A novel analytical platform based on a nanoliter needle for sampling and surface desorption atmospheric pressure chemistry ionization mass spectrometry(SDAPCI-MS) for analysis was developed for the direct,fast and micro-area analysis of different parts of a human tooth,including cavity,cavity edge,tooth cusp and tooth sulcus.The results showed that the mass spectra from the four sampling spots on the same tooth were different,and that SDAPCI-MS detected lactic acid,pyruvic acid,phenylacetic acid and propanoic acid were confirmed using tandem mass spectrometry(MS/MS).Principal component analysis(PCA) of the mass spectral data successfully differentiated the different sampling spots,levels of tooth decay and levels of gum disease.Therefore,our nano-SDAPCI-MS approach provides a promising way for micro-area analysis with fast,minimal pretreatment sampling,enabling rapid,simple and reliable surface MS investigation.