Construction And Applications Of Electrochemical Sensors Based On Functionalized Single-Atom Nanozymes

Single-atom nanozymes（SANs）,derived from single-atom catalysts（SACs）,have drawn tremendous attention due to homogeneous active sites,high catalytic selectivity,and the proximity of full atom utilization,which can make up for the shortcomings of poor stability and high cost of biological enzymes and can also overcome the problems of low activity density and complex structure of traditional nanozymes.Therefore,single-atom nanozymes have promising applications in the field of electrochemical sensors.Phenolic substances are an important chemical raw material and are widely used in many industries,such as the petroleum industry,pharmaceutical synthesis,and pesticide preparation.Most phenolic substances are highly toxic and are not easily degradable and soluble in water,posing a great danger to the ecological environment,human life,and health.Other phenolic substances,such as chlorogenic acid,are widely found in some traditional Chinese pharmaceuticals.Clinical studies revealed that the consumption of chlorogenic acid could lower blood glucose levels as well as fight against hypertension.However,excessive intake of chlorogenic acid will lead to more severe diseases.Therefore,designing an electrochemical sensor with high sensitivity and good selectivity is necessary for real-time trace detection of phenolics.In this paper,MOF-derived porous carbon was used as carbon support to synthesize high-density single-atom nanozymes to construct electrochemical sensors for real-time trace detection of phenolics.Part one:Simultaneous detection of catechol and hydroquinone by a novel electrochemical sensor based on cobalt single-atom nanozymesWe constructed an electrochemical sensor for cobalt-based single-atom nanozymes（Co-Ac NC-3）based on MOF-derived porous carbon:Co-Ac NC-3/GCE and applied it for ultra-sensitive detection of catechol and hydroquinone simultaneously.Firstly,ZIF-8 was synthesized at room temperature,and the product was activated with KOH after high-temperature carbonization,and then the cobalt atom was anchored by a cascade anchoring strategy to obtain the single-atom nanozyme Co-Ac NC-3.The successful preparation of single atoms was demonstrated by scanning electron microscopy（SEM）,transmission electron microscopy（TEM）,High-angle annular dark-field scanning transmission electron microscopy（HAADF-STEM）,X-ray diffraction（XRD）,Fourier Transform infrared spectroscopy（FT-IR）and X-ray photoelectron spectroscopy（XPS）.Activated MOF-derived porous carbon can increase the surface area and porosity and the number of oxygen-containing functional groups,thereby achieving high-density single-atom loading.The obtained sensor illustrated a wide linear range of catechol and hydroquinone was 4×10^-6-3×10^-4 M,and the detection limits were 7.2×10^-8 M and 3.4×10^-8 M,respectively.Part two:Novel electrochemical sensors based on iron single-atom nanozymes for sensitive detection of chlorogenic acidsWe designed an electrochemical sensor based on MOF-derived porous carbon-based iron-based single-atom nanozyme（Fe-KAC）for sensitive detection of chlorogenic acid.ZIF-8 was impregnated with KOH followed by high-temperature carbonization,and the resulting porous carbon was used as a carrier loaded with single iron atoms to obtain Fe-KAC nanozymes.The materials were characterized by SEM,TEM,XRD,FT-IR and XPS technical means,which demonstrated the successful loading of single atoms.The one-step activation method was superior to the two-step method of carbonization followed by activation,and the constructed porous carbon carrier has superior properties for better loading of single iron atoms.Fe-KAC/GCE demonstrated a wide linear range of 4×10^-8-1×10^-4 M,with a low detection limit of 1.3×10^-8 M to chlorogenic acid.Both electrochemical sensors based on single-atom nanozymes in this work have wide detection ranges and low detection limits.They are highly resistant to interference,stable and reproducible,which have been verified to be applied to the practical detection of phenols,providing technical support for the real-time trace detection of phenols.