A near-infrared excited Förster resonance energy transfer-based fluorescent sensor using core–shell upconversion nanoparticles functionalized with rhodamine B derivative for highly selective detection of Hg2+

A near-infrared (NIR)-excitable ratiometric fluorescent nanosensor, CS-UCNP@mSiO 2 –RBPA, was developed for the selective and sensitive detection of Hg 2+ . The nanosensor is constructed by grafting a rhodamine B-derived probe (RBPA) onto mesoporous silica-coated core–shell NaYF 4 :Yb,Er upconversion nanoparticles (UCNPs). Upon 980 nm excitation, the UCNPs exhibit characteristic green emission at ~ 543 nm and red emission at ~ 655 nm. In the presence of Hg 2+ , the spirolactam ring of RBPA opens specifically, producing a yellow-emitting species that enables efficient Förster resonance energy transfer (FRET) from the UCNP donor. This leads to a Hg 2+ concentration-dependent quenching of green emission and a synchronous enhancement of yellow fluorescence at ~ 584 nm, with the red emission acting as a stable internal reference. The nanosensor shows outstanding selectivity toward Hg 2+ against other competing metal ions and performs optimally at neutral pH. It presents a good linear response in the Hg 2+ concentration range 0–70 µM via UV–vis absorption, and achieves an ultra-low detection limit of 14 nM based on the ratiometric fluorescence signal (I 584 /I 655 ). Benefiting from NIR excitation, ratiometric self-calibration and excellent specificity, this fluorescent nanoplatform holds great potential for practical applications in environmental monitoring and biological analysis. Section Graphical The alternative text for this image may have been generated using AI.