Using Nanomaterials as Excellent Immobilisation Layer for Biosensor Design

The endless development in nanotechnology has introduced new vitality in device fabrication including biosensor design for biomedical applications. With outstanding features like suitable biocompatibility, good electrical and thermal conductivity, wide surface area and catalytic activity, nanomaterials have been considered excellent and promising immobilisation candidates for the development of high-impact biosensors after they emerged. Owing to these reasons, the present review deals with the efficient use of nanomaterials as immobilisation candidates for biosensor fabrication. These include the implementation of carbon nanomaterials-graphene and its derivatives, carbon nanotubes, carbon nanoparticles, carbon nanodots-and MXenes, likewise their synergistic impact when merged with metal oxide nanomaterials. Furthermore, we also discuss the origin of the synthesis of some nanomaterials, the challenges associated with the use of those nanomaterials and the chemistry behind their incorporation with other materials for biosensor design. The last section covers the prospects for the development and application of the highlighted nanomaterials.

Unprecedented enhancement and preservation of the peroxidase activity of cytochrome-c packaged with ionic liquid-modified gold nanoparticles by offsetting temperature and time stresses

Inspired by the biocompatibility of ionic liquids and their dexterousness for the preservation of enzyme structure and activity, herein, the interactions of Cyt-c with naked AuNPs and four IL-mediated AuNPs, which were formed by the fabrication of ILs with common cation 1-ethyl-3-methyl-imidazolium (EMIM) and different anions, to obtain AuNP-IL1 [(BF4)^-1 anion], AuNP-IL2 [(CH₃OSO₃)^-1 anion], AuNP-IL3 [(CH₃CH₂OSO₃)^-1 anion], and (AuNP-IL4) [Cl^-1 anion], were studied. Through this work, the peroxidase activity observed in the presence of a lower concentration IL-AuNPs is exceptionally increased (16 fold). IL-AuNPs preferentially counteract the temperature gradient change and long-term solvent preservation effects while persistently maintaining the Cyt-c peroxidase activity without much depreciation. The hydrodynamic diameter (d_H) of the Cyt-c-AuNP system was obtained, which supported the TEM results. Furthermore, to evaluate the effect of Cyt-c interaction with the AuNPs, a Zeta potential analysis was performed. Taken together, the binding of IL-AuNPs with Cyt-c, diameter size analysis, zeta potential, structural integrity evaluation using the DichroWeb software and morphology results suggest the interaction order of the IL-AuNPs to be in a sequence of AuNP-IL2 > AuNP-IL3 > AuNP- IL4 > AuNP-IL1 > Naked AuNPs. Moreover, results indicate that the IL anions play a dominating role in the modulation of interactions between IL-mediated AuNPs and Cyt-c. The study strongly supports the promising character of sulfur-containing IL-mediated AuNPs for Cyt-c immobilization simultaneously opening new avenues for the application of greener and biocompatible nanoparticles with drug delivery and therapeutic applications.

Improved Oxygen Reduction on GC-Supported Large-Sized Pt Nanoparticles by the Addition of Pd

PdPt bimetallic nanoparticles on carbon-based supports functioning as advanced electrode materials have attracted attention due to their low content of noble metals and high catalytic activity for fuel cell reactions. Glassy carbon (GC)-supported Pt and PdPt nanoparticles, as promising catalysts for the oxygen reduction reaction (ORR), were prepared by the electrochemical deposition of Pt and the subsequent spontaneous deposition of Pd. The obtained electrodes were examined using X-ray Photoelectron Spectroscopy (XPS), Atomic Force Microscopy (AFM), and electroanalytical techniques. An XPS analysis of the PdPt/GC with the highest ORR performance revealed that the stoichiometric ratio of Pd: Pt was 1:2, and that both Pt and Pd were partially oxidized. AFM images of PdPt2/GC showed the full coverage of GC with PdPt nanoparticles with sizes from 100–300 nm. The ORR activity of PdPt2/GC in an acid solution approached that of polycrystalline Pt (E1/2 = 0.825 V vs. RHE), while exceeding it in an alkaline solution (E1/2 = 0.841 V vs. RHE). The origin of the improved ORR on PdPt2/GC in an alkaline solution is ascribed to the presence of a higher amount of adsorbed OH species originating from both PtOH and PdOH that facilitated the 4e-reaction pathway.

SERS and Indicator Paper Sensing of Hydrogen Peroxide Using Au@Ag Nanorods

The detection of hydrogen peroxide and the control of its concentration are important tasks in the biological and chemical sciences. In this paper, we developed a simple and quantitative method for the non-enzymatic detection of H₂O₂ based on the selective etching of Au@Ag nanorods with embedded Raman active molecules. The transfer of electrons between silver atoms and hydrogen peroxide enhances the oxidation reaction, and the Ag shell around the Au nanorod gradually dissolves. This leads to a change in the color of the nanoparticle colloid, a shift in LSPR, and a decrease in the SERS response from molecules embedded between the Au core and Ag shell. In our study, we compared the sensitivity of these readouts for nanoparticles with different Ag shell morphology. We found that triangle core-shell nanoparticles exhibited the highest sensitivity, with a detection limit of 10^-4 M, and the SERS detection range of 1 × 10^-4 to 2 × 10^-2 M. In addition, a colorimetric strategy was applied to fabricate a simple indicator paper sensor for fast detection of hydrogen peroxide in liquids. In this case, the concentration of hydrogen peroxide was qualitatively determined by the change in the color of the nanoparticles deposited on the nitrocellulose membrane.

Tuning the structure and magnetic behavior of Ni–Ir-based nanoparticles in ionic liquids

We report on a simple preparation of extremely small diameter (ca. 2 nm) Ni–Ir-based NPs with either core–shell like or alloy-like microstructures.

Confined naked gold nanoparticles in ionic liquid films

Surface-clean Au nanoparticles (NPs) confined in films of ionic liquids (ILs) can be easily fabricated by sputtering deposition. A silicon wafer coated with films of both hydrophobic (bis((trifluoromethyl)sulfonyl)amide, NTf₂^-) and hydrophilic (tetrafluoroborate, BF₄^-) imidazolium-based ILs forms an 'ionic carpet-like' structure that can be easily decorated with Au NPs of 5.1 and 6.5 nm mean diameter, respectively. The depth profile distribution of the Au NPs depends on the arrangement of the IL, which is controlled mainly by the anion volume. Higher concentrations of Au NPs are found closer to the IL surface for the system containing a larger anion (NTf₂) whereas Au NPs are located deeper in the IL for the system containing a smaller anion (BF₄). The Au NPs are well distributed over the IL/Si support and are strictly confined in a single layer of the IL. This method is among the most simple and versatile for the generation of liquid layers containing surface-clean, stable and confined Au NPs.

A sensitive electrochemical immunosensor for the detection of squamous cell carcinoma antigen by using PtAu nanoparticles loaded on TiO2colloidal spheres as labels

A sensitive sandwich-type electrochemical immunosensor for detection of squamous cell carcinoma antigen (SCCA) was developed by using PtAu nanoparticles loaded on TiO₂colloidal spheres (PtAu/TiO₂) as secondary-antibody (Ab₂) labels.

Straightforward synthesis of bimetallic Co/Pt nanoparticles in ionic liquid: atomic rearrangement driven by reduction-sulfidation processes and Fischer-Tropsch catalysis

Unsupported bimetallic Co/Pt nanoparticles (NPs) of 4.4 ± 1.9 nm can be easily obtained by a simple reaction of [bis(cylopentadienyl)cobalt(ii)] and [tris(dibenzylideneacetone) bisplatinum(0)] complexes in 1-n-butyl-3-methylimidazolium hexafluorophosphate IL at 150 °C under hydrogen (10 bar) for 24 h. These bimetallic NPs display core-shell like structures in which mainly Pt composes the external shell and its concentration decreases in the inner-shells (CoPt3@Pt-like structure). XPS and EXAFS analyses show the restructuration of the metal composition at the NP surface when they are subjected to hydrogen and posterior H2S sulfidation, thus inducing the migration of Co atoms to the external shells of the bimetallic NPs. Furthermore, the isolated bimetallic NPs are active catalysts for the Fischer-Tropsch synthesis, with selectivity for naphtha products.

A facile one-pot method to synthesize a polypyrrole/hemin nanocomposite and its application in biosensor, dye removal, and photothermal therapy

In this work, we introduced a facile method for the construction of a polypyrrole/hemin (PPy/hemin) nanocomposite via one-pot chemical oxidative polymerization. In this process, a hemin molecule serving as a dopant was entrapped in the PPy nanocomposite during chemical oxidative polymerization. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), and UV-visible spectroscopy results demonstrated that the PPy/hemin nanocomposite was successfully synthesized. The as-prepared nanocomposite exhibited intrinsic peroxidase-like catalytic activities, strong adsorption properties, and an excellent near-infrared (NIR) light-induced thermal effect. We utilized the nanomaterials to catalyze the oxidation of a peroxidase substrate 3,3,5,5-tetramethylbenzidine by H2O2 to the oxidized colored product which provided a colorimetric detection of glucose. As low as 50 μM glucose could be detected with a linear range from 0.05 to 8 mM. Moreover, the obtained nanocomposite also showed excellent removal efficiency for methyl orange and rhodamine B and a photothermal effect, which implied a promising application as the pollutant adsorbent and photothermal agent. The unique nature of the PPy/hemin nanocomposite makes it very promising for the fabrication of inexpensive, high-performance bioelectronic devices in the future.