OD means optical density, i.e you are shining a beam of light through the sample and working out how much light reaches the detector and how much light has been absorbed or reflected by the sample. this if often used to measure density of bacterial culture - once a certain amount of light is filtered out you know the population is dense enough.

Colorimitry is similar to OD but uses specific colours: So for example, in an ELISA using TMB, you are measuring how much light is absorbed at 450nm rather than the whole spectrum of light.

Chemiluminescence is slightly different, instead of forming a reaction product which changes colour (such as with TMB) the reaction product generates light (When broken down the name chemiluminescence literally means the production of light from a chemical reaction). So the reaction product is produced in an excited state, when it drops down to a ground state it gives off a photon of light which can be quantified.

So in summary using TMB you have absorbance (which is kind of like a specialised OD) - you shine 450nm through a sample and measure how much light is filtered out where as using Femto you get generation of light from the sample itself which you measure.

Chemiluminescence for elisa is more sensitive than using TMB as long as you are using an enhanced Femto product such as supersignal. I would say though that for most applications Femto is not necessary, TMB is substantially cheaper (like ~100 times) and is almost always fine for ELISA. Occasionally supersignal femto is needed for dotblots or western blots instead of a colorimetric substrate.

OD means optical density, i.e you are shining a beam of light through the sample and working out how much light reaches the detector and how much light has been absorbed or reflected by the sample. this if often used to measure density of bacterial culture - once a certain amount of light is filtered out you know the population is dense enough.

Colorimitry is similar to OD but uses specific colours: So for example, in an ELISA using TMB, you are measuring how much light is absorbed at 450nm rather than the whole spectrum of light.

Chemiluminescence is slightly different, instead of forming a reaction product which changes colour (such as with TMB) the reaction product generates light (When broken down the name chemiluminescence literally means the production of light from a chemical reaction). So the reaction product is produced in an excited state, when it drops down to a ground state it gives off a photon of light which can be quantified.

So in summary using TMB you have absorbance (which is kind of like a specialised OD) - you shine 450nm through a sample and measure how much light is filtered out where as using Femto you get generation of light from the sample itself which you measure.

Chemiluminescence for elisa is more sensitive than using TMB as long as you are using an enhanced Femto product such as supersignal. I would say though that for most applications Femto is not necessary, TMB is substantially cheaper (like ~100 times) and is almost always fine for ELISA. Occasionally supersignal femto is needed for dotblots or western blots instead of a colorimetric substrate.

"how much light has been absorbed or reflected by the sample" right how much is absorbed and scattered for estimating bacterial OD.

Okay I have a unusually question here after adding stop solution from blue it changes to yellow and yellow falls in 570–590 nm range and due to this they choose 450nm?

Colorimitry uses specific colours? can u explain it with a very basic example say I have orange or blue what wavelength they absorb how do I find that?

450nm for eg is in visible range why does yellow absorb more at 450nm doesn't make sense?

"you shine 450nm through a sample and measure how much light is filtered out" filtered?

Chemiluminescence generates visible light and we quantify the visible light?

and off note what is min and max concentration that an ELISA can detect?

You are talking about 2 different things, absorbance and emmison or transmission.

The colour yellow is in the 570-590nm range, this means that the light you see (reaches your eyes) is in that range, i.e the light which is not absorbed. If the light was absorbed at 570-590nm you wouldn't see that colour as none of that light would reach your eyes.

TMB which has had the stop solution added absorbs the most light at 450nm, that is the peak of its absorbance spectra which is why 450nm is used for measurement.

Yes, in a chemiluminescence assay you measure the light emitted, this may be in the visible range or it may be outside the visible range, it depends entirely on the assay you are doing.

So in a chemiluminsecence assay the sample produces its own light and you measure how much has been emitted. In an absorbance assay you shine a light on the sample and measure how much light the sample has absorbed.

I can't really tell you what the min and max concentrations that an ELISA can detect are, this depends on many factors, such as your antigen, your antibody quality and the level of background fluorescence in your sample. These will be different for each experiment.

Your plate reader will have an upper detection limit which dictates the maximum signal it can read. So for example if most plate reader can read a maximum absorbance of 2 (which means 1% of the light is transmitted and 99% is absorbed) but this depends entirely on your equipment.

"So in a chemiluminsecence assay the sample produces its own light and you measure how much has been emitted"

In western blot "Depending on the system, the luminescence can last for 3 days, permitting multiple exposures of the same blot."

what does it mean luminescence can last for 3 days?