Optogenetic Applications Research Articles

ATP-dependent conformational dynamics in a photoactivated adenylate cyclase revealed by fluorescence spectroscopy and small-angle X-ray scattering

Structural insights into the photoactivated adenylate cyclases can be used to develop new ways of controlling cellular cyclic adenosine monophosphate (cAMP) levels for optogenetic and other applications. In this work, we use an integrative approach that combines biophysical and structural biology methods to provide insight on the interaction of adenosine triphosphate (ATP) with the dark-adapted state of the photoactivated adenylate cyclase from the cyanobacterium Oscillatoria acuminata (OaPAC). A moderate affinity of the nucleotide for the enzyme was calculated and the thermodynamic parameters of the interaction have been obtained. Stopped-flow fluorescence spectroscopy and small-angle solution scattering have revealed significant conformational changes in the enzyme, presumably in the adenylate cyclase (AC) domain during the allosteric mechanism of ATP binding to OaPAC with small and large-scale movements observed to the best of our knowledge for the first time in the enzyme in solution upon ATP binding. These results are in line with previously reported drastic conformational changes taking place in several class III AC domains upon nucleotide binding.

Development of an optogenetics tool, Opto-RANK, for control of osteoclast differentiation using blue light

Optogenetics enables precise regulation of intracellular signaling in target cells. However, the application of optogenetics to induce the differentiation of precursor cells and generate mature cells with specific functions has not yet been fully explored. Here, we focused on osteoclasts, which play an important role in bone remodeling, to develop a novel optogenetics tool, Opto-RANK, which can manipulate intracellular signals involved in osteoclast differentiation and maturation using blue light. We engineered Opto-RANK variants, Opto-RANKc and Opto-RANKm, and generated stable cell lines through retroviral transduction. Differentiation was induced by blue light, and various assays were conducted for functional analysis. Osteoclast precursor cells expressing Opto-RANK differentiated into multinucleated giant cells on light exposure and displayed upregulation of genes normally induced in differentiated osteoclasts. Furthermore, the differentiated cells exhibited bone-resorbing activities, with the possibility of spatial control of the resorption by targeted light illumination. These results suggested that Opto-RANK cells differentiated by light possess the features of osteoclasts, both morphological and functional. Thus, Opto-RANK should be useful for detailed spatiotemporal analysis of intracellular signaling during osteoclast differentiation and the development of new therapies for various bone diseases.

Insights into the photoswitch based on 5-deazaFMN and LOV2 from Avena sativa: a combined absorption and NMR spectroscopy study.

The LOV2 domain from Avena sativa (As) is a blue light receptor that undergoes adduct formation with the native flavin mononucleotide (FMN) cofactor [Salomon et al., Biochemistry, 2000, 39, 9401]. We report the photochemical changes of AsLOV2 through cofactor exchange with the FMN analogue 5-deazaFMN. Absorption spectroscopy shows that upon illumination a thermodynamically stable adduct is formed. We were able to confirm the structure of the adduct by introducing 13C-labelled 5-deazaFMN isotopologues in solution NMR experiments. Dark-adapted state recovery can be photo-induced, providing a photoswitch that is easy to manipulate. The robust photocycle is repeatable without significant loss. Based on the data presented we propose the system as an alternative to wild-type AsLOV2 for applications in optogenetics.

Optogenetics Neuromodulation of the Nose.

Recently developed optogenetic technology, which allows high-fidelity control of neuronal activity, has been applied to investigate the neural circuits underlying sensory processing and behavior. The nasal cavity is innervated by the olfactory nerve and trigeminal nerve, which are closely related to common symptoms of rhinitis, such as impairment of smell, itching, and sneezing. The olfactory system has an amazing ability to distinguish thousands of odorant molecules at trace levels. However, there are many issues in olfactory sensing mechanisms that need to be addressed. Optogenetics offers a novel technical approach to solve this dilemma. Therefore, we review the recent advances in olfactory optogenetics to clarify the mechanisms of chemical sensing, which may help identify the mechanism of dysfunction and suggest possible treatments for impaired smell. Additionally, in rhinitis patients, alterations in the other nerve (trigeminal nerve) that innervates the nasal cavity can lead to hyperresponsiveness to various nociceptive stimuli and central sensitization, causing frequent and persistent itching and sneezing. In the last several years, the application of optogenetics in regulating nociceptive receptors, which are distributed in sensory nerve endings, and amino acid receptors, which are distributed in vital brain regions, to alleviate overreaction to nociceptive stimuli, has gained significant attention. Therefore, we focus on the progress in optogenetics and its application in neuromodulation of nociceptive stimuli and discuss the potential clinical translation for treating rhinitis in the future.

Photoactivation of LOV domains with chemiluminescence.

Optogenetics has opened new possibilities in the remote control of diverse cellular functions with high spatiotemporal precision using light. However, delivering light to optically non-transparent systems remains a challenge. Here, we describe the photoactivation of light-oxygen-voltage-sensing domains (LOV domains) with in situ generated light from a chemiluminescence reaction between luminol and H2O2. This activation is possible due to the spectral overlap between the blue chemiluminescence emission and the absorption bands of the flavin chromophore in LOV domains. All four LOV domain proteins with diverse backgrounds and structures (iLID, BcLOV4, nMagHigh/pMagHigh, and VVDHigh) were photoactivated by chemiluminescence as demonstrated using a bead aggregation assay. The photoactivation with chemiluminescence required a critical light-output below which the LOV domains reversed back to their dark state with protein characteristic kinetics. Furthermore, spatially confined chemiluminescence produced inside giant unilamellar vesicles (GUVs) was able to photoactivate proteins both on the membrane and in solution, leading to the recruitment of the corresponding proteins to the GUV membrane. Finally, we showed that reactive oxygen species produced by neutrophil like cells can be converted into sufficient chemiluminescence to recruit the photoswitchable protein BcLOV4-mCherry from solution to the cell membrane. The findings highlight the utility of chemiluminescence as an endogenous light source for optogenetic applications, offering new possibilities for studying cellular processes in optically non-transparent systems.

Merocyanines form bacteriorhodopsins with strongly bathochromic absorption maxima

There is a need to shift the absorbance of biomolecules to the optical transparency window of tissue for applications in optogenetics and photo-pharmacology. There are a few strategies to achieve the so-called red shift of the absorption maxima. Herein, a series of 11 merocyanine dyes were synthesized and employed as chromophores in place of retinal in bacteriorhodopsin (bR) to achieve a bathochromic shift of the absorption maxima relative to bR’s λmaxa\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\lambda }_{\\mathrm{max}}^{a}$$\\end{document} of 568 nm. Assembly with the apoprotein bacterioopsin (bO) led to stable, covalently bound chromoproteins with strongly bathochromic absorbance bands, except for three compounds. Maximal red shifts were observed for molecules 9, 2, and 8 in bR where the λmaxa\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\lambda }_{\\mathrm{max}}^{a}$$\\end{document} was 766, 755, and 736 nm, respectively. While these three merocyanines have different end groups, they share a similar structural feature, namely, a methyl group which is located at the retinal equivalent position 13 of the polyene chain. The absorption and fluorescence data are also presented for the retinal derivatives in their aldehyde, Schiff base (SB), and protonated SB (PSB) forms in solution. According to their hemicyanine character, the PSBs and their analogue bRs exhibited fluorescence quantum yields (Φf) several orders of magnitude greater than native bR (Φf 0.02 to 0.18 versus 1.5 × 10–5 in bR) while also exhibiting much smaller Stokes shifts than bR (400 to 1000 cm−1 versus 4030 cm−1 in bR). The experimental results are complemented by quantum chemical calculations where excellent agreement between the experimental λmaxa\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\lambda }_{\\mathrm{max}}^{a}$$\\end{document} and the calculated λmaxa\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\lambda }_{\\mathrm{max}}^{a}$$\\end{document} was achieved with the second-order algebraic-diagrammatic construction [ADC(2)] method. In addition, quantum mechanics/molecular mechanics (QM/MM) calculations were employed to shed light on the origin of the bathochromic shift of merocyanine 2 in bR compared with native bR.Graphical abstract

Modulating signalling lifetime to optimise a prototypical animal opsin for optogenetic applications

Animal opsins are light activated G-protein-coupled receptors, capable of optogenetic control of G-protein signalling for research or therapeutic applications. Animal opsins offer excellent photosensitivity, but their temporal resolution can be limited by long photoresponse duration when expressed outside their native cellular environment. Here, we explore methods for addressing this limitation for a prototypical animal opsin (human rod opsin) in HEK293T cells. We find that the application of the canonical rhodopsin kinase (GRK1)/visual arrestin signal termination mechanism to this problem is complicated by a generalised suppressive effect of GRK1 expression. This attenuation can be overcome using phosphorylation-independent mutants of arrestin, especially when these are tethered to the opsin protein. We further show that point mutations targeting the Schiff base stability of the opsin can also reduce signalling lifetime. Finally, we apply one such mutation (E122Q) to improve the temporal fidelity of restored visual responses following ectopic opsin expression in the inner retina of a mouse model of retinal degeneration (rd1). Our results reveal that these two strategies (targeting either arrestin binding or Schiff-base hydrolysis) can produce more time-delimited opsin signalling under heterologous expression and establish the potential of this approach to improve optogenetic performance.

Structural framework for the understanding spectroscopic and functional signatures of the cyanobacterial Orange Carotenoid Protein families

The Orange Carotenoid Protein (OCP) is a unique photoreceptor crucial for cyanobacterial photoprotection. Best studied Synechocystis sp. PCC 6803 OCP belongs to the large OCP1 family. Downregulated by the Fluorescence Recovery Protein (FRP) in low-light, high-light-activated OCP1 binds to the phycobilisomes and performs non-photochemical quenching. Recently discovered families OCP2 and OCP3 remain structurally and functionally underexplored, and no systematic comparative studies have ever been conducted. Here we present two first crystal structures of OCP2 from morphoecophysiologically different cyanobacteria and provide their comprehensive structural, spectroscopic and functional comparison with OCP1, the recently described OCP3 and all-OCP ancestor. Structures enable correlation of spectroscopic signatures with the effective number of hydrogen and discovered here chalcogen bonds anchoring the ketocarotenoid in OCP, as well as with the rotation of the echinenone's β-ionone ring in the CTD. Structural data also helped rationalize the observed differences in OCP/FRP and OCP/phycobilisome functional interactions. These data are expected to foster OCP research and applications in optogenetics, targeted carotenoid delivery and cyanobacterial biomass engineering.

Full-field exposure of larval zebrafish to narrow waveband LED light sources at defined power and energy for optogenetic applications

BackgroundOptogenetic approaches in transparent zebrafish models have provided numerous insights into vertebrate neurobiology. The purpose of this study was to develop methods to activate light-sensitive transgene products simultaneously throughout an entire larval zebrafish. New methodWe developed a LED illumination stand and microcontroller unit to expose zebrafish larvae reproducibly to full field illumination at defined wavelength, power, and energy. ResultsThe LED stand generated a sufficiently flat illumination field to expose multiple larval zebrafish to high power light stimuli uniformly, while avoiding sample bath warming. The controller unit allowed precise automated delivery of predetermined amounts of light energy at calibrated power. We demonstrated the utility of the approach by driving photoconversion of Kaede (398 nm), photodimerization of GAVPO (450 nm), and photoactivation of dL5**/MG2I (661 nm) in neurons throughout the CNS of larval zebrafish. Observed outcomes were influenced by both total light energy and its rate of delivery, highlighting the importance of controlling these variables to obtain reproducible results. Comparison with existing methodsOur approach employs inexpensive LED chip arrays to deliver narrow-waveband light with a sufficiently flat illumination field to span multiple larval zebrafish simultaneously. Calibration of light power and energy are built into the workflow. ConclusionsThe LED illuminator and controller can be constructed from widely available materials using the drawings, instructions, and software provided. This approach will be useful for multiple optogenetic applications in zebrafish and other models.

Optogenetics for sensors: On-demand fluorescent labeling of histone epigenetics

Post-translational modifications of histones to a large extent determine the functional state of chromatin loci. Dynamic visualization of histone modifications with genetically encoded fluorescent sensors makes it possible to monitor changes in the epigenetic state of a single living cell. At the same time, the sensors can potentially compete with endogenous factors recognizing these modifications. Thus, prolonged binding of the sensors to chromatin can affect normal epigenetic regulation. Here, we report an optogenetic sensor for live-cell visualization of histone H3 methylated at lysine-9 (H3K9me3) named MPP8-LAMS (MPP8-based light-activated modification sensor). MPP8-LAMS consists of several fusion protein parts (from N- to C-terminus): i) nuclear export signal (NES), ii) far-red fluorescent protein Katushka, iii) H3K9me3-binding reader domain of the human M phase phosphoprotein 8 (MPP8), iv) the light-responsive AsLOV2 domain, which exposes a nuclear localization signal (NLS) upon blue light stimulation. In the dark, due to the NES, MPP8-LAMS is localized in the cytosol. Under blue light illumination, MPP8-LAMS underwent an efficient translocation from cytosol to nucleus, enabling visualization of H3K9me3-enriched loci. Such an on-demand visualization minimizes potential impact on cell physiology as most of the time the sensor is separated from its target. In general, the present work extends the application of optogenetics to the area of advanced use of genetically encoded sensors.

Optogenetic control of neural activity: The biophysics of microbial rhodopsins in neuroscience.

Optogenetics, the use of microbial rhodopsins to make the electrical activity of targeted neurons controllable by light, has swept through neuroscience, enabling thousands of scientists to study how specific neuron types contribute to behaviors and pathologies, and how they might serve as novel therapeutic targets. By activating a set of neurons, one can probe what functions they can initiate or sustain, and by silencing a set of neurons, one can probe the functions they are necessary for. We here review the biophysics of these molecules, asking why they became so useful in neuroscience for the study of brain circuitry. We review the history of the field, including early thinking, early experiments, applications of optogenetics, pre-optogenetics targeted neural control tools, and the history of discovering and characterizing microbial rhodopsins. We then review the biophysical attributes of rhodopsins that make them so useful to neuroscience - their classes and structure, their photocycles, their photocurrent magnitudes and kinetics, their action spectra, and their ion selectivity. Our hope is to convey to the reader how specific biophysical properties of these molecules made them especially useful to neuroscientists for a difficult problem - the control of high-speed electrical activity, with great precision and ease, in the brain.

Experimental Assessment of the Electronic and Geometrical Structure of a Near-Infrared Absorbing and Highly Fluorescent Microbial Rhodopsin.

The recently discovered Neorhodopsin (NeoR) exhibits absorption and emission maxima in the near-infrared spectral region, which together with the high fluorescence quantum yield makes it an attractive retinal protein for optogenetic applications. The unique optical properties can be rationalized by a theoretical model that predicts a high charge transfer character in the electronic ground state (S0) which is otherwise typical of the excited state S1 in canonical retinal proteins. The present study sets out to assess the electronic structure of the NeoR chromophore by resonance Raman (RR) spectroscopy since frequencies and relative intensities of RR bands are controlled by the ground and excited state's properties. The RR spectra of NeoR differ dramatically from those of canonical rhodopsins but can be reliably reproduced by the calculations carried out within two different structural models. The remarkable agreement between the experimental and calculated spectra confirms the consistency and robustness of the theoretical approach.

Diminishing neuronal acidification by channelrhodopsins with low proton conduction.

Many channelrhodopsins are permeable to protons. We found that in neurons, activation of a high-current channelrhodopsin, CheRiff, led to significant acidification, with faster acidification in the dendrites than in the soma. Experiments with patterned optogenetic stimulation in monolayers of HEK cells established that the acidification was due to proton transport through the opsin, rather than through other voltage-dependent channels. We identified and characterized two opsins which showed large photocurrents, but small proton permeability, PsCatCh2.0 and ChR2-3M. PsCatCh2.0 showed excellent response kinetics and was also spectrally compatible with simultaneous voltage imaging with QuasAr6a. Stimulation-evoked acidification is a possible source of disruptions to cell health in scientific and prospective therapeutic applications of optogenetics. Channelrhodopsins with low proton permeability are a promising strategy for avoiding these problems.

Diminishing neuronal acidification by channelrhodopsins with low proton conduction

Many channelrhodopsins are permeable to protons. We found that in neurons, activation of a high-current channelrhodopsin, CheRiff, led to significant acidification, with faster acidification in the dendrites than in the soma. Experiments with patterned optogenetic stimulation in monolayers of HEK cells established that the acidification was due to proton transport through the opsin, rather than through other voltage-dependent channels. We identified and characterized two opsins which showed large photocurrents, but small proton permeability, PsCatCh2.0 and ChR2-3M. PsCatCh2.0 showed excellent response kinetics and was also spectrally compatible with simultaneous voltage imaging with QuasAr6a. Stimulation-evoked acidification is a possible source of disruptions to cell health in scientific and prospective therapeutic applications of optogenetics. Channelrhodopsins with low proton permeability are a promising strategy for avoiding these problems.

Application of optogenetic glial cells to neuron-glial communication.

Optogenetic techniques combine optics and genetics to enable cell-specific targeting and precise spatiotemporal control of excitable cells, and they are increasingly being employed. One of the most significant advantages of the optogenetic approach is that it allows for the modulation of nearby cells or circuits with millisecond precision, enabling researchers to gain a better understanding of the complex nervous system. Furthermore, optogenetic neuron activation permits the regulation of information processing in the brain, including synaptic activity and transmission, and also promotes nerve structure development. However, the optimal conditions remain unclear, and further research is required to identify the types of cells that can most effectively and precisely control nerve function. Recent studies have described optogenetic glial manipulation for coordinating the reciprocal communication between neurons and glia. Optogenetically stimulated glial cells can modulate information processing in the central nervous system and provide structural support for nerve fibers in the peripheral nervous system. These advances promote the effective use of optogenetics, although further experiments are needed. This review describes the critical role of glial cells in the nervous system and reviews the optogenetic applications of several types of glial cells, as well as their significance in neuron-glia interactions. Together, it briefly discusses the therapeutic potential and feasibility of optogenetics.

Design study of a micro illumination platform based on GaN microLED arrays.

The design study of a micro illumination tool based on GaN microLED arrays is presented. The high spatio-temporal resolution and the capability of generating fully customized optical patterns that characterize the proposed platform would enable the manipulation of biological systems, e.g.,for optogenetics applications. Based on ray tracing simulations, the design aspects that mainly affect the device performance have been identified, and the related structural parameters have been optimized to improve the extraction efficiency and the spatial resolution of the resulting light patterns. Assuming that the device is a bottom emitter, and the light is extracted from the n-side, the presence of mesa-structures on the p-side of the GaN layer can affect both the efficiency and the resolution, being optimized for different values of the mesa-side inclination angle. The full width at half maximum (FWHM) of the extracted spots is mainly determined by the substrate thickness, and the relation between the FWHM and the array pitch represents a criterion to define the resolution. Namely, when F W H M<p i t c h, the spots are assumed to be resolved, while, when F W H M=p i t c h, a homogeneous distribution of light intensity is observed. The best performance is obtained when an in-GaN micro-lens array is included in the simulated structure, assuming that the substrate has been removed. The spatial resolution of the generated light pattern results as fully preserved, while the extraction efficiency in the best case is up to three times larger than that of a planar GaN/air interface.

K+-Dependent Photocycle and Photocurrent Reveal the Uptake of K+ in Light-Driven Sodium Pump.

Engineering light-controlled K+ pumps from Na+-pumping rhodopsins (NaR) greatly expands the scope of optogenetic applications. However, the limited knowledge regarding the kinetic and selective mechanism of K+ uptake has significantly impeded the modification and design of light-controlled K+ pumps, as well as their practical applications in various fields, including neuroscience. In this study, we presented K+-dependent photocycle kinetics and photocurrent of a light-driven Na+ pump called Nonlabens dokdonensis rhodopsin 2 (NdR2). As the concentration of K+ increased, we observed the accelerated decay of M intermediate in the wild type (WT) through flash photolysis. In 100 mM KCl, the lifetime of the M decay was approximately 1.0 s, which shortened to around 0.6 s in 1 M KCl. Additionally, the K+-dependent M decay kinetics were also observed in the G263W/N61P mutant, which transports K+. In 100 mM KCl, the lifetime of the M decay was approximately 2.5 s, which shortened to around 0.2 s in 1 M KCl. According to the competitive model, in high KCl, K+ may be taken up from the cytoplasmic surface, competing with Na+ or H+ during M decay. This was further confirmed by the K+-dependent photocurrent of WT liposome. As the concentration of K+ increased to 500 mM, the amplitude of peak current significantly dropped to approximately ~60%. Titration experiments revealed that the ratio of the rate constant of H+ uptake (kH) to that of K+ uptake (kK) is >108. Compared to the WT, the G263W/N61P mutant exhibited a decrease of approximately 40-fold in kH/kK. Previous studies focused on transforming NaR into K+ pumps have primarily targeted the intracellular ion uptake region of Krokinobacter eikastus rhodopsin 2 (KR2) to enhance K+ uptake. However, our results demonstrate that the naturally occurring WT NdR2 is capable of intracellular K+ uptake without requiring structural modifications on the intracellular region. This discovery provides diverse options for future K+ pump designs. Furthermore, we propose a novel photocurrent-based approach to evaluate K+ uptake, which can serve as a reference for similar studies on other ion pumps. In conclusion, our research not only provides new insights into the mechanism of K+ uptake but also offers a valuable point of reference for the development of optogenetic tools and other applications in this field.

Conformational change in an engineered biliverdin-binding cyanobacteriochrome during the photoconversion process

Cyanobacteriochromes (CBCRs) derived from cyanobacteria are linear-tetrapyrrole-binding photoreceptors related to the canonical red/far-red reversible phytochrome photoreceptors. CBCRs contain chromophore-binding cGMP-specific phosphodiesterase/adenylate cyclase/FhlA (GAF) domains that are highly diverse in their primary sequences and are categorized into many subfamilies. Among this repertoire, the biliverdin (BV)-binding CBCR GAF domains receive considerable attention for their in vivo optogenetic and bioimaging applications because BV is a mammalian intrinsic chromophore and can absorb far-red light that penetrates deep into the mammalian body. The typical BV-binding CBCR GAF domain exhibits reversible photoconversion between far-red-absorbing dark-adapted and orange-absorbing photoproduct states. Herein, we applied various biochemical and spectral studies to identify the details of the conformational change during this photoconversion process. No oligomeric state change was observed, whereas the surface charge would change with a modification of the α-helix structures during the photoconversion process. Combinatorial analysis using partial protease digestion and mass spectrometry identified the region where the conformational change occurred. These results provide clues for the future development of optogenetic tools.

Assessment of Different Niosome Formulations for Optogenetic Applications: Morphological and Electrophysiological Effects.

Gene therapy and optogenetics are becoming promising tools for treating several nervous system pathologies. Currently, most of these approaches use viral vectors to transport the genetic material inside the cells, but viruses present some potential risks, such as marked immunogenicity, insertional mutagenesis, and limited insert gene size. In this framework, non-viral nanoparticles, such as niosomes, are emerging as possible alternative tools to deliver genetic material, avoiding the aforementioned problems. To determine their suitability as vectors for optogenetic therapies in this work, we tested three different niosome formulations combined with three optogenetic plasmids in rat cortical neurons in vitro. All niosomes tested successfully expressed optogenetic channels, which were dependent on the ratio of niosome to plasmid, with higher concentrations yielding higher expression rates. However, we found changes in the dendritic morphology and electrophysiological properties of transfected cells, especially when we used higher concentrations of niosomes. Our results highlight the potential use of niosomes for optogenetic applications and suggest that special care must be taken to achieve an optimal balance of niosomes and nucleic acids to achieve the therapeutic effects envisioned by these technologies.

Semi-Implantable Wireless Power Transfer (WPT) System Integrated With On-Chip Power Management Unit (PMU) for Neuromodulation Application

Miniaturization of the neuromodulation system is important for non-invasive or sub-invasive optogenetic application. This work presents an optimized wireless power transfer (WPT) system integrated with an on-chip rectification circuitry and an off-chip stimulation circuitry for optogenetic stimulation of freely moving rodents. The proposed WPT system is built using parallel transmitter (TX) coils on printed circuit board (PCB) and wire-wound based receiver (RX) coil followed by a seven-stage voltage doubler and a low dropout regulator (LDO) circuit designed in 180 nm standard Complementary Metal Oxide Semiconductor (CMOS) process. A pulse stimulation is used to stimulate the neurons which is generated using a commercially available off-the-shelf (COTS) components based oscillator circuit. The intensity of the stimulation is controlled by using a COTS based LED driver circuit which controls the current through the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula> LED. The total dimension of the RX coil is 8 mm × 3.4 mm. The maximum power transfer efficiency (PTE) of the proposed WPT system is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\sim$</tex-math></inline-formula> 35% and the power conversion efficiency (PCE) of the rectifier is 52%. The proposed system with reconfigurable stimulation frequency is suitable for exciting different brain areas for long-term health monitoring.