Abstract
Bare lanthanide-doped nanoparticles (LnNPs), in particular, NaYF(4):Yb(3+),Tm(3+) NPs (UC(Tm)), have been seeded in situ with gold cations to be used in the subsequent growth of gold nanoclusters (AuNCs) in the presence of glutathione (GSH) to obtain a novel UC(Tm)@AuNC nanoheterostructure (NHS) with a raspberry-like morphology. UC(Tm)@AuNC displays unique optical properties (multiple absorption and emission wavelengths). Specifically, upon 350 nm excitation, it exhibits AuNC photoluminescence (PL) (500-1200 nm, λ(max) 650 nm) and Yb emission (λ(max) 980 nm); this is the first example of Yb sensitization in a UC(Tm)@AuNC NHS. Moreover, under 980 nm excitation, it displays (i) upconverting PL of the UC(Tm) (at the blue, red and NIR-I, ca. 800 nm, regions); (ii) two-photon PL of AuNC; and (iii) down-shifting PL of thulium (around 1470 nm). The occurrence of energy transfer from UC(Tm) to AuNCs in the UC(Tm)@AuNC NHS was evidenced by the drastic lengthening of the AuNC PL lifetime (τ(PL)) (from few hundred nanoseconds to more than one hundred microseconds). Initial biological assessment of UC(Tm)@AuNC NHSs in vitro revealed high biocompatibility and bioimaging capabilities upon near-infrared excitation.