A Flexible Platform of Electrochemically Functionalized Carbon Nanotubes for NADH Sensors

Electrochemical Sensors Based on the Electropolymerized Natural Phenolic Antioxidants and Their Analytical Application

The design and fabrication of novel electrochemical sensors with high analytical and operational characteristics are one of the sustainable trends in modern analytical chemistry. Polymeric film formation by the electropolymerization of suitable monomers is one of the methods of sensors fabrication. Among a wide range of the substances able to polymerize, the phenolic ones are of theoretical and practical interest. The attention is focused on the sensors based on the electropolymerized natural phenolic antioxidants and their analytical application. The typical electropolymerization reaction schemes are discussed. Phenol electropolymerization leads to insulating coverage formation. Therefore, a combination of electropolymerized natural phenolic antioxidants and carbon nanomaterials as modifiers is of special interest. Carbon nanomaterials provide conductivity and a high working surface area of the electrode, while the polymeric film properties affect the selectivity and sensitivity of the sensor response for the target analyte or the group of structurally related compounds. The possibility of guided changes in the electrochemical response for the improvement of target compounds' analytical characteristics has appeared. The analytical capabilities of sensors based on electropolymerized natural phenolic antioxidants and their future development in this field are discussed.

Xurography-Enabled Thermally Transferred Carbon Nanomaterial-Based Electrochemical Sensors on Polyethylene Terephthalate-Ethylene Vinyl Acetate Films

A novel benchtop approach to fabricate xurography-enabled thermally transferred (XTT) carbon nanomaterial-based electrochemical sensors is proposed. Filtered nanomaterial (NM) films were transferred from Teflon filters to polyethylene terephthalate-ethylene vinyl acetate (PET-EVA) substrates by a temperature-driven approach. Customized PET-EVA components were xurographically patterned by a cutting plotter. The smart design of PET-EVA films enabled us to selectively transfer the nanomaterial to the exposed EVA side of the substrate. Hence, the substrate played an active role in selectively controlling where nanomaterial transfer occurred allowing us to design different working electrode geometries. Counter and reference electrodes were integrated by a stencil-printing approach, and the whole device was assembled by thermal lamination. To prove the versatility of the technology, XTT materials were exclusively made of carbon black (XTT-CB), multiwalled carbon nanotubes (XTT-MWCNTs), and single-walled carbon nanotubes (XTT-SWCNTs). Their electrochemical behavior was carefully studied and was found to be highly dependent on the amount and type of NM employed. XTT-SWCNTs were demonstrated to be the best-performing sensors, and they were employed for the determination of l-tyrosine (l-Tyr) in human plasma from tyrosinemia-diagnosed patients. High analytical performance toward l-Tyr (linear range of 0.5-100 μM, LOD = 0.1 μM), interelectrode precision (RSD i_p,a = 3%, n = 10; RSD calibration slope = 4%, n = 3), and accurate l-Tyr quantification in plasma samples with low relative errors (≤7%) compared to the clinical declared values were obtained. The proposed benchtop approach is cost-effective and straightforward, does not require sophisticated facilities, and can be potentially employed to develop pure or hybrid nanomaterial-based electrodes.

A water-soluble boronic acid sensor for caffeic acid based on double sites recognition

Due to reversibly and covalently binding with Lewis bases and polyols, boronic acid compounds as fluorescent sensors have been widely reported to recognize carbohydrates, ions, hydrogen peroxide, and so on. However, boronic acid sensors for highly selective recognition of caffeic acid rather than catechol or catechol derivatives have not been reported yet. Herein a novel water-soluble sensor 5c with double recognition sites based on a boronic acid was reported. When 2.3 × 10-4 M of caffeic acid was added, the fluorescence intensity of sensor 5c decreased by 99.6% via inner filter effect (IFE) because its excitation spectrum well overlaps with the absorption spectrum of caffeic acid under neutral condition, while the fluorescence increased or did not change obviously after binding with other analytes including carbohydrates and other catechol derivatives. In addition, the response time to caffeic acid is fast at room temperature, and a high binding constant (9245.7 ± 348.3 M-1) and low LOD (1.81 × 10-6 M) was calculated. Moreover, determination of caffeic acid content in caffeic acid tablets was studied, and the recovery rate is sufficient. Therefore, sensor 5c can be used as a potential tool for detecting biologically significant caffeic acid in real samples.