In vivo endoscopic mass spectrometry using a moving string sampling probe†
At present, endoscopy relies almost exclusively on optical microscopy and the accurate analysis such as MS interrogation is performed ex situ using biopsy. In this work, a novel probing system is developed to perform in situ and in vivo endoscopic mass spectrometry using a moving string for the sampling and transportation of material. A prototype of a mass spectrometric endoscope is constructed using an industrial endoscope and a commercial mass spectrometer. The sampling system consists of a moving cotton thread driven by motorized pulleys. When the target surface is touched by the sampling probe, the cotton thread “wipes” and transports the adhered sample to the ion source. Depending on the target analytes, desorption electrospray and atmospheric pressure chemical ionization sources are employed interchangeably for the desorption and ionization. The surface under analysis is not subjected to heat, organic solvents, high voltage or charged droplets. In situ endoscopic MS of a living mouse and surface analysis inside a volunteer subject's mouth are demonstrated.