## 1 Introduction  
Research related to the use of nano-systems in drugs and genes has increased in recent decades due to a number of innovative applications of nano-systems in health-related issues. The global market for drug delivery systems and genes is projected to reach $175.6 billion by 2016, which represents an increase of $44 billion from 2010 [1]. The main focus of such nano-systems administered drugs and genes research is to deliver a specific amount of the component of interest in the right place, at the right time, and nano-formulation has received the most attention out of others. The exposure of cells/tissues/tumors to therapeutic agents increases when nano-formulations are designed as drug delivery vehicles. Various therapeutic and immunization agents, such as anticancer drugs and plasmid DNA (pDNA), could be encapsulated and administered simultaneously to enhance the effectiveness of such therapy and/or immunization [2; 3]. Among different materials used for drug delivery, one of the most successful is poly (ester): poly-dl-lactic-_co_-glycolic (PLGA), which has immense potential as a drug delivery vehicle as well as a platform for tissue engineering [4; 5]. PLGA is a biodegradable polymer mostly used for developing nano-medicines. It hydrolyzed in body to produce lactic acid and glycolic acid monomers, which subsequently degraded to carbon dioxide and water [4; 6; 7]. Degradation rates and structural/mechanical properties of PLGA depend on the proportion of monomers formed [4; 6]. PLGA contains carboxylic acid, which can also be functionalized with other molecules before or after the preparation of nanoparticles (NPs). One of the possible modifications of PLGA is coupling with polymer polyethylene glycol (PEG). It has been shown that PEG-coated carriers have increased circulation half-life in blood, reduced rate of uptake by the liver and prevented its recognition by the mononuclear phagocytic system [8]. In addition, they can facilitate a full control of drug release rates [9]. Furthermore, PLGA and PEG are already approved by the Food and Drug Administration (FDA) and the European Medicine Agency (EMA) and used in therapeutic devices [4; 10]. Another desirable characteristic of these nano-systems is possible functionalization to target specific cells. Selective gene delivery to folate receptor overexpressing tissues by decorating NPs with folic acid (FA) as targeting ligand is of great interest [11; 12; 13]. Chemical coupling of PLGA, PEG and FA will enable us to produce NPs with blood compatibility, drug release rate control and targeting characteristics. Polymer NPs have been prepared using different methods and the most common of them is emulsification--solvent evaporation technique [4; 6; 14; 15]. Other available methods are emulsification--diffusion of solvent [16; 17], nanoprecipitation [18; 19] and others. Leishmaniasis is the third most important vector-borne disease worldwide, caused by protozoan _Leishmania_ parasites that are transmitted by the bite of infected sandflies. There is consensus that vaccines ought to become a major tool in the control of such group of diseases [20]. In the specific case of leishmaniasis, a recent review confirms that, to date, there is no drug therapy or human vaccine available [21]. The inherent features of pDNA make them promising vaccine candidates in a variety of diseases like leishmaniasis [22; 23; 24; 25] and pDNA-based therapeutic and immunization methods relay on genes transfer to human cells to encode the synthesis of a protein, which, when expressed, carries an immunizing or therapeutic action. In this regard, the _NH36_ gene is one of the candidates for DNA vaccines against leishmaniasis and has already been tested in several animal models [26; 27]. On the other hand, reports have shown limitations and restrictions in transport of pDNA through intramuscular, cutaneous and intracutaneous routes [28]. Therefore, an improved system for transferring pDNA to a specific site are necessary to address these limitations. [PERSON] et al.