Red phosphorus and gold nanoparticles as novel candidates for intact cell MALDI TOF MS

Abstract

Mass spectrometry (MS) is a widely used technique in many different fields such as proteomics, drug discovery and genomics. It measures the m/z ratio of the different components of a sample producing a mass spectrum, which has to be calibrated with internal or external calibration standards. In this project we studied if flower-like gold nanoparticles (AuNFs), red gold nanoparticles (red AuNPs) and red phosphorus (red P) could be used as internal calibration standards for matrix assisted laser desorption/ionization (MALDI) time-of-flight (TOF) MS analyses of intact eukaryotic (HEK 293) cells. These elements form distinct monoisotopic clusters by laser desorption/ionization (LDI) which makes them ideal for being used as external calibration standards. When studying their capability as internal calibration standards for MALDI TOF MS technique we realized that sinapinic acid (SA) interacted with gold nanoparticles (AuNPs) impeding gold clusters to appear on the spectrum. Still AuNPs could not be used as internal calibration standards when we removed the matrix using surface-assisted laser desorption/ionization (SALDI) TOF MS technique as no organic compounds of HEK 293 cells at a high m/z range could be seen on the spectrum. Thus, we let crystallize the matrix with the cells before adding the AuNFs. By doing so, we minimized the interaction between sinapinic acid and gold and at the same time enhanced the ionization of high molecular compounds of HEK 293 cells. We partially succeeded by following this methodology as HEK 293 organic compounds could be seen at a high m/z range but gold clusters could only be seen at a low m/z range (800 m/z). The same methodology was used for red P and obtained better results. Phosphorus clusters could be seen up to 2600 m/z together with HEK 293 organic compounds at a high m/z range. Cytotoxicity of these three elements was also studied in HEK 293 cells. Gold nanoparticles have numerous applications in the medicine field, thus studying its toxicity is of great importance. Red phosphorus is not as widely used but still its toxicity was also studied. Cell viability and proliferation was not affected by AuNPs whereas it was negatively altered by red phosphorus in dose dependent manner. A further analysis was done by comparing the mass spectra of treated cells (with AuNPs and red P) and non-treated cells. We determined that AuNPs geometry is an important issue to be considered. Regarding red P, no differences were observed when comparing the mass spectra