What is the purpose of the BCA protein quantitation kit? (Product manual included)

The BCA (bicinchoninic acid) assay is currently one of the most widely used methods for determining protein concentration. It is based on the biuret reaction: under alkaline conditions, proteins reduce Cu²⁺ to Cu⁺, which then forms a purple-colored complex with the BCA reagent, exhibiting a strong absorbance at 562 nm. The amount of this reaction product is directly proportional to the protein concentration. By measuring the absorbance at 562 nm and comparing it to a standard curve, the concentration of the protein sample can be calculated. This method is rapid, sensitive, stable, and reliable, with a very low coefficient of variation across different protein types. The kit includes a stable protein standard solution for constructing the standard curve.

Function of the BCA Protein Quantitation Kit
Accurate and sensitive, with a wide linear range: The BCA assay has a protein quantitation range of 10–2000 μg/mL.

Speed: The assay can be completed in 45 minutes, which is four times faster and more convenient than the conventional Lowry method.

Economical and practical: Assays performed in microtiter plates can significantly reduce the amounts of sample and reagents required.

Stable performance: Unaffected by both ionic and non-ionic detergents in the sample, the coefficient of variation for detecting different protein molecules is significantly lower than that of Coomassie Brilliant Blue.

BCA Protein Quantitation Kit Instructions (For the detailed manual, please visit: BCA Product Manual )

I. Preparation of Standard Solutions and Working Solutions

1. Prepare the BSA standard curve (linear range: 20–2000 μg/mL, or 5–250 μg/mL). Two preparation methods are provided for each concentration; please follow...

According to custom, choose the appropriate method.

2. Prepare the BCA working solution

(1) Calculate the total volume of BCA working solution required. Total BCA working solution volume = (number of standards + number of samples to be tested) × number of replicates × per well.

The BCA working solution required for the sample.

(2) Prepare the BCA working solution: Add 1 volume of BCA Reagent B to 50 volumes of BCA Reagent A (A:B = 50:1), and mix thoroughly.

II. Testing Methods

1. Test tube assay method (sample: BCA working solution = 1:20)

(1) Add 100 μL of the standard and the sample to be tested into the reaction tubes, respectively.

(2) Add 2.0 mL of BCA working solution to each tube and mix thoroughly. Select the incubation time and temperature based on the concentration range of the sample to be analyzed.

Standard incubation procedure: Incubate at 37°C for 30 minutes, or at room temperature for 2 hours (detection range: 20–2000 μg/mL).

Enhanced incubation method: Incubate at 60°C for 30 min (detection range: 5–250 μg/mL)

(3) Cool to room temperature. Perform the measurement on a spectrophotometer, set the wavelength to 562 nm, and record readings for all samples within 10 minutes.

(4) Based on the absorbance values of the BSA standards (subtracting the OD value of the blank well in the standard series to obtain the final reading), construct a standard curve (X—protein concentration).

μg/mL; Y—final OD at 562 nm). The protein concentration of the sample was calculated based on the standard curve and the sample’s dilution factor.

2. Microplate assay method (sample: BCA working solution = 1:20)

(1) Add 10 μL of the standard solution and the sample to be tested into the microtiter plate.

(2) Add 200 μL of BCA working solution to each well, and gently pipette up and down to ensure thorough mixing. Cover the microplate and incubate at 37°C for 30 minutes.

(3) Cool to room temperature, then measure the absorbance at 562 nm using a microplate reader.

(4) Based on the absorbance values of the BSA standards (subtracting the OD value of the blank well in each standard to obtain the final reading), construct a standard curve (X-axis: protein concentration).

μg/mL; Y—final OD at 562 nm). The protein concentration of the sample was calculated based on the standard curve and the sample’s dilution factor.

Precautions for the BCA Protein Quantitation Kit

1. To ensure the accuracy of protein concentration measurements, it is recommended to perform triplicate wells and, when necessary, exclude outliers.

2. The BCA assay for protein quantification is susceptible to variations in time and temperature; therefore, it is advisable to generate a standard curve for each assay.

3. When adding samples, ensure accurate dispensing and minimize bubble formation to avoid compromising the assay results. After sample addition, use a syringe to gently puncture any remaining bubbles, then place the 96-well plate on a shaker for a brief period to ensure thorough mixing and complete contact between the sample and the reaction buffer.

4. Upon completion of incubation, measure the absorbance as soon as possible and proceed with the assay at the fastest feasible rate to minimize potential errors.

5. Ensure that all reagents are thoroughly mixed before use and stored at the recommended temperature. The freshness of reagents significantly affects experimental results; expired or improperly stored reagents may yield inaccurate outcomes.

6. During the BCA assay, strictly follow the reagent addition sequence and procedural steps, and avoid reversing or omitting any steps.