Paper-based device for the colorimetric assay of bilirubin based on in-situ formation of gold nanoparticles.

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. Graphical abstractSchematic representation of the paper-based colorimetric assay for the detection of bilirubin based on the in-situ formation of gold nanoparticles. A color band is generated for visual interpretation and used for the testing of bilirubin in urine.

Gold nanoparticles decorated reduced graphene oxide nanolabel for voltammetric immunosensing.

This study describes the development and testing of a simple and novel enzyme-free nanolabel for the detection and signal amplification in a sandwich immunoassay. Gold nanoparticles decorated reduced graphene oxide (rGOAu) was used as the nanolabel for the quantitative detection of human immunoglobulin G (HIgG). The rGOAu nanolabel was synthesised by one pot chemical reduction of graphene oxide and chloroauric acid using sodium borohydride. The pseudo-peroxidase behaviour of rGOAu makes the nanolabel unique from other existing labels. The immunosensing platform was fabricated using self-assembled monolayers of 11-mercaptoundecanoic acid (11-MUDA) on a gold disc electrode. The covalent immobilisation of antibody was achieved through the bonding of the carboxyl group of 11-MUDA and the amino group of the antibody using chemical linkers [1-ethyl-3-(3-dimethylaminopropyl)carbodiimide] and N-hydroxysuccinimide. The fabricated immunosensor exhibited a linear range that included HIgG concentrations of 62.5-500 ng ml-1. The sensor was also used for the testing of HIgG in the blood sample.