Spectrochimica acta. Part A, Molecular and biomolecular spectroscopySep 9, 2025

Viscosity-sensitive fluorescent probes for tracking specific cell parts during self-digestion and iron-related cell death

Longevity & Aging Weekly Brief ↗PubMed ↗DOI ↗

Updated Jan 7, 2026

Abstract

Two hemicyanine-based probes showed a 3.4-fold increase in fluorescence intensity during the ferroptosis process in HeLa cells.

Probes 5a and 5b demonstrated correlation with viscosity changes, with R values exceeding 0.98.
Both probes emitted near-infrared fluorescence between 652-666 nm and retained over 92% photostability.
Probe 5a selectively targeted mitochondria with a Pearson correlation coefficient of 0.90, independent of mitochondrial membrane potential.
Probe 5b localized to lysosomes with a Pearson correlation coefficient of 0.90, independent of pH.
In starvation and drug-induced autophagy models, probe 5a showed a 1.9-2.3-fold increase in fluorescence intensity.
Probes 5a-5b exhibited significant fluorescence enhancements during various cellular processes, indicating their potential for real-time monitoring.

Simplified

The dynamic monitoring of cell death processes remains a significant challenge due to the scarcity of highly sensitive molecular tools. In this study, two hemicyanine-based probes (5a-5b) with D-π-A structures were developed for organelle-specific viscosity monitoring. Both probes exhibited correlation with the Förster-Hoffmann viscosity-dependent relationship (R > 0.98) and emitted near-infrared (NIR) fluorescence (652-666 nm). Key advantages of these probes included good photostability (retention over 92 %), minimal cytotoxicity (cell viability over 90 %), and an OFF-ON response to viscosity changes, confirming their suitability for continuous monitoring from physiological to pathological conditions. Moreover, probe 5a selectively targeted mitochondria (Pearson correlation coefficient (Pr) of 0.90) in a manner independent of mitochondrial membrane potential (MMP), while probe 5b localized to lysosomes (Pr = 0.90) independent of pH. In starvation and drug-induced autophagy models, probe 5a exhibited a 1.9-2.3-fold increase in fluorescence intensity. Furthermore, 5a monitored the gradual fusion of mitochondria with lysosomes, achieving a maximum colocalization coefficient of 0.78. Probe 5b demonstrated a 1.8-2.4-fold enhancement in fluorescence intensity during lysosomal autophagy. Additionally, in the ferroptosis process, probes 5a-5b exhibited 3.4-fold and 2.4-fold increase in fluorescence intensity in HeLa cells, showcasing the probes' real-time monitoring capabilities. These findings establish 5a-5b as versatile tools for studying autophagy and ferroptosis via mitochondrial and lysosomal viscosity dynamics, respectively. 2

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Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

PubMed

Viscosity-sensitive fluorescent probes for tracking specific cell parts during self-digestion and iron-related cell death

Abstract

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Funding

Competing interests

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