Drug Delivery<unk> s can be utilized for a number of different functions, the main one being drug delivery. The<unk>  that forms when nanoparticles come in contact with biological fluid has long been investigated for its potential to deliver important drug molecules or proteins to sites of need within the human body. Nanoparticles are known to have high drug-loading efficiency as well as the ability to easily pass through biological barriers due to their nano scalability. Their composition tunability allows for their toxicity to be controlled, and they can be modified to contain diverse sets of functional groups that can perform specific activities. These qualities of nanoparticles make them ideal for drug delivery capabilities. A major area of study within the sphere of<unk>  drug delivery, is the study of the circulation time of nanoparticles in the body. In order to optimize the effectiveness of a drug, specifying the location where it is delivered and how long it stays there can be extremely useful. Often, macrophages within the blood will detect the presence of the nanoparticles and immediately work to eliminate them from the body. This is not always a good thing from the perspective of drug delivery, and thus studies were performed to prolong circulation time. It was found that when opsonins, like fibrinogen, are numerous in the<unk> , the proteins tend to induce macrophage recognition and subsequent consumption of nanoparticles. Conversely, when the<unk>  is saturated with dysopsonins, like albumin, the macrophages show decreased recognition of the particles and thus, circulation time of the particles is greatly increased. This technique is loosely referred to as the "stealth effect". By tailoring the contents of the<unk> , the length of time a nanoparticle stays in your body can be controlled. As mentioned previously, nanoparticles can be grown with particular functional groups on their surfaces that induce chemoselectivity. Functional biomolecules like transferrin, insulin, and folic acid are commonly used in cancer-targeting drug delivery systems. Other smaller molecules like anhydride, amine, carboxyl, and thiol can be used to direct nanoparticles to high cellular association with endothelial cells, pancreatic cells, and activated human macrophages. Certain apolipoproteins, such as Apo E, ApoA1, and ApoB-100, could potentially functionalize nanoparticles to target the nervous system. Another more pressing problem with nanoparticle drug delivery is the tendency for nanoparticles to accumulate at the target site or in various organs, which can become toxic. It is known that the size of nanoparticles dictates their distribution within the body, meaning that nanoparticles with different sizes will tend to accumulate in certain organs. Therefore, size is a very important control factor when considering nanoparticle distribution and accumulation at target sites during drug delivery.
Protein corona
Matrix-core
Virulence factor
Immunogen
Antigen
Self-protein
Immune complex
Bioactive compound