A dual-functional module cellular electrochemical sensing platform for simultaneous detection guanine and xanthine

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.

A ratiometric SERS sensor with one signal probe for ultrasensitive and quantitative monitoring of serum xanthine

Xanthine can be converted into uric acid, and a high concentration of xanthine in the human body can cause many diseases. Therefore, it is important to develop a sensitive, simple, and reliable approach for measuring xanthine in biological liquids. Hence, a ratiometric surface-enhanced Raman spectroscopy (SERS) sensing strategy with one signal probe was exploited for reliable, sensitive, and quantitative monitoring of serum xanthine. 3-Mercaptophenylboronic acid (3-MPBA) was used as a typical reference with a Raman peak at 996 cm-1. First, 3-MPBA was bound to gold nanoflowers@silica (GNFs@Si) through Au-S bonds. Xanthine oxidase (XOD) catalyzed the oxidation of xanthine into H2O2 on GNFs@Si. Afterward, the obtained H2O2 further reduced 3-MPBA to 3-hydroxythiophenol (3-HTP) accompanied by the emergence of a new Raman peak at 883 cm-1. Meanwhile, the Raman intensity at 996 cm-1 remained constant. Therefore, the ratio of I883/I996 increased with the increasing of xanthine concentration, thus realizing quantitative detection of xanthine. As a result, a ratiometric SERS sensor for the detection of xanthine was proposed with a detection limit of 5.7 nM for xanthine. The novel ratiometric SERS sensor provides a new direction for analyzing other biomolecules with high sensitivity and reliability.