RNA stands for ribonucleic acid and siRNA – small interfering RNA (also known as silencing RNA). siRNA is a short (21-23 bp), double-stranded RNA nucleotide in molecules performing various functions of biological system in cells. siRNA transfection is “transference”, intracellular transfer of siRNA into cells, a process involved in silencing of genes. To successfully optimize siRNA transfection, the proper transfection reagent and method of transfection is required to enable RNAi experiments in vitro and in vivo. These processes differ according to cell types and protocols. There are many in vitro siRNA transfection reagents optimized for specific cell types (see cell line transfection reagents). In vivo siRNA applications require nanoparticle-, polymer-, or liposome-based technologies that have different biodistribution delivery profiles.

Scientists have discovered that siRNA is extremely valuable in silencing gene expression and studying gene functions in a large scale. The success of such experiments often dependent on the method of delivery of siRNA. siRNA can be transfected in vitro and in vivo using optimized transfection reagents and kits. In many cases, cell types may make such transfection hard, limited, or even impossible.

Commercial in vitro and in vivo siRNA transfection services are provided by contract research laboratories such as Altogen Labs (www.altogenlabs.com).

Determining satisfactory transfection parameters can result in success or failure of RNAi effects in different cell cultures. Parameters may include culture conditions, the type and the amount of transfection agent used, the length of time transfection agents are exposed to cells, and the purity and quantity of siRNA used in experiments.

Choosing the correct procedures is also critical. For example, a pre-plated transfection procedures enable cells to attach, recover from the processes, and grow for about 24 hours prior to transfection process. In some cases, reverse transfection (also known as an alternative transfection procedure) may offer enhanced benefits compared to this more traditional pre-plating methodology.

Reverse transfection is a process of translating and plating cells simultaneously; a process that is faster and easier because it enables researchers to bypass multiple steps of traditional methodology.

Other considerations enabling siRNA transfection are the health of the cultured cells, conditions under which transfection occur, the method of transfection introduced, the quality and quantity of siRNA used in a particular experiment. Cells must be healthy to ensure maximum cell viability. Also, healthy cells are easier to transfect than poor quality or damaged cells. Various helpful methods ensure the physical condition as well as tolerable quantity of cells and offer guidelines to enhance success of various experiments.

Cell density, on top of volume, exposure time, and amount of siRNA cells also play an significant role in the success of siRNA transfection, as well as establishing stable RNAi knockdown cell line in stable transfection experiment.