Controlling wettability of PECVD-deposited dual organosilicon/carboxylic acid films to influence DNA hybridisation assay efficiency†
Herein, plasma polymerisation of a dual-layer tetraethyl orthosilicate (TEOS) and acrylic acid (AA) film under a specific recipe is performed. Newly deposited films are found to retain a weakly-bound soft layer of partially polymerised acrylic acid (wbAA), which can be ultimately removed by washing. However, when on the surface, this soft layer is shown to be influential in manipulating the properties of a robust covalently-bound AA (cbAA) underlayer when treated appropriately. Specifically, treatment of the as-deposited dual-layer TEOS/AA films via timed incubation in a humidity-controlled environment results in changes in the water contact angle (WCA) of the cbAA, and ultimately the surface of the TEOS/AA, enabling tuning of the wettability of the acrylic acid layer. Through the use of a controlled incubation environment of the TEOS/AA, followed by washing, we have demonstrated that carboxylic-acid containing surfaces with a WCA between 85° and 10° can be routinely generated, using basic apparatus and simple methodology. Moreover, these surfaces not only retain their AA functionality, demonstrated by covalent-linking of amine-terminated single-stranded DNA, but also strongly inhibit non-specific binding of the DNA strands. The efficiency of these surfaces to be used in DNA direct-binding hybridisation assays has been demonstrated, with limits of detection of 1.11 and 1.66 nM being measured.