Imine-linked covalent organic framework with high crystallinity for constructing sensitive purine bases electrochemical sensor.

In this work, a covalent organic framework (TADM-COF) with high crystallinity and large specific surface area (2597 m2 g-1) has been successfully synthesized using 1,3,5-(4-aminophenyl) benzene (TAPB) and 2,5-dimethoxy-p-phenyldiformaldehyde (DMTP). The COF was grown in situ on oxide particles to form core-shell nanocomposites (SiO2@TADM COF, Fe3O4@TADM COF and Co3O4@TADM COF) to realize its function as a shell material. Among them, the Co3O4@TADM COF with the highest electrochemical response to purine bases was further cross-linked with multi-walled carbon nanotubes (MWCNT) to construct a novel electrochemical sensor (Co3O4@TADM COF/MWCNT/GCE) for detection of purine bases. In this nanocomposite, Co3O4 possesses rich catalytic active sites, MWCNT ensures superior electrical conductivity and COF provides a stable environment for electrocatalytic reactions as the shell. At the same time, regular pore structure of the COFs also offers smooth channels for the transfer of analytes to the catalytic site. The synergistic effect among the three components showed remarkable sensing performance for the simultaneous detection of guanine (G) and adenine (A) with a wide linear range of 0.6-180 µM and low limits of detection (LODs) of 0.020 µM for G and 0.024 µM for A (S/N = 3), respectively. The developed sensor platform was also successfully applied in the detection of purine bases in thermally denatured herring DNA extract. The work provided a general strategy for amplifying signal of COF and its composite in the electrochemical sensing.

Highly crystalline polyimide covalent organic framework as electrochemical sensing platform for the ultrasensitive detection of purine bases in DNA.

It is of great significance to propose simple methods to detect DNA bases sensitively for biological analysis and medical diagnosis. Herein, a highly crystalline polyimide covalent organic framework (TAPM-COF) has been successfully synthesized via a solvothermal route using pyromellitic dianhydride (PMDA) and tris(4-aminophenyl) amine (TAPA), which possessed large specific surface area (2286 m2 g-1) and excellent thermal stability. Intriguingly, the crystallinity of the TAPM-COF improved significantly with the increase of water content in the reaction medium. To verify this phenomenon, we synthesized TPPM-COF with two pores by pyromellitic dianhydride (PMDA) and N,N,N',N'-tetrakis(4-aminophenyl)-1,4-benzenediamine (TPDA), which bonding was similar to TAPM-COF. Furthermore, the prepared TAPM-COF-0.3 was used to construct a novel and independent electrochemical biosensor on glassy carbon electrode for simultaneously determination of adenine (A) and guanine (G) without other additives. However, to further improve signal of TAPM-COF in electrochemical sensing, the crystalline TAPM-COF-0.3 can be readily integrated with amino-functionalized multiwalled carbon nanotubes (NH2-MWCNT) to form core-shell TAPM-COF-0.3@NH2-MWCNT driven by a π-π stacking interaction for more sensitive electrochemical sensing toward purine bases. In comparison to TAPM-COF/GCE, the TAPM-COF@NH2-MWCNT/GCE exhibited more favorable linear range and lower limit of detection. The work provided a new strategy for amplifying signal of COF in the field of electrochemical sensors.

Eu3+-Modified Covalent Organic Frameworks for the Detection of a Vinyl Chloride Monomer Exposure Biomarker.

The vinyl chloride monomer (VCM), a common raw material in the plastics industry, is one of the environmental pollutants to which humans are mostly exposed. Thiodiglycolic acid (TDGA) in human urine is a specific biomarker of its exposure. TDGA plays an important role in understanding the relationships between exposure to the VCM and the identification of subgroups that are at increased risk for disease diagnosis. Therefore, its detection is of great significance. Here, we designed and established a ratiometric fluorescent sensor for TDGA by using Eu3+ as a bridge connecting the covalent organic framework (COF) and the energy donor molecule 2,6-dipicolinic acid (DPA) and named it DPA/Eu@PY-DHPB-COF-COOH. The sensor not only possesses the advantages of a ratiometric fluorescent sensor that can provide built-in self-calibration to correct a variety of target-independent factors but also presents high selectivity and high sensitivity. Currently, there are only a few reports on the detection of TDGA, and to the extent of our knowledge, this report is the first work on the detection of TDGA based on a COF system; so, it has an important reference value and lays a solid foundation for designing advanced sensors of TDGA.

A novel electrochemical sensing platform based on double-active-center polyimide covalent organic frameworks for sensitive analysis of levofloxacin.

The development of a simple and sensitive electrochemical sensing platform for levofloxacin (LVF) analysis is of great significance to human health. In this work, a covalent organic framework (TP-COF) was in situ grown on the surface of Sn-MoC nanospheres with nanoflower-like morphology through a one-pot method to obtain the TP-COF@Sn-MoC composite. The prepared composite was used to modify a glassy carbon electrode (GCE) to realize the sensitive detection of levofloxacin. TP-COF was formed by polycondensation of 2,4,6-tris(4-aminophenyl)-1,3,5-triazine (TAPT) and pyromellitic dianhydride (PMDA), in which C = O and C = N groups served as double active centers for the recognition and electrocatalytic oxidation of the target molecule. Meanwhile, the introduction of Sn-MoC improved the conductivity of the electrode. The TP-COF@Sn-MoC composite produced a strong synergistic effect and showed a high electrocatalytic ability toward levofloxacin oxidation. The linear range of LVF was 0.6-1000 µM and the limit of detection (LOD) was 0.029 µM (S/N = 3). In addition, the sensor has been successfully applied for the analysis of LVF in human urine and blood serum samples with acceptable recovery rates, demonstrating that the sensor was promising in practical applications.