Flow count radiation detector

Radiolabeling was performed referring to the method of Zhao et al.^{22 (link)} In brief, 10 µL NaOH (0.15 M) was added to the PNA solution (1.7 nmol, 20 μL) and mixed. Subsequently, 200 µL (148-185 MBq) fresh [^99mTc]-pertechnetate and 10 µL SnCl₂·2H₂O (1 mg/mL, 0.01 M HCl) were added immediately in sequence. The mixture was then reacted for 45 minutes at 37°C. At the end of reaction, phosphate-buffered saline (PBS, pH 7.0, 1 ×) was added for dilution, and the final pH was approximately 7.0. Afterward, the reaction mixture was subjected to high-performance liquid chromatography (HPLC) for analysis using a 4.6 × 250 mm Ultimate XB-C18 column (Welch Materials, Inc, Shanghai, China). High-performance liquid chromatography was performed on LC-20AT (Shimadzu Corporation, Tokyo, Japan) equipped with a SPD-20A UV/VIS detector and a flow count radiation detector (Bioscan, Washington, DC). The column was eluted at a flow rate of 1 mL/min at 25°C with a gradient of 5% to 90% MeCN/H₂O with 0.1% trifluoroacetic acid for 20 minutes monitoring at 260 nm.