Semiconducting polymers owe their optoelectronic properties to the delocalized electronic structure along their conjugated backbone. Their spectral features are therefore uniquely sensitive to the conformation of the polymer, where mechanical stretching of the chain leads to distinct vibronic shifts. Here we demonstrate how the optomechanical response of conjugated polyelectrolytes can be used to detect their encapsulation in a protein capsid. Coating of the sensor polymers by recombinant coat proteins induces their stretching due to steric hindrance between the proteins. The resulting mechanical planarizations lead to pronounced shifts in the vibronic spectra, from which the process of capsid formation can be directly quantified. These results show how the coupling between vibronic states and mechanical stresses inherent to conjugated polymers can be used to noninvasively measure strains at the nanoscale.

Diatoms are characterized by very efficient photoprotective mechanisms where the excess energy is dissipated as heat in the main antenna system constituted by fucoxanthin-chlorophyll (Chl) protein complexes (FCPs). We performed Stark fluorescence spectroscopy on FCPs in their light-harvesting and energy dissipating states. Our results show that two distinct emitting bands are created upon induction of energy dissipation in FCPa and possibly in FCPb. More specifically one band is characterized by broad red shifted emission above 700nm and bears strong similarity with a red shifted band that we detected in the dissipative state of the major light-harvesting complex II (LHCII) of plants [26]. We discuss the results in the light of different mechanisms proposed to be responsible for photosynthetic photoprotection.

Responsive materials, which can adapt and operate autonomously under dynamic conditions, are a stepping stone towards functional, life-like systems inspired by fueled self-assembly processes in nature. Complex coacervate core micelles (C3Ms) comprising oppositely charged macromolecules constitute a novel class of polymeric micelles ideally suited for use as responsive nanoscopic delivery vehicles of hydrophilic and hydrophobic cargo. To fully exploit their potential, it is important that the C3Ms form and fall apart in an autonomous fashion as orchestrated by dynamic cues in their environment. Herein a means to temporally program the self-regulated C3M coassembly pathway, using a modulated base-catalyzed feedback system, is presented. Incorporated in the C3Ms is a pH responsive polyfluorene-based conjugated polyelectrolyte (CPF) as a building block and trace amounts of a molecular sensor (doxorubicin HCl) as cargo, both of which report on micellar coassembly and disassembly via binding-induced fluorescence quenching. CPF additionally reports on the pH of its microenvironment as its pH-dependent conformational states are mirrored in the transitions of its vibronic bands. This experimental design enables one to monitor solution pH, C3M disassembly and reassembly, as well as cargo release and recapture noninvasively in a closed system with real time florescence experiments.

The coassembly of well-defined biological nanostructures relies on a delicate balance between attractive and repulsive interactions between biomolecular building blocks. Viral capsids are a prototypical example, where coat proteins exhibit not only self-interactions but also interact with the cargo they encapsulate. In nature, the balance between antagonistic and synergistic interactions has evolved to avoid kinetic trapping and polymorphism. To date, it has remained a major challenge to experimentally disentangle the complex kinetic reaction pathways that underlie successful coassembly of biomolecular building blocks in a noninvasive approach with high temporal resolution. Here we show how macromolecular force sensors, acting as a genome proxy, allow us to probe the pathways through which a viromimetic protein forms capsids. We uncover the complex multistage process of capsid assembly, which involves recruitment and complexation, followed by allosteric growth of the proteinaceous coat. Under certain conditions, the single-genome particles condense into capsids containing multiple copies of the template. Finally, we derive a theoretical model that quantitatively describes the kinetics of recruitment and growth. These results shed new light on the origins of the pathway complexity in biomolecular coassembly.

Thermally expandable microspheres (TEMs) consist of a copolymer shell encapsulating a liquid hydrocarbon core and expand irreversibly to many times their original volume on heating. In this work commercial TEMs with a mean diameter of approximately 13 mm were coated with either polypyrrole, polyaniline or poly (3,4-ethylenedioxythiophene) [PEDOT] at conducting polymer mass loadings of 0.1 to 1.5%. Laser diffraction showed that aqueous suspensions of these conducting polymer-coated TEMs were well-dispersed, indicating minimal particle aggregation. Scanning electron microscopy studies indicated that these TEMs have relatively rough surfaces both before and after coating with conducting polymer. Raman spectroscopy was very sensitive to the presence of conducting polymer and could be used to confirm the presence of polypyrrole at target mass loadings as low as 0.1 wt%. The presence of polypyrrole at the TEM surface was confirmed from the Cl/N atomic ratios determined by X-ray photoelectron spectroscopy. This technique allowed the polypyrrole-coated TEMs to be ranked correctly according to their targeted conducting polymer loadings. All the conducting polymer-coated TEMs were subjected to irradiation using a near-infrared lamp with a l max of 1200 nm. Since conducting polymers absorb strongly in the near-infrared region, this leads to efficient localised heating of the coated TEMs. Thus the onset time required for the expansion of conducting polymer-coated TEMs under a given set of irradiation conditions is reduced significantly compared to control experiments conducted with uncoated TEMs (from 162 AE 2 seconds to 11 AE 1 seconds). For the polypyrrole-coated TEMs, systematic reduction of the target polypyrrole mass loading from 1.5 to 0.3% had surprisingly little effect on the observed onset times for volumetric expansion. Polypyrrole, polyaniline and PEDOT-coated TEMs all exhibited similar onset times (10 AE 1 seconds) when compared at the same mass loading (1.5%). However, EDOT is relatively expensive compared to pyrrole and polymerisation of the former monomer is substantially incomplete even at 50 C. Moreover, aniline is significantly more toxic than pyrrole and its polymerisation requires a more expensive oxidant. Thus it is concluded that polypyrrole is the preferred conducting polymer for coating TEMs in order to optimise their thermo-responsive volumetric expansion behaviour.