Two-photon fluorescence imaging of mitochondria viscosity with water-soluble pyridinium inner salts

Rational design of mitochondrial viscosity probes with water-soluble two-photon (TP) fluorescence probe still remains a challenge in practical biological applications. Herein, three novel water-soluble TP active sulfosalt derivatives (Mito-Z, Mito-H,...

Photoluminescence mechanism of carbon dots: triggering high-color-purity red fluorescence emission through edge amino protonation

Due to complex structure and surface functionalities, photoluminescence mechanisms of Carbon Dots are unknown, and it is challenging to synthesize Carbon Dots to achieve the desired optical properties. Herein, Carbon Dots simultaneously exhibiting high-color-purity (FWHM~24 nm) long wavelength one-photon fluorescence emission at 620 nm and NIR induced two-photon fluorescence emission at 630 and 680 nm are prepared by edge amino protonation treatment. Systematic analysis reveals that the protonation of 2,3-diaminophenazine changes the molecular state of Carbon Dots, decreases the photon transition band gap, and triggers red fluorescence emission with the dramatically narrowed peak width. As the oxidation products of reactant o-phenylendiamine, the emergence of 2,3-diaminophenazine as a photoluminescence determiner suggests that fluorophore products of precursor conversion are viable determinants of the desired luminescence properties of Carbon Dots. This work shows a new way for predicting and controlling photoluminescence properties of Carbon Dots, and may guide the development of tunable Carbon Dots for a broad range of applications.

3-photon fluorescence and third-harmonic generation imaging of myelin sheaths in mouse digital skin in vivo: A comparative study

Myelin sheaths wrapping axons are key structures that help maintain the propagation speed of action potentials in both central and peripheral nervous systems (CNS and PNS). However, noninvasive, deep imaging technologies visualizing myelin sheaths in the digital skin in vivo are lacking in animal models. 3-photon fluorescence (3PF) imaging excited at the 1700-nm window enables deep imaging of myelin sheaths, but necessitates labeling by exogenous fluorescent dyes. Since myelin sheaths are lipid-rich structures which generate strong third-harmonic signals, in this paper, we perform a detailed comparative experimental study of both third-harmonic generation (THG) and 3PF imaging in the mouse digital skin in vivo. Our results show that THG imaging also enables visualization of myelin sheaths deep in the mouse digital skin, which shows colocalization with 3PF signals from labeled myelin sheaths. Besides its superior label-free advantage, THG does not suffer from photobleaching due to its 3PF property.