Surface Modification of Thermoplastic Polymers for Lateral Flow Assay Applications

Mahmud, MD Shamim
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Lateral flow immunoassay (LFIA) is the technology behind low-cost, simple, rapid and portable detection devices which is popular in biomedicine, agriculture, food and environmental sciences. In this research, a simple and inexpensive manufacturing procedure has been introduced to develop lateral flow assay device. Laser micromachining was applied on the thermoplastic poly (methyl methacrylate) (PMMA) polymer to change the surface topography, and the surfactant solution added to the following laser treated surface to achieve the capillary driven flow. A nanosecond pulsed excimer laser was used to ablate a rectangular area of 4 mm × 40 mm on a precleaned PMMA substrate under an ambient condition to introduce capillary driven flow on the PMMA substrate and to change the surface chemistry. It was found that the density of the functional groups (-C-O-, -O-H) created by the laser irradiation and capillary flow rates depend on the laser scanning steps, surface roughness and laser fluence. Since the surface recover from hydrophilic to hydrophobic following the laser treatment, the ionic surfactant AOT (dioctyl sulfosuccinate sodium salt) with 0.08 M was applied to the surface to introduce more polar group on the surface. The surfactant solution reduces the liquid-solid interfacial tension, and therefore induces capillary driven flow. A speed of capillary driven flow up to 16 mm/s can be achieved on the laser and surfactant treated surface when the step sizes of scanning the laser beam in the x-y directions were 50 μm and 500 μm, respectively. However, no capillary driven flows were observed when the step size of scanning laser beam were 250 μm and 250 μm or 500 μm and 500 μm in the x - y directions respectively. Therefore, the capillary flow rate on the treated surface could be controlled by changing the laser scanning steps which helped to create more microgrooves on the surface. The proposed method of combining laser and surfactant treatment is suitable for cost-effective manufacturing of long-lasting thermoplastic polymer-based lateral flow strips. Finally, the performance of the laser modified PMMA strip had been successfully tested by introducing antibody and antigen reaction on the fabricated device. The overall result entails the better prospect of the PMMA device as a possible replacement of nitrocellulose membrane.
Microfluidics, Lateral flow assay, Lab-on-a-chip, Laser micromachining, Superhydrophilic, Micro-nanostructure
Mahmud, M. S. (2018). <i>Surface modification of thermoplastic polymers for lateral flow assay applications</i> (Unpublished thesis). Texas State University, San Marcos, Texas.