Highly sensitive and selective label-free optical detection of mercuric ions using photon upconverting nanoparticles

We demonstrate a fluorescence-based, label-free detection scheme that reports the presence of Hg(II) ion using photon upconverting nanoparticles. A single-stranded DNA containing a number of thymine bases to be used as the Hg2+-capturing element is covalently attached to the photon upconverting NaYF4:Yb3+,Tm3+ nanoparticles. Under the illumination of 980 nm laser, energy transfer takes place between the NaYF4:Yb3+,Tm3+ nanoparticles as the donor and SYBR Green I. a DNA intercalating dye, as the acceptor. By monitoring the ratio of the acceptor emission to the donor emission, we can quantitatively detect the presence of the mercuric ions with a directly observed detection limit of 0.06 nM. The remarkably high signal-to-noise ratio of photon upconverting particles leads to very high sensitivity and specificity without the need of fluorophore labeling. The sensor also does not suffer from photobleaching. (C) 2010 Elsevier B.V. All rights reserved.