Organosilanes have a prominent role in silica based biosensor design for obtaining surface functionalities such as bioconjugation for specific detection and resistance against non-specific interactions. For silica surface multifunctionalization, different silane molecules could be combined; yet, this approach suffers from limitations in terms of obtaining a surface with all the desired functionalities, mostly due to unpredictable nature of silane self-assembly.1 Designing a silica surface with more than one functionality thus represents a challenge. An alternative strategy regarding this issue could be utilization of an organosilane possesing a simultaneously protein resistant and bioconjugable functional group. It was shown before that phosphonate molecules could be utilized for preventing aggregation of silica nanoparticles2, reducing non-specific protein adsorption over silica nanoparticles3, and also tissues could be covalently conjugated with phosphonate bearing molecules from their primary amines using EDC activation4. Although phosphonates were studied in terms of such applications, they have previously not been applied directly over a silica surface, and physical/chemical nature of their protein resistant and bioconjugable characteristics has not been simultaneously demonstrated.
Recently, we have developed a facile technique to obtain an anti-fouling silica surface via a methylphosphonate containing organosilane, 3-(Trihydroxysilyl) propyl methylphosphonate.5 This technique, on top of obtaining protein-resistance, also has the advantage of producing bioconjugable surfaces simultaneously, which makes it quite promising and superior to its alternatives. We initially conducted XPS, contact angle, AFM and ellipsometry analyses to characterize the surface. Then, protein resistance of the surface against proteins with different characteristics were shown with XPS and confocal microscopy measurements. To induce bioconjugation, bovine serum albumin was covalently attached to the surface after EDC activation. Chemical characterization of the EDC activated surface was performed using XPS, and a possible mechanism for the bioconjugation was suggested according to the XPS data. With the advantage of forming unstable O-acylisourea groups after EDC activation, the surface was treated with ultrapure water to regain its anti-fouling characteristics, as confirmed by confocal microscopy. Among applications of such a surface, besides its potential role in designing high selectivity and sensitivity biosensors, smart biocompatible implants, and targeted drug delivery are some other possible applications.