Gold nanoparticles coated polystyrene/reduced graphite oxide microspheres with improved dispersibility and electrical conductivity for dopamine detection

1-D Carbon Nano-Coils Derived from Almond Skin: Exhibiting Density of State, Diffusivity, Electron Transfer Rate, and Dopamine Redox Modulation Properties Akin to Graphene Oxide

The quest to develop graphene-like biomass-carbon for advanced biomolecule redox modulation and sensing remains a challenge. The primary obstacle is the limited ability of biomass to undergo extensive graphitization during pyrolysis resulting in the formation of amorphous carbon materials with a small carbon-double-bond-carbon domain size (Lsp2), density of state (LDOS), ion diffusivity (D), and electron transfer rate constant (Ks). Herein, using almond skin (AS) the morphology of biomass is demonstrated as the key to overcoming these limitations. AS consists of 1D syringyl/guaiacyl lignin nano-coils which under H2/H2 annealing transform into pyrolytic 1D carbon nano-coils (r-gC). Spectroscopy and microscopy analyses reveal that the sheet layering structure, crystallinity, LDOS, and Lsp2 of r-gC mimic those of graphene oxide (GO). Moreover, its unique 1D morphology and profound microstructure facilitate faster charge transfer and ion diffusion than GO's planar structure, leading to better redox modulation and sensing of the neurotransmitter dopamine (DA) in physiological fluids. r-gC's DA detection limit of 3.62 nM is below the lower threshold found in humans and on par with the state-of-the-art. r-gC is also DA-selective over 14 biochemicals. This study reveals that biomasses with well-defined and compact lignin structures are best suited for developing highly electroactive graphene-like biomass carbon.

Polystyrene microsphere-mediated optical sensing strategy for ultrasensitive determination of aflatoxin M1 in milk

Aflatoxin M₁ (AFM₁) contamination poses a serious threat to human health globally. Hence, it is necessary to develop reliable and ultrasensitive methods for the determination of AFM₁ residue in food products at low levels. In this study, a novel polystyrene microsphere-mediated optical sensing (PSM-OS) strategy was constructed to solve the problems of low sensitivity and susceptibility to interference from the matrix in AFM₁ determination. Polystyrene (PS) microspheres have the advantages of low cost, high stability, and controllable particle size. They can be useful optical signal probes for qualitative and quantitative analyses attributed to the fact that they have strong ultraviolet-visible (UV-vis) characteristic absorption peaks. Briefly, magnetic nanoparticles were modified with the complex of bovine serum protein and AFM₁ (MNP₁₅₀-BSA-AFM₁), and biotinylated antibodies of AFM₁ (AFM₁-Ab-Bio). Meanwhile, PS microspheres were also functionalized with streptavidin (SA-PS₉₅₀). In the presence of AFM₁, a competitive immune reaction was triggered leading to the changes in AFM₁-Ab-Bio concentrations on the surface of MNP₁₅₀-BSA-AFM₁. The complex of MNP₁₅₀-BSA-AFM₁-Ab-Bio binds with SA-PS₉₅₀ to form the immune complexes due to the special binding of biotin and streptavidin. The remaining SA-PS₉₅₀ in the supernatant was determined by UV-Vis spectrophotometer after magnetic separation, which positively correlated with the concentration of AFM₁. This strategy allows for ultrasensitive determination of AFM₁ with limits of detection as low as 3.2 pg/mL. It was also successfully validated for AFM₁ determination in milk samples, and a high consistency was found with the chemiluminescence immunoassay. Overall, the proposed PSM-OS strategy can be used for the rapid, ultrasensitive, and convenient determination of AFM₁, as well as other biochemical analytes.

Recent Advances in Electrochemical and Optical Sensing of Dopamine

Nowadays, several neurological disorders and neurocrine tumours are associated with dopamine (DA) concentrations in various biological fluids. Highly accurate and ultrasensitive detection of DA levels in different biological samples in real-time can change and improve the quality of a patient's life in addition to reducing the treatment cost. Therefore, the design and development of diagnostic tool for in vivo and in vitro monitoring of DA is of considerable clinical and pharmacological importance. In recent decades, a large number of techniques have been established for DA detection, including chromatography coupled to mass spectrometry, spectroscopic approaches, and electrochemical (EC) methods. These methods are effective, but most of them still have some drawbacks such as consuming time, effort, and money. Added to that, sometimes they need complex procedures to obtain good sensitivity and suffer from low selectivity due to interference from other biological species such as uric acid (UA) and ascorbic acid (AA). Advanced materials can offer remarkable opportunities to overcome drawbacks in conventional DA sensors. This review aims to explain challenges related to DA detection using different techniques, and to summarize and highlight recent advancements in materials used and approaches applied for several sensor surface modification for the monitoring of DA. Also, it focuses on the analytical features of the EC and optical-based sensing techniques available.

One-Pot Green Synthesis of Graphene Nanosheets Encapsulated Gold Nanoparticles for Sensitive and Selective Detection of Dopamine

We report a simple new approach for green preparation of gallic acid supported reduced graphene oxide encapsulated gold nanoparticles (GA-RGO/AuNPs) via one-pot hydrothermal method. The as-prepared composites were successfully characterized by using Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, X-ray powder diffraction techniques (XRD), scanning electron microscope (SEM), high resolution transmission electron microscopy (HRTEM) and elemental analysis. The GA-RGO/AuNPs modified electrode behaves as a hybrid electrode material for sensitive and selective detection of dopamine (DA) in presence of ascorbic acid (AA) and uric acid (UA). The GA-RGO/AuNPs modified electrode displays an excellent electrocatalytic activity towards the oxidation of DA and exhibits a wide linear response range over the DA concentrations from 0.01-100.3 μM with a detection limit (LOD) of 2.6 nM based on S/N = 3. In addition, the proposed sensor could be applied for the determination of DA in human serum and urine samples for practical analysis.

Cage to cage study of ionic liquid and cyclic oligosaccharides to form inclusion complexes

Encapsulation of trihexyltetradecylphosphonium chloride inside α and β-cyclodextrins in both aqueous solution and solid state with 1 : 1 stoichiometry.

Study to explore the mechanism to form inclusion complexes of β-cyclodextrin with vitamin molecules

Host–guest inclusion complexes of β-cyclodextrin with two vitamins viz., nicotinic acid and ascorbic acid in aqueous medium have been explored by reliable spectroscopic, physicochemical and calorimetric methods as stabilizer, carrier and regulatory releaser of the guest molecules. Job’s plots have been drawn by UV-visible spectroscopy to confirm the 1:1 stoichiometry of the host-guest assembly. Stereo-chemical nature of the inclusion complexes has been explained by 2D NMR spectroscopy. Surface tension and conductivity studies further support the inclusion process. Association constants for the vitamin-β-CD inclusion complexes have been calculated by UV-visible spectroscopy using both Benesi–Hildebrand method and non-linear programme, while the thermodynamic parameters have been estimated with the help of van’t Hoff equation. Isothermal titration calorimetric studies have been performed to determine the stoichiometry, association constant and thermodynamic parameters with high accuracy. The outcomes reveal that there is a drop in ΔS^o, which is overcome by higher negative value of ΔH^o, making the overall inclusion process thermodynamically favorable. The association constant is found to be higher for ascorbic acid than that for nicotinic acid, which has been explained on the basis of their molecular structures.

Probing inclusion complexes of cyclodextrins with amino acids by physicochemical approach

Formations of host-guest inclusion complexes of two natural amino acids, viz., l-Leucine and l-Isoleucine as guests with α and β-cyclodextrins have been investigated which include diverse applications in modern science such as controlled delivery in the field of pharmaceuticals, food processing etc. Surface tension and conductivity studies establish the formation of inclusion complexes with 1:1 stoichiometry. The interactions of cyclodextrins with amino acids have been supported by density, viscosity, refractive index, hydration and solvation number measurements indicating higher degree of inclusion in case of α-cyclodextrin. l-Leucine interacts more with the hydrophobic cavity of cyclodextrin than its isomer. With the help of stability constant by NMR titration, hydrophobic effect, H-bonds and structural effects the formations of inclusion complexes have been explained.

3-Aminopropyltrimethoxysilane and graphene oxide/reduced graphene oxide-induced generation of gold nanoparticles and their nanocomposites: electrocatalytic and kinetic activity

The role of graphene oxide (GO)/reduced graphene oxide (rGO) in the 3-aminopropyltrimethoxysilane-mediated synthesis of gold nanoparticles in the presence of formaldehyde is reported.

Nanocomposites Based on Thermoplastic Polymers and Functional Nanofiller for Sensor Applications

Thermoplastic polymers like polyolefins, polyesters, polyamide, and styrene polymers are the most representative commodity plastics thanks to their cost-efficient manufacturing processes, excellent thermomechanical properties and their good environmental compatibility, including easy recycling. In the last few decades much effort has been devoted worldwide to extend the applications of such materials by conferring on them new properties through mixing and blending with different additives. In this latter context, nanocomposites have recently offered new exciting possibilities. This review discusses the successful use of nanostructured dispersed substrates in designing new stimuli-responsive nanocomposites; in particular, it provides an updated description of the synthetic routes to prepare nanostructured systems having the typical properties of thermoplastic polymers (continuous matrix), but showing enhanced optical, conductive, and thermal features dependent on the dispersion topology. The controlled nanodispersion of functional labeled clays, noble metal nanoparticles and carbon nanotubes is here evidenced to play a key role in producing hybrid thermoplastic materials that have been used in the design of devices, such as NLO devices, chemiresistors, temperature and deformation sensors.

Biogenic gold nanoparticles-reduced graphene oxide nanohybrid: synthesis, characterization and application in chemical and biological reduction of nitroaromatics

The biogenic AuNPs/rGO can participate in and accelerate electron transfer, and catalyze both chemical and biological reduction of nitroaromatics efficiently.

Electrodeposition of gold nanoparticles on a pectin scaffold and its electrocatalytic application in the selective determination of dopamine

Electrodeposition of gold nanoparticles on a pectin scaffold for the selective determination of dopamine.

Graphene and its nanocomposite material based electrochemical sensor platform for dopamine

In this review, the recent progress in the electrochemical sensing of dopamine with various graphene and their nanocomposite materials modified electrodes are presented.