Rhodamine-based lysosome-targeted fluorescence probes: high pH sensitivity and their imaging application in living cells

Rhodamine-Based Cyclic Hydroxamate as Fluorescent pH Probe for Imaging of Lysosomes

Monitoring the microenvironment within specific cellular regions is crucial for a comprehensive understanding of life events. Fluorescent probes working in different ranges of pH regions have been developed for the local imaging of different pH environments. Especially, rhodamine-based fluorescent pH probes have been of great interest due to their ON/OFF fluorescence depending on the spirolactam ring's opening/closure. By introducing the N-alkyl-hydroxamic acid instead of the alkyl amines in the spirolactam of rhodamine, we were able to tune the pH range where the ring opening and closing of the spirolactam occurs. This six-membered cyclic hydroxamate spirolactam ring of rhodamine B proved to be highly fluorescent in acidic pH environments. In addition, we could monitor pH changes of lysosomes in live cells and zebrafish.

Lysosome-targeting pH indicator based on peri-fused naphthalene monoimide with superior stability for long term live cell imaging

Lysosomal pH is altered in many pathophysiological conditions. We describe synthesis and spectral properties of a new lysosomal fluorescent marker dye suitable for microscopic evaluation of lysosomal distribution and pH changes.

Multifunctional gold nanoparticles as smart nanovehicles with enhanced tumour-targeting abilities for intracellular pH mapping and in vivo MR/fluorescence imaging

A number of multimodal agents have been developed for tumour imaging and diagnosis, but most of them cannot be used to study the detailed physiological or pathological changes in living cells at the same time. Herein, a series of pH-responsive magnetic resonance and fluorescence imaging (MRI/FI) dual-modal "nanovehicles" are developed and tested. These new dual-modal materials allow for intercellular pH sensing, and those with units that are dually sensitive towards both acidic and basic environments have the ability for intracellular pH mapping and can be used to quantify pH at the cellular level. In addition, detailed pH changes in organelles (including lysosomes and mitochondria) can be investigated at the same time. On the other hand, with the tumour-targeting peptide (cRGD)-modified dual-modal nanovehicles, in vivo tumour MR and fluorescence imaging, which is suitable for cancer diagnosis, can be achieved. Moreover, it has been proved that these materials can pass through the blood brain barrier (BBB). By combining the above mentioned promising properties, these novel multifunctional "nanovehicles" may provide a new method for studying the role of pH during cancer diagnosis and treatment.

Small-molecule fluorescent probes for specific detection and imaging of chemical species inside lysosomes

In the past few years, the preparation of novel small-molecule fluorescent probes for specific detection and imaging of chemical species inside lysosomes has attracted considerable attention because of their wide applications in chemistry, biology, and medical science. This feature article summarizes the recent advances in the design and preparation of small-molecule fluorescent probes for specific detection of chemical species inside lysosomes. In addition, their properties and applications for the detection and imaging of pH, H2O2, HOCl, O2˙-, lipid peroxidation, H2S, HSO3-, thiols, NO, ONOO-, HNO, Zn2+, Cu2+, enzymes, etc. in lysosomes are discussed as well.

Nanoporous silica nanoparticles functionalized with a fluorescent turn-on spirorhodamineamide as pH indicators

pH sensing by silica nanoparticles carrying a fluorescent turn-on spirorhodamineamide. Left/Right: Confocal imaging pH 7.4/2.0. Inset: SEM.

Lysosome-specific sensing and imaging of pH variations in vitro and in vivo utilizing a near-infrared boron complex

A NIR lysosome-targeting boron complex has been developed based on hemicyanine for monitoring pH variations in vitro and in vivo.

A quinoline-based fluorometric and colorimetric dual-modal pH probe and its application in bioimaging

The compound (E)-8-hydroxyl-2-[(E)-2-(2, 4-dihydroxyphenyl)vinyl]-quinoline (1) has been developed as a fluorometric and colorimetric dual-modal probe for pH detection in solution and in vivo. Remarkable changes in the fluorescence intensity with large Stokes shifts and colorimetric responses were observed as a function of pH. The sensing mechanisms involving protonation and deprotonation processes over the acidic and alkaline pH ranges were confirmed by ¹H NMR and IR spectroscopic analysis. Furthermore, the application of probe 1 for the imaging of live PC3 cells was successfully achieved. Test strips based on probe 1 were fabricated, and were found to act as a convenient and efficient pH test kits.

Construction of pH-Sensitive "Submarine" Based on Gold Nanoparticles with Double Insurance for Intracellular pH Mapping, Quantifying of Whole Cells and in Vivo Applications

A series of "submarines", which composed of gold nanoparticles and modified with rhodamine and fluorescein derivatives, were presented. With dual sensitive units for both acidic and basic environment, these "gold nano-submarines" not only allow efficient intracellular pH mapping but also provide more accurate quantitative detection of pH alteration under different stimuli with distinct pH quantification range. Moreover, they even have the ability to pass through the blood brain barrier (BBB).

A water-soluble pH fluorescence probe based on quaternary ammonium salt for bioanalytical applications

A novel fluorescence probe Rhodamine-Ethanediamine-Iodomethane (REI) was successfully prepared to serve as an efficient sensing platform for H(+) with fully reversibility mainly between the pH 4.2 and 7.2 in simple buffer solution. The introduction of quaternary ammonium salt with positive charge can not only manage to increase the solubility and sensitivity of probe REI, but also avoid the "alkalizing effect" due to charge-induced effect compared to the reference probe Rhodamine-Ethanediamine (RE). In particular, probe REI was well used for monitoring the weak acid pH fluctuations in lysosome of the live HeLa cells due to its excellent biological properties, including low cytotoxicity, high selectivity, good sensitivity and membrane permeability.

A novel pH probe based on a rhodamine–rhodamine platform

A novel pH probe based on rhodamine–rhodanine platform.