Metal−organic frameworks (MOFs) have been previously investigated as electrode materials for developing electrochemical sensors. They have usually been reported to suffer from poor conductivity and improvement in the conductivity of MOFs is still a great challenge. Here, we reported the fabrication of an electrochemical sensor based on the in situ growth of framework HKUST-1 on conductive graphene oxide nanoribbons (GONRs)-modified glassy carbon electrode (GCE) (HKUST-1/ GONRs/GCE). The as-fabricated modified electrode was characterized using field emission scanning electron microscopy, transmission electron microscopy (TEM), high-resolution TEM, Fourier transform infrared, X-ray diffraction, electrochemical impedance spectroscopy, cyclic voltammetry, and Raman spectroscopy. The voltammetric response of HKUST-1/GONRs/GCE toward Imatinib (IMA), as an anticancer drug, is dramatically higher than HKUST-1/GCE because of the synergic effect of the GONRs and HKUST-1 framework. The calibration curve at the HKUST-1/GONRs/GCE for IMA covered two linear dynamic ranges, 0.04−1.0 and 1.0−80 μmol L −1 , with a detection limit of 0.006 μmol L −1 (6 nmol L −1 ). Taking advantage of the conductivity of GONRs and large surface area of HKUST-1, a sensitive modified electrode was developed for the electrochemical determination of IMA. The present method provides an effective strategy to solve the poor conductivity of the MOFs. Finally, the obtained electrochemical performance made this modified electrode promising in the determination of IMA in urine and serum samples.

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A three-dimensional and highly porous polypyrrole (PPy) film was successfully coated onto a copper interdigital electrode (Cu-IDE) surface by electrospinning of soluble PPy nanoparticles.The chemical composition of PPy nanoparticles was analyzed using X-ray photoelectron spectroscopy (XPS) and fourier transform infrared spectroscopy (FT-IR). The Brunauer-Emmett-Teller (BET) analysis confirmed the porous nature of PPy nanoparticles. The field emission scanning electron microscopy (FE-SEM) images of polymer coated Cu-IDE revealed that PPy nanoparticles were assembled by electrical forces to form an outstanding honeycomb-like architecture. As a proof-of-concept demonstration of the functional properties of the electrospun PPy (Es-PPy) film, the polymer coated Cu-IDE was investigated as a sensing device for gas sensor.The as-prepared Es-PPy film proved to be a viable aliphatic amines sensing material with large response, low detection limit, fast response and good repeatability at a low operating temperature of 150˚C. Moreover, the sensor demonstrated an extremely high sensitivity and selectivity to nbutylamine. The calibration sensitivity to n-butylamine is up to three orders of magnitude higher than that of other common aliphatic amines. The detection limit and linear range for determination of n-butylamine were 0.42 ppm and 10.54-21.08 ppm, respectively. Es-PPy gas sensor exhibited good repeatability with RSD ≤ 8% at temperature ranges 90-200°C. The response of the Es-PPy sensor to n-butylamine was compared with electrochemically and drop coated sensors and found that it has an extremely higher response. Finally, the Es-PPy gas sensor was successfully applied to real well water sample analysis.

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The increasing application of fluorescence spectroscopy in development of reliable sensing platforms has triggered a lot of research interest for the synthesis of advanced fluorescent materials. Herein, we report a simple, low-cost strategy for the synthesis of a series of water-soluble conjugated polymer nanoparticles with diverse emission range using cationic (hexadecyltrimethylammonium bromide, CTAB), anionic (sodium dodecylbenzenesulfonate, SDBS), and nonionic (TX114) surfactants as the stabilizing agents. The role of surfactant type on the photophisical and sensing properties of resultant polymers has been investigated using dynamic light scattering (DLS), FT-IR, UV-vis, fluorescence, and energy dispersive X-ray (EDS) spectroscopies. The results show that the surface polarity, size, and spectroscopic and sensing properties of conjugated polymers could be well controlled by the proper selection of the stabilizer type. The fluorescent conjugated polymers exhibited fluorescence quenching toward nitroaromatic compounds. Further studies on the fluorescence properties of conjugated polymers revealed that the emission of the SDBS stabilized polymer, N-methylpolypyrrole-SDBS (NMPPY-SDBS), is strongly quenched by 2,4,6-trinitrotoluene molecule with a large Stern -Volmer constant of 59 526 M(-1) and an excellent detection limit of 100 nM. UV-vis and cyclic voltammetry measurements unveiled that fluorescence quenching occurs through a charge transfer mechanism between electron rich NMPPY-SDBS and electron deficient 2,4,6-trinitrotoluene molecules. Finally, the as-prepared conjugated polymer and approach were successfully applied to the determination of 2,4,6-trinitrotoluene in real water samples.

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One of the serious complications of COVID-19 is acute kidney injury (AKI), leading to a decrease in kidney function and even death. The concentration of ammonia (NH 3 ) in the exhaled breath (EB) of COVID-19 patients suffering from AKI symptoms will be significantly increased. In this work, the detection of breath NH 3 was performed at gold interdigital electrodes modified with a soluble polypyrrole microparticle and silver nanoparticle film (Au-IDEs/S-PPyMPs/AgNPs) as a noninvasive chemiresistor gas sensor. The response behavior of unmodified and modified gas sensors toward NH 3 and other interfering compounds was studied. The Au-IDEs/S-PPyMPs/AgNPs exhibited NH 3 detection in the linear dynamic range of 1.00−19.23 ppm, with a limit of detection of 0.12 ppm. Finally, the fabricated gas sensor was used to monitor the NH 3 concentration in the EB of COVID-19 patients suffering from AKI symptoms. For this purpose, the gas sensor was validated in 19 EB samples (seven COVID-19−positive patients, four COVID-19−negative patients, and eight post−COVID-19 patients). The gas sensor was directly exposed to the EB samples, followed by recording the changes in electrical resistance via a low-cost digital multimeter. The sensing mechanism was explained as the interaction between breath NH 3 and sensing materials. The breath NH 3 concentrations have a desirable correlation (R 2 = 0.8463) with the estimated glomerular filtration rate (eGFR) values in COVID-19−positive patients. The fabricated gas sensor can distinguish COVID-19−positive patients suffering from AKI symptoms from COVID-19−negative patients and post−COVID-19 patients. The present work can pave the way for the development of a simple and efficient analytical approach for COVID-19 patients with AKI without the need for sample pretreatment.