Sputtering deposition of Pt nanoparticles on vertically aligned multiwalled carbon nanotubes for sensing L-cysteine

Electrochemical Amino Acid Sensing: A Review on Challenges and Achievements

The rapid growth of research in electrochemistry in the last decade has resulted in a significant advancement in exploiting electrochemical strategies for assessing biological substances. Among these, amino acids are of utmost interest due to their key role in human health. Indeed, an unbalanced amino acid level is the origin of several metabolic and genetic diseases, which has led to a great need for effective and reliable evaluation methods. This review is an effort to summarize and present both challenges and achievements in electrochemical amino acid sensing from the last decade (from 2010 onwards) to show where limitations and advantages stem from. In this review, we place special emphasis on five well-known electroactive amino acids, namely cysteine, tyrosine, tryptophan, methionine and histidine. The recent research and achievements in this area and significant performance metrics of the proposed electrochemical sensors, including the limit of detection, sensitivity, stability, linear dynamic range(s) and applicability in real sample analysis, are summarized and presented in separate sections. More than 400 recent scientific studies were included in this review to portray a rich set of ideas and exemplify the capabilities of the electrochemical strategies to detect these essential biomolecules at trace and even ultra-trace levels. Finally, we discuss, in the last section, the remaining issues and the opportunities to push the boundaries of our knowledge in amino acid electrochemistry even further.

Self-cascade reaction catalyzed by CuO nanoparticle-based dual-functional enzyme mimics

It is desirable but challenging to assemble various biomimetic properties into a functional catalytic cascade system. In this work, cupric oxide nanoparticles were investigated as oxidase mimics for the aerobic oxidation of cysteine to cystine with the generation of hydrogen peroxide. Coupling this property with the peroxidase-like activity of CuO nanoparticles, we constructed a self-organized cascade reaction system based on a single-component nanozyme, which includes the oxidation of cysteine to yield cystine and hydrogen peroxide and the hydrogen peroxide-mediated oxidation of terephthalic acid to produce a fluorescence change. Based on this artificial enzymatic cascade reaction system, a fluorometric assay method with a low detection limit of 6.6nM was established for cysteine determination. This platform was then applied for the detection of cysteine in pharmaceutical products and human plasma, which yielded satisfactory results. Our investigations open up a new route and holds promise for the development and applications of multifunctional nanomaterials as enzyme mimics.

Sensing properties of multiwalled carbon nanotubes grown in MW plasma torch: electronic and electrochemical behavior, gas sensing, field emission, IR absorption

Vertically aligned multi-walled carbon nanotubes (VA-MWCNTs) with an average diameter below 80 nm and a thickness of the uniform VA-MWCNT layer of about 16 μm were grown in microwave plasma torch and tested for selected functional properties. IR absorption important for a construction of bolometers was studied by Fourier transform infrared spectroscopy. Basic electrochemical characterization was performed by cyclic voltammetry. Comparing the obtained results with the standard or MWCNT‐modified screen-printed electrodes, the prepared VA-MWCNT electrodes indicated their high potential for the construction of electrochemical sensors. Resistive CNT gas sensor revealed a good sensitivity to ammonia taking into account room temperature operation. Field emission detected from CNTs was suitable for the pressure sensing application based on the measurement of emission current in the diode structure with bending diaphragm. The advantages of microwave plasma torch growth of CNTs, i.e., fast processing and versatility of the process, can be therefore fully exploited for the integration of surface-bound grown CNTs into various sensing structures.

Electrochemical sensing platform for L-CySH based on nearly uniform Au nanoparticles decorated graphene nanosheets

In this study, Au nanoparticles decorated graphene nanosheets were prepared using poly(vinylpyrrolidone) (PVP) covalently functionalized graphene oxide and chloroauric acid as template and Au precursor, respectively. Both the density and the size of Au nanoparticles deposited on the surface of graphene could be adjusted by the PVP grafting density. The graphene-Au hybrid nanosheets were then applied to fabricate a highly sensitive l-cysteine (L-CySH) electrochemical sensing platform. The cyclic voltammetry results showed that the modified glassy carbon electrode with graphene-Au hybrid nanosheets exhibited strong catalytic activity toward the electrooxidation of L-CySH. The current exhibited a widely linear response ranging from 0.1 to 24 μM with a low detection limit under the optimized conditions. The detection limit of L-CySH could reach as low as 20.5 nM (S/N=3). The enhanced electrochemical performance of the fabricated sensor was attributed to the combination of the excellent conductivity of graphene and strong catalytic property of uniform Au nanoparticles.