title: Single-Particle Ratiometric Pressure Sensing Based on "Double-Sensor" Colloidal Nanocrystals.
abstract: Ratiometric pressure sensitive paints (r-PSPs) are all-optical probes for monitoring oxygen flows in the vicinity of complex or miniaturized surfaces. They typically consist of a porous binder embedding mixtures of a reference and a sensor chromophore exhibiting oxygen-insensitive and oxygen-responsive luminescence, respectively. Here, we demonstrate the first example of an r-PSP based on a single two-color emitter that removes limitations of r-PSPs based on chromophore mixtures such as different temperature dependencies of the two chromophores, cross-readout between the reference and sensor signals and phase segregation. In our approach, we utilize a novel "double-sensor" r-PSP that features two spectrally separated emission bands with opposite responses to the O2pressure, which boosts the sensitivity with respect to traditional reference-sensor pairs. Specifically, we use two-color-emitting dot-in-bulk CdSe/CdS core/shell nanocrystals, exhibiting red and green emission bands from their core and shell states, whose intensities are respectively enhanced and quenched in response to the increased oxygen partial pressure that effectively tunes the position of the nanocrystal's Fermi energy. This leads to a strong and reversible ratiometric response at the single particle level and an over 100% enhancement in the pressure sensitivity. Our proof-of-concept r-PSPs further exhibit suppressed cross-readout thanks to zero spectral overlap between the core and shell luminescence bands and a temperature-independent ratiometric response between 0 and 70 °C.
authors.affiliation: Dipartimento di Scienza dei Materiali, Università degli Studi di Milano-Bicocca , via Cozzi 55, I 20125 Milano, Italy.
authors.forename: Monica
authors.identifier: 0000-0003-3524-9546
authors.initials: M
authors.lastname: Lorenzon
authors.affiliation: Dipartimento di Scienza dei Materiali, Università degli Studi di Milano-Bicocca , via Cozzi 55, I 20125 Milano, Italy.
authors.forename: Valerio
authors.initials: V
authors.lastname: Pinchetti
authors.affiliation: Dipartimento di Scienza dei Materiali, Università degli Studi di Milano-Bicocca , via Cozzi 55, I 20125 Milano, Italy.
authors.forename: Francesco
authors.initials: F
authors.lastname: Bruni
authors.affiliation: Chemistry Division and Center for Advanced Solar Photophysics, Los Alamos National Laboratory , Los Alamos, New Mexico 87545, United States.
authors.forename: Wan Ki
authors.identifier: 0000-0002-3832-2449
authors.initials: WK
authors.lastname: Bae
authors.affiliation: Dipartimento di Scienza dei Materiali, Università degli Studi di Milano-Bicocca , via Cozzi 55, I 20125 Milano, Italy.
authors.forename: Francesco
authors.initials: F
authors.lastname: Meinardi
authors.affiliation: Chemistry Division and Center for Advanced Solar Photophysics, Los Alamos National Laboratory , Los Alamos, New Mexico 87545, United States.
authors.forename: Victor I
authors.identifier: 0000-0003-1158-3179
authors.initials: VI
authors.lastname: Klimov
authors.affiliation: Dipartimento di Scienza dei Materiali, Università degli Studi di Milano-Bicocca , via Cozzi 55, I 20125 Milano, Italy.
authors.forename: Sergio
authors.identifier: 0000-0002-5993-855X
authors.initials: S
authors.lastname: Brovelli
keywords: Ratiometric oxygen sensing; core/shell; dot-in-bulk nanocrystals; dual color emission; photocharging; pressure sensitive paints