Conventional and inverted SERS configurations in pathogen diagnostics on the basis of plasmonic gold nanostars ink

Conventional surface-enhanced Raman spectroscopy (SERS) methodologies typically depend on prefabricated substrates, which can constrain their utility for rapid, in-situ diagnostics. While nano-inks offer a route toward flexible sensing, their application typically still follows a direct, substrate-based paradigm. Trends toward the miniaturization of Raman spectroscopy and on-site diagnostics necessitate a fundamental rethinking of sensor design, prioritizing minimal sample preparation and direct analysis.

Gold nanostar (AuNSs)-based plasmonic ink is presented as a versatile platform for surface-enhanced Raman spectroscopy (SERS)-based detection of pyocyanin - a key virulence factor of Pseudomonas aeruginosa. Two SERS configurations are explored: a conventional paper-based sensor, used to establish the analytical performance of the AuNSs ink (LOD 15 nM in saliva), and an inverted approach, where the ink is deposited directly onto a medical cotton swab pre-loaded with the sample. The inverted configuration, coupled with a portable Raman spectrometer (785 nm), enables direct, substrate-free detection of pyocyanin with a clinically relevant LOD of 5 μM and requires minimal sample pretreatment. Spike-and-recovery experiments in saliva yielded recoveries of 96-105% (s_r ≤ 0.10), confirming the accuracy of the method. The inverted SERS approach on cotton swabs thus offers a practical, rapid, and simple route for point-of-care screening of P. aeruginosa infections, circumventing the need for prefabricated sensors or laboratory equipment.

By transforming the standard clinical swab into an active SERS substrate, the inverted approach provides a practical, substrate-free, and equipment-light platform for direct pathogen screening at the patient's bedside. This strategy addresses key barriers to SERS implementation - reliance on prefabricated sensors, complex sample handling, and bulky instrumentation - offering a realistic and scalable solution for non-invasive screening. This approach is particularly significant for the analysis of potentially bio-contaminated surfaces, such as medical instruments or hospital environments, where direct contact with the analyte is hazardous or undesirable.