Joerg Fick

Interaction of self-assembled monolayers of oligo(ethylene glycol)-terminated alkanethiols with water studied by vibrational sum-frequency generation

Vibrational sum-frequency generation (VSFG) was used to investigate the conformational changes in self-assembled monolayers (SAMs) of (1-mercaptoundec-11-yl) hexa(ethylene glycol) monomethylether (EG6-OMe) on gold when exposed to liquid water. VSFG spectra of the EG6-OMe SAMs were recorded before, during, and after exposure of the films to water and after a subsequent evacuation step. While in contact with water the entire ethylene glycol chains are found in a random, solvated state, after removal from the fluid water molecules remain absorbed only at the terminal groups of the film giving rise to distinct conformational changes. After evacuation, the structure of the EG6-OMe SAM reverts to its original state, indicating that water has been removed from the monolayer. Our findings support recent ab initio calculations and Monte Carlo simulations on the interaction of ethylene glycol-terminated monolayers with water.

P0-9 A Lateral Field Excited Acoustic Wave Sensor for the Detection of Saxitoxin in Water

In the United States, approximately 20% of all foodborne disease outbreaks result from the consumption of seafood products. Specifically, the disease Paralytic Shellfish Poisoning (PSP) is caused by consuming molluscan shellfish contaminated with a suite of neurotoxins the most potent of which is saxitoxin (STX). The current method for detecting STX is the mouse bioassay in which a mouse is exposed to a shellfish sample and the time required for the mouse to perish is noted. The length of time required for the mouse to die is used to estimate the level of STX in the original sample. Since this technique is a time consuming and costly laboratory-based procedure, a rapid in situ sensor is needed to detect STX levels in shellfish and in sea water so timely closures of shellfish grounds can be made to protect public health. In this work, a novel Lateral Field Excited (LFE) acoustic wave sensor, which has been successfully used for chemical and biological sensing, is employed to detect STX in water, proving itself as a feasible alternative to the mouse bioassay in STX detection.

Surface-Specific Interaction of the Extracellular Domain of Protein L1 with Nitrilotriacetic Acid-Terminated Self-Assembled Monolayers

We report a study on the interaction of the extracellular domain of trans-membrane proteins N-cadherin and L1 with nitrilotriacetic acid (NTA)-terminated self-assembled monolayers (SAMs) grown on silver and gold surfaces. Quartz crystal microbalance (QCM) and reflection absorption infrared spectroscopy (RAIRS) measurements reveal that upon addition of protein to an NTA-SAM there is a subsequent change in the mass and average chemical structure inside the films formed on the metal substrates. By using vibrational sum frequency generation (VSFG) spectroscopy and making a comparison to SAMs prepared with n-alkanethiols, we find that the formed NTA-SAMs are terminated by ethanol molecules from solution. The ethanol signature vanishes after the addition of L1, which indicates that the L1 proteins can interact specifically with the NTA complex. Although the RAIRS spectra display signatures in the amide and fingerprint regions, the VSFG spectra display only a weak feature at 866 cm(-1), which possibly indicates that some of the abundant phenyl rings in the complex are ordered. Although cell biology experiments suggest the directional complexation of L1, the VSFG experiments suggest that the alpha-helices and beta-sheets of L1 lack any preferential ordering.