Better in the Near Infrared: Sulfonamide Perfluorinated-Phenyl Photosensitizers for Improved Simultaneous Targeted Photodynamic Therapy and Real-Time Fluorescence Imaging.

Tetraphenyloporphyrin derivatives are a useful scaffold for developing new pharmaceuticals for photodynamic therapy (PDT) and the photodiagnosis (PD) of cancer. We synthesized new sulfonamide fluorinated porphyrin derivatives and investigated their potential as photosensitizers and real-time bioimaging agents for cancer. We found that 5,10,15,20-tetrakis-[2',3',5',6'-tetrafluoro-4'-methanesulfamidyl)phenyl]bacteriochlorin (F4BMet) has intense absorption and fluorescence in the near-infrared, efficiently generates singlet oxygen and hydroxyl radicals, has low toxicity in the dark, and high phototoxicity. We increased its bioavailability with encapsulation in Pluronic-based micelles, which also improved the photodynamic effect. F4BMet exhibits pH-dependent properties (lower pH promoted its aggregation), and a GlyGly buffer was used to effectively solubilize the compound. In vitro findings with 2D cell culture were complemented with human-induced pluripotent stem cell (hiPSC)-derived organoids. F4BMet in P123 micelles showed enhanced efficacy compared to F4BMet in the GlyGly formulation. F4BMet was further evaluated in real-time bioimaging and PDT of BALB/c mice bearing CT26 tumors. After i.v. injection, the photosensitizer was visible in the tumor area 3 h after injection. The most successful therapeutic approach proved to be tumor-targeted PDT using P123-encapsulated F4BMet illuminated 24 h after administration with a light dose of 42 J/cm2, which led to a 30% long-term cure rate.

Efficient and Selective, In Vitro and In Vivo, Antimicrobial Photodynamic Therapy with a Dicationic Chlorin in Combination with KI.

Various cationic photosensitizers employed in antimicrobial photodynamic therapy (aPDT) have the ability to photoinactivate planktonic bacteria under conditions of low phototoxicity to mammalian cells and without generating antimicrobial resistance (AMR). However, the photoinactivation of biofilms requires orders-of-magnitude higher photosensitizer concentrations, which become toxic to host cells. Remarkably, the bactericidal effect of a dicationic di-imidazolyl chlorin toward planktonic S. aureus and E. coli was observed in this work for concentrations below 400 nM under illumination at 660 nm and below 50 µM for the corresponding biofilms. At the latter concentrations, the chlorin is phototoxic toward human keratinocyte cells. However, in the presence of 50 mM KI, bactericidal concentrations are reduced to less than 50 nM for planktonic bacteria and to less than 1 µM for biofilms. It is shown that the potentiation with KI involves the triiodide anion. This potentiation elicits a bactericidal effect without appreciable cytotoxicity to keratinocytes. It becomes possible to selectively inactivate biofilms with aPDT. An exploratory study treating mice with wounds infected with E. coli expressing GFP with 20 µM chlorin and 120 J cm-2 at 652 nm confirmed the potential of this chlorin to control localized infections.

Delivery of minoxidil encapsulated in cyclodextrins with photoacoustic waves enhances hair growth.

The current pharmacological management of androgenetic alopecia is inconvenient and requires a discipline that patients find difficult to follow. This reduces compliance with treatment and satisfaction with results. It is important to propose treatment regimens that increase patient compliance and reduce adverse effects. This work describes transdermal delivery of minoxidil partially encapsulated in ß-cyclodextrin and assisted by photoacoustic waves. Photoacoustic waves transiently increase the permeability of the skin and allow for the delivery of encapsulated minoxidil. A minoxidil gel formulation was developed and the transdermal delivery was studied in vitro in the presence and absence of photoacoustic waves. A 5-min stimulus with photoacoustic waves generated by light-to-pressure transducers increases minoxidil transdermal delivery flux by approximately 3-fold. The flux of a 1% minoxidil formulation promoted by photoacoustic waves is similar to the passive flux of a 2% minoxidil commercial formulation. Release of minoxidil from ß-cyclodextrin increases dermal exposure without increasing peak systemic exposure. This promotes hair growth with fewer treatments and reduced adverse effects. In vivo studies using encapsulated minoxidil and photoacoustic waves yielded 86% hair coat recovery (vs. 29% in the control group) and no changes in the blood pressure.

Photodynamic inactivation of E. coli with cationic imidazolyl-porphyrin photosensitizers and their synergic combination with antimicrobial cinnamaldehyde.

Bacterial infections are a global health concern, particularly due to the increasing resistance of bacteria to antibiotics. Multi-drug resistance (MDR) is a considerable challenge, and novel approaches are needed to treat bacterial infections. Photodynamic inactivation (PDI) of microorganisms is increasingly recognized as an effective method to inactivate a broad spectrum of bacteria and overcome resistance mechanisms. This study presents the synthesis of a new cationic 5,15-di-imidazolyl porphyrin derivative and the impact of n-octanol/water partition coefficient (logP) values of this class of photosensitizers on PDI efficacy of Escherichia coli. The derivative with logP = -0.5, IP-H-OH2+, achieved a remarkable 3 log CFU reduction of E. coli at 100 nM with only 1.36 J/cm2 light dose at 415 nm, twice as effective as the second-best porphyrin IP-H-Me2+, of logP = -1.35. We relate the rapid uptake of IP-H-OH2+ by E. coli to improved PDI and the very low uptake of a fluorinated derivative, IP-H-CF32+, logP ≈ 1, to its poor performance. Combination of PDI with cinnamaldehyde, a major component of the cinnamon plant known to alter bacteria cell membranes, offered synergic inactivation of E. coli (7 log CFU reduction), using 50 nM of IP-H-OH2+ and just 1.36 J/cm2 light dose. The success of combining PDI with this natural compound broadens the scope of therapies for MDR infections that do not add drug resistance. In vivo studies on a mouse model of wound infection showed the potential of cationic 5,15-di-imidazolyl porphyrins to treat clinically relevant infected wounds.

Repurposing anti-cancer porphyrin derivative drugs to target SARS-CoV-2 envelope.

Antiviral medicines to treat COVID-19 are still scarce. Porphyrins and porphyrin derivatives (PDs) usually present broad-spectrum antiviral activity with low risk of resistance development. In fact, some PDs are clinically approved to be used in anti-cancer photodynamic therapy and repurposing clinically approved PDs might be an alternative to treat COVID-19. Here, we characterize the ability of temoporfin, verteporfin, talaporfin and redaporfin to inactivate SARS-CoV-2 infectious particles. PDs light-dependent and -independent effect on SARS-CoV-2 infectivity were evaluated. PDs photoactivation successfully inactivated SARS-CoV-2 with very low concentrations and light dose. However, only temoporfin and verteporfin inactivated SARS-CoV-2 in the dark, being verteporfin the most effective. PDs treatment reduced viral load in infected Caco-2 cells, while not inducing cytotoxicity. Furthermore, light-independent treatment with temoporfin and verteporfin act on early stages of viral infection. Using lipid vehicles as membrane models, we characterized PDs interaction to the viral envelope. Verteporfin presented the lowest IC50 for viral inactivation and the highest partition coefficients (Kp) towards lipid bilayers. Curiously, although temoporfin and redaporfin presented similar Kps, redaporfin did not present light-independent antiviral activity, and only temoporfin and verteporfin caused lipid membrane disorder. In fact, redaporfin is located closer to the bilayer surface, while temoporfin and verteporfin are located closer to the centre. Our results suggest that viral envelope affinity, with penetration and destabilization of the lipid bilayer, seems critical to mediate PDs antiviral activity. Altogether, these findings open new avenues for the off-label application of temoporfin and verteporfin in the systemic treatment of COVID-19.

Nanodroplet vaporization with pulsed-laser excitation repeatedly amplifies photoacoustic signals at low vaporization thresholds.

Nanodroplets' explosive vaporization triggered by absorption of laser pulses produces very large volume changes. These volume changes are two orders of magnitude higher than those of thermoelastic expansion generated by equivalent laser pulses, and should generate correspondingly higher photoacoustic waves (PAW). The generation of intense PAWs is desirable in photoacoustic tomography (PAT) to increase sensitivity. The biocompatibility and simplicity of nanodroplets obtained by sonication of perfluoropentane (PFP) in an aqueous solution of bovine serum albumin (BSA) containing a dye make them particularly appealing for use as contrast agents in clinical applications of PAT. Their usefulness depends on stability and reproducible vaporization of nanodroplets (liquid PFP inside) to microbubbles (gaseous PFP inside), and reversible condensation to nanodroplets. This work incorporates porphyrins with fluorinated chains and BSA labelled with fluorescent probes in PFP nanodroplets to investigate the structure and properties of such nanodroplets. Droplets prepared with average diameters in the 400-1000 nm range vaporize when exposed to nanosecond laser pulses with fluences above 3 mJ cm-2 and resist coalescence. The fluorinated chains are likely responsible for the low vaporization threshold, ∼2.5 mJ cm-2, which was obtained from the laser fluence dependence of the photoacoustic wave amplitudes. Only ca. 10% of the droplets incorporate fluorinated porphyrins. Nevertheless, PAWs generated with nanodroplets are ten times higher than those generated by aqueous BSA solutions containing an equivalent amount of porphyrin. Remarkably, successive laser pulses result in similar amplification, indicating that the microbubbles revert back to nanodroplets at a rate faster than the laser repetition rate (10 Hz). PFP nanodroplets are promising contrast agents for PAT and their performance increases with properly designed dyes.

Selective, broad-spectrum antiviral photodynamic disinfection with dicationic imidazolyl chlorin photosensitizers.

The COVID-19 pandemic exposes our vulnerability to viruses that acquire the ability to infect our cells. Classical disinfection methods are limited by toxicity. Existing medicines performed poorly against SARS-CoV-2 because of their specificity to targets in different organisms. We address the challenge of mitigating known and prospective viral infections with a new photosensitizer for antimicrobial photodynamic therapy (aPDT). Photodynamic inactivation is based on local oxidative stress, which is particularly damaging to enveloped viruses. We synthesized a cationic imidazolyl chlorin that reduced by > 99.999% of the percentage inhibition of amplification of SARS-CoV-2 collected from patients at 0.2 µM concentration and 4 J cm-2. Similar results were obtained in the prevention of infection of human ACE2-expressing HEK293T cells by a pseudotyped lentiviral vector exhibiting the S protein of SARS-CoV-2 at its surface. No toxicity to human epidermal keratinocytes (HaCaT) cells was found under similar conditions. aPDT with this chlorin offers fast and safe broad-spectrum photodisinfection and can be repeated with low risk of resistance.

Photodynamic therapy changes tumour immunogenicity and promotes immune-checkpoint blockade response, particularly when combined with micromechanical priming.

Photodynamic therapy (PDT) with redaporfin stimulates colon carcinoma (CT26), breast (4T1) and melanoma (B16F10) cells to display high levels of CD80 molecules on their surfaces. CD80 overexpression amplifies immunogenicity because it increases same cell (cis) CD80:PD-L1 interactions, which (i) disrupt binding of T-cells PD-1 inhibitory receptors with their ligands (PD-L1) in tumour cells, and (ii) inhibit CTLA-4 inhibitory receptors binding to CD80 in tumour cells. In some cancer cells, redaporfin-PDT also increases CTLA-4 and PD-L1 expressions and virtuous combinations between PDT and immune-checkpoint blockers (ICB) depend on CD80/PD-L1 or CD80/CTLA-4 tumour overexpression ratios post-PDT. This was confirmed using anti-CTLA-4 + PDT combinations to increase survival of mice bearing CT26 tumours, and to regress lung metastases observed with bioluminescence in mice with orthotopic 4T1 tumours. However, the primary 4T1 responded poorly to treatments. Photoacoustic imaging revealed low infiltration of redaporfin in the tumour. Priming the primary tumour with high-intensity (~ 60 bar) photoacoustic waves generated with nanosecond-pulsed lasers and light-to-pressure transducers improved the response of 4T1 tumours to PDT. Penetration-resistant tumours require a combination of approaches to respond to treatments: tumour priming to facilitate drug infiltration, PDT for a strong local effect and a change in immunogenicity, and immunotherapy for a systemic effect.

Overcoming the challenges of infrared photosensitizers in photodynamic therapy: the making of redaporfin.

We offer a personal account of the discovery and development of a photosensitizer for photodynamic therapy (PDT) of cancer, from bench to bedside. We emphasize the more chemical aspects of drug discovery and drug development, namely the chemical landscape at the time of the discovery, the breakthrough in the field offered by stable bacteriochlorins, the challenges of synthesising a significant amount of the product with high purity for preclinical studies, the factors that relate molecular structure to pharmacology in PDT, the mechanistic interpretation of preclinical data and the management of unexpected results. Special attention is given to the implications of atropisomerism and immune responses in PDT.

Trial watch: an update of clinical advances in photodynamic therapy and its immunoadjuvant properties for cancer treatment.

Photodynamic therapy (PDT) is a medical treatment used to target solid tumors, where the administration of a photosensitizing agent and light generate reactive oxygen species (ROS), thus resulting in strong oxidative stress that selectively damages the illuminated tissues. Several preclinical studies have demonstrated that PDT can prime the immune system to recognize and attack cancer cells throughout the body. However, there is still limited evidence of PDT-mediated anti-tumor immunity in clinical settings. In the last decade, several clinical trials on PDT for cancer treatment have been initiated, indicating that significant efforts are being made to improve current PDT protocols. However, most of these studies disregarded the immunological dimension of PDT. The immunomodulatory properties of PDT can be combined with standard therapy and/or emerging immunotherapies, such as immune checkpoint blockers (ICBs), to achieve better disease control. Combining PDT with immunotherapy has shown synergistic effects in some preclinical models. However, the value of this combination in patients is still unknown, as the first clinical trials evaluating the combination of PDT with ICBs are just being initiated. Overall, this Trial Watch provides a summary of recent clinical information on the immunomodulatory properties of PDT and ongoing clinical trials using PDT to treat cancer patients. It also discusses the future perspectives of PDT for oncological indications.

Redaporfin Development for Photodynamic Therapy and its Combination with Glycolysis Inhibitors.

Photodynamic therapy (PDT) remains an underutilized treatment modality in oncology. Many efforts have been dedicated to the development of better photosensitizers, better formulations and delivery methods, rigorous planning of light dose distribution in tissues, mechanistic insight, improvement of treatment protocols and combinations with other therapeutic agents. Hopefully, progress in all these fields will eventually expand the use of PDT. Here we offer a brief review of our own contribution to the development of a photosensitizer for PDT - redaporfin - currently in Phase II clinical trials, and present data on its combination with two glycolysis inhibitors: 2-deoxyglucose and 3-bromopyruvate. We show that 3-bromopyruvate is more cytotoxic to a carcinoma cell line (CT26) than to a normal fibroblast (3T3) cell line, and that this selectivity is maintained in the in vitro combination with redaporfin-PDT. This combination was investigated in BALB/c mice with large subcutaneous CT26 tumors and it is shown that the cure rate in the combination is higher (33% cures) than in PDT (11% cures) or in 3-bromopyruvate (no cures) alone. The combination of redaporfin-PDT with 3-bromopyruvate illustrates the potential of combination therapies and how PDT benefits can be enhanced by systemic drugs with complementary targets.

Synthesis of Photosensitizers Based on Tetrapyrrolic Macrocycles for Combination with Antibiotics: Dual Inactivation of Bacteria.

The combination of photodynamic therapy with antibiotics or antimicrobial peptides for inactivation of bacteria is an area of growing interest due to the synergistic effect already observed by many authors. It has been shown that the efficiency of this dual antimicrobial therapy is highly dependent on the structure of the photosensitizer, being tetrapyrrolic macrocycles the ones with most promising results. There are a few review articles in the recent literature describing the main microbiological results concerning this dual inactivation of bacteria, but none of them focus on the synthetic processes of these photosensitizers and their remarkable chemical versatility. Therefore, herein we present an overview on synthetic methodologies for preparation of tetrapyrrolic macrocycles and their conjugates with antibiotics or antimicrobial peptides, for use in dual inactivation of bacteria. This review will be divided in two sections concerning the physical or covalent combinations of PS with antibiotic/cationic peptides, followed by brief critical analysis on their corresponding antimicrobial outcomes.

Unraveling the Pivotal Role of Atropisomerism for Cellular Internalization.

The intrinsic challenge of large molecules to cross the cell membrane and reach intracellular targets is a major obstacle for the development of new medicines. We report how rotation along a single C-C bond, between atropisomers of a drug in clinical trials, improves cell uptake and therapeutic efficacy. The atropisomers of redaporfin (a fluorinated sulfonamide bacteriochlorin photosensitizer of 1135 Da) are separable and display orders of magnitude differences in photodynamic efficacy that are directly related to their differential cellular uptake. We show that redaporfin atropisomer uptake is passive and only marginally affected by ATP depletion, plasma proteins, or formulation in micelles. The α4 atropisomer, where meso-phenyl sulfonamide substituents are on the same side of the tetrapyrrole macrocycle, exhibits the highest cellular uptake and phototoxicity. This is the most amphipathic atropisomer with a conformation that optimizes hydrogen bonding (H-bonding) with polar head groups of membrane phospholipids. Consequently, α4 binds to the phospholipids on the surface of the membrane, flips into the membrane to adopt the orientation of a surfactant, and eventually diffuses to the interior of the cell (bind-flip mechanism). We observed increased α4 internalization by cells of the tumor microenvironment in vivo and correlated this to the response of photodynamic therapy when tumor illumination was performed 24 h after α4 administration. These results show that properly orientated aryl sulfonamide groups can be incorporated into drug design as efficient cell-penetrating motifs in vivo and reveal the unexpected biological consequences of atropisomerism.

Efficient dermal delivery of ascorbic acid 2-glucoside with photoacoustic waves.

OBJECTIVE: Ascorbic acid (i.e., vitamin C) is an important antioxidant present in skin. The protective role of vitamin C against photoaging motivated numerous attempts to promote its topical delivery, with a success limited by its chemical instability and poor skin permeability. Vitamin C precursors, such as ascorbic acid 2-glucoside (AA2G), which are metabolized to vitamin C by enzymes present in the skin, solve the problem of stability but are limited by low skin permeability. We developed a 2% (w/v) gel formulation of AA2G application (viscosity 4.30 × 104 Pa.s, pH 5.94) and compared its passive dermal delivery with the delivery promoted by photoacoustic waves that transiently perturb the skin barrier. METHODS: Photoacoustic (PA) waves were generated by laser pulses absorbed by piezophotonic (light-to-pressure) transducers. Pig skin samples were exposed to the 2% AA2G formulation alone or combined with 5 min of PA waves. One hour later, AA2G was extracted from the skin and quantified by reverse-phase HPLC. AA2G transdermal fluxes using Franz cells with 760 µm thick pig skin samples were also measured. RESULTS: Photoacoustic waves transiently enhanced skin permeability and increased dermal delivery of AA2G. AA2G was released from the formulation nearly quantitatively (92.6 ± 6.2%) in 24 h, showing a non-Fickian behaviour controlled by diffusion and swelling. AA2G dermal delivery with exposure for 5 min to PA waves was compared with passive delivery to pig skin. PA waves increased the delivery of AA2G to the skin by a factor of 15-fold with respect to passive delivery, as measured from skin extracts after 1 h of contact of the formulation with the skin. CONCLUSION: Five minutes of exposure to PA waves is a safe and effective method to deliver large quantities of AA2G to the skin.

OBJECTIF: L'acide ascorbique (c.-à-d. la vitamine C) est un antioxydant important présent dans la peau. Le rôle protecteur de la vitamine C contre le photovieillissement a motivé de nombreuses tentatives pour favoriser son administration topique, avec un succès limité par son instabilité chimique et sa mauvaise perméabilité cutanée. Les précurseurs de la vitamine C, tels que l'acide ascorbique 2-glucoside (AA2G), qui sont métabolisés en vitamine C par les enzymes présentes dans la peau, résolvent le problème de stabilité, mais sont limités par une faible perméabilité de la peau. Nous avons développé une formulation type gel à 2 % (p/v) d'AA2G (viscosité 4,30 × 104 Pa.s, pH 5,94) et comparé son administration dermique passive à l'administration favorisée par des ondes photoacoustiques qui perturbent transitoirement la barrière cutanée. MÉTHODES: Les ondes photoacoustiques (PA) ont été générées par des impulsions laser absorbées par des transducteurs piézophotoniques (lumière vers pression). Des échantillons de peau de porc ont été exposés à la formulation d'AA2G à 2 % seule ou associée à 5 min d'ondes PA. Une heure plus tard, l'AA2G a été extrait de la peau et quantifié par chromatographie en phase liquide à haute performance en phase inverse. Les flux transdermiques d'AA2G utilisant des cellules de Franz avec des échantillons de peau de porc épaisse de 760 µm ont également été mesurés. RÉSULTATS: Les ondes photoacoustiques ont amélioré transitoirement la perméabilité de la peau et augmenté l'administration dermique d'AA2G. L'AA2G a été libéré de la formulation presque quantitativement (92,6 ± 6,2 %) en 24 h, montrant un comportement non-Fickian contrôlé par diffusion et gonflement. L'administration cutanée d'AA2G avec une exposition de 5 min aux ondes PA a été comparée à l'administration passive sur peau de porc. Les ondes PA ont augmenté l'administration d'AA2G dans la peau d'un facteur de 15 concernant l'administration passive, mesurée à partir d'extraits cutanés après 1 h de contact de la formulation avec la peau. CONCLUSIONS: Cinq minutes d'exposition aux ondes PA est une méthode sûre et efficace pour administrer de grandes quantités d'AA2G dans la peau.

Synergic dual phototherapy: Cationic imidazolyl photosensitizers and ciprofloxacin for eradication of in vitro and in vivo E. coli infections.

The emergence of new microorganisms with resistance to current antimicrobials is one of the key issues of modern healthcare that must be urgently addressed with the development of new molecules and therapies. Photodynamic inactivation (PDI) in combination with antibiotics has been recently regarded as a promising wide-spectrum therapy for the treatment of localized topical infections. However, further studies are required regarding the selection of the best photosensitizer structures and protocol optimization, in order to maximize the efficiency of this synergic interaction. In this paper, we present results that demonstrate the influence of the structure of cationic imidazolyl-substituted photosensitizers and light on the enhancement of ciprofloxacin (CIP) activity, for the inactivation of Escherichia coli. Structure-activity studies have highlighted the tetra cationic imidazolyl porphyrin IP-H-Me4+ at sub-bactericide concentrations (4-16 nM) as the most promising photosensitizer for combination with sub-inhibitory CIP concentration (<0.25 mg/L). An optimized dual phototherapy protocol using this photosensitizer was translated to in vivo studies in mice wounds infected with E. coli. This synergic combination reduced the amount of photosensitizer and ciprofloxacin required for full E. coli inactivation and, in both in vitro and in vivo studies, the combination therapy was clearly superior to each monotherapy (PDI or ciprofloxacin alone). Overall, these findings highlight the potential of cationic imidazolyl porphyrins in boosting the activity of antibiotics and lowering the probability of resistance development, which is essential for a sustainable long-term treatment of infectious diseases.

Photodynamic disinfection of SARS-CoV-2 clinical samples using a methylene blue formulation.

The amplitude of the coronavirus disease 2019 (COVID-19) pandemic motivated global efforts to find therapeutics that avert severe forms of this illness. The urgency of the medical needs privileged repositioning of approved medicines. Methylene blue (MB) has been in clinical use for a century and proved especially useful as a photosensitizer for photodynamic disinfection (PDI). We describe the use of MB to photo-inactivate SARS-CoV-2 in samples collected from COVID-19 patients. One minute of treatment can reduce the percentage inhibition of amplification by 99.99% under conditions of low cytotoxicity. We employed a pseudotyped lentiviral vector (LVs) encoding the luciferase reporter gene and exhibiting the S protein of SARS-CoV-2 at its surface, to infect human ACE2-expressing HEK293T cells. Pre-treatment of LVs with MB-PDI prevented infection at low micromolar MB concentrations and 1 min of illumination. These results reveal the potential of MB-PDI to reduce viral loads in the nasal cavity and oropharynx in the early stages of COVID-19, which may be employed to curb the transmission and severity of the disease.

Photodynamic disinfection and its role in controlling infectious diseases.

Photodynamic therapy is witnessing a revival of its origins as a response to the rise of multi-drug resistant infections and the shortage of new classes of antibiotics. Photodynamic disinfection (PDDI) of microorganisms is making progresses in preclinical models and in clinical cases, and the perception of its role in the clinical armamentarium for the management of infectious diseases is changing. We review the positioning of PDDI from the perspective of its ability to respond to clinical needs. Emphasis is placed on the pipeline of photosensitizers that proved effective to inactivate biofilms, showed efficacy in animal models of infectious diseases or reached clinical trials. Novel opportunities resulting from the COVID-19 pandemic are briefly discussed. The molecular features of promising photosensitizers are emphasized and contrasted with those of photosensitizers used in the treatment of solid tumors. The development of photosensitizers has been accompanied by the fabrication of a variety of affordable and customizable light sources. We critically discuss the combination between photosensitizer and light source properties that may leverage PDDI and expand its applications to wider markets. The success of PDDI in the management of infectious diseases will ultimately depend on the efficacy of photosensitizers, affordability of the light sources, simplicity of the procedures, and availability of fast and efficient treatments.

Imaging of photoacoustic-mediated permeabilization of giant unilamellar vesicles (GUVs).

Target delivery of large foreign materials to cells requires transient permeabilization of the cell membrane without toxicity. Giant unilamellar vesicles (GUVs) mimic the phospholipid bilayer of the cell membrane and are also useful drug delivery vehicles. Controlled increase of the permeability of GUVs is a delicate balance between sufficient perturbation for the delivery of the GUV contents and damage to the vesicles. Here we show that photoacoustic waves can promote the release of FITC-dextran or GFP from GUVs without damage. Real-time interferometric imaging offers the first movies of photoacoustic wave propagation and interaction with GUVs. The photoacoustic waves are seen as mostly compressive half-cycle pulses with peak pressures of ~ 1 MPa and spatial extent FWHM ~ 36 µm. At a repetition rate of 10 Hz, they enable the release of 25% of the FITC-dextran content of GUVs in 15 min. Such photoacoustic waves may enable non-invasive targeted release of GUVs and cell transfection over large volumes of tissues in just a few minutes.

Singlet Exciton Fission and Associated Enthalpy Changes with a Covalently Linked Bichromophore Comprising TIPS-Pentacenes Held in an Open Conformation.

A covalently linked bichromophore, embracing 6,13-bis(triisopropylsilylethinyl)pentacene (TIPS-pentacene) terminals bridged by a rigid fluorene spacer, generates a relatively high yield (i.e., 65 ± 6%) of the spin-correlated, triplet biexciton upon illumination in toluene. Under the same conditions, the extent of fluorescence quenching relative to the parent TIPS-pentacene approaches 97% and is insensitive to temperature. The biexciton, having overall singlet spin multiplicity, undergoes internal conversion in competition to spin decorrelation. These latter processes occur on the relatively slow time scale of a hundred or so nanoseconds, possibly reflecting the restricted level of electronic communication between the terminals. Spin decorrelation leads to evolution of an independent triplet pair with an overall quantum yield of 0.50 ± 0.06 and a lifetime of 8 ± 2 µs in deaerated toluene. Photoacoustic calorimetry (PAC) indicates three separate enthalpy changes: a very fast step associated with intramolecular singlet exciton fission to form the correlated triplet biexciton, a fast step essentially reflecting spin decorrelation, and a slow step associated with relaxation of the independent triplet pair. Analysis of the PAC data, in conjunction with the transient absorption results, establishes excitation energies for both spin-correlated and independent triplet pairs. Polar solvent enhances both fluorescence quenching and triplet formation at the expense of radiationless decay while temperature effects have been recorded for all important intermediate species.

Photoacoustic generation of intense and broadband ultrasound pulses with functionalized carbon nanotubes.

Carbon nanotubes (CNT) functionalized with siloxane groups were dissolved in polystyrene/tetrahydrofuran to produce thin films that generate broadband and intense ultrasound pulses when excited by pulsed lasers. These films absorb >99% of light in the visible and near-infrared and show no signs of fatigue after thousands of laser pulses. Picosecond laser pulses with fluences of 50 mJ cm-2 generate photoacoustic waves with exceptionally wide bandwidths (170 MHz at -6 dB) and peak pressures >1 MPa several millimeters away from the source. The ability to generate such broadband ultrasound pulses is assigned to the ultrafast dissipation of heat by CNT-siloxanes, and to the formation of very thin photoacoustic sources thanks to the high speed of sound of polystyrene. The wide bandwidths achieved allow for axial resolutions of 8 µm at depths less than 1 mm, similar to the resolution of histology but based on real-time non-invasive methods.