Micro-lithography on paper, surface process modifications for biomedical performance enhancement

We have enhanced the performance of lithographically patterned microchannels on paper and tailored it to a do it yourself method by examining the impact of each microfabrication step on surface properties. Modification of photoresist spreading, baking, exposure and developing steps improved paper and channels quality and decreased fabrication costs and time. The proper concentration of SU-8 in cyclopentene was found 1/8 (volumetric), to enable coating on paper by soaking, faster baking (10 min-65 degrees C), and improved paper hydrophilicity. The UV-exposure time and energy were modified to enhance the channel quality. Then, the patterned paper was washed in cyclopentene for 15 min, and baked for 1 min at 95 degrees C. The modified process leaves 100 mu m uniform channels on paper in around 26 min, from design to completion. Each step modification was assessed by analyze flow testing. The tuned process also improved the uniformity of channels, and eliminated the need for a spinner or hotplate. Exposure refinement alleviated the necessity for a mask aligner machine, and sunlight may also be used instead of UV. Channels were finally treated with BSA to improve partitioning and analyze flow, and reduce longitudinal binding, verified by IR absorption spectrum. The resulting mu PAD was used for detection of TSH on the onset of hypothyroidism at 4 mU/L in four minutes, using an ELISA protocol.