Small- and large-sized iron(II, III) oxide nanoparticles for surface-assisted laser desorption/ionization mass spectrometry of small biomolecules.

Rationale: Common surface-assisted laser desorption/ionization (SALDI) surfaces are functionalized to improve mass spectrometric detection. Such surfaces are selective to certain group(s) of compounds. The application of universal and sensitive SALDI surfaces with appropriate size/surface area is paramount. In this study, two different sizes/surface areas of Fe O are compared as SALDI surfaces.

Methods: For accurate surface area comparisons, the physical properties of the Fe O nanoparticles used as SALDI surfaces were determined using scanning electron microscopy, X-ray diffractometry, and N Brunauer-Emmet-Teller adsorption techniques. SALDI mass spectrometry (MS) data were acquired using a time-of-flight (TOF) mass spectrometer operated in the linear mode and equipped with a 50-Hz pulsed nitrogen laser (at 337 nm). Small biomolecules (adenosine, glucose, sucrose, tryptophan, and tripeptide) and a real sample (human serum) were analyzed.

Results: The average sizes/specific surface areas of the SALDI surfaces of the small- and large-sized Fe O nanoparticles were ~21 nm/~82 m /g and ~39 nm/~38 m /g, respectively. An overall ~2.0-fold enhancement in signal-to-noise ratios was observed for the ionic species of the analyzed biomolecules in SALDI-MS using small-sized Fe O in comparison to large-sized Fe O nanoparticles. MS sensitivity from adenosine calibration curves (concentration between 0.05 and 10.0 mM) was ~2.0-fold higher for small-sized than large-sized Fe O nanoparticles as SALDI surfaces.

Conclusions: We have shown that transition-metal oxides such as Fe O nanoparticles are suitable and efficient surfaces for SALDI-TOF-MS analysis of small biomolecules. We observed improvement in signal-to-noise ratios and detection sensitivity for the analyzed samples from SALDI surfaces using small-sized (possessing larger surface area) than large-sized Fe O nanoparticles.