Introduction
One of the most important aspects of drug delivery is the controlled release of drugs to targeted sites. Drug release depends on the chemical and physical properties of the drug carrier or biomolecules as well as the physiological conditions of the biological cells [1] and [2]. Targeted drug delivery helps to reduce the toxic side effects of the anticancer drug to the normal cells during cancer therapy whereas controlled delivery refers to a triggered release of therapeutic drugs in cellular microenvironment at a desired rate [3], [4] and [5]. In a targeted approach, the drug can be loaded onto a nanocarrier which is functionalized with the targeting antibody and receptor ligands. The latter includes folate, lectin and carbohydrate receptors which facilities nanocarrier binding to the specific cell surface and deliver drug to specific sites inside the cellular microenvironment [5]. Since cancer cell surface over expresses the folate receptors compared to the normal cell surface, FA has received wide attention as a targeting ligand because of its high stability at the nanocarrier surface [6]. The controlled drug delivery depends on a chemical or physical response such as enzymatic cleavage of chemical bond, changes of pH and redox potential which can initiate the drug release on demand and maintain an effective local concentration of the drug [4] and [5]. For example, the anticancer drug DOX can intercalate into the DNA and damage the adjacent healthy cells around the affected area depending on the duration and dose released [7]. The harmful leakage of the drug molecules from the nanocarrier surface during blood circulation in the body mostly occurs when the molecules are physically adsorbed on to the nanocarrier without any covalent functionalization.