Determining Estrogens Using Surface-Assisted Laser Desorption/Ionization Mass Spectrometry with Silver Nanoparticles as the Matrix

We describe the application of silver nanoparticles (Ag NPs) as matrices for the determination of three estrogens using surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS). Because Ag NPs have extremely high absorption coefficients (1.2 × 10⁸ M^-1 cm^-1) at 337 nm, they are effective SALDI matrices when using a nitrogen laser. Three tested estrogens-estrone (E1), estradiol (E2), and estriol (E3)-adsorb weakly onto the surfaces of the Ag NPs, through van der Waals forces. After centrifugation, the concentrated analytes adsorbed on the Ag NPs were subjected directly to SALDI-MS analyses, with the limits of detection for E1, E2, and E3 being 2.23, 0.23, and 2.11 μM, respectively. The shot-to-shot and batch-to-batch variations for the three analytes were less than 9% and 13%, respectively. We validated the practicality of this present approach through the quantitation of E2 in human urine. Using this approach, we determined the concentration of E2 in a sample of a pregnant woman's urine to be 0.16 ± 0.05 μM (n = 10).