**2.1. Plasmid DNA**

It is currently the most commonly investigated nucleic acid in gene delivery applications. When the pDNA is entering into the nucleus, the pDNA strand is transcribed, and the coding gene is translated to protein, which is then expressed from the cell.

## **2.2. RNA interference**

It is triggered by double-stranded RNA (dsRNA), activates the anti-viral interferon leads to shutdown of protein synthesis by degradation of messenger RNA (mRNA). Another mechanism involves the use of microRNAs (miRNA), which are small non-coding nucleic acids responsible for post-translational regulation of protein expression.

## **2.3. Small interfering RNA**

Small interfering RNA comprises around 21–23 nucleotides, which can be designed to be better targeted than long dsRNA and can eliminate the activation of the response of the interferon while still inhibiting target gene expression. The gene expression can be able to control/block transected siRNA into mammalian cells; this specific gene block can be used to treat certain infectious diseases and cancers [11–14].

To obtain an efficient vector system and to achieve a high rate of cell transfection, the following two limitations must be integrated in the development of an ideal genetic vector. In the gene transfer methods whether viral, physical, or chemical, these two major limitations must be overcome.

