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Should absorbance be between 0 and 1 for ELISA?
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Maura Rudd
Should absorbance be between 0 and 1 for ELISA?
David Schad If you view the spectrum, you can also see whether the absorbance has "saturated". As pointed out earlier, Absorbance is -log10 Transmission, so an absorbance of 2 is 1% transmission, of 3 is 0.1% transmission etc. "saturation of absorbance" means that the amount of light reaching the detector is as low as the noise levels of the detector, so you are dividing Noise by the reference signal, and taking the log. The peaks can look very noisy, and/or become flat.
David Schad If you view the spectrum, you can also see whether the absorbance has "saturated". As pointed out earlier, Absorbance is -log10 Transmission, so an absorbance of 2 is 1% transmission, of 3 is 0.1% transmission etc. "saturation of absorbance" means that the amount of light reaching the detector is as low as the noise levels of the detector, so you are dividing Noise by the reference signal, and taking the log. The peaks can look very noisy, and/or become flat.
Hi, I am a bit concerned/confused by the statement "The 570nm absorbance value is subtracted from the 450nm value to correct for optical imperfections. " In general, it is beneficial to be able to see the spectrum, rather than simply rely on a measurement of the loss of light at a single wavelength, as for example scattering can also be registered as a loss of light (absorbance). What instrument are you using? Can you measure a spectrum? If so, how has the spectrum changed between your later and earlier measurements?
Hi, I am a bit concerned/confused by the statement "The 570nm absorbance value is subtracted from the 450nm value to correct for optical imperfections. " In general, it is beneficial to be able to see the spectrum, rather than simply rely on a measurement of the loss of light at a single wavelength, as for example scattering can also be registered as a loss of light (absorbance). What instrument are you using? Can you measure a spectrum? If so, how has the spectrum changed between your later and earlier measurements?
David Schad This one? https://lifesciences.tecan.com/multimode-plate-reader It says it can do spectra - if you can, it is worth recording a spectrum at least at the beginning of a protocol. If there is a lot of scatter, you will see that the peaks are sitting on a large baseline - it is valid to then subtract the absorbance level where the baseline is flat, to give a peak absorbance. Large scatter could come from, for example, precipitation in the wells.
David Schad This one? https://lifesciences.tecan.com/multimode-plate-reader It says it can do spectra - if you can, it is worth recording a spectrum at least at the beginning of a protocol. If there is a lot of scatter, you will see that the peaks are sitting on a large baseline - it is valid to then subtract the absorbance level where the baseline is flat, to give a peak absorbance. Large scatter could come from, for example, precipitation in the wells.
depend on the plate reader, most of them works from 0-3, or 0-4. the USDA suggests using 0-2, see below. Optical density range. CVB recommends that the optical density (OD) of the saturation portion of the ELISA curve not be greater than 2.0 even though the instrument can measure higher OD values. Since higher ODs correspond to lower measured signal (transmitted light) in the spectrophotometer, small variations in the execution of the assay may have a greater impact at high ODs than at lower ODs. 2.2.2. Reagent blank. The reagent blank should produce ODs of 0.15 or less. 2.2.3. Signal to background (S/B) ratio. The S/B ratio is a key consideration in determining the optimum reagent working dilutions. An S/B ratio of 10 or greater when measured near the saturation portion of the ELISA curve is usually adequate.
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depend on the plate reader, most of them works from 0-3, or 0-4. the USDA suggests using 0-2, see below. Optical density range. CVB recommends that the optical density (OD) of the saturation portion of the ELISA curve not be greater than 2.0 even though the instrument can measure higher OD values. Since higher ODs correspond to lower measured signal (transmitted light) in the spectrophotometer, small variations in the execution of the assay may have a greater impact at high ODs than at lower ODs. 2.2.2. Reagent blank. The reagent blank should produce ODs of 0.15 or less. 2.2.3. Signal to background (S/B) ratio. The S/B ratio is a key consideration in determining the optimum reagent working dilutions. An S/B ratio of 10 or greater when measured near the saturation portion of the ELISA curve is usually adequate.
John Schloendorn The concept of molecules "hiding in the shadows" of other molecules is stemming from ray optics - it makes no sense for wave optics and in relation to the question if Beer's law can be applied or not. For details see a recent review on the topic of the Bouguer-Beer-Lambert law: ArticleThe Bouguer-Beer-Lambert Law: Shining Light on the Obscure
John Schloendorn The concept of molecules "hiding in the shadows" of other molecules is stemming from ray optics - it makes no sense for wave optics and in relation to the question if Beer's law can be applied or not. For details see a recent review on the topic of the Bouguer-Beer-Lambert law: ArticleThe Bouguer-Beer-Lambert Law: Shining Light on the Obscure
No. Look at the mathematical definition of absorbance, and the law of Beer and Lambert. Absorbance and transmitted light are in a logarithmic relationship that allows any value > 0.
In practice, absorbance saturates at high values, because some molecules hide in the "shadows" behind other molecules. There's no light left for them to absorb. In a typical ELISA, you'll see the linear relationship with concentration break down in the range of 1-3 ish -- depending on your molecule, path length and personal tolerance for error.
It's hard to say what's causing your problem. I guess something went wrong with your execution. Sounds like not all the enzyme got removed during the wash steps. You'll need to get your baseline signal back down into the linear range, before you can be sure about the inhibition.
No. Look at the mathematical definition of absorbance, and the law of Beer and Lambert. Absorbance and transmitted light are in a logarithmic relationship that allows any value > 0.
In practice, absorbance saturates at high values, because some molecules hide in the "shadows" behind other molecules. There's no light left for them to absorb. In a typical ELISA, you'll see the linear relationship with concentration break down in the range of 1-3 ish -- depending on your molecule, path length and personal tolerance for error.
It's hard to say what's causing your problem. I guess something went wrong with your execution. Sounds like not all the enzyme got removed during the wash steps. You'll need to get your baseline signal back down into the linear range, before you can be sure about the inhibition.
David Schad
If you view the spectrum, you can also see whether the absorbance has "saturated". As pointed out earlier, Absorbance is -log10 Transmission, so an absorbance of 2 is 1% transmission, of 3 is 0.1% transmission etc.
"saturation of absorbance" means that the amount of light reaching the detector is as low as the noise levels of the detector, so you are dividing Noise by the reference signal, and taking the log. The peaks can look very noisy, and/or become flat.
David Schad
If you view the spectrum, you can also see whether the absorbance has "saturated". As pointed out earlier, Absorbance is -log10 Transmission, so an absorbance of 2 is 1% transmission, of 3 is 0.1% transmission etc.
"saturation of absorbance" means that the amount of light reaching the detector is as low as the noise levels of the detector, so you are dividing Noise by the reference signal, and taking the log. The peaks can look very noisy, and/or become flat.
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Hi,
I am a bit concerned/confused by the statement "The 570nm absorbance value is subtracted from the 450nm value to correct for optical imperfections. "
In general, it is beneficial to be able to see the spectrum, rather than simply rely on a measurement of the loss of light at a single wavelength, as for example scattering can also be registered as a loss of light (absorbance).
What instrument are you using?
Can you measure a spectrum?
If so, how has the spectrum changed between your later and earlier measurements?
Hi,
I am a bit concerned/confused by the statement "The 570nm absorbance value is subtracted from the 450nm value to correct for optical imperfections. "
In general, it is beneficial to be able to see the spectrum, rather than simply rely on a measurement of the loss of light at a single wavelength, as for example scattering can also be registered as a loss of light (absorbance).
What instrument are you using?
Can you measure a spectrum?
If so, how has the spectrum changed between your later and earlier measurements?
More
VOTE
David Schad
This one? https://lifesciences.tecan.com/multimode-plate-reader
It says it can do spectra - if you can, it is worth recording a spectrum at least at the beginning of a protocol. If there is a lot of scatter, you will see that the peaks are sitting on a large baseline - it is valid to then subtract the absorbance level where the baseline is flat, to give a peak absorbance.
Large scatter could come from, for example, precipitation in the wells.
David Schad
This one? https://lifesciences.tecan.com/multimode-plate-reader
It says it can do spectra - if you can, it is worth recording a spectrum at least at the beginning of a protocol. If there is a lot of scatter, you will see that the peaks are sitting on a large baseline - it is valid to then subtract the absorbance level where the baseline is flat, to give a peak absorbance.
Large scatter could come from, for example, precipitation in the wells.
More
VOTE
depend on the plate reader, most of them works from 0-3, or 0-4.
the USDA suggests using 0-2, see below.
Optical density range. CVB recommends that the optical density (OD) of
the saturation portion of the ELISA curve not be greater than 2.0 even
though the instrument can measure higher OD values. Since higher ODs
correspond to lower measured signal (transmitted light) in the
spectrophotometer, small variations in the execution of the assay may have a
greater impact at high ODs than at lower ODs.
2.2.2. Reagent blank. The reagent blank should produce ODs of 0.15 or less.
2.2.3. Signal to background (S/B) ratio. The S/B ratio is a key consideration in
determining the optimum reagent working dilutions. An S/B ratio of 10 or
greater when measured near the saturation portion of the ELISA curve is
usually adequate.
depend on the plate reader, most of them works from 0-3, or 0-4.
the USDA suggests using 0-2, see below.
Optical density range. CVB recommends that the optical density (OD) of
the saturation portion of the ELISA curve not be greater than 2.0 even
though the instrument can measure higher OD values. Since higher ODs
correspond to lower measured signal (transmitted light) in the
spectrophotometer, small variations in the execution of the assay may have a
greater impact at high ODs than at lower ODs.
2.2.2. Reagent blank. The reagent blank should produce ODs of 0.15 or less.
2.2.3. Signal to background (S/B) ratio. The S/B ratio is a key consideration in
determining the optimum reagent working dilutions. An S/B ratio of 10 or
greater when measured near the saturation portion of the ELISA curve is
usually adequate.
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Hello Hugh,
Thank you for your answer. I am using a Tecan Spark plate reader. I have only measured absorbance at 450nm and 570nm, not a range.
Hello Hugh,
Thank you for your answer. I am using a Tecan Spark plate reader. I have only measured absorbance at 450nm and 570nm, not a range.
More
VOTE
John Schloendorn The concept of molecules "hiding in the shadows" of other molecules is stemming from ray optics - it makes no sense for wave optics and in relation to the question if Beer's law can be applied or not. For details see a recent review on the topic of the Bouguer-Beer-Lambert law: Article The Bouguer-Beer-Lambert Law: Shining Light on the Obscure
John Schloendorn The concept of molecules "hiding in the shadows" of other molecules is stemming from ray optics - it makes no sense for wave optics and in relation to the question if Beer's law can be applied or not. For details see a recent review on the topic of the Bouguer-Beer-Lambert law: Article The Bouguer-Beer-Lambert Law: Shining Light on the Obscure
More
VOTE
No. Look at the mathematical definition of absorbance, and the law of Beer and Lambert. Absorbance and transmitted light are in a logarithmic relationship that allows any value > 0.
In practice, absorbance saturates at high values, because some molecules hide in the "shadows" behind other molecules. There's no light left for them to absorb. In a typical ELISA, you'll see the linear relationship with concentration break down in the range of 1-3 ish -- depending on your molecule, path length and personal tolerance for error.
It's hard to say what's causing your problem. I guess something went wrong with your execution. Sounds like not all the enzyme got removed during the wash steps. You'll need to get your baseline signal back down into the linear range, before you can be sure about the inhibition.
No. Look at the mathematical definition of absorbance, and the law of Beer and Lambert. Absorbance and transmitted light are in a logarithmic relationship that allows any value > 0.
In practice, absorbance saturates at high values, because some molecules hide in the "shadows" behind other molecules. There's no light left for them to absorb. In a typical ELISA, you'll see the linear relationship with concentration break down in the range of 1-3 ish -- depending on your molecule, path length and personal tolerance for error.
It's hard to say what's causing your problem. I guess something went wrong with your execution. Sounds like not all the enzyme got removed during the wash steps. You'll need to get your baseline signal back down into the linear range, before you can be sure about the inhibition.
More
VOTE