A reconstituted peptide stored as a single large vial will lose 50–70% of its activity after three freeze-thaw cycles. The same peptide, divided into single-use aliquots before any freezing, can retain 80–90% of activity across weeks or months. This article walks through the exact steps to aliquot reconstituted peptides correctly.
When a peptide solution is frozen and thawed, ice crystals form, peptides concentrate at the ice-liquid interface, and aggregation occurs (see our article on freeze-thaw cycles). The damage is proportional to the number of times the same molecule is cycled through freezing and thawing. If you aliquot into single-use portions before any freezing, each aliquot is thawed only once, experiencing only one freeze-thaw event. A single cycle is much less damaging than repeated cycles, so overall activity is preserved.
Select low-binding polypropylene (PP) or polycarbonate (PC) microfuge tubes for aliquoting. Avoid polystyrene (PS) — peptides adsorb to polystyrene surfaces, reducing the amount in solution. Glass vials are acceptable but are heavier and risk breakage. For micro volumes (50–500 μL), use PCR tubes or 0.5 mL polypropylene strip tubes — they have minimal headspace and fit compactly in a −20°C or −80°C freezer block.
Determine the smallest volume you routinely withdraw from frozen storage. If you typically use 50 μL per experiment, aliquot into 50–100 μL portions (add a small buffer for pipetting loss). If you use 10 μL per experiment, aliquot into 20–50 μL portions. The goal is single-use — once an aliquot is thawed, discard any remainder. Never refreeze thawed peptide.
Example: If you reconstitute 1 mL of peptide and use 50 μL per assay, divide the 1 mL into 20 × 50 μL aliquots (in 0.5 mL tubes). Each tube is thawed once and discarded after use.
Headspace (air gap above the liquid) contains oxygen, which drives oxidation of methionine, tryptophan, and other sensitive residues. When aliquoting into a 0.5 mL tube with a 50 μL peptide solution, the headspace is ~450 μL — a lot of air. To reduce it:
Perform aliquoting in a laminar-flow hood or biosafety cabinet if available. If not, work in a clean area (bench top cleaned with 70% ethanol) with aseptic precautions:
Each tube must be labeled with:
Use a permanent marker or pre-printed labels. Include unit numbers if you have multiple aliquots (Aliquot #1, #2, etc.).
Transfer all aliquots to −20°C or −80°C immediately after preparation. Do not leave them at room temperature or refrigerator temperature — every hour at elevated temperature increases oxidation and degradation. Freezing halts most chemical reactions and extends shelf life.
−20°C (standard freezer): Preserves peptide activity for 3–6 months. Acceptable for short-term to medium-term storage.
−80°C (ultra-low freezer): Preserves peptide activity for 1–2 years. Recommended for long-term storage beyond 6 months.