I want to do a BCA protein microplate assay but I only have a 595 nm filter, while the manufacturer states that it should not be more than 590 nm. Has anyone been successful with a 595 nm filter?
5nm difference is hardly critical unless your protein concentration is extremely low. May not even be outside the error of your instrument. Try and measure a series of protein standards and have a blank sample (preferably in triplicate), and you will see that in all likelihood its perfectly good.
See also (http://www.openbiotech.com/v/vspfiles/assets/images/manual%20-%20bca%20assay%20-%20small.pdf): "If the optimum wavelength window is not available, we have obtained sensitivities < 10 ug/ml even at wavelengths as remote as 480 to 650 nm. So under non-extreme conditions, this assay is really quite forgiving in terms of the wavelength used"
The BCA assay is supposed to be read at 562 nm. This document shows how the sensitivity is affected by using different wavelengths:
https://tools.thermofisher.com/content/sfs/brochures/TR0025-Protein-assay-spectra.pdf
The sensitivity as 595 nm is less than half that at 560 nm, but it can still be used.
I assume you are following their protocol then regarding the volume per well, if it is the same. In general 5 nm is little, what is true for one well will be same (proportional effect of 590>595 is true for all wells).
the only prob is usually this method is used 540-590. so the peak is probably far from 590, and it won't be forgiving to do at 595, might be really deteriorated signal largely affected by other conditions.
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