Multicolour emissions through Bi-directional energy transfer in Nd3+-sensitized core/shell/shell upconverting nanoparticles for bio imaging applications

Abstract

Lanthanide (Ln3+)-doped upconverting nanoparticles (UCNPs) have attracted a great deal of research interestdue their wide range of biological applications, both in vitro and in vivo. Such UCNPs carry prominent advantagessuch as high spatial emission resolution, deep tissue penetration depth of near-infrared (NIR) excitation light,reduced light scattering and low autofluorescence background signal. However, the 980 nm laser, generallyapplied to trigger the Yb3+-sensitized upconversion processes is strongly absorbed by water molecules inbiological structures and could cause severe overheating effects that damage cells and tissues. To address thisproblem, recent research has focused on the extension of upconversion excitation spectrum to shorterwavelengths (especially, in the vicinity of 808 nm), where water molecules do not absorb significantly. There areonly few reports available on NIR dye-sensitized upconversion emission as a strategy to shift the excitation to ashorter wavelength without compromising the excitation efficiency. Taking this fundamental concept into account,we for the first time, successfully designed water dispersible NIR-II dye (IR- 1061) sensitized NaYF4:Yb3+(30)/Tm3+(0.5)@NaYF4:Yb3+(X = 0,2,5,10,20) core/active shell UCNPs, as part of my postdoctoral project atthe institute of origin (IQ, UNESP). We achieved around 70% enhancement in NIR-I emission (i.e. 800 nmemission of Tm3+ ion). Unfortunately, this emission is not suitable for bioimaging application under 980 laserexcitation since the emission of UCNPs overlaps strongly with the absorption of water dispersible IR-1061 dye inthis region. To address the issue of NIR laser induced tissue damage, we now are working to introduce Nd3+ ionsas NIR absorbers and sensitizers in the conventional Yb3+-doped core/shell/shell UCNPs to ensure successiveNd3+’Nd3+’Yb3+’X3+ ( X = Tm3+ and Ho3+, activator) energy transfer in a bi-directional manner. In the periodof 12 months research internship at INRS-EMT, located in Varennes (a suburb of Montréal), Canada, Nd3+-sensitized core/shell/shell UCNPs will be examined for their potential in bioimaging (in vitro and in vivo)applications using the state-of-the-art research infrastructure available in Prof. Vetrone's research group. Themain objectives of the proposed research work at the Canadian host institute will be (i) surface modification of theNd3+-sensitized core/shell/shell UCNPs following polymer coating, silica coating and ligand exchange methods (ii)characterization of structural and optical properties of these water dispersible biocompatible nanoparticles and (iii)finally, test these modified UCNPs for bioimaging (in vitro and in vivo) applications. Participation in this research... (AU)