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Optogenetics presents an alternative method for interfacing with the nervous system over the gold-standard of electrical stimulation. While electrical stimulation requires electrodes to be surgically embedded in tissue for in vivo studies, optical stimulation offers a less-invasive approach that may yield more specific, localized stimulation. The advent of optogenetic laboratory animals—whose motor neurons can be activated when illuminated with blue light—enables research into refining optical stimulation of the mammalian nervous system where subsets of nerve fibers within a nerve may be stimulated without embedding any device directly into the nerve itself. However, optical stimulation has a major drawback in that light is readily scattered and absorbed in tissue thereby limiting the depth with which a single emission source can penetrate. We hypothesize that the use of multiple, focused light emissions deployed around the circumference of a nerve can overcome these light-scattering limitations. To understand the physical parameters necessary to produce pinpointed light stimulation within a single nerve, we employed a simplified Monte Carlo simulation to estimate the size of nerves where this technique may be successful, as well as the necessary optical lens design for emitters to be used during future in vivo studies. By modeling multiple focused beams, we find that only fascicles within a nerve diameter less than 1 mm are fully accessible to focused optical stimulation; a minimum of 4 light sources is required to generate a photon intensity at a point in a nerve over the initial contact along its surface. To elicit the same effect in larger nerves, focusing lenses would require a numerical aperture $$> 1$$ > 1 . These simulations inform on the design of instrumentation capable of stimulating disparate motor neurons in mouse sciatic nerve to control hindlimb movement.

The application of microfluidics in Point of Care (PoC) testing was a breakthrough in PoC diagnostics, yet high precision testing remains a challenge. In order to extract and isolate pure RNA or DNA from biofluids containing a virus or virion, small spherical magnetic particles called magnetic beads are commonly used in laboratories. Magnetic beads have many applications ranging from purification of nucleic acids, magnetic cell separation, targeted drug delivery to brain or malignant tumors, magnetic chaining etc. Unfortunately, integrating magnetic beads into PoC devices is challenging. This paper delves into a comparative study of the behaviour and parameters of five different sizes of carboxyl coated paramagnetic beads along with silica coated dynabeads. Their behavior is characterized in a microcapillary channel for a SARS-CoV-2 virus PoC testing kit to enrich the sample, concentrating the nucleic acid. This step would increase the sensitivity and specificity for any nucleic acid-based PoC testing device.

Thin-film microelectrode arrays have a wide variety of applications in research and medical devices. Conventionally, these arrays are fabricated through the use of photolithography, which can be problematic for innovative medical device fabrication due to long process times, inflexibility to design changes, and the reliance on potentially harmful chemicals. Here, we present the use of laser micromachining as an alternative to photolithography processes to fabricate thin-film polyimide microelectrode arrays. This fabrication method lends itself to an iterative design process as it can reduce fabrication steps and is attractive for medical devices since it can be used without harmful chemicals. Several process parameters were explored and the performance of the fabricated electrodes was compared to similar electrodes that were fabricated with conventional photolithography processes.

We present a novel 3D printed Microfluidic Actuation System for lateral flow assay in low resource settings. The system is used to deliver reagents for multi-step assays from blisters placed into cavities in the 3D printed assembly. The system is operated by manually depressing the blister housing and rotating to the next blister location. This is repeated for each step in the assay to enable a simple and repeatable method of delivering specified volumes to the assay at arbitrary time intervals as required by the assay. The blisters provide for robust storage while maintaining consistent aliquots for the assay. We characterize the percent of the total volume delivered to the lateral flow assay from the blisters including the volume dispensed at given time intervals.

Lateral Flow Immunoassays (LFIAs) are among the most successful Point of Care (POC) tests. However, factors like reagent stability, reaction rates, and binding kinetics limit the performance and robustness of LFIAs. One of the factors that affects the overall performance of LFIA is the fluid flow rate, and hence, it is desirable to maintain a predictable fluid velocity in porous media. The main objective of this study is to build a statistical model that estimates the fluid velocity in porous media for any given ambient condition to enable us to determine the optimal design parameters for achieving a desired fluid velocity in porous media.

The work presents implementing a low cost pH sensing system for biological applications in a flexible electronics process. As a part of the system the work describes an ion sensitive field effect transistor, using indium tin oxide (ITO) as a sensing layer and gold as a reference electrode, on a flexible substrate. The devices presented here are designed and fabricated using the thin film transistor (TFT) display technology at the Arizona State University Flexible Electronics and Display Center. It was observed that ITO has a sensitivity of 50 mV/pH. The work also discusses the variability in these devices and signal processing that could be used to calibrate them. Toward this end, a readout circuit designed in a 0.5 μm CMOS process is presented to interface with the sensors.

We demonstrate a minimally invasive intracranial pressure (ICP) monitoring system using a piezoresistive sensor. Our previous work in ICP monitoring used an obscure sensor, small pressure range, and manual induction by hand compressions. In this work, we use a widely available FDA-approved sensor and extend the study to meet the ANSI/AAMI standards. We also include controlled mechanical and physiologically-induced ICP modulation. We verified the system using a water column up to 100 mmHg. We tested our system in vivo with a rat model. The results generally show excellent agreement between our custom ICP sensing system and a commercial gold standard.

ObjectiveThere is a need for low power, scalable photoelectronic devices and systems for emerging optogenetic needs in neuromodulation. Conventional light emitting diodes (LEDs) are constrained by power and lead-counts necessary for scalability. Organic LEDs (OLEDs) offer an exciting approach to decrease power and lead-counts while achieving high channel counts on thin, flexible substrates that conform to brain surfaces or peripheral neuronal fibers. In this study, we investigate the potential for using OLEDs to modulate neuronal networks cultured in vitro on a transparent microelectrode array (MEA) and subsequently validate neurostimulation in vivo in a transgenic mouse model.ApproachCultured mouse cortical neurons were transfected with light-sensitive opsins such as blue-light sensitive channel-rhodopsin (ChR2) and green-light sensitive chimeric channel-rhodopsin (C1V1tt) and stimulated using blue and green OLEDs (with 455 and 520 nm peak emission spectra respectively) at a power of 1 mW/mm2 under pulsed conditions.Main resultsWe demonstrate neuromodulation and optostimulus-locked, single unit-neuronal activity in neurons expressing stimulating and inhibiting opsins (n=4 MEAs, each with 16 recordable channels). We also validated the optostimulus-locked response in a channel-rhodopsin expressing transgenic mouse model, where at least three isolatable single neuronal cortical units respond to OLED stimulation.SignificanceThe above results indicate the feasibility of generating sufficient luminance from OLEDs to perform neuromodulation both in vitro and in vivo. This opens up the possibility of developing thin, flexible OLED films with multiple stimulation sites that can conform to the shape of the neuronal targets in the brain or the peripheral nervous system. However, stability of these OLEDs under chronic conditions still needs to be carefully assessed with appropriate packaging approaches.

This paper presents a new biophotonic application for large-area, high-resolution, flexible organic light-emitting diode (OLED) display technology currently used to manufacture low-cost color flexible displays on plastic substrates. The new concept uses a fully addressable high resolution flexible OLED pixel array on a thin, mechanically compliant biocompatible plastic substrate to selectively stimulate and/or silence small groups of neurons on either the cortical surface or, alternatively, within the deep brain. Optical measurements from a 455 nm blue flexible OLED test structure demonstrated the ability to emit 1 ${\hbox{mW/mm}}^{2}$ of instantaneous light intensity using a 13 V, 20 Hz pulse, which meets the minimum reported intensity at $\sim$ 450 nm to induce optical stimulation in genetically modified neural tissue. Biocompatibility was successfully demonstrated by the ability to grow human epithelial cells on the surface of a full TFT process flow plastic flexible display substrate. Additionally, a new active matrix array display architecture was designed to support pulsed mode OLED operation. These preliminary results demonstrate the initial viability of extending flexible plastic substrate OLED display technology to the development of large-area, high-resolution emissive active matrix arrays for chronic optogenetic applications.

In this work we present a system designed for continuous assessment of tumor cell extracellular pH using a fabricated quartz extended-gate ion-sensitive field effect transistor (EGFET). The extended gate structure was fabricated by patterning gold on a quartz substrate creating a pseudo-reference electrode and sensor below a Si 3 N 4 sensing membrane. Various electrode geometries and configurations were created and each pattern was characterized. A readout/data acquisition system was designed to convert the current output of the EGFET to a voltage that was recorded using a low-power single board computer, which performed a hard "reset" before every data acquisition interval. This setup was able to monitor the viability of SKBR3 mammary gland tumor cells treated with staurosporine. Over a span of 8 hours, the autonomous data acquisition system recorded a steady decrease in cell viability. Results were verified with periodic cell culture images. Future applications include design of an extended gate EGFET array, which allows for accurate monitoring of individual cell cultures.

The high per patient cost of quantitative, high-sensitivity molecular diagnostics is one of the key roadblocks limiting the transition of this technology from the clinical laboratory to point-of-care diagnostics in low-to-middle income countries (LMICs). As a solution, we present a low-cost system architecture for fluorescence-based point-of-care diagnostics using small volume patient sera samples. Our approach combines an inexpensive 4-site microscope slide reader with low per patient cost consumables using conventional glass microscope slides, pre-printed with biorecognition molecules. We use a neuromorphic-inspired, charge-integrating readout circuit architecture combined with optical filters in a sandwich-style configuration to achieve high-sensitivity while trading off detection time and number of biorecognition sites per slide. Our demonstrated lower limit of detection using Nile Red fluorescent microspheres was a 1,000,000:1 dilution corresponding to approximately 200 microspheres per detection site, approaching the sensitivity of a conventional high-cost desktop clinical laboratory microscope slide reader.

This work details the design and characterization of a low-cost, portable and highly sensitive fluorescence detection system intended for use in a compact and disposable point-of-care (POC) device. The detection device leverages time integration to improve the signal to noise ratio (SNR) compared to instantaneous measurements. It also eliminates complicated focusing optics and electronics typically found in bulky and expensive laboratory-scale devices. Characterization was performed by measuring a series of logarithmically scaled dilutions of 1 μm Nile Red fluorescent microspheres immobilized on microscope slides. This approach eliminates assay dependencies and elucidates the actual system performance. A theoretical model that predicts the time-integrated output voltage profile of the sensor was developed; this prediction is useful for evaluating any lens-free fluorescent system based on a set of filters and choice of fluorophore. By relating the fluorophore concentration, system design parameters, and the output voltage, the model matches well with the empirical data and the limit of determination (LOD) for Nile Red is 20 particles. This system provides a sensitive and potentially low-cost device for fluorescent diagnosis in an integrated and compact/miniaturized POC device, lab-on-chip or a table-top reader.

This paper described a novel physiologically compatible wafer bonding technique for bio-microelectromechanical systems (bio-MEMS) packaging. Room temperature bonding was performed between Parylene-C and silicon wafers with a thin Parylene-C coating using reactive Ni/Al nanofilms as localized heaters. Live NIH 3T3 mouse fibroblast cells were encapsulated in the package and they survived the bonding process owing to the localization of heating. A numerical model was developed to predict the temperature evolutions in the parylene layers, silicon wafer and the encapsulated liquid during the bonding process. The simulation results were in agreement with the cell encapsulation experiment revealing that localized heating occurred in this bonding approach. This study proved the feasibility of reactive nanofilm bonding technique for broad applications in packaging bio-MEMS and microfluidic systems.

Electrochemical Impedance Spectroscopy (EIS) is a label-free method of molecular detection of particular interest for biomedical applications. We aim to create a hand-held, easy to use EIS measurement device, for biomolecular detection. Electrochemical cyclic voltammetry systems help millions of diabetics monitor their blood glucose levels 2–8 times per day, but their use is very limited due to the poor lower limit of detection. The EIS technique can be used to detect a much larger array of biomolecules at very low concentration. Our EIS system generates the magnitude and phase of the impedance from test samples via MATLAB, which provides the real and imaginary components of the impedance. The circuit was integrated on a single chip and fabricated in a standard 0.5 μm CMOS technology. A hand-held EIS measurement system was built using the chip and an Arduino Uno to measure a Randles circuit equivalent over the frequency range from 1 Hz to 2 kHz, the measurement and simulation results show excellent agreement.

We demonstrate the cycling of electric fields within an ion-sensitive field-effect transistor (ISFET) as a method to control drift. ISFETs had a repeatable drift pattern when cycling the vertical electric field by changing the voltage between the reference electrode and the substrate. Cycling the horizontal electric field, the voltage between the drain and source of the device, showed no effect, causing the device to continue to drift as it would during normal operation. Results were confirmed with multiple pH buffer solutions. An ISFET was modeled using ATHENA. The simulation included the electrolyte modeled as a modified intrinsic semiconductor. Empirical results are confirmed with device-level simulations of an ISFET using Silvaco TCAD. The model produced a scaled current of 90 μA, which is of similar order to the experimental values of 146 μA. The repeatable drift behavior could be easily reconciled to permit the use of ISFETs for long-term continuous monitoring applications.

We presents an ion sensitive field effect transistor to measure the pH of the cell culture media of human mammary adenocarcinoma (SKBR3). We use a drift mitigation technique that cycles the transistor to reset the drift in the system. We use to technique in the system to demonstrate an integrated system to monitor the pH continuously. As a part of the system a pulse width modulation circuit is designed in a 0.5 μm CMOS process which cycles the vertical electric field of the ion sensitive field effect transistor to reset the threshold voltage drift. We demonstrate the viability of a complete integrated system implementing our drift mitigation technique to monitor cultured cells. The integration is important in this application to allow for autonomous operation inside an incubator during cell culture.

This paper presents a floating gate Ion Sensitive Field Effect Transistor (ISFET) to monitor the activity of breast cancer cells. We use an ISFET to monitor the change in pH of the cell culture media and to observe the apoptosis of the breast cancer cells when treated with staurosporine. Since ISFETs suffer from inherent mismatch and drift in the threshold voltage, predominantly caused due to accumulation of ions on the surface of the gate, we have integrated a floating gate ISFET to calibrate the device. Floating gate ISFETs have been used to program the threshold voltage of the device either by hot electron injection, Fowler-Nordheim tunneling, and UV to remove charges. In this work we use hot electron injection to precisely program the device and tunneling as a global erase. This enables us to precisely record the changes in pH. These floating gate devices have been fabricated in 0.5 μm CMOS process.

We demonstrate a CMOS (complementary metal oxide semiconductor) potentiostat chip fabricated in a standard 0.5 μm CMOS process to perform electrochemical analysis via cyclic voltammetry. This chip contains six independent channels for three electrode systems in electrochemical cells. Our low power circuit has been designed to drive electrochemical reactions in solution using class AB folded cascode amplifiers. The circuit operates with rail to rail input and output and has strong drive ability. We have shown the potentiostat chip is capable of performing cyclic voltammetry (CV) with both potassium ferricyanide and hexaammineruthenium chloride solutions. The chip is capable of differentiating both the composition and concentration of the solution. We compare our results with control experiments on a Gamry commercial electrochemical workstation and demonstrate they are consistent.

We present an optical localization chip capable of detecting the direction of incident light. The chip requires no offchip optical or mechanical components or post-processing (e.g. baffles, slits, mirrors, etc.). The chip was fabricated in a standard 0.5 μm CMOS (complementary metal oxide semiconductor) process. Our approach employs 100 light sensing cells, each having two detectors separated by a metal “wall”. The “wall” was created by stacking all metal layers, contacts and vias available in the process. This metal stack “wall” is used to create on-chip shadowing to facilitate detection. Each optical detection element produces a differential output with the normalized difference between the currents dependent upon the angle of the incident light. The width of the photodiodes is limited by the height of the metal wall to only a few micrometers. To achieve a good sensitivity, 100 cells are placed in parallel. Test results show good sensitivity to the direction and intensity of the incident light with accuracy of 1.9 degrees over a 100 degree range and 1.1 degrees over a 50 degree range.

We discuss the design, fabrication, and testing of a hybrid microsystem for stand-alone cell culture and incubation. The micro-incubator is engineered through the integration of a silicon CMOS die for the heater and temperature sensor, with multilayer silicone (PDMS) structures namely, fluidic channels and a 1.5-mm diameter 12-muL culture well. A 90-mum-thick PDMS membrane covers the top of the culture well, acting as barrier to contaminants while at the same time allowing the cells to breath and exchange gases with the ambient environment. The packaging for the microsystem includes a flexible polyimide electronic ribbon cable and four fluidic ports that provide external interfaces to electrical energy, closed-loop sensing and electronic control as well as solid and liquid supplies. The complete structure has a size of (2.5times2.5times0.6) cm(3). We have employed the device to successfully culture BHK-21 cells autonomously over a three day period in ambient environment.

A 1.5 mm × 3 mm CMOS chip with sensors for monitoring on-chip cell cultures has been designed. The chip is designed in a 0.5 µm CMOS process which has 3 metal layers and 2 poly layers and is a 5 volt process. The chip contains ion sensitive field effect transistors (ISFETs), as well as ISFETs with read-out circuitry, for monitoring the pH of solutions placed on top of the chip. Interdigitated electrode structures (IDESs) are made using the top metal of the process to be used for sensing cellular attachment and proliferation via impendence. IDES read-out circuits and IDES test structures are included. The chip also contains test amplifiers, bandgap reference test structures, and connections for post-processing. We designed the chip to accommodate packaging into an environment where it will be directly exposed to a cell culture environment. Specifically we designed the chip to have the incorporated sensors near the center of the chip allowing for connections made around the edge of the chip to be sealed off using an epoxy or similar material to prevent shorting. Preliminary electrical characterization results for our amplifier indicate a gain of 48 dB, a bandwidth of 1.65 kHz, and a common mode rejection ratio (CMRR) of 72 dB. We also present a packaging technique using a flexible pcb substrate.

We discuss the fabrication and characterization details of an optical oxygen sensor for use in a cell culture microsystem. The sensor operates by measuring changes in the fluorescence intensity of (2–2'-bipyridine) dichlororuthenium (II) hexahydrate molecules that are immobilized in a silicone film. The sensor we demonstrate herein is highly linear, reversible, and is compatible with common biomedical sterilization procedures.

We have designed and tested two amplification circuits for measuring HL-1 cardiac action potentials, single-ended and differential. We describe the improvements in performance resulting from the differential configuration. These improvements are especially important considering the cell culture's aqueous environment that experiences DC drift. In addition we have designed and fabricated a 4×4 gold microelectrode array and cultured HL-1 cells on the electrodes. The array is connected to our circuit through a custom made Pogo pin jig to allow for easy measurements from the electrodes while cells are being cultured. This setup allowed us to obtain initial results for modeling the transfer function of the cell culture as a passive device network. Testing has confirmed the circuits are capable of filtering low frequency signals including DC drift and frequencies above 5 kHz. The amplification was achieved through two gain stages with a total gain of 60 dB for the single-ended and 46 dB for the differential circuits.

In this paper, Si nanowire (NW) sensor in pH detection is presented. The conductance of device is analytically obtained and demonstrated the conductance increases with reducing the oxide thickness. To calculate the electrical conductance of sensor, the diffusion-drift model and nonlinear Poisson-Boltzmann equation are used. To improve the conductance a Si NW sensor with nanoscale side gate voltage is presented and its conductance is theoretically achieved. It is shown the conductance and consequently sensor sensitivity can be enhanced by adding suitable side gate voltage. Finally this effect is compared to the almost similar fabricated structure in literature which has a wire with rectangular cross section.

We present a system comprised of a PDMS microfluidic device and an injection system for dilution of DNA derived from whole blood to a single strand. We discuss two micro fluidic architectures for ultra-high ratio dilution (1:1000 or more) as well as the necessity to move beyond previously reported dilution architectures. We describe a custom injection system used both for fabrication and operation of the system. The system is operated by placing syringes, one filled with water and one filled with DNA extracted from whole blood, into the injection system. This system fixes and plunges the syringes simultaneously to introduce both solutions into the microfluidic channels that produce the ultra-high ratio dilutions. The most significant constraint on the design is that the system is designed for fabrication, characterization and use in a clinical setting.

We present hybrid silicon/silicone microsystem for closed-loop temperature control with applications in the life sciences. The system architecture includes an integrated CMOS die for localized thermal cycling and a disposable PDMS microfluidic structure for aseptic fluidic manipulation. Chip design, experimental results and finite element analysis are presented. This work is based on criteria for a clinical diagnostics system comprised of disposable microfluidics for use in tandem with CMOS electronics.

We discuss the design, fabrication and testing of a hybrid microsystem for stand-alone cell culture, incubation and imaging. The micro-incubator is engineered through the integration of two CMOS dies. The first for the heater and temperature sensor, and a second die for imaging. A multilayer PDMS (polydimethylsiloxane) structures is used to create not only the fluidic structures but to encapsulate the CMOS dies. The microfluidic features include fluidic channels, a 4 mm diameter, 30muL, culture well and a 25 micron thick PDMS membrane that covers the top of the culture well, acting as barrier to contaminants while allowing the cells to exchange gases with the ambient environment. The micro-incubator interface includes with a flexible polyimide ribbon cable and four fluidic ports. The complete structure has a size of (2.5times2.5times0.6 cm3). We have employed the device to successfully culture BHK-21 cells autonomously over a sixty hour period in ambient environment

We present a novel self-powered chip to detect the direction of incident light. This chip directly provides digitized output without the need of any off-chip power supply or optical or mechanical components. The chip was implemented in a standard 0.5 μm CMOS process. A microscale metal baffle was created by stacking all metal layers, contacts, and vias available in the process to produce on-chip shadowing. N-well/p+ photodiode arrays are located on both sides of the baffle to sense light. The photocurrent generated by a photodiode depends on the size of the photodiode and the shadowing. The shadowed area depends on the incident angle of the light. A current mirror circuit is used to compare the currents generated by the photodiodes on the opposite sides of the baffle and, consequently, provide a digital signal to indicate the incident light angle. Compared with the ideal linear digital light-angle detector with the same resolution, the presented sensor achieved the maximum error of only 2 deg over 110 deg test range.

We present an on-chip optical sensor capable of detecting the direction of incident light. No off-chip optical or mechanical components or modifications--for example, baffles, slit structures, mirrors, etc.--are needed. The sensor was implemented in a standard 0.5 μm complementary metal-oxide semiconductor process. A pair of on-chip photodiodes separated by a metal "wall" (created by stacking all metal layers, contacts, and vias available in the process) is used to detect the direction of the incident light. This metal stack wall creates on-chip shadowing to facilitate detection so that the two photodiodes produce different amounts of photocurrent. A model for this device is presented. The analysis indicts that the ratio of the difference of these two currents to the larger of the two currents has a linear relationship with the angle of the incident light. Moreover, we also demonstrate this ratio is almost independent of the incident light intensity. Test results verify these two conclusions and show good sensitivity to light direction and immunity to light intensity. An accuracy of 1.6 deg over a 100 deg range is achieved by the linear relationship.

We demonstrate the microassembly of PDMS (polydimethylsiloxane) microfluidics with integrated circuits made in complementary metal-oxide-semiconductor (CMOS) processes. CMOS-sized chips are flip chip bonded to a flexible polyimide printed circuit board (PCB) with commercially available solder paste patterned using a SU-8 epoxy. The average resistance of each flip chip bond is negligible and all connections are electrically isolated. PDMS is attached to the flexible polyimide PCB using a combination of oxygen plasma treatment and chemical bonding with 3-aminopropyltriethoxysilane. The total device has a burst pressure of 175 kPA which is limited by the strength of the flip chip attachment. This technique allows the sensor area of the die to act as the bottom of the microfluidic channel. The SU-8 provides a barrier between the pad ring (electrical interface) and the fluids; post-processing is not required on the CMOS die. This assembly method shows great promise for developing analytic systems which combine the strengths of microelectronics and microfluidics into one device.

This abstract described a novel physiologically compatible wafer bonding technique for bio-microelectromechnical systems (bio-MEMS) packaging. Room temperature bonding was performed between Parylene-C and silicon wafers with a thin Parylene-C coating using reactive Ni/Al multilayer foils as localized heaters. Live NIH 3T3 mouse fibroblast cells were encapsulated in the package and they survived the bonding process owing to the localization of heating. A numerical model was developed to predict the temperature evolutions in the parylene layers, silicon wafer and the encapsulated liquid during the bonding process. The simulation results were in agreement with the cell encapsulation experiment revealing that localized heating occurred in this bonding approach. This study proved the feasibility of reactive multilayer foil bonding technique for broad applications in packaging bio-MEMS and microfluidic systems.