Development of a Colorimetric Urease Test Based on Au NPS Capped with Anthocyanin for the Rapid Detection of Helicobacter pylori through Multiple Readouts

In this work, we have reported use of anthocyanin capped gold nanoparticles (Ant@Au NPs)‐incorporated colorimetric urease test for rapid, sensitive and economic detection of Helicobacter pylori (H. pylori). This test containing Ant@Au NPs, urea, sodium phosphate buffer (PBS) and sodium azide (NaN3) was prepared at pH 5 with red solution owing to dispersity of Ant@Au NPs, urease enzyme secreted from H. pylori cause production of ammonia (NH3) via hydrolysis of urea, then which makes reaction environment alkaline (pH 8.2). The limit of detection for this Ant@Au NPs based urease test was determined to be to 102 CFU/mL with proportional to increasing incubation time. However, distinct color change was observed with 104 CFU/mL H. pylori suspensions in 15 min. The anthocyanin molecules existing on surface of Ant@Au NPs were easily deprotonated from hydroxyl groups in the alkaline condition, which caused various changes on Ant@Au NPs including quite much negative charges on the surface of Ant@Au NPs analyzed by Zeta potential, aggregation of Ant@Au NPs demonstrated by STEM, DLS and spectrophotometer, and turning the color of test solution to purple evaluated by a naked eye and digital process imaging system. The Ant@Au NPs test based detection mechanism relies on hydrolysis of urea by urease enzyme released from the H. pylori, then, reaction environment became much alkaline and induces aggregation of the Au NPs with six different responses including changes in color of Ant@Au NPs solution visually detected by naked eye, RGB analysis, absorbance peaks, DLS size, zeta potential and STEM image.