2D scanning SERS probe for early biofilm boundary determination

Abstract

Surface-enhanced Raman scattering (SERS) enables the biofilm detection by the characteristic Raman spectrum of extracellular polymeric substance (EPS). However, its clinical application in wound biofilm delineation is hindered by long sampling time and unpredictable sampling errors. To overcome these limitations, we propose a two dimensional (2D) scanning SERS probe that combines the advantages of galvo mirrors and a custom designed SERS active substrate. In this design, the SERS active substrate with dendritic nano-silver structure is fixed on the focal plane of the scan lens to maintain not only the required distance of the sampling plane but also the stable sampling condition as the excitation laser beam driven by the galvo mirrors scans quickly over the region of interest (ROI). Our benchtop study shows that the ± 3.75 mm offset between the sampling plane and the focal plane results in less than 10% change in both laser spot size and fluctuation in Raman peak intensity for the 2D scanning SERS probe, superior to the commercial Raman probe where 1700% change in laser spot size and 95% fluctuation in Raman peak intensity. Our in vitro study in two typical biofilms shows that the 2D SERS scanning probe can detect the biofilm as early as 4 h of cultivation and delineate the biofilm boundary with accuracy at 8 h of cultivation. Furthermore, this substrate is disposable, antibacterial, and capable of enhancing Raman intensity with consistency. Our studies imply the clinical potential of using the 2D SERS scanning probe for biofilm delineation in chronic wound management.