A highly sensitive colorimetric sensor for Hg2+ detection based on the oxidative enzyme mimics-like activity of hierarchical porous carbon@chitosan-modified silver nanoparticles

In this paper, DMC was prepared via carbonization in nitrogen with plexiglass as the template and sucrose as the carbon source. The hierarchical porous carbon (DHPC) was prepared by treating DMC with potassium hydroxide. The DHPC was loaded on chitosan to prepare DHPC@CS, which was then doped into nanosilver via the one-pot process to prepare DHPC@CS-AgNPs. The morphology of DHPC@CS-AgNPs was characterized using the Scanning Electron Microscope (SEM) and the Transmission Electron Microscope (TEM). In the presence of Hg 2+ , DHPC@CS-AgNPs will catalyze the oxidation of TMB, resulting in an observable change of color, so a rapid, sensitive and highly selective method could be established to detect trace Hg 2+ colorimetric sensors. The conditions of the TMB color reaction, characteristics of the Hg 2+ -DHPC@CS-AgNPs oxidized enzyme mimics and their color reaction characteristics were studied. Under the optimized conditions, coloration could not be catalyzed in the DHPC@CS-AgNPs-TMB system, but with the addition of the mercury ions, the catalytic activity was enhanced and the oxidized enzyme mimic activity was observed. In the Hg 2+ -DHPC@CS-AgNPs-TMB system, when TMB was used as a substrate, K m  = 0.0165 mM, and V max  = 4.6512 × 10 −8  M·s −1 . Under the optimized conditions, the linear range of mercury ion was determined to be 1 × 10 −8 –1 × 10 −6  mol·L −1 using the above method, the linear relationship was r = 0.99753, the detection limit (S/N = 3) was 7 × 10 −9  mol·L −1 , and the recoveries of spiked water sample and fish sample ranged from 84.4% to 103%.