Nonenzymatic Electrochemical Glutamate Sensor Using Copper Oxide Nanomaterials and Multiwall Carbon Nanotubes

Electrochemical detection of the neurotransmitter glutamate and the effect of the psychotropic drug riluzole on its oxidation response

Glutamate is the main excitatory neurotransmitter in the brain and plays a leading role in degenerative diseases, such as motor neuron diseases. Riluzole is a glutamate regulator and a therapeutic drug for motor neuron diseases. In this work, the interaction between glutamate and riluzole was studied using cyclic voltammetry and square-wave voltammetry at a glassy carbon electrode (GCE). It was shown that glutamate underwent a two-electron transfer reaction on the GCE surface, and the electrochemical detection limits of glutamate and riluzole were 483 μmol/L and 11.47 μmol/L, respectively. The results confirm that riluzole can promote the redox reaction of glutamate. This work highlights the significance of electrochemical technology in the sensing detection of the interaction between glutamate and related psychotropic drugs.

Green synthesized gold nanoparticles and CuO-based nonenzymatic sensor for saliva glucose monitoring

Glucose, essential for brain and muscle functions, requires careful monitoring in diabetes and other chronic disease management. While blood glucose monitoring provides precise information about these diseases, it remains an invasive method. Saliva glucose monitoring could offer an alternative approach, but the glucose concentration in saliva is very low. In this work, we report a simple, low-cost, highly sensitive nonenzymatic electrochemical glucose sensor. We developed this sensor using green synthesized gold nanoparticles (AuNPs) and wet chemical synthesized copper oxide (CuO) nanoparticles on a screen-printed carbon electrode (Au/CuO/SPCE). The sensor's high sensitivity results from dual amplification strategies using AuNPs and CuO nanomaterials, each demonstrating catalytic activity towards glucose. This shows promising potential for saliva glucose monitoring. The AuNPs were synthesized using an Au precursor and orange peel extract (OPE), yielding stable colloidal AuNPs with a mean diameter of about 37 nm, thus eliminating the need for additional capping agents. Under optimal conditions, amperometric tests revealed that the sensor responded linearly to glucose concentrations ranging from 2 μM to 397 μM with a sensitivity of 236.70 μA mM-1 cm-2. Furthermore, the sensor demonstrated excellent reproducibility, stability and high selectivity for glucose in the presence of different biomolecules. We validated the sensor's efficacy by measuring glucose in human saliva, showing its potential for noninvasive glucose monitoring. This research advances the development of point-of-care devices, positioning the sensor as a promising tool for noninvasive glucose monitoring and improved diabetes management.

Highly Efficient Enzyme-Free Glutamate Sensors Using Porous Network Metal-Organic Framework-Ni-NiO-Ni-Carbon Nanocomposites

This study introduces an innovative electrochemical sensor designed to detect glutamate using a nonenzymatic approach. The sensor utilizes a porous network metal-organic framework (Ni-MOF)-NiO-Ni-Carbon nanocomposite (PNM-NiO-Ni-Carbon) as an electrode modifier, which was synthesized and assessed for its effectiveness. Cyclic voltammetry measurements demonstrated that the PNM-NiO-Ni-Carbon nanocomposite, synthesized at 450 °C, displayed remarkable electrocatalytic activity for glutamate oxidation. The linear range for detection spanned from 5 to 960 μmol/L, and the sensor achieved a low detection limit of 320 nmol/L (S/N = 3), which was comparable to previously reported data. Moreover, the sensor exhibited high accuracy and favorable recovery rates when tested with real samples, thus, demonstrating its potential for rapid glutamate detection. The real samples were analyzed using both electrochemical and high-performance liquid chromatography methods, and the results obtained from the two methods did not differ significantly, validating the sensor's excellent practical performance. Based on our findings, the PNM-NiO-Ni-Carbon system exhibits potential for a wide range of biomedical applications.

An Electrochemical Sensor of Theophylline on a Boron-Doped Diamond Electrode Modified with Nickel Nanoparticles

Theophylline is a drug with a narrow therapeutic range. Electrochemical sensors are a potentially effective method for detecting theophylline concentration to prevent toxicity. In this work, a simple modification of a boron-doped diamond electrode using nickel nanoparticles was successfully performed for a theophylline electrochemical sensor. The modified electrode was characterized using a scanning electron microscope and X-ray photoelectron spectroscopy. Square wave voltammetry and cyclic voltammetry methods were used to study the electrochemical behavior of theophylline. The modified nickel nanoparticles on the boron-doped diamond electrode exhibited an electrochemically active surface area of 0.0081 cm2, which is larger than the unmodified boron-doped diamond's area of 0.0011 cm2. This modified electrode demonstrated a low limit of detection of 2.79 µM within the linear concentration range from 30 to 100 µM. Moreover, the modified boron-doped diamond electrode also showed selective properties against D-glucose, ammonium sulfate, and urea. In the real sample analysis using artificial urine, the boron-doped diamond electrode with nickel nanoparticle modifications achieved a %recovery of 105.10%, with a good precision of less than 5%. The results of this work indicate that the developed method using nickel nanoparticles on a boron-doped diamond electrode is promising for the determination of theophylline.

Development of an Enzymatic Biosensor Using Glutamate Oxidase on Organic-Inorganic-Structured, Electrospun Nanofiber-Modified Electrodes for Monosodium Glutamate Detection

Herein, dendrimer-modified montmorillonite (Mt)-decorated poly-Ɛ-caprolactone (PCL) and chitosan (CHIT)-based nanofibers were prepared. Mt was modified with a poly(amidoamine) generation 1 (PAMAM_G1) dendrimer, and the obtained PAMAM_G1-Mt was incorporated into the PCL-CHIT nanofiber's structure. The PCL-CHIT/PAMAM_G1-Mt nanofibers were conjugated with glutamate oxidase (GluOx) to design a bio-based detection system for monosodium glutamate (MSG). PAMAM_G1-Mt was added to the PCL-CHIT backbone to provide a multipoint binding side to immobilize GluOx via covalent bonds. After the characterization of PCL-CHIT/PAMAM_G1-Mt/GluOx, it was calibrated for MSG. The linear ranges were determined from 0.025 to 0.25 mM MSG using PCL-CHIT/Mt/GluOx and from 0.0025 to 0.175 mM MSG using PCL-CHIT/PAMAMG₁-Mt/GluOx (with a detection limit of 7.019 µM for PCL-CHIT/Mt/GluOx and 1.045 µM for PCL-CHIT/PAMAMG₁-Mt/GluOx). Finally, PCL-CHIT/PAMAMG₁-Mt/GluOx was applied to analyze MSG content in tomato soup without interfering with the sample matrix, giving a recovery percentage of 103.125%. Hence, the nanofiber modification with dendrimer-intercalated Mt and GluOx conjugation onto the formed nanocomposite structures was performed, and the PCL-CHIT/PAMAM_G1-Mt/GluOx system was successfully developed for MSG detection.