Peptide adsorption and low-binding tubes
Why dilute peptide solutions lose material to tube walls, which compounds are worst affected, and the precautions that prevent it.
A dilute peptide solution left in an ordinary polypropylene tube for an hour can lose a surprising fraction of its peptide to the tube wall, and the loss is invisible: the solution looks the same, the label says the same concentration, and the assay quietly reads low. This note explains peptide adsorption, which compounds and conditions are most affected, and the inexpensive precautions (low-binding plastic, carrier protein, concentration management) that prevent it. All Alphex products are for laboratory and in-vitro research only.
Why peptides stick to plastic
Polypropylene and polystyrene surfaces are hydrophobic. Peptides with hydrophobic residues or a lipid modification orient those groups toward the surface and adhere; charged peptides can also bind through electrostatic interactions with charged surface groups on treated plastics. Adsorption is fast, often complete within minutes, and it is a fixed number of molecules per unit surface area. That last point is why concentration matters so much: at 1 mg/mL the surface takes an unmeasurable fraction of the total; at 1 µg/mL in the same tube it can take most of it.
Which peptides are most affected
- Lipidated peptides, such as GLP-3 (RT), are the worst case: the fatty diacid is designed to bind albumin and it binds plastic just as willingly.
- Peptides with aromatic residues, such as Ipamorelin (naphthylalanine, phenylalanine), adsorb noticeably at low concentration.
- Short, charged peptides such as BPC-157, TB-500 and GHK-Cu are less prone, but not immune at very low concentrations or in long incubations.
Precautions, in order of effectiveness
- Keep stocks concentrated. Reconstitute at 1-5 mg/mL and dilute to working concentration as late as possible, immediately before use.
- Use low-binding tubes and tips for anything below about 100 µg/mL. Low-protein-binding polypropylene has a hydrophilic surface treatment; the cost difference is small.
- Add a carrier where the assay allows: 0.1% BSA or 0.01-0.05% Tween-20 in the diluent occupies the surface so the peptide does not. Include the carrier in vehicle controls.
- Silanised or low-binding glass for very dilute solutions; plain glass is not the answer, since it has its own binding sites.
- Minimise transfers. Every new tube and tip is a new surface. Make dilutions in the tube you will use.
- Minimise time. Adsorption is fast, but so are you; prepare dilutions and use them.
How to tell it is happening
Standard curves that flatten at the low end, dose-response curves that shift right between days, or a discrepancy between what a fresh dilution and a stored dilution do in the same assay. A direct check: measure a dilute peptide solution's concentration (UV, HPLC, or a peptide assay) immediately after preparation and again after an hour in the tube; a drop with no chemical change is adsorption. See also recognising peptide degradation, since the symptoms overlap.
Frequently asked questions
Does adsorption affect the sealed vial?
Not meaningfully. Lyophilised peptide is not in solution, and Alphex vials are glass. Adsorption is a solution-phase problem, mostly downstream in your own tubes.
Are "low-binding" claims standardised?
No. Buy from a laboratory supplier that specifies low protein binding and, for critical work, validate with a recovery experiment.
Can I recover adsorbed peptide?
Partly, by rinsing with organic solvent or detergent, but you cannot know how much you recovered. Prevention is the only reliable approach.
Alphex research peptides are supplied for laboratory and in-vitro research by qualified researchers only. They are not authorised for human or veterinary use.
Research use only. Alphex products are supplied exclusively for laboratory and in-vitro research by qualified researchers. They are not authorised for human or veterinary use, and nothing in this note is advice on any such use.
Published 10 March 2026. Alphex reviews research notes when the testing method, the catalogue or UK guidance changes.