Two-Photon Excitation/Red Emission, Ratiometric Fluorescent Nanoprobe for Intracellular pH Imaging

Abstract

Herein, we describe a novel two-photon excitation/red emission-based ratiometric pH nanosensor consisting of a pH-sensitive two-photon dye and Tm3+-doped upconversion nanoparticles (UCNP). The fluorescence emission ratio between the dye (610 nm) and UCNPs (810 nm) (I610/I810) provides a linear indicator of pH values in the range from pH 4.0 to 6.5 with high sensitivity. These nanoprobes selectively accumulate in the lysosomes of cells, making them suitable for lysosomal pH tracking. This pH nanoprobe has been successfully applied in visualizing chemically stimulated changes of intracellular pH in living cells and tissues.

Carbon-Dot-Based Probe Designed to Detect Intracellular pH in Fungal Cells for Building Its Relationship with Intracellular Polysaccharide

“…As summarized in Table S1, this probe is quite different from the previous ratiometric probes based on CDs, commonly by combining pH-sensitive CDs and insensitive fluorescent dye or pH-insensitive CDs and sensitive fluorescent dye and by CDs loading pH-sensitive and -insensitive dyes. ,, …”

“…These CDs were just used to qualitatively investigate the activities of fungi; therefore, fluorescence intensity at a single wavelength as a signal was enough for the required accuracy. However, when accurate measurements are performed in cells, ratiometric fluorescent probes would be preferred because the ratio of two emission intensities at different wavelengths as a response signal can minimize and even eliminate the unwanted effects induced by the variations of distribution inhomogeneity, probe concentration, and environmental conditions. , To construct a ratiometric pH probe-based CDs, a pH-sensitive fluorescent molecule and a pH-insensitive moiety are generally conjugated into one system by covalent binding and electrostatic interaction or enclosed into one microsphere. , …”

Optical and magnetic resonance imaging approaches for investigating the tumour microenvironment: state-of-the-art review and future trends

“…The fluorophore or the sensor on the other hand can be excited in a small volume, where it can simultaneously absorb two photons that together provides enough energy for excitation. [173] Here the probability of this event is very unlikely outside the excitation cone that further reduces the noise from the sample and enhances the contrast in two photon microscopy. The pH-activatable nanoprobes are based on mechanisms like Förster Resonance Energy Transfer (FRET) and the Self-Aggregation Associated Energy Transfer (SAET).…”

Charge Neutralization Strategy to Construct Salt-Tolerant and Cell-Permeable Nanoprobes: Application in Ratiometric Sensing and Imaging of Intracellular pH

“…8−11 Determination of pH changes in living cells is of great importance for a better understanding of pH-related physiological and pathological processes, as well as providing a good reference for the diagnosis and treatment of some diseases. 12,13 Fluorescence spectroscopy is one of the most commonly used techniques to measure intracellular pH because of its inherent advantages such as high temporal−spatial resolution, minimal invasiveness, excellent signal-to-noise ratio, and simple operation. 14−17 A variety of fluorescent pH sensors have been designed based on fluorescent pH-sensitive dyes, including fluorescein and its derivatives, benzoxanthene dyes, cyanine dyes, and others.…”

“…The balance of intracellular pH is essential for maintaining normal physiological processes in cells and organisms. − In normal mammalian cells, intracellular pH varies from 4.5 (lysosomes) to 8.0 (mitochondria). − Abnormalities in intracellular pH regulation are frequently associated with cellular injury/dysfunction, which would cause various diseases such as cancers, neurodegenerative disorders, and vascular diseases. − Determination of pH changes in living cells is of great importance for a better understanding of pH-related physiological and pathological processes, as well as providing a good reference for the diagnosis and treatment of some diseases. , …”