Specification decides price, not the product name
Two vials carrying the same analyte name can differ in price by a factor of ten. The difference is never the name — it is the specification behind it. This page sets out what each variable actually buys you, so you can specify deliberately instead of buying the cheapest vial that carries the right word on the label.
1. Purity grade
| Grade | Where it is used | What you are paying for |
|---|---|---|
| ≥80% | Screening, method scouting, non-quantitative work | Lowest cost; impurities may interfere with sensitive detection |
| ≥90% | General immunoassay development | Reduced background from host-cell proteins and aggregates |
| ≥95% | Calibrators, controls, antibody pairing | The usual working grade for quantitative assay development |
| ≥98% | Reference material, structural and binding studies | Highest characterisation cost; tightest lot-to-lot control |
A note on methods: SDS-PAGE (reducing) reports subunit purity by molecular size, while SEC-HPLC reports how much of the protein is monomeric in solution. A preparation can read 97% by SDS-PAGE and 91% by SEC-HPLC — they measure different things. Always ask which method a quoted purity figure came from.
2. Endotoxin level
| Endotoxin level | Suitable for | Why the price differs |
|---|---|---|
| < 1.0 EU/µg | Standard immunoassay and biochemical work | Routine quality-control level |
| < 0.1 EU/µg | Cell-based assays, primary cells, stimulation and signalling studies | Requires stricter process control and additional testing per lot |
3. Tag format
| Format | Strengths | Trade-offs |
|---|---|---|
| Carrier-free / untagged | Closest to the native analyte; no tag interference in calibrators or binding studies | Harder to express and purify, therefore the most expensive format |
| His-tag | Simple purification; convenient for detection and immobilisation | Tag can affect folding or block an epitope; not ideal where the natural analyte is expected |
| hFc-tag | Dimerisation improves avidity; easy detection with anti-human-Fc reagents | Large tag alters molecular weight and can complicate calibrator preparation |
4. Expression system
| Expression system | Glycosylation | Typical fit |
|---|---|---|
| E. coli | None | Small, non-glycosylated proteins and peptides — fastest and least expensive |
| HEK293 (mammalian) | Human-like | Glycosylated receptors and biomarkers where correct folding drives activity |
| CHO (mammalian) | Human-like | Scale-up and formats intended for longer development programmes |
| Baculovirus / insect | Partial | Selected targets where insect glycosylation is acceptable |
5. Source: recombinant versus plasma-derived
| Source | Example | Cost profile |
|---|---|---|
| Recombinant protein | sST2, cTnI, NT-proBNP, CRP, IL-6 | Per-milligram cost is high because expression and purification are costly, but lot control is strong |
| Purified from human serum | D-dimer antigen | Material is comparatively inexpensive because it is isolated rather than manufactured — expect an order-of-magnitude lower price and different handling |
How we quote
Because these variables move the cost by a wide margin, we quote per order rather than publishing a single list price. Tell us the downstream application — antibody pairing, calibrator, cell stimulation, structural work — and we will recommend the grade that fits. If your protocol already specifies a purity and endotoxin level, send that and we will quote against it.
For research use and in-vitro diagnostic development only. Not for human or animal therapeutic use.
6. The same analyte at three specifications
The clearest way to see what specification decisions cost is to follow one analyte through three intended uses. This example is illustrative — it shows the reasoning, not a price list.
| Intended use | Reasonable specification | What you are buying |
|---|---|---|
| Screening and method scouting | Standard purity grade, ordinary endotoxin level, tagged format acceptable | Enough material to prove an assay concept; impurities may raise background but the reagent cost per experiment stays low |
| Calibrator or control | High purity, carrier-free, stated endotoxin figure, lot reserved if possible | A curve that reflects the analyte rather than a carrier protein, and a lot you can keep for the life of the assay |
| Cell-based or signalling work | High purity with a stated low endotoxin limit; carrier-free where the readout is sensitive | The endotoxin figure is the specification that matters — live cells read contamination that a plate reader does not |
The pattern to notice: the specification follows the readout, not the analyte name. Ask for the grade your readout can actually detect a problem with, and no more.
Where specification decisions usually go wrong
Buying on the purity number without asking for the method
A 95% figure means different things by SDS-PAGE and by SEC-HPLC. One reports subunit purity by size, the other how much protein is monomeric in solution. If a supplier quotes a number without a method, the number is not yet comparable to anything you measured.
Paying for low endotoxin where no cells are involved
Endotoxin control costs money and time. In a plate-based immunoassay with no live cells, a standard level is usually the right purchase — the money is better spent on carrier-free material or a reserved lot.
Ignoring the carrier, then wondering why the curve is flat
Carrier proteins such as BSA or gelatin are added to protect dilute protein, and they can interfere with a calibrator or compete with your antibody. If the material is destined for a calibrator, say carrier-free at the specification stage rather than discovering it at the curve.
Not sure which grade you need?
Describe your downstream application and we will recommend the specification rather than the nearest bottle on the shelf.