Methylene Blue (MB) is widely used as a redox indicator in nucleic acid research. Methylene Blue Azide is an excellent building block for preparing MB-labeled nucleic acid probes from alkyne-modified oligonucleotides, including DBCO-modified oligonucleotides. MB is also a well-known photosensitizer used in photodynamic therapy (PDT) and investigated for the topical treatment of various skin infections via PDT modality. It is a common biological stain, commonly used in medical laboratories to stain cells and tissues for microscopic examination. It can help visualize cellular structures and identify abnormalities. In addition, MB has been studied for its potential role in treating neurodegenerative diseases, such as Alzheimer's and Parkinson's disease. Some research suggests it might have a protective effect on neurons and mitochondrial function.