TY - JOUR
T1 - Cation-assisted laser desorption/ionization for matrix-free surface mass spectrometry of alkanethiolate self-assembled monolayers on gold substrates and nanoparticles
AU - Tae, Kyung Ha
AU - Tae, Geol Lee
AU - Nam, Woong Song
AU - Dae, Won Moon
AU - Sang, Yun Han
PY - 2008/11/15
Y1 - 2008/11/15
N2 - We propose a new scheme of matrix-free laser desorption/ionization with cation assistance for surface mass spectrometry of self-assembled monolayers (SAMs) of alkanethiolates on gold substrates and gold nanoparticles (NPs). In a proof-of-concept experiment, a simple treatment using an aqueous salt solution such as NaI(aq) was shown to lead to a significant laser desorption/ionization, producing the characteristic (disulfide) ions of alkanethiolate molecules from the monolayers. Further efforts to understand the mechanism were also given, including laser power and salt concentration dependence studies. In the power dependence study, the characteristic ions were found to be produced at low laser power where no gold substrate species was seen. At high laser power, the generation of gold species, Au+-Au5+, resulted in a saturation behavior in the characteristic mass peak for alkanethiolate molecules. In addition, characteristic ions with gold adducts were not observed at any laser power. With increasing salt concentration, the characteristic mass peak was gradually increased. The results suggest that the adduct formation of a cation with alkanethiolates in the monolayers provide a facile pathway to supply a charge to UV laser-desorbed secondary neutrals for mass spectrometric detection. This cation-assisted laser desorption/ionization (CALDI) mass spectrometry was further examined with the SAMs and mixed SAMs with various terminals such as -OH, -OCH3, -NH2, -ethylene (-CH=CH 2), and -acetylene (-C≡CH). The CALDI method was also successfully applied to surface mass spectrometry of monolayer-protected gold NPs (∼16 nm diameter) with OH- and COOH-terminated SAMs. The unique advantages of the matrix-free CALDI method may extend our capability in investigations of interfacial chemistry at SAMs as well as mass spectrometric applications using biochips and nanoparticles.
AB - We propose a new scheme of matrix-free laser desorption/ionization with cation assistance for surface mass spectrometry of self-assembled monolayers (SAMs) of alkanethiolates on gold substrates and gold nanoparticles (NPs). In a proof-of-concept experiment, a simple treatment using an aqueous salt solution such as NaI(aq) was shown to lead to a significant laser desorption/ionization, producing the characteristic (disulfide) ions of alkanethiolate molecules from the monolayers. Further efforts to understand the mechanism were also given, including laser power and salt concentration dependence studies. In the power dependence study, the characteristic ions were found to be produced at low laser power where no gold substrate species was seen. At high laser power, the generation of gold species, Au+-Au5+, resulted in a saturation behavior in the characteristic mass peak for alkanethiolate molecules. In addition, characteristic ions with gold adducts were not observed at any laser power. With increasing salt concentration, the characteristic mass peak was gradually increased. The results suggest that the adduct formation of a cation with alkanethiolates in the monolayers provide a facile pathway to supply a charge to UV laser-desorbed secondary neutrals for mass spectrometric detection. This cation-assisted laser desorption/ionization (CALDI) mass spectrometry was further examined with the SAMs and mixed SAMs with various terminals such as -OH, -OCH3, -NH2, -ethylene (-CH=CH 2), and -acetylene (-C≡CH). The CALDI method was also successfully applied to surface mass spectrometry of monolayer-protected gold NPs (∼16 nm diameter) with OH- and COOH-terminated SAMs. The unique advantages of the matrix-free CALDI method may extend our capability in investigations of interfacial chemistry at SAMs as well as mass spectrometric applications using biochips and nanoparticles.
UR - https://www.scopus.com/pages/publications/56449101069
U2 - 10.1021/ac801405k
DO - 10.1021/ac801405k
M3 - Article
C2 - 18847282
AN - SCOPUS:56449101069
SN - 0003-2700
VL - 80
SP - 8526
EP - 8531
JO - Analytical Chemistry
JF - Analytical Chemistry
IS - 22
ER -