Disclosed are peptides that contain up to about 35 amino acids, including a plurality of aromatic amino acid residues and either (i) an amino acid residue that is phosphorylated or sulfated, or (ii) an amino acid comprising an ester-moiety linked via peptide bond, or both (i) and (ii), wherein the peptide is capable of self-assembly to form nanofibrils in the presence of an enzyme that hydrolyzes the phosphate group, the sulfate group, or the ester-moiety. These peptides are enzymatically responsive hydrogelators, and they can be used to form pericellular hydrogels/nanofibrils upon exposure to target cells that secrete or express a surface bound ectoenzyme having hydrolase activity suitable to induce peptide gelation. These materials, and compositions containing the same, can be used for in vitro and in vivo cellular imaging, treating cancerous conditions, collecting a secretome from a cell upon which the pericellular hydrogels/nanofibrils form, and screening the collected secretome.
