Hello everybody!

I'm trying to label some M13 phage particles with FITC. I checked some papers; I use 0.3- 1 M bicarbonate buffer (pH 9) as conjugation buffer. I prepare 1mg/ml stock solution of FITC in conjugation buffer and add 100 micro liters of this solution to 10^13 pfu of phages. I let the reaction to proceed for 2 hours at room temperature at dark. Then I precipitate phages through 2 rounds of NaCl/ PEG precipitation. I measure the 495nm absorbance on UV spectrometer to see if conjugation reaction has been successful, but I get very low absorbance values!

The protocol seems to be easy and simple, but I haven't got any results! By the way, the phage stock does not look much yellow after conjugation!

Any suggestion would be highly appreciated! :)