UAS regulatory sequences and a minimal Hsp70 promoter (derived from the pUASTLOTattB vector) are fused upstream of a fusion protein that encodes an apically enriched nanobody-based GFP trap for extracellular proteins. The fusion protein contains the T48 coding sequence with the GFP-binding VHH(GFP4) nanobody inserted near the N-terminal end. In addition, an mCherry fluorescent tag followed by the minimal apical localization sequence of baz are present at the C-terminal end of the T48 coding sequence. The VHH(GFP4) nanobody faces the extracellular space. (Generated by P1cre-mediated excision of the lexAop regulatory sequences present in T48^{lexAop.UAS.GrabFP.A.Ext.mCherry}).