Fluorescent Au nanoclusters (NCs) have been the subject of intense studies owing to their increasing applications in imaging, sensing, and nanomedicine. Herein, highly fluorescent bovine serum albumin (BSA)-directed Au–BSA NCs are synthesized as a platform for further conjugation with human antistaphylococcal immunoglobulin (antiSAIgG) and the photodynamic (PD) synthesizer PhotosensTM (PS) to fabricate Au–BSA–antiSAIgG–PS complexes. The complexes possess three theranostic modalities: biospecific detection of Staphylococcus aureus bacteria, intense red fluorescence due to Au–BSA NCs (quantum yield, ~14%), and synergistic PD inactivation due to the PS dye. Owing to biospecific targeting and intense red fluorescence, the Au–BSA–antiSAIgG probe can detect pathogenic bacteria in bacterial mixtures through fluorescent microscopy or even through naked eye inspection of sediments under UV illumination. The developed complexes can be used at physiological pH of ~7, in contrast to nonspecific electrostatic binding of Au–human serum albumin NCs to S. aureus at pH <5–6. PD treatment of methicillin-sensitive and methicillin-resistant S. aureus with Au–BSA–antiSAIgG–PS complexes and 660 nm light irradiation significantly inactivates both types of bacteria. By using the developed strategy, Au–BSA–PS complexes can be further modified with other targeting and chemotherapeutic molecules, thus ensuring new theranostic applications in current nanomedicine.