Platinum Nanoparticles as Photoactive Substrates for Mass Spectrometry and Spectroscopy Sensors

Platinum nanomaterials are the focus of great expectations to expand the reach of modern sensor technology. In this work, we have evaluated the ability of different types of platinum nanoparticles to enhance the response of analytical techniques based on optical excitation methods, namely nanoparticle-assisted laser desorption/ionization (NALDI), Raman scattering (SERS), and infrared absorption (SEIRA). Physical (laser ablation) and chemical (redox) methods of synthesis have been employed to produce spherical particles with sizes ranging from a few to tens of nanometers, stabilized with different coating agents. The nanoparticles have then been tested as active substrate materials to enhance the sensitivity of NALDI of a model peptide (angiotensin I) and a synthetic polymer (PEG600) and those of SERS and SEIRA of a common chromophore (rhodamine 6G). A fairly similar overall performance is found for nanoparticles homogeneous in size synthesized by chemical reduction as for heterogeneous sets of particles produced either chemically or by laser ablation in solution. These results indicate that size monodispersity is not crucial to attain enhancement effects. Quantitative differences in the relative NALDI, SERS, and SEIRA responses are attributed to the different roughness and porosity of the nanoparticles. The use of a low weight coating agent for nanoparticle stabilization also leads to a better performance compared to bulkier polymeric coatings.