4800 plus maldi tof ms

The MS analyses and MS/MS analyses were performed using a 4800 Plus MALDI-TOF MS (AB Sciex, Redwood City, US) and an Autoflex maX MALDI-TOF/TOF system (Bruker Daltonik GmbH, Bremen, Germany). The MS spectra were acquired in linear positive-ionization mode. Afterwards, the target MS peak was selected for the MS/MS analysis in a reflector mode. The MS/MS spectra were interpreted primarily with the FlexAnalysis^TM software (Bruker Daltonics, Bremen, Germany) (See supporting information).

The sample preparation and MALDI-TOF MS analytical procedures were the same as reported by Zheng et al.^{22 (link)} Briely, the Apt-LC-19 aptamer (5 × 10⁻⁶ mol L⁻¹, 20 μL) and the pooled lung cancer serum (20 μL) were incubated respectively for 30 min at 37 °C, the pooled normal serum as a negative control. The initial ssDNA library binds to pooled lung cancer serum and pooled normal serum as randomized sequence. Then, these complexes were separated on 8% native polyacrylamide gel. The gel retarded band was excised and the protein components in it were recovered, digested with trypsin digest solution (proteomics grade, Roche). The resulting digests were analyzed by 4800 Plus MALDI-TOF MS (ABSciex, Applied Biosystems, Foster City, CA) and then analyzed by MS with secondary peptide sequencing. The identification of the mixture proteins was searched in S. Mansoni Swiss-Prot protein database. The corresponding position in the control lane (the complex of the initial ssDNA library and pooled lung cancer serum, the complex of the Apt-LC-19 and pooled normal serum) was excised and identified by MS simultaneously to exclude the protein mobilized similarly with the complex. The candidate serological biomarkers of lung cancer were thus gained.