design: 1. Small RNA enrichment and purification. 2. 3' end adaptor ligation: Ligate the 5-adenylated and 3-blocked adaptor to the 3' end of the small RNA fragment. 3. Add Unique molecular identifiers (UMI) labeled Primer. 4. 5' end adaptor ligation. 5. First strand synthesis with Unique molecular identifiers (UMI) labeled Primer. 6. Second strand synthesis. 7. Fragment selection. 8. Library quality control. 9. Circularization: The double stranded PCR products were heat denatured and circularized by the splint oligo sequence. The single strand circle DNA (ssCir DNA) were formatted as the final library. 10. Sequencing on DNBSEQ.