A dual-readout paper-based sensor for on-site detection of penicillinase with a smartphone.

• Dual-readout paper-based sensor via enzyme-mediated alginate hydrogelation. • Converting solution viscosity and pH to diameter and color readout. • Smartphone-based device to record and analyze both signals for quantitative detection. • Excellent reproducibility and selectivity for on-site detection of penicillinase. A dual-readout paper-based sensor with smartphone detection is developed for quantitative determination of penicillinase. The sensor is accomplished with the aid of penicillinase-mediated alginate hydrogelation, which changes both the viscosity and pH of the reaction solution. The solution is dropped on a mixed cellulose ester filter paper for sensing, which is coated with a color indicator, bromothymol blue-cetyltrimethylammonium bromide-alginate complex. Dual signals of the targets are easily achieved from the sensing spot on the paper since the modulations of viscosity and pH of the reaction solution would result in changes of diffusion diameter and color of the spot, respectively. A smartphone-based readout device is developed to record and analyze both the diffusion diameter and color signal for quantitative detection of penicillinase. The wide linear range (8.00 × 10−3 - 2.67 mU/μL for distance-readout and 8.00 × 10-2 to 2.67 mU/μL for color-readout) with low limit-of-detection (2.67 × 10-3 mU/μL for distance-readout and 2.67 × 10-2 mU/μL for color-readout) have been achieved using the dual-readout paper-based sensors. The proposed method is successfully applied for the detection of penicillinase in milk samples with excellent sensitivity and reproducibility, showing its potential value for analysis of complex real samples. [ABSTRACT FROM AUTHOR]