Sol-gel-derived silver-nanoparticle-embedded thin film for mass spectrometry-based biosensing.

A porous silver-nanoparticle (AgNP)-embedded thin film biosensor was produced by the sol-gel method. The thin films were used as matrix-free laser desorption ionization mass spectrometry (LDI-MS) biosensors applicable to several chemical classes. In these experiments, UV laser irradiation (337 nm) of the AgNP facilitates desorption and ionization of a number of peptides, triglycerides, and phospholipids. Preferential ionization of sterols from vesicles composed of olefinic phosphosphatidylcholines is also demonstrated, offering the possibility for a simplified approach for sterol analysis from complex mixtures. The composition of the nanoparticles was confirmed by X-ray photoelectron spectroscopy (XPS) and UV-vis spectroscopy. XPS data revealed a binding energy of 368.2 eV, consistent with the previous assignment of the binding energy for the Ag 3d(5/2) peak from Ag(0) at 368.1 ± 0.1 eV. The surface morphology of the thin films was studied by field-emission scanning electron microscopy (FE-SEM) and revealed the presence of nanoparticles and the porous nature of the biosensor.