Highlighting the Phototherapeutical Potential of Fungal Pigments in Various Fruiting Body Extracts with Informed Feature-Based Molecular Networking.

Fungal pigments are characterized by a diverse set of chemical backbones, some of which present photosensitizer-like structures. From the genus Cortinarius, for example, several biologically active photosensitizers have been identified leading to the hypothesis that photoactivity might be a more general phenomenon in the kingdom Fungi. This paper aims at testing the hypothesis. Forty-eight fruiting body-forming species producing pigments from all four major biosynthetic pathways (i.e., shikimate-chorismate, acetate-malonate, mevalonate, and nitrogen heterocycles) were selected and submitted to a workflow combining in vitro chemical and biological experiments with state-of-the-art metabolomics. Fungal extracts were profiled by high-resolution mass spectrometry and subsequently explored by spectral organization through feature-based molecular networking (FBMN), including advanced metabolite dereplication techniques. Additionally, the photochemical properties (i.e., light-dependent production of singlet oxygen), the phenolic content, and the (photo)cytotoxic activity of the extracts were studied. Different levels of photoactivity were found in species from all four metabolic groups, indicating that light-dependent effects are common among fungal pigments. In particular, extracts containing pigments from the acetate-malonate pathway, e.g., extracts from Bulgaria inquinans, Daldinia concentrica, and Cortinarius spp., were not only efficient producers of singlet oxygen but also exhibited photocytotoxicity against three different cancer cell lines. This study explores the distribution of photobiological traits in fruiting body forming fungi and highlights new sources for phototherapeutics.

Antiproliferative and Cytotoxic Activities of Fluorescein-A Diagnostic Angiography Dye.

Fluorescein is a fluorescent dye used as a diagnostic tool in various fields of medicine. Although fluorescein itself possesses low toxicity, after photoactivation, it releases potentially toxic molecules, such as singlet oxygen (1O2) and, as we demonstrate in this work, also carbon monoxide (CO). As both of these molecules can affect physiological processes, the main aim of this study was to explore the potential biological impacts of fluorescein photochemistry. In our in vitro study in a human hepatoblastoma HepG2 cell line, we explored the possible effects on cell viability, cellular energy metabolism, and the cell cycle. We observed markedly lowered cell viability (≈30%, 75-2400 µM) upon irradiation of intracellular fluorescein and proved that this decrease in viability was dependent on the cellular oxygen concentration. We also detected a significantly decreased concentration of Krebs cycle metabolites (lactate and citrate < 30%; 2-hydroxyglutarate and 2-oxoglutarate < 10%) as well as cell cycle arrest (decrease in the G2 phase of 18%). These observations suggest that this photochemical reaction could have important biological consequences and may account for some adverse reactions observed in fluorescein-treated patients. Additionally, the biological activities of both 1O2 and CO might have considerable therapeutic potential, particularly in the treatment of cancer.

Effects of zinc porphyrin and zinc phthalocyanine derivatives in photodynamic anticancer therapy under different partial pressures of oxygen in vitro.

Photodynamic therapy (PDT) is gradually becoming an alternative method in the treatment of several diseases. Here, we investigated the role of oxygen in photodynamically treated cervical cancer cells (HeLa). The effect of PDT on HeLa cells was assessed by exposing cultured cells to disulphonated zinc phthalocyanine (ZnPcS2) and tetrasulphonated zinc tetraphenylporphyrin (ZnTPPS4). Fluorescence microscopy revealed their different localizations within the cells. ZnTPPS4 seems to be mostly limited to the cytosol and lysosomes, whereas ZnPcS2 is most likely predominantly attached to membrane structures, including plasmalemma and the mitochondrial membrane. Phototoxicity assays of PDT-treated cells carried out under different partial pressures of oxygen showed dose-dependent responses. Interestingly, ZnPcS2 was also photodynamically effective at a minimal level of oxygen, under a nitrogen atmosphere. On the other hand, hyperbaric oxygenation did not lead to a higher PDT efficiency of either photosensitizer. Although both photosensitizers can induce a significant drop in mitochondrial membrane potential, ZnPcS2 has a markedly higher effect on mitochondrial respiration that was completely blocked after two short light cycles. In conclusion, our observations suggest that PDT can be effective even in hypoxic conditions if a suitable sensitizer is chosen, such as ZnPcS2, which can inhibit mitochondrial respiration.

Palladium porphyrin complexes for photodynamic cancer therapy: effect of porphyrin units and metal.

Photodynamic therapy (PDT) has been extensively explored for malignant tissue treatment. In this work, we successfully synthesized and characterized a series of porphyrin compounds by connecting porphyrin units with alkyl chains, which were then coordinated with palladium to yield related metal complexes, named Pd-Monopor, Pd-Dipor, and Pd-Tripor, respectively. The generation of reactive oxygen species (ROS) of six porphyrin compounds was investigated by the dichlorofluorescein (DCFH) method. As expected, the palladium porphyrin complexes showed the higher efficiency of ROS generation relative to free base porphyrins, probably due to the heavy atom effect. Remarkably, the efficiency of ROS generation increased with the number of porphyrin units in the photosensitizers. The order of ROS generation efficiency of the synthesized porphyrins was Pd-Tripor > Tripor > Dipor > Pd-Monopor > Pd-Dipor > Monopor. MTT assay suggested the good biocompatibility of the synthesized photosensitizers in the dark. Upon light irradiation, the palladium porphyrin complex exhibited higher therapeutic activity than free base porphyrin. The half-maximal inhibitory concentration (IC50) of Tripor and Pd-Tripor under light irradiation was calculated to be 18.2 and 9.6 µM, respectively. The cellular uptake and subcellular localization experiments indicated that Tripor was mainly localized in the lysosomes of cancer cells.

Determination and analysis of singlet oxygen quantum yields of talaporfin sodium, protoporphyrin IX, and lipidated protoporphyrin IX using near-infrared luminescence spectroscopy.

In photodynamic therapy (PDT), singlet oxygen ([Formula: see text]) is the main species responsible for promoting tumor cell death. The determination of the quantum yield (ΦΔ) of a photosensitizer (PS) is important for dosimetry. The purpose of this paper is to quantify the [Formula: see text] generated by the PS by near-infrared spectroscopy (NIRS). The ΦΔ of different PS species were measured by the detection of near-infrared [Formula: see text] luminescence. From the measurement results, the ΦΔ of talaporfin sodium, protoporphyrin IX (PpIX), and lipidated PpIX (PpIX lipid) were measured as 0.53, 0.77, and 0.87, respectively. In addition, the ΦΔ values of PpIX in a hypoxic and oxic solution were evaluated, since tumors are associated with regions of hypoxia. The measured ΦΔ indicated a same value at high (DO: 20%) and low (DO: 1%) oxygen concentrations. Using the measured ΦΔ, the amount of [Formula: see text] generated by the PSs was estimated using [[Formula: see text]] = D*ΦΔ, where D* is the total excited PS concentration. The generated [Formula: see text] amounts were little different at the high and the low oxygen concentrations, and the generated [Formula: see text] amount for each PS was different depending on each ΦΔ. The NIRS measurement determined the ΦΔ of talaporfin sodium, PpIX, and PpIX lipid. The quantitative evaluation based on the measured ΦΔ will support the development of PDT treatment monitoring and design.

Basic Investigations of Singlet Oxygen Detection Systems with ESR for the Measurement of Singlet Oxygen Quenching Activities.

Singlet oxygen (1O2) is highly oxidative and exerts strong cytotoxic effects. We tried to establish the best combination of a singlet oxygen generation system and a detection method with ESR, for measurement of the quenching activities of various substances. The photosensitizing reaction of rose bengal or thermal decomposition of 4-methyl-1,4-etheno-2,3-benzodioxin-1(4H)-propanoic acid (endoperoxide, EP) was used for the generation of 1O2, and a sterically hindered secondary amine, 2,2,6,6-tetramethyl-4-piperidone (TEMPD) or 2,2,6,6-tetramethyl-4-piperidinol (TEMP-OH), was used as the 1O2 detection probe. These secondary amines were oxidized by 1O2 to form stable nitroxide radicals, which were detectable by ESR. TEMPD was found to be readily oxidized by air, causing large background signals in comparison with TEMP-OH. The ESR signal obtained by the irradiation of rose bengal with visible light in the presence of TEMP-OH consisted of two kinds of nitroxide radical overlapping. In contrast, only a single nitroxide signal was observed when TEMP-OH was reacted with 1O2 generated from EP. Therefore, the best combination should be EP as the 1O2 generator and TEMP-OH as the detection probe. When using this combination, we found that the concentrations of some organic solvents such as dimethyl sulfoxide and acetonitrile should be kept constant for reliable quantification, because the concentrations of organic solvents affect the ESR signal intensity.

Real-Time Mapping of Ultratrace Singlet Oxygen in Rat during Acute and Chronic Inflammations via a Chemiluminescent Nanosensor.

Sensing nonradiation-induced singlet oxygen (1 O2 ) in whole-animal is deemed as one of the most challenging tasks in noninvasive techniques due to the µs level lifetime of 1 O2 and quenching by numerous reductants in tissues. Here a distinct chemiluminescent (CL) nanosensor (NTPE-PH) that boasts ultrahigh concentrated CL units in one nanoparticle is reported. Taking advantage of the intramolecular energy transfer mechanism that promises high energy transfer efficiency and the aggregation-induced emission behavior that guarantees high CL amplification, the NTPE-PH sensor is sensitive to a nm level 1 O2 . Experiments demonstrate that the NTPE-PH yields a highly selective CL response toward 1 O2 among common reactive oxygen species. With proved low cytotoxicity and good animal compatibility, real-time mapping of ultratrace 1 O2 in whole-animal during acute and chronic inflammations is first achieved. It is anticipated that the NTPE-PH sensor can be a useful tool for monitoring 1 O2 variation during immune response and pathological processes corresponding to different stimuli, even with drug treatment included.

Singlet oxygen phosphorescence detection in vivo identifies PDT-induced anoxia in solid tumors.

Real-time surveillance of photodynamic therapy (PDT) has been desired by the research community for a long time. The impact of the treatment is encoded in the phosphorescence kinetics of its main mediator: singlet oxygen. We report successful in vivo measurements of these weak kinetics through the skin of living mice after systemic drug application. Using special high transmission optics centered around 1200, 1270 and 1340 nm, singlet oxygen phosphorescence can be clearly discriminated from other signals. N-(2-Hydroxypropyl)methacrylamide copolymers conjugated with pyropheophorbide-a exhibit highly selective accumulation in tumors. Signals of this drug in tumors were compared to those in normal tissue. In both places, the major part of the signal could be identified as arising from drug still circulating in the bloodstream. Despite high concentrations of extravasated drug in the tumors due to the EPR effect, nearly no signal could be detected from these photosensitizers in vivo, contradicting in vitro experiments. We propose that the reason for this discrepancy is oxygen depletion in tumor tissue in vivo, even at moderate (at PDT scale) illumination intensities, soon after the start of the illumination. These results underline the importance of singlet oxygen surveillance during PDT treatment.

Novel ruthenium(ii) and iridium(iii) BODIPY dyes: insights into their application in photodynamic therapy in vitro.

Organic-metal complexes are promising molecules for use in photodynamic therapy (PDT). The aim of this study was to investigate in vitro effects of novel Ru(ii) and Ir(iii) BODIPY complexes for PDT. These hybrid organic-metal molecules (Ru-BD and Ir-BD) have been synthesized via reactions of a BODIPY precursor (BD) with a phenanthroline unit bearing Ru(ii) (3) and novel Ir(iii) (4) compounds. The crystal structures of the new distyryl BODIPY (BD) and Ru(ii) complex (3) are also reported. The photophysical and singlet oxygen generation properties of Ru-BD and Ir-BD were investigated in comparison with unsubstituted BODIPY (BD). Moreover, Ru-BD and Ir-BD have been biologically evaluated in vitro in chronic myeloid leukemia and cervical cancer cell lines in terms of photodynamic therapy efficacy in the presence of BD control. These complexes were not toxic in the dark but red light was needed to induce cell death. These data support the fact that Ru-BD could be accepted as a valuable photosensitizer-drug for further PDT treatment.

Hybrids of a 9-anthracenyl moiety and fluorescein as chemodosimeters for the detection of singlet oxygen in live cells.

Singlet oxygen (1O2) plays an important role in human innate immune response, plant physiology and anticancer photodynamic therapy (PDT). Therefore, its monitoring by convenient and sensitive methods (e.g. by detecting a fluorescence signal) by using non-toxic reagents would be advantageous. Known fluorogenic 1O2-chemodosimeters can potentially consume reducing agents in cells leading to the generation of toxic side products that limit their applications. In this paper we report on a series of 9-anthracenyl-fluorescein hybrids, which do not require any reducing agents for their reaction with 1O2. The selected compound 8d at a very low concentration of 100 nM is able to detect 1O2 in live human promyelocytic leukemia HL-60 cells with over 35-fold fluorescence signal enhancement within only 20 min assay time. This chemodosimeter is not toxic to HL-60 cells at concentrations ≤1 µM (higher concentrations were not tested) even at long incubation times ≤48 h.

A folate-conjugated platinum porphyrin complex as a new cancer-targeting photosensitizer for photodynamic therapy.

A new folate-conjugated platinum porphyrin complex (Por 4) was synthesized and characterized. The singlet oxygen production of the conjugates was evaluated through a 1,3-diphenylisobenzofuran method. The targeting ability and subcellular localization of Por 4 were confirmed by confocal laser scanning microscopy in HeLa cells (overexpression of FR) as well as in A549 cells (low expression of FR). The results suggested that the modification of the carboxyl group with a porphyrin compound did not decrease the binding affinity of folic acid to FR positive cancer cells. Moreover, the MTT assay using HeLa cells and A549 cells verified the low cytotoxicity of Por 4 in the dark. Upon irradiation, Por 4 showed noticeable improvement in toxicity against cancer cells with the overexpression of FR. Upon the treatment of Por 4 at the concentration of 20 µM, the cell viability was determined as 22% and 75% for HeLa and A549 cells, respectively, indicating that the folate-conjugated platinum porphyrin complex could be a promising PDT agent for cancer with overexpression of the folate receptor.

Efficiency comparison of the imidazole plus RNO method for singlet oxygen detection in biorelevant solvents.

Singlet oxygen (1O2) is the focus of study in many fields, including phototoxicity, antioxidant activity, pollutant weathering, photodynamic therapy, and water disinfection. The imidazole plus RNO (Imd/RNO) method, originated by Kraljic and El Mohsni, is commonly used to monitor singlet oxygen production. In this method, 1O2 is quenched by an acceptor, imidazole (Imd), during the formation of a trans-annular peroxide intermediate that bleaches the sensor, p-nitrosodimethylaniline (RNO). Though the method has been widely used, including to monitor 1O2 production in complex environments, such as surfactants and cells, studies reporting the efficiency of the assay in complex solvents have not been reported. In this research, the Imd/RNO method in complex, biorelevant solvents, i.e., sodium dodecyl sulfate, octanol, and phosphate buffer-saturated octanol, was compared with reference solvents, i.e., phosphate buffer, ethanol, and methanol, for monitoring 1O2 produced by Rose Bengal photosensitization using time-resolved, broadband UV-Vis absorbance measurements. Rates of sensor bleaching and sensitizer photodegradation were simultaneously monitored in each solvent to investigate correlations between the disappearance rates of sensor and sensitizer. The quantum yields of 1O2 production (ϕ∆) in each solvent were calculated using a relative actinometric method. The dependence of sensor bleaching and sensitizer degradation on acceptor concentration and solvent polarity, and the results of assay controls suggest mechanistic differences underlying the reactions comprising the Imd/RNO method. These results demonstrate the need for caution and controls when using the method in complex samples including those containing cells, tissues, or nanoscale particles.

Polylysine modified conjugated polymer nanoparticles loaded with the singlet oxygen probe 1,3-diphenylisobenzofuran and the photosensitizer indocyanine green for use in fluorometric sensing and in photodynamic therapy.

Conjugated polymer hybrid nanoparticles (NPs) loaded with both indocyanine green (ICG) and 1,3-diphenylisobenzofuran (DPBF) are described. The NPs are dually functional in that ICG acts as the photosensitizer, and DPBF as a probe for singlet oxygen (1O2 probe). The nanoparticle core consists of the energy donating host poly(9,9-dioctylfluorenyl-2,7-diyl)-co-(2,5-p-xylene) (PFP). The polymer is doped with the energy acceptor DPBF. Ratiometric fluorometric detection of singlet oxygen is accomplished by measurement of fluorescence at wavelengths of 415 and 458 nm. In addition, the shell of the positively charged polymeric nanoparticles was modified, via electrostatic interaction, with negatively charged PDT drugs ICG. The integrated nanoparticles of type ICG-DPBF-PFP display effective photodynamic performance under 808-nm laser irradiation. The 1O2 sensing behaviors of samples are evaluated based on the ratiometric fluorescent responses produced by DPBF and PFP. 1O2 can be fluorimetically sensed with a detection limit of 28 µM. The multifunctional nanoprobes exhibit effortless cellular uptake, superior photodynamic activity and a rapid ratiometric response to 1O2. Graphical abstractSchematic of a dual-functional nanoplatform for photodynamic therapy (PDT) and singlet oxygen (1O2) feedback. It offers a new strategy for self-monitoring photodynamic ablation. FRET: fluorescence resonance energy transfer. Indocyanine green is attached in the shell of nanoparticles, and 1,3-diphenylisobenzofuran is doped into the energy donating host conjugated polymer.

Ratiometric Fluorescent Detection of Intracellular Singlet Oxygen by Semiconducting Polymer Dots.

Singlet oxygen (1O2) plays important roles in many biological processes. However, it is very difficult to detect 1O2 in the intracellular environment because of its relatively low concentration and short lifetime. Here, we developed a ratiometric probe based on semiconducting polymer dots (Pdots) that can sensitively detect 1O2 in live cells. An organic dye, singlet oxygen sensor green (SOSG), was doped in polyfluorene Pdots, and excitation energy was efficiently transferred from the polymer to the SOSG dye. Accordingly, the Pdots showed constant blue fluorescence as a reference, and increased green fluorescence upon singlet oxygen generation. The ratiometric response of Pdots was examined in the intracellular environment by in situ 1O2 generation with a photosensitizer and light irradiation. Both spectroscopic measurements and confocal imaging were performed to monitor intracellular 1O2 generation during photodynamic therapy using the Pdot probe. Our results indicate that the SOSG-doped Pdots are promising for intracellular 1O2 detection.

Flexible Cationic Nanoparticles with Photosensitizer Cores for Multifunctional Biomedical Applications.

One challenge for multimodal therapy is to develop appropriate multifunctional agents to meet the requirements of potential applications. Photodynamic therapy (PDT) is proven to be an effective way to treat cancers. Diverse polycations, such as ethylenediamine-functionalized poly(glycidyl methacrylate) (PGED) with plentiful primary amines, secondary amines, and hydroxyl groups, demonstrate good gene transfection performances. Herein, a series of multifunctional cationic nanoparticles (PRP) consisting of photosensitizer cores and PGED shells are readily developed through simple dopamine-involving processes for versatile bioapplications. A series of experiments demonstrates that PRP nanoparticles are able to effectively mediate gene delivery in different cell lines. PRP nanoparticles are further validated to possess remarkable capability of combined PDT and gene therapy for complementary tumor treatment. In addition, because of their high dispersities in biological matrix, the PRP nanoparticles can also be used for in vitro and in vivo imaging with minimal aggregation-caused quenching. Therefore, such flexible nanoplatforms with photosensitizer cores and polycationic shells are very promising for multimodal tumor therapy with high efficacy.

Cell cycle modulation through subcellular spatially resolved production of singlet oxygen via direct 765 nm irradiation: manipulating the onset of mitosis.

Reactive oxygen species, ROS, are acknowledged signaling molecules in cellular processes. Singlet molecular oxygen, O2(a1Δg), is one ROS that can initiate cell responses that range from death to proliferation. To better understand the mechanisms involved, it is necessary to further investigate cell response to the "dose" of O2(a1Δg) that has been selectively produced at the expense of other ROS. In this context, dose refers not just to the amount of O2(a1Δg) produced, but also to the subcellular spatial domain in which it is produced. In this study, we selectively produced small and non-toxic amounts of O2(a1Δg) in sensitizer-free experiments by irradiating oxygen at 765 nm using a laser focused either into the nucleus or cytoplasm of HeLa cells. We find that O2(a1Δg)-mediated cell proliferation depends appreciably on the site of O2(a1Δg) production. At the same incident laser power, irradiation into the cytoplasm elicits moderate enhancement of proliferation, whereas irradiation into the nucleus leads to an appreciable delay in the onset and completion of mitosis. We discuss these results in light of what is known about the intracellular photophysics of O2(a1Δg) and the redox state of different cell domains.

Emerging technologies for optical spectral detection of reactive oxygen species.

This review surveys recent advances in optical spectral detection of reactive oxygen species (ROS), particularly singlet oxygen, superoxide, hydroxyl radical, and hydrogen peroxide. Advances using nanoparticles and self-organizing nanostructures as well as optical detection schemes are included. Measurements using plasmonic, luminescent, photocatalytic, or self-organizing nanoparticles are highlighted. The large number of spectrophotometric and luminescent probe methods are categorized by ROS sensing mechanism, signaling mode, (de)activation mechanism, if any, and spectral chromaticity. Reports describing multicomponent ROS detection or novel nanoscale probes are discussed. Measurements using ratiometric, multichannel, or time-resolved detection and nonlinear spectral transitions are reviewed. The focus on developing probe molecules for spectral detection documented over the last 20 years has continued, with sustained emphasis on luminescence detection, but with less focus on spectrophotometric measurements. Use of nanoparticles as probes, probe carriers, and compartmentalization agents in ROS detection is increasing. On the other hand, incorporation of advanced spectral methods, such as nonlinear transition and multichannel detection, is increasing slowly in ROS analysis. This indicates there is a substantial opportunity to develop ROS measurements with use of a synergistic combination of (multi)functional nanoscale systems and advanced optical detection methods to optimize the detection limit, selectivity, and response time. Graphical abstract ᅟ.

A fluorescent nanoprobe for real-time monitoring of intracellular singlet oxygen during photodynamic therapy.

Sensing of intracellular singlet oxygen (1O2) is required in order to optimize photodynamic therapy (PDT). An optical nanoprobe is reported here for the optical determination of intracellular 1O2. The probe consists of a porous particle core doped with the commercial 1O2 probe 1,3-diphenylisobenzofuran (DPBF) and a layer of poly-L-lysine. The nanoparticle probes have a particle size of ~80 nm in diameter, exhibit good biocompatibility, improved photostability and high sensitivity for 1O2 in both absorbance (peak at 420 nm) and fluorescence (with excitation/emission peaks at 405/458 nm). Nanoprobes doped with 20% of DPBF are best suited even though they suffer from concentration quenching of fluorescence. In comparison with the commercial fluorescent 1O2 probe SOSG, 20%-doped DPBF-NPs (aged) shows higher sensitivity for 1O2 generated at an early stage. The best nanoprobes were used to real-time monitor the PDT-triggered generation of 1O2 inside live cells, and the generation rate is found to depend on the supply of intracellular oxygen. Graphical abstract A fluorescent nanoprobe featured with refined selectivity and improved sensitivity towards 1O2 was prepared from the absorption-based probe DBPF and used to real-time monitoring of the generation of intracellular 1O2 produced during PDT.

Core-Shell-Shell Multifunctional Nanoplatform for Intracellular Tumor-Related mRNAs Imaging and Near-Infrared Light Triggered Photodynamic-Photothermal Synergistic Therapy.

A multifunctional nanoplatform, which generally integrates biosensing, imaging diagnosis, and therapeutic functions into a single nanoconstruct, has great important significance for biomedicine and nanoscience. Here, we developed a core-shell-shell multifunctional polydopamine (PDA) modified upconversion nanoplatform for intracellular tumor-related mRNAs detection and near-infrared (NIR) light triggered photodynamic and photothermal synergistic therapy (PDT-PTT). The nanoplatform was constructed by loading a silica shell on the hydrophobic upconversion nanoparticles (UCNPs) with hydrophilic photosensitizer methylene blue (MB) entrapped in it, and then modifying PDA shells through an in situ self-polymerization process, thus yielding a core-shell-shell nanoconstruct UCNP@SiO2-MB@PDA. By taking advantages of preferential binding properties of PDA for single-stranded DNA over double-stranded DNA and the excellent quenching property of PDA, a UCNP@SiO2-MB@PDA-hairpin DNA (hpDNA) nanoprobe was developed through adsorption of fluorescently labeled hpDNA on PDA shells for sensing intracellular tumor-related mRNAs and discriminating cancer cells from normal cells. In addition, the fluorescence resonance energy transfer from the upconversion fluorescence (UCF) emission at 655 nm of the UCNPs to the photosensitizer MB molecules could be employed for PDT. Moreover, due to the strong NIR absorption and high photothermal conversion efficiency of PDA, the UCF emission at 800 nm of the UCNPs could be used for PTT. We demonstrated that the UCNP@SiO2-MB@PDA irradiated with NIR light had considerable PDT-PTT effect. These results revealed that the developed multifunctional nanoplatform provided promising applications in future oncotherapy by integrating cancer diagnosis and synergistic therapy.

Microscopic time-resolved imaging of singlet oxygen by delayed fluorescence in living cells.

Singlet oxygen is a highly reactive species which is involved in a number of processes, including photodynamic therapy of cancer. Its very weak near-infrared emission makes imaging of singlet oxygen in biological systems a long-term challenge. We address this challenge by introducing Singlet Oxygen Feedback Delayed Fluorescence (SOFDF) as a novel modality for semi-direct microscopic time-resolved wide-field imaging of singlet oxygen in biological systems. SOFDF has been investigated in individual fibroblast cells incubated with a well-known photosensitizer aluminium phthalocyanine tetrasulfonate. The SOFDF emission from the cells is several orders of magnitude stronger and much more readily detectable than the very weak near-infrared phosphorescence of singlet oxygen. Moreover, the analysis of SOFDF kinetics enables us to estimate the lifetimes of the involved excited states. Real-time SOFDF images with micrometer spatial resolution and submicrosecond temporal-resolution have been recorded. Interestingly, a steep decrease in the SOFDF intensity after the photodynamically induced release of a photosensitizer from lysosomes has been demonstrated. This effect could be potentially employed as a valuable diagnostic tool for monitoring and dosimetry in photodynamic therapy.