## 3 Results and Discussion
### Spectral Data Comparison between the Instruments  
The use of portable devices for recording Raman spectra leads to a higher noise level compared to laboratory instruments due to their smaller size and reduced analysis time, both in the length of one scan and in the number of accumulations [26]. The SNR value is essential for the efficacy of portable Raman devices since the relatively high noise level is their drawback. Using the example of calf thymus DNA Raman spectra, SNR values were obtained for ten selected bands, and they are represented in a histogram (Figure 3a). For all these bands and devices, this value exceeded 9, which confirmed acceptable signal detection. The differences between the devices were significant for all bands, and the DXR SmartRaman showed the highest SNR values (-42-131), followed by i-Raman Plus (-15-30) and Ahura FirstDefender (-9-18). The median SNR value was 70.7 for the DXR SmartRaman, 20.9 for i-Raman Plus, and 12.2 for Ahura; the corresponding mean SNR values were 75.6, 21.2, and 13.1. Relatively low SNR values obtained for portable Raman devices do not limit the use of these instruments for various routine applications where such extremely high sensitivity is not necessary.  
The spectral resolution of a portable Raman spectrometer is a crucial measurement parameter to distinguish between several adjacent Raman bands in the spectrum [27]. It is useful, especially in the spectroscopic analysis of animal tissues. Biological macromolecules that constitute cells and tissues, such as proteins, nucleic acids, and polysaccharides, are characterized by complex Raman spectra with many often overlapping bands [5].  
Figure 2: Raw Raman spectra of calf thymus DNA measured using handheld, modular, and laboratory Raman instruments: (a) Ahura FirstDefender (75 mW); (b) i-Raman Plus (90 mW; 3 scans; 60 s per scan); (c) DXR SmartRaman (90 mW; 3 scans; 60 s per scan). The dash-line frame indicates the working region ranging from 600 to 1800 cm\({}^{-1}\).  
Narrower signals in the spectrum enable a better resolution of adjacent bands or shoulders. Otherwise, when the bands become broader, they may appear as shoulders or become indistinguishable. This is especially true for the handheld equipment. Figure S1 represents the multiple-curve fitting analysis of the Raman spectra of calf thymus DNA recorded using the laboratory, modular, and handheld instruments, yielding 18 Voigt components for each spectrum. The histogram in Figure 3 represents bandwidth comparison for selected strong- or moderate-intensity bands detected in the calf thymus DNA spectrum for each instrument. The spectral intervals corresponded to the positions of the Voigt maxima obtained by approximating the peaks, and the bandwidths were also attributes of these components. The BWHM values varied from ~15 to 73 cm\({}^{-1}\) between bands and devices, and the corresponding average values slightly increased in the order of DXR SmartRaman (33.1 cm\({}^{-1}\)), i-Raman Plus (35.2 cm\({}^{-1}\)), and Ahura (35.9 cm\({}^{-1}\)). Based on the analysis of glycine spectral data, the median BWHM value reported earlier for the Ahura instrument was 14.4 cm\({}^{-1}\)[28], which is more than twice lower than the value obtained in the present study for the Raman spectrum of DNA. This difference can be explained by the fact that polymeric substances like DNA typically have much wider vibration bands compared to small crystalline molecules, and this broadening of the signals is especially pronounced in amorphous polymers. All instruments of the current study showed more or less similar BWHM values, probably due to the significant overlap of the bands used for calculation. However, it is clear that, at least for the bands at around 1668, 1577, 1373, 1305, 788, and 732-736 cm\({}^{-1}\), the laboratory DXR SmartRaman instrument provided spectra with the lowest BWHM compared to the portable systems, for which the handheld device mostly showed higher BWHM values. However, this trend was not observed for the remaining bands at 1100-1336 cm\({}^{-1}\).