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An improved, laser-induced fluorescence-based micro-optical biosensor was designed and fabricated, with cyclic olefin copolymer (COC) optical waveguides, a poly(methyl methacrylate) (PMMA) fluidic substrate with an array of microlenses, and a COC coupling prism integrated with the waveguide substrate or cover plate. The double-sided hot embossed fluidic substrate had sampling zone microchannels on the bottom and microlenses on the top. Dissolved COC injected into polydimethylsiloxane (PDMS) lost molds embedded the waveguides in the PMMA cover plate and formed the integrated coupling prism. The embedded COC waveguide was flycut down to $50~\mu \text{m}$ . The cover plate and shallow, 1:20 aspect ratio, microchannels were thermal fusion bonded using a pressure-assisted boiling point control system, without sagging. The large COC prism coupled better to the waveguide. The highest intensity evanescent excitation of the waveguide was obtained near the critical angle. The maximum signal-to-noise ratio (SNR) was 119 and the lowest detection limit was 7.34 $\times 10^{\mathbf {-20}}$ mol at a SNR of 2 for a $100~\mu \text{m}$ wide by $50~\mu \text{m}$ deep waveguide. The microlenses highly focused the fluorescent radiation in the sampling zone. The microfabricated waveguide enables rapid, low-cost detection of fluorescent samples with high SNR, a low detection limit, and high sampling efficiency. [2020-0067]

A prominent field of study in biosensor development is the study of electric properties which provide valuable insight into the fluids contents. In this research, a non-enzymatic glucose sensor is fabricated, characterised, and employed. The developed device determines the effects of electrode surface area on sensing efficacy, the effects of glucose concentration on impedimetric response, and a real-time measurement of glucose concentration. Deviations throughout the entire glucose range are detected as an inverse of the impedance in the cell due to the inverse relationship of glucose concentration and charge transfer resistance. The continuous monitoring of glucose is demonstrated by a rapid device response over two iterations of glucose concentration in ascending order: 50 μM, 400 μM, and 3.2 mM. At a sustained frequency of 10 kHz, the result shows a stable impedimetric response of 1038, 752, and 688 kΩ, respectively. The validity of the device as a continuous glucose monitoring method is carried out by repeating the cycle and observing the response.

Among various growth processes, hydrothermal synthesis has been widely employed to produce ZnO nanowires because of its simplicity and cost effectiveness. However, the successful hydrothermal synthesis of ZnO nanowires on multi-layered polymer structures has been limited due to growth inhibitors in the polymer. For example, alpha-hydroxy ketone resolved in a UV-curable polyurethane acrylate (PUA) resin forms carboxyl groups (COOH) consisting of hydroxyl groups (OH) on the -position of a carbonyl group (CO) during the UV-curing process. The carboxyl groups suppress the nucleation and growth of ZnO nanowires. In this paper, multi-layered polymer structures were fabricated by liquid transfer imprint lithography (LTIL), and the enriched carboxyl groups on the UV-cured PUA structures were pre-treated with hexamethylenetetramine (HMTA) solution to reduce the inhibitive influence of the carboxyl groups. The HMTA pre-treatment enabled ZnO nanowires to grow hydrothermally on multi-layered PUA structures despite the initial presence of carboxyl groups. Display Omitted Multi-layered polymer structures were fabricated using a polyurethane acrylate by liquid transfer imprint lithography.UV-cured PUA structures have carboxyl groups that suppress the nucleation and growth of ZnO nanowires.Carboxyl groups were pretreated in aqueous hexamethylenetetramine (HMTA) solution prior to ZnO seed layer coating.ZnO nanowires were grown on the multi-layered polymer structures by hydrothermal synthesis.

Demand has increased for the double-sided moulding of microfluidic devices for a series of biochemical analyses. Accurate alignment of mould inserts is a critical aspect to transfer doubled-sided patterns on the top and bottom surfaces of a moulded part. A method of mould alignment was studied for double-sided hot embossing of polymer microfluidic devices. An alignment method was designed using kinematic constraints, and a set of three locating pins. To validate the alignment method, two brass mould inserts with fluidic reservoirs were used for the double-sided moulding of prototype microfluidic devices. The kinematic constraints were used to align the mould inserts with each other on the hot embossing machine. The misalignment of double-sided features on the moulded parts was measured using a measuring microscope. The X- and Y-magnitudes of the mismatches ranged from −28 to 118 µm along the X-axis of the moulded parts. The X- and Y-magnitudes of the mismatches along the Y-axis of the moulded parts varied from −38 to 141 µm. The results of the experiments showed that the mould alignment using kinematic constraints is applicable to the fabrication of double-sided patterns for microfluidic devices.

A novel electrical modelling for a vertically movable gate field effect transistor (VMGFET) for sensing applications is conducted. Presented is the manipulation of threshold voltage and drain current of the VMGFET as a function of the effective charge density and the air gap between the gate and the substrate body. The usage of the VMGFET in depletion mode, while operating in the saturation region, is proposed to prevent an electrostatic attraction between the suspended gate and substrate and to have a linear response of drain current over a varying air gap. The sensitivity of the VMGFET is simulated and shows a constant slope by changing the air gap under the operating conditions, such as working in depletion mode and operating in the saturation region. The sensitivity independence of the gate position is desirable when the VMGFET is applied for physical sensor applications.

The article aimed to analytically investigate the thermophysical behaviors of a ferrofluid in a vertical rectangle with the variation of intensity of the magnetic field, viscosity of the ferrofluid and boundary conditions. The governing equations of the ferrofluid include the continuity, momentum and energy equations for describing the thermal-fluidic behaviors of the ferrofluid and the Maxwell equation and magnetization equation are also added to consider rotating effect of the nano-sized particles. The flow behavior and heat transfer characteristics of the ferrofluid with the intensity of the magnetic field, viscosities of the ferrofluid and boundary conditions were analyzed through isotherms, velocity profiles and both mean and local Nusselt numbers. As a result, the isotherms of the ferrofluid in the vertical rectangle increased with the increase of the magnetic volume fractions and magnetic field intensities. In addition, the mean Nusselt numbers increased with the increase of magnetite volume fractions at all magnetic field intensities because of the combined effects of both heat conduction by magnetite and the magnetic volume force.

Low-cost modular polymer microfluidic platforms integrating several different functional units may potentially reduce the cost of molecular and environmental analyses, and enable broader applications. Proper function of such systems depends on well-characterized assembly of the instruments. Passive alignment is one approach to obtaining such assemblies. Model modular devices containing passive alignment features, hemispherical pins in v-grooves, and integrated alignment standards for characterizing the accuracy of the assemblies were replicated in polycarbonate using doubled-sided injection molding. The dimensions and locations of the assembly features and alignment standards were measured. The assemblies had mismatches from 16 ± 4 to $20\pm 6~\mu $ m along the x -axis and from 103 ± 7 to $118\pm 11~\mu $ m along the y -axis. The vertical variation from the nominal value of $287~\mu $ m ranged from −10 ± 4 to $34\pm 7~\mu $ m. An assembly tolerance model was used to estimate the accuracy of the assemblies based on the manufacturing variations of the alignment structures. Variation of the alignment structure features were propagated through the assembly using Monte Carlo methods. The estimated distributions matched the measured experimental results well, with differences of 2%–13% due to unmodeled aspects of the variations Accurate assembly of advanced polymer microsystems is feasible and predictable in the design phase. [2014-0125]

Minimizing misalignments during the interconnection of microfluidic modules is extremely critical to develop a fully integrated microfluidic device. Misalignments arising during chip-to-chip or world-to-chip interconnections can be greatly detrimental to efficient functioning of microfluidic devices. To address this problem, we have performed numerical simulations to investigate the effect of misalignments arising in three types of interconnection methods: (i) end-to-end interconnection (ii) channel overlap when chips are stacked on top of each other, and (iii) tube-in-reservoir misalignment occurring due to the offset between the external tubing and the reservoir. For the case of end-to-end interconnection, the effect of misalignment was investigated for 0, 13, 50, 58, and 75% reduction in the available flow area at the location of geometrical misalignment. In the channel overlap interconnection method, various possible misalignment configurations were simulated by maintaining the same amount of misalignment (75% flow area reduction). The effect of misalignment in a tube-in-reservoir interconnection was investigated by positioning the tube at an offset of 164 μm from the reservoir center. All the results were evaluated in terms of the equivalent length of a straight pipe. The effect of Reynolds number (Re) was also taken into account by performing additional simulations of aforementioned cases at Re ranging between 0.075 ≤ Re ≤ 75. Correlations were developed and the results were interpreted in terms of equivalent length (Le ). Equivalent length calculations revealed that the effect of misalignment in tube-in-reservoir interconnection method was the least significant when compared to the other two methods of interconnection.

Minimizing misalignments during the interconnection of microfluidic modules is extremely critical to develop a fully integrated microfluidic device. Misalignments arising during chip-to-chip or world-to-chip interconnections can be greatly detrimental to efficient functioning of microfluidic devices. To address this problem, we have performed numerical simulations to investigate the effect of misalignments arising in three types of interconnection methods: (i) end-to-end interconnection (ii) channel overlap when chips are stacked on top of each other, and (iii) tube-in-reservoir misalignment occurring due to the offset between the external tubing and the reservoir. For the case of end-to-end interconnection, the effect of misalignment was investigated for 0, 13, 50, 58, and 75% reduction in the available flow area at the location of geometrical misalignment. In the channel overlap interconnection method, various possible misalignment configurations were simulated by maintaining the same amount of misalignment (75% flow area reduction). The effect of misalignment in a tube-in-reservoir interconnection was investigated by positioning the tube at an offset of 164 μm from the reservoir center. All the results were evaluated in terms of the equivalent length of a straight pipe. The effect of Reynolds number (Re) was also taken into account by performing additional simulations of aforementioned cases at Re ranging between 0.075 ≤ Re ≤ 75. Correlations were developed and the results were interpreted in terms of equivalent length (Le ). Equivalent length calculations revealed that the effect of misalignment in tube-in-reservoir interconnection method was the least significant when compared to the other two methods of interconnection.

This paper presents a numerical study to investigate the effect of geometrical and material transition on the flow and progression of a sample plug in electrokinetic flows. Three cases were investigated: (a) effect of sudden cross-sectional area change (geometrical transition or mismatch) at the interface, (b) effect of only material transition (i.e. varying ζ-potential), and (c) effect of combined material transition and cross-sectional area change at the interface. The geometric transition was quantified based on the ratio of reduced flow area A2 at the mismatch plane to the original cross-sectional area A1. Multiple simulations were performed for varying degrees of area reduction i.e. 0–75% reduction in the available flow area, and the effect of dispersion on the sample plug was quantified by standard metrics. Simulations showed that a 13% combined material and geometrical transition can be tolerated without significant loss of sample resolution. A 6.54% reduction in the flow rates was found between 0% and 75% combined material and geometrical transition.

Arrays of continuous flow thermal reactors were designed, configured, and fabricated in a 96-device (12 × 8) titer-plate format with overall dimensions of 120 mm × 96 mm, with each reactor confined to a 8 mm × 8 mm footprint. To demonstrate the potential, individual 20-cycle (740 nl) and 25-cycle (990 nl) reactors were used to perform the continuous flow polymerase chain reaction (CFPCR) for amplification of DNA fragments of different lengths. Since thermal isolation of the required temperature zones was essential for optimal biochemical reactions, three finite element models, executed with ANSYS (v. 11.0, Canonsburg, PA), were used to characterize the thermal performance and guide system design: (1) a single device to determine the dimensions of the thermal management structures; (2) a single CFPCR device within an 8 mm × 8 mm area to evaluate the integrity of the thermostatic zones; and (3) a single, straight microchannel representing a single loop of the spiral CFPCR device, accounting for all of the heat transfer modes, to determine whether the PCR cocktail was exposed to the proper temperature cycling. In prior work on larger footprint devices, simple grooves between temperature zones provided sufficient thermal resistance between zones. For the small footprint reactor array, 0.4 mm wide and 1.2 mm high fins were necessary within the groove to cool the PCR cocktail efficiently, with a temperature gradient of 15.8 °C/mm, as it flowed from the denaturation zone to the renaturation zone. With temperature tolerance bands of ±2 °C defined about the nominal temperatures, more than 72.5% of the microchannel length was located within the desired temperature bands. The residence time of the PCR cocktail in each temperature zone decreased and the transition times between zones increased at higher PCR cocktail flow velocities, leading to less time for the amplification reactions. Experiments demonstrated the performance of the CFPCR devices as a function of flow velocity, fragment length, and copy number. A 99 bp DNA fragment was successfully amplified at flow velocities from 1 mm/s to 3 mm/s, requiring from 8.16 min for 20 cycles (24.48 s/cycle) to 2.72 min for 20 cycles (8.16 s/cycle), respectively. Yield compared to the same amplification sequence performed using a bench-top thermal cycler decreased nonlinearly from 73% (at 1 mm/s) to 13% (at 3 mm/s) with shorter residence time at the optimal temperatures for the reactions due to increased flow rate primarily responsible. Six different DNA fragments with lengths between 99 bp and 997 bp were successfully amplified at 1 mm/s. Repeatable, successful amplification of a 99 bp fragment was achieved with a minimum of 8000 copies of the DNA template. This is the first demonstration and characterization of continuous flow thermal reactors within the 8 mm × 8 mm footprint of a 96-well micro-titer-plate and is the smallest continuous flow PCR to date.

A vertically movable gate field effect transistor (VMGFET) is proposed and demonstrated for a micro-accelerometer application. The VMGFET using air gap as an insulator layer allows the gate to move on the substrate vertically by external forces. Finite element analysis is used to simulate mechanical behaviors of the designed structure. For the simulation, the ground acceleration spectrum of the 1952 Kern County Earthquake is employed to investigate the structural integrity of the sensor in vibration. Based on the simulation, a prototype VMGFET accelerometer is fabricated from silicon on insulator wafer. According to current–voltage characteristics of the prototype VMGFET, the threshold voltage is measured to be 2.32 V, which determines the effective charge density and the mutual transconductance of 1.545×10−8 C cm−2 and 6.59 mA V−1, respectively. The device sensitivity is 9.36–9.42 mV g−1 in the low frequency, and the first natural frequency is found to be 1230 Hz. The profile smoothness of the sensed signal is in 3 dB range up to 1 kHz.

Cooling of an embossed part has been recognized as one of the critical steps in the hot embossing of polymer microdevices. Numerical analysis was performed to study the stress developed in an embossed microstructure during the cooling process of hot embossing. A hemisphere-tipped post was selected as an example structure to demonstrate the stress evolution. The posts are located at 5, 10, 15, and 20 mm from the center of the embossed part. The results of the analysis showed that stresses of the posts increased as the radial locations of the post increased. In addition, the stress rapidly increased until the cooling time reached about 100.0 s. The maximum stresses of 28.9, 30.2, 32.3, and 34.5 MPa were estimated at the post locations of 5, 10, 15, and 20 mm from the center of the part, respectively. Experiments were performed to verify the numerical models. Undercut at the bottom of a post was observed as it was predicted in the numerical analysis.