Dual Modality FeS Nanoparticles with Reactive Oxygen Species-Induced and Photothermal Toxicity toward Pathogenic Bacteria

Inorganic Fe-O and Fe-S oxidoreductases: paradigms for prebiotic chemistry and the evolution of enzymatic activity in biology

Oxidoreductases play crucial roles in electron transfer during biological redox reactions. These reactions are not exclusive to protein-based biocatalysts; nano-size (<100 nm), fine-grained inorganic colloids, such as iron oxides and sulfides, also participate. These nanocolloids exhibit intrinsic redox activity and possess direct electron transfer capacities comparable to their biological counterparts. The unique metal ion architecture of these nanocolloids, including electron configurations, coordination environment, electron conductivity, and the ability to promote spontaneous electron hopping, contributes to their transfer capabilities. Nano-size inorganic colloids are believed to be among the earliest 'oxidoreductases' to have 'evolved' on early Earth, playing critical roles in biological systems. Representing a distinct type of biocatalysts alongside metalloproteins, these nanoparticles offer an early alternative to protein-based oxidoreductase activity. While the roles of inorganic nano-sized catalysts in current Earth ecosystems are intuitively significant, they remain poorly understood and underestimated. Their contribution to chemical reactions and biogeochemical cycles likely helped shape and maintain the balance of our planet's ecosystems. However, their potential applications in biomedical, agricultural, and environmental protection sectors have not been fully explored or exploited. This review examines the structure, properties, and mechanisms of such catalysts from a material's evolutionary standpoint, aiming to raise awareness of their potential to provide innovative solutions to some of Earth's sustainability challenges.

Green synthesis of silver and iron oxide nanoparticles mediated photothermal effects on Blastocystis hominis

The evolution of parasite resistance to antiparasitic agents has become a serious health issue indicating a critical and pressing need to develop new therapeutics that can conquer drug resistance. Nanoparticles are novel, promising emerging drug carriers that have demonstrated efficiency in treating many parasitic diseases. Lately, attention has been drawn to a broad-spectrum nanoparticle capable of converting absorbed light into heat via the photothermal effect phenomenon. The present study is the first to assess the effect of silver nanoparticles (Ag NPs) and iron oxide nanoparticles (Fe3O4 NPs) as sole agents and with the combined action of the light-emitting diode (LED) on Blastocystis hominins (B. hominis) in vitro. Initially, the aqueous synthesized nanoparticles were characterized by UV-Vis spectroscopy, zeta potential, and transmission electron microscopy (TEM). The anti-blastocyst efficiency of these NPs was tested separately in dark conditions. As these NPs have a wide absorption spectrum in the visible regions, they were also excited by a continuous wave LED of wavelength band (400-700 nm) to test the photothermal effect. The sensitivity of B. hominis cysts was evaluated using scanning laser confocal microscopy whereas the live and dead cells were accurately segmented based on superpixels and the k-mean clustering algorithm. Our findings showed that this excitation led to hyperthermia that induced a significant reduction in the number of cysts treated with photothermally active NPs. The results of this study elucidate the potential role of photothermally active NPs as an effective anti-blastocystis agent. By using this approach, new therapeutic antiparasitic agents can be developed.

Nanomaterials as multimodal photothermal agents (PTAs) against 'Superbugs'

Superbugs, also known as multidrug-resistant bacteria, have become a lethal and persistent threat due to their unresponsiveness toward conventional antibiotics. The main reason for this is that superbugs can rapidly mutate and restrict any foreign drug/molecule in their vicinity. Herein, nanomaterial-mediated therapies have set their path and shown burgeoning efficiency toward the ablation of superbugs. Notably, treatment modalities like photothermal therapy (PTT) have shown prominence in killing multidrug-resistant bacteria with their ability to generate local heat shock-mediated hyperthermia in such species. However, photothermal treatment has some serious limitations, such as high cost, complexity, and even toxicity to some extent. Hence, it is important to resolve such shortcomings of PTTs as they provide substantial tissue penetration. This is why multimodal PTTs have emerged and taken over this domain of research for the past few years. In this work, we have summarized and critically reviewed such exceptional works of recent times and provided a perspective to enhance their efficiencies. Profoundly, we discuss the design rationales of some novel photothermal agents (PTAs) and shed light on their mechanisms. Finally, challenges for PTT-derived multimodal therapy are presented, and capable synergistic bactericidal prospects are anticipated.

A bioinspired polydopamine-FeS nanocomposite with high antimicrobial efficiency via NIR-mediated Fenton reaction

Ferrous and sulfur ions are essential elements for the human body, which play an active role in maintaining the body's normal physiology. Meanwhile, mussel-inspired polydopamine (PDA) possesses good hydrophilicity and biocompatibility. In the present work, ferrous sulfide embedded into polydopamine nanoparticles (PDA@FeS NPs) was designed and synthesized via a simple predoping polymerization-coprecipitation strategy and the intelligent PDA matrix successfully prevented the oxidation and agglomeration of FeS nanoparticles. Importantly, there was an obvious synergistic enhancement of the photothermal effect between polydopamine and ferrous sulfide. The PDA@FeS NPs exhibited excellent photothermal antibacterial effects against both E. coli and S. aureus. The near-infrared (NIR) light-mediated release of ferrous ions could reach about 26.5% under weakly acidic conditions, further triggering the Fenton reaction to produce toxic hydroxyl radicals (·OH) in the presence of hydrogen peroxide. The antibacterial mechanism could be attributed to cell membrane damage and cellular content leakage with the synergistic effect of PTT and CDT. This study highlighted the germicidal efficacy of PDA@FeS NPs and provided a new strategy for designing and developing next-generation antibacterial platforms.

FeS/FeS2 nanoscale structures synthesized in one step from Fe(ll) dithiocarbamate complexes as a single source precursor

Nanoscale FeS and FeS2 mixed phases were synthesized by one-pot decomposition of (N-anil-N-piperldtc)Fe1 as FeS#1), (N-piperldtc)Fe2 as FeS#2) and (N-anildtc)Fe3 as FeS#3) complexes as precursors, with the help of tri-n-octylphosphine oxide (TOPO) coordinating solvent. Their morphology, stability, size, optical and structural characteristics were observed using various material characterization instruments. In comparison to the FeS#2 nano-flower shape, FeS#1 and FeS#3 have a uniform nano-rod shape. A one-step decomposition pattern was obtained from the thermal gravimetric analysis (TGA) results with 3% final mass residual. The high-resolution transmission electron microscopy (HRTEM) image reveals an aggregation and size diameter of around 14.47–30.25 nm for the three samples. The optical response between 3.8 and 4.2 eV from the three samples shows that they are inconsiderable materials for solar cells application. The diffraction peaks for the three samples matched well with the FeS/FeS2. These nanoscale materials can be used in a variety of applications, including lithium-ion batteries, biosensors, hydrogen evolution, and multifunctional nanocomposite materials.

Biomedical applications of iron sulfide-based nanozymes

Nanozymes have attracted great interest owing to their marvelous advantages, such as high stability, facile preparation, and high tunability. In particular, iron sulfide-based nanozymes (termed as ISNs), as one of the most researched nanomaterials with versatile enzyme-mimicking properties, have proved their potential in biomedical applications. In this review, we briefly summarize the classification, catalytic mechanisms of ISNs and then principally introduce ISNs’ biomedical applications in biosensors, tumor therapy, antibacterial therapy, and others, demonstrating that ISNs have promising potential for alleviating human health.

Polyethyleneimine Functionalized Mesoporous Magnetic Nanoparticles with Enhanced Antibacterial and Antibiofilm Activity in an Alternating Magnetic Field

Despite a lot of research on the antibacterial effect of Fe₃O₄ nanoparticles, their interactions with biofilm matrix have not been well understood. The surface charge of nanoparticles mainly determines their ability to adhere on the biofilm. In this work, negatively charged Fe₃O₄ nanoparticles were synthesized via a trisodium citrate-assisted solvothermal method and then the surfaces were functionalized using polyethyleneimine (PEI) to obtain positively charged Fe₃O₄ nanoparticles. The antibacterial and antibiofilm activities of both negatively and positively charged Fe₃O₄ nanoparticles in an alternating magnetic field were then systematically investigated. The positively charged Fe₃O₄ nanoparticles showed a strong self-adsorbed attachment ability to the planktonic and sessile cells, resulting in a better antibacterial activity and enhanced biofilm eradication performance compared to the conventional Fe₃O₄ nanoparticles with negative charges. Fe₃O₄@PEI nanoparticles produced physical stress and thermal damage in response to an alternating magnetic field, inducing the accumulation of intracellular reactive oxygen species into live bacterial cells, bacterial membrane damage, and biofilm dispersion. Utilizing an alternating magnetic field along with positively charged nanoparticles leads to a synergistic antibacterial approach to improve the antibiofilm performance of magnetic nanoparticles.

Combating Drug-Resistant Bacteria Using Photothermally Active Nanomaterials: A Perspective Review

Injudicious use of antibiotics has been the main driver of severe bacterial non-susceptibility to commonly available antibiotics (known as drug resistance or antimicrobial resistance), a global threat to human health and healthcare. There is an increase in the incidence and levels of resistance to antibacterial drugs not only in nosocomial settings but also in community ones. The drying pipeline of new and effective antibiotics has further worsened the situation and is leading to a potentially "post-antibiotic era." This requires novel and effective therapies and therapeutic agents for combating drug-resistant pathogenic microbes. Nanomaterials are emerging as potent antimicrobial agents with both bactericidal and potentiating effects reported against drug-resistant microbes. Among them, the photothermally active nanomaterials (PANs) are gaining attention for their broad-spectrum antibacterial potencies driven mainly by the photothermal effect, which is characterized by the conversion of absorbed photon energy into heat energy by the PANs. The current review capitalizes on the importance of using PANs as an effective approach for overcoming bacterial resistance to drugs. Various PANs leveraging broad-spectrum therapeutic antibacterial (both bactericidal and synergistic) potentials against drug-resistant pathogens have been discussed. The review also provides deeper mechanistic insights into the mechanisms of the action of PANs against a variety of drug-resistant pathogens with a critical evaluation of efflux pumps, cell membrane permeability, biofilm, and quorum sensing inhibition. We also discuss the use of PANs as drug carriers. This review also discusses possible cytotoxicities related to the therapeutic use of PANs and effective strategies to overcome this. Recent developments, success stories, challenges, and prospects are also presented.

Ultrasmall FeS2 Nanoparticles-Decorated Carbon Spheres with Laser-Mediated Ferrous Ion Release for Antibacterial Therapy

Recent progress in nanotechnology and the ancient use of sulfur in treating dermatological disorders have promoted the development of nano-sulfides for antimicrobial applications. However, the variable valences and abundant forms of nano-sulfides have complicated investigations on their antibacterial activity. Here, carbon nanospheres (CNSs) with decoration of ultrasmall FeS₂ nanoparticles (CNSs@FeS₂ ) is synthesized, and their antibacterial ability and mechanism are explored. The CNSs@FeS₂ released Fe²⁺ and sulfur ions simultaneously through dissolution and disproportionation. In vitro study indicated that the released Fe²⁺ killed bacteria by increasing the oxidative state of bacterial surfaces and intracellular molecules. Importantly, the released sulfur exhibited a protective effect on Fe²⁺ , ensuring the stable existence of Fe²⁺ to continuously combat bacteria. Moreover, the carbon shells of CNSs@FeS₂ not only prevented the aggregation of FeS₂ but also accelerated the release of Fe²⁺ through photothermal effects to achieve synergistic hyperthermia/Fe²⁺ therapy. In vivo experiments indicated that treatment with CNSs@FeS₂ resulted in a marked reduction in bacterial number and improvement in survival in an acute peritonitis mouse model, and antibacterial wound experiments demonstrated high efficacy of CNSs@FeS₂ -enabled synergistic hyperthermia/Fe²⁺ therapy. Thus, this study clarifies the antibacterial mechanism of FeS₂ and offers a synergetic therapeutic platform with laser-mediated Fe²⁺ release for antibacterial applications.

Emerging photothermal-derived multimodal synergistic therapy in combating bacterial infections

Due to the emerging bacterial resistance and the protection of tenacious biofilms, it is hard for the single antibacterial modality to achieve satisfactory therapeutic effects nowadays. In recent years, photothermal therapy (PTT)-derived multimodal synergistic treatments have received wide attention and exhibited cooperatively enhanced bactericidal activity. PTT features spatiotemporally controllable generation of hyperthermia that could eradicate bacteria without inducing resistance. The synergy of it with other treatments, such as chemotherapy, photo-dynamic/catalytic therapy (PDT/PCT), immunotherapy, and sonodynamic therapy (SDT), could lower the introduced laser density in PTT and avoid undesired overheating injury of normal tissues. Simultaneously, by heat-induced improvement of the bacterial membrane permeability, PTT is conducive for accelerated intracellular permeation of chemotherapeutic drugs as well as reactive oxygen species (ROS) generated by photosensitizers/sonosensitizers, and could promote infiltration of immune cells. Thereby, it could solve the currently existing sterilization deficiencies of other combined therapeutic modes, for example, bacterial resistance for chemotherapy, low drug permeability for PDT/PCT/SDT, adverse immunoreactions for immunotherapy, etc. Admittedly, PTT-derived synergistic treatments are becoming essential in fighting bacterial infection, especially those caused by antibiotic-resistant strains. This review firstly presents the classical and newly reported photothermal agents (PTAs) in brief. Profoundly, through the introduction of delicately designed nanocomposite platforms, we systematically discuss the versatile photothermal-derived multimodal synergistic therapy with the purpose of sterilization application. At the end, challenges to PTT-derived combinational therapy are presented and promising synergistic bactericidal prospects are anticipated.

Nano-Sized Iron Sulfide: Structure, Synthesis, Properties, and Biomedical Applications

Nano-sized iron sulfides have attracted intense research interest due to the variety of their types, structures, and physicochemical properties. In particular, nano-sized iron sulfides exhibit enzyme-like activity by mimicking natural enzymes that depend on an iron-sulfur cluster as cofactor, extending their potential for applications in biomedicine. The present review principally summarizes the synthesis, properties and applications in biomedical fields, demonstrating that nano-sized iron sulfides have considerable potential for improving human health and quality of life.