Principles of molecular self-assembly into giant hierarchical structures of hundreds of micrometers in size are studied in aggregates of meso-tetra(4-sulfonatophenyl)porphine (TPPS4). The aggregates form a central tubular core, which is covered with radially protruding filamentous non-branching aggregates. The filaments cluster and orient at varying angles from the core surface and some filaments form bundles. Due to shape resemblance, the structures are termed giant sea urchin (GSU) aggregates. Spectrally resolved fluorescence microscopy reveals J- and H-bands of TPPS4 aggregates in both the central core and the filaments. The fluorescence of the core is quenched while filaments exhibit strong fluorescence. Upon drying, the filament fluorescence gets quenched while the core is less affected, showing stronger relative fluorescence. Fluorescence-detected linear dichroism (FDLD) microscopy reveals that absorption dipoles corresponding to J-bands are oriented along the filament axis. The comparison of FDLD with scanning electron microscopy (SEM) reveals the structure of central core comprised of multilayer ribbons, which wind around the core axis forming a tube. Polarimetric second-harmonic generation (SHG) and third-harmonic generation microscopy exhibits strong signal from the filaments with nonlinear dipoles oriented close to the filament axis, while central core displays very low SHG due to close to centrosymmetric organization. Large chiral nonlinear susceptibility points to helical arrangement of the filaments. The investigation shows that TPPS4 molecules form distinct aggregate types, including chiral nanotubes and nanogranular aggregates that associate into the hierarchical GSU structure, prototypical to complex biological structures. The chiral TPPS4 aggregates can serve as harmonophores for nonlinear microscopy.

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Background With the rapid development of nanotechnology, more and more nanoproducts are being released into the environment where they may both pose ecological risks and be toxic to living organisms. The ecotoxicological impact of quantum dots (QDs), a class of nanoparticles (NPs), on aquatic organisms is becoming an emerging issue, this due to their nano-specific properties, to the physico-chemical transformation in the environment and to the possible release of toxic metals from their structure such as Cd. Methods In this work, (i) spectroscopic measurements of commercially available Cd-based QDs (CdSe/ZnS-COOH) were made at various pH values (5.0 and 7.0) to study their interactions (at a concentration of 4 nm) with various strains of Gram-positive and Gram-negative gut bacteria after short-term exposure and (ii) the antibacterial efficacy of QDs and Cd 2+ (at a concentration 0.09–3.56 mM) against gut bacteria isolated from wild freshwater Salmo trutta fry was studied at different temperatures (15 °C and 25 °C) and pH values (5.0 and 7.0) by applying a well-established disc diffusion assay. Results Twenty-six gut bacterial isolates from wild Salmo trutta fry were identified as Aeromonas spp., A. popoffii , A. salmonicida , A. sobria , Carnobacterium maltaromaticum , Buttiauxella sp., Listeria sp., Microbacterium sp., Shewanella putrefaciens and Serratia sp. Cd-based (CdSe/ZnS-COOH) QDs at a concentration of 4 nm were found to be stable in aqueous media (with pH 7.0) or starting to form aggregates (at pH 5.0), thus, apparently, did not release heavy metals (HMs) into the media over 48 h in conditions of light or dark and did not show antibacterial efficacy on the gut bacteria isolated from wild Salmo trutta fry after short-term (9 h and 48 h) incubations. Cd 2+ was found to produce significant dose-dependent toxic effects on bacterial growth, and the size of the inhibition zones on some of the tested strains significantly correlated with temperature. The most sensitive and the most resistant to Cd 2+ were the Gram-positive bacteria, for which the minimum inhibitory concentration (MIC) values of Cd 2+ were 0.09–0.27 mM and 3.11–3.29 mM respectively and varied significantly between the tested temperatures (15 °C and 25 °C). The MIC values of Cd 2+ for the Gram-negative bacteria (18 out of 22 strains) ranged from 0.44 to 0.71 mM and did not differ significantly between the tested temperatures. Among the selected Gram-positive and Gram-negative strains, those wit...

The effect of exposure to the green laser light on the photoluminescence (PL) stability of CdSe/ZnS quantum dots (QDs) capped with either mercaptopropionic (MPA) or thioglycolic (TGA) acid was studied in aqueous suspensions and in the presence of bovine serum albumin (BSA). The results of absorbance and luminescence measurements suggest that the capacity of protein to change the coating structure of thiol-capped QDs and the stability of photoluminescence depends on the nature of stabilizing surface ligands. The interaction of BSA molecules with TGA-capped quantum dots increases their PL quantum yield (QY) and makes PL more stable, however, the effect is opposite for MPA-capped QDs. The light exposure instantly increases the PL intensity and the quantum yield of TGA-capped QDs but does not change those of MPA-capped QDs. In the medium with BSA, however, the occurrence of light-induced PL enhancement does not depend on stabilizing thiol ligands of QDs and it lasts for a relatively long period of time.