What are possible causes of non-specific amplification in negative control samples when using the NadPrep Single Cell WGA Kit? How to solve them?

Exogenous DNA contamination: this kit is highly sensitive to trace DNA; ultra-low amounts of contaminating DNA can yield microgram-level amplification products. Perform all procedures in a clean, DNA-free environment (e.g., PCR-clean area or laminar-flow hood), and use nuclease-free, DNA-free consumables and reagents. Thoroughly decontaminate work surfaces, pipettes and equipment, and include and closely monitor negative controls throughout the workflow to rapidly identify and trace contamination sources.