Functionalized gold nanoparticles for point-of-care nucleic acid detection

Abstract

Gold nanoparticles (AuNPs) have been extensively investigated for colorimetric detection of nucleic acid. This is enabled by the unique interparticle distance-dependent optical property of AuNPs. The solution color for monodispersed particles appears red (for widely used 13 nm AuNPs) but turns purple upon aggregation due to a red-shift in the surface plasmon resonance absorption band. Until now, all the reported platforms are not practical for point-of-care testing. To address this, our group developed a new platform by incorporating 11-mercaptoundecanoic acid-modified AuNPs (MUA–AuNPs) into loop-mediated isothermal amplification (LAMP). When added into the LAMP reaction mixture, MUA–AuNPs aggregated as a result of ion-templated chelation between the carboxyl groups and magnesium ion (Mg2+, which plays an indispensable role in LAMP reaction as an enzyme cofactor). The solution color changed from red to purple. In the presence of a specific target DNA sequence, the LAMP reaction occurred and pyrophosphate ion (P2O74−) was generated as a reaction by-product. The chelated Mg2+ was then extracted by P2O74−, leading to the deaggregation/redispersion of the MUA–AuNPs and the solution color turned red. This new platform possesses all the ideal features for point-of-care testing, including simple preparation and operation, low cost, high sensitivity, and worry-free carryover contamination control.