Synthesis of [99mTc]Tc-HYNIC-FAPI Radiotracer

The HYNIC-FAPI probe was chemically modified and synthesized from Nanchang Tanzhen Biotechnologies Co., Ltd. (Jiangxi, China). The purity of HYNIC-FAPI was 98%, and the structure of the product was identified by MS (Fig. 1). ^99mTc is obtained from the ⁹⁹Mo-^99mTc generator supplied by China Atomic Energy Research Institute (Beijing, China). 10 mg tricine (Tricine buffer, free acid) and 20 mg TPPTS (Tris(3-sulfonatophenyl) phosphine, sodium salt) dissolved in 5 ml saline (95%), then 50 μl HYNIC‑FAPI (1 μg/μl), 50 μl ^99mT (185 MBq) and 25 μl fresh SnCl₂·2H₂O(1 mg/ml in 0.2 M HCL) were added into 200 μl mixture above in turn. All the reagents were mixed and heated at 100 °C for 30 min to synthesize [^99mTc]Tc-HYNIC-FAPI.