T7 RNA Polymerase-mediated in vitro transcription is an easy, fast and currently the most cost-efficient way of guide RNAs synthesis.
HighYield T7 sgRNA Synthesis Kit (SpCas9) allows the cloning-free preparation of SpCas9-specific single-guide RNA (sgRNA).[1,2] Other (s)gRNA-encoding T7 DNA templates (e.g with a different SpCas9 scaffold or for different Cas endonucleases) can efficiently be in vitro transcribed with the HighYield T7 RNA Synthesis Kit.
 Jinek et al. (2012) A programmable dual-RNA guided DNA Endonuclease in adaptive bacterial immunity. Science 337:816.
 Modzelewski et al. (2018) Efficient mouse genome engineering by CRISPR-EZ technology. Nature Protocols 13 (6) :1253.
 Hendel et al. (2015) Chemically modified guide RNAs enhance CRISPR-Cas genome editing in human primary cells. Nature Biotechnology 33 (9):985.