Gold and Silver Nanoparticles as Biosensors: Characterization of Surface and Changes in the Adsorption of Leucine Dipeptide under the Influence of Substituent Changes.

Early detection of diseases can increase the chances of successful treatment and survival. Therefore, it is necessary to develop a method for detecting or sensing biomolecules that cause trouble in living organisms. Disease sensors should possess specific properties, such as selectivity, reproducibility, stability, sensitivity, and morphology, for their routine application in medical diagnosis and treatment. This work focuses on biosensors in the form of surface-functionalized gold (AuNPs) and silver nanoparticles (AgNPs) prepared using a less-time-consuming, inexpensive, and efficient synthesis route. This allows for the production of highly pure and stable (non-aggregating without stabilizers) nanoparticles with a well-defined spherical shape, a desired diameter, and a monodisperse distribution in an aqueous environment, as confirmed by transmission electron microscopy with energy-dispersive X-ray spectroscopy (TEM-EDS), X-ray diffraction (XRD), photoelectron spectroscopy (XPS), ultraviolet-visible (UV-VIS) spectroscopy, and dynamic light scattering (DLS). Thus, these nanoparticles can be used routinely as biomarker sensors and drug-delivery platforms for precision medicine treatment. The NPs' surface was coated with phosphonate dipeptides of L-leucine (Leu; l-Leu-C(R1)(R2)PO3H2), and their adsorption was monitored using SERS. Reproducible spectra were analyzed to determine the orientation of the dipeptides (coating layers) on the nanoparticles' surface. The appropriate R2 side chain of the dipeptide can be selected to control the arrangement of these dipeptides. This allows for the proper formation of a layer covering the nanoparticles while also simultaneously interacting with the surrounding biological environment, such as cells, tissues, and biological fluids.

Homogeneous Pt nanostructures surface functionalized with phenylboronic acid phosphonic acid derivatives as potential biochemical nanosensors and drugs: SERS and TERS studies.

Here, surface-enhanced Raman scattering (SERS) and tip-enhanced Raman scattering (TERS) were used to characterize the selective adsorption of N-substituted 4-[(NH-R)(phosphono)-S-methyl]phenylboronic acids on the surface of platinum nanoparticles (PtNPs) from an aqueous solution and from air. The nature of the interaction of the studied compounds with the PtNPs/H2 O and PtNPs/air interfaces was discussed and compared. For this purpose, 4-[(N-anilino)(phosphono)-S-methyl]phenylboronic acid (1-PBA-PA) and its two analogs (2-PBA-PA and bis{1-PBA-PA}) as well as the PtNPs were synthesized in surfactant/ion-free solution via a synthetic route that allows control of the size and morphology of the NPs. The positively charged PtNPs with a size of ~12 nm were characterized by ultraviolet-visible spectroscopy (UV-Vis), dynamic light scattering (DLS), scanning electron microscopy (SEM), and X-ray powder diffraction (XRD).

Spectroscopic characterization and in vitro studies of biological activity of bradykinin derivatives.

Eleven multiple analogs of bradykinin-a peptide that is a natural ligand of B1 and B2 receptors but does not bind or activate the B1 receptor unless Arg9 is removed from the sequence by the action of carboxypeptidase N-were synthesized. Their biological activity was examined on T-REx cell lines expressing B1 or B2 receptors using the intracellular IP1 assay. The mRNA expression of B1R and B2R in the lysate of tumor cell lines, e.g., U87-MG (human astrocytoma), SHP-77 (human small cell lung cancer), and H4 (human brain glioma), was determined. For five B1R antagonists, adsorption at the liquid/solid interface (Au nanoparticles (AuNPs) served as the solid surface) was discussed in terms of the vibrations of molecular fragments (structural factors) responsible for the biological properties of these analogs.

SERS/TERS Characterization of New Potential Therapeutics: The Influence of Positional Isomerism, Interface Type, Oxidation State of Copper, and Incubation Time on Adsorption on the Surface of Copper(I) and (II) Oxide Nanoparticles.

The aim of this study was to investigate how the oxidation state of copper (Cu(I) vs Cu(II)), the nature of the interface (solid/aqueous vs solid/air), positional isomerism, and incubation time affect the functionalization of the surface of copper oxide nanostructures by [(butylamino)(pyridine)methyl]phenylphosphinic acid (PyPA). For this purpose, 2-, 3-, and 4-isomers of PyPA and the nanostructures were synthesized. The nanostructure were characterized by UV-visible spectroscopy (UV-vis), scanning electron microscopy (SEM), Raman spectroscopy (RS), and X-ray diffraction (XRD) analysis, which proved the formation of spherical Cu2O nanoparticles (Cu2ONPs; 1500-600 nm) and leaf-like CuO nanostructures (CuONSs; 80-180/400-700 nm, width/length). PyPA isomers were deposited on the surface of NSs, and adsorption was investigated by surface-enhanced Raman scattering (SERS) and tip-enhanced Raman scattering (TERS). The changes of adsorption on the surface of copper oxide NSs caused by the above-mentioned factors were described and the enhancement factor on this substrate was calculated.

Determination of the Influence of Various Factors on the Character of Surface Functionalization of Copper(I) and Copper(II) Oxide Nanosensors with Phenylboronic Acid Derivatives.

In this work, we attempt to determine the influence of the oxidation state of copper [Cu(I) vs Cu(II)], the nature of the interface (solid/aqueous vs solid/air), the incubation time, and the structure of N-substituted phenylboronic acids (PBAs) functionalizing the surface of copper oxide nanostructures (NSs) on the mode of adsorption. For this purpose, 4-[(N-anilino)(phosphono)-S-methyl]phenylboronic acid (1-PBA) and its two analogues (2-PBA and bis{1-PBA}) and the copper oxide NSs were synthesized in a surfactant-/ion-free solution via a synthetic route that allows controlling the size and morphology of NSs. The NSs were characterized by scanning electron microscopy, ultraviolet-visible spectroscopy, Raman spectroscopy, and X-ray diffraction, which confirmed the formation of spherical Cu2O nanoparticles (Cu2ONPs) with a size of 1.5 µm to 600 nm crystallized in a cubic cuprite structure and leaf-like CuO nanostructures (CuONSs) with dimensions of 80-180 nm in width and 400-700 nm in length and crystallized in a monoclinic structure. PBA analogues were deposited on the surface of the copper oxide NSs, and adsorption was investigated using surface-enhanced Raman spectroscopy (SERS). The changes in the orientation of the molecule relative to the substrate surface caused by the abovementioned factors were described, and the signal enhancement on the copper oxide NSs was determined. This is the first study using vibrational spectroscopy for these compounds.

Application of Alanine Scanning to Determination of Amino Acids Essential for Peptide Adsorption at the Solid/Solution Interface and Binding to the Receptor: Surface-Enhanced Raman/Infrared Spectroscopy versus Bioactivity Assays.

The article describes the application of the alanine-scanning technique used in combination with Raman, surface-enhanced Raman, attenuated total reflection Fourier transform infrared, and surface-enhanced infrared absorption (SEIRA) spectroscopies, which allowed defining the role of individual amino acid residues in the C-terminal 6-14 fragment of the bombesin chain (BN6-14) on the path of its adsorption on the surface of Ag (AgNPs) and Au nanoparticles (AuNPs). A reliable analysis of the SEIRA spectra of these peptides was possible, thanks to a curve fitting of these spectra. By combining alanine-scanning with biological activity studies using cell lines overexpressing bombesin receptors and the intracellular inositol monophosphate assay, it was possible to determine which peptide side chains play a significant role in binding a peptide to membrane-bound G protein-coupled receptors (GPCRs). Based on the analysis of spectral profiles and bioactivity results, conclusions for the specific peptide-metal and peptide-GPCR interactions were drawn and compared.

SERS activity and spectroscopic properties of Zn and ZnO nanostructures obtained by electrochemical and green chemistry methods for applications in biology and medicine.

This work for the first time evaluates the ability of homogeneous, stable, and pure zinc oxide nanoparticles (ZnONPs-GS) synthesized by "green chemistry" - an environmentally friendly, cheap, and easy method that allows efficient use of plant waste, such as banana peels, for the selective detection of four neurotransmitters present in body fluids and promotion of the SERS effect. Selective adsorption on ZnONPs-GS was compared with adsorption on the surface of (1) ZnONPs, which were obtained by electrochemical dissolution of zinc in a solution free of surfactants and (2) mechanically polished surface of bare Zn. The study showed that SERS spectroscopy using unique marker bands allows distinguishing whether the adsorbate is deposited on the surface of zinc or zinc oxide. Thus, the combination of the SERS technique with an optical probe can allow an in vivo determination of the condition of galvanized implants. The use of SERS has been extended to monitor the photocatalytic properties of surface-functionalized ZnO nanoparticles. It has been shown that despite the same structure, purity, and adsorption properties, ZnONPs-GS obtained using "green chemistry" are more bio-friendly for biological material than those obtained by the electrochemical method. This is because the surface of ZnONPs-GS is free of hydroxyl groups, which can easily form reactive oxygen species when the surface is exposed to visible radiation. Thus, surface-functionalized ZnONPS-GS can protect the biological material from the damage caused by the production and attack of an excess of ROS. Also, for an exemplary neurotransmitter, structural changes when it is not-covalently bound to Zn/ZnO were compared with the structural changes of this neurotransmitter deposited on the surface of various metals (Cu, α-Ti, and α-Fe) and metal oxides (leaf-like CuO, rutile-TiO2, and γ-Fe2O3). It has been shown that adsorption only slightly depends on the type of metallic surface and the development of this surface for roughness up to 1 micron. Metal substrates were characterized before and after the neurotransmitters' adsorption. UV-Vis, Raman, and ATR-FTIR confirmed the formation of ZnO nanoparticles. XRD showed a high crystalline structure of wurtzite. TEM and DLS showed that nanoparticles are spherical, well dispersed, and have a uniform size.

Guar Gum as an Eco-Friendly Corrosion Inhibitor for Pure Aluminium in 1-M HCl Solution.

Guar gum (GG) was investigated as a possible eco-friendly corrosion inhibitor for pure aluminium in a 1-M HCl solution at different temperatures and immersion times using gravimetric and electrochemical techniques. The results showed that GG was a good corrosion inhibitor for pure aluminium in the studied environment. The inhibition efficiency of GG increased with increasing inhibitor concentration and immersion time but decreased with increasing temperature. Polarisation measurements revealed that GG was a mixed type inhibitor with a higher influence on the cathodic reaction. The adsorption behaviour of the investigated inhibitor was found to obey the Temkin adsorption isotherm and the calculated values of the standard free adsorption energy indicate mixed-type adsorption, with the physical adsorption being more dominant. The associated activation energy (Ea) and the heat of adsorption (Qa) supported the physical adsorption nature of the inhibitor. Fourier-transform infrared spectroscopy (FTIR) and Raman/SERS were used to explain the adsorption interaction between the inhibitor with the surface of the metal. The results suggested that most inhibition action of GG is due to its adsorption of the metal surface via H-bond formation.

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.

Interaction of bombesin and its fragments with gold nanoparticles analyzed using surface-enhanced Raman spectroscopy.

This work demonstrates the application of commercially available stable surface composed of gold nanograins with diameters ranging from 70 to 226nm deposited onto silicon wafer for surface-enhanced Raman scattering investigations of biologically active compounds, such as bombesin (BN) and its fragments. BN is an important neurotransmitter involved in a complex signaling pathways and biological responses; for instance, hypertensive action, contractive on uterus, colon or ileum, locomotor activity, stimulation of gastric and insulin secretion as well as growth promotion of various tumor cell lines, including: lung, prostate, stomach, colon, and breast. It has also been shown that 8-14 BN C-terminal fragment partially retains the biological activity of BN. The SERS results for BN and its fragment demonstrated that (1) three amino acids from these peptides sequence; i.e., l-histidine, l-methionine, and l-tryptophan, are involved in the interaction with gold coated silicon wafer and (2) the strength of these interactions depends upon the aforementioned amino acids position in the peptide sequence.

SERS characterization of neuropeptide Y and its C-terminal fragments deposited onto colloidal gold nanoparticle surface.

It has been suggested that the family of neuropeptide Y (NPY) peptides is a promising target for the neuroprotective therapy; therefore, knowledge of the structure of these biologically active compounds and their behavior at solid/liquid interface is important in order to design new analogues. Because there is still a lack of detailed information on the behavior of NPY and its mutated analogues at the solid/liquid interfaces, in this work surface-enhanced Raman spectroscopy (SERS) analysis was used to investigate NPY and its native NPY3-36, NPY13-36, and NPY22-36 and mutated acetyl-(Leu28,31)-NPY24-36C-terminal fragments, acting on Y2 receptors (Y2R), in order to determine their possible metal surface/molecule interactions. In these studies, colloidal gold nanoparticle surface served as a solid surface, whereas an aqueous solution was used as a liquid medium. The observed differences in the band intensities, wavenumbers, and widths allowed us to draw conclusions on an adsorption mode of NPY and on changes in this mode upon the shortening of the peptide chain and increase in solution pH (from pH 3 to pH 11). Briefly, three different species of Tyr were identified onto the colloidal gold surface depending upon the length of the peptide chain and solution pH. Tyrosine (TyrOH) is present in a basic medium. Tyrosinate (TyrO-) is present in an acidic solution, whereas phenoxyl radical (Tyr*) appears at neutral pH for peptides having relatively short peptide chain (acetyl-(Leu28,31)-NPY24-36). The elongation of the peptide chain partially (NPY13-36 and NPY22-36) or completely (NPY3-36 and NPY) protects the Tyr residue against conversion to the radical form.

Study of cellulolytic enzyme immobilization on copolymers of N-vinylformamide.

This study was focused on finding of effective carriers suitable for the immobilization of cellulase. Copolymers of N-vinylformamide (NFV) and divinylbenzene (DVB) were synthesized by free radical crosslinking polymerization in inverse suspension. Methyl silicone oil was used as the continuous phase. Three polymeric carriers based on P(NVF-co-DVB) with varying degrees of crosslinking and spherical particles with different grain sizes were obtained. The formamide groups in these carriers were hydrolyzed to amino groups, yielding three P(VAm-co-DVB) polymers with vinylamine units. Enzyme, cellulase (Novozym® 476), was immobilized onto carriers with vinylamine (through glutaraldehyde) and vinylformamide groups (without glutaraldehyde). The efficiency of the enzyme immobilization was determined based on the enzymatic activity of the enzyme during the catalytic reaction relative to that of the native enzyme. All tested carriers were found to be effective carriers for the immobilization of cellulase. However, the catalytic activity of cellulase immobilized on the P(VAM-co-DVB0.27)/2000/350 carrier was higher than that for the native enzyme. In addition, two molecular spectroscopy methods, Fourier-transform absorption infrared spectroscopy (FT-IR) and Fourier-transform Raman spectroscopy (FT-Raman), were used to analyze the carriers. These studies provided complete information regarding the structure of the studied copolymers.

Neuropeptide Y and its C-terminal fragments acting on Y2 receptor: Raman and SERS spectroscopy studies.

In this paper, we present spectroscopic studies of neuropeptide Y (NPY) and its native NPY(3-36), NPY(13-36), and NPY(22-36) and mutated acetyl-(Leu(28,31))-NPY(24-36)C-terminal fragments acting on Y2 receptor. Since there is some evidence for the correlation between the SERS patterns and the receptor binding ability, we performed a detailed analysis for these compounds at the metal/water interface using Raman spectroscopy (RS) and surface-enhanced Raman spectroscopy (SERS) methods. Many studies have suggested that interactions of this kind are crucial for a variety of biomedical and biochemical phenomena. The identification of amino acids in these peptide sequences by SERS allowed us to determine which molecular fragments were responsible for the interaction with the silver nanoparticle surface. Our findings demonstrated that in all of the investigated compounds, the NPY(32-36)C-terminal fragment (Thr(32)-Arg(33)-Gln(34)-Arg(35)-Tyr(36)NH2) was involved in the adsorption process onto metal substrate. The results of the present study suggest that the same molecular fragment interacts with the Y2 receptor, what proved the usefulness of the SERS method in the study of these biologically active compounds. The search for analogs acting on Y2 receptor may be important from the viewpoint of possible future clinical applications.

Pigment characterization of important golden age panel paintings of the 17th century.

Samples were obtained from two world-famous 17th century panel paintings of the Gdansk school of panting: 'Seven Acts of Charity' (1607, in St. Mary's Church in Gdansk, Poland) by Anton Möller and 'Angelic Concert' (1611, in Diocesan Museum in Pelplin, Poland) by Hermann Han. Micro-Raman spectroscopy (MRS), optical microscopy (OM), and X-ray fluorescence (XRF) spectroscopy studies of the samples were performed to characterize the pigments present in the individual painting layers (a rich palette of white, black, blue, red, and yellow pigments) and the pictorial techniques used by the artists.

Raman, surface-enhanced Raman, and density functional theory characterization of (diphenylphosphoryl)(pyridin-2-, -3-, and -4-yl)methanol.

This work presents near-infrared Raman spectroscopy (FT-RS) and surface-enhanced Raman scattering (SERS) studies of three pyridine-α-hydroxymethyl biphenyl phosphine oxide isomers: (diphenylphosphoryl)(pyridin-2-yl)methanol (α-Py), (diphenylphosphoryl)(pyridin-3-yl)methanol (ß-Py), and (diphenylphosphoryl)(pyridin-4-yl)methanol (γ-Py) adsorbed onto colloidal and roughened in oxidation-reduction cycles silver surfaces. The molecular geometries in the equilibrium state and vibrational frequencies were calculated by density functional theory (DFT) at the B3LYP 6-311G(df,p) level of theory. The results imply that the most stable structure of the investigated molecules is a dimer created by two intermolecular hydrogen bonds between the H atom of the α-hydroxyl group (in up (HOU) or down (HOD) stereo bonds position) and the O atom of tertiary phosphine oxide (═O) of the two monomers. Comparison the FT-RS spectra with the respective SERS spectra allowed us to predict the orientation of the hydroxyphosphonate derivatives of pyridine that depends upon both the position of the substituent relative to the ring N atom (in α-, ß-, and γ-position, respectively) and the type of silver substrate.

Vibrational characterization and adsorption mode on SERS-active surfaces of guanidino-(bromophenyl)methylphosphonic acid.

This work presents adsorption geometry of [N-butyl-guanidino-(4-bromophenyl)methyl] phosphonic acid (4-BrPhG(n-But)P) on different SERS-active substrates (colloidal and specifically prepared Ag and Au roughened substrates). The adsorption mode is deduced from the SERS selection rules and several characteristic bands of the 4-BrPhG(n-But)P molecular fragments. The SERS spectra are compared to the experimental FT-Raman spectrum. In addition, the vibrational wavenumbers and PED's obtained for 4-BrPhG(n-But)P by using density functional theory methods with B3LYP/6-311++G(**) level of theory and PCM model is briefly presented.

Crystalline transition and morphology variation of polyamide 6/CaCl2 composite during the decomplexation process.

In this work, we developed a new method to prepare porous PA6 with different morphologic feature and crystalline forms via the decomplexation of PA6/CaCl2 composite. The structures and morphology of thus obtained materials were characterized by vibrational spectroscopy (FT-IR and Raman) and scanning electron microscope (SEM) method. When amorphous PA6/CaCl2 composite films were treated in water at room temperature, PA6 re-arranges into γ form. However, decomplexation of the PA6/CaCl2 composite in boiling water produces PA6 in α crystalline form. If the PA6/CaCl2 composite is soaked in methanol, part of PA6 is dissolved or swollen in methanol/metal salt solutions. As a result, a dissolve/precipitation process occurred during the decomplexation process, which led to the formation of PA6 in α crystalline form. Further investigation demonstrates that the morphologies of the porous PA6 could be adjusted by using different solvents and/or different decomplexation conditions.

Influence of substituent type and position on the adsorption mechanism of phenylboronic acids: infrared, Raman, and surface-enhanced Raman spectroscopy studies.

This paper shows systematic spectroscopic studies using Fourier-transform infrared absorption (FT-IR), Fourier-transform Raman (FT-Raman), and surface-enhanced Raman (SERS) in an aqueous silver sol of fluoro and formyl analogues of phenylboronic acids: 2-fluorophenylboronic acid (2-F-PhB(OH)2), 3-fluorophenylboronic acid (3-F-PhB(OH)2), 4-fluorophenylboronic acid (4-F-PhB(OH)2), 2-formylphenylboronic acid (2-CHO-PhB(OH)2), 3-formylphenylboronic acid (3-CHO-PhB(OH)2), and 4-formylphenylboronic acid (4-CHO-PhB(OH)2). To produce an extensive table of vibrational spectra, density functional theory (DFT) calculations with the B3LYP method at the 6-311++G(d,p) level of theory were performed for the ground state geometry of the most stable species, dimers in cis-trans conformation. On the basis of the SERS spectral profile, the adsorption modes of the phenylboronic acid isomers were proposed. The type of substituent and its position in the phenyl ring have a strong influence on the geometry of isomers on the silver nanoparticle's surface. This effect was especially evident in the case of 4-CH-PhB(OH)2, for which dearomatization of the phenyl ring took place upon adsorption.

Vibrational and theoretical studies of the structure and adsorption mode of m-nitrophenyl α-guanidinomethylphosphonic acid analogues on silver surfaces.

This work presents Fourier transform Raman (FT-Raman), Fourier transform absorption infrared (FT-IR), and surface-enhanced Raman scattering (SERS) spectroscopic investigations of three m-nitrophenyl α-guanidinomethylphonic acids, including m-NO2PhG(cHex)P, m-NO2PhG(Morf)P, and m-NO2PhG(An)P, adsorbed onto colloidal and roughened silver surfaces. The SERS spectra were deconvoluted to determine the overlapped bands from which the specific molecular orientation can be deducted. The vibrational wavenumbers are calculated through density functional theory (DFT) at the B3LYP/6-31++G** level with the Gaussian 03, Raint, GaussSum 0.8, and GAR2PED software packages. The experimental and calculated vibrational bands are compared to those from SERS for the investigated compounds adsorbed on colloidal and roughened silver surfaces. The geometry of these molecules on the SERS-active silver surfaces is deduced from the observed changes in both the intensity and width of the Raman bands in the spectra of the bound species relative to the free species.

Investigation of adsorption mode of a novel group of N-benzylamino(boronphenyl)methylphosphonic acids using SERS.

Here, we report a systematic surface-enhanced Raman spectroscopy (SERS) study of the structures of five N-benzylamino(boronphenyl)-methylphosphonic acids: N-benzylamino-(3-boronphenyl)-S-methylphosphonic acid (m-PhS), N-benzylamino-(4-boronphenyl)-S-methylphosphonic acid (p-PhS), N-benzylamino-(2-boronphenyl)-R-methylphosphonic acid (o-PhR), N-benzylamino-(3-boronphenyl)-R-methyl-phosphonic acid (m-PhR), and N-benzylamino-(4-boronphenyl)-R-methylphosphonic acid (p-PhR) adsorbed on nanometer-sized colloidal particles (20-25 nm). For example, we showed that all of these molecules interact with the colloidal surface through a boronophenyl ring, which plane remained vertical on the surface. For p-PhS, a preferential interaction between the P=O bond and the colloidal silver surface is observed to be stronger than for the remaining compounds. The -P(OH)(2) and -B(OH)(2) fragments take part in the adsorption process. However, the B-O bond of p-PhS and p-PhR seemed to be tilted with respect to the silver surface.