An ALD aluminum oxide passivated Surface Acoustic Wave sensor for early biofilm detection

We present a successful demonstration of a reusable Surface Acoustic Wave (SAW) sensor for bacterial biofilm growth monitoring in an animal serum and bacterial growth media. Bacterial biofilms produce harmful metabolic by-products and are a characteristic of severe infections. Thus, continuous monitoring of bacterial biofilm growth is critical. Here, we report a highly sensitive SAW sensor for biofilm growth monitoring fabricated by depositing zinc oxide (ZnO) piezoelectric thin film by pulsed laser deposition (PLD). To prevent ZnO damage from long term exposure to bacterial growth media or to an animal serum, the ZnO layer of the sensor was effectively protected by aluminum oxide (Al2O3) using atomic layer deposition (ALD). As a result, the sensor was reusable for consecutive biofilm formation experiments. The detection limit of the SAW sensor was approximately 5.3 pg. The SAW sensor was tested with Escherichia coli W3110 in Lysogeny Broth (LB) media, and in 10% diluted Fetal Bovine Serum (FBS) as an approximation to an in vivo environment. The resonant frequency shift measured at the output of the SAW sensor in both LB media and 10% FBS corresponded to natural biofilm growth. These repeatable results support the novel application of a SAW sensor for real time biofilm sensing.