Tracer technology of probiotics based on optical imaging

Abstract

Probiotics refers to live microorganisms, which is beneficial for host health mainly by adjusting the gastrointestinal tract flora, improving intestinal epithelial barrier function and regulating immune function. Common probiotic strains include Bifidobacteria (such as Bifidobacterium longum, Bifidobacterium thermophilus ), Lactobacillus (such as Lactobacillus acidophilus, Lactobacillus plantarum and Lactobacillus reuteri ), Bacillus (such as Bacillus subtilis ), yeast Bacteria (such as saccharomyces ) etc. In the past, probiotics were counted by analyzing the number of bacteria in feces or dissecting animals gastrointestinal tracts at different times. The action mechanism of probiotics is still unclear. Genetic labeling of probiotics by modern biological techniques is one of important research methods and it provides a basis for researching the mechanisms of probiotics. Tracer technology of probiotics is based on optical imaging, which includes bioluminescence, traditional fluorescence (fluorescent protein and fluorescent dye) and nanomaterials fluorescence. The main applications in the past decade are bioluminescence technology and fluorescence technology. The difference between them is that bioluminescence refers to self-luminescence. It catalyzes the substrate reaction and emits visible light by expressing and secreting different sources of luciferase. This reaction does not require exciting light. The luciferase derived from bacteria does not require the addition of substrate through expressing Lux CDABE. The luminescent reaction catalyzed by luciferase derived from fungus has a longer luminescence wavelength and is more permeable to tissue for imaging, but this reaction requires the substrate. Fluorescence is the expression of different fluorescent proteins, which emit fluorescence under the stimulation of exciting light. This reaction does not require the participation of the substrate, but requires external exciting light, so the background interference is relatively intense. Nanomaterial luminescence is a new type of probiotic tracer technology in recent years. The fluorescence imaging of new nanomaterials mainly includes quantum dots, upconversion nanomaterials and persistent luminescence nanomaterials. Persistent luminescence nanomaterials can even maintain the luminescence phenomenon for a few days after stopping the excitation. Compared to traditional fluorescence imaging technology, fluorescent imaging of nanomaterials may have more extensive applications, due to the lack of introduction of fluorescent protein genes. However fluorescent imaging of nanomaterials still has some disadvantages, such as high cost and toxicity etc. The characteristics, advantages and disadvantages of the three techniques are reviewed in order to provide theoretical and reference basis for further development and research on the tracing technology of probiotics.