Bravo spectrometer

In order to determine the textural characterization of the samples, a Tristar 3000 device was used. To calculate the SSA (specific surface area), the BET principle was used. The pore characteristics were obtained, based on the BJH principle. Analysis of the carbon materials’ surface morphology was conducted using a scanning electron microscopy (SEM) method via FESEM (Zeiss Merlin, Oberkochen, Germany) equipment. The degree of graphitization and level of disorder of the carbon structure of SB-Biochar and SB-N-Biochar was determined using Raman spectroscopy. The spectra were obtained using a Bruker BRAVO spectrometer. Analysis of the surface functionalities was carried out via X-ray photoelectron spectroscopy (XPS). The value for the point of zero charge (pH_pzc) was obtained by plotting the measured zeta potential value, with the pH measured via a Zetasizer Nano ZSE 3700 (Malvern Instrument Co., Malvern, UK) at 298 K, identifying a pH varying from 2 to 10.

The measurements were performed using Bruker’s BRAVO spectrometer equipped with Duo LASER™ (700–1100 nm) and CCD camera. The laser power was 100 mW for both LASERs and the spectral resolution was 2–4 cm⁻¹. Typically, 15 SERS spectra for each sample were acquired. Each spectrum was measured for 30 s. In these studies, we measured and presented the data based on 149 samples of saliva and 104 samples of nasopharyngeal swabs (15 spectra for each sample; total 3795 spectra). Both sets of samples (saliva and swabs) were from different individuals and were independent of each other. All experiments with clinical samples were conducted in accordance with relevant institutional regulations and guidelines and were approved by the Ethics and Bioethics Committee of Cardinal Stefan Wyszynski University in Warsaw.

Measurements were performed by using Bruker’s BRAVO spectrometer equipped with Duo LASER™ (700 nm–1100 nm) and a CCD camera. The spectral resolution was 2–4 cm⁻¹, while the laser power was 100 mW for both LASERs. The background was automatically removed. To demonstrate the reproducibility of our experiments, SERS measurements were recorded repeatedly to obtain 50 single measurements for each tested bacterial strain. The recording time of a single spectrum was about 6000 ms and 3 accumulations. Using OPUS software (Bruker Optic GmbH, 2012 version, Leipzig, Germany), all obtained spectra were processed: baseline correction (concave rubber band correction, number of iterations 6, number of baseline points 6), smoothing (number of smoothing points 5), normalization (min-max normalization, the whole range) and then cutting in the range between 600 cm⁻¹ and 1750 cm⁻¹. Finally, all the preprocessed data were put into Unscrambler (CAMO software AS, version 10.3, Oslo, Norway), where the Partial Least Square Regression (PLSR) was performed.