Inkjet-printed paper-based sensor array for highly accurate pH sensing

Highlights: • A paper-based colorimetric sensor array was developed, achieving the nearly whole pH range detection with high resolution. • Hydrophilic polymer PEG 400 was utilized for the immobilization of pH indictors. • Hierarchical cluster analysis (HCA) and principal component analysis (PCA) were used to discriminate different pH values. • The volume of samples needed for analysis was less than 10 μL. In this work, a novel paper-based colorimetric sensor array was developed by inkjet printing method with polyethylene glycol (PEG) immobilization system. Eight commercially available pH indicators with sequential pH segments in nearly whole pH range were dissolved in nine mixed inks to fabricate the 3 × 3 sensor array on mixed cellulose ester (MCE) paper. Based on homogeneous deposition of inkjet printing, the eight pH indicators were sufficiently immobilized on MCE paper with the assistance of PEG-400, which guaranteed pH detection of aqueous samples on sensor array without hydrophobic barriers. Besides, the indicating range of each indicator obtained an extension through the addition of PEG 400, which remarkably enriched the distinguishable capability of sensor array and benefited for high resolution of pH detection. As such, the as-fabricated paper-based sensor array exhibited an excellent discrimination ability in pH range of 1.00–13.60 with a high resolution of 0.20 pH unit, not only for standard pH buffer solutions but for real aqueous samples.