Highly Specific Non-Enzymatic Electrochemical Sensor for the Detection of Uric Acid Using Carboxylated Multiwalled Carbon Nanotubes Intertwined with GdS-Gd2O3 Nanoplates in Human Urine and Serum

Herein, the electrochemical sensing efficacy of carboxylic acid functionalized multiwalled carbon nanotubes (C-MWCNT) intertwined with coexisting phases of gadolinium monosulfide (GdS) and gadolinium oxide (Gd2O3) nanosheets is explored for the first time. The nanocomposite demonstrated splendid specificity for nonenzymatic electrochemical detection of uric acid (UA) in biological samples. It was synthesized using the coprecipitation method and thoroughly characterized. The presence of functional groups and disorder in the as-synthesized nanocomposite are confirmed using Fourier transform infrared spectroscopy and Raman spectroscopy. Furthermore, field emission scanning electron microscopy, high-resolution transmission electron microscope, X-ray powder diffraction, and X-ray photoelectron spectroscopy provides a clear understanding of the morphology, coexisting phases, and elemental composition of the as-synthesized nanocomposites. The differential pulse voltammetry technique was utilized to elaborate the electrochemical sensing of UA using a GdS-Gd2O3/C-MWCNT modified glassy carbon electrode (GCE), The sensor showed an enhanced current response by more than 2-fold compared to bare GCE. Also, the sensor's performance was further improved by dispersing the nanocomposite in an ionic liquid with the exceptional reproducibility (SD = 0.0025, n = 3). The fabricated UA sensor GdS-Gd2O3/C-MWCNT/IL/GCE demonstrated a wide linear detection range from 0.5-30 μM and 30-2000 μM, effectively covering the entire physiological range of UA in biological fluids with a limit of detection (LOD) of 0.380 μM (+3SD of blank) and a sensitivity of 356.125 μA mM-1 cm-2. Moreover, the electrodes exhibited storage stability for 2 weeks with decrease in zero-day current by only 4.5%. The sensor was validated by quantifying UA in 12 unprocessed clinical human urine and serum samples, and its comparison with the gold standard test yielded remarkable results (p < 0.05). Hence, the proposed nonenzymatic electrochemical UA sensor is selective, sensitive, reproducible, and stable, making it reliable for point-of-care diagnostics.

Highly efficient green up-conversion emission from fluoroindate glass nanoparticles functionalized with a biocompatible polymer

Up-conversion nanoparticles have garnered lots of attention due to their ability to transform low energy light (near-infrared) into high-energy (visible) light, enabling their potential use as remote visible light nano-transducers. However, their low efficiency restricts their full potential. To overcome this disadvantage, fluoroindate glasses (InF3) doped at different molar concentrations of Yb3+ and Er3+ were obtained using the melting-quenching technique, reaching the highest green emission at 1.4Yb and 1.75Er (mol%), which corresponds to the 4S3/2 → 4I15/2 (540-552 nm) transition. The particles possess the amorphous nature of the glass and have a high thermostability, as corroborated by thermogravimetric assay. Furthermore, the spectral decay curve analysis showed efficient energy transfer as the rare-earth ions varied. This was corroborated with the absolute quantum yield (QY) obtained (85%) upon excitation at 385 nm with QYEr = 17% and QYYb = 68%. Additionally, InF3-1.4Yb-1.75Er was milled and functionalized using poly(ethylene glycol) to impart biocompatibility, which is essential for biomedical applications. Such functionalization was verified using FTIR, TG/DSC, and XRD.

Development of Methanol Sensor Based on Sol-Gel Drop-Coating Co3O4·CdO·ZnO Nanoparticles Modified Gold-Coated µ-Chip by Electro-Oxidation Process

Herein, novel Co₃O₄·CdO·ZnO-based tri-metallic oxide nanoparticles (CCZ) were synthesized by a simple solution method in basic phase. We have used Fourier Transform Infrared Spectroscopy (FTIR), X-ray Diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Field Emission Scanning Electron Microscope (FESEM), Dynamic Light Scattering (DLS), Tunneling Electron Microscopy (TEM), and Energy-Dispersive Spectroscopy (EDS) techniques to characterize the CCZ nanoparticles. XRD, TEM, DLS, and FESEM investigations have confirmed the tri-metallic nanoparticles’ structure, while XPS and EDS analyses have shown the elemental compositions of the CCZ nanoparticles. Later, a Au/μ-Chip was modified with the CCZ nanoparticles using a conducting binder, PEDOT: PSS (poly(3,4-ethylenedioxythiophene) polystyrene sulfonate) in a sol-gel system, and dried completely in air. Then, the CCZ/Au/μ-Chip sensor was used to detect methanol (MeOH) in phosphate buffer solution (PBS). Outstanding sensing performance was achieved for the CCZ/Au/μ-Chip sensor, such as excellent sensitivity (1.3842 µAµM⁻¹cm⁻²), a wide linear dynamic range of 1.0 nM–2.0 mM (R² = 0.9992), an ultra-low detection limit (32.8 ± 0.1 pM at S/N = 3), a fast response time (~11 s), and excellent reproducibility and repeatability. This CCZ/Au/μ-Chip sensor was further applied with appropriate quantification results in real environmental sample analyses.

An Electrochemical Approach for the Selective Detection of Cancer Metabolic Creatine Biomarker with Porous Nano-Formulated CMNO Materials Decorated Glassy Carbon Electrode

The facile wet-chemical technique was used to prepare the low-dimensional nano-formulated porous mixed metal oxide nanomaterials (CuO.Mn2O3.NiO; CMNO NMs) in an alkaline medium at low temperature. Detailed structural, morphological, crystalline, and functional characterization of CMNO NMs were performed by X-ray photoelectron spectroscopy (XPS), powder X-ray diffraction (XRD), ultraviolet-visible spectroscopy (UV-vis), Fourier-transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FESEM), and energy-dispersive X-ray spectroscopy (EDS) analyses. An efficient and selective creatine (CA) sensor probe was fabricated by using CMNO NMs decorated onto glassy carbon electrode (GCE) as CMNO NMs/GCE by using Nafion adhesive (5% suspension in ethanol). The relation of current versus the concentration of CA was plotted to draw a calibration curve of the CMNO NMs/GCE sensor probe, which was found to have a very linear value (r2 = 0.9995) over a large dynamic range (LDR: 0.1 nM~0.1 mM) for selective CA detection. The slope of LDR by considering the active surface area of GCE (0.0316 cm2) was applied to estimate the sensor sensitivity (14.6308 µAµM-1 cm-2). Moreover, the detection limit (21.63 ± 0.05 pM) of CMNO MNs modified GCE was calculated from the signal/noise (S/N) ratio at 3. As a CA sensor probe, it exhibited long-term stability, good reproducibility, and fast response time in the detection of CA by electrochemical approach. Therefore, this research technique is introduced as a promising platform to develop an efficient sensor probe for cancer metabolic biomarker by using nano-formulated mixed metal oxides for biochemical as well as biomedical research for the safety of health care fields.

Fabrication of an ultra-sensitive para-nitrophenol sensor based on facile Zn-doped Er2O3 nanocomposites via an electrochemical approach

In this study, a semiconductor-doped nanocomposite material (Zn-doped Er2O3 nano-composites) was prepared via a single-step wet-chemical technique at alkaline pH. Fourier-transform infrared spectroscopy (FT-IR), UV/Vis spectroscopy, photoluminescence spectroscopy (PL), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (XEDS), and X-ray powder diffractometry (XRD) were applied to determine the structural and morphological properties of the Zn-doped Er2O3 nanocomposite. A thin layer of aggregated Zn-doped Er2O3 nanocomposite was fabricated on the flat surface of a glassy carbon electrode (GCE) with 5% ethanolic Nafion as conducting coating binder for the development of a selective and sensitive p-nitrophenol (para-NP) capturing electrochemical probe for environmental remediation. After the fabrication of the sensor, a novel current-potential (I-V) electrochemical approach was applied to determine its selectivity and sensitivity together with all the necessary analytical parameters against para-NP. Moreover, the calibration plot was found to be linear with the linear dynamic range (LDR) of para-NP concentration. The limit of detection (LOD) at a signal-to-noise ratio of 3 (S/N ∼ 3) and sensitivity were also calculated to be 0.033 ± 0.002 pM and 28.481 × 10-2 μA μM-1 cm-2, respectively, based on the gradient of the calibration plot, and the limit of quantification (LOQ) was determined to be 0.11 ± 0.02 pM. This work demonstrates a well-known approach for the first time that can be used for the development of efficient electrochemical sensors. These sensors based on semiconductor doped nanomaterials embedded onto the GCE for the detection of toxic chemicals in an aqueous system as an environmental remediation. It can be further applied for the analysis of real environmental samples and in the healthcare field.

Chemical-resistant ammonia sensor based on polyaniline/CuO nanoparticles supported on three-dimensional nitrogen-doped graphene-based framework nanocomposites

A novel ammonia (NH₃) chemical sensor is presented with ultra-high response, good selectivity, fast response, and long-term stability using detecting layer of polyaniline/cupric oxide nanoparticles supported on three-dimensional nitrogen-doped graphene-based frameworks (PANI/CuO@3D-NGF) nanocomposite. The NH₃ gas sensing response of the PANI/CuO@3D-NGF nanocomposite was studied by resistivity method in low concentration range of 50 ppb-100 ppm at room temperature. The PANI/CuO@3D-NGF nanocomposite was prepared through in situ polymerization of PANI on the CuO@3D-NGF with a high surface area. Morphological and structural analysis revealed that the ultrathin 3D interconnected graphene substrate maximizes the surface area. It is also shown that the CuO nanoparticles offer active adsorption sites for free NH₃ molecule. The PANI/CuO@3D-NGF nanocomposite gas sensor shows the response of 930% to 100 ppm NH₃ with an outstanding low detection limit of 50 ppb and an average response time of 30 s at room temperature. The excellent sensing performance of the PANI/CuO@3D-NGF nanocomposite was attributed to 3D interconnected porous structure, remarkable enhancement of charge carriers as a result of CuO@3D-NGF, and modified π-interactions between molecules. Graphical abstract.

Facile and efficient 3-chlorophenol sensor development based on photolumenescent core-shell CdSe/ZnS quantum dots

Quantum dots (QDs) are semiconducting inorganic nanoparticles, tiny molecules of 2-10 nm sizes to strength the quantum confinements of electrons. The QDs are good enough to emit light onto electrons for exciting and returning to the ground state. Here, CdSe/ZnS core/shell QDs have been prepared and applied for electrochemical sensor development in this approach. Flat glassy carbon electrode (GCE) was coated with CdSe/ZnS QDs as very thin uniform layer to result of the selective and efficient sensor of 3-CP (3-chlorophenol). The significant analytical parameters were calculated from the calibration plot such as sensitivity (3.6392 µA µM-1 cm-2) and detection limit (26.09 ± 1.30 pM) with CdSe/ZnS/GCE sensor probe by electrochemical approach. The calibration curve was fitted with the regression co-efficient r2 = 0.9906 in the range of 0.1 nM ∼ 0.1 mM concentration, which denoted as linear dynamic range (LDR). Besides these, it was performed the reproducibility in short response time and successfully validated the fabricated sensor for 3-CP in the real environmental and extracted samples. It is introduced as a noble route to detect the environmental phenolic contaminants using CdSe/ZnS QDs modified sensor by electrochemical method for the safety of healthcare and environmental fields at broad scales.

Assessment of environmentally unsafe pollutants using facile wet-chemically prepared CeO2–ZrO2 nanocomposites by the electrochemical approach

Selective and sensitive 4-methoxyphenol chemical sensor was developed with a co-doped CeO₂–ZrO₂ nanocomposite modified glassy carbon electrode as a sensor probe by electrochemical approach for the safety of environmental and ecological fields in broad scales.

Development of 3-methoxyaniline sensor probe based on thin Ag2O@La2O3 nanosheets for environmental safety

An electrochemical sensor based on glassy carbon electrode modified by Ag₂O@La₂O₃ nanosheets with 5% ethanolic nafion as conducting binder was developed for the selective and ultra-sensitive determination of 3-methoxyanaline in the presence of other interfering toxic chemicals in aqueous system by electrochemical approach for the first time.

Development of a selective and sensitive Ga3+ sensor for environmental safety: a comparative study of cyclohexyl and aromatic bis-sulphonamide fabricated glassy carbon electrodes

The aim of this study was to synthesize the new chelating agents CDBDMBS and PBDMBD for environmental remediation by sensing of Ga³⁺ in aqueous solution. The electrochemical technique is introduced a new approach of development of cost effective toxic cationic sensors for environmental and healthcare fields.