An enzyme free detection of L-Glutamic acid using deposited CuO.GdO nanospikes on a flat glassy carbon electrode
Introduction
Electrochemical sensors are less-expensive and sensitive tools to use in the arena of bio-molecules detection. Electrochemical signal transduction technique may be an advanced over other transduction methods in point of correctness, expenditure, selectivity, sensitivity, and stability [1]. Sensors based on CuO nano-crystals have been attracted more attention and applied for synthesis of different types of morphologies (Nanostructure and mesoporous films), nanocubes, nanorods, nanowires, quasi spherical, urchin like micro architectures, fiber like and worm like structures, and other nanostructures [2]. Gadolinium oxide (GdO) nanoparticles are very significant as catalyst, electronic, laser, optical, nuclear, and phosphor materials. GdO is bearing potential applications in biomedicine, magnetic resonance, multimodal contrast agent, and cancer treatment [3]. L-Glutamic acid (L-GA: 2-Aminopentanedioic acid) is an important excitatory amino acid neurotransmitter in the mammalian nervous system. The changes of the amount of l-GA in specific area in brain are closely related to Alzheimer disease and Parkinson's disease [4]. Previous research notified that the l-GA rich chain of bone sialoprotein, osteonectin, and osteopontin are concerned in growth and nucleation [5]. l-GA is a rich amino acid ingredient of plant biomass and is highly attractive for producing industrially considerable bio-based chemicals for example 3-cyanopropionate, γ-amino-butyric acid, and succinonitrile [6]. It is a well-known flavor enhancer and normally found in diverse foods. The excessive ingestion of this flavor enhancer can cause allergic effects (Headache and stomach pain) [7]. l-GA is a distinctive synthetic amino acid may be an outstanding biopolymer for use in electrochemical sensor due to its suitable structure and green in environment [8]. Recently, due to synthetic technique limitations, research has been carried out on the fabrication and catalytic surface activation of CuO.GdO based nanostructures for selective and sensitive enzyme less sensor development. Here, CuO is a promising p-type semiconductor with a narrow band gap, with strong absorption in the solar spectrum region [9]. In addition, CuO has been used as a component to build hetero-junction photo-electrodes with other semiconductors [10] while the high conductivity of CuO makes it a good candidate for selective sensor applications [11]. Copper oxides doped semiconductor GdO nanomaterials can be synthesized using a number of methods, e.g. metal-organic chemical vapor deposition [12], electro-deposition sputtering [13, 14], and template-based sol–gel approaches [15]. However, none of these methods are suitable for the preparation of CuO.GdO hetero-structures for enzyme free sensor development. CuO.GdO nanospike material is an appropriate choice for promising implementation in chemical sensing, due to its high sensitivity, large active surface area, suitable chemical stability, facile, and low cost. The main benefit associated with CuO.GdO embedded sensor is its satisfied selectivity and operated at room temperature. Advantages such as utilizing catalyst and promoters, control of operating temperature, and employing proper physical or chemical filters have been suggested to solve the nanostructure materials for selectivity [16]. Doping CuO with rare earth oxides such as GdO makes the sensor more selective to a certain chemicals and reduces the un-stability of sensor operating temperature with lower power consumption [17]. On the other hand, biochemical sensing properties of CuO doped GdO sensor are extremely dependent on its size, morphology, and texture. The most of the batch synthesis methods are complicated, time consuming, and uncontrollable for uniform size distribution of nanostructures and need templates, especial solvents, and/or additives. In recent years, researchers have focused on synthesizing nano-structured materials in micro-reactors, due to their advantages over controversial batch methods [18]. The advantages include precise control on size distribution of nanomaterials, considerable productivity, flexibility in changing the experimental condition or reagent compositions, and shortening the development time from laboratory to commercial production [19].
Among bio-sensing technique, electrochemical techniques have attended wide intensions because of economical approaches of instrumentation, high sensitivity, and simplicity for operators and portability. In order to enhance the electrochemical response of l-GA, some chemically modified electrodes have been already reported [20, 21]. The common electroanalytical techniques were moderately sensitive, but some of them showed pitiable selectivity and sensitivity. Furthermore, these electrochemical sensors are mostly applied to l-GA detection in biological samples. Therefore, it is necessary to seek a facile, cheap, stable and highly selective method to determine l-GA using CuO.GdO NSs with flat GCE in biological samples. The easy-fabrication method for the construction with CuO.GdO NSs within conducting nafion binding agent is executed for the preparation of thin material films onto GCE. In this approach, CuO.GdO NSs/Nafion/GCE fabricated films with conducting binders are utilized towards the target toxic analytes using reliable I-V method. The main aim is to improve qualities of the prepared CuO.GdO NSs/Nafion/GCE sensor, such as fabrication simplicity, lower detection limit, higher sensitivity, and selectivity. The function of CuO.GdO NSs/Nafion/GCE with the selectivity of the fabricated film towards l-GA was thoroughly investigated with various electrochemical measurements in detail. By clarifying the recognition and optimizing some of the operating conditions, this study provided a new way for constructing sensitive and selective electrochemical sensors. Here, it is confirmed that the fabricated bio-chemical sensor is new and noble research work for ultra-sensitive recognition of L-Glutamic acid with CuO.GdO NSs/Nafion/GCE in short response-time and practically monitored in the real biological samples analyses.
Section snippets
Materials and methods
The analytical grade chemicals for example ammonium hydroxide, ethanol, nafion (5% ethanolic solution), bilirubin, chloramphenicol, creatine, l-cysteine, glycine, glucose, l-leucine, l-glutamic acid, l-glutathione, penicillin G, Thionine acetate, thiourea, l-tyrocine, and uric acid were purchased from the Sigma-Aldrich company and used as received. FTIR and UV–visible spectra of the CuO.GdO NSs were recorded on a Thermo scientific NICOLET iS50 FTIR spectrometer (Madison, USA) and 300
Optical and structural characteristics
Optical feature is one of the important criteria for the examination of photo-catalytic activity of the CuO.GdO NSs. According to the hypothesis of the UV–visible spectroscopy, the external electrons of the atom may be shifted to the upper energy level and the spectrum including band-gap energy of the doped metal oxide can be achieved due to the adsorption of radiant energy. UV–visible spectrum of the CuO.GdO NSs was recorded at 200 ~ 800 nm and a wide absorption band at around 306.4 nm was
Conclusion
In this approach, CuO.GdO NSs were synthesized using a facile hydrothermal method in alkaline phase at low temperature. The optical characteristics of NSs were examined by FTIR, UV–visible, XRD, FESEM, XEDS, and XPS techniques. An easy modification method was used in order to fabricate GCE with CuO.GdO NSs using conducting binder (5% Nafion). A selective and sensitive L-Glutamic acid sensor were developed successfully based on the GCE as well as established with CuO.GdO NSs by using
CRediT authorship contribution statement
Mohammed M. Rahman: Writing - original draft, Writing - review & editing. Mohammad Musarraf Hussain: Writing - original draft, Writing - review & editing. Abdullah M. Asiri: Writing - review & editing. K.A. Alamry: Writing - review & editing. M.A. Hasnat: Writing - review & editing.
Declaration of Competing Interest
There is no conflict of interest to be reported in this research work.
Acknowledgment
This project was funded by the Deanship of Scientific Research (DSR), King Abdulaziz University, Jeddah, Saudi Arabia under grant no. (KEP-45-130-40). The authors, therefore, acknowledge with thanks DSR for technical and financial support.
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