TiO2 Nanocoral Structures as Versatile Substrates for Surface-Assisted Laser Desorption/Ionization Mass Spectrometry

Matrix-free surface-assisted laser desorption/ionization (SALDI) is a powerful technique for rapidly analyzing a myriad of compounds including biomolecules and polymers. However, previous studies were limited to detecting natural/organic-based molecules. Biphasic TiO2 nanocoral (TNC) structures consisting of an anatase base film and a rutile nanocoral layer allow analysis of not only organic compounds and polymers but also inorganic clusters by SALDI mass spectrometry (MS). TNC structures with microscopic surface roughness and porosity, which are indispensable for efficient desorption/ionization (D/I) in SALDI, form on Si wafers immersed in aqueous TiOSO4-H2O2 at 80 degrees C. Various organic and biological molecules with a wide range of molecular weights such as amino acids, hormones, antioxidants, steroids, organic dyes, sugars, drugs, proteins, and polymers are successfully analyzed by using TNC substrates in SALDI-MS. After SALDI-MS, the TNC substrates can be reused for detecting water-soluble molecules. TNC substrates also allow efficient detection of polyoxometalates and gold clusters as representative inorganic clusters. Survival yield measurements are employed to investigate the D/I mechanism of TNC substrates, and these indicate that the rutile nanocoral layer plays a critical role in ensuring efficient D/I. TNC as a versatile substrate for SALDI-MS is a potentially important analysis tool in a wide range of chemical and biological fields.