Molecular gradients : An efficient approach for optimizing the surface properties of biomaterials and biochips

A variety of molecular gradients of alkanethiols with the structure HS−(CH2)m−X (m = 15; X = COOH, CH2NH2, or CH3) and oligo(ethylene glycol)-terminated alkanethiols with the structures HS−(CH2)15−CO−NH−Egn (n = 2, 4, or 6), HS−(CH2)15−CO−NH−Eg2−(CH2)2−NH−CO−(CH2)4−biotin, and HS−(CH2)15−CO−NH−Eg6−CH2−COOH were prepared on polycrystalline gold films. These gradients were designed to serve as model surfaces for fundamental studies of protein adsorption and immobilization phenomena. Ellipsometry, infrared spectroscopy, and X-ray photoelectron spectroscopy, operating in scanning mode, were used to monitor the layer composition, gradient profiles, tail group conformation, and overall structural quality of the gradient assemblies. The gradient profiles were found to be 4−10 mm wide, and they increased in width with increasing difference in molecular complexity between the thiols used to form the gradient. The oligo(ethylene glycol) thiols are particularly interesting because they can be used to prepare so-call...