Linear stimuli-responsive upconversion luminescent nanoprobes coupled with graphene

Upconversion nanoparticles (UCNPs) have been widely used as powerful bio-probes, but still suffer from low sensitivity and complex nonlinear response. Here, we show that local optical mode and surface scattering and absorption of core-shell UCNPs can be manipulated by coupling to the whispering-gallery modes of glass microfibers with graphene interlayer (a composite nanosystem). Graphene can tune the refraction and scattering of glass microfibers to excitation light, and simultaneously the photon transmission from glass microfibers to upconversion nanoparticles, so that the composite nanosystem with graphene presents different luminescent property from that without graphene. The linear stimuli-responsive upconversion luminescence is indirectly realized via stimuli of graphene in the composite nanosystem since graphene plays a role of ‘light gate’. This composite nanosystem could be used as a linear-response and highly-sensitive luminescent sensor for the detection of methanol with a limit of 0.052 ppm at room temperature.