Colorimetric sensor based on cotton thread for the quantification of ascorbic acid using Prussian blue and digital...

In this study, we report the development of an innovative cotton thread-based colorimetric sensor coupled with a smartphone digital image-based (DIB) method for the quantification of L-ascorbic acid (L-AA). The designed microfluidic cotton thread-based analytical device (µTAD) relies on a redox reaction involving Prussian Blue (PB) and L-AA, which reduces PB, causing a reduction in its blue colour. The experimental conditions optimized using a central composite design lead to a microanalytical device with a sample consumption of only 30 µL, a linear range from 1.0 to 4.6 mg L^-1 (R² = 0.993), and a limit of detection of 0.18 mg L^-1. Moreover, a satisfactory recovery from 87.2% to 106% for complex samples such as fruit pulps was obtained. Moreover, using iodometric titration as a reference method, no significant differences at a 95% confidence level were obtained, confirming the reliability and effectiveness of the proposed method. Thus, this new method is fast (10 to 25 min) and cost-effective (USD 10 cents for a device) with a score of 0.85 (85%) for a green metric based on the AGREE calculator, providing a precise (<3.5%) and accurate (<6.5%) approach.