One of the main challenges for any applications of nanoparticles in biological media is to control the surface chemistry of the nanomaterials preventing chemical disintegration and agglomeration. When the surface effects dominate over the bulk properties, which is especially the case for small lanthanide doped NaYF4 nanocrystals, the surface capping significantly affects the brightness of the upconversion luminescence. Here, we present the influence of commonly used buffer systems such as N-(2-hydroxyethyl)piperazine-N’-(2-ethanesulfonic acid) (HEPES) and 2-(N morpholino)ethanesulfonic acid hydrate (MES) on the stability and surface chemistry of NaYF4:Yb,Er nanoparticles. The results indicate that surface modifications by ligand exchange provide a simple strategy for attaching many different ligands to the particle surface and render them water dispersible. Nevertheless, one has to take into account that particle surfaces are not fully covered and certain buffers, especially those with sulfo groups, may alter the surface chemistry with time.
Upconverting luminescent nanoparticles (UCNPs) represent an interesting class of nanomaterials for bioanalytical applications. Due to their excitation in the near infrared region of the spectra, no fluorescence of biological compounds is trigged. Compared to other nanomaterials like quantum dots they exhibit low cytotoxicity, high photostability, no blinking and chemical inertness. Nevertheless, UCNPs suffer from low quantum efficiency. Here we report on two different core-shell particle systems which have a core consisting of NaYF4 doped with Yb3+/ Tm3+ and an additional inert shell (NaYF4) or an active shell (NaYF4 doped with Yb3+/Nd3+). Nanoparticles without Yb3+ as sensitizer can be excited at 980 nm. However, water has an absorption band in this region. This results in a reduction of the upconversion efficiency in aqueous systems and a heating of the solution. For bioanalytical application, more beneficial is the shifting of the wavelength to 808 nm by additional doping of the shell with Nd3+. Both core-shell systems were investigated in respect to the monitor enzymatic reactions of dehydrogenases and oxidases involving the generation of either NADH or FADH2.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.