A simple, openable and electroosmotic flow-free PMMA chip for electrophoretic titration of moving reaction boundary

Poor control of electroosmotic flow (EOF) often occurs in chip electrophoretic titration (ET) of moving reaction boundary due to both absence of PMMA channel coating and coexistence of acid-base. Also, chip ET still suffers from low reproducibility, instability, disposability and high cost as well. To address these issues, a reusable ET chip (60 mm × 60 mm × 5.0 mm) was designed via an upper PMMA sheet, a middle silicon membrane and a lower sheet. In the upper sheet, enlarged channel (500 μm × 200 μm × 12 mm) was fabricated and linked to the anodic and cathodic wells. The upper sheet, middle membrane and lower sheet could be easily assembled together in 20 s as an ET chip of supporting 1.4 kg tension force, indicating good mechanical stability. Regeneration and reassembling of chip could be finished in 50 s. EOF could be simply suppressed by mass chemical cross-linked polyacrylamide gel or physical agarose gel in the enlarged channel. The EOF-free chip could be well used for: (i) acid-base ET; (ii) EOF monitoring; (iii) pKa determination; (iv) protein content analysis. The EOF-free chip showed the following merits: (i) 98% success rate in contrast to less than 30% in normal channels (80 μm × 20 μm × 5.0 mm); (ii) more than 30 times reuse, indicating reusability and low cost; (iii) less than 10% of relative standard deviation, suggesting fair stability; and (iv) good recovery and accuracy. The developed chip makes great advancement towards real use of chip in acid- base titration, EOF monitoring, pKa determination and protein content analysis.