Flexible Graphene Substrate for Fluorescence Quenching in Upconversion Lanthanide Nanoparticles.
Mukesh Kumar Thakur1*, Akash Gupta1, Cheang Weng Lam1, Surojit Chattopadhyay1
1Institute of Biophotonics, National Yang-Ming University, Taipei, Taiwan
* presenting author:Mukesh Kumar Thakur, email:mukeshkumar1111@gmail.com
Graphene has various proven applications due to its unique optical, electrical, thermal and mechanical properties [1-2]. Among them, fluorescence quenching is a powerful technique for bio-sensing applications. Graphene showed efficient fluorescent quenching property, in downconversion fluorophores, compared to metals [3]. In this work, we demonstrate how graphene quenches the fluorescence in lanthanide doped up-conversion nanoparticles (UCNPs). The UCNPs are special fluorophores because it emits higher energy photons when excited by low energy photons. We proceed to demonstrate that the fluorescence quenching can be controlled with the graphene quality, especially by the number of graphene layers. For this, we prepared four sets of graphene samples by varying the CH4 flow rate (15-45 sccm) in a thermal chemical vapour deposition system (T-CVD) to obtain multi- to few – layer graphene. The number of layers in graphene can be estimated from the ratio of the 2D, and G bands in Raman spectroscopy. After optimizing graphene, by using Raman spectroscopy, it was conjugated with NaYF4:Yb,Er UCNPs that showed prominent green emission when irradiated with 980 nm laser. The fluorescence of the UCNPs in presence and absence of the graphene layer shows strong modulation. In presence of graphene the fluorescence was quenched nearly 75%, the highest being the few-layer graphene. The entire study was performed on as grown graphene on copper so this result need to be investigated further on other substrate to see if total quenching could be observed in these UCNP fluorophores.
[1] Geim, A. K.; Novoselov, K. S. “The rise of graphene” Nat. Mater. 2007, 6, 183−191
[2] Geim, A. K. “Graphene: status and prospects” Science 2009, 324, 1530−1534
[3] Amal Kasry, et al. “Highly Efficient Fluorescence Quenching with Graphene”J. Phys.Chem.C 2012, 116, 2858-2862

Keywords: Graphene, upconversion nanoparticles, fluorescence spectroscopy, CVD, Lanthanide