Surface enhanced infrared absorption spectroscopy based on gold nanostars and spherical nanoparticles

In this study, we prepared different shapes of gold nanoparticles by seed-mediated growth method and applied them on the photoelectrodes of dye-sensitized solar cells (DSSCs) to study the surface plasma resonant (SPR) effect of gold nanoparticles on the photoelectrodes of dye-sensitized solar cells. The analyses of field emission scanning electron microscopy show that the average diameter of the spherical gold nanoparticles is 45 nm, the average length and width of the short gold nanorods were 55 and 22 nm, respectively, and the average length and width of the long gold nanorods were 55 and 14 nm, respectively. The aspect ratio of the short and long gold nanorods was about 2.5 and 4, respectively. The results of ultraviolet–visible absorption spectra show that the absorption wavelength is about 540 nm for spherical gold nanoparticles, and the absorption of the gold nanorods reveals two peaks. One is about 510 to 520 nm, and the other is about 670 and 710 nm for the short and long gold nanorods, respectively. The best conversion efficiency of the dye-sensitized solar cells with spherical gold nanoparticles and short and long gold nanorods added in is 6.77%, 7.08%, and 7.29%, respectively, and is higher than that of the cells without gold nanoparticles, which is 6.21%. This result indicates that the effect of gold nanoparticles on the photoelectrodes can increase the conductivity and reduce the recombination of charges in the photoelectrodes, resulting in the increase of conversion efficiency for DSSCs. In addition, the long gold nanorods have stronger SPR effect than the spherical gold nanoparticles and short gold nanorods at long wavelength. This may be the reason for the higher conversion efficiency of DSSCs with long gold nanorods than those of the cells with spherical gold nanoparticles and short gold nanorods.

In this study, we prepared different shapes of gold nanoparticles by the seed-mediated growth method to apply on the photoelectrode of dye-sensitized solar cells. Analyses of field emission scanning electron microscopy and ultraviolet–visible absorption spectra show that the average diameter of spherical gold nanoparticles is 66 nm and gold nanorods in aspect ratio is 2. The best conversion efficiencies of dye-sensitized solar cell with spherical gold nanoparticles and gold nanorods added in are 6.77 and 7.08%, and are higher than that without gold nanoparticles. These results indicate that the effect of gold nanoparticles on the photoelectrode can increase the conductivity and reduce the recombination of charges in the photoelectrode, resulting in the increase of conversion efficiency for dye-sensitized solar cells. Futhermore, gold nanorods have stronger surface plasmon resonance intensity than spherical gold nanoparticles at long wavelength. This may be the reason why conversion efficiency of dye-sensitized solar cells with gold nanorods is higher than that of spherical gold nanoparticles.

The kinetics of the self-assembled monolayer (SAM) formation of 3-mercaptopropionic acid (MPA) on Au surface and of the adsorption of hexadecyltrimethylammonium chloride (C16TAC) on the SAM was investigated by surface-enhanced infrared absorption spectroscopy (SEIRAS) of attenuated total reflection (ATR) mode. The SAM formation of MPA depended on solvents. At the first stage of MPA adsorption in a chloroform-d solution, hydrogen-bonded MPA coexisted with free (non-hydrogen-bonded) MPA which was partly protonated. During the process of the adsorption, the free nonprotonated MPA was protonated or hydrogen-bonded. After the abundant SAM formation, alkyl backbone was rearranged. With adsorption in an ethanol solution, the hydrogen-bonded MPA SAM increased in content without any structural rearrangement. No free species and no protonated species were observed. The molecular orientation was also different between SAMs in chloroform-d and in ethanol. The dependence of the CH2 antisymmetric stretching vibration band intensity on adsorption time was examined on the basis of the adsorption kinetics. It was confirmed that the MPA SAM formation on Au surface proceeds according to the simple Langmuir (monolayer) adsorption theory. On the other hand, the adsorption of C16TAC on the MPA SAM obeyed the kinetics where the fast adsorption at an early stage is followed by the slow adsorption. ATR-SEIRAS indicated that there are the adsorption of C16TAC on the MPA SAM and the transition of carboxylic acid to carboxylate. Finally, ion pairs connected by the electrostatic interaction are formed.

Spherical gold nanoparticles with a hydrodynamic diameter between 25 and 37 nm were prepared and stabilised with poly(N-vinylpyrrolidone) (PVP) or tris(sodium-m-sulfonatophenyl)phosphine (TPPTS). They were subjected to different cell culture media, e.g. pure RPMI, RPMI containing up to 10% of fetal calf serum (FCS), and RPMI containing up to 10% of bovine serum albumin (BSA), and the rate of agglomeration was studied by dynamic light scattering. In pure RPMI, a strong agglomeration was observed whereas in the RPMI–FCS and RPMI–BSA mixtures the particles remained well dispersed above 1 wt% protein concentration. The effect of PVP-stabilised gold nanoparticles on human mesenchymal stem cells (hMSC) was studied as well. No significant influence on the viability and chemotaxis was observed after incubation of hMSC with gold nanoparticles. However, gold nanoparticles induced the activation of hMSC as indicated by the release of IL-6 and IL-8.

We exploit the concept of SERS optophysiology, which combines a SERS nanosensor on the tip of a pulled fiber to provide spatially and temporally specific molecular information near or inside biological material. A SERS nanofiber decorated with a dense and well-dispersed array of Au NPs was developed for the measurement of neurotransmitters and proteins near neurons and in brain tissue. For neurotransmitters, unfunctionalized Au nanoraspberries or gold nanostars were synthesized in batch or continuous flow and immobilized on a pulled fiber functionalized with a block copolymer. For protein sensing, spherical gold nanoparticles are deposited on the optical fiber and modified with a capture antibody for a SERS immunoassay using a secondary gold nanoparticle modified with a SERS tag. The sensors were tested in animal models for sensing neurochemicals and neuroproteins. In this presentation, three main research results will be presented. Dynamic SERS will be shown to detect neurotransmitters secreted upon neuronal stimulation and in the presence of therapeutic compounds. Different levels of neurotransmitters were seen for cultured neurons from different regions of mouse brain tissue. In a second example, the detection of S100B will be demonstrated using a SERS nanoendoscope to monitor this protein in brain tissue and in living animals. The levels of this protein will be shown for different stimulation protocols. Finally, the synthesis of short wavelength IR nanomaterials will be demonstrated using machine learning driven flow synthesis of gold nanostars, where the size and shape of the nanomaterial is controlled by the pumping ratio and flow rate of the reagents in the tube. In-line detection of plasmon and SERS properties will also be demonstrated. Overall, the presentation will show our recent progress in creating a SERS toolbox for neuroscience.

In this study, the surfaces of two gold nanoparticles of different shapes were modified with hexadecyltrimethylammonium bromide (CTAB) and used for contact lenses. The polymer was based on 2-hydroxyethyl methacrylate (HEMA), and spherical and sea urchin-shaped gold nanoparticles were used as additives. CTAB was used to modify the surface of the sea urchin-shaped gold nanoparticles. To analyze the physical properties of the prepared contact lens, optical transmittance, refractive index, water content, contact angle, and atomic force microscope (AFM) were measured and evaluated. The results showed the nanoparticles did not significantly affect optical transmittance, refractive index, or water content of the lens, and tensile strength increased according to the ratio of the additive. The addition of the sea urchin-shaped nanoparticles resulted in lower wettability compared with the spherical nanoparticles, but somewhat superior tensile strength. In addition, it was found that the wettability of the lens was improved when the surface-modified sea urchin-shaped gold nanoparticles were added. The types of gold nanoparticles and surface modification methods used in this study are considered to have great potential for use in ophthalmic materials.

Energy and environment are two of the most primary concerns of this century, thus leading to holistic research across numerous disciplines.1 Ammonia electro-oxidation reaction (AOR) is extremely crucial with regards to energy and environment as it holds spotlight in several fields such as wastewater remediation, analytical chemistry and as a source of renewable energy in direct ammonia fuel cells. In addition, AOR is also useful by being the producer of hydrogen via electrolysis.2 Ammonia has a greater promise compared to other compounds like ethanol and methanol due to its carbon-free nature, well-defined production, storage and transportation network and no net increase in carbon dioxide content of the environment.3 However, inadequate performance due to slow kinetics and expensive nature of electrocatalysts have impeded the utilization of ammonia oxidation technology on a large scale. Consequently, large amount of efforts have been put over the years to understand the mechanism properly which can assist in developing highly active and stable electrocatalysts. In this study, a powerful in-situ surface enhanced infrared absorption spectroscopy (SEIRAS) technique with the attenuated total reflection (ATR) was used to examine the mechanism and intermediates over Pt-Ir nanofilm deposited on a silicon hemispherical prism. Pt-Ir was chosen as it is the most promising alloy as electrocatalyst for AOR till date. Intermediates such as NO at 1478-1488 cm-1 previously found over Pt electrode6 and NO2 at 1331 cm-1 earlier found with CeO2-modified platinum catalyst7 were also observed in this study with Pt-Ir, thus establishing their presence at higher potential range. Most importantly, a weak band at 2140 cm-1 representing azide intermediate was also observed for the 1st time using FTIR, previously only seen using in-situ Raman spectroscopy.8 This work, confirming azide intermediate presence at higher potential and affirming the NO and NO2 for Pt-Ir too, provided much clearer understanding of the mechanism and intermediates within the most renowned Gerischer and Mauerer framework, henceforth opening pathway for further efficient AOR electrocatalyst design in future. Fig 1. Time-resolved IR spectra of the Pt-Ir nanofilm acquired simultaneously with the linear sweep voltammogram in 0.2 M NH3-10mM PBS buffer solution (pH 6.96). The reference spectrum was taken at 0.1V. References Liu, J., Liu, B., Ni, Z., Deng, Y., Zhong, C., & Hu, W., Electrochimica Acta 2014, 150, 146-150.Diaz, L. A., Valenzuela-Muñiz, A., Muthuvel, M., & Botte, G. G., Electrochimica Acta 2013, 89, 413-421.Zhong, C., Hu ,W. B., and Cheng Y. F., Journal of Materials Chemistry A 2013, 10, 3216-3238.Vitse, Frederic, Cooper, M., and Botte, G. G., Journal of Power Sources 2005, 1, 18-26.Satyapal, Sunita, et al. Catalysis Today 2007, 3, 246-256.Matsui, T., Suzuki, S., Katayama, Y., Yamauchi, K., Okanishi, T., Muroyama, H., and Eguchi, K.. Langmuir 2015, 31, 11717-11723.Katayama, Y., Okanishi, T., Muroyama, H., Matsui, T., and Eguchi, K., ACS Catalysis 2016, 3, 2026-2034.Vidal-Iglesias, F. J., Solla-Gullón, J., Pérez, J. M., and Aldaz, A.. Electrochemistry Communications 2006, 8, 102-106. Figure 1

The structure rearrangement of polyelectrolyte shell on the surface of a charged spherical nanoparticle is investigated by methods of statistical theory of macromolecules and molecular dynamics. A mathematical model of conformational changes of adsorbed polyelectrolyte on the surface of a spherical nanoparticle is presented, and radial dependences of the concentration of macrochain links depending on the sign and magnitude of the nanoparticle charge are obtained. Molecular dynamic modeling of polypeptides with different degrees of polyelectrolyte on the surface of a charged spherical gold nanoparticle was performed. When the absolute value of the opposite sign charge on the spherical nanoparticle increased with respect to the charge of the macrochain, the polyelectrolyte shell at the surface of the nanoparticle was dense, while a loose layer of neutral macrochain links was formed at the periphery. On the uniformly charged surface of the spherical nanoparticle, the polyelectrolyte shell gradually swelled with increase in the absolute value of the nanoparticle charge and desorbed the earlier the higher the degree of polyelectrolyticity of the macrochain was.

2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) has emerged as an environmentally benign catalyst for the electrochemical oxidation of primary and secondary alcohols to aldehydes and ketones (1). This simple organic free radical reagent possesses high activity, and versatility, and is one of the most promising alternatives to noble metal catalysts that were previously studied. The catalytic activity and reactivity of TEMPO is mostly studied in bulk solutions, for fuel cells, aqueous redox flow batteries and sensors (2, 3). For more practicality, various approaches were developed to immobilize TEMPO on active supports, such as anionic polyelectrolytes, and the electropolymerization of TEMPO-substituted pyrrole or thiophene (4, 5). However, these substrates suffer from instability, loss of catalytic activity, degradation of the polymer film in alkaline environment mostly used for TEMPO regeneration. One other way, is to use carbon-based substrates that are stable in aqueous acid and base environment, as well as non-aqueous solutions and have shown enhanced electrocatalytic behavior (6, 7).In this work, we studied the electro-grafting of amino-TEMPO on graphene using in-situ attenuated total reflection infrared absorption spectroscopy (ATR-IRAS). We observed that TEMPO is attached on the surface through covalent bonding between the amine and the graphene lattice, as previously reported (6, 7). While grafting was successfully demonstrated via the oxidation of the primary amine to a radical cation which reacted with the graphene surface, ATR-surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) provided additional spectral feature confirming TEMPO grafting through plasmon induced signal enhancement. Hickey, D. P.; Milton, R. D.; Chen, D.; Sigman, M. S.; Minteer, S. D., TEMPO-Modified Linear Poly(ethylenimine) for Immobilization-Enhanced Electrocatalytic Oxidation of Alcohols. ACS Catalysis 2015, 5 (9), 5519-5524. Mishra, A.; Kim, J.; Zorigt, M.; Romo, A. I. B.; Gaddam, R.; Braun, J. E.; Ziviani, D.; Rodríguez-López, J., Highly Selective TEMPO Catalyzed Bulk Electrooxidation of Isopropanol to Acetone for Application in Electrochemical Heat Pumping. ACS Sustainable Chemistry & Engineering 2023, 11 (16), 6241-6249. Elouarzaki, K.; Mandoc, L.-R. P.; Gorgy, K.; Holzinger, M.; Amarandei, C.-A.; Ungureanu, E.-M.; Cosnier, S., Synthesis and electrochemical characterization of original “TEMPO” functionalized multiwall carbon nanotube materials: Application to iron (II) detection. Electrochemistry Communications 2015, 60, 131-134. Belgsir, E. M.; Schäfer, H. J., Selective oxidation of carbohydrates on Nafion®–TEMPO-modified graphite felt electrodes. Electrochemistry Communications 2001, 3 (1), 32-35. Grimshaw, J.; Perera, S. D., Poly(pyrrole-pyromellitimide) modified electrodes. Journal of Electroanalytical Chemistry and Interfacial Electrochemistry 1990, 278 (1), 279-286. Barman, K.; Askarova, G.; Jia, R.; Hu, G.; Mirkin, M. V., Efficient Voltage-Driven Oxidation of Water and Alcohols by an Organic Molecular Catalyst Directly Attached to a Carbon Electrode. Journal of the American Chemical Society 2023, 145 (10), 5786-5794. Yuan, B.; Xu, C.; Zhang, D.; Zhang, R.; Su, H.; Guan, P.; Nie, J.; Fernandez, C., Electrografting of amino-TEMPO on graphene oxide and electrochemically reduced graphene oxide for electrocatalytic applications. Electrochemistry Communications 2017, 81, 18-23.

Thermal transport enhancement in gold nanofluid containing network like structure

Over the past three decades, plasmonic nanostructures, particularly spherical ones, have seen remarkable advancements. Recently, attention has shifted toward anisotropic nanoparticles, especially star‐shaped/branched structures such as plasmonic nanostars (PNS), due to their distinct properties. PNS offers superior electromagnetic enhancement effects, larger surface areas, and as well as non‐linear and unusual photothermal properties, setting them apart from spherical counterparts. Despite significant progress in synthetic methods and characterization of the particles, challenges remain in transitioning PNS technology into practical use. In this perspective article, the distinctive attributes of PNS in biosensing applications are discussed, beginning with an exploration of synthesis methodologies. Their optoelectronic properties are examined and discussed how these properties influence their interaction with different molecules from a biosensing perspective. With a focus on PNS, detailed insights are offered into their unique properties, current applications, and future potential. By fostering discussion and understanding of PNS development, this article aims to facilitate the translation of PNS technology into practical applications, encouraging targeted improvements and advancements.

Systematically investigation of interactions between BSA and different charge-capped CdSe/ZnS quantum dots

Quantitative approach to the sample contact problem in attenuated total reflection spectroscopy: Theoretical considerations

Photooxidation of organic compounds on the surface of titanium dioxide (TiO2) is a potential method of removing organic pollutants from water. By coating TiO2 on transparent substrates and illuminating the catalyst with internally reflected light, it may be possible to increase the amount of illuminated photocatalyst in a given reactor volume. Planar, silica internal reflection elements (IREs) were coated with thin, porous, nanoparticulate films of TiO2. UV−visible internal reflection spectroscopy was performed in order to determine that visible and near-UV light propagated through the modified IREs in an attenuated total reflection (ATR) mode. The TiO2-coated IREs were employed in a photocatalytic reactor, and their ability to oxidize formic acid was assessed. Apparent quantum yields and quantum efficiencies of formic acid oxidation as a function of catalyst film thickness and incident angles of internally propagating UV light (310−380 nm) were determined. Quantum efficiency was enhanced when UV light propagated through the TiO2-coated waveguide in an ATR mode. Photocatalytic reactors based on waveguide-supported TiO2 films operating in an ATR mode may utilize light more effectively than reactors based on direct irradiance of TiO2 and could facilitate the scale-up of photocatalytic oxidation processes for commercial remediation applications.

The performance of polymer electrolyte fuel cells (PEFCs) is strongly affected by interfaces between the catalyst and ionomer in the cathode catalyst layer. While searching and synthesizing new catalysts have been major strategies for improving the catalytic activity for oxygen reduction reaction (ORR) until recently, modifying the other side of the interface, i.e.the ionomer, is becoming another big challenge because recent studies have revealed its significance on both the activity and oxygen transport. One of the most important properties of ionomers is the strength of the interaction between the anionic groups and Pt surface as already confirmed for real and model catalysts [1 - 3], and therefore, detailed understandings of the adsorption mechanisms of the anionic groups on Pt is essential for developing desirable ionomers. Figure 1 shows the cyclic voltammograms and ORR Tafel plots in 0.1 M HClO4 for Pt (111) surfaces bare and coated with Nafion® film, which was confirmed to be uniform by scanning electron microscopy. The results indicate that ORR activity is suppressed significantly (by over 80%) by the ionomer, while the coverage of the sulfonate moieties adsorbed on the Pt surface is estimated to be small (0.08 ML) from the adsorption peak in the CV by assuming that the adsorption is a one-electron-transfer process (-SO3 – + Pt → -SO3 – Pt + e-). To further investigate the effect of ionomers, low-molecular-weight sulfonic acids were employed as model compounds for the side-chains of ionomers, and the interface was analyzed by in-situ surface enhanced infrared absorption spectroscopy (SEIRAS). Figure 2a shows the SEIRA spectrum of perfluoro-(2-ethoxyethane) sulfonic acid (PESA, C2F5OC2F4SO3H) adsorbed on polycrystalline Pt film. The spectrum reveals the presence of strong bands due to the asymmetric stretching modes of SO3 -and the absence of them due to the asymmetric stretching mode of COC. These observations and the surface selection rule in SEIRAS suggest that the perfluoroalkyl chain is almost parallel to the surface as depicted in Fig. 2b. The orientation of the molecule is presumably determined by the interaction between the ether group and surface and can elucidate the significant ORR suppression by the small coverage with the sulfonate; not only the sulfonate moiety but also the perfluoroalkyl chain blocks Pt sites for ORR. In the meeting, further analytical results as well as promising strategies for suppressing the catalyst poisoning with ionomers will be discussed.