Enhancing Magnetic Micro- and Nanoparticle Separation with a Cost-Effective Microfluidic Device Fabricated by Laser Ablation of PMMA

Abstract

Superparamagnetic iron oxide micro- and nanoparticles have significant applications in biomedical and chemical engineering. This study presents the development and evaluation of a novel low-cost microfluidic device for the purification and hyperconcentration of these magnetic particles. The device, fabricated using laser ablation of polymethyl methacrylate (PMMA), leverages precise control over fluid dynamics to efficiently separate magnetic particles from non-magnetic ones. We assessed the device's performance through Multiphysics simulations and empirical tests, focusing on the separation of magnetite nanoparticles from blue carbon dots and magnetite microparticles from polystyrene microparticles at various total flow rates (TFRs). For nanoparticle separation, the device achieved a recall of up to 93.3 ± 4% and a precision of 95.9 ± 1.2% at an optimal TFR of 2 mL/h, significantly outperforming previous models, which only achieved a 50% recall. Microparticle separation demonstrated an accuracy of 98.1 ± 1% at a TFR of 2 mL/h in both simulations and experimental conditions. The Lagrangian model effectively captured the dynamics of magnetite microparticle separation from polystyrene microparticles, with close agreement between simulated and experimental results. Our findings underscore the device's robust capability in distinguishing between magnetic and non-magnetic particles at both micro- and nanoscales. This study highlights the potential of low-cost, non-cleanroom manufacturing techniques to produce high-performance microfluidic devices, thereby expanding their accessibility and applicability in various industrial and research settings. The integration of a continuous magnet, as opposed to segmented magnets in previous designs, was identified as a key factor in enhancing magnetic separation efficiency.

Keywords: CFD; SWOT; magnetite; microfluidic; purification; separation.

Figure 1

Computational domain and boundary conditions. (a) Computational domain, and mesh used for the simulation. (b) Microfluidic device manufactured in PMMA using laser ablation. The particle inlet is shown in green and labeled ‘1’, and the water buffer inlet, facilitating the washing and separation of magnetic from non-magnetic particles, is in blue and labeled ‘2’. The outlet, marked in red and denoted by ‘3’, is where non-magnetic particles exit first, followed by magnetic particles after the magnet is removed.

Figure 2

Manufacturing process of microfluidic devices using CO₂ laser ablation in PMMA. (1) The microfluidic device is manufactured in AutoCAD (AutoDesk Inc., Mill Valley, CA, USA). (2) The design is transferred to a CO₂ laser system for engraving and cutting. A 2 mm-thick PMMA sheet is engraved to a depth of 1 mm to create the microfluidic channels, while a 4 mm-thick PMMA sheet is cut to form the inlets and outlets. (3) Then, PMMA layers are cleaned with a 70% ethanol solution to remove any residues. (4) Next, layers are bonded using 96% ethanol, pressure, and heat at 110 °C for 3 min. (5) Finally, the inlets and outlets are assembled into the microfluidic device.

Figure 3

Synthesis and functionalization of magnetite micro- and nanoparticles. (a) Schematic of the magnetite micro- and nanoparticle synthesis using the coprecipitation technique. The process involves the preparation of an iron chloride solution, followed by the addition of NaOH. Rapid addition yields micro-sized particles (~2405 nm), while slow, dropwise addition results in nano-sized particles (~155 nm). (b) Silanization of magnetite nanoparticles to functionalize their surface and facilitate further modifications. (c) Subsequent labeling of silanized magnetite nanoparticles with rhodamine B (Rhod-B). (d) Synthesis of carbon dots through a separate process involving heating, sonication, and filtration, yielding purified carbon dots.

Figure 4

Evaluation of magnetic nanoparticle separation microfluidic device. (a) Simulated magnetic flux density distribution around the continuous magnet. (b) Distribution of the magnetic scalar potential across the microfluidic device, indicating areas of maximum potential (up to ±2 amperes). (c) Trajectory simulation of magnetic nanoparticles in the microfluidic channel, demonstrating their response to the applied magnetic field. (d) Photographic evidence of nanoparticle retention within the microfluidic device, aligning with areas of high magnetic flux density. (e) Comparative bar graph showcasing recall, precision, and accuracy metrics for nanoparticle separation at varying total flow rates (2, 20, and 200 mL/h), as obtained from both in silico simulations (dark shades) and experimental results (light shades).

Figure 5

Microparticle separation efficacy: (a) Fluorescence microscope images: non-magnetic polystyrene particles exhibit red fluorescence, while magnetite particles are non-fluorescent and visible in the transmitted BF (Bright Field) overlay. Scale-bar 50 $\mathsf{\mu }\mathrm{m}$. (b) Analysis of recall, precision, and accuracy, derived from the fluorescence microscope images, illustrating the device’s performance.

Figure 6

Microparticle sedimentation in microchannels: Bright Field and fluorescent images show minimal sedimentation of rhodamine B-labeled polystyrene microparticles, primarily in curved regions. The sedimentation is minimal and does not significantly obstruct the microchannel or impact the device’s functionality. Black arrows show the direction flow.

Figure 7

SWOT analysis of the magnetic separator microfluidic device. Strengths (S), weaknesses (W), opportunities (O), and threats (T).