Surface characterization and platelet adhesion studies of self-assembled monolayer with phosphonate ester and phosphonic acid functionalities

Abstract

Because of its well-defined surface configuration and creative chemical structure, an alkanethiol self-assembled monolayer (SAM) on gold is a model surface for a blood compatibility investigation. In this study two laboratory-synthesized long-chain alkanethiols, HS(CH(2))(10)PO(3)-(C(2)H(5))(2) and HS(CH(2))(10)PO(3)H(2), were employed for the direct preparation of SAMs with nonionic and ionic functional groups. Various instrumental analyses confirmed the high purity of the phosphonate ester and phosphonic acid terminated alkanethiols. The surface characterization results showed the -PO(3)H(2) terminated SAM was more hydrophilic than the -PO(3)(C(2)H(5))(2) one. Higher hysteresis values for the -PO(3)(C(2)H(5))(2) and -PO(3)H(2) terminated SAMs were noted, which were possibly due to the steric hindrance of the bulky terminal groups. In addition, the O(2) plasma + EtOH-rinse pretreated Au sample was hydrophilic because of the residual gold oxide on the surface. This finding was supported by electron spectroscopy for chemical analysis (ESCA) as well. The ESCA analysis also indicated bulky and polar terminal groups [-PO(3)(C(2)H(5))(2) and -PO(3)H(2)] were situated in the outermost layer of its monolayer. The platelet reactivity on the SAM with the nonionic group -PO(3)(C(2)H(5))(2) was less than those of the ionic terminated SAMs -COOH and -PO(3)H(2). The O(2) plasma + EtOH-rinse pretreated gold substrate exhibited the least platelet-activating surface among the different pretreated Au substrates studied.