Micro- and nanodisk lasers are promising for on-chip and free-space applications. However, their precise fabrication is challenging, which, in turn, affects wavelength control. Now, researchers have developed a novel photoelectrochemical etching-based technique that enables the precise tuning of the lasing wavelength with sub-nanometer accuracy. They developed microdisk lasers with deterministic wavelengths and demonstrated their potential by tagging cells in culture. Their technique is expected to enable various nanophotonic and biomedical applications.