Low Overpotential Amperometric Sensor Using Yb2O3.CuO@rGO Nanocomposite for Sensitive Detection of Ascorbic Acid in Real Samples

The ultimate objective of this research work is to design a sensitive and selective electrochemical sensor for the efficient detection of ascorbic acid (AA), a vital antioxidant found in blood serum that may serve as a biomarker for oxidative stress. To achieve this, we utilized a novel Yb₂O₃.CuO@rGO nanocomposite (NC) as the active material to modify the glassy carbon working electrode (GCE). The structural properties and morphological characteristics of the Yb₂O₃.CuO@rGO NC were investigated using various techniques to ensure their suitability for the sensor. The resulting sensor electrode was able to detect a broad range of AA concentrations (0.5-1571 µM) in neutral phosphate buffer solution, with a high sensitivity of 0.4341 µAµM^-1cm^-2 and a reasonable detection limit of 0.062 µM. The sensor's great sensitivity and selectivity allowed it to accurately determine the levels of AA in human blood serum and commercial vitamin C tablets. It demonstrated high levels of reproducibility, repeatability, and stability, making it a reliable and robust sensor for the measurement of AA at low overpotential. Overall, the Yb₂O₃.CuO@rGO/GCE sensor showed great potential in detecting AA from real samples.

What Is Left for Real-Life Lactate Monitoring? Current Advances in Electrochemical Lactate (Bio)Sensors for Agrifood and Biomedical Applications

Monitoring of lactate is spreading from the evident clinical environment, where its role as a biomarker is notorious, to the agrifood ambit as well. In the former, lactate concentration can serve as a useful indicator of several diseases (e.g., tumour development and lactic acidosis) and a relevant value in sports performance for athletes, among others. In the latter, the spotlight is placed on the food control, bringing to the table meaningful information such as decaying product detection and stress monitoring of species. No matter what purpose is involved, electrochemical (bio)sensors stand as a solid and suitable choice. However, for the time being, this statement seems to be true only for discrete measurements. The reality exposes that real and continuous lactate monitoring is still a troublesome goal. In this review, a critical overview of electrochemical lactate (bio)sensors for clinical and agrifood situations is performed. Additionally, the transduction possibilities and different sensor designs approaches are also discussed. The main aim is to reflect the current state of the art and to indicate relevant advances (and bottlenecks) to keep in mind for further development and the final achievement of this highly worthy objective.

Glucose determination using amperometric non-enzymatic sensor based on electroactive poly(caffeic acid)@MWCNT decorated with CuO nanoparticles

A novel non-enzymatic glucose sensor based on poly(caffeic acid)@multi-walled carbon nanotubes decorated with CuO nanoparticles (PCA@MWCNT-CuO) was developed. The described approach involves the complexation/accumulation of Cu(II) on PCA@MWCNT followed by electrochemical CuO deposition in an alkaline electrolyte. The morphology and surface characteristics of the nanomaterial were determined by transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS), atomic force microscopy (AFM), Raman spectroscopy, and inductively coupled plasma mass spectrometry (ICP-MS). A hybrid-support sensor device was then developed to assess the glucose concentration in different solutions. The sensitivity of the electrode is 2412 μA mM^-1 cm^-2. The electrode exhibited a broad linear range of 2 µM to 9 mM and a low limit of detection (LOD) of 0.43 µM (relative standard deviation, RSD = 2.3%) at + 0.45 V vs Ag/AgCl. The excellent properties obtained for glucose detection were most likely due to the synergistic effect of the combination of individual components: poly(caffeic acid), MWCNTs, and CuO. Good accuracy and high precision were demonstrated for quantifying glucose concentrations in human serum and blood samples (the recovery ranged from 95.0 to 99.5%). The GC/PCA@MWCNT-CuO sensor represents a novel, simple, and low-cost approach to the fabrication of devices for amperometric sensing of glucose.

Development of L-cysteine sensor based on thallium oxide coupled multi-walled carbon nanotube nanocomposites with electrochemical approach

Here, Nanocomposites of thallium oxide doped multi-walled carbon nanotube (Tl2O.MWCNT NCs) were prepared by utilizing the wet-chemical method (WCM) in an alkaline phase at low temperature. Different optical procedures (FTIR: Fourier Transform Infra-Red Spectroscopy, XRD: Powder X-ray diffraction, FESEM: Field-Emission Scanning Electron Microscopy, XEDS: X-ray Electron Dispersive Spectroscopy, TEM: Tunneling Electron Microscopy, and XPS: X-ray photoelectron spectroscopy) were used to fully characterize (Optical, structural, crystalline, morphological, and elemental etc.) of the prepared Tl2O.MWCNT NCs. Modification of the thin-layer with NCs onto glassy carbon electrode (GCE) is prepared and applied for the enzyme-free detection of selective and sensitive L-cysteine by electrochemical approach. Using a reliable current-voltage approach, analytical sensing indexes such as sensitivity, LDR, LOD, LOQ, durability, and interference were assessed by fabricated sensor probe (GCE/Tl2O.MWCNT NCs/CPM) in selective detection of L-cysteine in a room condition, whereas nafion was used as conducting polymer matrix (CPM) during the fabrication of GCE with NCs. L-cysteine calibration plot was found to be linear over an extensive range of concentration. The calibration curve was used to calculate the sensing parameters such as sensitivity (316.46 pAμM-1cm-2), LOD down to (~18.90 ± 1.89 pM), and LOQ (63.0 pM) of the prepared sensor. The use of a simple WCM to validate the Tl2O.MWCNT NCs is a good approach for developing a NCs-based sensor for enzyme-free biomolecule identification and detection in the biomedical and health care fields in a broad scale. This proposed sensor (GCE/Tl2O.MWCNT NCs/CPM) is used to detect selective L-cysteine in real biological samples such as human, mouse, and rabbit serum and found acceptable and satisfactory results.

An enzyme free simultaneous detection of γ-amino-butyric acid and testosterone based on copper oxide nanoparticles

Herein, an easy wet-chemical process was used in basic medium with low temperature to prepare low-dimensional copper oxide nanoparticles (CuO NPs). A variety of optical and structural techniques such as UV-visible, FT-IR, XRD, FESEM, XEDS, and XPS were used to characterize the synthesized CuO NPs in detail. Two sensitive and selective sensor probes for γ-amino-butyric acid (GABA) and testosterone (TST) were achieved after modification; a thin layer of NPs on a flat glassy carbon electrode (GCE). Sensor analytical parameters such as sensitivity (SNT), linear dynamic range (LDR), limit of detection (LOD), limit of quantification (LOQ), robustness, and interference effects, were evaluated for the proposed sensor (GCE/CuO NPs) for GABA and TST, based on a dependable current-voltage technique. Calibration curves were found to be linear (R ² = 0.9963 and 0.9095) over a broad concentration range of GABA and TST (100.0 pM to 100.0 mM and 10.0 pM to 10.0 mM, respectively). Sensor parameters - SNT (316.46 and 2848.10 pA μM^-1 cm^-2), LDR (100.0 nM to 10.0 mM and 10.0 pM to 1.0 mM), LOD (≈11.70 and 96.67 pM), and LOQ (39.0 and 322.2 pM) - for GABA and TST were calculated from the calibration plot successively. Preparation of CuO NPs using the wet-chemical technique is a good approach for perspective expansion of NPs-based sensors for the enzyme-free detection of biomolecules. Our sensor probe (GCE/CuO NPs) is applied for the cautious recognition of GABA and TST in real biological samples -human, mouse, and rabbit serum - and achieved good and acceptable results.

Enzyme-free detection of uric acid using hydrothermally prepared CuO·Fe2O3 nanocrystals

Copper oxide doped iron oxide nanocrystals (CuO·Fe₂O₃ NCs) were prepared using a simple hydrothermal technique at low temperature in an alkaline medium.