# Moving towards Personalized Medicine--The Broad Use of Aptamers for Targeted Theranostic
## 2 Cancer Therapeutics
### Microbiota and Infection  
The human microbiome is a vast collection of microorganisms that live inside the human body, with bacteria, viruses, fungi, protozoa, and archaea all involved in this environment, playing a crucial role in human health and disease [108]. The microbiota is involved in a variety of physiological processes, including digestion, metabolism, immune system development, and protection against pathogens, and their composition is influenced by several factors such as diet, age, genetics, and environment [108, 109]. However, disruption of the microbiota can lead to an increased risk of infection, which is a major cause of morbidity and mortality worldwide, and it has also been associated with several diseases like cardiovascular and gastrointestinal diseases, neurological disorders, cancer, among others [110]. Understanding the microbiota and its interactions with the host is becoming an active area of research, with potential applications in the diagnosis and treatment of diseases. Therefore, the development of new tools for the detection and treatment of infections is of utmost importance. The microbiota plays a crucial role in protecting against pathogens and preventing infections, competing with pathogenic microorganisms for resources and space and preventing them from colonizing and infecting the host, producing antimicrobial peptides that can kill or inhibit the growth of pathogenic microorganisms and modulate the immune system's response to pathogens [111, 112]. However, when a disruption of this microbiota occurs, it can lead to harmful situations, particularly respiratory, gastrointestinal, and skin infections [111]. One example is antibiotics that can disrupt this balance, promoting pathogenic bacteria overgrowth and increased risk of infection, with _Streptococcus_ and _Staphylococcus_ being among the most common [113]. Also, the overgrowth of Clostridium difficile can lead to a severe infection, which can cause symptoms ranging from diarrhea to life-threatening complications [114]. Aptamers have been increasingly used in microbiome diagnostics, where they can identify and characterize the microorganisms present in a specific environment, such as the human gut, skin, or oral cavity, because of their unique binding properties and their ability to detect specific microbial biomarkers in complex biological samples [1]. Their use in the gut microbiota field has several advantages, including high sensitivity and specificity, easy modulation and synthesis, low cost, and high stability, making them valuable tools for studying the complex interactions between the microbiota and the host and help to develop personalized microbiota-based therapies [1, 2]. One application of aptamers in microbiota research is the identification and quantification of specific microbial species or strains [115]. Aptamers can be designed to specifically bind to the surface molecules or antigens of certain bacteria or other microorganisms, facilitating the identification and quantification of those organisms [115]. This method can be particularly useful in identifying and monitoring specific pathogenic or beneficial microorganisms in complex microbial communities, with studies by [PERSON] et al. and [PERSON] et al. describing this novel approach in strains like _Bifidobacterium bifidum_ (CCFM641-5) and _Lactobacillus casei_, at the same time, demonstrating the potential of aptamer-based strategies for the rapid and accurate detection and quantification of bacteria in food products [116, 117]. Another application of aptamers in microbiome research is the study of microbial metabolites and signaling molecules, where aptamers can be designed to specifically recognize and bind to small molecules, such as short-chain fatty acids, neurotransmitters, and other signaling molecules produced by the microbiota, where aptamers can profile and characterize at the species, strain, or function level.