Single-neuron analysis using CE combined with MALDI MS and radionuclide detection

Capillary electrophoresis (CE) has been combined with matrix-assisted laser desorption/ionization mass spectrometry (MALDI MS) and radionuclide detection to assay mass-limited biological samples. Nanovial sampling techniques enable injections into the CE capillary from 50 to 150-nL volume samples; after the separation, nanoliter fraction collection combines the CE effluent with a MALDI matrix and minimizes sample spreading, thus allowing both MALDI MS and radionuclide detection on the CE fractions. MALDI MS complements the elution time information of CE by providing accurate molecular mass data, and radionuclide detection provides zeptomole limits of detection with quantitative information. While MALDI MS detects all fully processed peptides at sufficient concentration, culturing the neuron in media containing ³⁵S-Met provides selective radionuclide detection of newly synthesized methionine-containing peptides. The analysis and detection of the expected neuropeptides and hormones in a single 40-μm bag cell neuron from Aplysia californica with CE/MALDI MS/radionuclide detection demonstrates the ability of this hyphenated approach to work with chemically complex mass-limited samples.