Enhanced Photodynamic Therapy

The following sections are included:

• Preface
• About the Editors
• Contents

Irradiance uniformity is an important parameter for a Photodynamic Therapy (PDT) device. The calibration and verification of a LED array light source based on computer vision technology were implemented and carried out. First, the correlation coefficients between the pulse width modulate value and the irradiance were calibrated. Then, the correction of the actual light center and divergence angle were solved by image processing to reduce errors from each LED lens. Finally, uniformity was optimized according to the irradiance formula of the Lambertian source. The lowest coefficients of variation of irradiance were 4.87% in a 5 cm × 12 cm area and 3.55% in a 3 cm × 10 cm area within the depth range of 8–12 cm when the expected irradiance was 100 mW/cm². This finding indicated that the light source can achieve a more uniform illumination and provide a better therapeutic effect for the PDT of port-wine stains.

Photodynamic therapy (PDT) is a minimally invasive method for treating oral leukoplakia. In this paper, we propose a portable PDT device consisting of a flexible circuit board with a liquid flow cooling module on the back. The light source size was 17 mm × 11 mm × 4 mm, and the irradiation area of the light source was up to 100 mm². The irradiance range of this device was from 10 mW/cm² to 100 mW/cm². Simulation and experimental results showed that the irradiance coefficient variation for a treatment area of 81 mm² was less than 7%. At an irradiance of 100 mW/cm², a device surface temperature of lower than 42^°C can be achieved to satisfy the safety requirements under the conditions that the temperature of cooling liquid is 10^°C and the liquid flow speed is above 12 mL/min.

Rosacea presents as transient or persistent erythema, papules, pustules, flushing, and telangiectasia on the middle of the face, which has some clinical similarity with actinic keratosis (AK). These two conditions can coexist in the same patient. Dermoscopy and reflectance confocal microscopy (RCM) could be useful methods for diagnosis and monitoring treatment efficacy. Novel intense pulsed light-photodynamic therapy (IPL-PDT) may have better tolerance and curative effect than traditional red-light 5-aminolevulinic acid photodynamic therapy (ALA-PDT). Herein, we present a case of facial AKs concomitant with rosacea where combination therapy of novel IPL-PDT and oral minocycline was effective in that AK lesions were eliminated and the patient’s facial erythema and telangiectasia were significantly improved.

Photodynamic therapy (PDT) has become an attractive tumor treatment modality because of its noninvasive feature and low side effects. However, extreme hypoxia inside solid tumors severely impedes PDT therapeutic outcome. To overcome this obstacle, various strategies have been developed recently. Among them, in situ oxygen generation, which relies on the decomposition of tumor endogenous H₂O₂, and oxygen delivery tactic using high oxygen loading capacity of hemoglobin or perfluorocarbons, have been widely studied. The in situ oxygen generation strategy has high specificity to tumors, but its oxygen-generating efficiency is limited by the intrinsically low tumor H₂O₂ level. In contrast, the oxygen delivery approach holds advantage of high oxygen loading efficiency, nevertheless lacks tumor specificity. In this work, we prepared a nanoemulsion system containing H₂O₂-responsive catalase, highly efficient oxygen carrier perfluoropolyether (PFPE), and a near-infrared (NIR) light activatable photosensitizer IR780, to combine the high tumor specificity of the in situ oxygen generation strategy and the high efficiency of the oxygen delivery strategy. This concisely prepared nanoplatform exhibited enhanced and H₂O₂-controllable production of singlet oxygen under light excitation, satisfactory cytocompatibility, and ability to kill cancer cells under NIR light excitation. This highlights the potential of this novel nanoplatform for highly efficient and selective NIR light mediated PDT against hypoxic tumors. This research provides new insight into the design of intelligent nanoplatform for relieving tumor hypoxia and enhancing the oxygen-dependent PDT effects in hypoxic tumors.

Photodynamic therapy (PDT) takes advantage of photosensitizers (PSs) to generate reactive oxygen species (ROS) for cell killing when excited by light. It has been widely used in clinic for therapy of multiple cancers. Currently, all the FDA-approved PSs, including porphyrin, are all small organic molecules, suffering from aggregation-caused quenching (ACQ) issues in biological environment and lacking tumor targeting capability. Nanoparticles (NPs) with size between 20 nm and 200 nm possess tumor targeting capability due to the enhanced permeability and retention (EPR) effect. It is urgent to develop a new strategy to form clinical-approved-PSs-based NPs with improved ROS generation capability. In this study, we report a strategy to overwhelm the ACQ of porphyrin by doping it with a type of aggregation-induced emission (AIE) luminogen to produce a binary NPs with high biocompatibility, and enhanced fluorescence and ROS generation capability. Such NPs can be readily synthesized by mixing a porphyrin derivative, Ce6 with a typical AIE luminogen, TPE-Br. Here, our experimental results have demonstrated the feasibility and effectiveness of this strategy, endowing it a great potential in clinical applications.

Bacterial infection is an acute infection caused by pathogens or conditional pathogens, which leads to severe disease and even death. It has become a significant reason for diseases and deaths worldwide. Therefore, rapid and precise detection, diagnosis, and treatment in the early stage are the key to deal with bacterial infections. Over recent years, along with the advances in biomaterials and nanotechnology, numerous nanomaterial-based multifunctional probes have been extensively explored in the biomedical field. Because of their excellent optical properties, inorganic optical nanoprobes are used to rapidly detect bacterial infection in the early stage and show excellent antibacterial properties, which has a great application prospect in antibacterial therapy expected to reduce the risk of bacterial infection. In this mini-review, we generally overviewed and summarized recent progress on inorganic nanoparticle-based optical imaging techniques as a platform to construct functional theranostics for the efficient treatment of bacterial infections. The opportunities and challenges in the application of fluorescent optical nanoprobes are prospected.

Photodynamic antibacterial therapy shows great potential in bacterial infection and the reactive oxygen species (ROS) production of the photosensitizers is crucial for the therapeutic effect. Introducing heavy atoms is a common strategy to enhance photodynamic performance, while dark toxicity can be induced to impede further clinical application. Herein, a novel halogen-free photosensitizer Aza-BODIPY-BODIPY dyad NDB with an orthogonal molecular configuration was synthesized for photodynamic antibacterial therapy. The absorption and emission peaks of NDB photosensitizer in toluene were observed at 703 nm and 744 nm, respectively. The fluorescence (FL) lifetime was measured to be 2.8 ns in toluene. Under 730 nm laser illumination, the ROS generation capability of NDB was 3-fold higher than that of the commercial ICG. After nanoprecipitation, NDB NPs presented the advantages of high photothermal conversion effciency (39.1%), good photostability, and excellent biocompatibility. More importantly, in vitro antibacterial assay confirmed that the ROS and the heat generated by NDB NPs could extirpate methicillin-resistant S. aureus effectively upon exposure to 730 nm laser, suggesting the potential application of NDB NPs in photo-initiated antibacterial therapy.

Photodynamic inactivation of microorganisms known as antibacterial photodynamic therapy (APDT) is one of the most promising and innovative approaches for the destruction of pathogenic microorganisms. Among the photosensitizers (PSs), compounds based on cationic porphyrins/metalloporphyrins are most successfully used to inactivate microorganisms. Series of meso-substituted cationic pyridylporphyrins and metalloporphyrins with various peripheral groups in the third and fourth positions of the pyrrole ring have been synthesized in Armenia. The aim of this work was to determine and test the most effective cationic porphyrins and metalloporphyrins with high photoactivity against Gram negative and Gram positive microorganisms. It was shown that the synthesized cationic pyridylporphyrins/metalloporphyrins exhibit a high degree of phototoxicity towards both types of bacteria, including the methicillin-resistant S. aureus strain. Zinc complexes of porphyrins are more phototoxic than metal-free porphyrin analogs. The effectiveness of these Zn–metalloporphyrins on bacteria is consistent with the level of singlet oxygen generation. It was found that the high antibacterial activity of the studied cationic porphyrins/metalloporphyrins depends on four factors: the presence in the porphyrin macrocycle of a positive charge (+4), a central metal atom (Zn²⁺) and hydrophobic peripheral functional groups as well as high values of quantum yields of singlet oxygen. The results indicate that meso-substituted cationic pyridylporphyrins/metalloporphyrins can find wider application in photoinactivation of bacteria than anionic or neutral PSs usually used in APDT.

Near-infrared (NIR) spectral analysis, which has the advantages of rapidness, nondestruction and high-effciency, is widely used in the detection of feed, food and mineral. In terms of qualitative identification, it can also be used for the discriminant analysis of medicines. Long short-term memory (LSTM) neural network, bidirectional long short-term memory (BiLSTM) neural network and gated recurrent unit (GRU) network are variants of the recurrent neural network (RNN). The potential relationship between nonlinear features learned from the sequence by these variants is used to complete the missions in fields such as natural language processing, signal classification and video analysis. Since the effect of these variants in drug identification is still to be studied, this paper constructs a multiclassifier of these three variants, using compound α-keto acid tablets produced by four manufacturers and repaglinide tablets produced by five manufacturers as the research object. Then, the paper analyzes the impacts of seven different pre-processed methods on the drug NIR data by constructing different layers of LSTM, BiLSTM and GRU networks and compares different classification model indicators and training time of each model. When the spectrum data are pre-processed by z-score normalization, the GRU-3 model has the best accuracy in all models. The BiLSTM models are better for analyzing high coincidence data. The method proposed in this paper can be further extended to other NIR spectroscopy data sets.

Near infrared (NIR) fluorescence imaging guided photodynamic therapy (PDT) is a technique which has been developed in many clinical trials due to its advantage of real-time optical monitoring, specific spatiotemporal selectivity, and minimal invasiveness. For this, photosensitizers with NIR fluorescence emission and high ¹O₂ generation quantum yield are highly desirable. Herein, we designed and synthesized a “donor–acceptor” (D-A) structured semiconductor polymer (SP), which was then wrapped with an amphiphilic compound (Pluronic^® F127) to prepare water-soluble nanoparticles (F-SP NPs). The obtained F-SP NPs exhibit good water solubility, excellent particle size stability, strong absorbance at deep red region, and strong NIR fluorescent emission characteristics. The maximal mass extinction coeffcient and fluorescence quantum yield of these F-SPs were calculated to be 21.7 L/(g·cm) and 6.5%, respectively. Moreover, the ¹O₂ quantum yield of 89% for F-SP NPs has been achieved under 635 nm laser irradiation, which is higher than Methylene Blue, Ce6, and PpIX. The outstanding properties of these F-SP NPs originate from their unique D-A molecular characteristic. This work should help guide the design of novel semiconductor polymer for NIR fluorescent imaging guided PDT applications.

The discovery of aggregation-induced emission (AIE) effect provides opportunities for the rapid development of fluorescence imaging-guided photodynamic therapy (PDT). In this work, a boron dipyrromethene (BODIPY)-based photosensitizer (ET-BDP-O) with AIE characteristics was developed, in which the two linear arms of BODIPY group were linked with triphenylamine to form an electron Donor–Acceptor–Donor (D–A–D) architecture while side chain was equipped with triethylene glycol group. ET-BDP-O was able to directly self-assemble into nanoparticles (NPs) without supplement of any other matrices or stabilizers due to its amphiphilic property. The as-prepared ET-BDP-O NPs had an excellent colloid stability with the size of 125 nm. Benefiting from the AIE property, ET-BDP-O NPs could generate strong fluorescence and reactive oxygen species under light-emitting diode light irradiation (60 mW/cm². After internalized in cancer cells, ET-BDP-O NPs were able to emit bright red fluorescence signal for bioimaging. In addition, the cell viability assay demonstrated that the ET-BDP-O NPs exhibited excellent photo-cytotoxicity against cancer cells, while negligible cytotoxicity under dark environment. Thus, ET-BDP-O NPs might be regarded as a promising photosensitizer for fluorescence imagingguided PDT in future.

Photodynamic therapy (PDT) is a new and rapidly developing treatment modality for clinical cancer therapy. Semiconductor polymer dots (Pdots) doped with photosensitizers have been successfully applied to PDT, and have made progress in the field of tumor therapy. However, the problems of severe photosensitivity and limited tissue penetration depth are needed to be solved during the implementation process of PDT. Here we developed the Pdots doped with photosensitizer molecule Chlorin e6 (Ce6) and photochromic molecule 1,2-bis(2,4-dimethyl-5-phenyl-3-thiophene)-3,3,4,5-hexafluoro-1-cyclopentene (BTE) to construct a photo-switchable nanoplatform for PDT. The Ce6-BTE-doped Pdots were in the green region, and the tissue penetration depth was increased compared with most Pdots in the blue region. The reversible conversion of BTE under different light irradiation was utilized to regulate the photodynamic effect and solve the problem of photosensitivity. The prepared Ce6-BTE-doped Pdots had small size, excellent optical property, efficient ROS generation and good photoswitchable ability. The cellular uptake, cytotoxicity, and photodynamic effect of the Pdots were detected in human colon tumor cells. The experiments in vitro indicated that Ce6-BTE-doped Pdots could exert excellent photodynamic effect in ON state and reduce photosensitivity in OFF state. These results demonstrated that this nanoplatform holds the potential to be used in clinical PDT.

Metal- and metal-oxide-based nanoparticles have been widely exploited in cancer photodynamic therapy (PDT). Among these materials, cerium-based nanoparticles have drawn extensive attention due to their superior biosafety and distinctive physicochemical properties, especially the reversible transition between the valence states of Ce(III) and Ce(IV). In this review, the recent advances in the use of cerium-based nanoparticles as novel photosensitizers for cancer PDT are discussed, and the activation mechanisms for electron transfer to generate singlet oxygen are presented. In addition, the types of cerium-based nano-particles used for PDT of cancer are summarized. Finally, the challenges and prospects of clinical translations of cerium-based nanoparticles are briefly addressed.

Targeted photodynamic therapy (TPDT) based on the photosensitizers responsive for tumor microenvironment is promising because of the better anti-tumor effect and less phototoxicity against normal tissue than the traditional PDT. Nanoparticle-based stimuli-responsive photosensitizers have been widely explored for TPDT. Based on the acidic microenvironments in solid tumors, an ultrasmall pH-responsive silicon phthalocyanine nanomicelle (PSN) (smaller than 10 nm) was designed for selective PDT of tumor. PSN had high drug loading efficacy (more than 28%) and exhibited morphological transitions, enhanced fluorescence and improved singlet oxygen yield under acidic environments. PSN was renal clearable and could rapidly accumulate and be retained at tumor sites, achieving a tumor-inhibiting effect better than phthalocyanine micelle without pH response. Tumors of mice treated with PSN for PDT were completely ablated without recurrence. Thus, we have developed a phthalocyanine-based pH-responsive micelle with excellent tumor targeting ability, which is expected to realize the selective PDT of tumor.

Optical coherence tomography angiography (OCTA) has emerged as an advanced in vivo imaging modality, which is widely used for the clinic ophthalmology and neuroscience research in the rodent brain cortex among others. Based on the high numerical aperture (NA) probing lens and the motion-corrected algorithms, a high-resolution imaging technique called OCT micro-angiography is applied to resolve the small blood capillary vessels ranging from 5 μm to 10 μm in diameter. As OCT-based techniques are recently evolving further from the structural imaging of capillaries toward spatio-temporal dynamic imaging of blood flow in capillaries, here we present a review on the latest techniques for the dynamic flow imaging. Studies on capillary blood flow using these techniques will help us better understand the roles of capillary blood flow for normal functioning of the brain as well as how it malfunctions in diseases.

Structured illumination microscopy (SIM) is a rapidly developing super-resolution technology. It has been widely used in various application fields of biomedicine due to its excellent two- and three-dimensional imaging capabilities. Furthermore, faster three-dimensional imaging methods are required to help enable more research-oriented living cell imaging. In this paper, a fast and sensitive three-dimensional structured illumination microscopy based on asymmetric three-beam interference is proposed. An innovative time-series acquisition method is employed to halve the time required to obtain each raw image. A segmented half-wave plate as a substantial linear polarization modulation method is applied to the three-dimensional SIM system for the first time. Although it needs to acquire 21 raw images instead of 15 to reconstruct one super-resolution image, the SIM setup proposed in this paper is 30% faster than the traditional spatial light modulator-SIM (SLM-SIM) in imaging each super-resolution image. The related theoretical derivation, hardware system, and verification experiment are elaborated in this paper. The stable and fast 3D super-resolution imaging method proposed in this paper is of great significance to the research of organelle interaction, intercellular communication, and other biomedical fields.

The current work is focused on the study of optical clearing of skeletal muscles under local compression. The experiments were performed on in vitro bovine skeletal muscle. The time dependence of optical clearing was studied by monitoring the luminescence intensity of NaYF₄:Er,Yb upconverting particles located under tissue layers. This study shows the possibility to use upconverting nanoparticles (UCNPs) both for studying the dynamics of the optical clearing of biological tissue under compression and to detect moments of cell wall damage under excessive pressure. The advantage of using UCNPs is the presence of several bands in their luminescence spectra, located both at close wavelengths and far apart.

We propose a high-speed all-optic dual-modal system that integrates spectral-domain optical coherence tomography and photoacoustic microscopy (PAM). A 3 * 3 coupler-based interferometer is used to remotely detect the surface vibration caused by photoacoustic (PA) waves. Three outputs of the interferometer are acquired simultaneously with a multi-channel data acquisition card. One channel data with the highest PA signal detection sensitivity is selected for sensitivity compensation. Experiment on the phantom demonstrates that the proposed method can successfully compensate for the loss of intensity caused by sensitivity variation. The imaging speed of the PAM is improved compared to our previous system. The total time to image a sample with 256 × 256 pixels is ∼20 s. Using the proposed system, the microvasculature in the mouse auricle is visualized and the blood flow state is accessed.

Singlet oxygen (¹O₂) is the main cytotoxic substance in Type II photodynamic therapy (PDT). The luminescence of ¹O₂ at 1270 nm is extremely weak with a low quantum yield, making the direct detection of ¹O₂ at 1270 nm very challenging. In this study, a set of highly sensitive optical fiber detection system is built up to detect the luminescence of photosensitized ¹O₂. We use this system to test the luminescence characteristics of ¹O₂ in pig skin tissue ex vivo and mouse auricle skin in vivo. The experimental results show that the designed system can quantitatively detect photosensitized ¹O₂ luminescence. The ¹O₂ luminescence signal at 1270 nm is successfully detected in pig skin ex vivo. Compared with RB in an aqueous solution, the lifetime of ¹O₂ increases to 17.4 ±1.2 μs in pig skin tissue ex vivo. Experiments on living mice suggest that an enhancement of ¹O₂ intensity with the increase of the TMPyP concentration. When the dose is 25 mg/kg, the vasoconstriction can reach more than 80%. The results of this study hold the potential application for clinical PDT dose monitoring using an optical fiber detection system.

The MINimal emission FLUXes (MINFLUX) technique in optical microscopy, widely recognized as the next innovative fluorescence microscopy method, claims a spatial resolution of 1–3 nm in both dead and living cells. To make use of the full resolution of the MINFLUX microscope, it is important to select appropriate fluorescence probes and labeling strategies, especially in living-cell imaging. This paper mainly focuses on recent applications and developments of fluorescence probes and the relevant labeling strategy for MINFLUX microscopy. Moreover, we discuss the deficiencies that need to be addressed in the future and a plan for the possible progression of MINFLUX to help investigators who have been involved in or are just starting in the field of super-resolution imaging microscopy with theoretical support.