Best Practices in Nanocrystal Synthesis and Characterization

Colloidal nanocrystals exhibit quantum-mechanical phenomena inaccessible in bulk matter, and their properties can be tuned via chemically manipulating their composition, size, shape, and surface chemistry. Decades of development have produced a remarkable synthetic library spanning quantum dots, metal and metal oxide nanocrystals, halide perovskites, and complex multicomponent heterostructures. Yet, the field faces a persistent tension between the sophistication of what can be made and the rigor with which it is reported. Batch-to-batch variability, incomplete characterization, and poorly documented protocols challenge reproducibility and slow the translation of laboratory discoveries into reliable technologies or emerging autonomous workflows. This Tutorial offers guidance across four themes that highlight best practices in colloidal nanochemistry with the aim of fostering rigorous reporting in the field. The first theme concerns synthesis. Every nanocrystal synthesis is, at its most fundamental level, a set of chemical reactions and, therefore, should be communicated with explicit stoichiometries, including by-products where known, and with experimental sections detailed enough for an independent researcher to reproduce the outcome. Attention to hidden variables such as heating rates, reagent purity, atmosphere, and order of addition is essential, and we provide practical guidance on identifying and reporting them. The second theme is surface chemistry, where the influence of ligands on nanocrystal stability, functional properties, and device performance is profound. We discuss ligand coordination across nanocrystal families, from II-VI quantum dots to lead halide perovskites. We also describe how complementary techniques, such as infrared and nuclear magnetic resonance spectroscopy, thermogravimetric analysis, isothermal titration calorimetry, and elemental analysis, can together provide a quantitative picture of the ligand shell. The third theme addresses ex situ characterization, with an emphasis on the minimum suite of measurements needed to unambiguously establish nanocrystal identity. We discuss transmission electron microscopy, powder X-ray diffraction, and X-ray photoelectron spectroscopy as complementary and mutually reinforcing tools while highlighting the statistical and analytical rigor required to extract meaningful information from each. Finally, we discuss in situ and advanced characterization as the bridge between empirical synthesis and mechanistic understanding. Real-time probes, such as synchrotron X-ray scattering and absorption, liquid-cell transmission electron microscopy, and time-resolved optical spectroscopy, are increasingly accessible to the community via user facilities. While not required in every study, these advanced tools have fundamentally reshaped our understanding of nucleation, growth, and stability. Thus, we highlight the importance of chemical understanding developed through in situ characterization for establishing a more rational synthesis design that bypasses the current trial-and-error approach. We close by looking toward the future where synthesis sensitivity maps, artificial intelligence, and automation become partners in accelerating discovery, open data practices, and the scientific rigor that must underpin all of it. Good (nano)science today depends on the same foundation it always has, including rigorous, thoroughly documented experiments with an eye towards the future, where advanced characterization and data science are expected to play an increasingly important role.