Scheme 2. Schematic Illustration of the Action Mechanism of the Proposed Sensor.

(A) The presence of the target sequence allows the hybridization and brings in close proximity the azide group on probe 1 and the DBCO groups on probes 1 and 2 producing the SPAAC reaction that gives NaYF₄;Yb,Er@SiO₂-dsDNA-biotin nanoparticles. (B) Biotin moieties on the surface of the UCNPs allow their immobilization on the surface of the streptavidin-coated well-plates. (C) The fluorescence detection was performed using the homemade device.