Why is my cDNA yield low?

Answer:
Low cDNA yield is a common warning signal in single-cell sequencing experiments. It is typically not caused by a single factor, but rather reflects the combined effects of multiple upstream issues. Low cDNA yield will directly impact library construction efficiency and final data quality.

Key troubleshooting directions:

• Sample and cell quality (most fundamental factor):
  Low viability or poor cellular condition (e.g., stress, apoptosis) can lead to mRNA degradation, resulting in insufficient cDNA synthesis.
  Certain cell types (e.g., neutrophils) naturally contain low RNA content and typically yield lower cDNA concentrations. 
• Insufficient cell input:
  Inaccurate cell counting may lead to fewer cells being loaded than expected, reducing total cDNA output. 
• Clogging leading to insufficient emulsion volume:
  If droplet generation is compromised (e.g., emulsion volume <100 μL), fewer cells are successfully encapsulated, reducing total cDNA yield. 

• Loss during demulsification: 
  • Incomplete demulsification may result in cDNA remaining trapped in the oil phase or interphase 
  • Accidental removal of aqueous phase during oil removal can directly reduce cDNA recovery 

• Reagent-related issues:
  Improper storage (e.g., repeated freeze-thaw cycles) may reduce enzyme activity, particularly reverse transcriptase and PCR enzymes. 
• Insufficient PCR amplification cycles:
  For low-input samples, insufficient amplification cycles may prevent cDNA from reaching detectable concentrations. 
• Loss during purification:
  Improper magnetic bead handling (e.g., insufficient equilibration, incorrect phase removal) may lead to physical loss of cDNA. 

Pipetting inaccuracies and bubble introduction:
These may reduce effective reaction volume or interfere with reactions.