The invention generally relates to a method for an analysis of protein or peptide in samples. Specifically, the method comprises the steps: the samples containing protein or peptide contact with a probe, the probe comprises a porous material which gradually become finer until having a cusp, wherein the probe has no need to operate with a pneumatic assist; voltage is applied on the porous material, so that an electric field is generated at the cusp of the material to generate an ion of protein or peptide in the sample, and the ion is exhausted from the cusp; the exhausted ion is analyzed, so that protein or peptide of the samples can be analyzed.