Photoactive Hybrid Nanomaterial for Targeting, Labeling, and Killing Antibiotic-Resistant Bacteria

Studying the viability and growth kinetics of vancomycin-resistant Enterococcus faecalis V583 following femtosecond laser irradiation (420-465 nm)

Enterococcus faecalis is among the most resistant bacteria found in infected root canals. The demand for cutting-edge disinfection methods has rekindled research on photoinactivation with visible light. This study investigated the bactericidal activity of femtosecond laser irradiation against vancomycin-resistant Enterococcus faecalis V583 (VRE). The effect of parameters such as wavelength and energy density on the viability and growth kinetics of VRE was studied to design an optimized laser-based antimicrobial photoinactivation approach without any prior addition of exogenous photosensitizers. The most effective wavelengths were 430 nm and 435 nm at a fluence of 1000 J/cm2, causing a nearly 2-log reduction (98.6% and 98.3% inhibition, respectively) in viable bacterial counts. The colony-forming units and growth rate of the laser-treated cultures were progressively decreased as energy density or light dose increased at 445 nm but reached a limit at 1250 J/cm2. At a higher fluence of 2000 J/cm2, the efficacy was reduced due to a photobleaching phenomenon. Our results highlight the importance of optimizing laser exposure parameters, such as wavelength and fluence, in bacterial photoinactivation experiments. To our knowledge, this is the first study to report an optimized wavelength for the inactivation of VRE using visible femtosecond laser light.

A silver metal-organic cage with antibacterial activity for wound healing

Bacterial infection is one of the most threatening diseases in humans and can result in tissue necrosis, inflammation, and so on. Although a large number of antibacterial materials have been developed, there are still some disadvantages in this field, including decreasing antibacterial activity in the aqueous solution or a short duration of time. Herein, a metal-organic cage named Ag-TBI-TPE with excellent antibacterial activity was prepared and applied in wound healing. Owing to the photosensitive production of the toxic ROS species and the positive charge of the surface, the Ag-TBI-TPE cage exhibits high antibacterial activity, especially under UV irradiation. It could accelerate the healing process of the infected wounds in vivo with satisfactory biocompatibility and bio-safety. The results indicated that after treatment with the Ag-TBI-TPE cage, with and without UV irradiation, the healing rates of wounds infected by E. coli and S. aureus were 89.59% and 93.05%, and 83.48% and 90.84%, respectively, which were much higher than those shown by the positive control group at 51.38% and 67.74%, respectively. This study not only sheds light on a design idea for a new antibacterial material but also further expands the potential application field of metal-organic cages.

Starch and chitosan-based antibacterial dressing for infected wound treatment via self-activated NO release strategy

In this work, a positively charged chitosan-grafted-polyarginine (CS-N-PArg) as the macro-molecular NO donor, and a negatively charged acetalated starch (AcSt-O-PAsp) as a glucose donor, have been synthesized. To achieve the multi-enzymatic cascade system for local generation of self-supply glucose to increase the H₂O₂ concentration for the subsequent oxidization of L-Arg into NO, the designed positively charged CS-N-PArg, negatively charged AcSt-O-PAsp, glucoamylase (GA) and glucose oxidase (GOx) are absorbed and assembled in the pore of the gelatin sponge via electrostatic interaction to establish a smart antibacterial dressings (CS/St + GOx/GA). Once stimulated by Escherichia coli (E. coli)-infected wounds (a slightly acidic environment), the cascade reaction system can sequentially induce to generate glucose, H₂O₂ and NO, which exhibits a meaningful alternative idea for a high-performance antibacterial therapy.

Recent advances in nanoparticle-based targeting tactics for antibacterial photodynamic therapy

Abstract

The rise of antibacterial drug resistance means treatment options are becoming increasingly limited. We must find ways to tackle these hard-to-treat drug-resistant and biofilm infections. With the lack of new antibacterial drugs (such as antibiotics) reaching the clinics, research has switched focus to exploring alternative strategies. One such strategy is antibacterial photodynamic therapy (aPDT), a system that relies on light, oxygen, and a non-toxic dye (photosensitiser) to generate cytotoxic reactive oxygen species. This technique has already been shown capable of handling both drug-resistant and biofilm infections but has limited clinical approval to date, which is in part due to the low bioavailability and selectivity of hydrophobic photosensitisers. Nanotechnology-based techniques have the potential to address the limitations of current aPDT, as already well-documented in anti-cancer PDT. Here, we review recent advances in nanoparticle-based targeting tactics for aPDT.

Graphical Abstract

Aggregation-Induced Emission-Active Poly(phenyleneethynylene)s for Fluorescence and Raman Dual-Modal Imaging and Drug-Resistant Bacteria Killing

Poly(phenyleneethynylene) (PPE) is a widely used functional conjugated polymer with applications ranging from organic optoelectronics and fluorescence sensors to optical imaging and theranostics. However, the fluorescence efficiency of PPE in aggregate states is generally not as good as their solution states, which greatly compromises their performance in fluorescence-related applications. Herein, a series of PPE derivatives with typical aggregation-induced emission (AIE) properties is designed and synthesized. In these PPEs, the diethylamino-substituted tetraphenylethene units function as the long-wavelength AIE source and the alkyl side chains serve as the functionalization site. The obtained AIE-active PPEs with large π-conjugation show strong aggregate-state fluorescence, interesting self-assembly behaviors, inherently enhanced alkyne vibrations in the Raman-silent region of cells, and efficient antibacterial activities. The PPE nanoparticles with good cellular uptake capability can clearly and sensitively visualize the tumor region and residual tumors via their fluorescence and Raman signals, respectively, to benefit the precise tumor resection surgery. After post-functionalization, the obtained PPE-based polyelectrolyte can preferentially image bacteria over mammalian cells and possesses efficient photodynamic killing capability against Gram-positive and drug-resistant bacteria. This work provides a feasible design strategy for developing functional conjugated polymers with multimodal imaging capability as well as photodynamic antimicrobial ability.

Umbelliferone Decorated Water-soluble Zinc(II) Phthalocyanines - In Vitro Phototoxic Antimicrobial Anti-cancer Agents

In this contribution we report on the synthesis, characterization and application of water-soluble zinc(II) phthalocyanines, which are decorated with four or eight umbelliferone moieties for photodynamic therapy (PDT). These compounds are linked peripherally to zinc(II) phthalocyanine by a triethylene glycol linker attached to pyridines, leading to cationic pyridinium units, able to increase the water solubility of the system. Beside their photophysical properties they were analyzed concerning their cellular distribution in human hepatocyte carcinoma (HepG2) cells as well as their phototoxicity towards HepG2 cells, Gram-positive (S. aureus strain 3150/12 and B. subtilis strain DB104) and Gram-negative bacteria (E. coli strain UTI89 and E. coli strain Nissle 1917). At low light doses and concentrations, they exhibit superb antimicrobial activity against Gram-positive bacteria as well as anti-tumor activity against HepG2. They are even capable to inactivate Gram-negative bacteria, whereas the dark toxicity remains low. These unique water-soluble compounds can be regarded as all-in-one type photosensitizers with broad applications ranges in the future.

When metal-organic framework mediated smart drug delivery meets gastrointestinal cancers

Cancers of the gastrointestinal tract constitute one of the most common cancer types worldwide and a ∼58% increase in the global number of cases has been estimated by IARC for the next twenty years. Recent advances in drug delivery technologies have attracted scientific interest for developing and utilizing efficient therapeutic systems. The present review focuses on the use of nanoscale MOFs (Nano-MOFs) as carriers for drug delivery and imaging purposes. In pursuit of significant improvements to current gastrointestinal cancer chemotherapy regimens, systems that allow multiple concomitant therapeutic options (polytherapy) and controlled release are highly desirable. In this sense, MOF-based nanotherapeutics represent a significant step towards achieving this goal. Here, the current state-of-the-art of interdisciplinary research and novel developments into MOF-based gastrointestinal cancer therapy are highlighted and reviewed.

The effect of femtosecond laser irradiation on the growth kinetics of Staphylococcus aureus: An in vitro study

We investigated the effect of femtosecond laser irradiation on the growth kinetics of Staphylococcus aureus. In order to improve laser-based antimicrobial therapy and develop a clinically viable modality, various laser parameters such as laser light wavelength, laser power, exposure time, and energy density were studied. The INSPIRE HF100 laser system (Spectra Physics) provided the femtosecond laser light, which was pumped by a mode-locked femtosecond Ti: sapphire laser MAI TAI HP (Spectra Physics). The survival of the bacterial cells was monitored after irradiation by determination of growth rate using optical density, which is a rapid, simple, and reliable method. The growth rate of laser-exposed cultures was compared to control cultures. Fifteen minutes of exposure to femtosecond laser radiation with a wavelength of 390 nm and 400 nm at an average power of 50 mW was enough to significantly reduce bacterial viability, with a lag in the growth phase of 5 h longer than the control culture (P < 0.0001 by ANOVA and Tukey test).

Self-assembly of Amphiphilic Porphyrins To Construct Nanoparticles for Highly Efficient Photodynamic Therapy

Hydrophobic photosensitizers greatly affect cell permeability and enrichment in tumors, but they cannot be used directly for clinical applications because they always aggregate in water, preventing their circulation in the blood and accumulation in tumor cells. As a result, amphiphilic photosensitizers are highly desirable. Although nanomaterial-based photosensitizers can solve water solubility, they have the disadvantages of complicated operation, poor reproducibility, low drug loading, and poor stability. In this work, an efficient synthesis strategy is proposed that converts small molecules into nanoparticles in 100 % aqueous solution by molecular assembly without the addition of any foreign species. Three photosensitizers with triphenylphosphine units and ethylene glycol chains of different lengths, TPP-PPh₃ , TPP-PPh₃ -2PEG and TPP-PPh₃ -4PEG, were synthesized to improve amphiphilicity. Of the three photosensitizers, TPP-PPh₃ -4PEG is the most efficient (singlet oxygen yield: 0.89) for tumor photodynamic therapy not only because of its definite constituent, but also because its amphiphilic structure allows it to self-assemble in water.

Efficient Killing of Multidrug-Resistant Internalized Bacteria by AIEgens In Vivo

Bacteria infected cells acting as "Trojan horses" not only protect bacteria from antibiotic therapies and immune clearance, but also increase the dissemination of pathogens from the initial sites of infection. Antibiotics are hard and insufficient to treat such hidden internalized bacteria, especially multidrug-resistant (MDR) bacteria. Herein, aggregation-induced emission luminogens (AIEgens) such as N,N-diphenyl-4-(7-(pyridin-4-yl) benzo [c] [1,2,5] thiadiazol-4-yl) aniline functionalized with 1-bromoethane (TBP-1) and (3-bromopropyl) trimethylammonium bromide (TBP-2) (TBPs) show potent broad-spectrum bactericidal activity against both extracellular and internalized Gram-positive pathogens. TBPs trigger reactive oxygen species (ROS)-mediated membrane damage to kill bacteria, regardless of light irradiation. TBPs effectively kill bacteria without the development of resistance. Additionally, such AIEgens activate mitochondria dependent autophagy to eliminate internalized bacteria in host cells. Compared to the routinely used vancomycin in clinic, TBPs demonstrate comparable efficacy against methicillin-resistant Staphylococcus aureus (MRSA) in vivo. The studies suggest that AIEgens are promising new agents for the treatment of MDR bacteria associated infections.

Turning Photons into Drugs: Phthalocyanine-Based Photosensitizers as Efficient Photoantimicrobials

One of the most promising alternatives for treating bacterial infections is antimicrobial photodynamic therapy (aPDT), making the synthesis and application of new photoactive compounds called photosensitizers (PS) a dynamic research field. In this regard, phthalocyanine (Pc) derivatives offer great opportunities due to their extraordinary light-harvesting and tunable electronic properties, structural versatility, and stability. This Review, rather than focusing on synthetic strategies, intends to overview current progress in the structural design strategies for Pcs that could achieve effective photoinactivation of microorganisms. In addition, the Review provides a concise look into the recent developments and applications of nanocarrier-based Pc delivery systems.

Halo-fluorescein for photodynamic bacteria inactivation in extremely acidic conditions

Aciduric bacteria that can survive in extremely acidic conditions (pH < 4.0) are challenging to the current antimicrobial approaches, including antibiotics and photodynamic bacteria inactivation (PDI). Here, we communicate a photosensitizer design concept of halogenation of fluorescein for extremely acidic PDI. Upon halogenation, the well-known spirocyclization that controls the absorption of fluorescein shifts to the acidic pH range. Meanwhile, the heavy atom effect of halogens boosts the generation of singlet oxygen. Accordingly, several photosensitizers that could work at even pH < 2.0 were discovered for a broad band of aciduric bacteria families, with half maximal inhibitory concentrations (IC50) lower than 1.1 μM. Since one of the discovered photosensitizers is an FDA-approved food additive (2',4',5',7'-tetraiodofluorescein, TIF), successful bacteria growth inhibition in acidic beverages was demonstrated, with greatly extended shelf life from 2 days to ~15 days. Besides, the in vivo PDI of Candidiasis with TIF under extremely acidic condition was also demonstrated.

Supramolecular subphthalocyanine complexes-cellular uptake and phototoxicity

In this communication we report on the synthesis and application of axially functionalized boron-subphthalocyanines (SubPC) which are able to form host-guest complexes with cyclodextrins. Here, a tert-butylphenyl substituted SubPC was investigated concerning its complexation with β-cyclodextrin (β-CD) and a β-cyclodextrin polymer. NMR-titrations showed the formation of a 1 : 1 complex with β-CD. These assemblies were analyzed for their cellular distribution as well as their phototoxicity towards HeLa cells.

Host-guest complexes - Boosting the performance of photosensitizers

In this review, we will show the diversity of supramolecular host-guest complexes of cyclodextrins, cucurbit[n]urils, calix[n]- and pillar[n]arenes with photosensitizers, like porphyrins and phthalocyanines. Host-guest complexes are one of the main building blocks in supramolecular chemistry. For example, they have been widely used to encapsulate hydrophobic drug molecules to enhance the bioavailability in the human body. In these days of multiresistant bacteria and difficulties in cancer therapy, supramolecular host-guest systems with photosensitizers for the photodynamic therapy(PDT) gain more and more interest. In general, photosensitizers with a (large) conjugated aromatic π-system are used, which tend to π-πstacking in aqueous media suppressing the cell toxicity by singletoxygen production quenching. This can be overcome by the formation of host-guest complexes. Besides that, encapsulation of the photosensitizers in host molecules can enhance the solubility, increase cellular uptake, lead to hydrogels, rotaxanes, and switchable systems.

Microporous Frameworks as Promising Platforms for Antibacterial Strategies Against Oral Diseases

Nowadays, the heavy burden of oral diseases such as dental caries, periodontitis, endodontic infections, etc., and their consequences on the patients' quality of life indicate a strong need for developing effective therapies. Bacterial infections played an important role in the field of oral diseases, in-depth insight of such oral diseases have given rise to the demand for antibacterial therapeutic strategies. Recently, microporous frameworks have attracted tremendous interest in antibacterial application due to their well-defined porous structures for drug delivery. In addition, intensive efforts have been made to enhance the antibacterial performance of microporous frameworks, such as ion doping, photosensitizer incorporation as building blocks, and surface modifications. This review article aims on the major recent developments of microporous frameworks for antibacterial applications against oral diseases. The first part of this paper puts concentration on the cutting-edge researches on the versatile antibacterial strategies of microporous materials via drug delivery, inherent activity, and structural modification. The second part discusses the antibacterial applications of microporous frameworks against oral diseases. The applications of microporous frameworks not only have promising therapeutic potential to inhibit bacterial plaque-initiated oral infectious diseases, but also have a wide applicability to other biomedical applications.

Platinum-Doped Dendritic Structure as a Phosphorescent Label for Bacteria in Two-Photon Excitation Microscopy

Herein, we present a water-soluble dendritric Pt(II) complex as a phosphorescent label for bacterial cells. The dendritic moiety endows the Pt(II) complex with unique properties such as water solubility, shielding from quenching by dioxygen, and binding to bacterial surfaces. The new biosensor was employed for two-photon excitation microscopy, and the binding was confirmed by electron microscopy, which demonstrates that such hybrid arrays can provide orthogonal yet complementary readouts.

Synthesis of Amino Terminal Clicked Dendrimers. Approaches to the Application as a Biomarker

Herein, we present an easy and efficient synthesis of amino terminal dendrons, combining protection/deprotection reactions with copper-catalyzed azide alkyne cycloaddition in a convergent way. This new approach affords dendrons in gram scale with excellent yields and easy purification. By choosing the appropriate azido-functionalized core, these dendrons lead to a more efficient and controlled convergent synthesis of dendrimers with different sizes and shapes and multivalence. The amino terminal dendrimers were analyzed by diffusion-ordered spectroscopy experiments. The observed dendrimer size is in excellent correlation with the expected size and shape by molecular dynamic simulations. The construction of these kinds of nanostructures, in a simple and efficient way, opens new opportunities for biomedical applications. Moreover, by choosing the appropriate core, these versatile macromolecules become an excellent fluorescent biomarker.

Supramolecular Antibacterial Materials for Combatting Antibiotic Resistance

Antibiotic-resistant bacteria have emerged as a severe threat to human health. As effective antibacterial therapies, supramolecular materials display unprecedented advantages because of the flexible and tunable nature of their noncovalent interactions with biomolecules and the ability to incorporate various active agents in their platforms. Herein, supramolecular antibacterial materials are discussed using a format that focuses on their fundamental active elements and on recent advances including material selection, fabrication methods, structural characterization, and activity performance.

Antibacterial properties of subphthalocyanine and subphthalocyanine-TiO2 nanoparticles on Staphylococcus aureus and Escherichia coli

Nowadays the problem of antimicrobial resistance is the most important cause of morbidity and mortality in the treatment of infectious diseases worldwide. Treatment options for antimicrobial-resistant microorganisms are quite limited. Therefore, alternative treatment strategies are needed to control infectious diseases. Antimicrobial photodynamic therapy (aPDT) is one of the new treatment modalities proposed for a wide variety of infections. In the basic principle of aPDT, photosensitizers (PS) produce free radicals by irradiating them with harmless light at the appropriate wavelength, and this causes microorganism cell cytotoxicity.

In this study, light emitting diodes (LED) (630–700 nm, 17.4 mW/cm[Formula: see text] were used on Gram-positive Staphylococcus aureus (S. aureus) and Gram-negative Escherichia coli (E. coli) at different light doses under the minimum inhibitory concentration (MIC) values of SubPc and SubPc-integrated TiO2 nanoparticles (SubPc-TiO[Formula: see text] concentration. Both compounds show good phototoxicity toward S. aureus when high light doses (16, 24[Formula: see text]J/cm[Formula: see text] were applied. In addition, SubPc-TiO2 were found to be more effective than SubPc in aPDT of S. aureus. In E. coli, the success of aPDT has been shown to be dependent on the increased light dose (20, 30[Formula: see text]J/cm[Formula: see text] for both compounds. As a result, the aPDT activity of SubPc-TiO2 is more effective than SubPc in increasing light doses.

Recent Trends in Covalent and Metal Organic Frameworks for Biomedical Applications

Materials science has seen a great deal of advancement and development. The discovery of new types of materials sparked the study of their properties followed by applications ranging from separation, catalysis, optoelectronics, sensing, drug delivery and biomedicine, and many other uses in different fields of science. Metal organic frameworks (MOFs) and covalent organic frameworks (COFs) are a relatively new type of materials with high surface areas and permanent porosity that show great promise for such applications. The current study aims at presenting the recent work achieved in COFs and MOFs for biomedical applications, and to examine some challenges and future directions which the field may take. The paper herein surveys their synthesis, and their use as Drug Delivery Systems (DDS), in non-drug delivery therapeutics and for biosensing and diagnostics.

Red Fluorescence Conjugated Polymer with Broad Spectrum Antimicrobial Activity for Treatment of Bacterial Infections In Vivo

To address the problem of bacterial resistance, a practical strategy for broad spectrum antimicrobial based on conjugated polymers was proposed in the work. Three red fluorescence conjugated polymers (P1, P2, and P3) bearing quaternary ammonium groups with different length of side chains were designed and synthesized. By virtue of inserting capacity of the longer side chain, conjugated polymer (P3) displayed well broad spectrum antimicrobial activity toward Gram-negative and Gram-positive bacteria and fungi under a white light density of 25 mW cm^-2 and short time (15 min) by aid of dark toxicity and light toxicity, derived from the quaternary ammonium groups and reactive oxygen species produced by the backbone, respectively. Notably, for ampicillin-resistant Escherichia coli TOP10, P3 could kill the bacteria 100% at a very low concentration of 5 μM upon light irradiation. Furthermore, wound healing tests indicated that the polymer could be expediently employed for wound disinfection in vivo without any tissue damaging. The contribution of the work not only provides an efficient and broad spectrum antimicrobial material but also offers a multimodal antimicrobial strategy to fight against bacterial infections in vivo.

A catalase-loaded hierarchical zeolite as an implantable nanocapsule for ultrasound-guided oxygen self-sufficient photodynamic therapy against pancreatic cancer

Photodynamic therapy (PDT) is an alternative strategy for treating pancreatic cancer (PC) in clinics. However, the therapeutic efficacy is generally suppressed by inadequate oxygen supply in the hypoxic tumor microenvironment. Herein, hierarchical zeolite nanocarriers with hydrophilic mesoporous nanostructures and excellent biodegradability are synthesized via a one-pot wet chemical method. By co-loading with catalase and methylene blue (MB), a new type of oxygen self-sufficient PDT platform, a zeolite-catalase-MB nanocapsule (ZCM nanocapsule), is developed. After precision implantation of the ZCM nanocapsule into the tumor area under the real-time ultrasound (US) imaging guidance, the nanocapsule with 90% relative activity of equivalent free catalase enzyme efficiently modulates the tumor hypoxia and enhances the intratumoral US contrast by sustained decomposition of endogenous H2O2 and in situ production of O2 gas bubbles. Meanwhile, the MB loading in hierarchical zeolite matrices prevents the rapid leaching of the photosensitizer in tumor tissue, achieving a good sustained photosensitizer release effect. Based on the synchronous mechanisms, upon near-infrared laser irradiation, the local PC cells are completely killed, and no therapy-induced toxicity and recurrence are observed. This highly biocompatible and biodegradable hierarchical nanozeolite would further facilitate the development of catalase-based catalytic nanomedicine for enhancing chemotherapy, radiotherapy and combination therapy.

Quantum dots modified with quaternized poly(dimethylaminoethyl methacrylate) for selective recognition and killing of bacteria over mammalian cells

Copper-free click chemistry has been used to graft quaternized poly(dimethylaminoethyl methacrylate) (QPA) modified with azide to the quantum dots (QDs) derived with dibenzocyclooctynes (DBCO). The success of the quaternary ammonium polymer-modified QDs was confirmed by ultraviolet-visible spectrophotometry (UV-Vis), fluorescence spectroscopy, zeta (ζ) potential, size distribution, and transmission electron microscopy (TEM). The QPA-modified QDs exhibited properties of selective recognition and killing of bacteria. The novelty of this study lies in fact that the synthesis method of the antimicrobial QPA-modified QDs is simple. Moreover, from another standpoint, QPA-modified QDs simultaneously possess abilities of selective recognition and killing of bacteria over mammalian cells, which is very different from the currently designed multifunctional antimicrobial systems composed of complicated systematic compositions.

Green Fabrication of Amphiphilic Quaternized β-Chitin Derivatives with Excellent Biocompatibility and Antibacterial Activities for Wound Healing

Bacterial infection has always been a great threat to public health, and new antimicrobials to combat it are urgently needed. Here, a series of quaternized β-chitin derivatives is prepared simply and homogeneously in an aqueous KOH/urea solution, which is a high-efficiency, energy-saving, and "green" route for the modification of chitin. The mild reaction conditions keep the acetamido groups of β-chitin intact and introduce quaternary ammonium groups on the primary hydroxyl at the C-6 position of the chitin backbone, allowing the quaternized β-chitin derivatives (QCs) to easily form micelles. These QCs are found to exhibit excellent antimicrobial activities against Escherichia coli, Staphylococcus aureus, Candida albicans, and Rhizopus oryzae with minimum inhibitory concentrations (MICs) of 8, 12, 60, and 40 µg mL-1 , respectively. As a specific highlight, their inherent outstanding biocompatibility and significant accelerating effects on the healing of uninfected, E. coli-infected, and S. aureus-infected wounds imply that these novel polysaccharide-based materials can be used as dressings for clinical skin regeneration, particularly for infected wounds.

Supramolecular Organization in Confined Nanospaces

Empty spaces are abhorred by nature, which immediately rushes in to fill the void. Humans have learnt pretty well how to make ordered empty nanocontainers, and to get useful products out of them. When such an order is imparted to molecules, new properties may appear, often yielding advanced applications. This review illustrates how the organized void space inherently present in various materials: zeolites, clathrates, mesoporous silica/organosilica, and metal organic frameworks (MOF), for example, can be exploited to create confined, organized, and self-assembled supramolecular structures of low dimensionality. Features of the confining matrices relevant to organization are presented with special focus on molecular-level aspects. Selected examples of confined supramolecular assemblies - from small molecules to quantum dots or luminescent species - are aimed to show the complexity and potential of this approach. Natural confinement (minerals) and hyperconfinement (high pressure) provide further opportunities to understand and master the atomistic-level interactions governing supramolecular organization under nanospace restrictions.

Synchronous, efficient and fast removal of phosphate and organic matter by carbon-coated lanthanum nanorods

Both phosphate and organic carbon can serve as nutrients for microorganism growth. Simultaneous removal of both nutrients would realize the antibacterial strategy of nutrient starvation better to ensure water quality safety. In addition, a short treatment time is the premise for the application of a material in water treatment. Herein, carbon-coated lanthanum nanorods with a uniform distribution of La and C (C–La-MOF) were rationally prepared through glucose and La-MOF hydrothermal treatment and further carbonization to synchronously and rapidly remove phosphate and organic matter. The carbon layer thickness was tuned by varying the hydrothermal time to find the optimal balance between excellent phosphate intake and low lanthanum leakage. C–La-MOF had a strong anti-interference ability and high phosphate capture capacity over a wide pH range of 2–12. Impressively, when phosphate and organic carbon coexisted in solution, their removal performances remained relatively unchanged compared with that when the two nutrients existed independently, and their adsorption equilibriums could be easily reached within 10 min. All of the above results prove that C–La-MOF is a promising material for practical drinking water treatment.

The carbon-coated lanthanum nanorods with uniform distribution of La and C can synchronously remove phosphate and organic matter, efficiently and rapidly.

Synthesis of Multifunctional Cationic Poly(p-phenylenevinylene) for Selectively Killing Bacteria and Lysosome-Specific Imaging

In this work, a cationic polymer was synthesized to bear quaternized N-methyl-imidazole groups in the side chains. Positively charged PPV-M could selectively bind to Gram-negative and Gram-positive bacteria over fungi and exhibit enhanced antibacterial activity with the aid of white light because PPV-M could sensitize oxygen to generate reactive oxygen species (ROS) that would damage bacteria. In addition, green fluorescent and positively charged PPV-M has the ability to enter mammalian cells and be specifically accumulated in lysosome. Moreover, PPV-M could stay in live cells for a relatively long time, which implies that PPV-M has the potential to be a long-term imaging agent.

Combatting AMR: photoactivatable ruthenium(ii)-isoniazid complex exhibits rapid selective antimycobacterial activity

The novel photoactive ruthenium(ii) complex cis-[Ru(bpy)2(INH)2][PF6]2 (1·2PF6, INH = isoniazid) was designed to incorporate the anti-tuberculosis drug, isoniazid, that could be released from the Ru(ii) cage by photoactivation with visible light. In aqueous solution, 1 rapidly released two equivalents of isoniazid and formed the photoproduct cis-[Ru(bpy)2(H2O)2]2+ upon irradiation with 465 nm blue light. We screened for activity against bacteria containing the three major classes of cell envelope: Gram-positive Bacillus subtilis, Gram-negative Escherichia coli, and Mycobacterium smegmatis in vitro using blue and multi-colored LED multi-well arrays. Complex 1 is inactive in the dark, but when photoactivated is 5.5× more potent towards M. smegmatis compared to the clinical drug isoniazid alone. Complementary pump-probe spectroscopy measurements along with density functional theory calculations reveal that the mono-aqua product is formed in <500 ps, likely facilitated by a 3MC state. Importantly, complex 1 is highly selective in killing mycobacteria versus normal human cells, towards which it is relatively non-toxic. This work suggests that photoactivatable prodrugs such as 1 are potentially powerful new agents in combatting the global problem of antibiotic resistance.

Photoactive antimicrobial nanomaterials

Nanomaterials for killing pathogenic bacteria under light irradiation.

A bacteria-activated photodynamic nanosystem based on polyelectrolyte-coated silica nanoparticles

A novel bacteria-activated photodynamic nanosystem (SiO₂/PAH–Ce6) has been reported for selective fluorescence sensing and photodynamic elimination of pathogenic bacteria.

An investigation of the interactions between an E. coli bacterial quorum sensing biosensor and chitosan-based nanocapsules

We examined the interaction between chitosan-based nanocapsules (NC), with average hydrodynamic diameter ∼114-155nm, polydispersity ∼0.127, and ζ-potential ∼+50mV, and an E. coli bacterial quorum sensing reporter strain. Dynamic light scattering (DLS) and nanoparticle tracking analysis (NTA) allowed full characterization and assessment of the absolute concentration of NC per unit volume in suspension. By centrifugation, DLS, and NTA, we determined experimentally a "stoichiometric" ratio of ∼80 NC/bacterium. By SEM it was possible to image the aggregation between NC and bacteria. Moreover, we developed a custom in silico platform to simulate the behavior of particles with diameters of 150nm and ζ-potential of +50mV on the bacterial surface. We computed the detailed force interactions between NC-NC and NC-bacteria and found that a maximum number of 145 particles might interact at the bacterial surface. Additionally, we found that the "stoichiometric" ratio of NC and bacteria has a strong influence on the bacterial behavior and influences the quorum sensing response, particularly due to the aggregation driven by NC.

Fast Targeting and Cancer Cell Uptake of Luminescent Antibody-Nanozeolite Bioconjugates

Understanding the targeted cellular uptake of nanomaterials is an essential step to engineer and program functional and effective biomedical devices. In this respect, the targeting and ultrafast uptake of zeolite nanocrystals functionalized with Cetuximab antibodies (Ctxb) by cells overexpressing the epidermal growth factor receptor are described here. Biochemical assays show that the cellular uptake of the bioconjugate in the targeted cancer cells already begins 15 min after incubation, at a rate around tenfold faster than that observed in the negative control cells. These findings further show the role of Ctxb exposed at the surfaces of the zeolite nanocrystals in mediating the targeted and rapid cellular uptake. By using temperature and pharmacological inhibitors as modulators of the internalization pathways, the results univocally suggest a dissipative uptake mechanism of these nanomaterials, which seems to occur using different internalization pathways, according to the targeting properties of these nanocrystals. Owing to the ultrafast uptake process, harmless for the cell viability, these results further pave the way for the design of novel theranostic tools based on nanozeolites.

Surface-Mediated Stimuli Responsive Delivery of Organic Molecules from Porous Carriers to Adhered Cells

The alternating layer-by-layer deposition of oppositely charged polyelectrolytes on fluorescence-dye-(Hst)-loaded zeolites L ((Hst) Zeo-PSS/PLL) is described. The arrays and nanocomposite (NC) hydrogels of (Hst) Zeo-PSS/PLL are prepared. The subsequent cell experiments show the potential application of arrays and NC hydrogels of (Hst) Zeo-PSS/PLL as alternative 2D- and 3D-surfaces, respectively, for 2D- and 3D-surface-mediated controlled organic molecules delivery applications.

Spatiotemporally Resolved Tracking of Bacterial Responses to ROS-Mediated Damage at the Single-Cell Level with Quantitative Functional Microscopy

Herein we report on the implementation of photofunctional microparticles in combination with optical tweezers for the investigation of bacterial responses to oxidative stress by means of quantitative functional microscopy. A combination of a strongly hydrophobic axially substituted Si(IV) phthalocyanine adsorbed onto silica microparticles was developed, and the structural and photophysical characterization was carried out. The microparticles are able to produce reactive oxygen species under the fluorescence microscope upon irradiation with red light, and the behavior of individual bacteria can be consequently investigated in situ and in real time at the single cell level. For this purpose, a methodology was introduced to monitor phototriggered changes with spatiotemporal resolution. The defined distance between the photoactive particles and individual bacteria can be fixed under the microscope before the photosensitization process is started, and the photoinduced damage can be monitored by tracing the time-dependent fluorescence turn-on of a suitable marker. The results showed a distance-dependent photoinduced death time, defined as the onset of the incorporation of propidium iodide. Our methodology constitutes a new tool for the in vitro design and evaluation of photosensitizers for the treatment of cancer and infectious diseases with the aid of functional optical microscopy, as it enables a quantitative response evaluation of living systems toward oxidative stress. More generally, it provides a way to understand the response of an ensemble of living entities to reactive oxygen species by analyzing the behavior of a set of individual organisms.

Silicon(IV) Phthalocyanine-Decorated Cyclodextrin Vesicles as a Self-Assembled Phototherapeutic Agent against MRSA

The host-guest complexation of a tailored Si(IV) phthalocyanine with supramolecular β-cyclodextrin vesicles (CDV) was studied, revealing a reduced aggregation of the photoactive center upon binding to the CDV, even in aqueous environments. For this purpose, a photosensitizing unit axially decorated with one adamantyl group and one pyridinium moiety on the other side was obtained by two successive click reactions on a bis-azido-functionalized derivative of Si(IV) phthalocyanine. To evaluate its potential as a photosensitizer against antibiotic-resistant bacteria, comparative studies of the photophysical properties including absorption and emission spectroscopy, lifetimes as well as fluorescence and singlet oxygen quantum yields were determined for the Si(IV) phthalocyanine alone and upon self-assembly on the CDV surface. In vitro phototoxicity against the methicillin-resistant Staphylococcus aureus (MRSA) USA300 was evaluated, showing an almost complete inactivation.