Black　phosphorus　(BP)　has　attracted　much　attention　as　a　new　member　of　2D　materials　due　to　its　unique　electronic　and　optical　properties　and　a　wide　range　of　promising　applications.　Here,　for　the　first　time,　we　report　the　photoluminescence　lifetime　of　BP　nanomaterial　and　its　applications　as　an　efficient　agent　for　live　cell　imaging.　With　a　lateral　size　of　similar　to　35　nm　and　a　thickness　of　similar　to　6　nm,　the　fabricated　BP　nanoparticles　(BPNPs)　exhibited　a　unique　photoluminescent　(PL)　emission　at　similar　to　690　nm.　The　photoluminescence　lifetime　(PLT)　of　BPNPs　was　determined　to　be　110.5　ps.　Coating　a　layer　of　mesoporous　silica　on　the　surface　of　BPNPs　(BPNPs@mSiO(2))　extended　the　lifetime　to　267　ps,　suggesting　a　change　in　the　microenvironment.　The　lifetime　was　also　influenced　by　ionic　strength　and　intracellular　microenvironment,　which　implies　BPNPs　as　valuable　probes　for　sensing　variations　in　the　microenvironment.　Live　cell　imaging　was　achieved　via　directly　probing　the　photoluminescence　intensity　or　the　photoluminescence　lifetime.　Our　findings　are　significant,　implying　that　BPNPs　can　be　of　large　value　in　sensing　variations　of　the　cellular　microenvironment　and　in　probing　cells　with　distinct　cytosolic　contents.　This　research　leads　to　promising　prospects　for　BPNPs　in　multiple　biomedical　applications.