Polarization Modulation Infrared Reflection Absorption Spectroscopy Research Articles

Nanostructured functional peptide films and their application in C-reactive protein immunosensors

Peptides with an active redox molecule are incorporated into nanostructured films for electrochemical biosensors with stable and controllable physicochemical properties. In this study, we synthesized three ferrocene (Fc)-containing peptides with the sequence Fc-Glu-(Ala)n-Cys-NH2, which could form self-assembled monolayers on gold and be attached to antibodies. The peptide with two alanines (n=2) yielded the immunosensor with the highest performance in detecting C-reactive protein (CRP), a biomarker of inflammation. Using electrochemical impedance-derived capacitive spectroscopy, the limit of detection was 240pM with a dynamic range that included clinically relevant CRP concentrations. With a combination of electrochemical methods and polarization-modulated infrared reflection-absorption spectroscopy, we identified the chemical groups involved in the antibody-CRP interaction, and were able to relate the highest performance for the peptide with n=2 to chain length and efficient packing in the organized films. These strategies to design peptides and methods to fabricate the immunosensors are generic, and can be applied to other types of biosensors, including in low cost platforms for point-of-care diagnostics.

Role of sphingomyelin on the interaction of the anticancer drug gemcitabine hydrochloride with cell membrane models

The fight against drug resistance in chemotherapy requires a molecular-level understanding of the drug interaction with cell membranes, which today is feasible with membrane models. In this study, we report on the interaction of gemcitabine (GEM), a pyrimidine nucleoside antimetabolite used to treat pancreatic cancer, with Langmuir films that mimic healthy and cancerous cell membranes. The cell membrane models were made with eight compositions of a quaternary mixture containing 1,2-dipalmitoyl-sn-glycerol-3-phosphocholine (DPPC), 1,2-dipalmitoyl-sn-glycero-3-phosphoserine (DPPS), sphingomyelin (SM), and cholesterol (CHOL). The relative concentration of SM was increased so that four of these compositions represented cancerous cells. GEM was found to increase the mean molecular area, also increasing their surface elasticity, with stronger interactions being observed for membranes corresponding to cancerous cells. More specifically, GEM penetrated deepest in the membrane with the highest SM concentration (40 mol%), as inferred from polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS). This finding was confirmed with molecular dynamics simulations that also indicated how GEM approaches the membrane, which could be useful for guiding the design of drug delivery systems. The experimental and simulation results are consistent with the preferential attachment of GEM onto cancerous cells and highlight the role of SM on drug-cell interactions.

Design of A Low-Cost and Disposable Paper-Based Immunosensor for the Rapid and Sensitive Detection of Aflatoxin B1

We report a paper-based electrochemical immunosensor made with sustainable materials to detect aflatoxin B1 (AFB1), a highly toxic, carcinogenic mycotoxin found in food. The immunosensor was prepared with a waterproof paper substrate and low-cost graphite-based conductive ink through a simple cut-printing method. The working electrode was functionalized with a drop-cast film of multiwalled carbon nanotubes (MWCNT)/chitosan on which a layer of anti-AFB1 monoclonal antibodies was immobilized covalently. The architecture of the immunosensor was confirmed with polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS) and electrochemical impedance spectroscopy (EIS), including the effective immobilization of the active layer of anti-AFB1. With EIS as the principle of detection, the immunosensor could detect AFB1 in the range from 1 to 30 ng·mL−1, and detection limit of 0.62 ng·mL−1. This sensitivity is sufficient to detect AFB1 in food according to regulatory agencies. The immunosensor exhibited good repeatability, reproducibility, stability, and selectivity in experiments with a possible interferent. Furthermore, detection of AFB1 in maize flour samples yielded recovery of 97–99%, in a demonstration of the possible use of the paper-based immunosensor to detect AFB1 using extraction solutions from food samples.

Multilayer adsorption of methanol on platinum at low temperatures

• Multilayer adsorption of methanol on Pt(1 1 1) was studied by TPD and PM IRRAS. • At 80–90 K, methanol is adsorbed on the surface in the form of an amorphous phase. • Above 100 K the amorphous phase crystallized to form long (CH 3 OH) n chains. • Amorphous and crystallized phases of condensed methanol are distinguished by PM IRRAS. Multilayer adsorption of methanol on the Pt(1 1 1) surface has been studied in the temperature range between 80 and 120 K by temperature-programmed desorption and polarization-modulation infrared reflection absorption spectroscopy. It has been found that the adsorption at 80–90 K leads to the formation of an amorphous layer of condensed methanol. This layer is thermally unstable, and heating to 100 K leads to the ordering of its structure via the formation of long (CH 3 OH) n chains, which are typical of the α phase of solid methanol. At 100 K, the adsorption of methanol directly leads to the formation of a well crystallized condensed phase.

Langmuir and Langmuir-Blodgett Films of Poly[(9,9-dioctylfluorene)-co-(3-hexylthiophene)] for Immobilization of Phytase: Possible Application as a Phytic Acid Sensor.

In this work, the copolymer poly[(9,9-dioctylfluorene)-co-(3-hexylthiophene)] was employed as a matrix for immobilizing phytase, aiming at the detection of phytic acid. The copolymer was spread on the air-water interface forming Langmuir monolayers and phytase adsorbed from the aqueous subphase. The interactions between the copolymer and the enzyme components were investigated with surface pressure and surface potential-area isotherms, Brewster angle microscopy, and polarization modulation infrared reflection-absorption spectroscopy (PM-IRRAS). The enzyme could be incorporated in the monolayers from the aqueous subphase, expanding the copolymer films and maintaining its secondary structure. The polymeric films presented a morphological heterogeneous pattern at the air-water interface because of the ability of their chains to fold and entangle, causing inherent defects in the organization as well as unbalanced lateral distribution at the air-water interface because of the formation of aggregates. The interfacial films were transferred to solid supports as Langmuir-Blodgett films and characterized by PM-IRRAS and scanning electronic microscopy, which showed not only the co-transfer of the enzyme but also the maintenance of their heterogeneous morphological pattern. The enzymatic activity of the blended film was analyzed by UV-vis spectroscopy and allowed the estimation of the value of the Michaelis constant (13.08 mM), demonstrating the feasibility of the system to selectively detect phytic acid for biosensing purposes.

Ionophore properties of valinomycin in the model bilayer lipid membrane 1. Selectivity towards a cation

The electrochemical impedance spectroscopy (EIS) and polarization-modulation infrared reflection absorption spectroscopy (PM-IRRAS) techniques were employed to study the ionophore properties of valinomycin in a model floating bilayer lipid membrane (fBLM) in perchlorate supporting electrolytes with potassium and sodium cations. Valinomycin decreases the membrane resistance of the fBLM in KClO4 solution by about 180 times, while it has a negligible effect on the membrane resistivity in NaClO4 solution. The IR spectra indicate that valinomycin forms a complex with K+, but not with Na+. The valinomycin-K+ complex adopts a small tilt angle with respect to the electrode surface normal and is well interdigitated between the acyl chains of the bilayer. The EIS and PM-IRRAS results indicate that valinomycin forms complexes with K+ and transports K+ across the lipid bilayer. This transport is potential independent and hence has a passive character.

Enzyme activity preservation for galactose oxidase immobilized in stearic acid Langmuir-Blodgett films

Abstract The adsorption of the enzyme galactose oxidase onto stearic acid Langmuir monolayers was investigated with surface pressure-area isotherms, Brewster Angle Microscopy and polarization-modulated infrared reflection-absorption spectroscopy. The enzyme was incorporated in the monolayer at low surface pressures, expanding the lipid films, and further monolayer compression expelled it from the contact with the air phase and repositioned the enzyme below the lipid polar heads. The enzyme-lipid system was then stabilized by electrostatic interactions, leading the monolayer to condense at higher surface pressures, reducing the number of interfacial aggregates. The lipid-enzyme interactions at the interface made the monolayer less viscoelastic and more disordered as pointed by the reduced compressional modulus and decreased trans/gauche ratio for the lipid acyl chains. Also, the secondary structures of the adsorbed enzyme were kept as demonstrated with infrared spectroscopy. The condensed enzyme-lipid monolayer was transferred to solid supports as Langmuir-Blodgett films and the enzyme activity was detected, being preserved for one month. These results show how the molecular organization provided by the ultrathin films can help maintain the catalytic activity for immobilized enzymes, which is important, general speaking, for nanotechnology and biosensing manufacturing.

Chain Cleavage of Bioinspired Bacterial Membranes Photoinduced by Eosin Decyl Ester.

Photodynamic therapy (PDT) is promising for bacterial inactivation since cellular internalization of photosensitizers (PS) is not crucial for the treatment effectiveness. Photoinduced damage in the lipid envelope may already induce microbial inactivation, which requires PS capable of easily penetrating into the membrane. Herein, we report on the insertion of the PS eosin decyl ester (EosDec) into Langmuir films of 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE), 1,2-dioleoyl-sn-glycero-3-phospho-(1'-rac-glycerol) (DOPG), and cardiolipin (CLP) used as mimetic systems of bacterial membranes. Surface pressure isotherms and polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS) indicated that the hydrophobic nature of EosDec favored deeper penetration in all the phospholipid monolayers. The incorporation of EosDec led to monolayer expansion, especially in the anionic DOPG and CLP owing to repulsive electrostatic interactions, and induced disorder in the lipid chains. Light irradiation of DOPE, DOPG, and CLP monolayers containing EosDec increased the rate of material loss to the subphase, which is attributed to cleavage of lipid chains triggered by contact-dependent reactions between excited states of EosDec and lipid unsaturations. The latter is key for membrane permeabilization and efficiency in microbial inactivation.

Polysaccharide Multilayer Films in Sensors for Detecting Prostate Tumor Cells Based on Hyaluronan-CD44 Interactions.

The increasing need for point-of-care diagnosis has sparked the development of label-free sensing platforms, some of which are based on impedance measurements with biological cells. Here, interdigitated electrodes were functionalized with layer-by-layer (LbL) films of hyaluronan (HA) and chitosan (CHI) to detect prostatic tumor cells (PC3 line). The deposition of LbL films was confirmed with atomic force microscopy and polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS), which featured the vibrational modes of the HA top layer capable of interacting specifically with glycoprotein CD44 receptors overexpressed in tumor cells. Though the CHI/HA LbL films cannot be considered as a traditional biosensor due to their limited selectivity, it was possible to distinguish prostate tumor cells in the range from 50 to 600 cells/µL in in vitro experiments with impedance spectroscopy. This was achieved by treating the impedance data with information visualization methods, which confirmed the distinguishing ability of the films by observing the absence of false positives in a series of control experiments. The CD44–HA interactions may, therefore, be exploited in clinical analyses and point-of-care diagnostics for cancer, particularly if computational methods are used to process the data.

Molecular-level effects on cell membrane models to explain the phototoxicity of gold shell-isolated nanoparticles to cancer cells

Metallic nanoparticles are promising agents for photothermal cancer therapy (PTT) owing to their photostability and efficient light-to-heat conversion, but their possible aggregation remains an issue. In this paper, we report on the photoinduced heating of gold shell-isolated nanoparticles (AuSHINs) in in vitro experiments to kill human oropharyngeal (HEp-2) and breast (BT-474 and MCF-7) carcinoma cells, with cell viability reducing below 50 % with 2.2 × 1012 AuSHINs/mL and 6 h of incubation. This toxicity to cancer cells is significantly higher than in previous works with gold nanoparticles. Considering the AuSHINs dimensions we hypothesize that cell uptake is not straightforward, and the mechanism of action involves accumulation on phospholipid membranes as the PTT target for photoinduced heating and subsequent generation of reactive oxygen species (ROS). Using Langmuir monolayers as simplified membrane models, we confirmed that AuSHINs have a larger effect on 1,2-dioleoyl-sn-glycero-3-phospho-l-serine (DOPS), believed to represent cancer cell membranes, than on 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) taken as representative of healthy eukaryotic cells. In particular, data from polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS) revealed an increased conformational order of DOPS tails due to the stronger adsorption of AuSHINs. Furthermore, light irradiation reduced the stability of AuSHINs containing DOPC and DOPS monolayers owing to oxidative reactions triggered by ROS upon photoinduced heating. Compared to DOPC, DOPS lost nearly twice as much material to the subphase, which is consistent with a higher rate of ROS formation in the vicinity of the DOPS monolayer.

Structural modifications of lipid membranes exposed to statins – Langmuir monolayer and PM-IRRAS study

Abstract The effects of selected statins on the structure and properties of lipid membranes composed of zwitterionic (1,2-dimyristoyl-sn-glycero-3-phosphocholine, DMPC, 1,2-dimyristoyl-sn-glycero-3-phosphoethanolamine, DMPE) or anionic (1,2-dimyristoyl-sn-glycero-3-phospho- l -serine, DMPS) lipids were studied for the first time by Langmuir technique combined with polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS) and Brewster angle microscopy (BAM). The interactions of statins of different hydrophobicity: pravastatin, fluvastatin, and cerivastatin with the polar region of the lipids forming the membrane were monitored by PM-IRRAS and the changes of the overall monolayer structure and organization were described on the basis of surface pressure vs. area per molecule measurements and Brewster angle microscopy. Large differences in the action of each of the statins on the lipid monolayers were observed and explained by their different hydrophobicity combined with the different degree of hydration of the lipid polar headgroups in the monolayer. Monolayer fluidizing effect was connected with the interaction of statins in the headgroup region of the membrane affecting the original hydrogen bonding in the lipid layers. The most hydrophilic pravastatin interacted only with the polar head groups of the monolayer and affected the organization of the polar part of the lipid membrane by increasing the headgroups hydration. In the case of DMPS, the contribution of electrostatic interactions between the negatively charged headgroups and the drug was observed, and for this lipid especially strong dehydration effect of cerivastatin was revealed. It facilitated the incorporation of the hydrophobic part of the drug into the nonpolar region of the DMPS layer and in this case there was almost no fluidization of the layer. Strong dehydration effects may be dangerous for the lipid membranes and may also be one of the reasons to avoid cerivastatin in the therapies, despite its known efficacy especially in view of the large doses and prolonged application that are usually needed.

DNA Binding on Self-Assembled Monolayers Terminated with Mixtures of Ammonium and Trimethylammonium Groups: Toward a Gene-Delivery Platform

The formation of binary self-assembled monolayers (SAMs) via the use of ammonium-terminated adsorbates offers an ionic platform for the binding of oligonucleotides and their subsequent delivery for therapeutic applications. Four different types of ammonium-terminated adsorbates were used in the present study: two ammonium-terminated and two trimethylammonium-terminated dithiols of different chain lengths, which were designed to provide a foundation for the development of a high-capacity nanoscale loading system for oligonucleotides. The maximum number of oligonucleotides immobilized on the surface was achieved by adjusting the ratio of the adsorbates in correlation with the relative packing density of the SAMs. The techniques of ellipsometry, X-ray photoelectron spectroscopy, polarization modulation infrared reflection-absorption spectroscopy, and electrochemical quartz crystal microbalance were used to analyze the SAMs. Analysis of the films revealed an optimum ratio of 75:25 of the long-chained adsorbate (ammonium-terminated) to the short-chained adsorbate (trimethylammonium-terminated) for maximum oligonucleotide loading. Further analysis indicated that burying the trimethylammonium termini into the lower interface of the monolayer provided the highest mass loading of oligonucleotides. The results presented in this study provide a foundation for the development of a gene-therapy platform when constructed on the surface of, for example, light-responsive gold nanoparticles or gold nanoshells as photo-triggerable delivery vehicles.

Immunosensors containing solution blow spun fibers of poly(lactic acid) to detect p53 biomarker.

This paper reports on biosensors made with a matrix of polylactic acid (PLA) fibers, which are suitable for immobilization of the anti-p53 active layer for detection of p53 biomarker. The PLA fibers were produced with solution blow spinning, a method that is advantageous for its simplicity and possibility to tune the fiber properties. For the biosensors, the optimized time to deposit the fibers was 60s, with which detection of p53 could be achieved with the limit of detection of 11pg/mL using electrical impedance spectroscopy. This sensitivity is also sufficient to detect the p53 biomarker in patient samples, which was confirmed by distinguishing samples from cell lines with distinct p53 concentrations in a plot where the impedance spectra were visualized with the interactive document mapping (IDMAP) technique. The high sensitivity and selectivity of the biosensors may be attributed to the specific interaction between the active layer and p53 modeled with a Langmuir-Freundlich and Freundlich isotherms and inferred from the analysis of the vibrational bands at 1550, 1650 and 1757cm-1 using polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS). The successful immobilization of the active layer is evidence that the approach based on solution blown spun fibers may be replicated to other types of biosensors.

The impact of blue light in monolayers representing tumorigenic and nontumorigenic cell membranes containing epigallocatechin-3-gallate

Natural products such as epigallocatechin-3-gallate (EGCG) have been suggested for complementary treatments of cancer, since they lower toxic side effects of anticancer drugs, and possess anti-inflammatory and antioxidant properties that inhibit carcinogenesis. Their effects on cancer cells depend on interactions with the membrane, which is the motivation to investigate Langmuir monolayers as simplified membrane models. In this study, EGCG was incorporated in zwitterionic dipalmitoyl phosphatidyl choline (DPPC) and anionic dipalmitoyl phosphatidyl serine (DPPS) Langmuir monolayers to simulate healthy and cancer cells membranes, respectively. EGCG induces condensation in surface pressure isotherms for both DPPC and DPPS monolayers, interacting mainly via electrostatic forces and hydrogen bonding with the choline and phosphate groups of the phospholipids, according to data from polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS). Both monolayers become more compressible upon interaction with EGCG, which may be correlated to the synergy between EGCG and anticancer drugs reported in the literature. The interaction with EGCG is stronger for DPPC, leading to stronger morphological changes in Brewster angle microscopy (BAM) images and higher degree of condensation in the surface pressure isotherms. The changes induced by blue irradiation on DPPC and DPPS monolayers were largely precluded when EGCG was incorporated, thus confirming its antioxidant capacity for both types of membrane.

Observing the Migration of Hydrogen Species in Hybrid Perovskite Materials through D/H Isotope Exchange.

Unlike heavier elements, the migration of hydrogen species in perovskite materials cannot be directly tracked using imaging or mass spectrocopy techniques. Our results show that quantitative analysis of D/H exchange in PbCH3ND3I3 allows indirect monitoring of H migration by following the N-D vibration using polarization-modulated infrared reflection-absorption spectroscopy. Kinetic analysis shows that the isotope exchange process is pseudo-first order and particularly sensitive to the intensity of light and relative humidity, and, to a lesser degree, sample thickness. In the presence of light (450 nm), the D/H exchange is accelerated up to 10-fold with respect to samples in the dark but slows again for higher light intensities.. The technique also allows the direct assessment of the efficiency of protective layers toward deterioration of hybrid organic-inorganic perovskite devices by moisture. Comparison of different monolayer-forming fluorinated molecules reveals important differences in rates attesting to variations between their efficiency in blocking access to the active layer by water molecules.

Correlating mono- and bilayers of lipids to investigate the pronounced effects of steroid hormone 17α-ethynylestradiol on membrane models of DPPC/cholesterol

Risks to human health have been reported owing to prolonged exposure to hormones, whose action depends on their molecular-level interaction with cell membranes. In this study, we investigate the interaction of the synthetic hormone 17 α-ethynylestradiol (EE2) in two different membrane models, Langmuir monolayers and giant unilamellar vesicles (GUVs) made with a binary mixture of 1,2-dipalmitoyl-sn-glycerol-3-phosphocholine (DPPC) and cholesterol (Chol) in order to mimic the plasma membrane of mammalian cells. EE2 was found to expand the Langmuir monolayers, with shifts to larger areas per molecule in the surface pressure isotherm. In all of these observations, stronger effects were noted for the DPPC/Chol monolayers with XChol = 0.3, which mimics the proportion of phospholipid/sterol in the plasma membrane. At high surface pressures, EE2 is believed to weaken the attractive interactions between DPPC and Chol, in addition to affecting the ordering of the lipid chains as indicated in polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS) measurements. In GUVs obtained with XChol = 0.3 mixtures, EE2 induced a phase contrast loss as a result of increased permeability of the lipid bilayer. The results with Langmuir monolayers and GUV combined point to EE2 action on representative cell membranes, which can be correlated with physiological effects caused by indirect intake of EE2.

Enhanced chitosan effects on cell membrane models made with lipid raft monolayers

Langmuir monolayers have been used as cell membrane models, where lipid composition is normally varied to mimic distinct types of membranes. For eukaryotic membranes, for instance, rather than using only zwitterionic phospholipids there is now a trend to employ mixtures to simulate the lipid rafts known to be relevant for various cellular processes. In this study, we demonstrate that effects from chitosans on Langmuir monolayers are considerably higher if lipid raft compositions (ternary mixtures of dipalmitoyl phosphatidyl choline (DPPC), sphingomyelin (SM) and cholesterol) are used. Significantly, measurable effects on the surface pressure isotherms start at 10-6 mg mL-1 for chitosans in lipid rafts, to be compared with 10-2 mg mL-1 for neat dipalmitoyl phosphatidylcholine (DPPC). This applies to both a commercial chitosan and chitosans soluble at physiological pH. Incorporation of these chitosans in the raft monolayers was confirmed in polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS) experiments, where both the tail groups and headgroups were found to interact with chitosan. Since the effects on membrane models may be observed at such small concentrations for chitosans and probably other molecules, some studies may have to be revisited where neat phospholipids should be replaced by lipid raft compositions.

Direct Evidence of Graphene‐Induced Molecular Reorientation in Polymer Films

AbstractFor the first time, direct evidence of graphene‐induced molecular reorientation in polymer films using polarization modulated infrared reflection absorption spectroscopy (PM‐IRRAS) is presented. By creating favorable electrostatic interactions, graphene–polymer interfaces can be controlled by varying polymer and solvent composition. After transfer of unmodified graphene from copper onto a polymer substrate, polymer chain rearrangement relative to the orientation at the polymer‐copper interfaces is observed using PM‐IRRAS. Transfer success is characterized using both optical transmission measurements and Raman spectroscopy to quantify the transfer fidelity, that is, graphene coverage fraction. Taken together, oxygen‐containing poly(ethylene‐co‐vinyl acetate) shows more polymer chain rearrangement and better graphene coverage compared to oxygen‐free polyethylene. Polymer composition seems to dominate graphene–polymer interactions while solvent choice has a smaller effect on transfer quality. These results are the first direct measurement of this effect and point toward the possibility of engineering graphene–polymer interactions for specific applications.

Electrochemical Modification of Ni-Rich Bimetallic Ni1-x Mx (M= Bi, Pd and Au) Nanoparticles for Glycerol Electro-Oxidation in Alkaline Media

Glycerol partial electro-oxidation to produce various chemicals has attracted a great amount of attention in the decade [1]. Glycerol is the main by-product of biodiesel production and could be converted into high value-added chemicals. The control of catalyst selectivity and activity could be achieved through formulation of novel, nano-structured electrocatalysts. Nickel (Ni) is an attractive material for glycerol electro-oxidation (GEOR) in alkaline media [2], due to its natural abundance, anti-poising and good stability in alkaline media. Designing inexpensive nano-structured 3D Ni electrodes could improve the catalytic activity of Ni, whereas its selectivity could be modified by adding second metal [1].In the present work, GEOR was investigated on Ni-based mono and bi-metallic Ni x Au 1-x, Ni x Bi 1-x and Ni x Pd 1-x (x = 98, 95 and 90 at. %) nanoparticles in 1M KOH. Ni nanoparticles were synthesized by heatless chemical reduction in ethanol using sodium borohydride (NaBH4) as the reducing agent. Resulting Ni-based NPs were characterized using XRD, XPS, TEM, SEM, EDS mapping, HAADF imaging and EELS. Electrochemical measurements were carried out on Ni-based NPs using cyclic voltammetry (CV), chronoamperometry (CA) and linear sweep voltammetry (LSV) at room temperature. Results showed that Ni, NiAu and NiBi NPs are active for GEOR and that reaction proceeds through the formation of NiOOH active phase similar to bulk Ni electrodes [3]. Coupling CA with in-situ polarization modulation infrared-reflection absorption spectroscopy (PM-IRRAS) for the simultaneous analysis of products in the bulk electrolyte solution and on the Ni surface demonstrated that the main reaction products on Ni surface are glyceraldehyde, carbonyl and carboxylate ions. Whereas HPLC analysis reveals that Au, Bi and Pd adatoms strongly influence the reaction products by suppressing the pathways with C–C bond cleavage, hindering the formation of formate and enhancing the production of C2 and C3 products at different applied potentials (1.3, 1.4 and 1.55 V) and temperatures (25 and 50 oC).The correlation of electrocatalytic activity and selectivity with nanoparticle will be discussed in terms of mass activities and product distribution during GEOR.

Insertion of carbon nanotubes in Langmuir-Blodgett films of stearic acid and asparaginase enhancing the catalytic performance

In this paper, carbon nanotubes (CNT) were adsorbed on stearic acid (SA) Langmuir monolayers to serve as matrices for the incorporation of asparaginase. The interaction between the components at the air-water interface was evaluated by surface pressure-area isotherms, surface potential-area isotherms, polarization-modulation reflection absorption infrared spectroscopy (PM-IRRAS), and Brewster angle microscopy (BAM). The enzyme expanded the monolayers and changed the thermodynamic and electrical properties of the SA-CNT monolayers, as detected with the isotherms. PM-IRRAS spectra showed that the enzyme keeps its secondary structure when adsorbed at the monolayers and also alters the morphology of the air-water interface, as identified with BAM. The hybrid floating films were transferred to solid supports through the Langmuir-Blodgett (LB) technique, and the cotransfer of the enzyme was confirmed with fluorescence spectroscopy. The catalytic activity of asparaginase in the LB films was studied with UV-vis spectroscopy, which showed that the presence of CNT in the enzyme-lipid LB film not only tuned the catalytic activity, but also helped conserve its enzyme activity after weeks, showing higher persisting values of activity. UV-vis spectroscopy also showed that the catalytic activity is dependent basically on the enzyme molecules present on the surface of the LB films since multilayer films did not provide a proportional increase of enzyme activity. These results are related to the synergism between the compounds on the active layer, leading to a molecular architecture that allowed the adequate molecular accommodation of the analyte with the catalytic sites of the enzyme, which also preserved the asparaginase activity. This work then demonstrates the feasibility of employing LB films composed of fatty acids, CNT, and enzymes as devices for biosensing applications.