MALDI-TOF Analysis of Nanoparticles

MALDI-TOF was conducted as mentioned previously [4 (link)]. Briefly, purified nanoparticles (1 μL) were loaded onto an AnchorChip^TM target plate (Bruker-Daltonics, Bremen, Germany), covered by 1 μL matrix solution (0.5 μg/μL 2,5—dihydroxybenzoic acid in 90% (v/v) acetonitrile, 0.1% (v/v) trifluoroacetic acid (TFA), and washed with 0.5% (v/v) TFA. All the analyses were performed by a MALDI-TOF mass spectrometer (Ultraflex II, Bruker-Daltonics, Bremen, Germany) in positive ion reflector modes with 1000 laser shots per spectrum using Flex Control v3.4. Spectra were processed by Flex Analysis v3.0 (Bruker-Daltonics, Bremen, Germany), and mass calibration was performed using protein standards (tryptic digest of β-lactoglobulin, 5 pmol/μL) [21 (link)].