Application and Operational Considerations of Transfection Reagents in Cell Experiments

Cell state is the foundation of transfection.

The impact of cell state on transfection results is often underestimated. It is generally recommended to use cells in the logarithmic growth phase, with normal morphology and free of mycoplasma contamination for transfection. Cell density that is too high or too low may lead to reduced transfection efficiency. A common practice is to seed cells at an appropriate density before transfection so that the cell confluence on the day of transfection remains within a certain range; for adherent cells, a commonly recommended range is approximately 50%–80%, but the specific value should be adjusted according to different cell lines and reagent instructions. When the cell passage number is too high, cells have been passaged too many times, or cell condition is poor after recovery, transfection reproducibility may become worse.

Preparation of reagent and nucleic acid complexes

The preparation of transfection complexes is a key step affecting experimental results. Usually, the transfection reagent and nucleic acid need to be diluted separately in serum-free medium or a dedicated diluent, and then the two are mixed and allowed to stand for a certain period of time so that the complexes form fully. The preparation time, temperature, and mixing order of the complexes may all affect particle size and surface charge, thereby changing transfection efficiency. It is generally recommended to follow the ratios and standing times specified in the reagent instructions, and not to arbitrarily extend or shorten them. For difficult-to-transfect cells, the effect can be improved by optimizing the mass ratio or volume ratio of reagent to nucleic acid.

Effects of serum and antibiotics

Many transfection reagents require a serum-free or low-serum environment during the complex formation stage, because proteins in serum may interfere with complex formation. However, when the complexes are added to the cell culture system after formation, some transfection reagents allow transfection to be performed in serum-containing medium; the specific conditions should be based on the product instructions. The use of antibiotics also requires attention. Some aminoglycoside antibiotics may affect cell survival in physical transfection methods such as electroporation, while in chemical transfection the effect is generally small, but it is still recommended to wash the cells with antibiotic-free medium before transfection and then replace with normal culture medium as needed after transfection.

Observation and optimization strategies after transfection

After transfection, observation or detection is usually required at a certain time point. For transient transfection, protein expression or RNA levels are generally detected 24–72 hours after transfection, and the specific time depends on promoter activity, nucleic acid half-life, and cell growth rate. If transfection efficiency is low, troubleshooting can be carried out step by step from aspects such as cell state, plasmid quality, reagent-to-nucleic acid ratio, complex incubation time, and cell density at the time of transfection. It is recommended to design positive and negative controls to distinguish operational problems from the intrinsic characteristics of the cells. For primary cells or suspension cells that are difficult to transfect, consideration may be given to changing the transfection method or using a dedicated protocol.

In addition, transfection procedures should be kept sterile, and repeated freeze-thaw cycles of reagents should be avoided. After opening, transfection reagents are generally stored at low temperature as required and used within the expiration date. Experimental records should include as much detail as possible on batches, operating conditions, and results to provide a basis for subsequent optimization.