{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,9,3]],"date-time":"2026-09-03T00:39:52Z","timestamp":1788395992389,"version":"build-2803163510"},"reference-count":41,"publisher":"American Scientific Publishers","issue":"11","content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["j biomed nanotechnol"],"published-print":{"date-parts":[[2021,11,1]]},"abstract":"<jats:p>Hypoxia is an important phenomenon due to insufficient oxygen supply in tumor tissue, and nitroreductase (NTR) is a characteristic enzyme used for evaluating hypoxia level in tumors. In this work, we designed a smart gold nanoparticle (AuNPs), modified by 16-mercaptoundecanoic acid\n (MHDA) and hypoxia-responsive 11-(2-nitro-1H-imidazol-1-yl)undecane-1-thiol (NI) ligand, that responds to the hypoxic environment in tumor sites. With proper surface ligand composition, the responsive nanoprobe exhibited aggregation through the bioreduction of the nitro group on NI ligands\n under hypoxic conditions and the UV-vis absorption peak maximum would shift to 630 nm from 530 nm, which acts as an \u201coff\u2013on\u201d contrast agent for tumor hypoxic photoacoustic (PA) imaging. <jats:italic>In vitro<\/jats:italic> and <jats:italic>in vivo<\/jats:italic> experiments revealed that AuNPs@MHDA\/NO<jats:sub>2<\/jats:sub>\n exhibited an enhanced PA signal in hypoxic conditions. This study demonstrates the potential of hypoxia-responsive AuNPs as novel and sensitive diagnostic agents, which lays a firm foundation for precise cancer treatment in the future.<\/jats:p>","DOI":"10.1166\/jbn.2021.3195","type":"journal-article","created":{"date-parts":[[2021,12,15]],"date-time":"2021-12-15T04:31:17Z","timestamp":1639542677000},"page":"2186-2197","source":"Crossref","is-referenced-by-count":3,"title":["Nitroreductase-Induced Aggregation of Gold Nanoparticles for \u201cOff\u2013On\u201d Photoacoustic Imaging of Tumor Hypoxia"],"prefix":"10.1166","volume":"17","author":[{"given":"Xin","family":"Li","sequence":"first","affiliation":[{"name":"Department of Applied Biology and Chemical Technology, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Xueyang","family":"Fang","sequence":"additional","affiliation":[{"name":"Department of Applied Biology and Chemical Technology, The Hong 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