Mass spectrometry identifies substances by measuring their mass-to-charge ratios and had long been limited to small molecules. Fenn’s electrospray ionisation (ESI) subjects a sample solution to a high electric field, forming charged micro-droplets that shrink by evaporation and finally release protein ions. Tanaka’s soft laser desorption (SLD) irradiates a solid or viscous sample with a laser pulse, gently ejecting intact macromolecular ions and paving the way for MALDI. By bringing large biomolecules into the gas phase without damage and coupling the ions to time-of-flight analysers, both methods enabled highly sensitive, high-throughput measurements. Modern proteomics studies and early-stage drug-screening workflows rely heavily on these breakthroughs.

In ESI, charged droplets undergo Coulombic fission and desolvation, ultimately producing highly charged protein ions; the resulting low m/z values allow conventional quadrupole or TOF analysers to detect macromolecules. SLD, on the other hand, exploits energy-absorbing matrices and carefully tuned laser fluence to induce local sublimation and co-evaporation, releasing low-charge macromolecular ions. The method enables rapid profiling of proteins and glycans up to ~100 kDa, and mass-fingerprint analysis has become a routine route to protein identification. ESI’s compatibility with online liquid chromatography permits detailed characterisation of post-translational modifications and even weak non-covalent assemblies while preserving their native interactions.

Fenn analysed electrospray dynamics by incorporating Rayleigh–Taylor instability into nozzle design and demonstrated that multicharge distributions follow Poisson statistics, yielding the well-known Iⁿ⁻¹ rule that underpins deconvolution of peak clusters in quantitative proteomics. Tanaka employed cobalt nanoparticle-containing matrices to optimise laser-energy partitioning, suppressing high-m/z background and extending the detectable mass range. These innovations catalysed the development of hybrid MS platforms such as TOF/TOF, Orbitrap and Q-TOF, enabling high-resolution HDX-MS and ion-trap CID for higher-order structural studies. The methodologies now underpin native MS, MALDI imaging, and top-down proteomics workflows.