Hey Mayank, your question is a little unclear. Do you want your entire library to have a specific barcode (to distinguish it from another library) or do you want each variant to have a unique barcode? The former can be easily done just through, say, watermarking the DNA using PCR primers, the latter I cannot figure out why would you want. Presumably, the variance between library members is, in and of itself, a distinguishing feature and makes the phage "unique" from other library members.

Could you clarify what you want to do?

I want a unique surface barcode with each variant... its only theoretical question.. is it possible...?

The DNA sequence itself can serve as barcode. Can you make it clear?

I know it can serve as barcode but i want additional peptide barcode which is unique to each variant..

OK, Mayank. Wish you good luck with your plan.

You could ligate your insert with linkers that have redundant codons during the library construction.

@ Michael... can you direct me to a paper which has published such stretegy..?

Honestly, I don't know how but am curious why you want to do this? How big this barcode you want to be and how many such "unique" barcodes you can generate for each insert in your library?

krishan, I am sorry I can not tell you why, but i want just one unique peptide fused to protein displayed on phage surface.. one unique peptide for each protein displayed.. this peptide will be used to detect the phage later without the need to sequencing whole phage DNA...

Mayank, if you want to detect each of those proteins without DNA sequencing, you will need antibodies or something like that. Did you realize this problem?

yes, devraja.. I know about this.. we have the labelled antibodies...

Do you have antibodies for every combination of amino acids? Just curious.

For 10^9 clones in your phage-displayed library, you need 10^9 unique peptide barcodes for tagging every insert in your library, right? You didn't say how big you want this tag to be but assuming this barcode is 5 aa in length, you can only generate enough to cover just 0.32% of your total library. So unless this barcode is at least 7 aa in length, you cannot achieve this. If you play with permutations and combinations, keeping in mind your requirements of library size, insert length, and barcode length, you would see this more clearly. But now most important of all, as Devraraja Mudeppa rightly pointed out: how are you gonna detect and distinguish phages using these surface barcodes??? Maybe I am confused or completely wrong, so, would greatly appreciate if you could help me understand this. Thanks!

we dont need so many protein dispalyed and so many barcodes.. there is limited amount of proteins and limited barcodes with limited antibodies to detect them.. I am sorry this is all I can divulge at the moment. but i would tell you more if it works..