Many essential biological molecules exist only in one of two possible mirror-image structures, either because they possess a chiral unit or through their structure (helices, for example, are intrinsically chiral), but so far the origin of this homochirality has not been unraveled. Here we demonstrate that the handedness of helical supramolecular aggregates formed by achiral molecules can be directed by applying rotational, gravitational and orienting forces during the self-assembly process. In this system, supramolecular chirality is determined by the relative directions of rotation and magnetically tuned effective gravity, but the magnetic orientation of the aggregates is also essential. Applying these external forces only during the nucleation step of the aggregation is sufficient to achieve chiral selection. This result shows that an almost instantaneous chiral perturbation can be transferred and amplified in growing supramolecular self-assemblies, and provides evidence that a falsely chiral influence is able to induce absolute enantioselection.

Samples containing J-aggregates formed by the porphyrin meso-tetrakis(4-sulfonatophenyl)porphine (H 2 TPPS 4 4-) were studied by a combination of elastic (ELS) and dynamic (DLS) light scattering techniques. Aggregation was fostered by lowering the pH and increasing the ionic strength (I; selected experimental conditions: (i) pH ) 0.7; (ii) pH ) 2.8, I ) 0.5 M; (iii) pH ) 0.7, I ) 2 M). The ELS data suggest the presence of self-similar structures, whose fractal dimension are d f ) 1.7, 2.13, and 2.09 (for case i, ii, and iii, respectively). The DLS experiments indicate the presence of large (1-1.5 µm)-, medium (100-200 nm)-, and small (3-6 nm)-sized aggregates. An aggregation number (N) ranging between 6 and 32 was calculated for the smaller components, whereas a range of 10 5 to 10 6 was found in the case of the large clusters. The aggregation kinetics were followed by the resonance light scattering technique. The average aggregation time and the growth models, as derived from the ELS experiments, are in agreement with the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory for aggregation of colloidal particles. The experimental findings point out the different ability of H + and Na + in driving the final mesoscopic structure.

Strategies for in-liquid molecular detection via Surface Enhanced Raman Scattering (SERS) are currently based on chemically-driven aggregation or optical trapping of metal nanoparticles in presence of the target molecules. Such strategies allow the formation of SERS-active clusters that efficiently embed the molecule at the “hot spots” of the nanoparticles and enhance its Raman scattering by orders of magnitude. Here we report on a novel scheme that exploits the radiation pressure to locally push gold nanorods and induce their aggregation in buffered solutions of biomolecules, achieving biomolecular SERS detection at almost neutral pH. The sensor is applied to detect non-resonant amino acids and proteins, namely Phenylalanine (Phe), Bovine Serum Albumin (BSA) and Lysozyme (Lys), reaching detection limits in the μg/mL range. Being a chemical free and contactless technique, our methodology is easy to implement, fast to operate, needs small sample volumes and has potential for integration in microfluidic circuits for biomarkers detection.

The chirality of (nano)structures is paramount in many phenomena, including biological processes, self-assembly, enantioselective reactions, and light or electron spin polarization. In the quest for new chiral materials, metallo-organic hybrids have been attractive candidates for exploiting the aforementioned scientific fields. Here, we show that chiral carbon nanoparticles, called carbon nanodots, can be readily prepared using hydrothermal microwave-assisted synthesis and easily purified. These particles, with a mean particle size around 3 nm, are highly soluble in water and display mirror-image profile both in the UV–Vis and in the infrared regions, as detected by electronic and vibrational circular dichroism, respectively. Finally, the nanoparticles are used as templates for the formation of chiral supramolecular porphyrin assemblies, showing that it is possible to use and transfer the chiral information. This simple (and effective) methodology opens up exciting opportunities for developing a variety of chiral composite materials and applications.

We show that percolation and structural arrest transitions coexist in different regions of the phase diagram of a copolymer-micellar system and relate them to short-range intermicellar attraction. The intermediate scattering function shows a nonergodic transition along a temperature and concentration dependent line. Analyses show a logarithmic time dependence, attributed to a higher-order glass transition singularity predicted by mode-coupling theory, followed by a power law.