In this review we outline the various methods that have been explored to synthesize architecturally defined nanoparticles from discrete polymer chains, summarize the methods of characterization that are required to prove their formation and probe their morphology, and introduce a number of potential applications that are being explored currently. Given the small size of the nanostructures produced by these methods and the relative ease with which they can be tailored to specific end use applications it is likely such efforts will intensify in the coming years. So far, simple chemistry has been utilized and high-level characterization and modeling studies have been applied to understand the process by which these particles form and how they behave, both in the bulk and in solution. Although impossible to predict where this work will lead, we hope this "user's guide" will prove useful to the community as research on singlechain nanoparticles continues to evolve.From left to right:

With the increasing appeal of nanotechnology, there is a demand for development of synthetic techniques for the fabrication of nanosized objects that allow for precise size control and tailored functionalization. To this end, the collapse or folding of single polymer chains into architecturally defined nanostructures is a rapidly growing research topic in polymer science. Many synthetic approaches have been developed for the formation of single-chain nanoparticles (SCNP), and a variety of characterization methods and computational efforts have been utilized to detail their formation and probe their morphological characteristics. Interest in this field continues to grow partially due to the variety of potential applications of SCNP including catalysis, sensors, nanoreactors, and nanomedicine. While numerous developments have been made, the field is continuing to evolve, and there are still many unanswered questions regarding synthesis and characterization of SCNP. This Perspective serves to identify recent accomplishments in the synthesis and characterization of SCNP while distinguishing areas that are in need of advancement and innovation to move forward. This includes exploring more complex synthetic strategies, obtaining folding control, employing nanoparticle functionalization, developing scalable methods, investigating hierarchical self-assembly of SCNP, and exploiting unique characterization techniques and in-depth simulations.

The structure and activity of proteins is the gold standard for functional polymeric materials. This highlight seeks to calibrate the reader with respect to recent attempts to mimic the various structural and functional traits of proteins using the techniques of modern polymer chemistry. From advances in sequence-controlled polymers (primary structure), to peptidomimetics, foldamers, single-chain nanoparticles (secondary and tertiary structure), accessing the various structural aspects of protein chemistry is a vibrant research area. Likewise, the properties and utility of proteins in applications such as catalysis and molecular recognition are being emulated in the laboratory to great effect. Rather than provide an exhaustive review on any one of these topics, this article seeks to highlight the common thread among them, encouraging discussion and collaboration that will result in the next generation of smart materials with advanced structure and function.

We present a scalable route to single-chain nanoparticles (SCNP) under mild conditions using intramolecular atom transfer radical coupling (ATRC). Typical methods to SCNP, a class of soft nanomaterials in the sub-10 nm size regime, rely on complicated synthetic techniques, high temperatures unsuitable to fragile functional groups, or ultradilute conditions (solutions less than 1 wt %), all of which greatly complicate scale-up. Our method uses a minimal number of synthetic steps and mild reaction conditions amenable to a wide array of solvents and tolerant to a variety of functional groups. Using this scalable method, gram quantities of nanoparticles in the 5−10 nm size regime are accessible.

We describe a method to fold single polymer chains into nanoparticles using simple thermal Diels–Alder (DA) chemistry.

We investigated intra-chain multicomponent reactions to synthesize single-chain nanoparticles (SCNP) containing sequence-defined segments at each cross-link, creating materials featuring multiple protein-inspired elements.

Porphyrin-cored polymer nanoparticles (PCPNs) were synthesized and characterized to investigate their utility as heme protein models. Created using collapsible heme-centered star polymers containing photodimerizable anthracene units, these systems afford model heme cofactors buried within hydrophobic, macromolecular environments. Spectroscopic interrogations demonstrate that PCPNs display redox and ligand-binding reactivity similar to that of native systems and thus are potential candidates for modeling biological heme iron coordination.

Electroactive poly(amic acid)-Cu 2+ (EPAA-Cu) composites on the substrates have been prepared, whose electrochemical properties, including electroactivity, electrochromism and anticorrosion, reveal drastic enhancement after incorporation of Cu 2+ ions.