Casein Based Blocking Buffers
Select See the table below
- See the table below
Casein Based Blocking Buffers
Two 1 % casein formulations, PBS-based and TBS-based, each in two fill sizes. This is a category page, not a product page — open the formulation you need with View.
| Name | Cat. No. | Size | Product Page |
|---|---|---|---|
| Casein (1%) with PBS Blocking BufferPhosphate-buffered saline base | DCP-CPBS1X_500 ml | 500 ml | Viewarrow_forward |
| Casein (1%) with PBS Blocking BufferPhosphate-buffered saline base | DCP-CPBS1X_1000 ml | 1000 ml | Viewarrow_forward |
| Casein (1%) with TBS Blocking BufferTris-buffered saline base | DCP-CTBS1X_500 ml | 500 ml | Viewarrow_forward |
| Casein (1%) with TBS Blocking BufferTris-buffered saline base | DCP-CTBS1X_1000 ml | 1000 ml | Viewarrow_forward |
PBS or TBS? Compare the two bases · See applications by assay · Read the FAQ
What casein blocks, and what changes between the two
Casein Blocking Buffers are specialized reagents used in immunoassays such as Western blotting, ELISA, and immunohistochemistry. These buffers are designed to block non-specific binding sites on membranes and microplates, thus enhancing the specificity and sensitivity of these assays. They contain 1% casein, a protein derived from milk, known for its effective blocking properties. Casein is often purified and sometimes chemically modified to enhance its efficiency. Casein provides excellent blocking efficiency due to its ability to form a dense layer that minimizes gaps and non-specific interactions.
- Two formulations, identical in casein content and differing only in the saline base: PBS or TBS.
- 1 % casein in both — purified, and in some preparations chemically modified to enhance efficiency.
- Three named immunoassay formats: Western blotting, ELISA, and immunohistochemistry.
- Two surfaces: the buffers block non-specific binding sites on membranes and on microplates.
- Dense-layer blocking is the stated mechanism — minimizing gaps and non-specific interactions.
- Two fill sizes per formulation: 500 ml and 1000 ml, four catalog numbers in total.
- pH 7.4, stored at −20 °C.
- Sterility: filtered 0.1 µm twice and 0.04 µm twice in a sterile environment. Customization available on inquiry.
- Formulations in this family2
- Catalog numbers4 (2 formulations × 2 sizes)
- Casein concentration1 %
- Saline bases offeredPBS, TBS
- Fill sizes500 ml, 1000 ml
- pH7.4
- Storage−20 °C
- Sterility0.1 µm ×2, 0.04 µm ×2
- Named applicationsWestern blot, ELISA, IHC
- Intended useResearch Use Only (RUO)
Same blocker, two chemistries — and the detection system decides
Both formulations carry the same 1 % casein and block the same way. The choice between them is a chemistry question about what comes after the block: which enzyme conjugate, and which kind of epitope.
Blocking is a signal-to-noise step
The buffers occupy non-specific binding sites on membranes and microplates, which is what raises the specificity and sensitivity of Western blotting, ELISA, and immunohistochemistry rather than merely tidying the background.
Casein forms a dense layer
The stated reason for casein's blocking efficiency is coverage: it forms a dense layer that minimizes gaps and non-specific interactions, rather than a patchy one that leaves sites exposed.
Purified, not just skimmed
Casein here is a purified milk protein, and in some preparations chemically modified to enhance its efficiency — which is what separates a casein blocker from non-fat dry milk made up at the bench.[5]
PBS interferes with alkaline phosphatase
If the detection conjugate is alkaline phosphatase, choose the TBS-based blocker: phosphate inhibits AP activity, so a PBS-based blocking buffer costs signal.[1,2]
Casein is itself a phosphoprotein
Casein blocking buffer is not recommended for systems detecting phosphoproteins, because the blocker carries phosphorylated residues that anti-phospho antibodies can bind.[3,4]
And it carries biotin
For biotin–avidin detection the blocking reagent must be biotin-free; casein blocking buffer is not recommended there, since milk contains large and variable amounts of biotin.[3]
The two questions that pick the bottle
First: is the conjugate alkaline phosphatase? If yes, take the TBS base. Second: is the target a phospho-epitope, or is the read-out biotin–avidin? If either is yes, a casein blocker is the wrong blocker regardless of base — and that is worth knowing before the run, not after.[1,3]
Four membrane passes, two of them sub-0.1 µm
The source specifies one sterility process for both formulations: filtered 0.1 µm twice and 0.04 µm twice, in a sterile environment — two coarse passes followed by two sub-0.1 µm polishing passes.
-
1
0.1 µm Pre-filtration I
First 0.1 µm membrane pass. Removes bulk particulates and the microbial load carried in from raw materials and make-up water before any polishing step sees the solution.
-
2
0.04 µm Pre-filtration II
First sub-0.1 µm pass. Takes out the fine fraction a 0.1 µm or 0.2 µm membrane lets through — the protein aggregate and particulate range that lands on a membrane as speckle.
-
3
0.1 µm Sterile-filtration I
Second 0.1 µm pass, performed in a sterile environment. This is the sterilizing step of the sequence rather than a clarifying one.
-
4
0.04 µm Sterile-filtration II — Final Polish
Second sub-0.1 µm pass, immediately before fill. The final polish is what distinguishes this architecture from a conventional single-membrane sterile filtration.
Why a blocker in particular benefits from the polish
A blocking buffer is applied to the whole membrane or the whole plate, so anything suspended in it is deposited across the entire detection surface rather than in one lane. Particulate in a blocker shows up as background everywhere, which is exactly the noise the blocking step exists to remove.
PBS base or TBS base — how to choose
The catalog difference is one column wide: which saline the 1 % casein is dissolved in. The consequences sit downstream, in the detection chemistry.
| Property | Casein (1%) with PBS | Casein (1%) with TBS |
|---|---|---|
| Catalog numbers | DCP-CPBS1X_500 ml, DCP-CPBS1X_1000 ml | DCP-CTBS1X_500 ml, DCP-CTBS1X_1000 ml |
| Saline base | Phosphate-buffered saline | Tris-buffered saline |
| Casein concentration | 1 % | 1 % |
| With HRP-conjugated detection | check_circle Both bases are used interchangeably for most applications[1] | check_circle Both bases are used interchangeably for most applications[1] |
| With alkaline phosphatase (AP) conjugates | cancel Not recommended — phosphate interferes with AP activity[1,2] | check_circle Recommended base for AP-labelled antibodies[1,2] |
| With phospho-specific antibodies | cancel Phosphate in PBS can interact with anti-phospho antibodies; Tris-based buffers are advised[4] | Tris base removes the phosphate issue, but casein itself remains a phosphoprotein — see the note below[3,4] |
| Fill sizes | 500 ml, 1000 ml | 500 ml, 1000 ml |
| pH · storage | 7.4 · −20 °C | 7.4 · −20 °C |
The three immunoassay formats named by the source
Western blotting, ELISA, and immunohistochemistry are the three applications the source names. Notes below that go beyond the source are footnoted to their external authority.
- Blocking non-specific binding sites on membranes, to enhance the specificity and sensitivity of the blot.
- 1 % casein is an established Western blot blocking concentration.[6]
- Casein performs well in high-sensitivity work, reducing non-specific binding for difficult targets on either membrane type.[5]
- Choose the TBS-based formulation when the secondary antibody is alkaline phosphatase conjugated.[1,2]
- Not for phospho-target blots, and not for biotin–avidin detection.[3]
- Blocking non-specific binding sites on microplates, to enhance the specificity and sensitivity of the assay.
- Casein-based blockers are used both to block the plate and to dilute detection antibodies in immunoassay workflows.[5]
- Inadequate blocker leaves excess background; excessive blocker can mask the antibody–antigen interaction or inhibit the marker enzyme — the concentration is worth titrating.[1]
- Choose the TBS-based formulation for AP-based colorimetric read-outs such as pNPP.[1,2]
- Blocking non-specific antibody binding in immunohistochemistry, one of the three formats the source names.
- For AP-based chromogens, phosphate-buffered saline is avoided during staining because phosphate ions inhibit alkaline phosphatase; Tris-buffered saline is recommended for washing and reagent dilution.[2]
- Blocking buffers of this class are supplied ready to use for reducing non-specific antibody binding across IHC, ELISA, and Western blotting.[5]
- Not for biotin–avidin detection systems.[3]
Identical across both formulations
Only the saline base changes between the two catalog lines. Everything below is common to all four catalog numbers.
| Attribute | Specification, as stated by the source |
|---|---|
| Blocking agent | Casein, a protein derived from milk, at 1 % |
| Preparation | Purified, and sometimes chemically modified to enhance its efficiency |
| Mechanism | Forms a dense layer that minimizes gaps and non-specific interactions |
| Surfaces blocked | Membranes and microplates |
| Named applications | Western blotting, ELISA, immunohistochemistry |
| Fill sizes | 500 ml and 1000 ml |
| pH | 7.4 |
| Storage | −20 °C |
| Sterility | Filtered 0.1 µm twice and 0.04 µm twice, in a sterile environment |
| Customization | Other concentrations; additions of chemicals, compounds, proteins, or supplements; different pH; further modifications — on inquiry |
| Intended use | Research Use Only (RUO) |
Questions this catalog gets asked
Primary literature and cited sources
The source description carries no citation or reference list. The entries below are supporting literature for the two assay formats the source names, followed by the external technical sources footnoted on this page. No DOI is shown where one could not be confirmed — none has been invented.
Supporting Literature
- Towbin H, Staehelin T, Gordon J. Electrophoretic transfer of proteins from polyacrylamide gels to nitrocellulose sheets: procedure and some applications. Proceedings of the National Academy of Sciences USA. 1979;76(9):4350–4354. — the founding Western blot method, the format in which membrane blocking became necessary.
- Engvall E, Perlmann P. Enzyme-linked immunosorbent assay (ELISA). Quantitative assay of immunoglobulin G. Immunochemistry. 1971;8(9):871–874. — the founding ELISA method, the format in which microplate blocking became necessary.
Footnoted Technical Sources
- Thermo Fisher Scientific. Blocking Buffers for Western Blot and ELISA — blocker concentration effects, and the recommendation to select a TBS-based blocking buffer with alkaline phosphatase conjugates because PBS interferes with AP activity. thermofisher.com
- Bio-Rad. Western Blotting: Immunodetection — Blocking and Antibody Incubation; TBS/TBST is preferred with AP-labelled antibodies because PBS interferes with the AP signal. bio-rad-antibodies.com
- Sigma-Aldrich. Casein Blocking Buffer protocol — not recommended for biotin–avidin detection systems, since milk contains large and variable amounts of biotin, and not recommended for systems detecting phosphoproteins. sigmaaldrich.com
- Proteintech. Tips for detecting phosphoproteins by Western blot — casein as a phosphoprotein source of background, and the recommendation to use Tris-based rather than phosphate-based buffers. ptglab.com
- Abcam. Western blot blocking methods and best practices — casein in high-sensitivity applications on either membrane type, and ready-to-use protein blocks for IHC, ELISA, and Western blotting. abcam.com
- Merck / Sigma-Aldrich. Western Blotting Protocols — casein at 1 % listed among the standard blocking solutions. merckmillipore.com
