Labeling and Selective Inactivation of Gram-Positive Bacteria Employing Bimodal Photoprobes with Dual Readouts.

Carbohydrate-conjugated silicon(IV) phthalocyanines with bimodal photoactivity were developed as probes with both fluorescent labeling and photosensitizing capabilities, and the concomitant fluorescent labeling and photoinduced inactivation of Gram-positive and Gram-negative models was explored. The maltohexaose-conjugated photoprobe provides a dual readout to distinguish between both groups of pathogens, as only the Gram-positive species was inactivated, even though both appeared labeled with near-infrared luminescence. Antibiotic resistance did not hinder the phototoxic effect, as even the methicillin-resistant pathogen Staphylococcus aureus (MRSA) was completely photoinactivated. Time-resolved confocal fluorescence microscopy analysis suggests that the photoprobe sticks onto the outer rim of the microorganisms, explaining the resistance of Gram-negative species on the basis of their membrane constitution. The mannose-conjugated photoprobe yields a different readout because it is able to label and to inactivate only the Gram-positive strain.

Photosensitizing nanoclays for efficient cell uptake and in vitro photodynamic therapy.

In this study a straightforward strategy to deliver photosensitizing molecules into cancer cells by using Laponite RD® (LAP) nanodisks as carrier is presented. We report the application of LAP functionalized with a highly hydrophobic Silicon phthalocyanine photosensitizer (SiPc) for efficient cell uptake and photodynamic therapy (PDT) of MCF-7 breast cancer cells in vitro. This inorganic-organic hybrid nanomaterial caused a threefold increase in intracellular ROS levels and 99.7% of cancer cell inactivation after light treatment (630 nm; fluency of 108 J/cm²). With its theranostic capabilities (simultaneous fluorescence and singlet oxygen generation), uptake into cancer cells was monitored to control the photo-inactivation. The functionalized nanodisks already proved to be an efficient photo-inactivator of pathogenic Gram-(+) bacteria and were previously reported as LS10. By extending the use of LS10 to PDT of cancer cells, it is an example of a photosensitizer functionalized nanoclay with multipurpose drug characteristics, demonstrating an intriguing potential for future phototherapeutic studies and applications.

Axially Decorated SiIV -phthalocyanines Bearing Mannose- or Ammonium-conjugated Siloxanes: Comparative Bacterial Labeling and Photodynamic Inactivation.

Herein, we present a comparative study about the photoinactivation of Staphylococcus aureus (Gram-positive model) and Escherichia coli (Gram-negative model) employing a neutral and a dicationic axially functionalized SiIV -phthalocyanine. Depending on the charge of the siloxane moiety (neutral monosaccharide or cationic ammonium salt), different interactions with the bacteria were observed, and a differential photoinactivation was facilitated. The intensity of the fluorescence labeling correlated with the photoinactivation of the two types of bacteria: While the neutral species only significantly affected the Gram-positive cells, we observed that the positively charged photosensitizer interacted both with the Gram-positive and with the Gram-negative models. The dicationic photosensitizer labeled both models with a characteristic deep-red fluorescence and photoinactivated both classes of prokaryotes. In general, our study clearly demonstrates that axially ammoniumsiloxane-functionalized Si(IV) phthalocyaninates constitute excellent photosensitizers due to their weak aggregation in aqueous environments. In particular, we also show that charge-based targeting with axial ammonium groups leads toward broad-spectrum SiIV -phthalocyanines for photodynamic inactivation of bacteria.

Functionalizing the Mesoporous Silica Shell of Upconversion Nanoparticles To Enhance Bacterial Targeting and Killing via Photosensitizer-Induced Antimicrobial Photodynamic Therapy.

Core-shell nanoparticles operating by infrared-to-visible energy upconversion (UCNPs) have been proposed as theranostic carriers for photosensitizers to increase deep-tissue penetration of photodynamic therapy against tumors and bacterial infections. Herein we present a series of core-shell mesoporous silica-coated NaYF4:Yb:Er UCNPs (mSiO2@UCNP) with different surface functionalizations to enhance bacterial targeting and loaded with the hydrophobic photosensitizer SiPc (silicon 2,9,16,23-tetra-tert-butyl-29H,31H-phthalocyanine dihydroxide) to boost the bactericidal effect against Gram-positive and Gram-negative bacteria upon near-infrared irradiation. Förster resonance energy transfer (FRET) from the UCNP core to loaded SiPc was facilitated, while its efficiency depended on UCNP shell functionalization, which influences the SiPc penetration depth into the mesoporous silica, constituting a convenient tool to modify FRET intensity. Functionalized UCNPs displayed dark toxicity toward Gram-negative E. coli of up to 5 orders of magnitude, while Gram-positive S. aureus viability was not decreased in the dark, offering practical means for discriminating between the two bacterial strains. Directly exciting SiPc on the UNCP led to complete eradication of E. coli and a drastic decrease of colony-forming units of S. aureus of up to 7 orders of magnitude. With this study, we demonstrate strategies to potentiate antimicrobial photodynamic therapy on nanoparticular structures that can lead to next-generation photosensitizing systems based on UCNPs to help encounter and eradicate resistant bacteria, as well as for theranostics and future in vivo applications.

Reaching Biocompatibility with Nanoclays: Eliminating the Cytotoxicity of Ir(III) Complexes.

Cyclometalated IrIII complexes are promising candidates for biomedical applications but high cytotoxicity limits their use as imaging and sensing agents. We herein introduce the use of Laponite as carrier for triplet-emitting cyclometalated IrIII complexes. Laponite is a versatile nanoplatform because of its biocompatibility, dispersion stability and large surface area that readily adsorbs functional nonpolar and cationic molecules. These inorganic-organic hybrid nanomaterials mask cytotoxicity, show efficient cell uptake and increase luminescent properties and photostability. By camouflaging intrinsic cytotoxicity, this simple method potentially extends the palette of available imaging and sensing dyes to any metal-organic complexes, especially those that are usually cytotoxic.