Abstract
The use of light diffraction for the microbiological diagnosis of bacterial colonies was a significant breakthrough with widespread implications for the food industry and clinical practice. We previously confirmed that optical sensors for bacterial colony light diffraction can be used for bacterial identification. This paper is focused on the novel perspectives of this method based on digital in-line holography (DIH), which is able to reconstruct the amplitude and phase properties of examined objects, as well as the amplitude and phase patterns of the optical field scattered/diffracted by the bacterial colony in any chosen observation plane behind the object from single digital hologram. Analysis of the amplitude and phase patterns inside a colony revealed its unique optical properties, which are associated with the internal structure and geometry of the bacterial colony. Moreover, on a computational level, it is possible to select the desired scattered/diffracted pattern within the entire observation volume that exhibits the largest amount of unique, differentiating bacterial features. These properties distinguish this method from the already proposed sensing techniques based on light diffraction/scattering of bacterial colonies. The reconstructed diffraction patterns have a similar spatial distribution as the recorded Fresnel patterns, previously applied for bacterial identification with over 98% accuracy, but they are characterized by both intensity and phase distributions. Our results using digital holography provide new optical discriminators of bacterial species revealed in one single step in form of new optical signatures of bacterial colonies: digital holograms, reconstructed amplitude and phase patterns, as well as diffraction patterns from all observation space, which exhibit species-dependent features. To the best of our knowledge, this is the first report on bacterial colony analysis via digital holography and our study represents an innovative approach to the subject.
Highlights
A variety of biosensors are routinely used for bacterial detection and identification [1,2,3,4]
Spectroscopic examination of absorption properties of the bacterial colonies In Point-Source Digital In-Line Holography (PSDIH), it is important to preserve the appropriate transmission properties of the illuminated object to allow the possibility of recording the high-contrast interference patterns of the non-scattered and scattered waves
To the best of our knowledge, this report is the first attempt at characterizing the species-dependent properties of bacterial colonies and their diffraction patterns by digital in-line holography
Summary
A variety of biosensors are routinely used for bacterial detection and identification [1,2,3,4]. We previously demonstrated that colonies from different bacterial species and strains generate specific diffraction signatures that can be used for microbiological diagnosis, as both the amplitude and phase spatial light are species- and strain-specific [7,11]. The experiments performed using our system with converging spherical wave illumination have shown that the Fresnel diffraction patterns of colonies were unique and allowed for species discrimination [12,13,14,15,16]. Experiments performed by other researchers on four different strains of Escherichia coli, demonstrated that it is possible to identify bacterial strains with a 82% recognition rate [9]. Further enhancement of the bacterial identification accuracy on the level of strain discrimination is possible by means of optical diffraction; an extended study of the interaction between bacterial colonies and light is necessary
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