Biotin Labeling Efficiency Detection Kit (HABA Method)

Detection Principle

    Due to the high affinity of biotin for avidin, biotin can displace the interaction between 4'-hydroxyazobenzene-2-carboxylic acid (HABA) and avidin, resulting in a proportional decrease in absorbance at 500 nm. The change in absorbance is correlated with the biotin concentration.

    When a biotin-labeled protein solution is added to the HABA-avidin mixture, the change in absorbance before and after the addition of the biotin sample can be measured. According to the Lambert-Beer law, the biotin content in the solution can be calculated.

Applications
Used in conjunction with the Rapid Biotin Conjugation Kit to evaluate biotin labeling efficiency.

Advantages
(1) Reliable—A mature and validated detection method
(2) Convenient—The kit provides all necessary reagents, including microplates
(3) Flexible—Freedom to choose between spectrophotometry or microplate detection methods

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5T (Spectrophotometry)
24T (Microplate Reader Method)

Here is the translated content in English, maintaining the original formatting:---**Unprovided Essentials:** - Spectrophotometer or microplate reader with 500nm detection capability. - Pipettes (20-1000µL). **Reagent Preparation** 1. **Sample**: Before analysis, biotin-labeled protein samples must be desalted or dialyzed to remove all unreacted and hydrolyzed biotin conjugates. 2. **HABA-Avidin Solution Preparation**: 1) Add 480µL of Reagent C (phosphate buffer, PBS) to the tube of Reagent B (avidin) to prepare a 5.2mg/mL avidin solution. 2) Calculate the required volume of HABA-Avidin mixed solution based on the measurement method (spectrophotometry/microplate assay): spectrophotometry requires 900µL per test; microplate assay requires 180µL per well. Prepare accordingly. 3) Prepare the HABA-Avidin mixed solution: Mix 138µL of Reagent A (HABA solution) with 460µL of the freshly prepared avidin solution and add to 4002µL of Reagent C (PBS). Mix thoroughly. (Alternatively, prepare proportionally as needed.) 4) The absorbance (A500) of this solution in a 1cm cuvette should be 0.9–1.3 at 500nm. 5) The mixed solution is stable for two weeks at 4°C. If precipitation occurs in the HABA solution, filter or centrifuge before use. **Choose either the spectrophotometric method or the microplate assay to measure absorbance at 500nm.** ### **I. Spectrophotometric Method** 1. Add 900µL of HABA-Avidin solution to a 1cm cuvette and measure the absorbance at 500nm (A1₅₀₀). 2. Add 100µL of biotin-labeled protein sample to the cuvette containing HABA-Avidin and mix well. 3. Measure the absorbance at 500nm. If the value is ≥0.3 and remains stable for at least 15 seconds, record it as A2₅₀₀. If the value is <0.3, dilute the biotin-labeled protein sample and repeat the measurement, accounting for the dilution factor in subsequent calculations. ### **Coupling Efficiency Calculation** According to the Beer-Lambert Law: A_λ = ε_λbC, where: - **A**: Absorbance at wavelength λ (500nm for HABA). - **ε**: Molar absorptivity at λ (34000 M^-1cm^-1 for HABA-avidin at pH 7.0). - **b**: Path length (cm). For a 1cm cuvette, b = 1cm. - **C**: Molar concentration (mol/L = mmol/mL). **Steps:** 1. Calculate protein molar concentration: Protein (mmol/mL) = Protein concentration (mg/mL) / Protein molecular weight (mg/mmol). 2. Calculate ΔA₅₀₀: ΔA₅₀₀ = 0.9 × A1₅₀₀ – A2₅₀₀ *(Note: 0.9 is a correction factor for dilution by the biotin-labeled protein sample.)* 3. Calculate biotin molar concentration: Biotin (mmol/mL) = ΔA₅₀₀ / 34000 *(for 1cm cuvette)*. 4. Calculate biotin-to-protein ratio: Biotin:Protein (molar ratio) = [Biotin (mmol/mL) × 10] / [Protein (mmol/mL) × dilution factor]. **Example Calculation** For a biotin-labeled antibody (MW = 150,000, concentration = 3.0mg/mL), A1₅₀₀ = 1.0, A2₅₀₀ = 0.56: - Protein molar concentration: 3 / 150,000 = 2×10^-5 mmol/mL. - ΔA₅₀₀: 0.9 × 1.0 – 0.56 = 0.34. - Biotin molar concentration: 0.34 / 34000 = 1×10^-5 mmol/mL. - Biotin:Protein ratio = (1×10^-5 × 10) / (2×10^-5) = 5:1. ### **II. Microplate Assay** 1. Add 180µL of HABA-Avidin solution to a microplate well and measure absorbance at 500nm (A1₅₀₀). 2. Add 20µL of biotin-labeled protein sample to the well and mix well. 3. Measure absorbance at 500nm. Record the stable value as A2₅₀₀ (after ≥15 seconds). ### **Coupling Efficiency Calculation** Beer-Lambert Law applies similarly, with: - **b**: Path length = 0.59cm (for 200µL in the provided 96-well microplate). **Steps:** 1. Protein molar concentration: Same as above. 2. ΔA₅₀₀ = A1₅₀₀ – A2₅₀₀ *(no correction factor needed for microplate)*. 3. Biotin molar concentration: Biotin (mmol/mL) = ΔA₅₀₀ / (34000 × 0.59). 4. Biotin-to-protein ratio: Same formula as above. **Example Calculation** For the same antibody (A1₅₀₀ = 0.9, A2₅₀₀ = 0.56): - ΔA₅₀₀: 0.9 – 0.56 = 0.34. - Biotin molar concentration: 0.34 / (34000 × 0.59) = 1.7×10^-5 mmol/mL. - Biotin:Protein ratio = (1.7×10^-5 × 10) / (2×10^-5) = 8.5:1. ---