Experimental To create a model substrate, we formed conductive and non-conductive parts using metal patterns (Au 100 nm/Cr 30 nm) on a 1-mm-thick quartz glass substrate, alternating conductive with non-conductive parts at intervals of 400 μm. We used a red permanent marker to ionize the main component without applying a matrix compound. The letters 'MS' were written with this marker so that they straddled the conductive and non-conductive parts on the model substrate. We then fixed the model substrate and the stainless-steel target plate with conductive tape (Fig. 2). Mass spectrometry imaging was performed without gold deposition. Thereafter, we used gold deposition on the same sample and performed mass spectrometry imaging again. All mass spectrometry imaging were performed in SpiralTOF positive-ion mode. Pixel size was 50 μm; number of laser shots was 50 per pixel.