In this work, we have fabricated a nanocapsule by using polystyrene sulfonate (PSS) to encapsulate AuNPs/HRP bioconjugate. As a proof-of-concept, the labeling capability of this nanocapsule was tested via ELISA by conjugating to anti-L. monocytogenes antibody for an actual bacteria L. monocytogenes detection. The preliminary result based on plate-trapped antigen ELISA showed that this AuNPs/HRP/PSS nanocapsule labeled Ab was capable of detecting L. monocytogenes with four times higher sensitivity and faster assay time than a typical HRP labeled Ab. Further experiment was carried out in sandwich ELISA and found that this AuNPs/HRP/PSS nanocapsule labeled Ab was 30-time more sensitive than the conventional HRP labeled Ab. The obtained results prove that a greater detection signal could be achieved through a simple enzyme encapsulation using LBL deposition technique. This encapsulation strategy will be useful for signal amplification for immunoassays as well as other detection platforms such as electrochemistry and array applications that require high sensitivity.