Neat Protein Single-Chain Nanoparticles from Partially Denatured BSA

Effect of the Protein Chain Conformation on the Collapse into Nanoparticles

Protein single-chain nanoparticles can outperform synthetic nanoparticles in biomedical applications due to enhanced biocompatibility. Compared to synthetic (co)polymers, the chemical complexity of proteins challenges chain conformation control. Here, we investigate the impact of the precursor chain conformation of bovine serum albumin (BSA) on the nanoparticle structure after intramolecular cross-linking. We explore the urea concentration (denaturant), pH, salt, cross-linker length, and concentration. Small-angle neutron scattering and dynamic light scattering experiments reveal a shrinking chain conformation upon cross-linking. However, the ability to collapse depends on solvent conditions: more expanded chains collapse more, whereas proteins that are already compact barely change in size upon cross-linking. Static light scattering measurements demonstrate that binding is primarily intramolecular. The use of a shorter cross-linker does not lead to collapse of extended chains. Overall, BSA exhibits a similar behavior to that of polymer nanoparticles, which then allows to harness the precursor conformation for morphological control.

Unified Understanding of the Structure, Thermodynamics, and Diffusion of Single-Chain Nanoparticle Fluids

Single-chain nanoparticles (SCNPs) are a fascinating class of soft nano-objects with promising properties and relevance to protein condensates, polymer nanocomposites, nanomedicine, bioimaging, catalysis, and drug delivery. We combine molecular dynamics simulations and equilibrium and time-dependent statistical mechanical theory to construct a unified understanding of how the internal conformational structure of SCNPs, of both a simple fractal globule-like form and more complex objects with multiple internal intermediate length scales, determines nm-scale intermolecular packing correlations, thermodynamic properties, and center-of-mass diffusion over a wide range of concentrations up to dense melts. The intermolecular pair correlations generically exhibit a distinctive deep correlation hole form due to SCNP internal connectivity structure and repulsive interparticle interactions associated with a globular-like conformation on the macromolecular scale, with concentration-dependent deviations at small separations. Unanticipated exponential-like dependences of the equation-of-state, osmotic compressibility, and center-of-mass diffusion constant on SCNP macromolecular packing fraction are theoretically predicted and confirmed via simulations. System-specific behaviors are found associated with SCNP internal structure, but overarching regularities are identified and understood based on a generalized effective globule conformation on macromolecular scales. Diffusivity slows down by 2-3 decades with increasing concentration and is understood as a consequence of a nonactivated excluded volume-driven weak-caging process associated with space-time correlated intermolecular forces experienced by the SCNP. Good agreement between the theory and simulations is established, testable predictions are made, and a quantitative comparison with viscosity measurements on a specific SCNP fluid is carried out. The basic theoretical approach can potentially be extended to treat the chemical and physical consequences of varying the structure of other classes of soft nanoparticles with distinctive internal nanoscale organization relevant in nanotechnology and nanomedicine, and the possible emergence of macromolecular kinetically arrested glasses.

Thermoresponsive swelling of photoacoustic single-chain nanoparticles

NIR-fluorescent LCST-type single-chain nanoparticles (SCNPs) change their photophysical behaviour upon heating, caused by depletion of water from the swollen SCNP interiors. This thermoresponsive effect leads to a fluctuating photoacoustic (PA) signal which can be used as a contrast mechanism for PA imaging.

Single-chain polymer nanoparticles in biomedical applications

Single-chain polymer nanoparticles (SCNPs) are a well-defined and uniquely sized class of polymer nanoparticles. The advances in polymer science over the past decades have enabled the development of a variety of intramolecular crosslinking systems, leading to particles in the 5-20 nm size regime. Which is aligned with the size regime of proteins and therefore making SCNPs an interesting class of NPs for biomedical applications. The high modularity of SCNP design and the ease of their functionalization have led to growing research interest. In this review, we describe different crosslinking systems, as well as the preparation of functional SCNPs and the variety of biomedical applications that have been explored.