Fig 1.
The comparison of already proposed forward scattering / diffraction sensors and novel digital holography sensor.
Fig 2.
The schematic set-up of the PSDIHS configuration.
Light generated by a coherent light source (LS) with a wavelength of 405 nm and output power of 25 mW is focused onto a 0.5-μm-diameter pinhole (PH), which acts as the point source emitting the divergent spherical wave. The wave illuminates an examined object, bacterial colonies grown on nutrient medium in a Petri dish on a sample holder with an X-Y translation stage, and forms magnified diffraction pattern in the recording plane (C) of the CMOS camera with the sensing area: 2048 × 2048 pixels (pixel size: 6 × 6 μm), mounted on a Z translation stage.
Fig 3.
Exemplary reflection absorbance spectra of the bacterial colonies of (a) S. intermedius and (b) E. coli.
Fig 4.
Representative holographic signatures of S. intermedius (A) and E. coli (B) bacteria. (I) The digital in-line holograms of bacterial colonies, and (II) the reconstruction of the spatial distribution of the optical field’s amplitude inside the space occupied by the colonies (dashed lines indicate the colony contour)). (III) The reconstruction of the spatial distribution of the optical field phase mod (2π) inside the space occupied by colonies.
Fig 5.
Representative results of optical microscopic investigation for S. intermedius (A) and E. coli (B) bacteria. (I) Representative transmission microscopy images of bacterial colonies (the dotted lines indicate the cross-section for which the transmission coefficient was evaluated). (II) The transmission coefficient along the cross-section (the dotted lines indicate the bacterial colony edge). (III) Phase contrast microscopy images of (A) S. intermedius and (B) E. coli bacterial colonies.
Fig 6.
Representative amplitude patterns of the optical field transformed by S. intermedius (I) and E. coli (II) colonies calculated for different observation plane distances.
Fig 7.
Representative results for S. intermedius (A) and E. coli (B) bacteria. (1) Phase and (2) intensity patterns of the optical fields obtained by the reconstruction of the point-source digital in-line hologram at a distance of 2.0 cm from the bacterial colony, and (3) the representative Fresnel diffraction patterns. (4) The demonstration of the wavelength-dependent differences between Fresnel patterns of bacterial colonies reconstructed from digital holograms (at 405 nm) and recorded in an optical system (at 635 nm) (the dashed lines indicate the wavelength-dependent differences of the diffraction rings spacing).
Fig 8.
Representative results of PCA analysis of the optical signatures: recorded digital holograms (A), amplitude (B) and phase (C) images, reconstructed diffraction intensity patterns (D) of both analyzed bacteria species colonies.