Evaluating the Photodynamic Biocidal Activity and Investigating the Mechanism of Thiazolium Cyanine Dyes

Selective antibacterial and antibiofilm activity of chlorinated hemicyanine against gram-positive bacteria

Antibiotic-free therapies are highly needed due to the limited success of conventional approaches especially against biofilm related infections. In this direction, antimicrobial phototherapy, either in the form of antimicrobial photothermal therapy (aPTT) or antimicrobial photodynamic therapy (aPDT), have appeared to be highly promising candidates in recent years. These are local and promising approaches for antibiotic resistant bacterial infections and biofilms. Organic small photosensitizers (PSs) are extensively preferred in antimicrobial phototherapy applications as they offer a great opportunity to combine therapeutic action (aPTT, aPDT or both) with fluorescence imaging on a single molecule. In this study, the bactericidal effect of cationic chlorinated hemicyanine (Cl-Hem)-based type I PS, which can function as a dual aPDT/aPTT agent, was investigated on both planktonic cells and biofilms of different gram-positive (E. faecalis and S. epidermidis) and gram-negative bacteria (P. aeruginosa and K. pneumoniae) with and without 640 nm laser irradiation. Cl-Hem was shown to induce a selective phototheranostic activity against gram-positive bacteria (E. faecalis and S. epidermidis). Cl-Hem exhibited both dose and laser irradiation time dependent bactericidal effect on planktonic and biofilms of S. epidermidis. These results clearly showed that highly potent Cl-Hem can treat resistant microbial infections, while allowing fluorescence detection at the same time. High biofilm reduction observed with combined aPDT/aPTT action of Cl-Hem together with its non-cytotoxic nature points out that Cl-Hem is a promising PS for antibacterial and antibiofilm treatments.

Near-Infrared Dyes: Towards Broad-Spectrum Antivirals

Broad antiviral activity in vitro is known for many organic photosensitizers generating reactive oxygen species under irradiation with visible light. Low tissue penetration of visible light prevents further development of antiviral therapeutics based on these compounds. One possible solution to this problem is the development of photosensitizers with near-infrared absorption (NIR dyes). These compounds found diverse applications in the photodynamic therapy of tumors and bacterial infections, but they are scarcely mentioned as antivirals. In this account, we aimed to evaluate the therapeutic prospects of various NIR-absorbing and singlet oxygen-generating chromophores for the development of broad-spectrum photosensitizing antivirals.

Functional Cyanine-Based PVA:PVP Polymers as Antimicrobial Tools toward Food and Health-Care Bacterial Infections

The rising of multidrug-resistant bacteria and their associated proliferation as harmful microorganisms boosts the creation of new antibacterial surfaces and biomaterials with applications ranging from health to food packing. Herein, low-cost antibacterial PVA:PVP copolymers containing cyanine derivatives (1, 2, and 3) and their respective Cu²⁺ complexes are successfully obtained and tested against Gram-negative and Gram-positive bacteria. The possible application in food packing is addressed by covering the surface of typical paper mockups with the doped polymers. All dye-doped polymers present a broad-spectrum antibacterial effect against Gram-positive bacteria, especially for Bacillus cereus (B. cereus), Staphylococcus aureus (S. aureus), and methicillin-resistant S. aureus (MRSA) strains, with PVA:PVP@3 and PVA:PVP@3-Cu being the most effective. Moreover, polymers containing cyanine derivatives present interesting inhibition effects against Pseudomonas aeruginosa (P. aeruginosa), where the production of its characteristic blue/green virulent pigment is not observed. Of the coated paper mockups, PVA:PVP:paper@2 and PVA:PVP:paper@2-Cu are most effective against B. cereus and S. aureus, while PVA:PVP:paper@3 and PVA:PVP:paper@3-Cu are most effective against the MRSA strain. In these formulations, direct contact inhibition mechanisms appear to be more significant than diffusional mechanisms, due to cyanine release hindrance, making them very interesting and versatile platforms for medical and food applications.

Recent Strategies to Develop Innovative Photosensitizers for Enhanced Photodynamic Therapy

This review presents a robust strategy to design photosensitizers (PSs) for various species. Photodynamic therapy (PDT) is a photochemical-based treatment approach that involves the use of light combined with a light-activated chemical, referred to as a PS. Attractively, PDT is one of the alternatives to conventional cancer treatment due to its noninvasive nature, high cure rates, and low side effects. PSs play an important factor in photoinduced reactive oxygen species (ROS) generation. Although the concept of photosensitizer-based photodynamic therapy has been widely adopted for clinical trials and bioimaging, until now, to our surprise, there has been no relevant review article on rational designs of organic PSs for PDT. Furthermore, most of published review articles in PDT focused on nanomaterials and nanotechnology based on traditional PSs. Therefore, this review aimed at reporting recent strategies to develop innovative organic photosensitizers for enhanced photodynamic therapy, with each example described in detail instead of providing only a general overview, as is typically done in previous reviews of PDT, to provide intuitive, vivid, and specific insights to the readers.

Comparison and Mechanism Study of Antibacterial Activity of Cationic and Neutral Oligo-Thiophene-Ethynylene

Photodynamic therapy (PDT) is a potential approach to resolve antibiotic resistance, and phenylene/thiophene-ethynylene oligomers have been widely studied as effective antibacterial reagents. Oligomers with thiophene moieties usually exhibit good antibacterial activity under light irradiation and dark conditions. In the previous study, we verified that neutral oligo-p-phenylene-ethynylenes (OPEs) exhibit better antibacterial activity than the corresponding cationic ones; however, whether this regular pattern also operates in other kinds of oligomers such as oligo-thiophene-ethynylene (OTE) is unknown. Also, the antibacterial activity comparison of OTEs bearing cyclic and acyclic amino groups will offer useful information to further understand the role of amino groups in the antibacterial process and guide the antibacterial reagent design as amino groups affect the antibacterial activity a lot. We synthesized four OTEs bearing neutral or cationic, cyclic, or acyclic amino groups and studied their antibacterial activity in detail. The experimental results indicated that the OTEs exhibited better antibacterial activity than the OPEs, the neutral OTEs exhibited better antibacterial activity in most cases, and OTEs bearing cyclic amino groups exhibited better antibacterial activity than those bearing acyclic ones in most cases. This study provides useful guidelines for further antibacterial reagent design and investigations.

Wide bandgap semiconductor-based novel nanohybrid for potential antibacterial activity: ultrafast spectroscopy and computational studies

The properties of nanomaterials generated by external stimuli are considered an innovative and promising replacement for the annihilation of bacterial infectious diseases. The present study demonstrates the possibility of getting the antibiotic-like drug action from our newly synthesized nanohybrid (NH), which consists of norfloxacin (NF) as the photosensitive material covalently attached to the ZnO nanoparticle (NP). The synthesized NH has been characterized using various microscopic and spectroscopic techniques. Steady state fluorescence and time-correlated single photon counting (TCSPC)-based spectroscopic studies demonstrate the efficient electron transfer from NF to ZnO. This enhances the reactive oxygen species (ROS) production capability of the system. First principles density functional theory has been calculated to gain insight into the charge separation mechanism. To explore the electron densities of the occupied and unoccupied levels of NH, we have verified the nature of the electronic structure. It is observed that there is a very high possibility of electron transfer from NF to ZnO in the NH system, which validates the experimental findings. Finally, the efficacy of NH compared to NF and ZnO has been estimated on the in vitro culture of E. coli bacteria. We have obtained a significant reduction in the bacterial viability by NH with respect to control in the presence of light. These results suggest that the synthesized NH could be a potential candidate in the new generation alternative antibacterial drugs. Overall, the study depicts a detailed physical insight for nanohybrid systems that can be beneficial for manifold application purposes.

Hydrolytic Degradability, Cell Tolerance and On-Demand Antibacterial Effect of Electrospun Photodynamically Active Fibres

Photodynamically active fibres (PAFs) are a novel class of stimulus-sensitive systems capable of triggering antibiotic-free antibacterial effect on-demand when exposed to light. Despite their relevance in infection control, however, the broad clinical applicability of PAFs has not yet been fully realised due to the limited control in fibrous microstructure, cell tolerance and antibacterial activity in the physiologic environment. We addressed this challenge by creating semicrystalline electrospun fibres with varying content of poly[(l-lactide)-co-(glycolide)] (PLGA), poly(ε-caprolactone) (PCL) and methylene blue (MB), whereby the effect of polymer morphology, fibre composition and photosensitiser (PS) uptake on wet state fibre behaviour and functions was studied. The presence of crystalline domains and PS-polymer secondary interactions proved key to accomplishing long-lasting fibrous microstructure, controlled mass loss and controlled MB release profiles (37 °C, pH 7.4, 8 weeks). PAFs with equivalent PLGA:PCL weight ratio successfully promoted attachment and proliferation of L929 cells over a 7-day culture with and without light activation, while triggering up to 2.5 and 4 log reduction in E. coli and S. mutans viability, respectively. These results support the therapeutic applicability of PAFs for frequently encountered bacterial infections, opening up new opportunities in photodynamic fibrous systems with integrated wound healing and infection control capabilities.