Plasmonic optical biosensors for the analysis of nucleic acids have drawn a great deal of interest in nanomedicine because of their capability to overcome major limitations of conventional methods. Within this realm, surface-enhanced Raman scattering (SERS)-based sensing is progressively emerging as a powerful analytical tool beyond the basic grounds of academia to viable commercial products. SERS benefits from the synergistic combination between the intrinsic structural specificity and experimental flexibility of Raman spectroscopy, the extremely high sensitivity provided by plasmonic nanomaterials, and the tremendous advances in nanofabrication techniques and spectroscopic instrumentation. SERS application to nucleic acids analysis has been largely restricted to indirect sensing approaches, where a SERS reporter and oligonucleotide ligands are typically combined onto the nanomaterials to enable extrinsic detection of the target sequences. On the other hand, the acquisition of the intrinsic SERS vibrational fingerprint of nucleic acids (direct sensing) has traditionally suffered from major limitations. However, recent years have witnessed a burst of interest in this area, largely driven by the efforts to address key reproducibility and sensitivity issues. In this tutorial review, we summarize and discuss the most recent cutting-edge research in the field of direct SERS sensing of nucleic acids by coherently organising the diverse data reported in the literature in a structurally logical fashion.

Blood-based biomarkers (liquid biopsy) offer extremely valuable tools for the non-invasive diagnosis and monitoring of tumors. The protein c-MYC, a transcription factor that has been shown to be deregulated in up to 70% of human cancers, can be used as a robust proteomic signature for cancer. Herein, we developed a rapid, highly specific and sensitive SERS assay for the quantification of c-MYC in real blood samples. The sensing scheme relies on the use of specifically designed hybrid plasmonic materials and their bioderivatization with a selective peptidic receptor modified with a SERS transducer. Peptide/c-MYC recognition events translate into measurable alterations of the SERS spectra associated with a molecular orientation of the transducer, in agreement with the surface selection rules. The efficiency of the sensor is demonstrated in cellular lines, healthy donors and a cancer patient.

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Exosomes are emerging as one of the most intriguing cancer biomarkers in modern oncology for early cancer diagnosis, prognosis and treatment monitoring. Concurrently, several nanoplasmonic methods have been applied and developed to tackle the challenging task of enabling the rapid, sensitive, affordable analysis of exosomes. In this review, we specifically focus our attention on the application of plasmonic devices exploiting surface-enhanced Raman spectroscopy (SERS) as the optosensing technique for the structural interrogation and characterization of the heterogeneous nature of exosomes. We summarized the current state-of-art of this field while illustrating the main strategic approaches and discuss their advantages and limitations.