Triplex DNA-Modified Gold Nanoparticles with a Tunable pH Detection Range for Multiple Colorimetric Sensing Scenarios

Here, we design triplex DNA-modified gold nanoparticles that respond to a tunable pH range. Homopyrimidine strand-modified gold nanoparticles and homopurine/homopyrimidine duplexes are utilized in the system. Upon acidification, the duplexes bind to gold nanoparticle-conjugated strands through Watson-Crick and Hoogsteen base pairing, forming triplex DNA with blunt ends on the nanoparticle. The modified DNA outer layer generates base stacking interaction during gold nanoparticle collision, forming aggregate networks and inducing color change. The responding pH range can be tuned by varying the A/T proportion. Its applications as an accurate indicator in acid-base titration, for visual determination of acid rain, and in colorimetric detection of 3-nitropropionic acid that exists in deteriorated sugar cane are demonstrated.