A Portable SERS Sensor for Pyocyanin Detection in Simulated Wound Fluid and through Swab Sampling

A portable surface-enhanced Raman spectroscopy (SERS) sensor for detecting pyocyanin (PYO) in simulated wound fluid and from bacteria samples was developed. Solution-phase SERS detection protocols are designed to be compatible with two different clinical practices for wound exudate collection, namely negative pressure liquid collection and swabbing. For citrate-coated metal nanoparticles of three different compositions, i.e. gold (AuNP), alloyed silver/gold (AgAuNP), and silver (AgNP), we firstly confirmed their interaction with PYO in the complex wound fluid, using fluorescent quenching experiments, which rationalized the Raman enhancement effects. We then demonstrated the Raman enhancement effects of the metal nanoparticles in an order of AgNP > AgAuNP > AuNP. The limit of detection (LOD) achieved for PYO is 1.1 µM (in a linear range of 0.1 – 25 µM by the AgNP), 10.9 µM (in a linear range of 5 – 100 µM, by the AgAuNP), and 17.7 µM (in a linear range of 10 – 100 µM by the AuNP). The AgNP and AgAuNP sensors together cover the sensitivity and dynamic range requirement for clinical detection of wound infection, where PYO is in 1-50 µM. In addition, sterilized cotton swabs were used to collect wound fluid and transfer samples into AgNP solution for SERS measurement. This detection protocol was completed within 5 minutes with a LOD of 23.1 µM (in a linear range of 15 – 100 µM). The SERS sensing protocol was validated by its successful detection of PYO from cultured Pseudomonas aeruginosa bacteria. The findings presented in this work paves the route towards point-of-care diagnostics of wound infections.