Abstract
Quantification of nanoparticle-molecule interaction at a single-molecule level remains a daunting challenge, mainly due to ultra-weak emission from single molecules and the perturbation of the local environment. Here we report the rational design of an intraparticle-surface energy transfer (i-SET) process, analogous to high doping concentration-induced surface quenching effects, to realize single-molecule sensing by nanoparticle probes. This design, based on a Tb3+-activator-rich core-shell upconversion nanoparticle, enables a much-improved spectral response to fluorescent molecules at single-molecule levels through enhanced non-radiative energy transfer with a rate over an order of magnitude faster than conventional counterparts. We demonstrate a quantitative analysis of spectral changes of one to four fluorophores tethered on a single nanoparticle through i-SET spectroscopy. Our results provide opportunities to identify photoreaction kinetics at single-molecule levels and provide direct information for understanding behaviors of individual molecules with unprecedented sensitivity.
Highlights
Quantification of nanoparticle-molecule interaction at a single-molecule level remains a daunting challenge, mainly due to ultra-weak emission from single molecules and the perturbation of the local environment
Single-nanoparticle probes can be used to monitor chemical and physical changes of individual molecules, especially for those occurring at the interface of catalytic materials[4,5]
We demonstrate that a high concentration of activators can facilitate non-radiative resonance energy transfer from upconversion nanoparticles to surface-decorated fluorescent molecules by adopting a intraparticlesurface energy transfer (i-SET) process (Fig. 1)
Summary
Quantification of nanoparticle-molecule interaction at a single-molecule level remains a daunting challenge, mainly due to ultra-weak emission from single molecules and the perturbation of the local environment. We report the rational design of an intraparticlesurface energy transfer (i-SET) process, analogous to high doping concentration-induced surface quenching effects, to realize single-molecule sensing by nanoparticle probes. This design, based on a Tb3+-activator-rich core-shell upconversion nanoparticle, enables a muchimproved spectral response to fluorescent molecules at single-molecule levels through enhanced non-radiative energy transfer with a rate over an order of magnitude faster than conventional counterparts. Lanthanide-doped upconversion nanoparticles are capable of converting multiphoton near-infrared excitation into singlephoton ultraviolet/visible emission[9,10] These nanoparticles demonstrate significant advantages over other luminescence probes including non-blinking, high photostability, and good brightness uniformity at a single particle level. The zero background from fluorescent acceptors upon anti-Stokes excitations can permit highly selective recognition and ultrasensitive quantification of single-molecule targets
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