Development of a Fluorescent Probe for Measurement of Singlet Oxygen Scavenging Activity of Flavonoids

Recent progress and outlooks in rhodamine-based fluorescent probes for detection and imaging of reactive oxygen, nitrogen, and sulfur species

Reactive oxygen species (ROS), reactive nitrogen species (RNS), and reactive sulfur species (RSS) serve as vital mediators essential for preserving intracellular redox homeostasis within the human body, thereby possessing significant implications across physiological and pathological domains. Nevertheless, deviations from normal levels of ROS, RNS, and RSS disturb redox homeostasis, leading to detrimental consequences that compromise bodily integrity. This disruption is closely linked to the onset of various human diseases, thereby posing a substantial threat to human health and survival. Small-molecule fluorescent probes exhibit considerable potential as analytical instruments for the monitoring of ROS, RNS, and RSS due to their exceptional sensitivity and selectivity, operational simplicity, non-invasiveness, localization capabilities, and ability to facilitate in situ optical signal generation for real-time dynamic analyte monitoring. Due to their distinctive transition from their spirocyclic form (non-fluorescent) to their ring-opened form (fluorescent), along with their exceptional light stability, broad wavelength range, high fluorescence quantum yield, and high extinction coefficient, rhodamine fluorophores have been extensively employed in the development of fluorescent probes. This review primarily concentrates on the investigation of fluorescent probes utilizing rhodamine dyes for ROS, RNS, and RSS detection from the perspective of different response groups since 2016. The scope of this review encompasses the design of probe structures, elucidation of response mechanisms, and exploration of biological applications.

Recent Development on Sensing Strategies for Small Molecules Detections

Sensors play a critical role in the detection and monitoring of various substances present in our environment, providing us with valuable information about the world around us. Within the field of sensor development, one area that holds particular importance is the detection of small molecules. Small molecules encompass a wide range of organic or inorganic compounds with low molecular weight, typically below 900 Daltons including gases, volatile organic compounds, solvents, pesticides, drugs, biomarkers, toxins, and pollutants. The accurate and efficient detection of these small molecules has attracted significant interest from the scientific community due to its relevance in diverse fields such as environmental pollutants monitoring, medical diagnostics, industrial optimization, healthcare remedies, food safety, ecosystems, and aquatic and terrestrial life preservation. To meet the demand for precise and efficient monitoring of small molecules, this summary aims to provide an overview of recent advancements in sensing and quantification strategies for various organic small molecules including Hydrazine, Glucose, Morpholine, Ethanol amine, Nitrosamine, Oxygen, Nitro-aromatics, Phospholipids, Carbohydrates, Antibiotics, Pesticides, Drugs, Adenosine Triphosphate, Aromatic Amine, Glutathione, Hydrogen Peroxide, Acetone, Methyl Parathion, and Thiophenol. The focus is on understanding the receptor sensing mechanism, along with the electrical, optical, and electrochemical response. Additionally, the variations in UV-visible spectral properties of the ligands upon treatment with the receptor, fluorescence and absorption titration analysis for limit of detection (LOD) determination, and bioimaging analysis are discussed wherever applicable. It is anticipated that the information gathered from this literature survey will be helpful for the perusal of innovation regarding sensing strategies.

Time-gated luminescent probes for lysosomal singlet oxygen: Synthesis, characterizations and bioimaging applications

BACKGROUD

Single oxygen (1O2), the molecular oxygen at its excited state, plays a crucial role in the photodynamic therapy (PDT) of some diseases owing to its strong oxidizing property to destroy malignant cells. Although the fluorescent probe technique has proven its powerful application abilities for detection of 1O2 in biological systems, most of the reported fluorescent probes suffered from the interference of background autofluorescence of biological samples. It is clear that the real-time and in situ, background-free fluorescent detection of 1O2 generated in live cells, especially in some organelles, is of great significance for understanding the action mechanism of PDT drugs.

RESULTS

By introducing a lysosome-anchoring motif, a morpholine moiety, into a 1O2-specifically-reactive terpyridine polyacid ligand, [4'-(9-anthryl)-2,2':6',2″-terpyridine-6,6″-diyl] bis(methylenenitrilo) tetrakis (acetic acid) (ATTA), and chelating with lanthanide ions (Eu3+ or Tb3+), two lanthanide complex-based "turn-on" luminescent probes that can be used for the background-free time-gated luminescent (TGL) detection of lysosomal 1O2, Lyso-ATTA-Eu3+ and Lyso-ATTA-Tb3+, have been developed. The probes exhibit fast luminescence responses (within 2.5 min) towards 1O2 with high selectivity and sensitivity (<0.75 μM) in a wide pH range (4-11). And the excellent lysosome-localization performance of the probes allowed them to be used for the monitoring of endogenous 1O2 in lysosomes, which enabled the variability of lysosomal-1O2 concentrations induced by different photosensitizers to be successfully discriminated. Furthermore, by doping Lyso-ATTA-Eu3+ into the polyethylene glycol (PEG) hydrogel, the smart luminescent sensor film, PEG-Lyso-ATTA-Eu3+, was prepared, and successfully used for the detection of the on-site 1O2 production during the PDT process of psoriatic disease in model mice.

SIGNIFICANT

Two lysosome-targetable background-free TGL probes for 1O2 were firstly reported. The developed smart luminescent sensor film could be a powerful tool for the clinical monitoring of PDT on skin diseases without using sophisticated and expensive instruments.

Quenching effects of (-)-Epigallocatechin gallate for singlet oxygen production and its protection against oxidative damage induced by Ce6-mediated photodynamic therapy in vitro

BACKGROUND

Singlet oxygen (¹O₂) is highly reactive to biological components such as lipids, proteins and DNA, which induces oxidative damage to cells and tissues. Natural antioxidants may function as ¹O₂ quencher to prevent ¹O₂ involved photosensitized oxidation in biological system.

METHODS

Time-resolved measurement of ¹O₂ luminescence was employed to evaluate the ¹O₂ quenching abilities of natural antioxidants in air-statured phosphate buffered saline (PBS), including (-)-Epigallocatechin gallate (EGCG), Proanthocyanidins, L-carnosine and Vitamin C. The ¹O₂ quenching effects and rate constant of EGCG were investigated by detecting the absorption, fluorescence and ¹H-NMR spectroscopy and ¹O₂ luminescence decay curves, respectively. In addition, the protective activity of EGCG against ¹O₂ oxidative damage caused by Ce6-mediated photodynamic therapy (PDT) was verified in cells.

RESULTS

EGCG, proanthocyanidins, L-carnosine and Vitamin C efficiently quenched ¹O₂ luminescence at 1270 nm. The triplet-state quenching rate constants of EGCG for Rose Bengal (RB), Chlorin e6, AlPcS and HiPorfin are 2.21 × 10⁹, 4.90 × 10⁸, 3.30 × 10⁸, 1.78 × 10⁹ M^-1s^-1, while the ¹O₂ quenching rate constants are 2.80 × 10⁸, 1.50 × 10⁸, 1.30 × 10⁸, 1.70 × 10⁸ M^-1s^-1, respectively. Furthermore, EGCG could effectively quench ¹O₂ production to prevent NIH/3T3 cells oxidative damage induced by Ce6-mediated PDT.

CONCLUSIONS

EGCG is an efficient quencher for both triplet-state photosensitizers and ¹O₂. The quenching ability of EGCG during photosensitization for selected photosensitizers is: RB > HiPorfin > Ce6 > AlPcS. EGCG could be used to protect normal cells and tissue against oxidative damage.

Rutin-Loaded Solid Lipid Nanoparticles: Characterization and In Vitro Evaluation

This study was aimed at preparing and characterizing solid lipid nanoparticles loading rutin (RT-SLNs) for the treatment of oxidative stress-induced diseases. Phospholipon 80H® as a solid lipid and Polysorbate 80 as surfactant were used for the SLNs preparation, using the solvent emulsification/diffusion method. We obtained spherical RT-SLNs with low sizes, ranging from 40 to 60 nm (hydrodynamic radius) for the SLNs prepared starting from 2% and 5% (w/w) theoretical amount. All prepared formulations showed negative zeta-potential values. RT was efficiently encapsulated within SLNs, obtaining high encapsulation efficiency and drug content percentages, particularly for SLNs prepared with a 5% theoretical amount of RT. In vitro release profiles and analysis of the obtained data applying different kinetic models revealed Fickian diffusion as the main mechanism of RT release from the SLNs. The morphology of RT-SLNs was characterized by scanning electron microscopy (SEM), whereas the interactions between RT and the lipid matrix were investigated by Raman spectroscopy, evidencing spectral modifications of characteristic bands of RT due to the establishment of new interactions. Finally, antioxidant activity assay on human glioblastoma astrocytoma (U373) culture cells showed a dose-dependent activity for RT-SLNs, particularly at the highest assayed dose (50 μM), whereas the free drug showed the lesser activity.

Quantitative kinetics of intracellular singlet oxygen generation using a fluorescence probe

Singlet oxygen (¹O₂) is a type of reactive oxygen species involved in numerous physiological activities. We previously reported that ¹O₂-specific oxidation products are increased in patients with prediabetes, suggesting that measurement of ¹O₂ may be an important indicator of physiological and pathological conditions. The turnover in the generation and quenching of ¹O₂ is extremely rapid during biological activities owing to it high reactivity and short lifetime in solution. However, the dynamic changes in ¹O₂ generation in living cells have not been fully explored. In this study, we investigated whether the kinetics of ¹O₂ generation can be quantified using a far-red fluorescent probe for mitochondrial ¹O₂, Si-DMA, following addition of the ¹O₂ generator, endoperoxide, to mammalian cells. The kinetics of Si-DMA fluorescence intensity dose-dependently increased following treatment of mammalian living cells with endoperoxide. Alternatively, treatment with ¹O₂ quenchers decreased the fluorescence intensities following endoperoxide treatment. Our results indicate that the kinetics of intracellular ¹O₂ can be readily obtained using Si-DMA and time-lapse imaging, which provides new insights into the mechanism of ¹O₂ generation in mammalian cells and the exploration of ¹O₂ generators and quenchers.