Erratum to: Plasmonic enhancement of the upconversion luminescence in a Yb3+ and Ho3+ co-doped gold-ZnO nanocomposite for use in multimodal imaging

Abstract

The authors report on upconversion (UC) nanocrystals based on a gold-ZnO nanocomposite that enables HeLa cells to be characterizes via fluorescence imaging (FI), magnetic resonance imaging (MRI) and upconversion luminescence (UCL) imaging. The Yb3+ and Ho3+ doped gold-ZnO nanocomposite (Au-ZnO:Yb3+/Ho3+) was fabricated through a microwave-assisted route and possesses an irregular morphology. Inductively coupled plasma mass spectrometry (ICP-MS) shows the doping fractions of Yb3+ and Ho3+ to be 4.0% and 0.38% respectively. The nanocomposite shows UCL upon NIR irradiation at a wavelength of 980 nm. The emission spectrum has two main emission bands, one peaking at 544 nm (green emission), and the other at 658 nm (red emission). The red emission is stronger than the green emission, and the pump power dependence of upconversion intensity underpins a 2-photon UC process. The inherent down-conversion luminescence (DCL) of ZnO is preserved with enhanced intensity in the gold-ZnO nanocomposite. The plasmonic enhancement of both UCL and DCL can be clearly observed. Doping with Ho3+ renders paramagnetism to the nanocomposite, with a magnetization value of 18.91 emu⋅g−1 at room temperature. The Au-ZnO:Yb3+/Ho3+ nanocomposite exhibit a longitudinal relaxivity (r1) of 0.12 s−1⋅mM−1 and a transverse relaxivity (r2) of 27.23 s−1⋅mM−1. Their substantial transverse relaxivity makes the nanocrystals most viable T2 MRI contrast agents. The cytotoxicity of nanocomposite was tested in HeLa cells by applying the MTT assay and by morphological studies. The nanocrystals are found to be biocompatible in up to50 μg⋅mL−1 concentration for an incubation time of 48 h. The nanocomposite is well taken up by HeLa cells. Its biocompatibility, UCL, DCL and its substantial magnetism make this nanocomposite as most viable nanoprobe for multimodal imaging.