Mtp anchorchip target plate

Bacterial cells were separated from the growing media by centrifugation (13 000 rpm × 3 min), and washed three times with DI water. Finally, the resulting cellular pellet was resuspended in DI water at a concentration of 10⁸ cells per mL. Bacteria solutions with different concentrations were obtained by dilution with DI water. 1 μL of each solution was deposited on a MALDI target plate, and dried at room temperature (RT). For sample deposition, three different protocols were conducted. In the first (the routine procedure), the whole 1 μL of solution was deposited on a Bruker ground steel target plate, and the dried sample spot size was about 3 mm in diameter. In the second, 1 μL of solution was deposited on the target plate with four repetitions (0.25 μL in each repetition), droplet-by-droplet, in order to keep the sample spot as small as possible (<0.8 mm in diameter). In the third, a Bruker MTP AnchorChip target plate was employed, where the dried sample spot from 1 μL of a bacteria solution could be confined within a well that was 0.8 mm in diameter. DHB matrix (1 μL, 10 mg mL^–1 in V_acetonitrile/V_water/V_TFA 50/49.5/0.1) was added to cover the dried sample spots with the corresponding protocol for MALDI-TOF MS analysis. Each test was repeated 3–5 times. A library of bacteria reference mass spectra was built from the spectra obtained with the reduced sample spot size.