Fabrication of Rugged and Reliable Fluidic Chips for Autonomous Environmental Analyzers Using Combined Thermal and Pressure Bonding of Polymethyl Methacrylate Layers

Abstract

The fabrication of highly reliable and rugged fluidic chips designed for use in autonomous analyses for nutrient monitoring is described. The chips are based on a two-layer configuration with the fluidic channels produced in one layer using precision micromilling. The second capping layer contains through holes for sample/standard and reagent addition and waste removal post-analysis. Two optically clear polymethyl methacrylate (PMMA) windows are integrated into the opaque PMMA chip, orthogonal to a 22.5 mm-long section of the channel downstream from a serpentine reagent and sample/standard mixing region. An LED source is coupled into the channel through one of the windows, and the light intensity is monitored with a photodiode located at the distal end of the channel outside the second optically clear window. Efficient coupling of the source through the channel to the detector is achieved using custom-designed alignment units produced using 3D printing. In contrast to fluidic chips produced using solvent adhesion, the thermal-/pressure-bonded simplified method presented removes the need for surface treatment. Optimization of the thermal/pressure conditions leads to very strong adhesion between the PMMA layers, requiring forces in the region of 2000 N to separate them, which is necessary for the use in long-term deployments. Profilometry imaging shows minimal evidence of channel distortion after bonding. Finally, we show the potential of these techniques for environmental applications. The fluidic chips were integrated into prototype nutrient analyzers that display no evidence of leakage in extensive lab tests involving 2500 phosphate measurements using the yellow (vanadomolybdophosphoric acid) method. Similarly, excellent analytical performance (LOD is 0.09 μM) is reported for a 28-day field trial comprising 188 in situ autonomous phosphate measurements (564 measurements) in total including calibration.

Real-Time Underway Mapping of Nutrient Concentrations of Surface Seawater Using an Autonomous Flow Analyzer

“…and system requirements (high reliability, low consumption, high frequency, etc. ). − Major advances in the development of devices utilizing different flow techniques (e.g., segmented continuous-flow analysis, , normal flow injection analysis, − reverse flow injection analysis, , sequential injection analysis, , microfluidic chips, − flow batch analysis, − programmable flow injection (pFI) in batch mode , ) to measure nutrients in seawater have been reported. Some of them have been applied for the underway measurement of specific single or dual-parameter nutrients in shipboard laboratories. ,− However, to the best of our knowledge, studies on the simultaneous underway analysis of all five key nutrients in estuarine and coastal waters are not available.…”

Investigation of Solvent-Assisted In-Mold Bonding of Cyclic Olefin Copolymer (COC) Microfluidic Chips

“…Otherwise, the bonded microfluidic chip with insufficient bonding quality often has defects such as leakage and channel blockage, which affect the analytical process in the microfluidic chip. Common bonding methods include thermal bonding [8][9][10], solvent bonding [11][12][13], laser bonding [14], adhesive bonding [15], and ultrasonic bonding [16].…”

Understanding and mitigating global change with aquatic sensors: current challenges and future prospects

“…Advances in microfluidics enables chemistry analyses that historically have been done in a laboratory to be performed at point-of-need, broadening the range of accessible analytes and providing early alerts of changes to water chemistry, thereby enabling rapid responses to pollution events in water bodies (Donohoe et al, 2019). In recent years, advanced fabrication techniques such as 3D printing (Weisgrab et al, 2019;Nadagouda et al, 2020) have driven down the unit cost of microfluidic chips through integration of sub-components that previously had to assembled to create the chip (Diamond et al, Frontiers in Sensors frontiersin.org 2020).…”