Improving detection of BSA protein by applying atmospheric pressure plasma jets in MALDI-TOF mass spectrometry

Abstract To enhance protein identification in mass spectrometry systems, plasma can be applied in the sample preparation step in addition to conventional use, which improves the ionization process. In the present study, cold plasma technology is evaluated to achieve highly sensitive detection of low analyte concentrations. Plasma treatments are performed by two different low-temperature atmospheric-pressure sources. The protein ion signal after plasma treatment is characterized by matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS). The sample preparation method, exposure time and gas type for bovine serum albumin (BSA) are optimized. Plasma characteristics are determined by optical emission spectroscopy (OES) method. Also, the temperatures of plasma environment and sample are measured during the treatment with a non-contact infra-red digital camera. The water-soluble BSA protein is irradiated by cold atmospheric-pressure plasma jet (CAP jet) and radio-frequency plasma jet (RF jet). Mass spectra showed that argon plasma treatment with two-layer method induced a significant increase in ion intensity of MALDI-TOF MS. Argon treated water-soluble BSA and powder BSA lead to ten-times and three-times enhancement of protein ion signals as compared to the control, respectively. Also, treatment with argon RF jet, increases the ion signal more than two-times. The results indicate that ion intensity of BSA treated with CAP jet is significantly higher than that of BSA treated with RF jet. This finding, in addition to frequency and geometry parameters, depends on more analyte protonation, resulting in more ion flux toward BSA surface. Further, two-layer technique is considered as an optimal sampling method for MALDI.