Single drop analysis of mercury ions by rational design of peptide coated gold nanoparticles integrated with MALDI-MS measurement.

In this study, a novel and rapid method for specific identification and accurate quantification of Hg2+ in environmental water was developed by using laser cleavable cysteine containing peptides modified gold nanoparticles coupled with high resolution matrix-assisted laser desorption ionization time-of-flight mass spectrometer (MALDI-TOF MS) measurement. First, gold nanoparticles were prepared by the reduction of tetrachloroauric (III) acid (HAuCl4) solution. Various cysteine containing peptides, photolabile linkers, including mercury ion binding motif with a proper molecular mass and amino acids were synthesized by solid phase peptide synthesis (SPPS). Subsequently, thiol-containing peptides were coated onto the surface of gold nanoparticles via the formation of gold-thiol (Au-S) bond. The resulting cysteine containing peptides modified gold nanoparticles were designed to specifically capture Hg2+ in water samples. After conjugated complex formation, ions of Hg2+-peptide complex were directly liberated by ultraviolet laser radiation by way of MALDI-MS using α-Cyano-4-hydroxycinnamic acid (CHCA) as matrix. The linear dynamic range of Hg2+ concentration in this study was 1-100 pmol/µL with coefficient of determination 0.9987. The limit of detection (LOD) and limit of quantification (LOQ) were 0.19 and 0.63 pmol/µL, respectively. Notably, the developed method allows rapid quantification of Hg2+ in 5 min and the desired sample volume was down to few µL.