Phagocytosis is an essential mechanism in innate immune defense, and in maintaining homeostasis to eliminate apoptotic cells or microbes, such as Mycobacterium tuberculosis, Salmonella enterica, Streptococcus pyogenes and Legionella pneumophila. After internalizing microbial pathogens via phagocytosis, phagosomes undergo a series of ‘maturation’ steps, to form an increasingly acidified compartment and subsequently fuse with the lysosome to develop into phagolysosomes and effectively eliminate the invading pathogens. Through this mechanism, phagocytes, including macrophages, neutrophils and dendritic cells, are involved in the processing of microbial pathogens and antigen presentation to T cells to initiate adaptive immune responses. Therefore, phagocytosis plays a role in the bridge between innate and adaptive immunity. However, intracellular bacteria have evolved diverse strategies to survive and replicate within hosts. In this review, we describe the sequential stages in the phagocytosis process. We also discuss the immune evasion strategies used by pathogens to regulate phagosome maturation during intracellular bacterial infection, and indicate that these might be used for the development of potential therapeutic strategies for infectious diseases.

As a new analytical technology, surface-enhanced Raman scattering (SERS) has received increasing attention, and researchers have discovered the importance of SERS-active materials. Considerable effort has been made by researchers to develop multiperformance and multipurpose SERS-active substrates ranging from coinage metals to transition metals and semiconductor materials. SERS-active substrates are critical for obtaining accurate and reproducible spectral information. Among all the substrate materials, semiconductors are considered one of the most promising materials, as they exhibit high chemical stability, good biocompatibility, high carrier mobility, and good controllability during fabrication. Here, we provide an overview of SERS enhancement mechanisms based on semiconductor materials, such as inorganic semiconductors, metal/semiconductor composites, and organic semiconductors.