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Publications (10 of 246) Show all publications
Andersson, M., Wilson, A., Hjort, K. & Klintberg, L. (2019). A microfluidic relative permittivity sensor for feedback control of carbon dioxide expanded liquid flows. Sensors and Actuators A-Physical, 285, 165-172
Open this publication in new window or tab >>A microfluidic relative permittivity sensor for feedback control of carbon dioxide expanded liquid flows
2019 (English)In: Sensors and Actuators A-Physical, ISSN 0924-4247, E-ISSN 1873-3069, Vol. 285, p. 165-172Article in journal (Refereed) Published
Abstract [en]

Binary CO2-alcohol mixtures, such as CO2-expanded liquids (CXLs), are promising green solvents for reaching higher performance in flow chemistry and separation processing. However, their compressibility and high working pressure makes handling challenging. These mixtures allow for a tuneable polarity but, to do so, requires precise flow control. Here, a high-pressure tolerant microfluidic system containing a relative permittivity sensor and a mixing chip is used to actively regulate the relative permittivity of these fluids and indirectly—composition. The sensor is a fluid-filled plate capacitor created using embedded 3D-structured thin films and has a linearity of 0.9999, a sensitivity of 4.88 pF per unit of relative permittivity, and a precision within 0.6% for a sampling volume of 0.3 μL. Composition and relative permittivity of CO2-ethanol mixtures were measured at 82 bar and 21 °C during flow. By flow and dielectric models, this relationship was found to be described by the pure components and a quadratic mixing rule with an interaction parameter, kij, of -0.63 ± 0.02. Microflows with a relative permittivity of 1.7–21.4 were generated, and using the models, this was found to correspond to compositions of 6–90 mol % ethanol in CO2. With the sensor, a closed loop control system was realised and CO2-ethanol flows were tuned to setpoints of the relative permittivity in 30 s.

Keywords
Relative permittivity, Process control, CO2-expanded liquids, Binary fluid mixtures, High-pressure microfluidics
National Category
Chemical Engineering Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:uu:diva-353945 (URN)10.1016/j.sna.2018.11.015 (DOI)000456902600021 ()
Funder
Knut and Alice Wallenberg Foundation
Available from: 2018-06-19 Created: 2018-06-19 Last updated: 2019-02-25Bibliographically approved
Cruz, J., Graells, T., Wallden, M. & Hjort, K. (2019). Inertial focusing with sub-micron resolution for separation of bacteria. Lab on a Chip, 19(7), 1257-1266
Open this publication in new window or tab >>Inertial focusing with sub-micron resolution for separation of bacteria
2019 (English)In: Lab on a Chip, ISSN 1473-0197, E-ISSN 1473-0189, Vol. 19, no 7, p. 1257-1266Article in journal (Refereed) Published
Abstract [en]

In this paper, we study inertial focusing in curved channels and demonstrate the alignment of particles with diameters between 0.5 and 2.0 m, a range of biological relevance since it comprises a multitude of bacteria and organelles of eukaryotic cells. The devices offer very sensitive control over the equilibrium positions and allow two modes of operation. In the first, particles having a large variation in size are focused and concentrated together. In the second, the distribution spreads in a range of sizes achieving separation with sub-micron resolution. These systems were validated with three bacteria species (Escherichia coli, Salmonella typhimurium and Klebsiella pneumoniae) showing good alignment while maintaining the viability in all cases. The experiments also revealed that the particles follow a helicoidal trajectory to reach the equilibrium positions, similar to the fluid streamlines simulated in COMSOL, implying that these positions occupy different heights in the cross section. When the equilibrium positions move to the inner wall as the flow rate increases, they are at a similar distance from the centre than in straight channels (approximate to 0.6R), but when the equilibrium positions move to the outer wall as the flow rate increases, they are closer to the centre and the particles pass close to the inner wall to elevate their position before reaching them. These observations were used along with COMSOL simulations to explain the mechanism behind the local force balance and the migration of particles, which we believe contributes to further understanding of the phenomenon. Hopefully, this will make designing more intuitive and reduce the high pressure demands, enabling manipulation of particles much smaller than a micrometer.

Place, publisher, year, edition, pages
ROYAL SOC CHEMISTRY, 2019
National Category
Biochemistry and Molecular Biology
Identifiers
urn:nbn:se:uu:diva-382383 (URN)10.1039/c9lc00080a (DOI)000462723900009 ()30821308 (PubMedID)
Funder
EU, Horizon 2020, 644669
Available from: 2019-04-25 Created: 2019-04-25 Last updated: 2019-04-25Bibliographically approved
Werr, G., Khaji, Z., Ohlin, M., Andersson, M., Klintberg, L., Searle, S., . . . Tenje, M. (2019). Integrated thin film resistive sensors for in situ temperature measurements in an acoustic trap. Journal of Micromechanics and Microengineering, 29(9), Article ID 095003.
Open this publication in new window or tab >>Integrated thin film resistive sensors for in situ temperature measurements in an acoustic trap
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2019 (English)In: Journal of Micromechanics and Microengineering, ISSN 0960-1317, E-ISSN 1361-6439, Vol. 29, no 9, article id 095003Article in journal (Refereed) Published
Abstract [en]

This work presents an acoustic trap with integrated thin film sensors to monitor temperature variations during operation. The acoustic trap is wet-etched in glass with a thermally bonded glass lid and the thin-film sensors are integrated during fabrication. We evaluated the performance of the integrated temperature sensors and measured a temperature sensitivity of +/- 0.01 degrees C and confirmed that the read-out of the thin film sensors was not affected neither by the ionic conductivity of the solution nor the addition of microparticles into the acoustic trap. From the experiments we observed a temperature increase of the acoustic trap during operation as a result of the dissipative heating of the the piezoelectric element used to actuate the trap. We also showed that when external convective cooling was applied to the system, the temperature increase of the acoustic trap was higher than the temperature increase of the piezoelectric element itself. This shows the importance of using integrated temperature sensors in acoustic trapping to monitor the local environmental conditions.

Place, publisher, year, edition, pages
IOP PUBLISHING LTD, 2019
Keywords
acoustophoresis, integrated RTD, external TC, acoustic trap, glass chip
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:uu:diva-391278 (URN)10.1088/1361-6439/ab2ac8 (DOI)000476561400001 ()
Funder
Knut and Alice Wallenberg Foundation
Available from: 2019-08-22 Created: 2019-08-22 Last updated: 2019-08-22Bibliographically approved
Andersson, M., Svensson, K., Klintberg, L. & Hjort, K. (2018). A microfluidic control board for high-pressure flow, composition, and relative permittivity. Analytical Chemistry, 90(21), 12601-12608
Open this publication in new window or tab >>A microfluidic control board for high-pressure flow, composition, and relative permittivity
2018 (English)In: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 90, no 21, p. 12601-12608Article in journal (Refereed) Published
Abstract [en]

Flow control is central to microfluidics and chromatography. With decreasing dimensions and high pressures, precise fluid flows are often needed. In this paper, a high-pressure flow control system is presented, allowing for the miniaturization of chromatographic systems and the increased performance of microfluidic setups by controlling flow, composition and relative permittivity of two-component flows with CO2. The system consists of four chips: two flow actuator chips, one mixing chip and one relative permittivity sensor. The actuator chips, throttling the flow, required no moving parts as they instead relied on internal heaters to change the fluid resistance. This allows for flow control using miniaturized fluid delivery systems containing only a single pump or pressure source. Mobile phase gradients between 49% to 74% methanol in CO2 were demonstrated. Depending on how the actuator chips were dimensioned, the position of this range could be set for different method-specific needs. With the microfluidic control board, both flow and composition could be controlled from constant pressure sources, drift could be removed, and variations in composition could be lowered by 84%, resulting in microflows of CO2 and methanol with a variation in the composition of 0.30%.

National Category
Chemical Engineering
Identifiers
urn:nbn:se:uu:diva-353953 (URN)10.1021/acs.analchem.8b02758 (DOI)000449722500039 ()30269500 (PubMedID)
Funder
Knut and Alice Wallenberg Foundation
Available from: 2018-06-19 Created: 2018-06-19 Last updated: 2018-12-21Bibliographically approved
Jiao, M., Nguyen, v. D., Nguyen, V. C., Nguyen, D. H., Nguyen, V. H., Hjort, K. & Nguyen, H. (2018). Comparison of NO2 Gas-Sensing Properties of Three Different ZnO Nanostructures Synthesized by On-Chip Low-Temperature Hydrothermal Growth. Journal of Electronic Materials, 47(1), 785-793
Open this publication in new window or tab >>Comparison of NO2 Gas-Sensing Properties of Three Different ZnO Nanostructures Synthesized by On-Chip Low-Temperature Hydrothermal Growth
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2018 (English)In: Journal of Electronic Materials, ISSN 0361-5235, E-ISSN 1543-186X, Vol. 47, no 1, p. 785-793Article in journal (Refereed) Published
Abstract [en]

Three different ZnO nanostructures, dense nanorods, dense nanowires, and sparse nanowires, were synthesized between Pt electrodes by on-chip hydrothermal growth at 90°C and below. The three nanostructures were characterized by scanning electron microscopy and x-ray diffraction to identify their morphologies and crystal structures. The three ZnO nanostructures were confirmed to have the same crystal type, but their dimensions and densities differed. The NO2 gas-sensing performance of the three ZnO nanostructures was investigated at different operation temperatures. ZnO nanorods had the lowest response to NO2 along with the longest response/recovery time, whereas sparse ZnO nanowires had the highest response to NO2 and the shortest response/recovery time. Sparse ZnO nanowires also performed best at 300°C and still work well and fast at 200°C. The current–voltage curves of the three ZnO nanostructures were obtained at various temperatures, and the results clearly showed that sparse ZnO nanowires did not have the linear characteristics of the others. Analysis of this phenomenon in connection with the highly sensitive behavior of sparse ZnO nanowires is also presented.

National Category
Other Materials Engineering
Identifiers
urn:nbn:se:uu:diva-320153 (URN)10.1007/s11664-017-5829-6 (DOI)000418580800093 ()
Available from: 2017-04-16 Created: 2017-04-16 Last updated: 2018-01-29Bibliographically approved
Andersson, M., Rodriguez-Meizoso, I., Turner, C., Hjort, K. & Klintberg, L. (2018). Dynamic pH determination at high pressure of aqueous additive mixtures in contact with dense CO2. Journal of Supercritical Fluids, 136, 95-101
Open this publication in new window or tab >>Dynamic pH determination at high pressure of aqueous additive mixtures in contact with dense CO2
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2018 (English)In: Journal of Supercritical Fluids, ISSN 0896-8446, E-ISSN 1872-8162, Vol. 136, p. 95-101Article in journal (Refereed) Published
Abstract [en]

A system consisting of a high-pressure tolerant microfluidic glass chip, high-speed absorbance imaging, and image processing has been developed to study rapid dynamic events like pH change in a multiphase flow. The system gives both kinetic and quantitative equilibrated information. By tracking the interactions of aqueous additive mixtures and liquid CO2, at 80 bar and 24 °C, under flow, measurement at a given P, T condition is done in 0.25 s. The acidification rate to steady state was found to be mass transport limited, occurring in less than 1 s. For 30 mM of the additives ammonium acetate and ammonium formate, equilibrium pH of 4.5 and 4.1, respectively, was seen. These additives are of key importance in common mobile phases used in SFC.

Keywords
Supercritical fluid chromatography, High-pressure microfluidics, Additive salts, Dense CO, Multiphase flow, Image analysis
National Category
Chemical Engineering Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-353940 (URN)10.1016/j.supflu.2018.02.012 (DOI)000430767400011 ()
Funder
Knut and Alice Wallenberg Foundation
Available from: 2018-06-18 Created: 2018-06-18 Last updated: 2018-08-02Bibliographically approved
Cruz, F. J. & Hjort, K. (2018). High pressure inertial focusing: integration in parallel and series. In: : . Paper presented at The Micronano System Workshop (MSW 2018), Aalto University, Espoo, Finland, May 13th-18th, 2018.
Open this publication in new window or tab >>High pressure inertial focusing: integration in parallel and series
2018 (English)Conference paper, Oral presentation only (Other academic)
Keywords
Microfluidics, Inertial focusing
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:uu:diva-368494 (URN)
Conference
The Micronano System Workshop (MSW 2018), Aalto University, Espoo, Finland, May 13th-18th, 2018
Funder
EU, Horizon 2020, 644669
Available from: 2018-12-05 Created: 2018-12-05 Last updated: 2018-12-10Bibliographically approved
Svensson, K., Södergren, S., Andersson, M., Klintberg, L. & Hjort, K. (2018). High-pressure microfluidic electrochemical and image analysis dual detection for HPLC. In: : . Paper presented at Micromechanics and Microsystems Europe Workshop (MME 2018), Aug. 26-29, Smolenice, Slovakia (pp. 113-119).
Open this publication in new window or tab >>High-pressure microfluidic electrochemical and image analysis dual detection for HPLC
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2018 (English)Conference paper, Oral presentation with published abstract (Other academic)
Abstract [en]

High-performance liquid chromatography (HPLC) is often set as the lab-based golden standard. For point-of-care and point-of-site applications, making HPLC portable, easy to use and low cost, is very desirable. To reach lower costs, one important task is the development of suitable detectors. Because of the potential for low cost and high performance, a dual-detection microfluidic chip with an electrochemical detector (ECD) and optical access for image analysis was evaluated at high pressure, downstream an HPLC column. For the image analysis, a camera and near-UV-light was used to extract absorption data. To validate the response, a spectrometer was coupled downstream the chip. The results of the three different detectors were comparable, with the camera providing similar absorbance-time chromatograms as the spectrometer. However, the ECD registered only peaks from one of two analytes. To conclude, this experimental setup has potential to provide better understanding of the capability for microfluidic HPLC systems.

National Category
Engineering and Technology Other Chemical Engineering
Research subject
Engineering Science with specialization in Microsystems Technology
Identifiers
urn:nbn:se:uu:diva-367300 (URN)
Conference
Micromechanics and Microsystems Europe Workshop (MME 2018), Aug. 26-29, Smolenice, Slovakia
Funder
The Kamprad Family Foundation, 20170169
Available from: 2018-11-29 Created: 2018-11-29 Last updated: 2018-12-10Bibliographically approved
Sahlberg, A., Nilsson, F., Berglund, A., Nguyen, H., Hjort, K. & Jeong, S. H. (2018). High-Resolution Liquid Alloy Patterning for Small Stretchable Strain Sensor Arrays. Advanced materials technologologies, 3(4), Article ID 1700330.
Open this publication in new window or tab >>High-Resolution Liquid Alloy Patterning for Small Stretchable Strain Sensor Arrays
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2018 (English)In: Advanced materials technologologies, ISSN 2365-709X, Vol. 3, no 4, article id 1700330Article in journal (Refereed) Published
Abstract [en]

Soft material applied technology has in recent years become more advanced, enabling for, e.g., soft robotics, skin electronics, and wearable systems. Yet, the processing technology of soft materials has not been sufficiently developed to create high performance in soft and stretchable systems, as compared to the processing technology of conventional electronics or electromechanical systems. Liquid alloys have shown excellent properties for soft and stretchable electrical interconnectors and conductors, which is a basic building block to produce electric or electromechanical systems. In order to overcome the limited resolution of previously developed liquid alloy patterning methods for large-area printed circuits, this work explores the possibility of employing shrinking substrates. By utilizing the characteristics of liquid alloys and elastomers the pattern resolution is improved through a stretch-shrink patterning (SSP) process. The process provides highly conductive liquid conductors of high resolution and can be combined with existing printing techniques for liquid alloys. The SSP process increases design flexibility of soft and stretchable systems that use liquid alloys and enables designs with finer and denser patterns, and cost-effective production for small scale systems.

Keywords
elastomers, high-resolution patterning, liquid alloys, shrink substrates, stretchable strain sensors
National Category
Other Materials Engineering
Identifiers
urn:nbn:se:uu:diva-353211 (URN)10.1002/admt.201700330 (DOI)000430164100012 ()
Available from: 2018-06-13 Created: 2018-06-13 Last updated: 2018-06-14Bibliographically approved
Jiao, M., Nguyen Viet, C., Duy, N. V., Nguyen Duc, H., Hieu, N. V., Hjort, K. & Nguyen, H. (2018). Influence of annealing temperature on theperformance and stability of on-chip hydrothermally grown ZnO nanorod gassensor toward NO2. Academia Journal of Scientific Research, 6(5), 180-189
Open this publication in new window or tab >>Influence of annealing temperature on theperformance and stability of on-chip hydrothermally grown ZnO nanorod gassensor toward NO2
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2018 (English)In: Academia Journal of Scientific Research, ISSN 2315-7712, Vol. 6, no 5, p. 180-189Article in journal (Refereed) Published
Abstract [en]

Nanorod-based gas sensors synthesized at low temperature should generally be stabilized by anneling before usage. However, the influence of annealing on the sensing performance and stability of these nanorods is rarely reported. In this study, we first fabricated gas sensors based on ZnO nanorods grown on-chip on glass substrate using hydrothermal method. Subsequently, these sensors were annealed at either 400 °C, 500 °C, or 600 °C in air for 4 h. The gas-sensing performance of the ZnO nanorods toward NO2 was tested before and after annealing. The sensitivity of the gas sensors to NO2 decreased, but the stability increased with the increase in annealing temperature. Photoluminescence spectroscopy and X-ray diffraction were used to investigate the material structure of ZnO nanorods. Results revealed that the oxygen-atom-related defects in the ZnO lattice in the region close to the surface influenced by annealing process were the most significant factors on the sensing properties and stability of ZnO nanorods.

Keywords
Annealing, defects in nanorods, gas sensor, hydrothermal, zinc oxide.
National Category
Other Natural Sciences Engineering and Technology
Research subject
Engineering Science with specialization in Microsystems Technology
Identifiers
urn:nbn:se:uu:diva-363650 (URN)10.15413/ajsr.2018.0104 (DOI)
Available from: 2018-10-18 Created: 2018-10-18 Last updated: 2018-10-19Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0003-2744-1634

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