Electrical Brain Computer Interfaces and Human Translation
Current work in the lab in the area of next-gen electrical brain computer interfaces (BCIs) revolves around a new neurotech tool we have recently developed which we call BISC (Bioelectronic Interface System to the Cortex) and which we use to gain an unprecedented window into the brain. BISC is a subdurally implanted µECoG 12×12 mm in area with front-end analog electronics, an on-chip controller, wireless powering, and a radio frequency transceiver fully integrated on a single CMOS substrate. With 65,536 recording and 16,384 stimulation channels, 1,024 simultaneous recording channels, and a total thickness of only 50 µm rendering it mechanically flexible and conformal to the brain surface, BISC serves as a platform technology which we leverage for the highest spatiotemporal resolution characterization of neural activity and potential for medical translation. And the BISC chip serves as a base to build up and package additional custom 2D and 3D materials to quickly iterate and create a plethora of neurotech electronic interface tools useful for specific studies and applications.
Wearable Near-Infrared (NIR) Imaging and Applications
Noninvasive functional neuroimaging methods, like functional magnetic resonance imaging (fMRI) and electroencephalography (EEG), are vital for studying brain function and cognition in various neurological and mental health disorders. fMRI provides high spatial resolution but suffers from poor temporal resolution and high cost, alongside the requirement of large, immobile equipment, limiting its practicality in many situations. EEG, while more affordable and portable, has restricted spatial resolution.
Optical Brain-Computer Interface
While traditional electrophysiological methods have shown promising results over the years, optical brain-computer interfaces that use light to interact with neurons offer several advantages, including cell-type specificity, low crosstalk bidirectionality, and highly scalable interfacing channels with high spatiotemporal resolution over large fields of view. Genetically Encoded Calcium and Voltage Indicators (GECIs and GEVIs) enable imaging of neural activity with cellular and subcellular resolution, while light-sensitive opsins allow precise temporal control of neural stimulation or inhibition. Combining these tools allows for all-optical interrogation of neural circuits by simultaneously monitoring and manipulating neural activity with unprecedented precision, paving the way for new neuroscientific discoveries and therapeutic applications.
Single-Molecule Bioelectronics
Since its advent in the late twentieth century, single-molecule imaging and sensing has transformed our study of the structure, function, and dynamics of molecules by enabling direct observation of details which would otherwise be obscured by bulk level analysis. Such observation is particularly relevant to molecular biology and our understanding of DNA and proteins as they relate to human health. However, the widely adopted fluorescent single-molecule techniques generally cannot directly resolve molecular events occurring on sub-millisecond timescales as they are limited by the relatively slow rate of photon emission from single fluorophores.
Wearable Ultrasound
The proven safety of ultrasound and its efficacy in soft-tissue imaging, along with the ability to integrate complex and large imaging systems into a compact system-on-chip using CMOS has enabled the development of portable ultrasound imaging devices for point-of-care use. We are developing an ultrasound imaging ASIC composed of a pitch-matched transceiver array mated to a 32×32 element 2-D transducer array made of composite PZT. This device is packaged into a flexible, compact and bio-compatible form factor which obviates the need for bulky and expensive ultrasonic imaging platforms while the patch-like form factor also allows for use in continuous monitoring. The 2-D transducer array enables the device to perform volumetric imaging while remaining stationary over the tissue. The device has in-pixel transmitters and programmability to allow high-frame imaging and performs 16-fold channel count reduction using micro-beamforming. Previous work in this area involved a flexible, surface-conforming transducer array and a 2-D phased ultrasound transmitter with integrated PZT.
Implantable Motes
We are developing novel ultrasound-based implants for temperature and electrochemical sensing. Our goal is for the wearable ultrasound patch to communicate with these motes, which would provide in-vivo data from inside a wound. The motes harvest power from ultrasound waves and are designed for biocompatibility. They are extremely miniscule with a volume of under 1.5 mm3 and have integrated PZTs on them. Several motes can be operated within the FOV of the imager due to each mote’s unique signature. They can be identified in real time with information about relative position to nearby organs, due to the non-interfering operating principle with the imaging session. The temperature-sensing motes operate on an oscillator’s frequency shift due to temperature and the pH-sensing motes use an ISFET-REFET topology to measure the pH of the medium. The sensed data is then digitized and transmitted to the patch for further analysis. From a circuit design perspective, this work involves ultra-low power design methodology and novel front-end topologies.
Photoacoustic Tomography
Optical imaging systems have a crucial role for studying brain function in animal models. However, traditional optical microscopy systems are inherently limited by their small volumetric coverage due to absorption and scattering of light. In contrast, photoacoustic imaging uses light to excite tissue, where a portion of the absorbed energy causes rapid heating, generating a wideband acoustic signal that is far less affected by scattering and absorption.
However, conventional ultrasound systems typically have resolutions in the millimeter range — significantly larger than the scale of neuronal structures. This limitation prevents current arrays from supporting high-resolution photoacoustic tomography (PAT). We are working on a high-resolution CMOS based ultrasound receiver which has been characterized using photoacoustic phantoms and in-vivo rodent models, achieving a lateral resolution of 30 µm and an axial resolution of 15 µm. The illustration diagram of the PAT chip is shown in the figure below.
