Combating　biofilm　infections　remains　a　challenge　due　to　the　shield　and　acidic　conditions.　Herein,　an　acid-responsive　nanoporphyrin　(PN3-NP)　based　on　the　self-assembly　of　a　water-soluble　porphyrin　derivative　(PN3)　is　constructed.　Additional　kinetic　control　sites　formed　by　the　conjugation　of　the　spermine　molecules　to　a　porphyrin　macrocycle　make　PN3　self-assemble　into　stable　nanoparticles　(PN3-NP)　in　the　physiological　environment.　Noteworthily,　near-infrared　(NIR)　fluorescence　monitoring　and　synergistic　photodynamic　therapy　(PDT)　and　photothermal　therapy　(PTT)　effects　of　PN3-NP　can　be　triggered　by　the　acidity　in　biofilms,　accompanied　by　intelligent　transformation　into　dot-like　nanospheres.　Thus,　damage　to　normal　tissue　is　effectively　avoided　and　accurate　diagnosis　and　treatment　of　biofilms　is　achieved　successfully.　The　good　results　of　fluorescence　imaging-guided　photo-ablation　of　antibiotic-resistant　strains　methicillin-resistant　Staphylococcus　aureus　(MRSA)　biofilms　verify　that　PN3-NP　is　a　promising　alternative　to　antibiotics.　Meanwhile,　this　strategy　also　opens　new　horizons　to　engineer　smart　nano-photosensitizer　for　accurate　diagnosis　and　treatment　of　biofilms.　©　2022　Wiley-VCH　GmbH.