We usually supply unmodified oligonucleotides in lyophilized state, since this form is less sensitive to degradation by nuclease and more stable for transportation. Oligo(dt) primer is suitable for use as a primer for first- strand cDNA synthesis with a reverse transcriptase. The primer hybridizes to the poly(A) tail of mRNA. Before opening, spin the tube for a short time to ensure that the oligos are at the bottom of the tube. We recommend dissolving the stock oligo in concentrated form in TE (10mM Tris pH 8.0,1 mM EDTA). Alternatively ,Sterile dH2O can be used.
You can also refer to cDNA synthesis kit .