Phytoplankton, as an important component of marine ecosystem, play a key role in understanding marine resources and monitoring marine environment. In this paper, under the suggestion of marine biology professional researcher, we selected six kinds of phytoplankton commonly found in China’s coastal areas and conducted digital holographic microscopic imaging experiments to obtain their holograms. Then, the angular spectrum reconstruction algorithm was used to conduct diffraction reconstruction of the phytoplankton hologram to achieve clear imaging of the algae target. A threshold based image segmentation algorithm is used to segment the phytoplankton target area and obtain image dataset. Finally, transfer learning is used to train on the pre-trained model. Experimental results show that the classification accuracy of the trained network on the test set can reach 95.7%.
In this paper, we improve reconstruction quality from in-line holograms of marine algae by two phase-retrieval-based reconstruction methods. Digital holographic microscopy, with its high-resolution and volume recording capability, has been applied in the area of monitoring marine algae. We designed a digital in-line holographic microscopy laboratory system to observe and analyze marine algae. Due to the “twin-image” problem caused by the loss of phase information in hologram recording, the reconstructed quality from holograms of marine algae reduced significantly. To enhance reconstruction quality, the alternating projections methods and inverse methods are introduced and implemented on the marine algae holograms. Compared with the traditional backpropagation method, both of the above methods have good performance in improving reconstruction quality from in-line marine algae holograms.
Surface plasmon resonance (SPR) sensing technology is widely used in the field of biosensors due to its non-marking, high-sensitivity, and non-invasive characteristics. However, SPR technology is still limited to sensing analysis in twodimensional plane, axial detection, as the key of SPR application in three-dimensional medium spatial detection, has not been well studied and solved. In an angle-interrogation SPR sensing system, the spatial characteristics of evanescent wave-dielectric interaction at multiple wavelengths are studied, and the factors affecting the spatial distribution of surface plasmon resonance are also analyzed. An axial spatial resolution method based on the particle swarm optimization (PSO) algorithm with multi-wavelength angle-interrogation structure is proposed, the refractive index distribution in axial space is determined by analyzing the characteristic SPR signal. In addition, the calculation and analysis of the applicable range of wavelengths are carried out. In the reliable spectral range of the incident light wavelength of 600-900 nm, the average error of the axial refractive index spatial resolution increases from 10-5 RIU to 10-4 RIU as the number of axial layers increases. The proposed multi-wavelength angle modulation structure analysis method based on PSO algorithm extends the SPR detection range from two-dimensional plane to three-dimensional space, which provides a new and promising analysis model for molecular biology.
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