Local similarity matching algorithm for determining SPR angle in surface plasmon resonance sensors

NRC publication: Ye

Silver cationization of thia fatty acids and esters in laser desorption/ionization time-of-flight mass spectrometry

A laser desorption/ionization (LDI) time-of-flight mass spectrometric (TOF-MS) technique was used for the molecular mass analysis of thia fatty acids and esters, samples without appreciable light absorption at the laser wavelength. After a sample overlayer is deposited by solvent evaporation on a thin silver film substrate, it is subjected to 355 or 532 nm Nd:YAG laser irradiation. Photoablation of the Ag film substrate occurs with sufficient laser fluence, producing silver cluster cations, which can react with the desorbed thia fatty acid or ester molecules in the gas phase. Silver cation attachment of thia fatty esters may produce a silver-cationized analyte and fragments of structural diagnostic value, whereas thia fatty acids would not. With oxygen(s) present on the sulfur in sulfoxy fatty acids and esters, a silver-cationized analyte and additional fragments are produced. Formation of these fragments is consistent with charge-remote mechanisms through simple cleavage and rearrangement pathways. The structural reactivity of these compounds with ablated silver cations is hence comprehensively analyzed

Surface Plasmon Resonance-Laser Desorption/ lonization-Time-of-Flight Mass Spectrometry

The laser desorption/ionization (LDI) process is investigated under surface plasmon resonance (SPR) conditions using time-of-flight mass spectrometry (TOFMS). We demonstrate that LDI-TOFMS at the SPR angle requires a lower minimum laser fluence for the production of silver monomer and cluster cations from ablation of a thin silver film substrate. In the LDI of gramicidin S deposited on a thin silver film substrate, the largest intensity for the molecular cation peak occurs when the laser light is incident on the substrate at a specific SPR angle. These results fully confirm SPR enhancement of the LDI process. The capability to perform SPR-LDI on a larger molecular weight analyte (1141 amu for gramicidin S) represents a new milestone beyond the previous achievement with rhodamine B (479 amu). A better understanding of the SPR mechanism is gained with respect to the substrate metals (silver vs aluminum), desorption (microscopic vs mesoscopic), and ionization (chemical vs multiphoton). These findings may be useful in the future design of SPR-LDI techniques for better TOFMS analysis of higher mass biomolecules

Time-of-flight mass spectrometry of bioorganic molecules by laser ablation of silver thin film substrates and particles

A laser desorption/ionization (LDI) technique, which uses laser ablation of a thin silver film substrate under vacuum conditions to desorb and ionize bioorganic molecules, was developed for molecular mass and structural reactivity analysis in time-of-flight mass spectrometry (TOF-MS). After a sample overlayer is deposited by solvent evaporation on a thin silver film substrate, it is subjected to 355 or 532 nm Nd: YAG laser light by back- irradiation. Photoablation of the silver film substrate occurs with sufficient laser fluence, producing Ag(n) + (n = 1-9) cluster cations which can react with the desorbed bioorganic molecules in the gas phase to form M + or [M + H] + and [M + Ag] + ions for TOF-MS analysis. This LDI technique has been successfully applied to dithizone, benzo[e]pyrene, 1,4,8,11- tetraazocyclotetradecane, dicyclohexyl-18-crown-6, [5]-helicene dendrimer, gramicidin S, substance P and melittin. One advantage of this method over conventional LDI techniques is that the sample does not need to have appreciable spectral absorption at the laser wavelength. The use of silver in thin-film substrates affords analyte-dependent efficiencies that may serve for the direct and accurate mass analysis of specific groups of bioorganic molecules in sample mixtures. In a new sample preparation method, gramicidin S is added to a Tollen's reagent mixture for direct impregnation on to silver particles during their formation and growth in the colloidal solution. These silver particles provide a silver matrix for the analyte molecules, which can enhance the LDI efficiency to produce greater [M + H] + and [M + Ag] + signals

Laser desorption ionization of gramicidin S on thin silver films with matrix isolation in surface plasmon resonance excitation

Laser desorption ionization (LDI)/laser ablation (LA) time-of-flight mass spectrometry (TOFMS) studies are performed via back-illumination on thin silver films deposited with gramicidin S, a cyclic decapeptide (1141 Da). Experimental results indicate an electronic excitation mechanism at low laser fluences and a thermal process at high laser fluences. In a perpendicular orientation of the thin silver film with respect to the drift tube axis, better success of chemical ionization (CI) of neutral silver atoms/clusters and gramicidin S molecules by Ag+ monomer cations within the ablation plume is evident. When these LDI/LA studies are repeated under surface plasmon resonance (SPR) conditions, the neutral atoms/clusters/molecules undergo SPR LDI/LA via a different laser energy transfer process compared to direct LDI/LA. These results also indicate an electronic excitation mechanism, only with a lower laser fluence requirement. Upon addition of a matrix, 2,5-dihydroxybenzoic acid (DHB), CI of gramicidin S molecules by Ag+ monomer cations is hindered while the CI of gramicidin S molecules by Na+ cations can occur at an even lower laser fluence. Thus, SPR LDI/LA with matrix isolation is an excellent technique for the mass analysis of gramicidin S