The present invention provides a vector construct comprising the following components: (i) a sequence encoding a signal peptide which directs proteins into the Tat secretory pathway; and (ii) a sequence encoding a fluorophore fused to a sequence encoding a pVIII phage coat protein. Nucleic acid molecules comprising components (i) and (ii) are also provided, together with phage particles comprising such vectors or nucleic acid molecules and expressing a fluorophore-pVIII fusion protein on the surface. Methods for producing such fluorescent phage particles are also provided.