Cost-Efficient Oceanographic Instrument with Microfabricated Sensors for Measuring Conductivity, Temperature and Depth of Seawater.

The design, fabrication and characterization of a cost-efficient oceanographic instrument with microfabricated sensors for measuring conductivity, temperature and depth of seawater are presented. Conductivity and temperature sensors were fabricated using MEMS technology, which allows for customized small footprints and low production costs. Dedicated electronics for reading, processing and storing acquired sensor data are described. The developed instrument enables the measurement of seawater conductivity in a range from 4 mS/cm to 70 mS/cm. The conductivity measurement is temperature-compensated in the range from 2 °C to 40 °C, with an accuracy of ±0.1 mS/cm. The temperature sensor's stability is 0.025 °C. The depth/pressure measurement range is up to 2000 m/200 bar, with a resolution of 0.1 bar. Temperature and conductivity sensor performance was assessed using laboratory equipment and designed electronics. The conductivity sensor was temperature-compensated to 0.01 mS/cm. The conductivity sensor electrode corrosion effect is presented below and was eliminated through adaptation of a signal acquisition circuit. Custom software was developed for monitoring critical conductivity sensor parameters (currents, voltages). A variation of 0.4% between cell conductance currents and voltages was established as a criterion for stable conductivity sensor operation.

Microfluidic Electrochemical Glucose Biosensor with In Situ Enzyme Immobilization.

The development and characterization of a microfluidic electrochemical glucose biosensor are presented herein. The transducer part is based on thin-film metal electrodes on a glass substrate. The biological recognition element of the biosensor is the pyrroloquinoline quinone-glucose dehydrogenase (PQQ-GdhB) enzyme, selectively in situ immobilized via microcontact printing of a mixed self-assembling monolayer (SAM) on a gold working electrode, while the microfluidic part of the device comprises microchannel and microfluidic connections formed in a polydimethylsiloxane (PDMS) elastomer. The electrode properties throughout all steps of biosensor construction and the biosensor response to glucose concentration and analyte flow rate were characterized by cyclic voltammetry and chronoamperometry. A measurement range of up to 10 mM in glucose concentration with a linear range up to 200 µM was determined. A detection limit of 30 µM in glucose concentration was obtained. Respective biosensor sensitivities of 0.79 nA/µM/mm2 and 0.61 nA/µM/mm2 were estimated with and without a flow at 20 µL/min. The developed approach of in situ enzyme immobilization can find a wide number of applications in the development of microfluidic biosensors, offering a path towards continuous and time-independent detection.

A Rapid Prototyped Thermal Mass Flowmeter.

An innovative rapid prototyping technique for embedding microcomponents in PDMS replicas was developed and applied on a thermal mass flowmeter for closed loop micropump flowrate control. Crucial flowmeter design and thermal parameters were investigated with a 3-D fully coupled electro-thermal-fluidic model which was built in Comsol Multiphysics 5.2. The flowmeter was characterized for three distinct measuring configurations. For precise low flowrate applications, a sensor-heater-sensor flowmeter configuration with a constant heater temperature was found to be the most appropriate yielding the measuring range of 0 to 90 µL·min-1 and the sensitivity of 1.3 °C·µL-1·min in the lower flowrate range of 0 to 40 µL·min-1.

Microfluidic Technology for Clinical Applications of Exosomes.

Exosomes, a type of nanovesicle, are distinct cellular entities specifically capable of carrying various cargos between cells. It has been hypothesized that exosomes, as an enriched source of biomolecules, may serve as biomarkers for various diseases. This review introduces general aspects of exosomes, presents the challenges in exosome research, discusses the potential of exosomes as biomarkers, and describes the contribution of microfluidic technology to enable their isolation and analysis for diagnostic and disease monitoring. Additionally, clinical applications of exosomes for diagnostic purposes are also summarized.

In Vivo Experimental Study of Noninvasive Insulin Microinjection through Hollow Si Microneedle Array.

An experimental study of in vivo insulin delivery through microinjection by using hollow silicon microneedle array is presented. A case study was carried out on a healthy human subject in vivo to determine the influence of delivery parameters on drug transfer efficiency. As a microinjection device, a hollow microneedle array (13 × 13 mm²) having 100 microneedles (220 µm high, 130 µm-outer diameter and 50 µm-inner diameter) was designed and fabricated using classical microfabrication techniques. The efficiency of the delivery process was first characterized using methylene blue and a saline solution. Based on these results, the transfer efficiency was found to be predominantly limited by the inability of viable epidermis to absorb and allow higher drug transport toward the capillary-rich region. Two types of fast-acting insulin were used to provide evidence of efficient delivery by hollow MNA to a human subject. By performing blood analyses, infusion of more-concentrated insulin (200 IU/mL, international units (IU)) exhibited similar blood glucose level drop (5⁻7%) compared to insulin of standard concentration (100 IU/mL), however, significant increase of serum insulin (40⁻50%) with respect to the preinfusion values was determined. This was additionally confirmed by a distinctive increase of insulin to C-peptide ratio as compared to preinfusion ratio. Moreover, we noticed that this route of administration mimics a multiple dose regimen, able to get a "steady state" for insulin plasma concentration.

A strip-type microthrottle pump: modeling, design and fabrication.

A novel design for a strip-type microthrottle pump with a rectangular actuator geometry is proposed, with more efficient chip surface consumption compared to existing micropumps with circular actuators. Due to the complex structure and operation of the proposed device, determination of detailed structural parameters is essential. Therefore, we developed an advanced, fully coupled 3D electro-fluid-solid mechanics simulation model in COMSOL that includes fluid inertial effects and a hyperelastic model for PDMS and no-slip boundary condition in fluid-wall interface. Numerical simulation resulted in accurate virtual prototyping of the proposed device only after inclusion of all mentioned effects. Here, we provide analysis of device operation at various frequencies which describes the basic pumping effects, role of excitation amplitude and backpressure and provides optimization of critical design parameters such as optimal position and height of the microthrottles. Micropump prototypes were then fabricated and characterized. Measured characteristics proved expected micropump operation, achieving maximal flow-rate 0.43 mL·min(-1) and maximal backpressure 12.4 kPa at 300 V excitation. Good agreement between simulation and measurements on fabricated devices confirmed the correctness of the developed simulation model.

Dielectrophoretic field-flow microchamber for separation of biological cells based on their electrical properties.

We describe the development, fabrication and testing of a microfluidic chamber for dielectrophoretic field-flow separation of biological cells based on their electrical properties. The chamber was constructed from a single Pyrex wafer with interdigitated Au electrodes, a spacer, and a top cover glass, making the events in the chamber observable under most optical microscopes. The dimensions were optimized based on numerical computations of the electric field, its gradient and the fluid-flow velocity profile. The electrodes were fabricated using photolithography. A double-sided self-adhesive tape of 100 µm thickness was used as a spacer, with an opening of 80 mm length and 20 mm width cut in its middle to form a channel of 100 µm height, and with water-resistant acrylic glue of the tape holding the glass plates together and providing a tight seal. The glue loses its adhesive properties above 70 °C, allowing for easy disassembly of the chamber in hot water and its thorough cleaning. A 1:1 mixture of normal and 50 °C -heat-treated CHO cells was used to test the chamber. A 93% efficiency of separation was obtained, confirming the usefulness of the chamber in separating cells with sufficient differences in electrical properties of their membranes.

Blumlein configuration for high-repetition-rate pulse generation of variable duration and polarity using synchronized switch control.

Blumlein generators are used in different applications such as radars, lasers, and also recently in various biomedical studies, where the effects of high-voltage nanosecond pulses on biological cells are evaluated. In these studies, it was demonstrated that by applying high-voltage nanosecond pulses to cells, plasma membrane and cell organelles are permeabilized. As suggested in a recent publication, the repetition rate and polarity of nanosecond high-voltage pulses could have an important effect on the electropermeabilization process, and consequently, on the observed phenomena. Therefore, we designed a new Blumlein configuration that enables a higher repetition rate of variable duration of either bipolar or unipolar high-voltage pulses. We achieved a maximal pulse repetition rate of 1.1 MHz. However, theoretically, this rate could be even higher. We labeled endocytotic vesicles with lucifer yellow and added propidium iodide to a cell suspension for testing the cell plasma membrane integrity, so we were able to observe the permeabilization of endocytotic vesicles and the cell plasma membrane at the same time. The new design of pulse generator was built, verified, and also tested in experiments. The resulting flexibility and variability allow further in vitro experiments to determine the importance of the pulse repetition rate and pulse polarity on membrane permeabilization -- both of the cell plasma membrane as well as of cell organelle membranes.