided.The system includes a sample assembly comprising a sample holder to hold a sample comprising a cell, and a magnetic measurement apparatus operable to detect a magnetic field in the sample, the magnetic measurement apparatus comprising an optical system having a light source configured to emit light and collimation optics configured to receive and collimate light emitted by the light source. The optical system also includes a first polarization filter configured to receive light collimated by the collimation optics, and generate a first beam of polarized light, wherein the first beam of polarized light is directed to the sample holder holding the sample, a second polarization filter configured to receive and filter a second beam of polarized light from the sample holder, wherein the second beam of polarized light is rotated- 1 -4900-3460-9014Atorney Docket No. 065472-000982WOPT relative to the first beam of polarized light by a rotation angle, and a detector configured to characterize light in the second beam of polarized light. The system further includes an electrical measurement apparatus operable to perform an electrical measurement on the sample.

[0006] In another aspect of the present disclosure, a method for investigating a cell is provided. The method includes directing a first beam of polarized light to a sample comprising a cell on a sample holder, and receiving a second beam of polarized light from the sample, wherein the second beam of polarized light is rotated relative to the first beam of polarized light by a rotation angle. The method also includes characterizing the second beam of polarized light using a detector, and determining a magnetic field about the sample based on characterization of the second beam of polarized light.

[0007] The foregoing summary is not intended to represent each embodiment or every aspect of the present disclosure. Rather, the summary merely provides an example of some of the novel aspects and features set forth herein. The above features and advantages, and other features and advantages of the present disclosure, will be readily apparent from the following detailed description of representative embodiments and modes for carrying out the present approach, when taken in connection with the accompanying drawings and the appended claims.BRIEF DESCRIPTION OF DRAWINGS

[0008] The present disclosure is described with reference to the attached drawings, where like reference numerals are used throughout the drawings to designate similar or equivalent elements. The drawings are not drawn to scale and are provided merely for illustration. Several aspects of the disclosure are described below with reference to example applications for illustration.

[0009] FIG. 1 is schematic diagram of an example system, according to aspects of the present disclosure.

[0010] FIG. 2 is an illustration depicting Faraday rotation of polarized light by a magnetic field, according to aspects of the present disclosure.

[0011] FIG. 3A is an illustration of another example system, according to aspects of the present disclosure.

[0012] FIG. 3B is a cross-section of an example sample holder of the system in FIG. 3A, according to aspects of the present disclosure.

[0013] FIG. 4 is an illustration showing a method of detecting a magnetic field in a cell using an evanescence wave, according to aspects of the present disclosure.- 2 -4900-3460-9014Atorney Docket No. 065472-000982WOPT

[0014] FIG. 5A is an illustration of yet another example system, according to aspects of the present disclosure.

[0015] FIG. 5B is an illustration of an example path of reflected light in the system of FIG. 5A, according to aspects of the present disclosure.

[0016] FIG. 5C is an illustration of an example path of transmitted light in the system of FIG. 5A, according to aspects of the present disclosure.

[0017] FIG. 6 is a flowchart setting forth steps of a process, according to aspects of the present disclosure.

[0018] Advantages of the present disclosure will become apparent upon reading the following detailed description and upon reference to the drawings.DETAILED DESCRIPTION

[0019] Understanding cellular and synaptic activity can be critical for determining neural circuit dynamics that support cognitive function. For instance, it is believed that sources of activity dependent magnetic fields at the sub-cellular level result from transmembrane currents through ion channels, in addition to intracellular axial currents that flow along neuronal processes. Whether these are sole contributors or significant sources of underlying magnetic field generation remains unclear. Generally, electro-diffusion phenomena generating magnetic fields within the micro- and nanodomains of synapses and cells have been largely unexplored. Notably, there are circumstances where a magnetic field signal can be a more faithful reporter of neural dynamics relative to an electric field signal. Indeed, electrically silent magnetic fields can arise in a variety of scenarios where the cyto-architectonic geometry of the neuropil is favorable, such as at bifurcation points of complex dendritic tree structures. Therefore, a significant knowledge gap remains regarding magnitude, dynamics, and functional impact of activity-dependent magnetic fields at the cellular and subcellular levels.

[0020] Previous measurements using conventional techniques have indicated that neuronal action potentials can generate detectable magnetic fields. Yet despite such indication, conventional approaches make magnetic field measurements relatively far from cells that generate such fields, potentially leading to inaccurate perception of contribution to physiological function. Hence, current tools fall short of measurement and perturbation of magnetic fields in live biological systems at the scale of individual neurons.

[0021] Further, conventional conceptual frameworks used to describe electro-diffusion phenomena in the brain make critical assumptions that may not be valid at the microscale of individual neurons and the nanoscale of subcellular compartments. For example, one current- 3 -4900-3460-9014Atorney Docket No. 065472-000982WOPT theoretical framework used to model and interpret physiological data assumes that no magnetic fields are present and relies on a principle of electroneutrality. Electroneutrality assumes that in a bulk electrolyte solution of freely moving ions, any transient local accumulation of electric charge and field strength is rapidly compensated by electro-diffusion of counterions. Thus, at relatively long length scales and time epochs, aqueous electrolyte in brain tissue (i.e., cerebrospinal fluid) can approximated to be electrically neutral.

[0022] By contrast, ions in solution have low magnetic susceptibility, which allows magnetic fields to propagate relatively unimpeded. Importantly, there are several physiological scenarios where electroneutrality may not apply. For example, electroneutrality can be violated at micrometer to nanometer length scales, such as an interface between a neuronal cell membrane and intracellular polyelectrolytes in aqueous electrolyte solution. At such spatial scales, solvated ions organize into capacitive layers along the membrane or polyelectrolyte interface giving rise to a junction potential. During neuronal action potentials, transmembrane currents mediated by ion channels can drive about 100 millivolt (mV) fluctuations in voltage over 1-2 milliseconds (ms). Such voltage dynamics can cause rapid fluctuations of ionic species, giving rise to micro- or nanodomain electrical currents mediated by ionic flux. Ionic fluctuations can occur over nanometers, and can produce magnetic fields with steep gradients that can interact over distances far longer than those of electric fields (which are shielded), the physiological significance of which remains to be determined. And so, juxta-membrane nanodomain and subcellular architectonics of neurons represent various scenarios in which conventional assumptions of electroneutrality may be violated. Such assumptions produce systematic knowledge gaps in physiological processes at the micro- and nano-scale that were previously considered to be understood.

[0023] It is therefore recognized herein that new technologies are needed for investigating one or more cell, and / or cellular tissue including, for instance, technologies that can measure activity-dependent magnetic fields with sufficient sensitivity and precision to achieve cellular resolution. As appreciated from description herein, the present disclosure provides a number of benefits and improvements over conventional fields of technology, such as conventional technologies for investigating cells and cellular tissue. For instance, the present approach combines super-resolution capabilities of total internal reflectance microscopy with sensitive magnetic field measurement capabilities of Faraday rotation spectroscopy.

[0024] Referring particularly to FIG. 1, an example of a system 100, according to aspects of the present disclosure, is illustrated. In general, the system 100 may include a sample assembly 102, an electrical measurement apparatus 104, and a magnetic measurement- 4 -4900-3460-9014Atorney Docket No. 065472-000982WOPT apparatus 106. In some embodiments, the system 100 may also include a controller 108.

[0025] The sample assembly 102 may include a variety of components and hardware, capable of holding, supporting, securing, positioning, and / or orienting one or more sample (e.g., neural cell, neural tissue, cardiac cell, cardiac tissue, muscle cell, muscle tissue, and so forth). In some embodiments, the sample assembly 102 may include a sample substrate such as a slide, a coverslip, and so forth. For example, the sample substrate may include a glass slide, a glass substrate, a glass coverslip, a coverglass, and so forth. In some embodiments, a material of the sample substrate has a high optical transmittance (e.g., greater than about 80%).

[0026] In some embodiments, the sample substrate may be coated with one or more material, and / or substances. For example, in some embodiments, the sample substrate may be coated with a semiconductor material or thin film. In another example, the sample substrate may be coated with one or more coating layer of graphene, for instance, by transference from a thin film or by liquid deposition of graphene ink. In some embodiments, the sample substrate may include a material that is doped. For example, the sample substrate may include a Lanthanide glass doped with paramagnetic Terbium ions (Tb4+). The sample substrate may also include various substances, such as one or more tissue, cell, and so forth.

[0027] In some embodiments, the sample assembly 102 may include a movable stage that may be configured or operable to move in one or more directions to position and / or orient the sample(s). For instance, the movable stage may include, or be engaged with, various components and / or hardware, such as one or more gear, actuator, motor, and so forth.

[0028] The electrical measurement apparatus 104 may include a variety of components and hardware operable to acquire various electrical measurements from one or more sample held in the sample assembly 102. For example, the electrical measurement apparatus 104 may include one or more amplifier, resistor, capacitor, inductor, digitizer, voltmeter, current meter, and so forth. In some embodiments, the electrical measurement apparatus 104 may be operable to perform a patch-clamp measurement. To this end, the electrical measurement apparatus 104 may include a patch-clamp pipette including a conducting solution (e.g., an electrolyte solution), an electrode electrically immersed in or connected to the conducting solution, an operational amplifier connected to the conducting solution via the electrode, one or more resistor (e.g., a feedback resistor) connected to the conducting solution, and a measurement device connected to the resistor(s) and operational amplifier. In particular, the patch-clamp pipette may be operable to engage one or more sample in the sample assembly 102 and provide various electrical measurements.

[0029] The magnetic measurement apparatus 106 may include a variety of components and- 5 -4900-3460-9014Atorney Docket No. 065472-000982WOPT hardware operable to acquire various magnetic measurements from one or more sample held in the sample assembly 102. In some embodiments, the magnetic measurement apparatus 106 may include an optical system that may perform optical magnetometry to detect activity dependent neuronal magnetic field dynamics. The optical system may include a variety of optical components and hardware, such as one or more light source, polarizer, filter, splitter, objective, mirror, condenser, collimator, grating, prism, diffuser, retarder, lens, wheel, polarimeter, detector, camera, and so forth. In some configurations, the optical system may be used to perform a total internal reflection (TIR) - Faraday rotation spectroscopy (FRS), as detailed further below. In other configurations, the optical system that may be used to image the sample(s) in the sample assembly 102.

[0030] In some embodiments, the system 100 may optionally include a controller 108. By way of example, the controller 108 may include a computing device (e.g., laptop, computer, and so forth), a personal device (e.g., smartphone, tablet, and so forth), as well as any other system, device, or apparatus suitable for carrying out steps, as described herein.

[0031] In some embodiments, the controller 108 may be programmed and / or hardwired to control functionality or operation of the sample assembly 102, electrical measurement apparatus 104, magnetic measurement apparatus 106, or a combination thereof. For instance, the controller 108 control acquisition (e.g., acquisition timing, sampling rate, triggering, and so forth) and / or processing of various signals (e.g., electrical signals, optical signals, magnetic signals, and so forth). The controller 108 may also control operation various components of the sample assembly 102, electrical measurement apparatus 104, and / or magnetic measurement apparatus 106, or a combination thereof. For instance, the controller 108 may control a position and / or orientation of a sample holder of the sample assembly 102 by communicating with and sending control signals to various hardware, such as a motor, gear, actuator, and so forth). The controller 108 may also control a position and / or orientation of an optical element or component, such as a filter, detector, polarizer, beamsplitter, detector, camera, and so forth.

[0032] To control functionality or operation, the controller 108 may include or communicate with various control, acquisition, and / or processing hardware. For example, the controller 108 may include and / or communicate with one or more data acquisition card, board, signal conditioner, module, relay, sensor, detector, camera and so forth. In some embodiments, the controller 108 may be operable to coordinate or synchronize acquisition of signals, for example, such as electric signals and optical signals. For instance, the controller 108 may utilize various timing control mechanisms, such as triggering, and so forth. For example, the controller 108 may send a trigger signal to both the magnetic measurement apparatus 106 and the- 6 -4900-3460-9014Atorney Docket No. 065472-000982WOPT electrical measurement apparatus 104 to initiate synchronized measurement, thereby producing correlated electric signals and magnetic signals. Further, in some embodiments, the controller 108 may be operable to control a configuration of the optical system, and / or components therein.

[0033] In some embodiments, the system 100, or one or more component therein, may be contained in a housing. The housing may include various materials. For instance, in some embodiments, the housing may include a magnetic shielding made, for instance, using a ferromagnetic material (e.g., mu-metal) that passively reduce or eliminates electromagnetic noise. In some embodiments, the housing may include a frame or cage containing one or more coil (e.g., Helmholtz coil), which may actively reduce or eliminate electromagnetic noise. In some embodiments, the system 100, or one or more component therein, may be installed on a vibration isolation table or air table frame, which may reduce or eliminate mechanical vibration noise.

[0034] The measurement system 100 described above may be used for a variety of applications, including investigating one or more cell, cellular tissue, as well as properties or functions thereof. For instance, the system 100 may be used to measure activity-dependent magnetic fields in a neuronal cell. As detailed further below, such measurement may be achieved by implementing optical magnetometry based on TIR-FRS or establishing a reflected light configuration of the system 100.

[0035] In some embodiments, a transmitted light configuration may also be established for the system 100. Such dual-pathway optical approach allows for using an inverted or reflected light pathway for magnetic field measurement, as well as a transmitted light pathway (e.g., Dodt imaging technique) for patch-clamp electrophysiology. In this manner, one or more neuron cultured, for example, on a glass coverslip or coverglass to be investigated. For instance, in one application, one or more neuron may be patch-clamped from above, current may be injected to drive action potentials in the neuron(s), and associated magnetic fields can be optically interrogated by TIR-FRS from below, according to methods described herein. In some embodiments, the system 100 may be further capable of establishing an additional optical pathway for super-resolution fluorescence imaging. In this manner, subcellular structures, for instance, may be imaged in conjunction with high-sensitivity magnetic measurements and simultaneous patch-clamp electrophysiology, as described.

[0036] FRS relies on a Faraday effect, which describes interactions between polarized light and a magnetic field. Referring particularly to FIG. 1, a polarization of a beam of light incident upon a material undergoes a Faraday rotation according to a linear relationship, namely 9 = V- 7 -4900-3460-9014Atomey Docket No. 065472-000982WOPTB d, where 9 is the angle of rotation, V is the material-dependent Verdet constant, B is the magnetic field strength parallel to the propagation direction of the beam of light, and d is the length of the pathway where the light and magnetic field interact. Specifically, the Verdet constant determines a strength of the Faraday effect in a particular material. In some implementations, using a material with a large Verdet constant would have a strong Faraday effect, and may be suitable for building an optical isolator since a short length of material can be used.

[0037] In some embodiments, a system based on a TIR-FRS or reflected pathway configuration, in accordance with aspects of the present disclosure, may be constructed as an inverted orientation microscope utilizing various optical elements and / or modular microscopy platforms, such as platforms available from Thorlabs, Inc. (Newton, New Jersey). In some implementations, the system may generate and utilize a reflected light pathway capable of TIR- FRS, in combination with a Dodt imaging technique utilizing a transmitted light pathway, to enable simultaneous electrophysiological measurements using a patch-clamp technique. As appreciated further from description below, spectroscopic measurements of activity-dependent magnetic fields in a sample (e.g., a neuron) on a sample substrate may be obtained using polarized light. In particular, the polarized light may be directed through a sample substrate (e.g., a glass substrate with high optical transmittance) from below, while electrical measurements of the sample may be simultaneously obtained (e.g., via patch clamp) from above the sample substrate. In some implementations, light may be used to optically guide electric measurements. Unlike prior approaches, a system as described herein allows for “gap- free” detection of magnetic fields, for instance, by virtue of an evanescence wave produced by total internal reflection, which can radiate approximately 100 nanometer (nm) above a surface of the sample substrate and spatially overlap with the sample (e.g., neuron) on the surface of the sample substrate.

[0038] Referring particularly to FIG. 3A, an example of a system 300, in accordance with aspects of the present disclosure, is illustrated. As shown, the system 300 may include a sample assembly 302, an electrical measurement apparatus 304, and a magnetic measurement apparatus 306. In some embodiments, the sample assembly 302 may include a sample holder 350 for holding a sample (e.g., a neuron).

[0039] In some embodiments, the electrical measurement apparatus 304 is operable to measure one or more electrical signal from the sample. For instance, as illustrated in FIG. 3A, the electrical measurement apparatus 304 may include a patch-clamp that is operable to engage the sample positioned on the sample holder 350 and provide various electrophysiological- 8 -4900-3460-9014Atorney Docket No. 065472-000982WOPT measurements. In some implementations, the electrophysiological measurements include timedependent electrical signals induced via somatic current injection in the sample. In this manner, action potentials may be induced, for example, in a neuron.

[0040] In some embodiments, the magnetic measurement apparatus 306 includes an optical system that includes a light source 352, collimation optics 354, a first polarization filter 356, a first mirror 358, an objective 360, a second mirror 362, a second polarization filter 364. The magnetic measurement apparatus 306 may also include a beamsplitter 366 (e.g., a 50 / 50 beamsplitter), a detector 368 (e.g., a sCMOS detector) or a first detector, and a polarimeter 370 or a second detector.

[0041] In particular, the light source 352 may be configured to generate light of various wavelengths, and / or temporal profiles. For example, the light source 352 (e.g., a laser) may be operable to provide stead-state or time-dependent beams of light (e.g., pulsed light). The generated light may be collimated using the collimation optics 354 to produce collimated light. The collimated light may then enter the first polarization filter 356 to produce a first beam of polarized light (i.e., linearly polarized light). The first beam of polarized light may then be redirected using the first mirror 358 to enter a back aperture of the objective 360. In particular, the polarized light may be redirected at a critical angle to achieve a TIR. As detailed further below, an evanescence wave may be generated by TIR, which when subjected to a magnetic field from the sample (e.g., a neuron) undergoes a Faraday rotation proportional to the strength of the magnetic field. A second beam of polarized light, that is rotated relative to the first beam of polarized light, may then redirected by the second mirror 362, and pass through second polarization filter 364. In some implementations, a polarization axis of the second polarization filter 364 may be oriented, for instance, at approximately 90° relative to the polarization axis of the first polarization filter 356. In some implementations, the second polarization filter 364 allows only light subjected to Faraday rotation to propagate further through the second polarization filter 364. While FIG. 3A illustrates the light source 352 and collimation optics 354 as being separate, in some embodiments, collimation may be integrated in the light source. For instance, in some embodiments, the light source 352 may include an optical fiber that can provide collimated light.

[0042] A spatial distribution of magnetic field can also be determined by splitting reflected light, as illustrated in FIG. 3A. In particular, the second beam of polarized light may be split using the beamsplitter 366, so that a first portion of the second beam of polarized is directed to the detector 368 and a second portion of the second beam of polarized light is directed to a polarimeter 370. The detector 368 can capture a spatial distribution of light subject to Faraday - 9 -4900-3460-9014Atomey Docket No. 065472-000982WOPT rotation, while the polarimeter 370 can measure a degree or angle of Faraday rotation. By way of example, a spatial distribution of magnetic field can be determined by splitting reflected light and directing respective portions of split light to a polarimeter and a camera (e.g., a scientific Complementary Metal-Oxide-Semiconductor (sCMOS) camera). In this manner, magnitude and spatial distribution of magnetic fields may be obtained to provide new insights into how activity dependent magnetic fields relate to neuronal morphology, for instance. Such non-invasive magnetic imaging modality has an advantage over previous approaches in the ability to access juxta-membrane domains without damaging or destroying the analyzed sample (e.g., a neuron), thereby enabling a previously unachievable magneto-physiological investigation of neuronal function.

[0043] As illustrated in the example of FIG. 3A, the sample assembly 302 may have a sample holder 350 as a glass substrate or glass coverslip. However, the sample holder 350 may include various materials and / or features for supporting, securing, positioning, and / or orienting the sample. In some embodiments, the sample holder 350 may be configured to optimize or enhance sensitivity of TIR-FRS, for example by virtue of enhancing Faraday rotation.

[0044] For instance, as shown in FIG. 3B, in some embodiments, the sample holder 350 may include a sample substrate 380 and a coating layer 382, where the sample holder 350 may be arranged such that the coating layer 382 is opposite where a sample 384 (e.g., neuron) may be positioned or cultured. In some embodiments, the coating layer 382 may include a thin film of material, such as semiconductor material, graphene, and so forth, incorporated and / or deposited on sample substrate 380 using various deposition techniques (e.g., physical vapor deposition, atomic layer deposition, chemical vapor deposition, sputtering, pulsed laser deposition, spin coating, dip coating, evaporation, plasma enhanced chemical vapor deposition, molecular beam epitaxy, and so on). In some embodiments, the coating layer 382 may include single or multi-layer graphene. In one example, graphene may be deposited on the sample substrate 380 of the sample holder 350 by transference from a thin film or liquid deposition of graphene ink.

[0045] Faraday rotation can also be enhanced by utilizing a material doped with doping material 386. For instance, in some embodiments, a sample holder 350 may include a glass doped to produce an electric field inside the glass. For example, the sample holder 350 may include a Lanthanide glass doped with paramagnetic Terbium ions (Tb4+). In some embodiments, Faraday rotation may be enhanced by selecting substrate material and / or doping material 386 that is optimized to one or more wavelength of the light source 352.

[0046] While FIGs. 3 A and 3B provide an illustration of a system 300, according to aspects- 10 -4900-3460-9014Atorney Docket No. 065472-000982WOPT of the present disclosure, the system 300 may include a variety of components and hardware not shown. For instance, the magnetic measurement apparatus 306 may include various components and hardware for controlling position, orientation, and so forth, of various components of the optical system. In some implementations, the first beam of polarized light redirected by the first mirror 358 may pass through a region of magnetic field 372 generated and controlled by an external source of magnetic field (e.g., a solenoid, a pair of Helmholtz coils, a permanent magnet, an electromagnet, and so forth). The region of magnetic field 372 may be used control or enhance the degree or angle of Faraday rotation measured by the polarimeter 370, or the sensitivity in the degree or angle of Faraday rotation measured. The extent of the region of magnetic field 372 in space may vary. Alternatively, or additionally, Faraday rotation may also be controlled or enhanced by utilizing a spin-laser for the light source 352.

[0047] In some implementations, the magnetic measurement apparatus 306 described above may be used to image a sample, for example, using a Dodt imaging technique. To this end, one or more component of the optical system may be controlled to generate a transmitted light configuration in which a transmitted light pathway may be utilized to image the sample. In some implementations, imaging may be combined with patch-clamp recording, in a concomitant manner. Further, in some implementations, the optical system may be switched between sample imaging and TIR-FRS, for example, using a precision mirror (e.g., mounted on a rail) whose position / orientation may be adjusted or toggled between two or more positions / orientations.

[0048] A configuration of the system 300, as described above, can be used to provide critically important ground-truth electrophysiological validation accompanying magnetic measurements in space (nanometer resolution) and in time (sub-millisecond resolution). Hence, in some implementations, electrical measurement, using electrical measurement apparatus 304, may be obtained concomitantly with magnetic field measurement, using the magnetic measurement apparatus 306. For instance, responsive to action potentials elicited by somatic current injection in a sample (e.g., a neuron), inducing magnetic fields in the sample, patchclamp electrophysiology measurement acquired simultaneously with magnetic field measurement, as described.

[0049] In some implementations, one or more neuron may be cultured on a specialized glass substrate with favorable magneto-optical properties, such as a high Verdet constant. The juxta-membrane domain may remain accessible to an evanescence wave produced by TIR, which may also increase a distance over which Faraday rotation occurs. As described, the- 11 -4900-3460-9014Atomey Docket No. 065472-000982WOPTVerdet constant measures a strength of the Faraday effect in a particular material, and a larger Verdet constant provides a stronger Faraday effect. In some implementations, a stronger Faraday effect may be achieved by including an optical isolator, which would allow for unidirectional light propagation.

[0050] As described, an evanescence wave may be generated by TIR, which can extend about one hundred nanometers above a surface of a glass substrate or glass coverslip, for example, thereby enabling linearly polarized light to be spatially overlapping with activitydependent magnetic fields produced, for instance, by a neuron cultured on surface of the glass coverslip. In particular, a glass substrate or glass coverslip can allow for easy culturing of neurons, for example, while achieving total internal reflection for measurement, as described. Yet most commercial Faraday rotators are thick (1 / 2-1”), and most coverslips are thin. Hence, in some embodiments, a sample substrate with a thickness between approximately 0.01” and approximately 0.5”, or more, may be used to enhance Faraday rotation, and hence measurement sensitivity.

[0051] Referring particularly to FIG. 4, an illustration of interactions between a cellular magnetic field and an evanescence wave generated by TIR, is shown. In particular, at the neuronal cell membrane-extracellular polyelectrolyte solution interface, ions organize into layers along the charged surface of the cell membrane. For instance, as shown layers may include a diffuse layer, a G-C double layer, a Helmholtz layer. Polarized laser light incident upon the substrate (e.g., a glass substrate or glass coverslip) is internally reflected to generate an evanescence wave. In some implementations, the evanescence wave may be controlled by the light source providing the light. For instance, an evanescence wave may be enhanced using fast light pulses (e.g., with pulse widths in a range between approximately 100 nanoseconds and approximately 1 femtosecond, or less). The interaction between the evanescence wave and the activity-dependent magnetic field can cause Faraday rotation, or a shift in the polarization state of the internally reflected light, as described. As shown, a cell membrane can behave like an RC circuit, and a magnetic field generated therein can be described using a double decay function, described by a first field parameter \| / 1 and a second field parameter \| / 2. A decay of evanescent wave may be described by a first wave parameter 61, a second wave parameter 62, and a third wave parameter 63, as shown. As described, a magnitude of the activity-dependent magnetic field can then be ascertained by the angle of Faraday rotation measured, for instance, with a high-sensitivity polarimeter (±0.25° Azimuth and Ellipticity accuracy).

[0052] Referring to FIGA. 5A-5C, another example of a system 500, in accordance with aspects of the present disclosure, is illustrated. As shown in FIG. 5A, in some embodiments,- 12 -4900-3460-9014Atorney Docket No. 065472-000982WOPT the system 500 may include an infrared light-emitting diode (IR LED) 502, a Dodt Optics Module 504, a condenser 506, a sample holder 508, a polarimeter 510, linear polarization filters 512A and 512B, a columnated fiber laser input 514, a 50 / 50 beam splitter 516, a beam dump 518, an IR camera 520, an objective holder 522, a light pathway integration module 524, a sample X / Y translation module + motorized focus 526, and an LED control module 528. As shown, the polarimeter 510, the linear polarization filters 512A and 512B, the columnated fiber laser input 514, the 50 / 50 beam splitter 516, the beam dump 518, the IR camera 520, the objective holder 522, and the light pathway integration module 524 are located below the plane on which the sample holder 508 is positioned.

[0053] As described, in some implementations, the system 500 may be used for imaging a sample positioned on the sample holder 508. For instance, as shown in FIG. 5B, transmitted light generated by the IR LED 502 may directed by the Dodt Optics Module 504 through the condenser 506 to a sample, from above the sample. In this manner, imaging along with using patch-clamp electrophysiology may be used to measure the sample. Also, in some implementations, reflected light may be used to perform TIR-FRS to detect and characterize magnetic fields (e.g., magnitude, spatial distribution, and so forth) in the sample. For instance, as shown in FIG. 5C, light may be generated by the columnated fiber laser input 514, and directed to and from the sample via the linear polarization filters 512A and 512B, and the objective holder 522, as described

[0054] Turning to FIG. 6, a flowchart setting forth steps of a process 600, according to aspects of the present disclosure, is illustrated. Steps of the process 600 may be carried out using any combination of suitable systems, such as systems described in the present disclosure. In some embodiments, steps of the process 600 may be implemented as instructions stored in non-transitory computer-readable media, as a program, firmware or software, and executed by a general-purpose, programmed or programmable computer, processor or other computing device. In other embodiments, steps of the process 600 may be hardwired in an applicationspecific computer, processor, dedicated system, or module. Although the process 600 is illustrated and described as a sequence of steps, it is contemplated that the steps may be performed in any order or combination, need not include all illustrated steps, and may include additional steps.

[0055] The process 600 may begin at process block 602 with directing a first beam of polarized light to a sample. As described, this step may include using a light source to generate and emit light. The emitted light may then be directed to collimation opts and a first polarization filter to generate the first beam of polarized light. The first beam of polarized light may then- 13 -4900-3460-9014Atomey Docket No. 065472-000982WOPT be directed to the sample, for using a first mirror. In some implementations, light emitted by the light source may be pulsed light having a pulse width in a range between approximately 100 nanoseconds and approximately 1 femtosecond, or less .

[0056] A second beam of polarized light may then be received from the sample, as indicated by process block 604. As described, the second beam of polarized light may rotated relative to the first beam of polarized light by a rotation angle due to Faraday rotation.

[0057] The second beam of polarized light may then be characterized, as indicated by process block 606. As such, the second beam of polarized light may be directed to a second polarization filter to filter the second beam of polarized light. The beam of light from the second polarization filter may then be, using a beamsplitter, wherein a first portion of the beam of light is directed to a first detector. As described, characterizing the second beam of polarized light may include determining the rotation angle of the second beam of polarized light providing the detector with the first portion of the beam of light. For instance, a polarimeter may be used to determine the rotation angle.

[0058] A magnetic field in the sample may then be determined based on the characterization. For instance, as described, a linear relationship between a rotation angle (e.g., provided as output by a polarimeter) and magnetic field may be utilized. In some implementations, such linear relationship may be stored, for example, in the form of a lookup table, graph, and so forth, and accessed to determine the magnetic field. For example, for a rotation angle value, a corresponding magnetic field value may be selected or retrieved. In other implementations, a computation according to a linear relationship 9 = V B d may be performed to determine the magnetic field. To this end, various parameters may be utilized (e.g., retrieved, accessed, and so forth), such as sample holder thickness, sample holder material, estimated decay of the magnetic field in the sample, and so forth.

[0059] In some implementations, a second portion of the beam of light may be directed to a second detector to determine a spatial distribution of the magnetic field using the detector. Alternatively, or additionally, the magnetic field may be induced by using a current injection in the sample, as described.

[0060] In some implementations, an electrical measurement may be made on the sample, for example, using a patch-clamp technique, as described. While the electrical measurement may be made at any time in the process 600, in some implementations, the electrical measurement may be made concomitant with determination of the magnetic field, according to the process 600. In this manner, correlated magnetic field and electrical measurements may be obtained, as described.- 14 -4900-3460-9014Atorney Docket No. 065472-000982WOPT

[0061] In some implementations, electrical measurement may be performed with, or aided by, imaging performed using a Dodt imaging technique, for instance.

[0062] A report may be also generated at step at process block 608. The report may be in any form (e.g., graphics, graph, table, image, listing, and so, forth) and include any signals, data, and information. For example, the report may include a determined magnetic field magnitude, a spatial distribution of magnetic field, and so forth. In some implementations, the report may include correlated (e.g., temporally correlated) electric and magnetic field measurement, as described herein.

[0063] As appreciated from description herein, the present approach can be applied in various applications. For instance, in some applications, systems and methods described herein may be used to evaluate efficacy of each measurement modality in nanoscale magnetophysiology. In other applications, the present approach may be used to perform a comparative analysis, for instance, using samples of rodent and human neocortical neurons, where the analysis can characterize similarities and / or differences in magneto-physiological attributes. This is an interesting comparison since human neurons are much larger than rodent neurons and therefore have the capability to generate significantly larger activity-dependent magnetic fields due to increased cell surface area, and hence capacity for larger currents that arise from fluctuations of ionic species with capacitive layers at the membrane-electrolyte interface.

[0064] In some applications, primary neural cultures may be made using postnatal (e.g., day 0-1) rodents using various culturing techniques. Also, live human brain tissue samples can be obtained from neurosurgical resections of, for example, brain tumor and epilepsy cases, and used to make primary cell cultures. For example, a custom designed cart with an oxygenated artificial cerebrospinal fluid perfusion system may be brought to an operating room for collecting live tissue samples and maintaining tissue integrity during transport. Using such tissues samples, various aspects may be investigated, such as magnitude, dynamics, and spatial distribution of magnetic fields generated by action potentials as well as the magnetic field strength needed to modify neural activity for a given cell type.

[0065] In some implementations, a calibration may also be performed on systems described herein. For instance, by controllably passing current through a wire of known diameter, a controlled magnetic field may be generated, according to the following: B=n°I / 27r:r, where B is the magnetic field, ° is the permittivity constant (for free space), I is the magnitude of the current flowing through the wire, and r is the distance to the wire. The controlled magnetic- 15 -4900-3460-9014Atomey Docket No. 065472-000982WOPT field may then be compared to magnetic field measurement obtained using systems described therein to provide calibration.

[0066] Following calibration, one investigation may proceed in the following manner. By configuring a system in a transmitted light configuration, as described herein, a patch-clamp electrical recording may be obtained from a neuron cultured on the glass substrate, for instance. Then, the system may be configured in a reflected light configuration, and a current injection may be performed to drive spiking activity, thereby enabling timing comparisons between magnetic field dynamics and action potential electrical signals. In some implementation, signal-to-noise may be increased by spike-triggered averaging of magnetic measurements made in accordance with the present disclosure.

[0067] The functional consequences that activity-dependent neuronal magnetic fields impart may be profound, and may have implications ranging from magnetic sensitivity of molecular function to cellular growth, differentiation, and integration, to macroscopic scales where traveling electromagnetic waves impact cognitive function. Activity-dependent fluctuations of ionic capacitive layers at a plasma membrane surface that produce currents and magnetic fields could significantly influence molecular signaling cascades in the juxta- membrane domain. Moreover, it is currently unknown if polyelectrolyte cytoskeletal structures such as microtubules and actin filaments within neurons can operate as electromagnetic propagation substrates, transmitting signals along the branched structure of neuronal dendrites and axons.

[0068] Analogous to a membrane-electrolyte interface where a Helmholtz layer forms, intracellular polyelectrolytes, like the cytoskeleton, also give rise to capacitive layers. Specifically, the possibility that the branched structure of the cytoskeleton can operate as a conductive network would have far reaching implications for dendritic integration beyond cable theory, and how computations are implemented in the brain. Therefore, the presently described approach provides a novel approach for investigating such mechanisms.

[0069] Unlike electric fields, spatial propagation of magnetic fields need not be restricted by local cancelation of field propagation. This property of magnetic fields to propagate relatively unimpeded indicates that endogenously generated magnetic fields may have a more significant impact on neural activity and brain function than previously considered through magneto-ephaptic interactions that could influence neuronal oscillations and coherence. Critically, to design the next generation of magnetic stimulation devices that enable cellular specificity, the magnetic field strength required to modulate cellular function must be determined. Systems described in the present disclosure can provide such vital information to- 16 -4900-3460-9014Atomey Docket No. 065472-000982WOPT devise strategies that can precisely stimulate, or interfere with neural activity for therapeutic purposes.

[0070] Further, current techniques used to measure magnetic fields in the brain are limited to macroscale magnetic fields that reflect neuronal activity across large regions of the brain. Systems and methods disclosed herein can be used to measure magnetic fields at cellular resolution. In addition, systems and methods disclosed herein can be used to investigate functional consequences of magnetic fields generated by neuronal activity at cellular resolution.

[0071] Systems and methods described herein allow for high-resolution magnetic field imaging by leveraging techniques of Total Internal Reflection (TIR) microscopy and Faraday Rotation Spectroscopy (FRS) to interrogate dynamics of magnetic fields in a nanodomain of a neuronal membrane - electrolyte solution interface. Moreover, integrating high-resolution magnetic field detection with patch-clamp electrophysiology provides an ability to perform synchronized electrophysiological and magnetic measurements not previously possible using conventional techniques. In intracellular recording of a membrane potential in a cell performed with integrated patch-clamp electrophysiology, along with magnetic measurements, allow for bridging knowledge gap in understanding properties and dynamics of activity-dependent neuronal magnetic fields in the cell. Moreover, the present approach enables precise control of cellular excitability and capability to significantly increase signal-to-noise ratio by generating a spike-triggered average for magnetic measurements.

[0072] Although the application has been disclosed in the context of certain embodiments and examples, it will be understood by those skilled in the art that the embodiments of the application extend beyond the specifically disclosed embodiments to other alternative embodiments and / or uses and modifications and equivalents thereof.

[0073] In some embodiments, the terms “a” and “an” and “the” and similar references used in the context of describing a particular embodiment of the application (especially in the context of certain of the following claims) can be construed to cover both the singular and the plural. The recitation of ranges of values herein is merely intended to serve as a shorthand method of referring individually to each separate value falling within the range. Unless otherwise indicated herein, each individual value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (for example, “such as”) provided with respect to certain embodiments herein is intended merely to better illuminate the application and does- 17 -4900-3460-9014Atorney Docket No. 065472-000982WOPT not pose a limitation on the scope of the application otherwise claimed. No language in the specification should be construed as indicating any non-claimed element essential to the practice of the application.

[0074] In some embodiments, use of the terms “about” and “approximately” in context or relation to a nominal value is intended to include the nominal value as well as values that differ from the nominal value by up to 10%, either positively or negatively.

[0075] Certain embodiments of this application are described herein, including the best mode known to the inventors for carrying out the application. Variations on those certain embodiments will become apparent to those of ordinary skill in the art upon reading the foregoing description. It is contemplated that skilled artisans can employ such variations as appropriate, and the application can be practiced otherwise than specifically described herein. Accordingly, many embodiments of this application include all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the application unless otherwise indicated herein or otherwise clearly contradicted by context.

[0076] It is to be understood that the embodiments of the application disclosed herein are illustrative of the principles of the embodiments of the application. Other modifications that can be employed can be within the scope of the application. Thus, by way of example, but not of limitation, alternative configurations of the embodiments of the application can be utilized in accordance with the teachings herein. Accordingly, embodiments of the present application are not limited to that precisely as shown and described.

[0077] One or more elements or aspects or steps, or any portion(s) thereof, from one or more of any of claims or Alternative Implementations below can be combined with one or more elements or aspects or steps, or any portion(s) thereof, from one or more of any of the other claims or Alternative Implementations or combinations thereof, to form one or more additional implementations and / or claims of the present disclosure.

[0078] ALTERNATIVE IMPLEMENTATIONS

[0079] Alternative Implementation 1. A system for investigating a cell, the system comprising: a sample assembly comprising a sample holder to hold a sample comprising a cell; a magnetic measurement apparatus operable to detect a magnetic field in the sample, the magnetic measurement apparatus comprising an optical system having: a light source configured to emit light; collimation optics configured to receive and collimate light emitted by the light source; a first polarization filter configured to receive light collimated by the- 18 -4900-3460-9014Atomey Docket No. 065472-000982WOPT collimation optics, and generate a first beam of polarized light, wherein the first beam of polarized light is directed to the sample holder holding the sample; a second polarization filter configured to receive and filter a second beam of polarized light from the sample holder, wherein the second beam of polarized light is rotated relative to the first beam of polarized light by a rotation angle; a detector configured to characterize light in the second beam of polarized light; and an electrical measurement apparatus operable to perform an electrical measurement on the sample.

[0080] Alternative Implementation 2. The system of Alternative Implementation 1, wherein the sample holder further comprises a sample substrate.

[0081] Alternative Implementation 3. The system of Alternative Implementation 2, wherein the sample substrate further comprises one or more cells cultured thereon.

[0082] Alternative Implementation 4. The system of Alternative Implementation 2 or Alternative Implementation 3, wherein the sample substrate further comprises a material with an optical transmittance greater than 80%.

[0083] Alternative Implementation 5. The system of any of one Alternative Implementations 2 to 4, wherein the sample substrate further comprises a coating layer comprising a semiconductor material or graphene.

[0084] Alternative Implementation 6. The system of any of one AlternativeImplementations 2 to 5, wherein the sample substrate further comprises a doping material.

[0085] Alternative Implementation 7. The system of any of one AlternativeImplementations 2 to 6, wherein the sample substrate comprises a glass doped with paramagnetic Terbium ions (Tb4+).

[0086] Alternative Implementation 8. The system of any of one Alternative Implementations 1 to 7, wherein the light source comprises a laser configured to emit pulsed light having a pulse width in a range between 100 nanoseconds and 1 femtosecond.

[0087] Alternative Implementation 9. The system of any of one Alternative Implementations 1 to 8, wherein an axis of polarization of the first polarization filter is oriented 90° relative to the axis of polarization of the second polarization filter.

[0088] Alternative Implementation 10. The system of any of one Alternative Implementations 1 to 9, wherein the optical system further comprises an objective for receiving the first beam of polarized light and providing the second beam of polarized light.

[0089] Alternative Implementation 11. The system of Alternative Implementation 10, wherein the optical system further comprises a first mirror configured to direct the first beam of polarized light to the objective, and a second mirror configured to direct the second beam of- 19 -4900-3460-9014Atomey Docket No. 065472-000982WOPT polarized light to the second polarization filter.

[0090] Alternative Implementation 12. The system of Alternative Implementation 10 or Alternative Implementation 11, wherein the optical system further comprises a beamsplitter configured to split a beam of light from the second polarization filter.

[0091] Alternative Implementation 13. The system of Alternative Implementation 12, wherein the beamsplitter is configured to direct a first portion of the beam of light to a first detector, and a second portion of the beam of light to a second detector.

[0092] Alternative Implementation 14. The system of Alternative Implementation 13, wherein the first detector is a polarimeter and the second detector is a scientific Complementary Metal-Oxide-Semiconductor (sCMOS) detector.

[0093] Alternative Implementation 15. The system of any of one Alternative Implementations 1 to 14, wherein the electrical measurement apparatus further comprises a patch-clamp pipette comprising a conducting solution, an electrode electrically connected to the conducting solution, an operational amplifier connected to the conducting solution, one or more feedback resistor connected to the conducting solution, and a measurement device connected to the feedback resistor and operational amplifier.

[0094] Alternative Implementation 16. The system of any of one Alternative Implementations 1 to 15, wherein the electrical measurement apparatus is operable to inject current into the sample to elicit an action potential and generate the magnetic field in the sample.

[0095] Alternative Implementation 17. A method for investigating a cell, the method comprising: directing a first beam of polarized light to a sample comprising a cell on a sample holder; receiving a second beam of polarized light from the sample, wherein the second beam of polarized light is rotated relative to the first beam of polarized light by a rotation angle; characterizing the second beam of polarized light using a detector; and determining a magnetic field about the sample based on characterization of the second beam of polarized light.

[0096] Alternative Implementation 18. The method of Alternative Implementation 17, wherein the method further comprises generating the first beam of polarized light using a light source, collimation optics, and a first polarization filter.

[0097] Alternative Implementation 19. The method of Alternative Implementation 18, wherein the method further comprises emitting, using the light source, pulsed light having a pulse width in a range between 100 nanoseconds and 1 femtosecond.

[0098] Alternative Implementation 20. The method of Alternative Implementation 17 or Alternative Implementation 18, wherein the method further comprises directing the second- 20 -4900-3460-9014Atorney Docket No. 065472-000982WOPT beam of polarized light to a second polarization filter to filter the second beam of polarized light.

[0099] Alternative Implementation 21. The method of Alternative Implementation 20, wherein the method further comprises splitting a beam of light from the second polarization filter, using a beamsplitter, wherein a first portion of the beam of light is directed to a first detector, and a second portion of the beam of light is directed to a second detector.

[0100] Alternative Implementation 22. The method of Alternative Implementation 21, wherein the method further comprises characterizing the second beam of polarized light by determining the rotation angle of the second beam of polarized light using the first portion of the beam of light measured using the first detector.

[0101] Alternative Implementation 23. The method of Alternative Implementation 22, wherein the method further comprises determining a spatial distribution of the magnetic field using the first detector or the second detector.

[0102] Alternative Implementation 24. The method of any of one Alternative Implementations 17 to 23, wherein the method further comprises inducing the magnetic field using a current injection in the sample.

[0103] Alternative Implementation 25. The method of any of one Alternative Implementations 17 to 24, wherein the method further comprises imaging the sample using a Dodt imaging technique.

[0104] Alternative Implementation 26. The method of any of one Alternative Implementations 17 to 25, wherein the method further comprises performing an electrical measurement on the sample using a patch-clamp technique.- 21 -4900-3460-9014

Claims

Atomey Docket No. 065472-000982WOPTCLAIMS1. A system for investigating a cell, the system comprising: a sample assembly comprising a sample holder to hold a sample comprising a cell; a magnetic measurement apparatus operable to detect a magnetic field in the sample, the magnetic measurement apparatus comprising an optical system having: a light source configured to emit light; collimation optics configured to receive and collimate light emitted by the light source; a first polarization filter configured to receive light collimated by the collimation optics, and generate a first beam of polarized light, wherein the first beam of polarized light is directed to the sample holder holding the sample; a second polarization filter configured to receive and filter a second beam of polarized light from the sample holder, wherein the second beam of polarized light is rotated relative to the first beam of polarized light by a rotation angle; a detector configured to characterize light in the second beam of polarized light; and an electrical measurement apparatus operable to perform an electrical measurement on the sample.

2. The system of claim 1, wherein the sample holder further comprises a sample substrate.

3. The system of claim 2, wherein the sample substrate further comprises one or more cells cultured thereon.

4. The system of claim 2, wherein the sample substrate further comprises a material with an optical transmittance greater than 80%.

5. The system of claim 2, wherein the sample substrate further comprises a coating layer comprising a semiconductor material or graphene.

6. The system of claim 2, wherein the sample substrate further comprises a doping material.- 22 -4900-3460-9014Atorney Docket No. 065472-000982WOPT7. The system of claim 2, wherein the sample substrate comprises a glass doped with paramagnetic Terbium ions (Tb4+).

8. The system of claim 1, wherein the light source comprises a laser configured to emit pulsed light having a pulse width in a range between 100 nanoseconds and 1 femtosecond.

9. The system of claim 1, wherein an axis of polarization of the first polarization filter is oriented 90° relative to the axis of polarization of the second polarization filter.

10. The system of claim 1, wherein the optical system further comprises an objective for receiving the first beam of polarized light and providing the second beam of polarized light.

11. The system of claim 10, wherein the optical system further comprises a first mirror configured to direct the first beam of polarized light to the objective, and a second mirror configured to direct the second beam of polarized light to the second polarization filter.

12. The system of claim 10, wherein the optical system further comprises a beamsplitter configured to split a beam of light from the second polarization filter.

13. The system of claim 12, wherein the beamsplitter is configured to direct a first portion of the beam of light to a first detector, and a second portion of the beam of light to a second detector.

14. The system of claim 13, wherein the first detector is a polarimeter and the second detector is a scientific Complementary Metal-Oxide-Semiconductor (sCMOS) detector.

15. The system of claim 1, wherein the electrical measurement apparatus further comprises a patch-clamp pipette comprising a conducting solution, an electrode electrically connected to the conducting solution, an operational amplifier connected to the conducting solution, one or more feedback resistor connected to the conducting solution, and a measurement device connected to the feedback resistor and operational amplifier.

16. The system of claim 1, wherein the electrical measurement apparatus is operable to- 23 -4900-3460-9014Atomey Docket No. 065472-000982WOPT inject current into the sample to elicit an action potential and generate the magnetic field in the sample.

17. A method for investigating a cell, the method comprising: directing a first beam of polarized light to a sample comprising a cell on a sample holder; receiving a second beam of polarized light from the sample, wherein the second beam of polarized light is rotated relative to the first beam of polarized light by a rotation angle; characterizing the second beam of polarized light using a detector; and determining a magnetic field about the sample based on characterization of the second beam of polarized light.

18. The method of claim 17, wherein the method further comprises generating the first beam of polarized light using a light source, collimation optics, and a first polarization filter.

19. The method of claim 18, wherein the method further comprises emitting, using the light source, pulsed light having a pulse width in a range between 100 nanoseconds and 1 femtosecond.

20. The method of claim 17, wherein the method further comprises directing the second beam of polarized light to a second polarization filter to filter the second beam of polarized light.

21. The method of claim 20, wherein the method further comprises splitting a beam of light from the second polarization filter, using a beamsplitter, wherein a first portion of the beam of light is directed to a first detector, and a second portion of the beam of light is directed to a second detector.

22. The method of claim 21, wherein the method further comprises characterizing the second beam of polarized light by determining the rotation angle of the second beam of polarized light using the first portion of the beam of light measured using the first detector.

23. The method of claim 22, wherein the method further comprises determining a spatial- 24 -4900-3460-9014Atorney Docket No. 065472-000982WOPT distribution of the magnetic field using the first detector or the second detector.

24. The method of claim 17, wherein the method further comprises inducing the magnetic field using a current injection in the sample.

25. The method of claim 17, wherein the method further comprises imaging the sample using a Dodt imaging technique.

26. The method of claim 17, wherein the method further comprises performing an electrical measurement on the sample using a patch-clamp technique.- 25 -4900-3460-9014

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