Multimodal Biofilm Inactivation Using a Photocatalytic Bismuth Perovskite-TiO2-Ru(II)polypyridyl-Based Multisite Heterojunction.

Infectious bacterial biofilms are recalcitrant to most antibiotics compared to their planktonic version, and the lack of appropriate therapeutic strategies for mitigating them poses a serious threat to clinical treatment. A ternary heterojunction material derived from a Bi-based perovskite-TiO2 hybrid and a [Ru(2,2'-bpy)2(4,4'-dicarboxy-2,2'-bpy)]2+ (2,2'-bpy, 2,2'-bipyridyl) as a photosensitizer (RuPS) is developed. This hybrid material is found to be capable of generating reactive oxygen species (ROS)/reactive nitrogen species (RNS) upon solar light irradiation. The aligned band edges and effective exciton dynamics between multisite heterojunctions are established by steady-state/time-resolved optical and other spectroscopic studies. Proposed mechanistic pathways for the photocatalytic generation of ROS/RNS are rationalized based on a cascade-redox processes arising from three catalytic centers. These ROS/RNS are utilized to demonstrate a proof-of-concept in treating two elusive bacterial biofilms while maintaining a high level of biocompatibility (IC50 > 1 mg/mL). The in situ generation of radical species (ROS/RNS) upon photoirradiation is established with EPR spectroscopic measurements and colorimetric assays. Experimental results showed improved efficacy toward biofilm inactivation of the ternary heterojunction material as compared to their individual/binary counterparts under solar light irradiation. The multisite heterojunction formation helped with better exciton delocalization for an efficient catalytic biofilm inactivation. This was rationalized based on the favorable exciton dissociation followed by the onset of multiple oxidation and reduction sites in the ternary heterojunction. This together with exceptional photoelectric features of lead-free halide perovskites outlines a proof-of-principle demonstration in biomedical optoelectronics addressing multimodal antibiofilm/antimicrobial modality.

Modulating Resonance Energy Transfer with Supramolecular Control in a Layered Hybrid Perovskite and Chromium Photosensitizer Assembly.

Recently, the low-dimensional organic-inorganic halide perovskites (OIHP) have been exploited heavily for their favorable exciton dynamics, broad-band emission, remarkable stability, and tunable band-edge excited-state energy compared to their 3D counterparts for potential optoelectronic applications. Low-dimensional perovskites are generally good candidates for utilization as room-temperature photoluminescence (PL) materials. Further, doping divalent transition metals like Mn2+ into OIHP is expected to introduce a 4T1-6A1-based low-energy luminescence emission around 600 nm; an optical property that is favorable for biomedical optoelectronics. Doping Mn2+ in the perovskite lattice is also expected to induce the generation of cytotoxic singlet oxygen species (1O2), a ROS that is being exploited for various therapeutic applications. To integrate these optical and therapeutic properties of a 2D (PEA)2PbBr4 (Pb PeV; PEA = phenylethylammonium cation) perovskite alloyed with Mn2+ ions (Mn:PbPeV) and the option for a photoinduced energy transfer process involving a Cr(III)-based 1O2 generating photosensitizer (CrPS), we designed a unique purpose-built nanoassembly (Mn:PbPeV@PCD) using the encapsulation properties of a water-soluble polymer derived from ß-cyclodextrin (PCD). Here the PCD is observed to modulate the classical internal energy transfer of Pb2+ exciton to alloyed Mn2+ orange emission, resulting in the emergence of a new blue emission. The addition of CrPS into the Mn:PbPeV@PCD to generate the CrPS@Mn:PbPeV@PCD assembly results in restoring perovskite luminescence followed by the external energy transfer to CrPS. We have elucidated the mechanism of these cascade energy transfer processes between multiple components using steady-state and time-resolved luminescence techniques. Efficient ROS generation and its potential to induce an oxidation reaction of a biomolecule are realized using guanine as the target molecule. Further photoinduced cleavage studies with biomolecules confirmed the efficacy of the nanoassembly in inducing the cleavage of guanine-rich DNA. The study opens up a new direction in the field of perovskite for biomedical applications.

Nanoparticles for super-resolution microscopy: intracellular delivery and molecular targeting.

Following an overview of the approaches and techniques used to acheive super-resolution microscopy, this review presents the advantages supplied by nanoparticle based probes for these applications. The various clases of nanoparticles that have been developed toward these goals are then critically described and these discussions are illustrated with a variety of examples from the recent literature.

Ultrasensitive Reagent for Ratiometric Detection and Detoxification of iAsIII in Water and Mitochondria.

Toxicity induced by inorganic arsenic as AsO33- (iAsIII) is of global concern. Reliable detection of the maximum allowed contaminant level for arsenic in drinking water and in the cellular system remains a challenge for the water quality management and assessment of toxicity in the cellular milieu, respectively. A new Ir(III)-based phosphorescent molecule (AS-1; λExt = 415 nm and λEms = 600 nm, Φ = 0.3) is synthesized for the selective detection of iAsIII in an aqueous solution with a ratiometric luminescence response even in the presence of iAsV and all other common inorganic cations and anions. The relatively higher affinity of the thioimidazole ligand (HPBT) toward iAsIII led to the formation of a fluorescent molecule iAsV-HPBT (λExt = 415 nm and λEms = 466 nm, Φ = 0.28) for the reaction of iAsIII and AS-1. An improved limit of quantitation (LOQ) down to 0.2 ppb is achieved when AS-1 is used in the CTAB micellar system. Presumably, the cationic surfactants favor the localization of AS-1@CTABMicelle in mitochondria of MCF7 cells, and this is confirmed from the images of the confocal laser fluorescence scanning microscopic studies. Importantly, cell viability assay studies confirm that AS-1@CTABMicelle induces dose-dependent detoxification of iAsIII in live cells. Further, luminescence responses at 466 nm could be utilized for developing a hand-held device for the in-field application. Such a reagent that allows for ratiometric detection of iAsIII with LOQ of 2.6 nM (0.5 ppb) in water, as well as helps in visualizing its distribution in mitochondria with a detoxifying effect, is rather unique in contemporary literature.

Graphene quantum dots alleviate ROS-mediated gastric damage.

The gastrointestinal (GI) tract is one of the major sites for reactive oxygen species generation (ROS). Physiological ROS, lower than the threshold concentration, is beneficial for human physiology to preserve gut functional integrity. However, ROS generated in large quantities in presence of external stimuli overwhelms the cellular antioxidant defense mechanism and results in oxidative damage and associated physiological disorder. Graphene quantum dots (GQDs) are a class of carbon-based nanomaterials that have attracted tremendous attention not only for their tunable optical properties but also for their broad-spectrum antioxidant properties. In this report we have shown that GQDs are highly efficient in scavenging ROS and suppressing stress-induced gastric ulcers by targeting the MMP-9 pathway and reducing the inflammatory burden by suppressing excessive oxidative stress by inducing high caspase activity, overproduction of Bax, and downregulation of BCL2.

Crystal-to-Crystal Synthesis of Photocatalytic Metal-Organic Frameworks for Visible-Light Reductive Coupling and Mechanistic Investigations.

Postmodification of reticular materials with well-defined catalysts is an appealing approach to produce new catalytic functional materials with improved stability and recyclability, but also to study catalysis in confined spaces. A promising strategy to this end is the postfunctionalization of crystalline and robust metal-organic frameworks (MOFs) to exploit the potential of crystal-to-crystal transformations for further characterization of the catalysts. In this regard, two new photocatalytic materials, MOF-520-PC1 and MOF-520-PC2, are straightforwardly obtained by the postfunctionalization of MOF-520 with perylene-3-carboxylic acid (PC1) and perylene-3-butyric acid (PC2). The single crystal-to-crystal transformation yielded the X-ray diffraction structure of catalytic MOF-520-PC2. The well-defined disposition of the perylenes inside the MOF served as suitable model systems to gain insights into the photophysical properties and mechanism by combining steady-state, time-resolved, and transient absorption spectroscopy. The resulting materials are active organophotoredox catalysts in the reductive dimerization of aromatic aldehydes, benzophenones, and imines under mild reaction conditions. Moreover, MOF-520-PC2 can be applied for synthesizing gram-scale quantities of products in continuous-flow conditions under steady-state light irradiation. This work provides an alternative approach for the construction of well-defined, metal-free, MOF-based catalysts.

Understanding light-driven H2 evolution through the electronic tuning of aminopyridine cobalt complexes.

A new family of cobalt complexes with the general formula [CoII(OTf)2(Y,XPyMetacn)] (1R , Y,XPyMetacn = 1-[(4-X-3,5-Y-2-pyridyl)methyl]-4,7-dimethyl-1,4,7-triazacyclononane, (X = CN (1CN ), CO2Et (1CO2Et ), Cl (1Cl ), H (1H ), NMe2 (1NMe2 )) where (Y = H, and X = OMe when Y = Me (1DMM )) is reported. We found that the electronic tuning of the Y,XPyMetacn ligand not only has an impact on the electronic and structural properties of the metal center, but also allows for a systematic water-reduction-catalytic control. In particular, the increase of the electron-withdrawing character of the pyridine moiety promotes a 20-fold enhancement of the catalytic outcome. By UV-Vis spectroscopy, luminescence quenching studies and Transient Absorption Spectroscopy (TAS), we have studied the direct reaction of the photogenerated [IrIII(ppy)2(bpy˙-)] (PSIr ) species to form the elusive CoI intermediates. In particular, our attention is focused on the effect of the ligand architecture in this elemental step of the catalytic mechanism. Finally, kinetic isotopic experiments together with DFT calculations provide complementary information about the rate-determining step of the catalytic cycle.

Two-photon fluorescence imaging and bimodal phototherapy of epidermal cancer cells with biocompatible self-assembled polymer nanoparticles.

We have developed herein an engineered polymer-based nanoplatform showing the convergence of two-photon fluorescence imaging and bimodal phototherapeutic activity in a single nanostructure. It was achieved through the appropriate choice of three different components: a ß-cyclodextrin-based polymer acting as a suitable carrier, a zinc phthalocyanine emitting red fluorescence simultaneously as being a singlet oxygen ((1)O2) photosensitizer, and a tailored nitroaniline derivative, functioning as a nitric oxide (NO) photodonor. The self-assembly of these components results in photoactivable nanoparticles, approximately 35 nm in diameter, coencapsulating a multifunctional cargo, which can be delivered to carcinoma cells. The combination of steady-state and time-resolved spectroscopic and photochemical techniques shows that the two photoresponsive guests do not interfere with each other while being enclosed in their supramolecular container and can thus be operated in parallel under control of light stimuli. Specifically, two-photon fluorescence microscopy allows mapping of the nanoassembly, here applied to epidermal cancer cells. By detecting the red emission from the phthalocyanine fluorophore it was also possible to investigate the tissue distribution after topical delivery onto human skin ex vivo. Irradiation of the nanoassembly with visible light triggers the simultaneous delivery of cytotoxic (1)O2 and NO, resulting in an amplified cell photomortality due to a combinatory effect of the two cytotoxic agents. The potential of dual therapeutic photodynamic action and two-photon fluorescence imaging capability in a single nanostructure make this system an appealing candidate for further studies in biomedical research.

Photoresponsive polymer nanocarriers with multifunctional cargo.

Nanoparticles with photoresponsive character can be assembled from amphiphilic macromolecular components and hydrophobic chromophores. In aqueous solutions, the hydrophobic domains of these species associate to produce spontaneously nanosized hosts with multiple photoresponsive guests in their interior. The modularity of this supramolecular approach to nanostructured assemblies permits the co-encapsulation of distinct subsets of guests within the very same host. In turn, the entrapped guests can be designed to interact upon light excitation and exchange electrons, energy or protons. Such photoinduced processes permit the engineering of properties into these supramolecular constructs that would otherwise be impossible to replicate with the separate components. Alternatively, noninteracting guests with distinct functions can be entrapped in these supramolecular containers to ensure multifunctional character. In fact, biocompatible luminescent probes with unique photochemical and photophysical signatures have already emerged from these fascinating investigations. Thus, polymer nanocarriers can become invaluable supramolecular scaffolds for the realization of multifunctional and photoresponsive tools for a diversity of biomedical applications.

A polymer-based nanodevice for the photoregulated release of NO with two-photon fluorescence reporting in skin carcinoma cells.

We have developed a multifunctional biocompatible nanoconstruct based on polymeric nanoparticles encapsulating a molecular conjugate, able to photorelease nitric oxide (NO) with a fluorescent reporting function. We demonstrate that two-photon excitation (TPE) using biofriendly NIR 700 nm laser light can be applied for monitoring as well as triggering the release of NO, wherein the uncaging of a strongly fluorescent co-product acts in turn as a TPE fluorescent reporter for the simultaneous NO release from the nanoassembly. This supramolecular nanodevice internalizes in skin carcinoma cells, induces significant cell death upon light excitation and preserves its TPE properties, allowing the nearly instantaneous quantification of the NO photoreleased in cancer cells by two-photon NIR fluorescence microscopy.

Layer-by-layer assembled gold nanoparticles with a tunable payload of a nitric oxide photocage.

We report herein the design, preparation and characterisation of a new, water soluble, nanoplatform for the light-triggered release of nitric oxide (NO). This nanoconstruct has been achieved by exploiting a layer-by-layer approach to assembly a polyelectrolyte modified with a NO photochemical precursor, around citrate stabilized gold colloidal template. Combined spectroscopic and transmission electron microscopy analysis show that the layered hybrid nanoparticles remain stable under physiological conditions without any significant clustering along the different coating processes. The photochemical properties of the NO photocage are well preserved upon its covalent grafting in the polymeric skeleton, before and after the of the metal colloids. The direct and in real time monitoring of NO using an ultrasensitive electrode unambiguously shows the light-stimulated NO release from modified gold nanoparticles and demonstrates that the approach used permits the accurate regulation of the NO reservoir on the nanoparticles surface.

An engineered nanoplatform for bimodal anticancer phototherapy with dual-color fluorescence detection of sensitizers.

A multifunctional nanoplatform with four-in-one photoresponsive functionalities has been achieved through the co-encapsulation of two chromo-fluorogenic components within biocompatible polymeric nanoparticles. This engineered nanoconstruct efficiently delivers different photosensitizers in melanoma cells, which can be detected through their dual-color fluorescence, and induces amplified cell mortality due to the simultaneous photogeneration of singlet oxygen and nitric oxide.

A NO photoreleasing supramolecular hydrogel with bactericidal action.

We have developed an engineered hydrogel formed, in the absence of any toxic solvents or reagents, by spontaneous self-assembly of three key components: a poly-ß-cyclodextrin polymer (1), a hydrophobically modified dextran (2) and a nitric oxide (NO) photodonor bearing an adamantyl appendage (3). The formation of this supramolecular assembly is based on a "lock-and-key" mechanism in which the alkyl side chains of 2 and the adamantane moiety of 3 form inclusion complexes with the ß-CD cavities of 1. The multivalent character of the interactions between all components and the insolubility of the NO photodonor in an aqueous medium ensure the stability of the hydrogel and the total lack of leaching of the photoactive component from the gel network under physiological conditions, even in the absence of protective coating agents. The photochemical properties of the NO photodonor are well preserved in the supramolecular matrix as demonstrated by the remote-controlled release of NO through visible light excitation and its transfer to a protein such as myoglobin. The utility of this NO photoreleasing platform is demonstrated in effective and strictly light-dependent bactericidal activity against the Gram-negative Escherichia coli bacterial colony suspension.

Photoinduced fluorescence activation and nitric oxide release with biocompatible polymer nanoparticles.

A viable strategy to encapsulate a fluorophore/photochrome dyad and a nitric oxide photodonor within supramolecular assemblies of a cyclodextrin-based polymer in water was developed. The two photoresponsive guests do not interact with each other within their supramolecular container and can be operated in parallel under optical control. Specifically, the dyad permits the reversible switching of fluorescence on a microsecond timescale for hundreds of cycles, and the photodonor enables the irreversible release of nitric oxide. Furthermore, these supramolecular assemblies cross the membrane of human melanoma cancer cells and transport their cargo in the cytosol. The fluorescence of one component allows the visualization of the labeled cells, and its switchable character could, in principle, be used to acquire super-resolution images, while the release of nitric oxide from the other induces significant cell mortality. Thus, our design logic for the construction of biocompatible nanoparticles with dual functionality might evolve into the realization of valuable photoresponsive probes for imaging and therapeutic applications.

A host-guest supramolecular complex with photoregulated delivery of nitric oxide and fluorescence imaging capacity in cancer cells.

Herein we report the design, preparation, and properties of a supramolecular system based on a tailored nitric oxide (NO) photodonor and a rhodamine-labeled ß-cyclodextrin conjugate. The combination of spectroscopic and photochemical experiments shows the absence of significant interchromophoric interactions between the host and the guest in the excited states. As a result, the complex is able to release NO under the exclusive control of visible light, as unambiguously demonstrated by direct detection of this transient species through an amperometric technique, and exhibits the typical red fluorescence of the rhodamine appendage. The supramolecular complex effectively internalizes in HeLa cancer cells as proven by fluorescence microscopy, shows a satisfactory biocompatibility in the dark, and induces about 50% of cell mortality upon irradiation with visible light. The convergence of all these properties in one single complex makes the present host-guest ensemble an appealing candidate for further delevopment of photoactivatable nanoscaled systems addressed to photostimulated NO-based therapy.

A cyclodextrin-based nanoassembly with bimodal photodynamic action.

We have developed a supramolecular nanoassembly capable of inducing remarkable levels of cancer cell mortality through a bimodal action based on the simultaneous photogeneration of nitric oxide (NO) and singlet oxygen ((1)O(2)). This was achieved through the appropriate incorporation of an anionic porphyrin (as (1)O(2) photosensitizer) and of a tailored NO photodonor in different compartments of biocompatible nanoparticles based on cationic amphiphilic cyclodextrins. The combination of steady-state and time-resolved spectroscopic techniques showed the absence of significant intra- and interchromophoric interaction between the two photoactive centers embedded in the nanoparticles, with consequent preservation of their photodynamic properties. Photodelivery of NO and (1)O(2) from the nanoassembly on visible light excitation was unambiguously demonstrated by direct and real-time monitoring of these transient species through amperometric and time-resolved infrared luminescence measurements, respectively. The typical red fluorescence of the porphyrin units was essentially unaffected in the bichromophoric nanoassembly, allowing its localization in living cells. The convergence of the dual therapeutic action and the imaging capacities in one single structure makes this supramolecular architecture an appealing, multifunctional candidate for applications in biomedical research.

Inhibiting intramolecular electron transfer in flavin adenine dinucleotide by host-guest interaction: a fluorescence study.

Modulation in the photophysical properties and intramolecular electron transfer behavior of the flavin adenine dinucleotide (FAD) molecule has been investigated in the presence of the macrocyclic hosts, alpha-, beta- and gamma-cyclodextrins (CDs), using absorption and steady-state and time-resolved fluorescence measurements. The results demonstrate that only the beta-CD host has a suitable cavity dimension to form a weak inclusion complex with FAD by encapsulating the adenine moiety, which is the preferred binding site in the large FAD molecule. Interestingly, in spite of the weak binding interaction, a significant enhancement in the fluorescence intensity of FAD is observed on complexation with beta-CD, and this has been attributed mainly to the modulation in the conformational dynamics of FAD in the presence of beta-CD. In aqueous solutions, a good fraction of FAD molecules exist in a "closed" conformation with the adenine and isoalloxazine rings stacked on each other, thus leading to very efficient fluorescence quenching due to the ultrafast intramolecular electron transfer from adenine to the isoalloxazine moiety. Complex formation with beta-CD inhibits this intramolecular electron transfer by changing the "closed" conformation of FAD to the "open" form, wherein the adenine and isoalloxazine moieties are widely separated, thus prohibiting the fluorescence quenching process. Further evidence for the conformational changes has been obtained by the observation of a long lifetime component in the fluorescence decay of FAD in the presence of beta-CD, which corresponds to the decay of the unquenched "open" form of FAD. Fluorescence up-conversion studies also indicate the absence of any ultrafast component in the fluorescence decay arising from the complexed FAD, thus supporting the formation of the "open" form in the presence of beta-CD, with no intramolecular electron transfer.

Host-guest interaction of 1,4-dihydroxy-9,10-anthraquinone (quinizarin) with cyclodextrins.

The interaction of 1,4-dihydroxy-9,10-anthraquinone, (quinizarin; QZ), with alpha-, beta- and gamma-cyclodextrin (CD) hosts, has been investigated using absorption, and steady-state and time-resolved fluorescence measurements, in order to understand the effects of cavity size of CDs on the binding of QZ molecule and the changes in the photophysical properties of QZ in the microenvironment of the hosts. The results demonstrate that QZ forms inclusion complexes with all the CDs. The low binding constants as well as the thermodynamic parameters indicate that the mode of interaction between QZ and CDs is mainly hydrophobic in nature. The relative magnitudes of the binding constants and the differential enhancements in the fluorescence intensity of QZ upon complexation with the CDs can be explained by considering the relative dimensions of the host cavity and the guest molecule, as well as the orientation of the guest molecule inside the CD cavity. It is proposed that the unsubstituted benzene ring of QZ is encapsulated within alpha- and beta-CD cavities whereas the dihydroxy-substituted aromatic ring is encapsulated within the gamma-CD cavity. This is further supported by the complexation studies of the QZ.CD systems with Al(III) ions. It is observed that the complexation of QZ with the metal ion is enhanced in the QZ.alpha-CD and QZ.beta-CD systems whereas it is significantly reduced in the QZ.gamma-CD system, due to shielding of the chelating groups of the dye inside the CD cavity in the latter case.