Bradford Assay Protocol for Protein Quantification

Research will be limited to:
- Assay: Bradford
- Analyte: Protein
- Standard: BSA
- Measurement: Spectrophotometry
- Quantification: Standard Curve

Strategy: The user needs a comprehensive, lab-ready protocol for a Bradford assay. While the general principle is well-known, the request specifically asks for precise reagent volumes (likely for both microplate and cuvette formats), specific incubation times, the exact wavelength (typically 595 nm), and critically, how to handle detergent interference (as Bradford is sensitive to SDS/Triton). I will search for standardized protocols from reputable sources (like Thermo Fisher, Bio-Rad, or Sigma-Aldrich) to provide accurate mixing ratios and a BSA dilution table for the standard curve.
Queries:
- detailed Bradford assay protocol BSA standard curve reagent volumes incubation wavelength
- Bradford assay detergent compatibility limits and interference handling
- BSA standard curve preparation table for Bradford assay microplate vs cuvette

🔍 Reading and summarizing 5 new websites...

1. Pierce Bradford Protein Assay Kit
2. Quick Start™ Bradford Protein Assay
3. [PDF] Coomassie Plus (Bradford) Assay Reagent - Fisher Scientific
4. Bradford Assay for Determining Protein Concentration - CSH Protocols
5. [PDF] Pierce Detergent Compatible Bradford Assay Kit

Found 5 websites. Summarized content:

Pierce Bradford Protein Assay Kit

Bradford Assay Protocol Summary (Based on Pierce Bradford Protein Assay Kit)

Here's a summary of the Bradford assay protocol for protein quantification using a BSA standard curve, based on the provided document:

Assay Principle: Colorimetric assay based on Coomassie dye binding to protein, shifting the absorption maximum from 465 nm to 595 nm (brown to blue color change).

Reagents:

• Bradford Reagent: Contains Coomassie G-250 dye, methanol, phosphoric acid, and solubilizing agents in water.
• BSA Standard: 2 mg/mL BSA in 0.9% saline and 0.05% sodium azide.

Standard Curve Preparation (BSA):

Two working ranges are possible: 100-1500 μg/mL (standard) and 1-25 μg/mL (micro). The protocol suggests dilutions using the provided BSA standard and appropriate diluent. See Table 1 in the source document for detailed dilution schemes.

Protocols:

Three protocols are described: Standard Test Tube, Micro Test Tube, Standard Microplate, and Micro Microplate.

1. Standard Test Tube Protocol (100-1500 μg/mL):

• Add 30 μL of standard or unknown sample to a test tube.
• Add 1.5 mL of Bradford reagent.
• Mix well.
• Incubate for 10 minutes at room temperature (RT).
• Measure absorbance at 595 nm using a spectrophotometer, zeroed with water.
• Subtract blank absorbance.
• Plot standard curve (Absorbance vs. concentration) and determine unknown sample concentrations.

2. Micro Test Tube Protocol (1-25 μg/mL):

• Add 1.0 mL of standard or unknown sample to a test tube.
• Add 1.0 mL of Bradford reagent.
• Mix well.
• Incubate for 10 minutes at RT.
• Measure absorbance at 595 nm using a spectrophotometer, zeroed with water.
• Subtract blank absorbance.
• Plot standard curve (Absorbance vs. concentration) and determine unknown sample concentrations.

3. Standard Microplate Protocol (100-1500 μg/mL):

• Add 5 μL of standard or unknown sample to a microplate well.
• Add 250 μL of Bradford reagent.
• Mix on a plate shaker for 30 seconds.
• Incubate for 10 minutes at RT.
• Measure absorbance at 595 nm using a plate reader.
• Subtract blank absorbance.
• Plot standard curve (Absorbance vs. concentration) and determine unknown sample concentrations.

4. Micro Microplate Protocol (1-25 μg/mL):

• Add 150 μL of standard or unknown sample to a microplate well.
• Add 150 μL of Bradford reagent.
• Mix on a plate shaker for 30 seconds.
• Incubate for 10 minutes at RT.
• Measure absorbance at 595 nm using a plate reader.
• Subtract blank absorbance.
• Plot standard curve (Absorbance vs. concentration) and determine unknown sample concentrations.

Wavelength: 595 nm (optimal), or between 570 nm and 610 nm. Sensitivity is reduced at wavelengths other than 595 nm.

Incubation Time: 10 minutes at room temperature (RT) for all protocols.

Detergent Handling:

• Many detergents interfere with the assay. See Table 2 ("Compatible substance concentrations in the Bradford Assay") in the original document for compatible concentrations.
• If detergents interfere, consider dialysis, dilution, or using a protein assay preparation reagent set (Compat-Able™).

Important Notes:

• Mix Bradford reagent gently before use.
• Equilibrate reagent to room temperature before use.
• Temperature affects absorbance; keep reagent at a constant temperature during the assay.
• Use a four-parameter or best-fit curve for standard curve fitting if available.

Quick Start™ Bradford Protein Assay

Bradford Assay Protocol Summary (Based on Quick Start™ Bradford Protein Assay)

This protocol details the Bradford assay using BSA as a standard for protein quantification via spectrophotometry at 595 nm.

I. Reagents:

• Dye Reagent: Ready-to-use at 1x concentration (contains methanol and phosphoric acid). Store at 4°C, warm to ambient temperature before use, and invert to mix.
• BSA Standard: Provided at 2 mg/ml, or as a set of 7 pre-diluted concentrations (2, 1.5, 1, 0.75, 0.5, 0.25, 0.125 mg/ml) in 0.9% NaCl, 0.05% NaN3 solution.

II. Standard Curve Preparation:

• Use the same buffer as the samples for dilutions.
• Prepare a series of BSA standards with known concentrations. Serial dilutions are provided in the appendix of the manual based on assay type (5 ml standard, 1 ml standard, Microplate standard)

III. Assay Protocols & Volumes:

• Standard Assay:

  • Linear range (BSA): 125–1,000 μg/ml

  Assay	Sample Volume	1x Dye Reagent Volume
  5 ml	100 μl	5 ml
  1 ml	20 μl	1 ml
  Microplate	5 μl	250 μl

• Microassay:

  • Linear range (BSA): 1.25–10 μg/ml

  Assay	Sample Volume	1x Dye Reagent Volume
  2 ml	1 ml	1 ml
  Microplate	150 μl	150 μl

IV. Procedure:

1. Pipette standards and unknown samples into separate tubes, cuvettes, or microplate wells.
2. Add the appropriate volume of 1x dye reagent to each.
3. Mix thoroughly (vortex, invert, or use a microplate mixer).
4. Incubation: Incubate at room temperature for at least 5 minutes, but no longer than 1 hour.
5. Spectrophotometry: Set the spectrophotometer to 595 nm. Zero the instrument with a blank sample (containing diluent and dye reagent). Measure the absorbance of standards and unknowns.

V. Data Analysis:

1. If the spectrophotometer/microplate reader wasn't zeroed with the blank, average the blank values and subtract from all readings.
2. Plot the standard curve: Absorbance at 595 nm (y-axis) vs. concentration (μg/ml) (x-axis).
3. Determine the unknown sample concentration using the standard curve.
4. Adjust for any dilution factors.

VI. Detergent Handling:

• Detergents can interfere with the assay. If detergent is present, dilute the sample to reduce the detergent concentration to ≤0.1% (if protein concentration allows).
• Consult Table 1 in the manual for a compatibility guide of common reagents.

VII. Important Notes:

• The dye reagent contains methanol and phosphoric acid.
• All kit components have a 1 year shelf life at 4°C.
• Use the same buffer for diluting the BSA standards and the protein samples.
• Samples should be clear solutions, not suspensions or unfiltered homogenates.
• Bio-Rad disposable polystyrene cuvettes are recommended.

[PDF] Coomassie Plus (Bradford) Assay Reagent - Fisher Scientific
Here's a detailed Bradford assay protocol based on the provided document, focusing on protein quantification using a BSA standard curve:

Assay: Bradford Assay (using Thermo Scientific Coomassie Plus Reagent)

Analyte: Protein

Standard: Bovine Serum Albumin (BSA)

Measurement: Spectrophotometry at 595nm

Quantification: Standard Curve

Reagents:

• Coomassie Plus (Bradford) Assay Reagent (containing coomassie G-250 dye, methanol, phosphoric acid and solubilizing agents in water). Store at 4°C. Mix gently before using. Equilibrate to Room temperature before use.

• BSA standard (e.g., Thermo Scientific Albumin Standard Ampules, 2mg/mL).

• Diluent: Use the same diluent as your sample. The document uses 0.9% saline as a diluent for BSA standards.

BSA Standard Curve Preparation:

Two working ranges are described: 100-1500 μg/mL (Standard) and 1-25 μg/mL (Micro). Prepare fresh dilutions as outlined in Table 1 of the provided document. Here is a summary of the Table 1 dilutions:

• Working Range = 100–1500 μg/m L

  • Vial A: 300 μL of Stock (2000 μg/mL) = 2000 μg/mL
  • Vial B: 125 μL Diluent + 375 μL Stock = 1500 μg/mL
  • Vial C: 325 μL Diluent + 325 μL Stock = 1000 μg/mL
  • Vial D: 175 μL Diluent + 175 μL of vial B dilution = 750 μg/mL
  • Vial E: 325 μL Diluent + 325 μL of vial C dilution = 500 μg/mL
  • Vial F: 325 μL Diluent + 325 μL of vial E dilution = 250 μg/mL
  • Vial G: 325 μL Diluent + 325 μL of vial F dilution = 125 μg/mL
  • Vial H: 400 μL Diluent + 100 μL of vial G dilution = 25 μg/mL
  • Vial I: 400 μL Diluent only = Blank (0 μg/mL)
  • Working Range = 1 –25 μg/m L
  • Vial A: 3555 μL Diluent + 45 μL of Stock (2mg/ml) = 25 μg/mL
  • Vial B: 6435 μL Diluent + 65 μL of Stock = 20 μg/mL
  • Vial C: 3970 μL Diluent + 30 μL of Stock = 15 μg/mL
  • Vial D: 3000 μL Diluent + 3000 μL of vial B dilution = 10 μg/mL
  • Vial E: 2500 μL Diluent + 2500 μL of vial D dilution = 5 μg/mL
  • Vial F: 1700 μL Diluent + 1700 μL of vial E dilution = 2.5 μg/mL
  • Vial G: 4000 μL Diluent only = Blank (0 μg/mL)

Test Tube Procedure:

• Standard Test Tube Protocol (100-1500 μg/mL):

  • Pipette 0.05 mL of each standard or unknown sample into labeled tubes.
  • Add 1.5 mL of Coomassie Plus Reagent to each tube. Mix well.
  • Incubate for 10 minutes at room temperature (optional, but recommended for consistency).
  • Zero spectrophotometer at 595 nm with water. Measure absorbance of all samples.
  • Subtract average blank absorbance from all standard and sample readings.
  • Plot blank-corrected 595 nm readings vs. concentration to generate standard curve.

• Micro Test Tube Protocol (1-25 μg/mL):

  • Pipette 1.0 mL of each standard or unknown sample into labeled tubes.
  • Add 1.0 mL of Coomassie Plus Reagent to each tube. Mix well.
  • Incubate for 10 minutes at room temperature (optional, but recommended for consistency).
  • Zero spectrophotometer at 595 nm with water. Measure absorbance of all samples.
  • Subtract average blank absorbance from all standard and sample readings.
  • Plot blank-corrected 595 nm readings vs. concentration to generate standard curve.

Microplate Procedure:

• Standard Microplate Protocol (100-1500 μg/mL):

  • Pipette 10 μL of each standard or unknown sample into microplate wells.
  • Add 300 μL of Coomassie Plus Reagent to each well. Mix on a plate shaker for 30 seconds.
  • Incubate for 10 minutes at room temperature (optional, but recommended for consistency).
  • Measure absorbance at 595 nm using a plate reader.
  • Subtract average blank absorbance from all standard and sample readings.
  • Plot blank-corrected 595 nm readings vs. concentration to generate standard curve.

• Micro Microplate Protocol (1-25 μg/mL):

  • Pipette 150 μL of each standard or unknown sample into microplate wells.
  • Add 150 μL of Coomassie Plus Reagent to each well. Mix on a plate shaker for 30 seconds.
  • Incubate for 10 minutes at room temperature (optional, but recommended for consistency).
  • Measure absorbance at 595 nm using a plate reader.
  • Subtract average blank absorbance from all standard and sample readings.
  • Plot blank-corrected 595 nm readings vs. concentration to generate standard curve.

Wavelength:

• Measure the absorbance at or near 595 nm. The color may be read at any wavelength between 575 nm and 615 nm, although the slope of the standard curve and overall assay sensitivity will be reduced.

Detergent Handling:

• Many detergents interfere with the assay. If your sample contains detergents, consult Table 2 of the document for compatible concentrations. You might need to dilute the sample, perform dialysis, or use a detergent removal kit (Product No. 23215).

Important Notes:

• Mix the Coomassie Plus Reagent gently before dispensing.
• For best accuracy, prepare the standard curve using a pure sample of the target protein.
• Maintain a constant temperature during the assay.
• If using curve-fitting algorithms for microplate readers, a four-parameter (quadratic) or best-fit curve will provide more accurate results than a purely linear fit.
• Ensure glassware is clean and free of detergent residue if reusing.

Bradford Assay for Determining Protein Concentration - CSH Protocols
Based on the provided text, a detailed Bradford assay protocol cannot be extracted. The website mentions a Bradford assay protocol published in Cold Spring Harbor Protocols in 2020, but access to the full protocol (including reagent volumes, incubation time, wavelength, detergent handling, and standard curve generation) requires a subscription or purchase.

Therefore, the response is: Not relevant.

[PDF] Pierce Detergent Compatible Bradford Assay Kit
Here's a detailed Bradford assay protocol based on the provided document, addressing the user's specific requirements:

Assay: Bradford (Pierce Detergent Compatible Bradford Assay Kit)

Analyte: Protein

Standard: BSA (Bovine Serum Albumin)

Measurement: Spectrophotometry (measuring absorbance)

Quantification: Standard Curve

Reagents:

• Pierce Detergent Compatible Bradford Assay Reagent: Contains coomassie G-250 dye, methanol, phosphoric acid, and solubilizing agents in water. Store at 4°C. Ensure it is at room temperature before use and gently mixed (inverted or stirred) to disperse any dye aggregates.
• BSA Standard: 2mg/mL BSA in 0.9% saline and 0.05% sodium azide. Store unopened ampules at room temperature.

BSA Standard Curve Preparation:

• Working Range = 100-1500 μg/mL (Standard Test Tube and Microplate Protocols):

  Vial	Volume of Diluent	Volume and Source of BSA	Final BSA Concentration (μg/mL)
  A	0	300 μL of stock	2000
  B	125 μL	375 μL of stock	1500
  C	325 μL	325 μL of stock	1000
  D	175 μL	175 μL of vial B dilution	750
  E	325 μL	325 μL of vial C dilution	500
  F	325 μL	325 μL of vial E dilution	250
  G	325 μL	325 μL of vial F dilution	125
  H	400 μL	100 μL of vial G dilution	25
  I	400 μL	0	0 = Blank
  * Working Range = 2-25 μg/mL (Micro Test Tube or Microplate Protocols):

  Vial	Volume of Diluent	Volume and Source of BSA	Final BSA Concentration (μg/mL)
  A	2370 μL	30 μL of stock	25
  B	4950 μL	50 μL of stock	20
  C	3970 μL	30 μL of stock	15
  D	2500 μL	2500 μL of vial B dilution	10
  E	2000 μL	2000 μL of vial D dilution	5
  F	1500 μL	1500 μL of vial E dilution	2.5
  G	5000 μL	0	0 = Blank

  Note: It is NOT necessary to include detergent in the standards. Dilute the BSA standard in the same diluent as the sample(s).

Test Tube Procedures:

• Standard Test Tube Protocol (100-1500 μg/mL):

  1. Add 50 μL of each standard or unknown sample to a test tube.
  2. Add 1.5 mL of Pierce Detergent Compatible Bradford Assay Reagent.
  3. Mix well.
  4. Incubate for 10 minutes at room temperature.
  5. Measure absorbance at 595 nm, blanking the spectrophotometer with water.

• Micro Test Tube Protocol (2-25 μg/mL):

  1. Add 1.0 mL of each standard or unknown sample to a test tube.
  2. Add 1.0 mL of Pierce Detergent Compatible Bradford Assay Reagent.
  3. Mix well.
  4. Incubate for 10 minutes at room temperature.
  5. Measure absorbance at 595 nm, blanking the spectrophotometer with water.

Microplate Procedures:

• Standard Microplate Protocol (100-1500 μg/mL):

  1. Add 10 μL of each standard or unknown sample to a microplate well.
  2. Add 300 μL of Pierce Detergent Compatible Bradford Assay Reagent.
  3. Mix by pipetting up and down 4-5 times. Do not use a plate shaker.
  4. Incubate for 10 minutes at room temperature.
  5. Measure absorbance at 595 nm using a plate reader.

• Micro Microplate Protocol (2-25 μg/mL):

  1. Add 150 μL of each standard or unknown sample to a microplate well.
  2. Add 150 μL of Pierce Detergent Compatible Bradford Assay Reagent.
  3. Mix by pipetting up and down 4-5 times. Do not use a plate shaker.
  4. Incubate for 10 minutes at room temperature.
  5. Measure absorbance at 595 nm using a plate reader.

Wavelength: 595 nm. Measurements can be taken between 575nm and 615nm, but sensitivity is reduced.

Incubation Time: 10 minutes at room temperature. The reaction is stable for one hour.

Detergent Handling: This kit is designed to be compatible with detergents. Standards do not need to contain detergent. See Table 3 in the original document for compatible concentrations. The micro assay (2-25 μg/mL) is compatible with 0.1% of Triton X-100, SDS, CHAPS, Tween™-20, Octyl β-thioglucopyranoside, and Brij™-35.

Standard Curve Generation & Quantification:

1. Subtract the average blank (0 μg/mL BSA) absorbance from all standard and sample readings.
2. Plot the blank-corrected 595 nm absorbance values versus the corresponding BSA concentrations (μg/mL).
3. Use the standard curve to determine the protein concentration of the unknown samples.
4. A four-parameter (quadratic) or best-fit curve provides more accurate results than a linear fit. If plotting results by hand, a point-to-point curve is preferable to a linear fit to the standard points.