Metered reagent injection into microfluidic continuous flow sampling for conductimetric ocean dissolved inorganic carbon sensing

Tweedie, Mark; Macquart, Antonin; Almeida, João Roberto Façanha de; Ward, Brian; Maguire, Paul

doi:10.1088/1361-6501/ab7405

Cited by 6 publications

(4 citation statements)

References 35 publications

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“…The channel shape, while being generally described as V-grooved, does become increasingly steep-walled as the laser power increases. Despite the gradual change in profile, the cross-sectional areas increase approximately linearly with laser power up to 25%, as previously reported (Tweedie et al 2020b).…”

Section: Bondingsupporting

confidence: 87%

“…This relates to laboratory investigations of dissolved CO 2 measurement. Comparisons have also been conducted between use of asymmetric Y meters and snake channel for the same application (Tweedie et al 2020b ). This work provides more detail on fabrication issues related to these 2 device types, however, as in Fig.…”

Section: Resultsmentioning

confidence: 99%

“…a seawater sample, and an acid for dissolved CO 2 liberation, will enable control over metering ratio of the 2 liquids, and improved analyte precision. This may be achieved by various combinations of asymmetric Y meters and snake channel flow restrictors (Tweedie et al 2020b ). Performance of various lengths of flow restrictors will be demonstrated graphically.…”

Section: Introductionmentioning

confidence: 99%

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Microfluidic ratio metering devices fabricated in PMMA by CO2 laser

Tweedie

Maguire

2020

Microsyst Technol

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We describe microfluidic fabrication results achieved using a 10.6 μm CO2 engraving laser on cast PMMA, in both raster and vector mode, with a 1.5″ lens and a High Power Density Focussing Optics lens. Raster written channels show a flatter base and are more U-shaped, while vector written channels are V shaped. Cross-sectional images, and, where possible, stylus profilometry results are presented. The sides of V-grooves become increasing steep with laser power, but broader shallower channels may be produced in vector mode by laser defocus, as illustrated. Smoothing of raster engraved channels by heated IPA etch, and transparency enhancement by CHCl3 vapour treatment are briefly discussed. An asymmetric Y meter is discussed as one method of diluting acid into seawater for dissolved CO2 analysis. Alternatively, microfluidic snake channel restrictors of different lengths in 2 channels may achieve the same result. Samples are fabricated with bases bonded by CHCl3 vapour treatment, and the devices are flow tested with either dilute food dye or DI water. Microfluidics fabricated in this manner have applications in ocean sensing of dissolved CO2 and other analytes, as well as broader sensing measurements, including biomedical sensors.

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Section: Bondingsupporting

confidence: 87%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Microfluidic ratio metering devices fabricated in PMMA by CO2 laser

Tweedie

Maguire

2020

Microsyst Technol

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“…A set of vectors, written at powers of 12.5, 15 and 20% levels, and speeds of 0.3 m/s, was used to produce narrow HCl input channels, giving Y meters of meter ratios ~ 14:1, 10:1 and 6:1. These devices have been separately described, along with various long channel restrictors, for controlling metering ratios (Tweedie et al 2020). The dimensions of the vectored channel for the 6:1 Y meter are ~ 130 µm top width, and depth ~ 230 µm, with a roughly V-shaped cross-sectional profile, Fig.…”

Section: Y Meter Fabricationmentioning

confidence: 99%

The analysis of dissolved inorganic carbon in liquid using a microfluidic conductivity sensor with membrane separation of CO2

Tweedie

Sun

Gajula

et al. 2020

Microfluid Nanofluid

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Autonomous continuous analysis of oceanic dissolved inorganic carbon (DIC) concentration with depth is of great significance with regard to ocean acidification and climate change. However, miniaturisation of in situ analysis systems is hampered by the size, cost and power requirements of traditional optical instrumentation. Here, we report a low-cost microfluidic alternative based on CO 2 separation and conductance measurements that could lead to integrated lab-on-chip systems for ocean float deployment, or for moored or autonomous surface vehicle applications. Conductimetric determination of concentration, in the seawater range of 1000-3000 µmol kg −1 , has been achieved using a microfluidic thin-film electrode conductivity cell and a membrane-based gas exchange cell. Sample acidification released CO 2 through the membrane, reacting in a NaOH carrier, later drawn through a sub-µL conductivity cell, for impedance versus time measurements. Precision values (relative standard deviations) were ~ 0.2% for peak height measurements at 2000 µmol kg −1. Comparable precision values of ~ 0.25% were obtained using a C4D electrophoresis headstage with similar measurement volume. The required total sample and reagent volumes were ~ 500 µL for the low volume planar membrane gas exchange cell. In contrast, previous conductivitybased DIC analysis systems required total volumes between 5000 and 10,000 µL. Long membrane tubes and macroscopic wire electrodes were avoided by incorporating a planar membrane (PDMS) in the gas exchange cell, and by sputter deposition of Ti/Au electrodes directly onto a thermoplastic (PMMA) manifold. Future performance improvements will address membrane chemical and mechanical stability, further volume reduction, and component integration into a single manifold.

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