A paper-based colorimetric assay for the determination of bilirubin has been developed. The method is based on the in-situ reduction of chloroauric acid to form gold nanoparticles. A chromatographic paper was patterned using a wax printer. Chloroauric acid was drop-cast onto the reagent zone. In the presence of bilirubin, gold(III) ions are reduced and form gold nanoparticles. This leads to a color change from yellow to purple. The intensity of the purple color (peak at 530 nm) increases with bilirubin concentration in the 5.0 to 1000 mg L−1 range. The detection limit is 1.0 mg L−1. For the quantification of bilirubin, images were captured using a digital camera, and data were processed with the help of machine learning-based supervised prediction using Random Forest classification. The method was applied to the determination of bilirubin in urine samples. The spiked urine samples exhibit more than 95% recovery.
R. P. Edachana, Kumaresan, A., Balasubramanian, V., Thiagarajan, R., Dr. Bipin G. Nair, and Dr. Satheesh Babu T. G., “Paper-based device for the colorimetric assay of bilirubin based on in-situ formation of gold nanoparticles”, Microchimica Acta, vol. 187, p. 60, 2019.