1. To prepare the AuNP (gold nanoparticle) conjugate, the recombinant protein dissolved in PBS (1 mg/mL) was added to the mixture of 1mL AuNP colloid (40nm in diameter, OD=1) and 0.1mL of borate buffer (0.1 M, pH 8.5). Incubation for 30 min at room temperature.

2. 0.1mL of 10mg/mL BSA in PBS was added to the solution to block the AuNP surface. Incubation for 15-30 min at room temperature.

3. The mixture was centrifuged at 10,000rpm and 4℃ for 20-30 min. The supernatant was discarded, and 1mL of 1mg/mL BSA in PBS was added to the AuNP conjugate to be re- suspended.

4. The centrifugation and suspension process were repeated twice, and the final suspension solution was PBS.