VHH(LaG-3) is a single-domain antibody fragment that binds GFP with a Kd of 25nM. It also binds the GFP derivatives CFP, BFP and YFP. VHH(LaG-3) corresponds to the antigen-binding variable domain (VHH domain) of a heavy chain antibody originally isolated from a llama (Lama glama) immunized with purified GFP protein (PMID:25362362).