Giant Light‐Harvesting in Dye‐Loaded Nanoparticles Enhanced by Blank Hydrophobic Salts

Abstract

Light‐harvesting is a fundamental process in nature, which inspires researchers to develop artificial systems for photocatalysis, photovoltaics, and biosensing. A previously introduced light‐harvesting nanoantenna, based on polymeric nanoparticles (NPs) loaded with rhodamine dyes and bulky hydrophobic counterions, provides a record‐breaking antenna effect ≈1000. However, the high dye cooperativity of its thousands of encapsulated dyes causes energy losses by traces of self‐quenched dye aggregates. Here, it is found that these imperfections can be suppressed by blank hydrophobic salts (BHS) formed by the same bulky counterion (fluorinated tetraphenylborate) with an optically inactive cation, analogs of ionic liquids. The presence of BHS increases twofold the fluorescence quantum yields and fluorescence lifetimes of NPs and suppresses their fluorescence blinking. This study assumes that BHS provides an excess of bulky counterions that excludes traces of dye aggregates. As a result, an efficient Forster resonance energy transfer (FRET) is achieved from 40 000 dye donors to a single acceptor within a 70 nm particle, leading to the antenna effect of 4800, which is by far the highest value reported to date. Using this nanoantenna, a single‐molecule detection of the FRET acceptor is realized at low excitation power using an RGB camera of a smartphone.

Photophysics of fluorescent nanoparticles based on organic dyes – challenges and design principles

“…by introducing non absorbing spacers either as an additional matrix or as "blank salts" in the case of ionic organization. 41,126,127 For dye loaded polymer NPs the local density of dyes can also be modulated by the polarity of the polymer matrix to either favour segregation or isotropic distribution of dyes. 115 A promising approach is to use the efficient energy migration as an advantage by introducing a red shied dopant emitter into the NP.…”