Fabrication of Nickel Tetrasulfonated Phthalocyanine Functionalized Multiwalled Carbon Nanotubes on Activated Glassy Carbon Electrode for the Detection of Dopamine

Green synthesis of naphthyl derivative as an optical sensor for the detection of l-carnitine in food samples

An economical and green approach to the synthesis of naphthyl derivative for detection of l-carnitine (3-hydroxy-4-N-trimethyl-aminobutyrate) is practically important. We developed a naphthyl derivative as a probe showing 'turn-on' response towards l-carnitine selectively at pH 7.2 through ICT mechanism with a good limit of detection (LOD) of 0.126 μM. Using Job's plot for determining the binding stoichiometry, it was found that probe could form a more stable complex (1:1) with carnitine. The binding constant (K) between probe and carnitine was calculated as 8 × 10⁷  M^-1 using the Benesi-Hildebrand plot. The binding interaction of the probe with l-carnitine was confirmed by nuclear magnetic resonance titrations, Fourier-transform infrared spectroscopy, photo physical studies and density functional theory calculations. Meanwhile, the probe can be used to quantitatively detect carnitine in food samples.

Synthesis and characterization of tetra-ganciclovir cobalt (II) phthalocyanine for electroanalytical applications of AA/DA/UA

Cobalt (II) phthalocyanine embedded with ganciclovir units has been synthesized by a novel method using tetracarboxylic phthalocyanine reported for the first time. The synthesized dark green colored complexes were characterized by electronic spectroscopy, elemental analysis, FT-IR, MASS and XRD. Thermal stability study reveals that the newly synthesized complex was stable up to 300 °C and XRD patterns showed amorphous nature of the complex. In the present work, the synthesized complex was characterized by cyclic voltammetry and shows the redox behavior corresponding to central metal (Co^+II/Co^+I) of the complex. Three biomolecules are well-separated by their oxidation peaks in simultaneous determination predicting the potentials for (-128, 335, and 723 mV) with highly increasing current. The low detection limit of AA, DA, and UA were 0.33, 0.03 and 0.10 μmol by CV method and good responses of amperometric and DPV technique. The modified tetra substituted CoTGPc/GCE exhibit an excellent electrocatalytic activity, stability, high sensitivity, good linearity, and selectivity without losing its catalytic activity and proves to be a versatile chemical sensor for commercial pharmaceutical samples, vitamin C tablets, and dopamine injections.

Phthalocyanine Doped Metal Oxide Nanoparticles on Multiwalled Carbon Nanotubes Platform for the detection of Dopamine

The electrocatalytic properties of metal oxides (MO = Fe₃O₄, ZnO) nanoparticles doped phthalocyanine (Pc) and functionalized MWCNTs, decorated on glassy carbon electrode (GCE) was investigated. Successful synthesis of the metal oxide nanoparticles and the MO/Pc/MWCNT composite were confirmed using UV-Vis, EDX, XRD and TEM techniques. Successful modification of GCE with the MO and their composite was also confirmed using cyclic voltammetry (CV) technique. GCE-MWCNT/ZnO/29H,31H-Pc was the best electrode towards DA detection with very low detection limit (0.75 μM) which compared favourably with literature, good sensitivity (1.45 μA/μM), resistance to electrode fouling, and excellent ability to detect DA without interference from AA signal. Electrocatalytic oxidation of DA on GCE-MWCNT/ZnO/29H,31H-Pc electrode was diffusion controlled but characterized with some adsorption of electro-oxidation reaction intermediates products. The fabricated sensors are easy to prepare, cost effective and can be applied for real sample analysis of dopamine in drug composition. The good electrocatalytic properties of 29H,31H-Pc and 2,3-Nc were related to their (quantum chemically derived) frontier molecular orbital energies and global electronegativities. The better performance of 29H,31H-Pc than 2,3-Nc in aiding electrochemical oxidation of DA might be due to its better electron accepting ability, which is inferred from its lower E_LUMO and higher χ.

Improvement of electrocatalytic effect in voltammetric sensors based on phthalocyanines

Voltammetric sensors based on phthalocyanines have been used to detect a variety of compounds. In this paper, the state of the art of sensors prepared using classical techniques will be revised. Then, new strategies to improve the performance of the sensors will be described using as example sensors chemically modified with lutetium bisphthalocyanine (LuPc[Formula: see text] dedicated to the detection of phenols of interest in the food industry. Classical LuPc2 carbon paste electrodes can detect phenols such as catechol, caffeic acid or pyrogallol with limits of detection in the range of 10[Formula: see text]–10[Formula: see text] M. The performance can be improved by using nanostructured Langmuir–Blodgett (LB) or Layer by Layer (LbL) films. The enhanced surface to volume ratio produce an increase in the sensitivity of the sensors. Limits of detection of 10[Formula: see text]–10[Formula: see text] M are attained, which are one order of magnitude lower than those obtained using conventional carbon paste electrodes. Moreover, these techniques can be used to co-immobilize two electrocatalytic materials in the same device. The limits of detection obtained in LB sensors combining LuPc2/AuNPs or LuPc2/CNT are further improved. Finally, the LB technique has been used to prepare biosensors where a phenol oxydase (such as tyrosinase or lacasse) is immobilized in a biomimetic environment that preserves the enzymatic activity. Moreover, LuPc2 can be co-immobilized with the enzyme in a lipidic film formed by arachidic acid (AA). LuPc2 can act as an electron mediator facilitating the electron transfer. These biomimetic sensors formed by LuPc2/AA/enzyme show Limits of detection of 10[Formula: see text] M and an enhanced selectivity.

Engineered Carbon-Nanomaterial-Based Electrochemical Sensors for Biomolecules

The study of electrochemical behavior of bioactive molecules has become one of the most rapidly developing scientific fields. Biotechnology and biomedical engineering fields have a vested interest in constructing more precise and accurate voltammetric/amperometric biosensors. One rapidly growing area of biosensor design involves incorporation of carbon-based nanomaterials in working electrodes, such as one-dimensional carbon nanotubes, two-dimensional graphene, and graphene oxide. In this review article, we give a brief overview describing the voltammetric techniques and how these techniques are applied in biosensing, as well as the details surrounding important biosensing concepts of sensitivity and limits of detection. Building on these important concepts, we show how the sensitivity and limit of detection can be tuned by including carbon-based nanomaterials in the fabrication of biosensors. The sensing of biomolecules including glucose, dopamine, proteins, enzymes, uric acid, DNA, RNA, and H2O2 traditionally employs enzymes in detection; however, these enzymes denature easily, and as such, enzymeless methods are highly desired. Here we draw an important distinction between enzymeless and enzyme-containing carbon-nanomaterial-based biosensors. The review ends with an outlook of future concepts that can be employed in biosensor fabrication, as well as limitations of already proposed materials and how such sensing can be enhanced. As such, this review can act as a roadmap to guide researchers toward concepts that can be employed in the design of next generation biosensors, while also highlighting the current advancements in the field.

A sensitive hydrazine hydrate sensor based on a mercaptomethyl-terminated trinuclear Ni(ii) complex modified gold electrode

A mercapto-terminated trinuclear Ni(ii) complex was synthesized and used as an electrocatalyst for the detection of hydrazine hydrate.