Modeling the effect of magnetoelectric nanoparticles on neuronal electrical activity: An analog circuit approach.

This paper introduces a physical neuron model that incorporates magnetoelectric nanoparticles (MENPs) as an essential electrical circuit component to wirelessly control local neural activity. Availability of such a model is important as MENPs, due to their magnetoelectric effect, can wirelessly and noninvasively modulate neural activity, which, in turn, has implications for both finding cures for neurological diseases and creating a wireless noninvasive high-resolution brain-machine interface. When placed on a neuronal membrane, MENPs act as magnetic-field-controlled finite-size electric dipoles that generate local electric fields across the membrane in response to magnetic fields, thus allowing to controllably activate local ion channels and locally initiate an action potential. Herein, the neuronal electrical characteristic description is based on ion channel activation and inhibition mechanisms. A MENP-based memristive Hodgkin-Huxley circuit model is extracted by combining the Hodgkin-Huxley model and an equivalent circuit model for a single MENP. In this model, each MENP becomes an integral part of the neuron, thus enabling wireless local control of the neuron's electric circuit itself. Furthermore, the model is expanded to include multiple MENPs to describe collective effects in neural systems.

Nanomedicine and nanobiotechnology applications of magnetoelectric nanoparticles.

Unlike any other nanoparticles known to date, magnetoelectric nanoparticles (MENPs) can generate relatively strong electric fields locally via the application of magnetic fields and, vice versa, have their magnetization change in response to an electric field from the microenvironment. Hence, MENPs can serve as a wireless two-way interface between man-made devices and physiological systems at the molecular level. With the recent development of room-temperature biocompatible MENPs, a number of novel potential medical applications have emerged. These applications include wireless brain stimulation and mapping/recording of neural activity in real-time, targeted delivery across the blood-brain barrier (BBB), tissue regeneration, high-specificity cancer cures, molecular-level rapid diagnostics, and others. Several independent in vivo studies, using mice and nonhuman primates models, demonstrated the capability to deliver MENPs in the brain across the BBB via intravenous injection or, alternatively, bypassing the BBB via intranasal inhalation of the nanoparticles. Wireless deep brain stimulation with MENPs was demonstrated both in vitro and in vivo in different rodents models by several independent groups. High-specificity cancer treatment methods as well as tissue regeneration approaches with MENPs were proposed and demonstrated in in vitro models. A number of in vitro and in vivo studies were dedicated to understand the underlying mechanisms of MENPs-based high-specificity targeted drug delivery via application of d.c. and a.c. magnetic fields. This article is categorized under: Nanotechnology Approaches to Biology > Nanoscale Systems in Biology Therapeutic Approaches and Drug Discovery > Nanomedicine for Neurological Disease Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease Therapeutic Approaches and Drug Discovery > Emerging Technologies.

Hybrid Electrical and Optical Neural Interfaces.

Neural interfaces bridge the nervous system and the outside world by recording and stimulating neurons. Combining electrical and optical modalities in a single, hybrid neural interface system could lead to complementary and powerful new ways to explore the brain. It has gained robust and exciting momentum recently in neuroscience and neural engineering research. Here, we review developments in the past several years aiming to achieve such hybrid electrical and optical microsystem platforms. Specifically, we cover three major categories of technological advances: transparent neuroelectrodes, optical neural fibers with electrodes, and neural probes/grids integrating electrodes and microscale light-emitting diodes. We discuss examples of these probes tailored to combine electrophysiological recording with optical imaging or optical neural stimulation of the brain and possible directions of future innovation.

Functionalized terahertz plasmonic metasensors: Femtomolar-level detection of SARS-CoV-2 spike proteins.

Effective and efficient management of human betacoronavirus severe acute respiratory syndrome (SARS)-CoV-2 virus infection i.e., COVID-19 pandemic, required sensitive and selective sensors with short sample-to-result durations for performing desired diagnostics. In this direction, one appropriate alternative approach to detect SARS-CoV-2 virus protein at low level i.e., femtomolar (fM) is exploring plasmonic metasensor technology for COVID-19 diagnostics, which offers exquisite opportunities in advanced healthcare programs, and modern clinical diagnostics. The intrinsic merits of plasmonic metasensors stem from their capability to squeeze electromagnetic fields, simultaneously in frequency, time, and space. However, the detection of low-molecular weight biomolecules at low densities is a typical drawback of conventional metasensors that has recently been addressed using toroidal metasurface technology. This research is focused on the fabrication of a miniaturized plasmonic immunosensor based on toroidal electrodynamics concept that can sustain robustly confined plasmonic modes with ultranarrow lineshapes in the terahertz (THz) frequencies. By exciting toroidal dipole mode using our quasi-infinite metasurface and a judiciously optimized protocol based on functionalized gold nanoparticles (AuNPs) conjugated with the specific monoclonal antibody specific to spike protein (S1) of SARS-CoV-2 virus onto the metasurface, the resonance shifts for diverse concentrations of the spike protein are monitored. Possessing molecular weight around ~76 kDa allowed to detect the presence of SARS-CoV-2 virus protein with significantly low as limit of detection (LoD) was achieved as ~4.2 fM. We envisage that outcomes of this research will pave the way toward the use of toroidal metasensors as practical technologies for rapid and precise screening of SARS-CoV-2 virus carriers, symptomatic or asymptomatic, and spike proteins in hospitals, clinics, laboratories, and site of infection.

Label-free detection of DNA by a dielectric modulated armchair-graphene nanoribbon FET based biosensor in a dual-nanogap setup.

A Double-Gate Armchair-Graphene Nanoribbon FET is proposed to realize a high-sensitive and small-size biosensor in order to detect DNA without high-cost and time-consuming labeling process. Two nanogap cavities open inside the top and bottom gate oxides by the method of sacrificed layer etching. When the DNA biomolecule is introduced to the nanogap cavity, the hybridization event which is actually the formation of a double-strand of DNA will occur thus electrically modulating the GNR channel leading to a change in the drain current. The important report of this research is about attained high sensitivity of the proposed biosensor for a vast spectrum of the DNA biological samples. It is worth noting that a DNA sequence by 23 nucleotides extracted from Neisseria gonorrhoeae can be detected as a special case. An extensive numerical approach has been applied in order to characterize the proposed biosensor. The suggested biosensor has been evaluated by solving Schrödinger equation )SE( with Non-Equilibrium Green Function (NEGF) method in the mode-space coupled into Poisson solver in a self-consistent manner assuming ballistic limit. Two different expressions of sensitivity in terms of the threshold voltage and current have been defined giving a good metric for the sensitivity analysis. The results revealed a relative sensitivity of 1 mV/nm2 by a filled area by the DNA about 120 nm2 showing the excellent superiority for the proposed biosensor as compared to other counterparts. The effective area of the proposed biosensor obtains 240 nm2 which is very small in comparison with other reports highlighting high capability of the biosensor in the detection. It has been shown that the proposed biosensor can be implemented in ultra-scaling domain resulting in considerable increase in the sensitivity promising a potent and reliable candidate for high-sensitive and small-size biosensors. Also, the technical issues on designing the suggested biosensor have been investigated to achieve a useful guideline in detection and identification of the target DNAs.

Generation of magnetoelectric photocurrents using toroidal resonances: a new class of infrared plasmonic photodetectors.

The detection of photons by plasmonic subwavelength devices underpins spectroscopy, low-power wavelength division multiplexing for short-distance optical communication, imaging, and time-gated distance measurements. In this work, we demonstrate infrared light-sensing using toroidal dipole-resonant plasmonic multipixel meta-atoms. As a key factor, the toroidal dipolar mode is an extremely localized electromagnetic excitation independent of the conventional multipoles. The exquisite behavior of this mode enables significant enhancements in the localized electromagnetic field and absorption cross-section, which boost the field confinement at the metal-dielectric interfaces. The proposed novel approach offers an advanced photodetection of the incident light based on substantial confinement of electromagnetic fields in a tiny spot, giving rise to the generation of hot carriers and a large photocurrent. Using both n- and p-type silicon (Si) substrates, we exploited the free-carrier absorption advantage of p-type Si to devise a high-responsivity device. Our findings show an unprecedented performance for infrared plasmonic photodetectors with low noises, high detectivity and remarkable internal quantum efficiency (IQE). Moreover, the tailored photodetection device provides a significant linear dynamic range of 46 dB and a fast operation speed. Our narrowband infrared light sensing photodevice offers a promising approach for further research studies over the optoelectronic and plasmonic tools and paves a viable route for low-dimensional photonic systems.

Gated graphene island-enabled tunable charge transfer plasmon terahertz metamodulator.

Graphene-enhanced optoelectronic terahertz (THz) signal processing offers an exquisite potential for tailoring extreme-subwavelength platforms to develop tunable and highly-responsive photonic tools. In this study, we propose a hybrid graphene island-mediated THz metadevice to support tunable charge transfer plasmon (CTP) resonances. We show that bias variations in the gated graphene significantly change the metadevice transmittance at the CTP frequency, while the capacitive dipolar mode remains unchanged. Our numerical and experimental studies show that tuning the conductivity of the graphene islands between a cluster of metallic blocks provides an active and exotic control over the charge transition across the assembly. To experimentally prove the viability of our concept in a practical photonic application, we utilized the presented tunable system as a high modulation-depth THz modulator. This enabled us to facilitate a THz modulation speed of 19 µs and 21 µs for rising and falling durations, respectively, with a modulation depth of 72%.