Rapid and highly sensitive protein extraction via cobalt oxide nanoparticle-based liquid-liquid microextraction coupled with MALDI mass spectrometry

A new approach for rapid and highly sensitive protein extraction using cobalt oxide nanoparticles modified with cetyltrimethylammonium (Co(3)O(4)/CTA(+) NP) using nanoparticle-based liquid-liquid microextraction (NP-LLME) coupled with matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) has been successfully demonstrated. For the first time, the metal oxide NPs (Co(3)O(4)/CTA(+) NP) prepared in the organic phase (toluene) have been successfully applied for the extraction and preconcentration of proteins from sample solutions and complex samples via electrostatic forces involved between the metal oxide NP and proteins. Lysozyme was used as the model protein to investigate the optimal extraction parameters of the current approach. The optimal conditions were obtained at pH > pI for 10 min of incubation time (extraction time) with 3% salt (NaCl) addition. The Co(3)O(4)/CTA(+) NP was successfully applied for the highly sensitive analysis of an array proteins such as insulin, chymotrypsinogen and lysozyme from aqueous solution, protein mixture and milk samples in nanoparticle-based liquid-phase microextraction coupled with MALDI-MS. The potentiality of the NP-LLME using Co(3)O(4)/CTA(+) NP for the extraction of proteins was also compared with other types of NP-liquid phase microextraction (LPME) methods. The current approach offers distinct advantages including rapidity, straightforwardness, high sensitivity for washing- and separation-free MALDI-MS analysis of proteins.