Paper chip-based colorimetric assay for detection of Salmonella typhimurium by combining aptamer-modified Fe3O4@Ag nanoprobes and urease activity inhibition

摘要

A rapid and sensitive colorimetric assay is described for Salmonella typhimurium(S. typhimurium) detection using urea/phenol red impregnated test paper. Aptamer-modified Fe3O4@Ag multifunctional hybrid nanoprobes (apt-Fe3O4@Ag NPs) were used to specifically captured S. typhimurium; the nanoprobes were quickly etched by H2O2 to form Ag+. The generated Ag(+)can inhibit the urease-catalyzed hydrolysis reaction of urea to produce NH4+. Consequently, the as-prepared test paper displayed a yellow color. In the presence of S. typhimurium, the target bacteria can cause aggregation of apt-Fe3O4@Ag NPs, and the deposited Ag on the nanoprobe's surface is shielded against H2O2-induced oxidative decomposition leading to reduced Ag(+)production. The catalytic activity of urease cannot be inhibited completely by inadequate amount of Ag+. An obvious color change from yellow to pink can be monitored directly using our test paper as a result of increased NH4+. The entire assay procedure could be completed within 1 h. A limit of detection of 48 cfu/mL is achieved with a linear range of 1 x 10(2)to 1 x 10(6) cfu/mL. The recoveries of S. typhimuriumspiked in pure milk samples were 92.48-94.05%.