All-Optical and Label-Free Stimulation of Action Potentials in Neurons and Cardiomyocytes by Plasmonic Porous Metamaterials.

Optical stimulation technologies are gaining great consideration in cardiology, neuroscience studies, and drug discovery pathways by providing control over cell activity with high spatio-temporal resolution. However, this high precision requires manipulation of biological processes at genetic level concealing its development from broad scale application. Therefore, translating these technologies into tools for medical or pharmacological applications remains a challenge. Here, an all-optical nongenetic method for the modulation of electrogenic cells is introduced. It is demonstrated that plasmonic metamaterials can be used to elicit action potentials by converting near infrared laser pulses into stimulatory currents. The suggested approach allows for the stimulation of cardiomyocytes and neurons directly on commercial complementary metal-oxide semiconductor microelectrode arrays coupled with ultrafast pulsed laser, providing both stimulation and network-level recordings on the same device.

Intracellular action potential recordings from cardiomyocytes by ultrafast pulsed laser irradiation of fuzzy graphene microelectrodes.

Graphene with its unique electrical properties is a promising candidate for carbon-based biosensors such as microelectrodes and field effect transistors. Recently, graphene biosensors were successfully used for extracellular recording of action potentials in electrogenic cells; however, intracellular recordings remain beyond their current capabilities because of the lack of an efficient cell poration method. Here, we present a microelectrode platform consisting of out-of-plane grown three-dimensional fuzzy graphene (3DFG) that enables recording of intracellular cardiac action potentials with high signal-to-noise ratio. We exploit the generation of hot carriers by ultrafast pulsed laser for porating the cell membrane and creating an intimate contact between the 3DFG electrodes and the intracellular domain. This approach enables us to detect the effects of drugs on the action potential shape of human-derived cardiomyocytes. The 3DFG electrodes combined with laser poration may be used for all-carbon intracellular microelectrode arrays to allow monitoring of the cellular electrophysiological state.

Mirroring Action Potentials: Label-Free, Accurate, and Noninvasive Electrophysiological Recordings of Human-Derived Cardiomyocytes.

The electrophysiological recording of action potentials in human cells is a long-sought objective due to its pivotal importance in many disciplines. Among the developed techniques, invasiveness remains a common issue, causing cytotoxicity or altering unpredictably cell physiological response. In this work, a new approach for recording intracellular signals of outstanding quality and with noninvasiveness is introduced. By taking profit of the concept of mirror charge in classical electrodynamics, the new proposed device transduces cell ionic currents into mirror charges in a microfluidic chamber, thus realizing a virtual mirror cell. By monitoring mirror charge dynamics, it is possible to effectively record the action potentials fired by the cells. Since there is no need for accessing or interacting with the cells, the method is intrinsically noninvasive. In addition, being based on optical recording, it shows high spatial resolution and high parallelization. As shown through a set of experiments, the presented methodology is an ideal candidate for the next generation devices for the reliable assessment of cardiotoxicity on human-derived cardiomyocytes. More generally, it paves the way toward a new family of in vitro biodevices that will lay a new milestone in the field of electrophysiology.

Intracellular Recording of Human Cardiac Action Potentials on Market-Available Multielectrode Array Platforms.

High quality attenuated intracellular action potentials from large cell networks can be recorded on multi-electrode arrays by means of 3D vertical nanopillars using electrical pulses. However, most of the techniques require complex 3D nanostructures that prevent the straightforward translation into marketable products and the wide adoption in the scientific community. Moreover, 3D nanostructures are often delicate objects that cannot sustain several harsh use/cleaning cycles. On the contrary, laser optoacoustic poration allows the recording of action potentials on planar nanoporous electrodes made of noble metals. However, these constraints of the electrode material and morphology may also hinder the full exploitation of this methodology. Here, we show that optoacoustic poration is also very effective for porating cells on a large family of MEA electrode configurations, including robust electrodes made of nanoporous titanium nitride or disordered fractal-like gold nanostructures. This enables the recording of high quality cardiac action potentials in combination with optoacoustic poration, providing thus attenuated intracellular recordings on various already commercial devices used by a significant part of the research and industrial communities.

An image registration protocol to integrate electrophysiology, MRI and neuropathology data in epileptic patients explored with intracerebral electrodes.

BACKGROUND: Several attempts have been made to coregister in vivo MRI with the histopathology of surgical samples, aiming to validate new MRI biomarkers and improve the detection of epileptogenic lesions. As a further implementation, we propose a method to reconstruct the anatomical localization of the intracerebral electrodes on the histological sections, developing a coregistration protocol to match the in vivo MRI onto the ex vivo MRI obtained from the surgical specimen. NEW METHOD: Since the ex vivo MRI is natively in geometrical correspondence with histology slices, the goal of the coregistration process is to compute the transform function mapping the clinical MRI space to the ex vivo MRI. Electrodes and leads, identified in CT-MRI, can then be segmented and translated onto the histological slices. RESULTS: Step-by-step, qualitative visual inspection showed an improved matching of the anatomical structures or boundaries and electrodes positions between the two modalities. The quantitative evaluation of the coregistration protocol reported a mean error ranging between 0.82 and 1.27 mm when a sufficient number of landmarks, particularly in the core of the specimen, were clearly identified. COMPARISON WITH EXISTING METHODS: Because histology was performed according to ex vivo MRI geometry we chose to transform the in vivo onto the ex vivo MRI, differently from other methods. CONCLUSIONS: Interesting applications of the method will include correlating the locally-generated pathological electrical activity with the subtle morphological alterations of the tissue, and histologically validating the origin of signal alterations or quantitative parameter variations in MRI studies.

In vitro labelling and detection of mesenchymal stromal cells: a comparison between magnetic resonance imaging of iron-labelled cells and magnetic resonance spectroscopy of fluorine-labelled cells.

BACKGROUND: Among the various stem cell populations used for cell therapy, adult mesenchymal stromal cells (MSCs) have emerged as a major new cell technology. These cells must be tracked after transplantation to monitor their migration within the body and quantify their accumulation at the target site. This study assessed whether rat bone marrow MSCs can be labelled with superparamagnetic iron oxide (SPIO) nanoparticles and perfluorocarbon (PFC) nanoemulsion formulations without altering cell viability and compared magnetic resonance imaging (MRI) and magnetic resonance spectroscopy (MRS) results from iron-labelled and fluorine-labelled MSCs, respectively. METHODS: Of MSCs, 2 × 106 were labelled with Molday ION Rhodamine-B (MIRB) and 2 × 106 were labelled with Cell Sense. Cell viability was evaluated by trypan blue exclusion method. Labelled MSCs were divided into four samples containing increasing cell numbers (0.125 × 106, 0.25 × 106, 0.5 × 106, 1 × 106) and scanned on a 7T MRI: for MIRB-labelled cells, phantoms and cells negative control, T1, T2 and T2* maps were acquired; for Cell Sense labelled cells, phantoms and unlabelled cells, a 19F non-localised single-pulse MRS sequence was acquired. RESULTS: In total, 86.8% and 83.6% of MIRB-labelled cells and Cell Sense-labelled cells were viable, respectively. MIRB-labelled cells were visible in all samples with different cell numbers; pellets containing 0.5 × 106 and 1 × 106 of Cell Sense-labelled cells showed a detectable 19F signal. CONCLUSIONS: Our data support the use of both types of contrast material (SPIO and PFC) for MSCs labelling, although further efforts should be dedicated to improve the efficiency of PFC labelling.