Sujittra Poorahong

A highly stable flow-injection amperometric sensor for dexamethasone (DEX) was developed using a pencil graphite electrode (PGE) modified with Fe-based metal organic frameworks, MIL-100(Fe) and graphene oxide composite materials (MIL-100(Fe)/GO). Scanning electron microscopy and energy-dispersive X-ray spectroscopy, transmission electron microscopy, powder X-ray diffraction, and Fourier-transform infrared spectroscopy were used to characterize the MIL-100(Fe) composites. The MIL-100(Fe)/GO-modified PGE (denoted MIL-100(Fe)/GO/PGE) was further electrochemically characterized using cyclic voltammetry. As an electrode material, MIL-100(Fe) is a sensing element that undergoes oxidation from Fe(II)-MOF to Fe(III)-MOF, and GO possesses high conductivity and a large surface area, which exhibits high absorbability. In the presence of DEX, Fe(III) is reduced, which accelerates electron transfer at the electrode interface. Therefore, DEX can be quantitatively detected by analyzing the anodic current of MIL-100(Fe). When coupled with amperometric flow injection analysis, excellent performance can be obtained even when a low detection potential is applied (+0.10 V vs. Ag/AgCl). The concentration was linear in the range 0.10–5.0 μM and 0.010–5.0 mM with LOD of 0.030 μM based on 3(sd/slope). The modified electrode also exhibited a remarkably stable response under optimized conditions, and up to 55 injections can be used per electrode. The sensor exhibits high repeatability, reproducibility, and anti-interference properties when used for DEX detection. The effective determination of dexamethasone in real pharmaceutical and cosmetic samples demonstrated the feasibility of the electrochemical sensor, and the results were in good agreement with those obtained from the HPLC-DAD analysis. Acceptable percentage recoveries from the spiked pharmaceutical and cosmetic samples were obtained, ranging from 93–111% for this new method compared with 84–107% for the HPLC-DAD standard method.

In this study, a one-pot synthesis of a molybdenum diselenide/nitrogen-doped graphene oxide (MoSe₂/NGO) composite was demonstrated and used for the fabrication of an electrochemical pH sensor.

A stable and magnetic graphene oxide (GO) foam–polyethyleneimine–iron nanoparticle (GO–PEI–FeNPs) composite has been fabricated for removal of endocrine disruptors—bisphenol A, progesterone and norethisterone—from aqueous solution. The foam with porous and hierarchical structures was synthesized by reduction of graphene oxide layers coupled with co-precipitation of iron under a hydrothermal system using polyethyleneimine as a cross linker. The presence of magnetic iron nanoparticles facilitates the separation process after decontamination. The foam was fully characterized by surface and structural scanning electron microscopy, Fourier transform infrared spectroscopy, Raman spectroscopy and X-ray photoelectron spectroscopy. The foam exhibits a high adsorption capacity, and the maximum adsorption percentages are 68%, 49% and 80% for bisphenol A, progesterone and norethisterone, respectively. The adsorption process of bisphenol A is explained according to the Langmuir model, whereas the Freundlich model was used for progesterone and norethisterone adsorption.

Three-dimensional (3D) reduced graphene oxide (rGO) modified by polyethyleneimine (PEI) was prepared and functionalized by fluorophore-labeled dexamethasone-aptamer (Flu-DEX-apt) via π–π stacking interaction. The rGO/PEI/Flu-DEX-apt was used as a selective membrane for dexamethasone hormone removal from water. The prepared rGO/PEI/Flu-DEX-apt membranes were stable, insoluble, and easily removable from liquid media. The membrane was characterized by Raman spectroscopy, scanning electron spectroscopy, and FTIR spectroscopy. The rGO/PEI/Flu-DEX-apt membrane showed high sensitivity and specificity toward the dexamethasone hormone in the presence of other steroid hormone analogs, such as progesterone, estrone, estradiol, and 19-norethindrone. The fluorescence and UV–visible spectroscopy were used to confirm the membranes performance and the quantification of hormones removal. The resulting data clearly show that the graphene oxide concentration influence the aptamers and analytes interaction (π–π stacking interaction). It was found that by varying the graphene oxide concentration yields to different porosities of rGO/PEI/Flu-DEX-apt membranes affects the adsorption recovery rate, as well as the specificity and selectivity toward the dexamethasone hormone.

This review details the key progress made on flexible and stretchable electrochemical sensing systems, along with their relevant challenges and opportunities for the future. Stepping forward from traditional rigid electrodes, recent advancements in non-rigid electrochemical sensors offer new and exciting opportunities for various applications, such as biomedical, fitness, or environmental monitoring. The key factors in developing such devices are the materials and integrated systems needed to retain mechanical compliance while maintaining electrochemical functions. This requires a devotion to judiciously engineer both the underlying substrates and electrode materials. However, the realization of compliant electrochemical sensing devices still faces many obstacles. The requirements and potential strategies to enable flexible and stretchable electrodes are further discussed in this review. In addition to such sensing units, which mainly consist of electrodes and functionalized transducers, integrated systems also require miniaturized viable and mechanically compliant energy sources, as well as low-power electronics for controlling the device and wirelessly communicating with users. Such advancements, alongside other attractive functionalities such as self-healing and transparent properties, are also discussed. The innovative flexible and stretchable sensing systems will extend a variety of non‐invasive, minimally invasive, wearable, and implantable applications to patients. Examples of compliant sensing systems and relevant challenges are included alongside perspectives of this emerging technology.