Fig. 3: Miniaturized Raman spectrometer used for fermentation monitoring and in-vivo skin measurements.

a Raman spectra of the main components contributing to the Raman signal of bacterial supernatant, b Raman signal of bacterial supernatant at 0 and 26.5 h of culture, c Raman spectra of bacterial supernatant containing Serine at 0 to 10 h of culture collected with step of 1 h; pink band indicates spectral region with prominent Serine peaks, d, e, f Raman and HPLC quantification of (d) pHCA, (e) glucose and (f) MgSO4/Na₂HPO₄ in bacterial supernatant (each Raman point is the average of triplicate acquisitions, whereas each HPLC point is the result of duplicate injections), g photograph of miniaturized Raman spectrometer during measurements of fermentation samples, h, i Raman and HPLC quantification of Serine in bacterial supernatant (each Raman and HPLC point is the average of triplicate acquisitions and injections, respectively), j optical schema of the Raman probe with high NA (0.95) developed for in vivo skin measurements, k photograph of “skin probe”, l, m CMOS image of the measurement process of skin in vivo, demonstrating sharp focusing of the Raman signal in the vertical dimension of the sensor under laser excitation wavelength of 785 nm (l) and 675 nm (m), n–s Raman spectra of normal skin collected at the depth of 10–20 µm under a laser excitation wavelength of 785 nm (n, p, r) and 675 nm (o, q, s); pink bands indicate spectral regions of CH and OH peaks; Raman spectra were collected on finger (n, o), hand (p, q) and cheek (r, s); spectrum color represents different probe locations over the skin area around 1 cm².