Transparent, Antibiofouling Window Obtained with Surface Nanostructuring.

Biofouling is one of the key factors which limits the long-term performance of seawater sensors. Common measures to hinder biofouling include toxic paints, mechanical cleaning and UV radiation. All of these measures have various limitations. A very attractive solution would be to prevent biofilm formation by changing the surface structure of the sensor. This idea has been implemented successfully in various settings, but little work has been done on structuring optically transparent materials, which are often needed in sensor applications. In order to achieve good antibiofouling properties and efficient optical transparency, the structuring must be on the nanoscale. Here, we investigate a transparent, antibiofouling surface obtained by patterning a semihexagonal nanohole structure on borosilicate glass. The nanoholes are approximately 50 nm in diameter and 200 nm deep, and the interparticle distance is 135 nm, allowing the structure to be optically transparent. The antibiofouling properties of the surface were tested by exposing the substrates to the microalgae for four different time intervals. This species was chosen because it is common in the Norwegian coastal waters. The tests were compared with unstructured borosilicate glass substrates. The experiments show that the nanostructured surface exhibits excellent antibiofouling properties. We attribute this effect to the relative size between the structure and the biofouling microorganism. Specifically, the small dimensions of the nanoholes, compared to the biofouling microorganism, make it more difficult for the microalgae to attach. However, lubrication of the substrates with FC-70 perfluorocarbon resulted in contamination at a rate comparable to the reference substrate, possibly due to the chemical attractiveness of the alkane chains in FC-70 for the microalgae.