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.
Chemical (s)gRNA Synthesis is an alternative approach e.g. if site-specific chemical modifications such as 2'Fluoro, 2'O-Methyl or phosphorothioate are required .
 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.