Surface-enhanced Raman scattering study of the redox adsorption of p-phenylenediamine on gold or copper surfaces

Surface-functionalized SERS platform for deep learning-assisted diagnosis of Alzheimer's disease

Early diagnosis of Alzheimer's disease is crucial to stall the deterioration of brain function, but conventional diagnostic methods require complicated analytical procedures or inflict acute pain on the patient. Then, label-free Surface-enhanced Raman spectroscopy (SERS) analysis of blood-based biomarkers is a convenient alternative to rapidly obtain spectral information from biofluids. However, despite the rapid acquisition of spectral information from biofluids, it is challenging to distinguish spectral features of biomarkers due to interference from biofluidic components. Here, we introduce a deep learning-assisted, SERS-based platform for separate analysis of blood-based amyloid β (1-42) and metabolites, enabling the diagnosis of Alzheimer's disease. SERS substrates consisting of Au nanowire arrays are fabricated and functionalized in two characteristic ways to compare the validity of different Alzheimer's disease biomarkers measured on our SERS system. The 6E10 antibody is immobilized for the capture of amyloid β (1-42) and analysis of its oligomerization process, while various self-assembled monolayers are attached for different dipole interactions with blood-based metabolites. Ultimately, SERS spectra of blood plasma of Alzheimer's disease patients and human controls are measured on the substrates and classified via advanced deep learning techniques that automatically extract informative features to learn generalizable representations. Accuracies up to 99.5% are achieved for metabolite-based analyses, which are verified with an explainable artificial intelligence technique that identifies key spectral features used for classification and for deducing significant biomarkers.

Ultra-sensitive SERS detection of perfluorooctanoic acid based on self-assembled p-phenylenediamine nanoparticle complex

PFOA is a representative perfluorinated compound that is used as a surfactant in various industrial fields. However, because PFOA has severe side effects due to its strong toxicity, such as carcinogenesis, liver damage, and immune system damage, it is crucial to enable PFOA detection with high sensitivity. Herein, we developed a perfluorooctanoic acid (PFOA) surface-enhanced Raman scattering (SERS) sensor using self-assembled p-phenylenediamine (SAp-PD) nanoparticles and an Ag SERS substrate. For the ultra-sensitive detection of PFOA, we synthesized and optimized SAp-PD, which shows a decrease in SERS intensities when reacting with PFOA. Using the Ag nanograss SERS substrate, the change in intensity that resulted from the SAp-PD and PFOA reaction was amplified. Consequently, we detected the 1.28 pM (detection limit) of PFOA in distilled water. Moreover, PFOA molecules were successfully detected in samples of the PFOA-coated frying pan and rice extraction at concentrations up to 1.69 nM and 10.3 μM, respectively.

Metallic nanoparticles as effective sensors of bio-molecules

This work describes biologically important nanostructures of metals (AgNPs, AuNPs, and PtNPs) and metal oxides (Cu₂ONPs, CuONSs, γ-Fe₂O₃NPs, ZnONPs, ZnONPs-GS, anatase-TiO₂NPs, and rutile-TiO₂NPs) synthesized by different methods (wet-chemical, electrochemical, and green-chemistry methods). The nanostructures were characterized by molecular spectroscopic methods, including scanning/transmission electron microscopy (SEM/TEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction analysis (XRD), photoelectron spectroscopy (XPS), ultraviolet-visible spectroscopy (UV-vis), dynamic light scattering (DLS), Raman scattering spectroscopy (RS), and infrared light spectroscopy (IR). Then, a peptide (bombesin, BN) was adsorbed onto the surface of these nanostructures from an aqueous solution with pH of 7 that did not contain surfactants. Adsorption was monitored using surface-enhanced Raman scattering spectroscopy (SERS) to determine the influence of the nature of the metal surface and surface evolution on peptide geometry. Information from the SERS studies was compared with information on the biological activity of the peptide. The SERS enhancement factor was determined for each of the metallic surfaces.

Experimental and DFT study of Cu(II) removed by Na-montmorillonite

The experimental and theoretical studies on the adsorption of Cu(II) on the surface of Na-montmorillonite (Na-Mt) were reported. Effects of batch adsorption experimental parameters were studied. Density functional theory and molecular dynamics simulations were used to study the adsorption of Cu(II) on montmorillonite (001) surface. The adsorption reached equilibrium within 80 min and the adsorption capacity was 35.23 mg·g^-1 at 25 °C. The adsorption data of Cu(II) were consistent with pseudo-second-order kinetics and Langmuir isotherm models. The adsorption process was dominated by physical adsorption (E_a was 37.08 kJ·mol^-1) with spontaneous endothermic behavior. The influence of coexisting cations on the adsorption capacity of Cu(II) was Mg(II) > Co(II) > Ca(II) > Na(I). The simulation results demonstrated that there were no significant differences in the adsorption energy of Cu(II) at the four adsorption sites on the montmorillonite (001) surface. Cu(II) had more electron transfer than Na(I). The diffusion coefficient of Cu(II) in the aqueous solution system containing montmorillonite was 0.85×10^-10 m²·s^-1. Considerable amounts of Cu(II) ions were adsorbed at a distance of 0.26 and 2.25 Å from the montmorillonite (001) surface. The simulation results provided strong supporting evidence for experimental conclusions.

Benzofurazan derivatives modified graphene oxide nanocomposite: Physico-chemical characterization and interaction with bacterial and tumoral cells

Two novel graphene oxide-benzofuran derivatives composites were obtained through the covalent immobilization of [4-hydrazinyl-7nitrobenz-[2,1,3-d]-oxadiazole (NBDH) and respectively, N1-(7-nitrobenzo[c][1,2,5]oxadiazol-4-yl)benzene-1,2-diamine (NBD-PD), on graphene oxide. This covalent functionalization was achieved by activating the carboxylic groups on the surface of graphene oxide by the reaction with thionyl chloride followed by coupling with the amino group of benzofurazane derivatives to obtain the NBD derivatives grafted on graphene oxide. The formation of new materials was check by Raman spectroscopy, fluorescence, infrared spectroscopy and X-ray photoelectron spectroscopy, thermal analysis, scanning electron microscopy, and elemental mapping. The antimicrobial effect of the new composites was evaluated on Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa, both on planktonic and adherent biofilm populations. The cytotoxic effects of the materials on human colon cancer HCT-116 cell line and the normal human fibroblast BJ cell line were evaluated by investigating cell viability and membrane integrity. Apoptosis and colony forming ability of tumor cells were also investigated following exposure to new materials. The biological results of this study have shown that the new materials have potential in combating biofilm formation and also, the tested materials induced cytotoxicity in human colon cancer HCT-116 cell line with limited effects on normal BJ fibroblasts, suggesting their antitumor potential.

Thin-layer chromatography combined with surface-enhanced Raman scattering for rapid detection of benzidine and 4-aminobiphenyl in migration from food contact materials based on gold nanoparticle doped metal-organic framework

In this work, a rapid and sensitive thin-layer chromatography combined with surface-enhanced Raman spectroscopy method was established for rapid detection of benzidine and 4-aminobiphenyl in migration from food contact materials based on Au nanoparticle doped metal-organic framework. Benzidine and 4-aminobiphenyl were firstly separated by thin-layer chromatography to solve the limitation of their overlapping Raman peaks. Then the target molecules were monitored by adding AuNPs/MIL-101(Cr) on the sample spots. Under the optimum conditions, the concentration of benzidine and 4-aminobiphenyl can be quantitatively measured in the range of 2.0-20.0 and1.0-15.0 μg/L, respectively with good linear relationship, and the limits of detection were 0.21 and 0.23 μg/L, respectively. Furthermore, the developed method was applied to analyze benzidine and 4-aminobiphenyl in migration of different food contact materials. The recoveries of benzidine and 4-aminobiphenyl for migration of food contact materials, including paper cups, polypropylene food containers, and polyethylene glycol terephthalate bottles, were 80.6-116.0 and 80.7-118% with relative standard deviations of 1.1-9.1 and 3.1-9.9%, respectively. Surface-enhanced Raman scattering detection was performed conveniently in the on-plate mode without additional elution process. The method shows great potential in rapid monitoring of hazardous substances with overlapping characteristic Raman peaks in food contact materials.

Ions-free electrochemically synthetized in aqueous media flake-like CuO nanostructures as SERS reproducible substrates for the detection of neurotransmitters

The process of catalytic destruction of tumor cells can be strengthened by introducing copper(II) oxide nanostructures (CuONSs) with receptor's agonists/antagonists immobilized on their surface. Here we show a simple and reliable electrochemical method for the fabrication ions-free flake-like CuO nanostructures in a surfactant/ions free aqueous environment. For the determination of the metal surface plasmon, size, rheology, and structure of the fabricated nanostructures ultraviolet-visible (UV-Vis), Fourier-transform infrared (FT-IR), Raman, and X-ray photoelectron (XPS) spectroscopies as well as scanning electron microscope (SEM), high-resolution transmission electron microscopy with energy dispersive X-ray (HDTEM-EDS), X-ray powder diffraction (XRD), and dynamic light scattering (DLS) analysis were used. The fabricated nanostructures were used as highly sensitive, uniform, and reproducible sensors of a natural ligand (bombesin) of some types of metabotropic seven transmembrane G protein-coupled superfamily receptors (GPCRs), which are over-express on the surface of many malignant tumors. Surface-enhanced Raman scattering (SERS) was used to monitor the geometry of adsorbate, separate, enrich, and detect various bombesin C-terminal fragments. It has been shown that the type of used substrate, surface development, and ions present in the solution have little effect on the mode of adsorption.

Energetic stabilities of thiolated pyrimidines on gold nanoparticles investigated by Raman spectroscopy and density functional theory calculations

The adsorption structures of 2-thiocytosine (2TC) on gold surfaces were examined by means of vibrational Raman spectroscopy and quantum mechanical density functional theory calculations. The 1H-thione-amino form was calculated to be most stable among the six examined tautomers. The three plausible binding geometries of sulfur, pyrimidine nitrogen, and amino group binding modes were calculated to estimate the binding energies of the 1H-thione-amino form with six gold cluster atoms. Thiouracils including 2-thiouracil (2TU), 4-thiouracil (4TU), and 6-methyl-2-thiouracil (6M2TU) were also studied to compare their relative binding energies on gold atoms. The intracellular localization of a DNA base analog of 2TC on gold nanoparticles (AuNPs) in HeLa cells was identified by means of surface-enhanced Raman scattering. AuNPs were modified with 2TC by self-assembly. Our dark-field microscopy and z-depth-dependent confocal Raman spectroscopy indicated that 2TC-assembled AuNPs could be found inside cancer cells. On the other hand, we did not observe noticeably strong Raman peaks in the cases of thiouracils including 2TU, 4TU, and 6M2TU. This may be due to the additional amino group of 2TC, which can lead to a stronger binding of adsorbates on AuNPs.