Interference free detection for small molecules: probing the Mn2+-doped effect and cysteine capped effect on the ZnS nanoparticles for coccidiostats and peptide analysis in SALDI-TOF MS.

For the first time, we report the applications of Mn(2+)-doped ZnS@cysteine nanoparticles (NPs) as matrices for analysis of coccidiostats (lasalocid, monensin, salinomycin and narasin) and peptide mixtures (Met-enk, Leu-enk, HW6 and gramicidin) in surface-assisted laser desorption/ionization time-of-flight mass spectrometry (SALDI-TOF MS). The Mn(2+)-doped ZnS@cysteine NPs have been successfully synthesized in aqueous phase and characterized by SEM, TEM and FT-IR spectroscopy. Comparison with the bare ZnS NPs, ZnS@cysteine NPs and CHCA to serve as matrices, we found that using Mn(2+)-doped ZnS@cysteine NPs as matrices offer better detection sensitivity and less background interferences for small molecule analysis. Current approach has been successfully applied for the analysis of peptide mixtures in urine samples and coccidiostats from egg samples by SALDI-TOF MS. The Mn(2+) ions doped in ZnS@cysteine NPs play a significant role for enhancing the detection sensitivity of analytes in SALDI-TOF MS. We believe that this approach is a promising tool to solve the low mass interference problems in MALDI-MS for complex mixture analysis of peptides and drugs.