*Article* **Characterization of the COPD Salivary Fingerprint through Surface Enhanced Raman Spectroscopy: A Pilot Study**

**Cristiano Carlomagno, Alice Gualerzi, Silvia Picciolini, Francesca Rodà, Paolo Innocente Banfi, Agata Lax and Marzia Bedoni \***

> IRCCS Fondazione Don Carlo Gnocchi ONLUS, Via Capecelatro 66, 20148 Milan, Italy; ccarlomagno@dongnocchi.it (C.C.); agualerzi@dongnocchi.it (A.G.); spicciolini@dongnocchi.it (S.P.); froda@dongnocchi.it (F.R.); pabanfi@dongnocchi.it (P.I.B.); alax@dongnocchi.it (A.L.) **\*** Correspondence: mbedoni@dongnocchi.it; Tel.: +39-0240308874

**Abstract:** Chronic Obstructive Pulmonary Disease (COPD) is a debilitating pathology characterized by reduced lung function, breathlessness and rapid and unrelenting decrease in quality of life. The severity rate and the therapy selection are strictly dependent on various parameters verifiable after years of clinical observations, missing a direct biomarker associated with COPD. In this work, we report the methodological application of Surface Enhanced Raman Spectroscopy combined with Multivariate statistics for the analysis of saliva samples collected from 15 patients affected by COPD and 15 related healthy subjects in a pilot study. The comparative Raman analysis allowed to determine a specific signature of the pathological saliva, highlighting differences in determined biological species, already studied and characterized in COPD onset, compared to the Raman signature of healthy samples. The unsupervised principal component analysis and hierarchical clustering revealed a sharp data dispersion between the two experimental groups. Using the linear discriminant analysis, we created a classification model able to discriminate the collected signals with accuracies, specificities, and sensitivities of more than 98%. The results of this preliminary study are promising for further applications of Raman spectroscopy in the COPD clinical field.

**Keywords:** SERS; COPD; multivariate analysis; saliva
