Carbon nanohoops (aka cycloparaphenylenes) are extraordinary structures with extraordinary properties. The shortest possible cross-sections of armchair carbon nanotubes, these structures were first pursued as challenging synthetic targets. Their preparation has led to myriad applications that exploit their unique optoelectronic and host–guest properties. See Leonhardt et al.

Over the past decade, liquid-phase electron microscopy has revolutionized direct mechanistic studies of reactions in liquid media. Scanning electron microscopy and (scanning) transmission electron microscopy of liquid samples have enabled breakthroughs in nanoparticle chemistry, soft-matter science, catalysis, electrochemistry, battery research and biochemistry. See Kashin et al.

In bulk aqueous solution, peptide self-association occurs through a process of hierarchical self-assembly. The small peptide building blocks first form primary assemblies and it is these that then go on to form a larger lattice. See Yuan et al.

Ribonucleic acids and intrinsically disordered proteins undergo phase separation inside cells to afford biomolecular condensates. Appreciating the associated enthalpy and entropy changes — including those of water — helps us better understand the ways in which cells regulate biochemical processes. SeeRibeiro et al.

Triboelectric charging is one of the oldest reported scientific observations. But until recently, our understanding of this process has been limited. New approaches, both experimental and theoretical, have begun to address the phenomenon from the perspective of quantum mechanics, surface chemistry and statistical physics and enable us to understand the competing and dynamic processes taking place. See Lacks & Shinbrot

A huge number of bacterial natural products are already known. Their astounding structural variation can increasingly be attributed to specific enzymatic pathways. But recent efforts have revealed that, excitingly, many remain to be discovered, potentially including entire substance classes. See Scott & Piel

Strong non-covalent interactions enable the formation of rotaxanes that seek out cellular targets and fluoresce on binding them. See Schreiber & Smith [https://www.nature.com/articles/s41570-019-0095-1]

Stimuli such as light, electric potential (pictured here), mechanical force and flow can effect reactions that are difficult to control by thermal means. See Robertson et al.

Metal organic cages can be designed to encapsulate multiple guests. Understanding the design rules that enable selective multiple binding of different guests will enable new guest–guest chemistry to be explored with possible applications in catalysis and sensing. See Rizzuto et al.

Heteroaryl azos are a readily tunable and functionalizable class of molecular switches. Responsive to light and/or heat, these switches find applications in chemistry, materials science, biology and photopharmacology. See Crespi et al.

Super-resolution microscopy is an established, powerful tool to look at biosystems in detail. The study and design of complex synthetic materials can also benefit from this technique which is minimally invasive while offering nanometric resolution and multicolour ability. This approach can provide information about the materials in action in their working environment. See Pujals et al. 10.1038/s41570-018-0070-2

Ion-mobility spectrometry separates ions according to their rate of travel through an inert gas. This technique can differentiate between complex ions with the same mass-to-charge ratio and tell us about their relative size. See Rissanen et al. 10.1038/s41570-018-0062-2