Micromachined Silicon Chip Research Articles

Molecular detection of SARS-COV-2 in exhaled breath at the point-of-need

The SARS-CoV-2 pandemic has highlighted the need for improved technologies to help control the spread of contagious pathogens. While rapid point-of-need testing plays a key role in strategies to rapidly identify and isolate infectious patients, current test approaches have significant shortcomings related to assay limitations and sample type. Direct quantification of viral shedding in exhaled particles may offer a better rapid testing approach, since SARS-CoV-2 is believed to spread mainly by aerosols. It assesses contagiousness directly, the sample is easy and comfortable to obtain, sampling can be standardized, and the limited sample volume lends itself to a fast and sensitive analysis. In view of these benefits, we developed and tested an approach where exhaled particles are efficiently sampled using inertial impaction in a micromachined silicon chip, followed by an RT-qPCR molecular assay to detect SARS-CoV-2 shedding. Our portable, silicon impactor allowed for the efficient capture (>85%) of respiratory particles down to 300 nm without the need for additional equipment. We demonstrate using both conventional off-chip and in-situ PCR directly on the silicon chip that sampling subjects’ breath in less than a minute yields sufficient viral RNA to detect infections as early as standard sampling methods. A longitudinal study revealed clear differences in the temporal dynamics of viral load for nasopharyngeal swab, saliva, breath, and antigen tests. Overall, after an infection, the breath-based test remains positive during the first week but is the first to consistently report a negative result, putatively signalling the end of contagiousness and further emphasizing the potential of this tool to help manage the spread of airborne respiratory infections.

Micro-ring based manipulation of magnetized particles.

The micromanipulation of untethered magnetic particles facilitates actuation, assembly, and characterization of samples for micro- and nanotechnology applications. Conventionally, macro-scale electromagnets combined with visual servo control are employed to manipulate untethered particles. Here, we propose to employ a micro-ring actuator and a strategy based on parametric excitation for manipulation of magnetized particles against a surface in a liquid medium, which does not require visual feedback. Experimentally, the system has been employed to smoothly manipulate magnetic particles of diameter in the range 30-50 µm to move along predefined trajectories. Subsequently, the particles have been demonstrated to be manipulated into a conventionally inaccessible region beneath the re-entrant walls of a micromachined silicon chip.

Near-field slit probe incorporating a micromachined silicon chip for millimeter-wave microscopy

A novel type of slit probe incorporating a micromachined silicon (Si) chip for millimeter-wave scanning near-field microscopy is proposed.To improve the spatial resolution and image contrast attainable in millimeter-wave microscopy, a metal-coated Si chip with a microslit aperture fabricated using a bulk micromachining technique was attached to the tip of an ordinary slit-type probe at the end of a tapered rectangular waveguide. The design and fabrication of the Si chip are described, and the results from experiments performed at U-band (40–60 GHz) frequencies to demonstrate the feasibility of this new probe configuration are presented. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett 53:660–664, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.25793

Silicon Chip Patch-clamp Electrodes Integrated With Pdms Microfluidics

We report on a silicon wafer-based device that can be used for recording macroscopic ion channel protein activities across a diverse group of cell-types. Gigaohm seals were achieved for CHO-K1 and RIN m5F cells, and both cell-attached and whole-cell mode configurations were also demonstrated. Two distinct intrinsic potassium ion channels were recorded in whole-cell mode for HIT-T15 and RAW 264.7 cells. Polydimethylsiloxane (PDMS) microfluidics were also coupled with the micromachined silicon chips in order to demonstrate that a single cell could be selectively directed to a micropore, and membrane protein currents could subsequently be recorded. These silicon chip-based devices have significant advantages over traditional micropipette approaches, and may serve as combinatorial tools for investigating membrane biophysics, pharmaceutical screening, and other bio-sensing tasks.

Microfluidic Mixer and Transporter Based on PZT Self-Focusing Acoustic Transducers

This paper describes noninvasive acoustic micromixer and transporter as well as a microfluidic subsystem (on a single silicon chip) based on the two microfluidic actuators. The actuators use a piezoelectric PZT sheet to generate about 10-12.5MHz acoustic waves (corresponding to the PZT thickness), an array of sectored Fresnel annular rings [for the electrodes sandwiching the piezoelectric transducer (PZT)] to self-focus the acoustic waves, and acoustic streaming effect to produce a body force for fluidic motion. The self-focused waves from the PZT array propagate through 200-/spl mu/m-thick silicon without any significant energy loss, and move the liquid contained in the channels and chambers (without a cover) on a micromachined silicon chip, up to 123 mm/s in-plane speed. The PZT array (consisting of a PZT sheet with an array of electrode patterns for sectored Fresnel rings) is bonded to the micromachined silicon chip to produce a fast in-plane liquid motion in the open channels and chambers. When the liquid motion is produced in a channel, we have a liquid transporter; while when the motion is produced in a large area chamber, we have a micromixer. Various channel and chamber structures have been fabricated to verify the efficacies of the liquid transport and mixing. A microfluidic subsystem integrating a micromixer, transporters and reservoirs has been shown to transport two types of liquids from their reservoirs to a mixer and to mix the liquids together within 2 s. The experimental results agree well with theoretical studies and simulation results.

Disposable real-time microPCR device: lab-on-a-chip at a low cost

We have designed, fabricated and tested a real-time micro polymerase chain reaction (microPCR) system. It consists of a microscope glass cover slip placed on top of a micromachined silicon chip integrated with a heater and a temperature sensor. A single microL of a sample containing DNA was placed on the glass and encapsulated with mineral oil to prevent the evaporation of water, thus forming a virtual reaction chamber (VRC). The PCR chip required half a second to heat up from 72 to 94 degrees C and two seconds to cool from 94 to 55 degrees C, corresponding to a cooling rate of -20 K s(-1). The real-time PCR yield was determined by a fluorescence method. The melting curve analysis method as well as capillary electrophoresis was performed to determine the purity of the PCR product. As the glass slip is disposable, cross-contamination from sample to sample is eliminated. The total cost of running the PCR is given by the value of the cover slip and its treatment.

An analytical model of a silicon MEMS vaporizing liquid microthruster and some experimental studies

A recent application of the MEMS technology is in the field of microthrusters for micro/nano satellites. A silicon MEMS vaporizing liquid microthruster (VLM) produces continuously variable thrust in the range from μN to mN. The theoretical simulation of a VLM involves complex numerical 3D micro-fluidic, thermodynamic and electro-thermal solutions. A fast analytical method is, however, desirable in the initial phase of development of a VLM. In this paper, a simple analytical model of a VLM is presented. The model is based on one-dimensional approximations for fluid-dynamical and heat-flow equations. VLMs are fabricated by bonding two micromachined silicon chips. The device consists of a microcavity, an inlet nozzle, an exit nozzle, a microchannel and an internal p-diffused resistor for heating. The thrust is measured by a sensitive cantilever and a laser based lamp-and-scale arrangement. The experimental results on the variation of thrust with heater power are interpreted with the help of the theoretical model. A novel iterative computation is performed to extract the chamber temperature and other important parameters corresponding to the measured values of thrust for different values of heater power. The model gives some physical insight into the operation of the VLM.

Protein patterning by micromachined silicon embossing on polymer surfaces

An automated method for creating micron-sized patterns of different proteins is described. Unlike other methods, the process requires no masks, photochemichal reagents, or alignment. The basic tools are a motorized x–y stage, a pneumatic drive, and a micromachined silicon chip with an array of micron scale pyramids. Upon pressing the chip on a plastic slide, inverted pyramids are created on the polymer surface, exposing areas that have no previous coating and can adsorb proteins. The method is suitable for the fast and inexpensive fabrication of dense arrays of different proteins on appropriate substrates.

Design and use of compact lensed fibers for low cost packaging of optical MEMS components

MEMS technology offers some unique product opportunities for optical networking applications. One of the critical factors that determine the commercial success of any optical MEMS components is the cost for packaging and optical fiber alignment. Small form factor MEMS components such as protection switches and variable optical attenuators require the integration of optical fibers and lenses with the MEMS silicon chip itself. This work uses a MEMS 2 × 2 optical switch as a test vehicle to demonstrate a fiber optic lens design, specifically engineered for use with the micromachined silicon chip, that enables the use of passive fiber optic lens alignment to significantly reduce component assembly cost.

Black Lipid Membranes: Visualizing the Structure, Dynamics, and Substrate Dependence of Membranes

The structure and long-time dynamics of suspended lipid bilayers made of 1-stearoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine (SOPE) in the gel phase was interrogated using electrical measurements co-recorded with second harmonic generation (SHG) micrographs. SHG microscopy was shown to be an efficient method for distinguishing between the regions of bilayer and annulus as well as probing structural and dynamical variations within a single bilayer. Micromachined silicon chips and two types of plastic partitions, delrin and polyethylene, were investigated as substrate materials. Silicon chips yielded the most stable bilayers, lasting for 1 or 2 days. The membrane characteristics, including the amount of incorporated solvent within the bilayer, the dynamics of bilayer formation, and the stability of the bilayer, were found to be strongly substrate-dependent. In a second set of experiments, SHG-active membrane dyes, di-8-ANEPPS and di-4-ANEPPS, were used to interrogate the domain structure of the same suspended bilayers using scanning two-photon fluorescence (2PF) and SHG microscopy, again correlated with capacitance measurements. Using these dyes, an enhancement in the SHG signal due to membrane potential was recorded, and the rates of molecular diffusion for di-4-ANEPPS through the membrane were investigated. Polarization-resolved SHG imaging was used to determine the orientation of the dye molecules within the membrane.

Silicon chip-based patch-clamp electrodes integrated with PDMS microfluidics

We report on a silicon wafer-based device that can be used for recording macroscopic ion channel protein activities across a diverse group of cell-types. Gigaohm seals were achieved for CHO-K1 and RIN m5F cells, and both cell-attached and whole-cell mode configurations were also demonstrated. Two distinct intrinsic potassium ion channels were recorded in whole-cell mode for HIT-T15 and RAW 264.7 cells. Polydimethylsiloxane (PDMS) microfluidics were also coupled with the micromachined silicon chips in order to demonstrate that a single cell could be selectively directed to a micropore, and membrane protein currents could subsequently be recorded. These silicon chip-based devices have significant advantages over traditional micropipette approaches, and may serve as combinatorial tools for investigating membrane biophysics, pharmaceutical screening, and other bio-sensing tasks.

Amperometric detection of quantal catecholamine secretion from individual cells on micromachined silicon chips.

We have fabricated electrochemical electrodes in picolitersized wells for measuring catecholamine release from individual cells with millisecond resolution. Each well-electrode roughly conforms to the shape of the cell in order to capture a large fraction of released catecholamine with high time resolution. Using this device, we can resolve spikes in amperometric current corresponding to quantal catecholamine release via exocytosis. In addition, we have combined amperometric recording on the chip with patch-clamp recordings of membrane capacitance as an assay of exocytosis. A quantitative comparison of the two methods suggests that a large fraction of catecholamine release is oxidized on the surface of the well-electrode. This technology has applications in cell-based biosensor development, high-throughput screening of drugs, and basic science investigations.

Characterization of Multicomponent Monosaccharide Solutions Using an Enzyme-Based Sensor Array

We report the development of a sensor for rapidly and simultaneously measuring multiple sugars in aqueous samples. In this strategy, enzyme-based assays are localized within an array of individually addressable sites on a micromachined silicon chip. Microspheres derivatized with monosaccharide-specific dehydrogenases are distributed to pyramidal cavities anisotropically etched in a wafer of silicon (100) and are exposed to sample solution that is forced through the cavities by a liquid chromatography pumping system. Production of fluorescent reporter molecules is monitored under stopped-flow conditions when localized dehydrogenase enzyme systems are exposed to their target sugars. We demonstrate the capability of this analysis strategy to quantify β-d-glucose and β-d-galactose at low micromolar to millimolar levels, with no detectable cross-talk between assay sites. Analysis is achieved either through fluorescence detection of an initial dehydrogenase product (NADH, NADPH) or by production of a secondary fluorescent product created by hydride transfer from the reduced nicotinamide cofactor to a fluorogenic reagent. The array format of this sensor provides capabilities for redundant analysis of sugars and for monitoring levels of other solution components known to affect the activity of enzymes. The use of this strategy to normalize raw fluorescence signals is demonstrated by the determination of glucose and pH on a single chip. Alternatively, uncertainties in the activity of an immobilized enzyme can be accounted for using standard additions, an approach used here in the determination of serum glucose.

A high-throughput silicon microphysiometer

We report on a micromachined silicon chip that is capable of providing a high-throughput functional assay based on calorimetry. A calorimeter has been fabricated by IC technology process steps in combination with micromachined techniques. A rubber membrane supports two identical chambers, situated at the cold and hot junction sites of a thermopile. The thermopile consists of 666 aluminum/p +-polysilicon thermocouples. The chambers can house up to 10 6 eukaryotic cells cultured to confluence, in volumes of 10–600 μl. Power and temperature sensitivity of the sensor are 23 V/W and 130 mV/K, respectively. The response time of the sensor is 70 s, when filled with 50 μl of water. Biological experiments were done with cultured kidney cells of Xenopus laevis (A6). The thermal equilibration time of the device is 45 min. Basal metabolism is measured to be 330 pW/cell. Stimulation of transport mechanisms by reducing bath osmolality by 50% increased metabolism by 40 pW/cell. Stimulation of transport mechanisms by adding the oxytocin hormone increased metabolism by 106 pW/cell.

A Biomedical Microphysiometer

We report on a micromachined silicon chip that is capable of providing a high-throughput functional assay based on calorimetry. A prototype twin microcalorimeter based on the Seebeck effect has been fabricated by using IC technology process steps in combination with micromachined postprocessing techniques. A biocompatible liquid rubber membrane supports two identical 0.5×2 cm2 measurement chambers, situated at the cold and hot junction sites of a thermopile. The thermopile consists of 666 aluminum/p+-polysilicon thermocouples. The chambers can house up to 106 eukaryotic cells cultured to confluence. The advantage of the device over microcalorimeters on the market, is the integration of the measurement channels on chip, rendering microvolume reaction vessels, ranging from 10 to 600 µl, in the closest possible contact with the thermopile sensor (no springs are needed). Power and temperature sensitivity of the sensor are 23 V/W and 130 mV/K, respectively. The small thermal inertia of the microchannels results in the short response time of 70 s, when filled with 50% of water.

Rat sciatic nerve regeneration through a micromachined silicon chip

The capacity of regenerating nerve fibres to grow through a perforated silicon chip was tested using the silicone chamber model for nerve regeneration. The chips were fabricated as circular membranes, 4 mm in diameter, thickness 60 μm, with a perforated area, 2 mm in diameter, in the centre. Three types of chips were fabricated utilizing anisotropic etching. The chips were glued with silicone adhesive between two halves of a silicone rubber tubing (total length 8 mm, inner diameter 1.8 mm, outer diameter 3.0 mm) which was used to bridge a 4 mm gap between the proximal and distal nerve stumps of a transected rat sciatic nerve. The capacity of regenerating nerve fibres to grow through the holes of the chip was analysed by light and scanning electron microscopy after 4 or 16 weeks of regeneration. Furthermore, the muscle contractility force of the gastrocnemius muscle was measured after 16 weeks of regeneration and compared as a percentage of the contralateral uninjured side. Nerves generated through chips with hole diameters of 10 or 50 μm were morphological and functional failures. The nerve structures distal to chips with hole diameters of 100 μm contained many myelinated nerve fibres in a minifascicular pattern after both 4 and 16 weeks of regeneration. The muscle contractility force was 56% of that of contralateral control muscles.

Whole cell biosensors

This paper reviews the field of biosensors in which the biological component consists of living cells. One of the most important reasons for using living cells is to obtain functional information, i.e. information about the effect of a stimulus on a living system. In many cases, functional rather than analytical information is ultimately desired. Whole-cell biosensors provide the opportunity to elicit such information, for applications such as pharmacology, cell biology, toxicology, and environmental measurements. One particularly important application is drug discovery, where the binding assays that are commonly used to provide high throughput need to be complemented with a functional assay. A micromachined silicon chip that is capable of providing a high throughput functional assay based on extracellular acidification is described.