A new covalent organic framework (COF) has been prepared with 1,3,6,8-tetra(4-formyl phenyl) pyrene (TFPPy) and 2,6-diaminopyridine (DP) as building units through a Schiff base reaction by a simple tube oven heating procedure and the structure of the COF has been characterized in detail. The obtained DP-Py COF is employed to fabricate a novel electrochemical sensing platform for sensitive and selective determination of theophylline (TP) and caffeine (CAF) simultaneously through compounding with AuNPs; the peak positions of TP and CAF are 0.95 V and 1.28 V, respectively. The synergistic effect between DP-Py COF and AuNPs effectively enhances the analytical sensitivity for the target analytes. Under the optimized experimental conditions, the electrochemical sensing platform shows a sensitive voltammetric response and wide linear range to both TP and CAF, and the detection limits are 0.19 μM and 0.076 μM (S/N = 3), respectively. This method has been successfully used for the determination of TP and CAF in compound paracetamol capsules and black tea samples. The recovery and relative standard deviations (RSD) of TP are 99.3~101% and 97.6~101% and 1.3~2.0% and 1.3~2.1%, respectively, and the recovery and RSD of CAF are 96.1~102% and 99.4~104% and 2.8~3.9% and 1.7~3.2%, respectively. Compared with traditional detection methods, the constructed sensing platform has better performance and is expected to be widely used also in other real sample analyses.
Keywords: Caffeine; Covalent organic frameworks (COFs); Differential pulse voltammetry; Electrochemical sensors; Gold nanoparticles; Theophylline.