Adalimumab

adalimumab (Humira, 40 mg/0.8 ml) was purchased from the manufacturer(Vetter Pharma-Fertigung GmbH & Co. KG, Germany), and etanercept (Enbrel, 25 mg) was purchased and used as received from the provider (P zer, New York, NY, USA). Recombinant human TNF-α (Peprotech) was used to capture the adalimumab or etanercept by being immobilized on the solid phase surface of ninety-six-well plates (Greiner, Germany). A 5% solution of nonfat dried milk (Dingguo Changsheng Biotechnology, China) was dissolved in phosphate-buffered saline (PBS) (Dingguo Changsheng Biotechnology) for sealing the solid phase surface of each well. 0.5% Tween-20 (Damao Chemical Reagent Factory, China) was added into PBS to prepare a wash solution. Horseradish peroxidase (HRP)-goat anti-human IgG (H+L) conjugate (ABclonal Technology, Woburn, MA, USA) was used for detecting adalimumab or etanercept. Tetramethyl benzidine (TMB) (Solarbio, China) was used as the substrate solution, and 2 mol/L hydrogen chloride (Sinopharm Chemical Reagent, China) were prepared in the laboratory to be used as a stop solution.