Primers in 2021

Tissue clearing techniques render biological samples transparent to allow for the deep imaging of large tissue volumes. This Primer presents tissue clearing techniques in a modular way and underlines the main principles of each stage of clearing to help researchers to develop a custom tissue clearing workflow for their sample of choice. The authors also discuss the current applications and limitations of tissue clearing.

Whispering-gallery-mode sensors use multiple-cavity passes of light for very sensitive measurements at the microscale and nanoscale. This Primer introduces various whispering-gallery-mode sensor setups, describes different sensing mechanisms and highlights in vivo and single-molecule sensing applications in biology and physics.

Raman microspectroscopy is a non-destructive analysis technique for assessing the chemical composition of live microorganisms. This Primer examines the adaptation of Raman microspectroscopy for microbiology, outlining potential applications and technical limitations. The authors describe a new database for sharing Raman spectral data to enhance reproducibility.

Material characterization by powder diffraction gives quantitative and qualitative insights into the phases present in a specimen. This Primer describes the key considerations during powder diffraction analysis, from data collection and specimen preparation to phase identification and structure solution.

3D extrusion bioprinting methods can be used to produce tissue constructs in vitro and in situ and are arguably the most commonly used bioprinting strategies. In this Primer, Zhang and colleagues describe the variants of 3D extrusion bioprinting methods and their specific applications, considerations for the formulation of bioinks and strategies for assessing print quality. The authors conclude by looking to recent and upcoming developments in 4D printing and artificial intelligence-assisted dynamic printing strategies.

Light sheet fluorescence microscopy (LSFM) is a technique that uses a thin sheet of light for illumination, allowing optical sectioning of the sample. In this Primer, Stelzer et al. outline the fundamental concepts behind LSFM, discuss the different experimental set-ups for light sheet microscopes and detail steps for processing LSFM images. The Primer also describes the range of applications for this technique across the biological sciences and concludes by discussing advances for enhancing imaging depth and resolution.

Optically stimulated luminescence dating uses the amount of energy stored in a crystal to measure time. Applying this technique to quartz enables sedimentary deposition processes to be derived. In this Primer, the technique of optically stimulated luminescence dating with quartz is introduced, including commonly used methods, limitations and applications.

This Primer provides an overview of the general principles of adaptive optics and explores the different ways in which adaptive optics can correct optical aberrations for high-resolution imaging in the fields of astronomy, vision science and microscopy.

Small-angle scattering can reveal the structural organization of bulk materials and materials at surfaces and quantify their response to changes in external conditions. This Primer provides an overview of small-angle scattering using both X-rays and neutrons, and includes instrumentation, data collection and the type of structural information gathered in various applications.

Electrolyte-gated transistors (EGTs) are fundamental building blocks of bioelectronics, which transduce biological inputs to electrical signals. This Primer examines the different architectures of EGTs, their mechanism of operation and practical considerations related to their wide range of applications.

Atomic force microscopy-based force spectroscopy can probe the strength and dynamics of cell adhesion to understand how physical forces influence cellular function, physiology and disease. Here, Dufrêne and colleagues discuss the ability of this technology to work as an ultra-sensitive force sensor to study the adhesion and elasticity of complex biological systems including viruses, bacteria, yeasts and mammalian cells.

Radiocarbon dating is a common and reliable tool for measuring the age of a range of objects, from trees to historical artefacts and human remains. Hajdas et al. outline best practices for selecting and processing samples, as well as obtaining accurate measurements and age ranges. Ethical considerations for rare and culturally valuable materials are discussed.

Uffelmann et al. describe the key considerations and best practices for conducting genome-wide association studies (GWAS), techniques for deriving functional inferences from the results and applications of GWAS in understanding disease risk and trait architecture. The Primer also provides information on the best practices for data sharing and discusses important ethical considerations when considering GWAS populations and data.

Network analysis allows the investigation of complex patterns and relationships by examining nodes and the edges connecting them. Borsboom et al. discuss the adoption of network analysis in psychological research.

This Primer highlights the range of new strategies for sustainable N₂ activation and the step by step protocol necessary for evaluating genuine activity. The required metrics and how to interpret data alongside the best practices to improve reproducibility and enable the development of practical technologies are discussed.

This Primer discusses approaches for characterizing ubiquitin-like proteins (UBLs), their targets and modification sites, and dynamic changes in modifications. The authors cover techniques for enriching modified proteins and mass spectrometry analysis strategies and workflows, describe how these techniques have been applied and outline how limitations are being addressed by new techniques.

This Primer on atom probe tomography introduces the fundamentals of the technique and its experimental set-up, describes recent developments in specimen preparation, highlights aspects of data reconstruction and analysis, and showcases various applications of atom probe tomography in the materials sciences, geosciences and biological sciences.

Cell-free gene expression is useful for expressing proteins with post-translational modifications, with special folding requirements and whose expression is difficult in prokaryotic systems. Garenne et al. outline the best practices for the expression of proteins in a cell-free environment.

This Primer describes contemporary fluorination and fluoroalkylation reactions in chemical synthesis. The authors describe the main fluorination and fluoroalkylation reactions. The many applications of these reactions in pharmaceuticals, imaging agents and agriculture are discussed, along with the history and future of synthetic organofluorine chemistry.

In this Primer, Flitsch and colleagues describe how biocatalysis is facilitating synthetic chemistry in both academia and industry. Detailed considerations required to find, select and optimize a biocatalyst are described, followed by an analysis of the performance metrics used to define a good industrial catalyst.