What are the general best practices for reagents and consumables?

Answer:
Proper handling of reagents and consumables is critical for reproducibility.

1. Reagent thawing and storage

• Buffers and premixes should be thawed on ice to preserve stability. 
• Reagents requiring room temperature equilibration:
  Specific reagents such as barcoded beads and cleanup beads should be equilibrated at room temperature prior to use (consult the manual). 
• Freeze–thaw control:
  All reagents should avoid repeated freeze–thaw cycles, as this may degrade performance, particularly for sensitive components. 

2. Handling of enzyme reagents

• Includes: RT enzyme, PCR master mix, fragmentation enzyme, DNA ligase, etc. 
• Storage:
  Must be stored at −20°C 
• During use:
  Keep on ice at all times.
  Remove only for short periods.
• Mixing method:
  Do not vortex enzyme reagents.
  Mix gently by pipetting. 
• Post-use handling:
  Immediately return to −20°C storage after use 

Enzyme activity is highly sensitive to temperature fluctuations and mechanical stress. Improper handling may directly reduce cDNA synthesis or amplification efficiency. 

3. Pipetting practices

Small-volume pipetting:

• Insert the tip into the middle of the liquid column (not near the surface or bottom) 
• Perform pre-wetting 1–3 times before aspiration to improve accuracy 
• Aspirate slowly to avoid introducing bubbles 

Handling viscous reagents (e.g., beads):

• Pre-wetting is not required 
• After aspirating to the target volume, hold the tip in the liquid for ~5 seconds before withdrawing. This ensures accurate volume uptake and reduces under-aspiration 

4. Preparation of multi-sample premixes

• When preparing master mixes for multiple samples, add ~10% extra volume. This compensates for pipetting loss and ensures all samples receive sufficient reagent. 

5. Consumables and general requirements

• Use low-retention, DNase/RNase-free tubes and pipette tips throughout the workflow. This minimizes adsorption of nucleic acids and prevents degradation. 

6. Ethanol preparation (critical for bead cleanup)

• Prepare 80% ethanol fresh on the day of use. 
• Do not reuse or store diluted ethanol. 

Ethanol concentration may change due to evaporation, which can affect washing efficiency and DNA recovery. 

7. Barcoded bead handling

• Equilibrate beads to room temperature for ~30 minutes before use.
• Return immediately to the −80 °C freezer after use. 
• Avoid more than 3 freeze–thaw cycles 
• If thawed but unused for more than 2 hours, return beads to −80°C storage. Do not exceed 2 hours at room temperature.
• Do not store at −20°C 

Improper storage or repeated freeze–thaw cycles may affect bead performance and barcode integrity.