Monitoring brain activity with light-mediated methods presents significant advancement over conventional electrophysiological methods, including cell-type specificity, high spatiotemporal resolution over large fields of view, and minimal signal interference. However, an implantable form factor with penetrating shanks is required to reach arbitrary depth in the brain due to highly scattering and absorptive nature of the surrounding tissue. In this paper, we present an implantable optical brain interface based on a scalable complementary metal-oxide semiconductor (CMOS) process. The device incorporates 4000 photodetectors interleaved with 40 micro-LED (mu LED) sites, spectral filters and an ultracompact metasurface in a sub-100-mu m profile to reach single-neuron resolution at depth with minimal tissue damage. A machine-learning-based optimization algorithm is used to design the metasurface with a working distance of less than 50 mu m, enabling direct integration with the CMOS imager array. Adaptation of the mixing matrix through wavefront shaping generated by the 25-mu m-thick metasurface allows for reconstruction of the volume above the mu LED sites with high precision. The imager is able to localize multiple 10-mu m fluorescent beads with frame rates up to 400 frames/sec within a field of view of 6300x200x200 mu m(3).

Optical imaging offers a number of advantages over electrophysiology including cell-type specificity. However, its application has been limited to the investigation of shallow brain regions (less than 2 mm) because of the light scattering property of brain tissue. Passive optical conduits, such as graded-index lenses and waveguides, have permitted access to deeper locales but with restricted resolution and field of view, while creating massive lesions along the inserted path. Here we report an implantable complementary metal–oxide–semiconductor fluorescence imager with single-neuron resolution. The imager has a 512-pixel silicon image sensor post-processed into a 4.1-mm-long, 120-μm-wide shank with a collinear fibre for illumination. It can record transient fluorescent signals in deep brain regions at 400 frames per second. We show that the system can offer single-neuron resolution in functional imaging of GCaMP6s-expressing neurons at a frame rate of 400 frames per second. A complementary metal–oxide–semiconductor (CMOS) imager that has a 512-pixel silicon image sensor post-processed into a 4.1-mm-long, 120-μm-wide shank with a collinear fibre for illumination can be used to record transient fluorescent signals in deep brain regions at 400 frames per second.

Retinitis pigmentosa and macular degeneration lead to photoreceptor death and loss of visual perception. Despite recent progress, restorative technologies for photoreceptor degeneration remain largely unavailable. Here, we describe a novel optogenetic visual prosthesis (FlexLED) based on a combination of a thin-film retinal display and optogenetic activation of retinal ganglion cells (RGCs). The FlexLED implant is a 30 µm thin, flexible, wireless µLED display with 8,192 pixels, each with an emission area of 66 µm 2 . The display is affixed to the retinal surface, and the electronics package is mounted under the conjunctiva in the form factor of a conventional glaucoma drainage implant. In a rabbit model of photoreceptor degeneration, optical stimulation of the retina using the FlexLED elicits activity in visual cortex. This technology is readily scalable to hundreds of thousands of pixels, providing a route towards an implantable optogenetic visual prosthesis capable of generating vision by stimulating RGCs at near-cellular resolution.

The use of optogenetic stimulation to evoke neuronal activity in targeted neural populations—enabled by opsins with fast kinetics, high sensitivity and cell-type and subcellular specificity—is a powerful tool in neuroscience. However, to interface with the opsins, deep-brain light delivery systems are required that match the scale of the spatial and temporal control offered by the molecular actuators. Here we show that organic light-emitting diodes can be combined with complementary metal–oxide–semiconductor technology to create bright, actively multiplexed emissive elements. We create implantable shanks in which 1,024 individually addressable organic light-emitting diode pixels with a 24.5 µm pitch are integrated with active complementary metal–oxide–semiconductor drive and control circuitry. This integration is enabled by controlled electrode conditioning, monolithic deposition of the organic light-emitting diodes and optimized thin-film encapsulation. The resulting probes can be used to access brain regions as deep as 5 mm and selectively activate individual neurons with millisecond-level precision in mice.

Implantable image sensors have the potential to revolutionize neuroscience. Due to their small form factor requirements; however, conventional filters and optics cannot be implemented. These limitations obstruct high-resolution imaging of large neural densities. Recent advances in angle-sensitive image sensors and single-photon avalanche diodes have provided a path toward ultrathin lens-less fluorescence imaging, enabling plenoptic sensing by extending sensing capabilities to include photon arrival time and incident angle, thereby providing the opportunity for separability of fluorescence point sources within the context of light-field microscopy (LFM). However, the addition of spectral sensitivity to angle-sensitive LFM reduces imager resolution because each wavelength requires a separate pixel subset. Here, we present a 1024-pixel, 50 µm thick implantable shank-based neural imager with color-filter-grating-based angle-sensitive pixels. This angular-spectral sensitive front end combines a metal–insulator–metal (MIM) Fabry–Perot color filter and diffractive optics to produce the measurement of orthogonal light-field information from two distinct colors within a single photodetector. The result is the ability to add independent color sensing to LFM while doubling the effective pixel density. The implantable imager combines angular-spectral and temporal information to demix and localize multispectral fluorescent targets. In this initial prototype, this is demonstrated with 45 μm diameter fluorescently labeled beads in scattering medium. Fluorescent lifetime imaging is exploited to further aid source separation, in addition to detecting pH through lifetime changes in fluorescent dyes. While these initial fluorescent targets are considerably brighter than fluorescently labeled neurons, further improvements will allow the application of these techniques to in-vivo multifluorescent structural and functional neural imaging.

We propose a new paradigm for dense functional imaging of brain activity to surmount the limitations of present methodologies. We term this approach "integrated neurophotonics"; it combines recent advances in microchip-based integrated photonic and electronic circuitry with those from optogenetics. This approach has the potential to enable lens-less functional imaging from within the brain itself to achieve dense, large-scale stimulation and recording of brain activity with cellular resolution at arbitrary depths. We perform a computational study of several prototype 3D architectures for implantable probe-array modules that are designed to provide fast and dense single-cell resolution (e.g., within a 1-mm3 volume of mouse cortex comprising ∼100,000 neurons). We describe progress toward realizing integrated neurophotonic imaging modules, which can be produced en masse with current semiconductor foundry protocols for chip manufacturing. Implantation of multiple modules can cover extended brain regions.

A new modality Photonic probes record fluorescent signals by using arrays of light emitters and detectors embedded in neural tissue. Neither the emitted nor collected light fields are focused. Instead, in proposed configurations, hundreds of emitters will form rapid sequences of structured illumination patterns—providing sufficient spatial and temporal differentiation of neural signals for computational demixing. Here we define criteria for evaluating probe designs for achieving better signal separability. We find that probe geometry has profound, often unintuitive, effects on the separability of neural signals, providing initial design guidelines to achieve separation of individual cells in densely labeled populations.### Competing Interest StatementThe authors have declared no competing interest.

This paper presents a device for time-gated fluorescence imaging in the deep brain, consisting of two on-chip laser diodes and 512 single-photon avalanche diodes (SPADs). The edge-emitting laser diodes deliver fluorescence excitation above the SPAD array, parallel to the imager. In the time domain, laser diode illumination is pulsed and the SPAD is time-gated, allowing a fluorescence excitation rejection up to O.D. 3 at 1 ns of time-gate delay. Each SPAD pixel is masked with Talbot gratings to enable the mapping of 2D array photon counts into a 3D image. The 3D image achieves a resolution of 40, 35, and 73 μm in the x, y, and z directions, respectively, in a noiseless environment, with a maximum frame rate of 50 kilo-frames-per-second. We present measurement results of the spatial and temporal profiles of the dual-pulsed laser diode illumination and of the photon detection characteristics of the SPAD array. Finally, we show the imager's ability to resolve a glass micropipette filled with red fluorescent microspheres. The system's 420 μm-wide cross section allows it to be inserted at arbitrary depths of the brain while achieving a field of view four times larger than fiber endoscopes of equal diameter.

Optical functional neural imaging has revolutionized neuroscience with optical reporters that enable single-cell-resolved monitoring of neuronal activity in vivo. State-of-the-art microscopy methods, however, are fundamentally limited in imaging depth by absorption and scattering in tissue even with the use of the most sophisticated two-photon microscopy techniques [1]. To overcome this imaging depth problem, we develop a lens-less, optical-filter-less, shank-based image sensor array that can be inserted into the brain, allowing cellular-resolution recording at arbitrary depths with excitation provided by an external laser light source (Fig. 11.5.1). Lens-less imaging is achieved generally by giving each pixel a spatial sensitivity function, which can be introduced by near-field or far-field, phase or amplitude masking. Since probe thickness must be less than $70 \mu \mathrm {m}$ to limit tissue damage and far-field masks are characterized by distances on the order of $200 \mu \mathrm {m}$ between the mask and the detector [2], we employ a near-field amplitude mask formed by Talbot gratings in the back-end metal of the CMOS process, which gives each pixel a diffraction-grating-induced angle-sensitivity [3]. Filter-less fluorescence imaging is achieved with time-gated operation in which the excitation light source is pulsed and pixel-level time-gated circuitry collects photons only after the excitation source has been removed.

We present an implantable single-photon shank-based imager, monolithically integrated onto a single CMOS IC. The imager comprises of 512 single-photon avalanche diodes distributed along two shanks, with a 6-bit depth in-pixel memory and an on-chip digital-to-time converter. To scale down the system to a minimally invasive form factor, we substitute optical filtering and focusing elements with a time-gated, angle-sensitive detection system. The imager computationally reconstructs the position of fluorescent sources within a 3-D volume of 3.4 mm $\times $ 600 $\mathrm {\mu }\text{m}\,\,\times $ 400 $\mu \text{m}$ .

A liquid-permeable concept in a metal insulator metal (MIM) structure is proposed to achieve highly sensitive color-tuning property through the change of the effective refractive index of the dielectric insulator layer. A semicontinuous top metal film with nanoapertures, adopted as a transreflective layer for MIM resonator, allows to tailor the nanomorphology of a dielectric layer through selective etching of the underneath insulator layer, resulting in nanopillars and hollow voids in the insulator layer. By allowing outer mediums to enter into the hollow voids of the dielectric layer, such liquid-permeable MIM architecture enables to achieve the wavelength shift as large as 323.5 nm/RIU in the visible range, which is the largest wavelength shift reported so far. Our liquid permeable approaches indeed provide dramatic color tunablility, a real-time sensing scheme, long-term durability, and reproducibility in a simple and scalable manner.

The thin film transistor (TFT) is a promising biosensor system with great sensitivity, label-free detection, and a quick response time. However, even though the TFT sensor has such advantageous characteristics, the disadvantages hamper the TFT sensor's application in the clinical field. The TFT is susceptible to light, noise, vibration, and limited usage, and this significantly limits its on-site potential as a practical biosensor. Herein, we developed a fully packaged, portable TFT electrochemical biosensor into a chip form, providing both portability through minimizing the laboratory equipment size and multiple safe usages by protecting the semiconductor sensor. Additionally, a safe environment that serves as a miniature probe station minimizes the previously mentioned disadvantages, while providing the means to properly link the TFT biosensor with a portable analyzer. The biosensor was taken into a biosafety level 3 (BSL-3) laboratory setting to analyze highly pathogenic avian influenza virus (HPAIV) samples. This virus quickly accumulates within a host, and therefore, early stage detection is critical to deterring the further spread of the deadly disease to other areas. However, current on-site methods have poor limits of detection (105-106 EID50/mL), and because the virus has low concentration in its early stages, it cannot be detected easily. We have compared the sample measurements from our device with virus concentration data obtained from a RT-PCR (virus range: 100-104 EID50/mL) and have identified an increasing voltage signal which corresponds to increasing virus concentration.

Photosensitive materials contain biologically engineered elements and are constructed using delicate techniques, with special attention devoted to efficiency, stability, and biocompatibility. However, to date, no photosensitive material has been developed to replace damaged visual-systems to detect light and transmit the signal to a neuron in the human body. In the current study, artificial nanovesicle-based photosensitive materials are observed to possess the characteristics of photoreceptors similar to the human eye. The materials exhibit considerably effective spectral characteristics according to each pigment. Four photoreceptors originating from the human eye with color-distinguishability are produced in human embryonic kidney (HEK)-293 cells and partially purified in the form of nanovesicles. Under various wavelengths of visible light, electrochemical measurements are performed to analyze the physiological behavior and kinetics of the photoreceptors, with graphene, performing as an electrode, playing an important role in the lipid bilayer deposition and oxygen reduction processes. Four nanovesicles with different photoreceptors, namely, rhodopsin (Rho), short-, medium-, and longwave sensitive opsin 1 (1SW, 1MW, 1LW), show remarkable color-dependent characteristics, consistent with those of natural human retina. With four different light-emitting diodes for functional verification, the photoreceptors embedded in nanovesicles show remarkably specific color sensitivity. This study demonstrates the potential applications of light-activated platforms in biological optoelectronic industries.

The charge transfer dynamics regarding an intimate contact between graphene and single-stranded deoxyribonucleic acid (ssDNA) is investigated from DC to the THz-regime. A graphene field-effect transistor (G-FET) is immersed in ssDNA solutions where the adsorption of ssDNA is controlled in terms of absolute coverage. DC-response of the G-FET is recorded and cross-validated by observing changes in Raman spectroscopy and further investigating THz-time domain spectroscopy using a nano-slot antenna. We find very good agreement between electrical and optical approaches where the Fermi level of the ssDNA-adsorbed graphene depends on the coverage nonlinearly. The results point towards a new doping method with sub-nanoscale patterning precision on graphene and its electronic applications based on electronic junction properties.

Current methods to detect avian influenza viruses (AIV) are time consuming and lo inw sensitivity, necessitating a faster and more sensitive sensor for on‐site epidemic detection in poultry farms and urban population centers. This study reports a field effect transistor (FET) based AIV sensor that detects nucleoproteins (NP) within 30 minutes, down to an LOD of 10 3 EID 50 mL −1 from a live animal cloacal swab. Previously reported FET sensors for AIV detection have not targeted NPs, an internal protein shared across multiple strains, due to the difficulty of field‐effect sensing in a highly ionic lysis buffer. The AIV sensor overcomes the sensitivity limit with an FET‐based platform enhanced with a disposable well gate (DWG) that is readily replaceable after each measurement. In a single procedure, the virus‐containing sample is immersed in a lysis buffer mixture to expose NPs to the DWG surface. In comparison with commercial AIV rapid kits, the AIV sensor is proved to be highly sensitive, fast, and compact, proving its potential effectiveness as a portable biosensor.

There is an explosive interest in the immediate and cost-effective analysis of field-collected biological samples, as many advanced biodetection tools are highly sensitive, yet immobile. On-site biosensors are portable and convenient sensors that provide detection results at the point of care. They are designed to secure precision in highly ionic and heterogeneous solutions with minimal hardware. Among various methods that are capable of such analysis, field-effect biosensors are promising candidates due to their unique sensitivity, manufacturing scalability, and integrability with computational circuitry. Recent developments in nanotechnological surface modification show promising results in sensing from blood, serum, and urine. This report gives a particular emphasis on the on-site efficacy of recently published field-effect biosensors, specifically, detection limits in physiological solutions, response times, and scalability. The survey of the properties and existing detection methods of four promising biotargets, exosomes, bacteria, viruses, and metabolites, aims at providing a roadmap for future field-effect and other on-site biosensors.

In article number 1700371, Kwan Hyi Lee and co-workers describe a dual-gate FET avian influenza sensor, developed at the Korea Institute of Science and Technology, that detects viruses directly from the cloacal swab of a live animal with the help of a disposable well gate. The disposable well gate, chemically optimized to a lysis buffer, allows both lysis and detection to occur in a single-well, single-buffer, 30-minute procedure.

Field-effect graphene biosensors have in general relied on irreversible surface modification for the detection of biological entities. However, restoring a sensor to a pre-sensing-event state is highly desirable in securing sensor data integrity, especially in the case of an electrolyte-gated graphene FET which is prone to drift and degradation. We present a graphene FET biosensor array that mimics an SPR(surface plasmon resonance) system in its use of a microfluidic channel for restoration of the sensor equilibrium. A steady flow of PBS through a 20-micron wide channel provides calibration for FET conductance before and after introducing human Thrombin to the base flow, successfully isolating the protein-induced field-effect from permanent changes made to the graphene device. Graphene conductance shows exponential saturation and de-saturation curves as governed by the the Nernst Equation. The sensors show a sub-microMolar limit-of-detection which can be dynamically tuned by the flow rate. Sensor specificity is provided by electrophoretic functionalization of DNA aptamers onto the graphene surface. We confirm successful aptamer functionalization with fluorescence microscopy, amperometry, and scanning electron microscopy. The current method of sensor state restoration adds reliability to biosensor data without the necessity of a matching-device control group and also maximizes manufacturing efficiency through device recycling.