No abstract

Molecular beacons typically use organic molecules or nanomaterials as quenchers. Many transition‐metal ions have excellent fluorescence quenching ability, and the aim of this study was to recruit them as small quenchers in DNA detection. Cr3+ has a slow ligand exchange rate, forming stable adducts with DNA. With its strong fluorescence quenching ability, the site‐specific labeling of Cr3+ on DNA to form a new type of molecular beacon was investigated. The kinetics of quenching by Cr3+ were measured for single‐ and double‐stranded DNA as a function of salt concentration, pH, and Cr3+ ion concentration. The goal was to achieve a selective reaction with the single‐stranded but not double‐stranded regions. The reaction mechanism was also probed by adding adenosine triphosphate, revealing two Cr3+‐binding modes: fast but unstable, and slow but stable. A partially complementary duplex was designed with a short polyguanine overhang, which, under optimal conditions, enabled selective labeling of the overhanging region with Cr3+. The resulting sequence was tested as a molecular beacon with a detection limit of 0.3 nm DNA and a saturated fluorescence enhancement of fivefold. With a 13‐nucleotide target DNA, the single mismatch discrimination of the beacon was 22‐fold. This study demonstrates the possibility of forming useful Cr3+ adducts with DNA. Such adducts are not only useful for developing biosensors but also for constructing new materials.

Opposite changing dual-emission luminescence of gold nanoparticles by sulfhydryl-containing compounds was found for the development of a pesticide biosensing strategy.