Alkaline phosphatase (AP) conjugated anti-human primary antibodies are enzyme-labeled immunoreagents for colorimetric, chemiluminescent, and fluorescent detection of human antigens in applications requiring prolonged signal stability and azide compatibility. Produced by immunizing hosts such as goat, rabbit, or mouse with purified human immunoglobulins or specific human proteins, the antibodies are affinity-purified and conjugated to alkaline phosphatase, a 140 kDa homodimeric metalloenzyme derived from calf intestine or bovine tissues. AP contains zinc and magnesium ions essential for catalytic activity, functioning optimally at pH 9.0–10.5. Unlike horseradish peroxidase (HRP), AP is not inhibited by sodium azide, allowing use with azide-containing buffers and storage reagents. The enzyme catalyzes the hydrolysis of phosphate esters, enabling detection with multiple substrate options: BCIP/NBT (5-bromo-4-chloro-3-indolyl phosphate/nitro blue tetrazolium) produces a blue-black precipitate for immunohistochemistry; pNPP (p-nitrophenyl phosphate) yields yellow soluble product quantified at 405 nm in ELISA; and CDP-Star® (chemiluminescent substrate) generates sustained light emission for Western blotting. AP conjugates offer superior stability with continuous signal generation and no substrate depletion effects, making them suitable for prolonged incubations. Available specificities include anti-human IgG (H+L), anti-human IgG (Fc), isotype-specific (IgG1–IgG4, IgA, IgM, IgE), and anti-human CD markers. Extensive cross-adsorption eliminates nonspecific binding.

Applications

AP conjugates are employed across multiple immunoassay formats. In ELISA, pNPP provides sensitive colorimetric quantification of human cytokines, antibodies, and disease biomarkers with linear detection ranges exceeding chromogenic HRP systems. In Western blotting, chemiluminescent substrates such as CDP-Star® enable detection of low-abundance human proteins (picogram sensitivity) with extended signal duration (hours to days), supporting repeated imaging. In immunohistochemistry and in situ hybridization, BCIP/NBT yields permanent chromogenic signals for human antigen localization in tissue sections, suitable for long-term slide archival. Additional applications include tissue microarrays, dot blots, and membrane-based assays. Typical working dilutions range from 1:500 to 1:10,000. These reagents are intended for research use only; not for diagnostic procedures.