Qubit Protein Assays Kit components

Rapid, accurate protein quantitation

The Qubit Protein Assays are protein quantitation assays optimized to work on your Qubit device. These assays provide low protein variability, rapid quantitation, and high sensitivity. Learn more about each of the available assays below.

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Qubit protein assays

  Qubit Protein BR Assay Qubit Protein Assay
  Qubit Protein BR Assay kit components  Qubit Protein Assay
Appropriate for A broad range of protein concentrations and types; samples containing detergents Testing dilute samples, <100 µg/mL
Compatible platform Qubit 4 Qubit Flex, Qubit 4*
Features Simple, rapid assay with 2-point standard curve Simple, rapid assay with 3-point standard curve
Sample volume required 10 or 20 µl 1–20 µL
Compatibility Detergents, reducing agents (e.g., TCEP, DTT) Reducing agents (e.g., TCEP, DTT)
Incompatibility Glycine Detergents (e.g., SDS, Tween 20, Triton X-100)
Initial sample range 100 µg/ml to 20 mg/ml 12.5 µg/mL to 5 mg/mL
Quantitation range 1–400 µg 0.25–5 µg
Cat. No. A50668 (100 assays)
A50669 (500 assays)
Q33211 (100 assays)
Q33212 (500 assays)

*The Qubit Protein Assay is also supported on older Qubit models–Qubit 2 and Qubit 3

Simple rapid quantitation

Qubit Protein Assays are easy to perform and only require a 10–15 minute room temperature incubation, eliminating the need to wait for long incubation periods or expose samples to elevated temperatures. The assays are easy to set up with just two or three standards to prepare, unlike traditional assays which typically require a 7-point standard curve for quantitation determination.

Accurate protein quantitation

Qubit Protein Assays provide accurate protein quantitation with low protein to protein variability as compared to traditional assays such as the Bradford assay. Proteins are diverse in their composition and structure. Differences in amino acid sequence, isoelectric point (pI), secondary structure, and side chains or prosthetic groups can result in variation in the quantitated amount.

To demonstrate the accuracy and low protein-to-protein variability of the Qubit Protein BR Assay, several different cell lysates were generated, and total protein concentration was determined with the Qubit Protein BR Assay and a Bradford Protein assay. The calculated concentrations were used to load 10 µg of each lysate onto a protein gel. Accuracy of total protein load was evaluated using No-Stain Protein Labeling Reagent. The load variation produced by Qubit Protein BR Assay was relatively low, with a CV of 11%, whereas the load variation produced by the Bradford assay was 2.5 times higher, with a CV of 28%.

An accurate protein assay for use in downstream applications. When loading an electrophoresis gel for western blot analysis to study protein expression, accurate protein loading is essential. Qubit Protein BR Assay and Bradford Protein Assay were used to determine a 10 µg protein load for 5 different cell lysates. No-Stain Protein Label Reagent was used to estimate the total protein lane loads. The Qubit Protein BR Assay accurately determined the protein concentration of the lysates as demonstrated by a CV of 11% between loads, whereas the Bradford assay exhibited higher variability with a CV of 28%.

Skip the dilutions with a wide dynamic range assay

The Qubit Protein Assays provide a large dynamic range in comparison to standard assays. This response curve allows accurate determination of unknown protein concentration at much higher protein concentrations than other standard assays (e.g., Bradford assays). The Qubit Protein BR Assay can be used to detect protein concentrations between 100 µg/mL to 20,000 µg/mL, enabling most samples to be used neat (undiluted), eliminating the guess work and dilution steps that accompany traditional protein quantitation methods.

Qubit Protein Assays provide a much larger dynamic range than standard protein quantitation assays such as Bradford assays. Qubit Protein Assay is capable of accurate quantitation down to 12.5 µg/mL and Qubit Protein BR Assay has a quantitation range up to 20,000 µg/mL.


Get quantitation data faster

The user-friendly Qubit Fluorometer delivers results using quick, simple assay procedures. The large, color touch screen allows you to easily navigate through the various options. Calculations and settings are automatically performed by the instrument—so no need for offline data calculation. The Qubit 4 Fluorometer will save the data for up to 1,000 samples, and you can transfer data using Wi-Fi, a USB drive, or direct connection with a USB cable.
 

Protein BR Assay user interface on the Qubit 4 fluorometer for assay setup
Protein BR Assay user interface on Qubit 4 fluorometer for displaying results

Protein BR Assay user interface on the Qubit 4 Fluorometer.

Assay compatibility with common buffer components

  Qubit Protein BR Assay Qubit Protein Assay
Contaminant Compatible concentration in sample Compatible concentration in sample
β-Mercaptoethanol 1 mM 10 mM
Acetonitrile 20%  
Ammonium sulfate 200 mM 50 mM*
Bicine 100 mM  
Borate (50 mM pH 8.5) Neat  
B-PER reagent Neat  
CHAPS 5%  
Carbonate-bicarbonate Neat  
DTT 5 mM 10 mM*
DMSO 10%  
EDTA 50 mM 10 mM
Glucose 1 M  
Glycerol 10% 10%*
Guanidine-HCl 4 M  
Imidazole 200 mM 12.5 mM
I-PER Neat  
Mem-PER Neat  
MES 125 mM  
MOPS 100 mM  
M-PER Neat  
Sodium acetate 100 mM  
Sodium azide   10 mM
Sodium chloride 5 M 200 mM*
NE-PER (CER) Neat  
NE-PER (NER) Neat  
NP-40 5% Ø
Phosphate-buffer saline (PBS), pH 7.4 Neat 10 mM KPO4, 150 mM NaCl*
Potassium phosphate, pH 7.4   5 mM
PMSF 1 mM  
RIPA Neat  
SDS 5% 0.1%*
Sucrose 20% 500 mM
T-PER Neat  
Tricine 50 mM  
Tris-buffer saline (TBS) Neat  
Tris-glycine, pH 8.0*** Ø  
Tris-glycine SDS, pH 8.3 Ø  
Tris-HCl 500 mM  
Tris-HEPES SDS, pH 8.0 Neat  
Triton X-100 5% Ø
Tween 20 3% Ø
Urea 3 M  
Y-Per Ø  
GPCR Extraction & Stabilization Reagent 1:2  
Cell Surface Protein Isolation Kit Neat  

*An acceptable result, but with some distortion of the standard curve. For best results, add the same amount of contaminant to the standard samples.

The Qubit Protein BR Assay and Qubit Protein Assay were performed according to instructions with samples of 1,000 µg/mL of BSA containing commonly used buffers and contaminants. Assays were performed in triplicate, and RFU values were compared to that of BSA in 0.9% NaCl, 0.05% NaN3. The assay was considered compatible with the tested substance at the indicated concentration if the error in protein concentration estimation caused by the presence of the substance was less than 10%. Concentrations listed refer to the actual concentration in the protein sample. Ø denotes compounds that were not compatible at the lowest concentration tested. Blank rows denote the compounds were not tested with that particular assay.


Buffer formulations used in compatibility testing

Buffer Formulation
Sodium carbonate-bicarbonate, pH 9.4 0.2 M sodium carbonate-bicarbonate, pH 9.4
Phosphate-buffered saline (PBS) 100 mM sodium phosphate, 150 mM NaCl, pH 7.2
RIPA buffer 25 mM Tris, 150 mM NaCl, 1% DOC, 1% NP-40, 0.1% SDS, pH 7.6
Tris-buffered saline (TBS) 25 mM Tris, 150 mM NaCl, pH 7.4
Tris-glycine, pH 8.0 25 mM Tris, 192 mM glycine, pH 8.0
Tris-glycine-SDS, pH 8.3 25 mM Tris, 192 mM glycine, 0.1% SDS, pH 8.3
Tris-HEPES-SDS 100 mM Tris, 100 mM HEPES, 3 mM SDS

Qubit protein assays

  Qubit Protein BR Assay Qubit Protein Assay
  Qubit Protein BR Assay kit components  Qubit Protein Assay
Appropriate for A broad range of protein concentrations and types; samples containing detergents Testing dilute samples, <100 µg/mL
Compatible platform Qubit 4 Qubit Flex, Qubit 4*
Features Simple, rapid assay with 2-point standard curve Simple, rapid assay with 3-point standard curve
Sample volume required 10 or 20 µl 1–20 µL
Compatibility Detergents, reducing agents (e.g., TCEP, DTT) Reducing agents (e.g., TCEP, DTT)
Incompatibility Glycine Detergents (e.g., SDS, Tween 20, Triton X-100)
Initial sample range 100 µg/ml to 20 mg/ml 12.5 µg/mL to 5 mg/mL
Quantitation range 1–400 µg 0.25–5 µg
Cat. No. A50668 (100 assays)
A50669 (500 assays)
Q33211 (100 assays)
Q33212 (500 assays)

*The Qubit Protein Assay is also supported on older Qubit models–Qubit 2 and Qubit 3

Simple rapid quantitation

Qubit Protein Assays are easy to perform and only require a 10–15 minute room temperature incubation, eliminating the need to wait for long incubation periods or expose samples to elevated temperatures. The assays are easy to set up with just two or three standards to prepare, unlike traditional assays which typically require a 7-point standard curve for quantitation determination.

Accurate protein quantitation

Qubit Protein Assays provide accurate protein quantitation with low protein to protein variability as compared to traditional assays such as the Bradford assay. Proteins are diverse in their composition and structure. Differences in amino acid sequence, isoelectric point (pI), secondary structure, and side chains or prosthetic groups can result in variation in the quantitated amount.

To demonstrate the accuracy and low protein-to-protein variability of the Qubit Protein BR Assay, several different cell lysates were generated, and total protein concentration was determined with the Qubit Protein BR Assay and a Bradford Protein assay. The calculated concentrations were used to load 10 µg of each lysate onto a protein gel. Accuracy of total protein load was evaluated using No-Stain Protein Labeling Reagent. The load variation produced by Qubit Protein BR Assay was relatively low, with a CV of 11%, whereas the load variation produced by the Bradford assay was 2.5 times higher, with a CV of 28%.

An accurate protein assay for use in downstream applications. When loading an electrophoresis gel for western blot analysis to study protein expression, accurate protein loading is essential. Qubit Protein BR Assay and Bradford Protein Assay were used to determine a 10 µg protein load for 5 different cell lysates. No-Stain Protein Label Reagent was used to estimate the total protein lane loads. The Qubit Protein BR Assay accurately determined the protein concentration of the lysates as demonstrated by a CV of 11% between loads, whereas the Bradford assay exhibited higher variability with a CV of 28%.

Skip the dilutions with a wide dynamic range assay

The Qubit Protein Assays provide a large dynamic range in comparison to standard assays. This response curve allows accurate determination of unknown protein concentration at much higher protein concentrations than other standard assays (e.g., Bradford assays). The Qubit Protein BR Assay can be used to detect protein concentrations between 100 µg/mL to 20,000 µg/mL, enabling most samples to be used neat (undiluted), eliminating the guess work and dilution steps that accompany traditional protein quantitation methods.

Qubit Protein Assays provide a much larger dynamic range than standard protein quantitation assays such as Bradford assays. Qubit Protein Assay is capable of accurate quantitation down to 12.5 µg/mL and Qubit Protein BR Assay has a quantitation range up to 20,000 µg/mL.


Get quantitation data faster

The user-friendly Qubit Fluorometer delivers results using quick, simple assay procedures. The large, color touch screen allows you to easily navigate through the various options. Calculations and settings are automatically performed by the instrument—so no need for offline data calculation. The Qubit 4 Fluorometer will save the data for up to 1,000 samples, and you can transfer data using Wi-Fi, a USB drive, or direct connection with a USB cable.
 

Protein BR Assay user interface on the Qubit 4 fluorometer for assay setup
Protein BR Assay user interface on Qubit 4 fluorometer for displaying results

Protein BR Assay user interface on the Qubit 4 Fluorometer.

Assay compatibility with common buffer components

  Qubit Protein BR Assay Qubit Protein Assay
Contaminant Compatible concentration in sample Compatible concentration in sample
β-Mercaptoethanol 1 mM 10 mM
Acetonitrile 20%  
Ammonium sulfate 200 mM 50 mM*
Bicine 100 mM  
Borate (50 mM pH 8.5) Neat  
B-PER reagent Neat  
CHAPS 5%  
Carbonate-bicarbonate Neat  
DTT 5 mM 10 mM*
DMSO 10%  
EDTA 50 mM 10 mM
Glucose 1 M  
Glycerol 10% 10%*
Guanidine-HCl 4 M  
Imidazole 200 mM 12.5 mM
I-PER Neat  
Mem-PER Neat  
MES 125 mM  
MOPS 100 mM  
M-PER Neat  
Sodium acetate 100 mM  
Sodium azide   10 mM
Sodium chloride 5 M 200 mM*
NE-PER (CER) Neat  
NE-PER (NER) Neat  
NP-40 5% Ø
Phosphate-buffer saline (PBS), pH 7.4 Neat 10 mM KPO4, 150 mM NaCl*
Potassium phosphate, pH 7.4   5 mM
PMSF 1 mM  
RIPA Neat  
SDS 5% 0.1%*
Sucrose 20% 500 mM
T-PER Neat  
Tricine 50 mM  
Tris-buffer saline (TBS) Neat  
Tris-glycine, pH 8.0*** Ø  
Tris-glycine SDS, pH 8.3 Ø  
Tris-HCl 500 mM  
Tris-HEPES SDS, pH 8.0 Neat  
Triton X-100 5% Ø
Tween 20 3% Ø
Urea 3 M  
Y-Per Ø  
GPCR Extraction & Stabilization Reagent 1:2  
Cell Surface Protein Isolation Kit Neat  

*An acceptable result, but with some distortion of the standard curve. For best results, add the same amount of contaminant to the standard samples.

The Qubit Protein BR Assay and Qubit Protein Assay were performed according to instructions with samples of 1,000 µg/mL of BSA containing commonly used buffers and contaminants. Assays were performed in triplicate, and RFU values were compared to that of BSA in 0.9% NaCl, 0.05% NaN3. The assay was considered compatible with the tested substance at the indicated concentration if the error in protein concentration estimation caused by the presence of the substance was less than 10%. Concentrations listed refer to the actual concentration in the protein sample. Ø denotes compounds that were not compatible at the lowest concentration tested. Blank rows denote the compounds were not tested with that particular assay.


Buffer formulations used in compatibility testing

Buffer Formulation
Sodium carbonate-bicarbonate, pH 9.4 0.2 M sodium carbonate-bicarbonate, pH 9.4
Phosphate-buffered saline (PBS) 100 mM sodium phosphate, 150 mM NaCl, pH 7.2
RIPA buffer 25 mM Tris, 150 mM NaCl, 1% DOC, 1% NP-40, 0.1% SDS, pH 7.6
Tris-buffered saline (TBS) 25 mM Tris, 150 mM NaCl, pH 7.4
Tris-glycine, pH 8.0 25 mM Tris, 192 mM glycine, pH 8.0
Tris-glycine-SDS, pH 8.3 25 mM Tris, 192 mM glycine, 0.1% SDS, pH 8.3
Tris-HEPES-SDS 100 mM Tris, 100 mM HEPES, 3 mM SDS
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