Sexually transmitted diseases (STDs) refer to infections and syndromes passed through sexual contact and caused by bacteria, viruses, and fungi. It was estimated that each year around 376 million people struggle with bacterial STDs. There are several methods that enable diagnosis of STDs, but each of them has some limitations e.g.: Gram staining is characterized by its low detection rate while microbial culture requires time-consuming incubation and specific conditions for bacterial growth. Even the most recommended tests - nucleic acid amplification tests (NAATs) are very expensive and not every laboratory can afford it. For the above-described reasons, there is still a need to establish rapid, reliable and sensitive method for STDs diagnosis.

More recently, a lot of studies have been done presenting the great potential of the application of SERS (Surface-enhanced Raman Spectroscopy) in diverse fields including medicine and biology. SERS is a kind of fingerprint technique based on the inelastic scattering of incident light by molecules adsorbed on the roughened metal surface (SERS-active substrate). The phenomenon of the SERS technique originates mainly from two main mechanisms: electromagnetic (EM) and chemical.

In this study, we present that SERS-based sensor and chemometric analysis can be performed successfully in direct as well as indirect manner for STD diagnosis. The indirect (confirmatory) approach is based on the identification of unknown pathogenic strain in clinical sample by comparison its spectral image to others spectral image of different bacteria. While the direct one guarantees ultrafast diagnosis (up to 15 min) by classifying SERS spectra of clinical sample to the correct group by means of supervised technique (SIMCA, PLS1-DA). The undoubted advantage of this approach is that it does not involve advance preparation of sample and any chemical reagents while maintaining ultrahigh sensitivity. Hence, both of these methods can compete with many currently used techniques.

This research may have a great impact in biomedical application since, the integration of SERS-based sensor with a small, portable Raman spectrometer could lead to the development of a handheld point-of-care device, which would enable the diagnosis of STD in extremely short time.