OPC is a column-based purification method that provides approximately 75% purity at a lower cost and is suitable for transfection of standard cell lines such as HEK293 and HeLa. HPLC provides ≥90% purity and removes failure products more thoroughly, making it suitable for primary cells, stem cells, animal studies, and experiments intended to generate publication-quality data.

Unmodified siRNA can be used directly in standard cell lines. Modification is recommended when you need to monitor transfection efficiency (FAM or Cy3 fluorescent labeling), improve serum stability (2′-OMe), enhance silencing efficiency (5′ phosphorylation), or promote uptake by difficult-to-transfect cells (5′ cholesterol). At least one fluorescently labeled control is recommended for monitoring transfection.

Labeling the 5′ or 3′ end of the sense strand has little effect because the sense strand does not mediate cleavage and is discarded after RISC loading. Labeling the antisense strand should be avoided because it can interfere with RISC loading and cleavage activity. Use FAM for routine monitoring, Cy3 plus Cy5 for multicolor colocalization or FRET, and Cy5.5 for deep-tissue in vivo imaging.

siRNA and miRNA tools generally produce detectable mRNA changes within 24–48 hours and clear protein-level changes within 48–72 hours. The effect typically lasts 3–7 days and gradually weakens as cells divide; for a longer effect, repeat transfection or use shRNA. saRNA acts more slowly, usually within 48–96 hours, and mRNA activation lasts about 3–7 days. Some sequences can induce epigenetic changes that extend the effect for several weeks.

Two main types of off-target effects may occur: miRNA-like silencing caused by partial complementarity between the seed region, bases 2–8 of the antisense strand, and the 3′ UTR of non-target mRNAs; and immune activation through receptors such as TLR3/7 or RIG-I. Risk can be reduced by genome-wide off-target analysis to exclude highly homologous candidates, introducing 2′-OMe modifications in the antisense-strand seed region, lowering the working concentration to 10–20 nM, and confirming a consistent phenotype with multiple independent sequences.

A negative control (NC) is an unrelated sequence used to verify phenotype specificity. If the NC group also changes, a nonspecific effect may be present. A Cy3- or FAM-labeled NC can also monitor transfection efficiency. A positive control targets a housekeeping gene such as GAPDH and verifies that the transfection and detection systems are functioning. If the positive control also fails, experimental conditions should be investigated before the target sequence.

An overexpression vector introduces exogenous cDNA, usually under a strong promoter, and can produce high expression but lacks native regulation and may create non-physiological expression levels. saRNA activates the endogenous gene, preserving native splicing, alternative splicing, and post-translational modification, which more closely reflects physiological conditions and is suitable for studying the true effects of gene upregulation.

Four saRNAs are designed against the target gene promoter. Under conditions where transfection efficiency exceeds 80%, at least one is expected to increase target-gene mRNA by ≥2-fold. The package includes a negative control, a FAM-labeled negative control for monitoring transfection, and a positive-control siRNA for validating the system. If the agreed performance target is not achieved and quantitative data are provided, four new target sites can be redesigned according to the agreed terms.