Intrarenal pH‐Responsive Self‐Assembly of Luminescent Gold Nanoparticles for Diagnosis of Early Kidney Injury

Metabolic acidosis‐induced kidney injury (MAKI) is asymptomatic and lack of clinical biomarkers in early stage, but rapidly progresses to severe renal fibrosis and ultimately results in end‐stage kidney failure. Therefore, developing rapid and noninvasive strategies direct responsive to renal tubular acidic microenvironment rather than delayed biomarkers are essential for timely renoprotective interventions. Herein, we develop pH‐responsive luminescent gold nanoparticles (p‐AuNPs) in the second near‐infrared emission co‐coated with 2,3‐dimethylaleic anhydride conjugated β‐mercaptoethylamine and cationic 2‐diethylaminoethanethiol hydrochloride, which showed sensitive pH‐induced charge reversal and intrarenal self‐assembly for highly sensitive and long‐time (~24 h) imaging of different stages of MAKI. By integrating advantages of pH‐induced intrarenal self‐assembly and enhanced interactions between pH‐triggered positively charged p‐AuNPs and renal tubular cells, the early‐ and late‐stage MAKI could be differentiated rapidly within 10 min post‐injection (p.i.) with contrast index (CI) of 3.5 and 4.3, respectively. The corresponding maximum CI could reach 5.1 and 9.2 at 12 h p.i., respectively. Furthermore, p‐AuNPs were demonstrated to effectively real‐time monitor progressive recovery of kidney injury in MAKI mice after therapy, and also exhibit outstanding capabilities for drug screening. This pH‐responsive strategy showed great promise for feedback on kidney dysfunction progression, opening new possibilities for early‐stage diagnosis of pH‐related diseases.