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

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 (<i>R</i>² = 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.