Labrafac®WL1349, Phospholipon90 H and Kolliphor®HS15 were obtained from Shanghai Macklin Biochemical Technology Ltd (Shanghai, China). 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-(folate(polyethylene glycol)2000) (DSPE-PEG2000-FA) was obtained from Chongqing Yusi Pharmaceutical Technology Ltd (Chongqing, China). The exenatide kit was obtained from Hangzhou Qiyu Biotechnology Ltd (Zhejiang, China). Fetal bovine serum and Dulbecco’s Modified Eagle Medium were obtained from Wuhan Punosai Life Sciences Ltd (Hubei, China). Db/db type II diabetic mice and Sprague–Dawley (SD) rats were obtained from Jiangsu Jizui Pharmaceutical Biotechnology Co Ltd (Jiangsu, China). 1,1′-Dioctadecyl-3,3,3′,3′-Tetramethylindodicarbocyanine,4-Chlorobenzenesulfonate Salt (DID) was obtained from Biyuntian Biotechnology Ltd (Shanghai, China).