Polarization Modulation Infrared Reflection Absorption Spectroscopy Research Articles

Direct Observation of Plasma-Stimulated Activation of Surface Species Using Multimodal In Situ/Operando Spectroscopy Combining Polarization-Modulation Infrared Reflection-Absorption Spectroscopy, Optical Emission Spectroscopy, and Mass Spectrometry.

Nonthermal plasmas (NTPs) produce reactive chemical environments, including electrons, ions, radicals, and vibrationally excited molecules, that can drive chemistry at temperatures at which such species are thermally inaccessible. There has been growing interest in the integration of conventional catalysis with reactive NTPs to promote novel chemical transformations. Unveiling the full potential of plasma-catalytic processes requires a comprehensive understanding of plasma-catalytic synergies, including characterization of plasma-catalytic surface interactions. In this work, we report on a newly designed multimodal spectroscopic instrument combining polarization-modulation infrared reflection-absorption spectroscopy (PM-IRAS), mass spectrometry, and optical emission spectroscopy (OES) for the investigation of plasma-surface interactions such as those found in plasma catalysis. In particular, this tool has been utilized to correlate plasma-phase chemistry with both surface chemistry and gas-phase products in situ (1) during the deposition of carbonaceous surface species via NTP-promoted nonoxidative coupling of methane and (2) during subsequent activation of surface deposits with an atmospheric pressure and temperature argon plasma jet on both nickel (Ni) and silicon dioxide (SiO2) surfaces. For the first time, the activation of carbonaceous surface species by a NTP on Ni and SiO2 surfaces to form hydrogen gas and C2 hydrocarbons was directly observed, where both PM-IRAS and OES measurements suggest that they may form through different pathways. This unique tool for studying plasma-surface interactions could enable more rational design of plasma-stimulated catalytic processes.

Infrared reflection spectroscopy of adsorbed intermediates in real time during chemical vapor deposition of oxides

In this paper, we develop multilayer optical theory to model the real-time (in operando) optical response of a growing dielectric film being deposited by chemical vapor deposition (CVD), with a particular emphasis on understanding the deposition mechanism through direct detection of the adsorbates responsible for film growth by infrared reflection-absorption spectroscopy (IRRAS). The model involves a four-layer stack consisting of a vacuum over a monolayer or submonolayer of molecules adsorbed on the surface of a dielectric thin film, which, in turn, is growing on a metal substrate. It is well known that, in IRRAS, the sensitivity of p-polarized light to absorption by the molecular adsorbates is a function of the incident angle of the IR beam: at high angles, the sensitivity is highest. We show that, for incident beam angles above 70° (which are typically used in IRRAS experiments), the sensitivity also depends on the thickness and refractive index of the insulating thin film; as a result, the sensitivity changes dynamically during the growth of the dielectric layer. Our analysis shows that, at incident beam angles of ∼60°–70°, the sensitivity to molecular adsorbates is somewhat lower, but is almost independent of the oxide thickness from 0 to 100 nm and also independent of the oxide refractive index from 1.0 to 2.5. Despite the loss of sensitivity relative to that achievable at higher incident beam angles, 1000 scans at an incident angle of 60° are sufficient to obtain IR spectra of the adsorbed molecules with reasonable signal-to-noise ratios even at submonolayer coverages. Because the sensitivity at this incident beam angle is not thickness dependent, it is not an issue (as it is at higher beam angles) that additional oxide grows during the time required to acquire 1000 scans. Experiments can be performed using a conventional vacuum deposition system, in which the internal beam path is tens of cm. We demonstrate the use of these smaller incident beam angles to study the mechanism of a CVD process in real time by polarization-modulation IRRAS, obtained by subtracting the s-polarized from the p-polarized infrared spectra in order to eliminate the unpolarized component due to molecules in the beam path and on windows. We explore the surface coverage of various adsorbed intermediates during CVD of HfO2 from tetrakis-(dimethylamido)-hafnium (TDMAH) and water in the presence of the consumable inhibitor magnesium N,N-dimethylamino-diboranate [Mg(DMADB)2]. We find that the addition of the Mg(DMADB)2 inhibitor causes a decrease in the IR absorption from the adsorbed TDMAH precursor that correlates with the observed decrease in the HfO2 growth rate; this result indicates that the mechanism of inhibition involves Mg(DMADB)2 acting as a dynamic site-blocker that lowers the surface coverage of TDMAH.

Shell–Matrix Interaction in Nanoparticle-Imprinted Matrices: Implications for Selective Nanoparticle Detection and Separation

Nanoparticle-imprinted matrices (NAIMs) are an innovative approach for the efficient and selective recognition of nanoparticles (NPs). The NAIM system comprises the preparation of thin films in which NPs are embedded as a template. The removal of the template forms nanometric voids, which are subsequently used for the selective reuptake of NPs identical to those imprinted. The recognition ability depends on several parameters such as the geometrical compatibility between the voids and imprinted NPs, the thickness of the matrix, and the supramolecular interactions between the matrix and the NP capping agents. Herein, we studied carefully the NP–matrix interactions in three NAIM systems, which were prepared by imprinting identical-sized AuNPs, bearing different carboxylic acid-functionalized thiols as capping agents, in a carboxylic acid-functionalized matrix. This experimental setup has enabled us to meticulously examine the selectivity of the NAIM systems driven by matrix–shell interactions. The three studied NAIM systems have shown high and selective reuptake ability once exposed to solutions of NPs stabilized with the same capping agent used for the imprinting process. In particular, the reuptake percentage of the originally imprinted AuNPs ranges from 50 to 80%, whereas the reuptake of AuNPs bearing different carboxylic capping agents than those imprinted was substantially lower (1–11%). Surface-sensitive polarization-modulation infrared reflection-absorption spectroscopy was utilized to correlate the selectivity of the NAIM systems and hydrogen bonding detected between the capping agents and the matrix. This study paves the way for the rational design of NAIM systems, which can be tuned according to the desired shell–matrix interactions and eventually applied in sensing and separation technologies.

Effect of Molecular Structure on Electrochemical Phase Behavior of Phospholipid Bilayers on Au(111).

Lipid bilayers form the basis of biological cell membranes, selective and responsive barriers vital to the function of the cell. The structure and function of the bilayer are controlled by interactions between the constituent molecules and so vary with the composition of the membrane. These interactions also influence how a membrane behaves in the presence of electric fields they frequently experience in nature. In this study, we characterize the electrochemical phase behavior of dipalmitoylphosphatidylcholine (DPPC), a glycerophospholipid prevalent in nature and often used in model systems and healthcare applications. DPPC bilayers were formed on Au(111) electrodes using Langmuir-Blodgett and Langmuir-Schaefer deposition and studied with electrochemical methods, atomic force microscopy (AFM) and in situ polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS). The coverage of the substrate determined with AFM is in accord with that estimated from differential capacitance measurements, and the bilayer thickness is slightly higher than for bilayers of the similar but shorter-chained lipid, dimyristoylphosphatidylcholine (DMPC). DPPC bilayers exhibit similar electrochemical response to DMPC bilayers, but the organization of molecules differs, particularly at negative charge densities. Infrared spectra show that DPPC chains tilt as the charge density on the metal is increased in the negative direction, but, unlike in DMPC, the chains then return to their original tilt angle at the most negative potentials. The onset of the increase in the chain tilt angle coincides with a decrease in solvation around the ester carbonyl groups, and the conformation around the acyl chain linkage differs from that in DMPC. We interpret the differences in behavior between bilayers formed from these structurally similar lipids in terms of stronger dispersion forces between DPPC chains and conclude that relatively subtle changes in molecular structure may have a significant impact on a membrane's response to its environment.

Deciphering the Orientation of the Aromatic Spacer Cation in Bilayer Perovskite Solar Cells through Spectroscopic Techniques.

Slowing the degradation of perovskite-based solar cells (PSCs) is of substantial interest. We engineered the surface by introducing a hydrophobic overlayer on a three-dimensional (3D) perovskite using fluorinated or nonfluorinated aryl ammonium cation spacers. The placement of a fluoroarene cation allows the formation of a bilayer structure, that is, layered/3D perovskites. By doing so, the surface hydrophobic character increases notably by the virtue of the perfluorinated benzene moiety. The fabricated devices thereof gave higher performance and longevity than control devices in addition to boosting reliability. The fluoro-phenethylammonium iodide (FPEAI)-based devices showed lower nonradiative carrier recombination. To decipher the orientation of the spacer cation in this bilayer structure, we probed the surface by polarization-modulated infrared reflection-absorption spectroscopy and noted substantial differences in the orientation due to the presence of fluorine substitution. We hypothesize that the stronger van der Waals interactions due to the higher electronegativity in FPEAI govern the orientation and performance enhancement and act as a barrier to moisture decomposition.

The hydrophobic core effect in model bacterial membranes upon interaction with tetra-p-guanidinoethylcalix[4]arene

The calixarene derivative used in this study (tetra-p-guanidinoethylcalix[4]arene) shows in vitro activity against different Gram-positive and Gram-negative bacteria. The interaction between bacterial cell membranes and the water-soluble calixarene was investigated using model lipids spread as monomolecular films at the air–water interface. Compression and adsorption experiments, as well as Brewster angle microscopy, polarization modulation-infrared reflection–absorption spectroscopy and computer modeling permitted understanding of the intra- and intermolecular interaction in several lipid-calixarene systems. Because the affinity of the calixarene derivative for the membranes may be linked to the interaction with negative charges, phosphatidylglycerols were used as model lipids; the phosphatidylglycerols contained saturated or unsaturated hydrocarbon chains with different lengths. It was showed that the affinity of the calixarene for the monolayer depends on the structure of the phosphatidylglycerols side chains. This observation may be of interest for a further development of new antibiotics.

Temperature dependence of vibrational motions of thin polystyrene films by infrared reflection-absorption spectroscopy: A single measurement tool for monitoring of glass transition and temperature history

A method for monitoring of vibrational response and temperature region of glass transition by a single analysis is introduced with the use of an otherwise well-known spectroscopic method. The temperature-dependent changes of polystyrene (PS) thin films were investigated by polarization-modulated infrared reflection-absorption spectroscopy. The study revealed that changes in individual spectral regions with the temperature increase are specific and provide the relation to the processing and thermal history of the thin film. Temperature responses of infrared spectral region areas; an abrupt change of Car-H stretching, a step-like change of Car-H out-of-plane bending, a linear decrease of C–H stretching and C–H bending area, granted information on the temperature domain represented by local molecular motion change (β-transition) of PS. The different behavior of spectral regions is rationalized by consideration of vibrational free volume contribution to the total free volume of the system that is certainly influenced by functional groups nature, such as their size, geometry and involvement of non-bonding interaction.

CO and H2 adsorption on Au-Ni bimetallic surfaces: a combined experimental and DFT theoretical study

Au-Ni bimetallic thin films were grown on refractory metal substrates. CO and H2 adsorption on Au-Ni bimetallic surfaces have been studied by a combination of in situ polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS), temperature-programmed desorption (TPD), and density functional theory (DFT) calculations. It is found CO desorption peak shifts from 413 K on pure Ni surfaces to 293 K on the isolated Ni atoms formed by alloying with Au atoms. The sharp decrease of CO desorption temperature on Au-Ni surfaces with increasing Au coverage is caused by the change of the favored CO adsorption sites from bridge/hollow sites on pure Ni surfaces to Ni top sites on Au-Ni bimetallic surfaces. In situ PM-IRRAS shows two CO adsorption bands on Au sites at 2119 cm−1 and 2103 cm−1 on Au-Ni surfaces at 80 K, which are due to CO bound on under-coordinated Au atoms and electron negatively charged Au sites modified with nearby Ni atoms, respectively. Even with the Au-Ni surface temperature at as low as 100 K, CO adsorption induced Ni surface segregation has been observed by in situ PM-IRRAS. Furthermore, DFT calculation results discover the adsorption energy of CO on Ni top sites continues to decrease with increasing Au coverage due to the geometric ensemble effect and the lowered d-band center after Ni alloying with Au. H2 desorption temperature decreases from 363 K on pure Ni thin films to 302 K with increasing Au coverage to 0.6 ML. A new H2 peak appears at around 170 K on the Au-Ni surfaces with Au coverages between 0.6 ML and 0.9 ML. This new H2 TPD peak is assigned to H2 desorption from the totally isolated Ni sites. With Au coverage above 1.5 ML, there is no any H2 desorption detected. The combined surface science studies and DFT calculations provide new insights into the surface structure-activity correlation of Ni-base bimetallic surface alloys.

Effect of cavitation intensity control on self-assembling of alkanethiols on gold in room temperature ionic liquids

This study investigates the effect of cavitation intensity on self-assembling of alkanethiol molecules on gold in room temperature ionic liquids (RTILs) under low frequency ultrasound irradiation (20 kHz). The use of RTILs, with low vapor pressure, enabled cavitation activity to be controlled up to quenching through pressure decrease within an argon-saturated atmosphere. This control possibility was used to acquire deeper insights into the role of cavitation on self-assembling processes. It was shown by electrochemical, contact angles and Polarization Modulation - Infrared Reflection Absorption Spectroscopy (PM-IRRAS) measurements that cavitation activates orientation and organization of self-assembled monolayers (SAM). X-ray Photoelectron Spectroscopy (XPS) revealed that, even if chemical adsorption of molecules is highly activated under ultrasound irradiation, it is not dependent on acoustic cavitation intensity.

Electrochemical tools to disclose the electrochemical reduction mechanism of CO2 in aprotic solvents and ionic liquids

Carbon dioxide (CO 2 ) plays a key role in controlling the temperature of the Earth. But the increase in the concentration of CO 2 in the atmosphere brings with it a series of consequences, originating several environmental problems. The use of electrochemical, spectroscopic and molecular dynamics techniques are useful toolkits to valorize carbon dioxide, and to know the reduction mechanism as a function of CO 2 concentration, the cathode nature, and the electrolyte. This manuscript will be mainly centered in the use of ionic liquids (IL) for efficient CO 2 capture and valorization into different valuable products thanks to the CO 2 electrochemical reduction. In this sense, spectroelectrochemistry based on cyclic voltammetry coupled with Polarization Modulation-Infrared Reflection-Absorption Spectroscopy (PM-IRRAS) and Infrared Reflection-Absorption Spectroscopy (IRRAS) appear to be an efficient instrument to follow the CO 2 reactivity in imidazolium ionic liquids. Finally, we present molecular dynamics paired with cyclic voltammetry in order to calculate the diffusion coefficient of CO 2 and the number of electrons involved in its reduction process, respectively. Therefore, the current research opens the door to the use of theoretical-experimental approaches altogether to determine how is the CO 2 reduction mechanism. The CO 2 reduction products in function of the solvent and nature of the cathode is suggested, proving that the product obtained from the electrochemical reduction of CO 2 depends on the electrode material and the solvent.

Interaction of LL-37 human cathelicidin peptide with a model microbial-like lipid membrane

The only representative of cathelicidin peptides in humans is LL-37, a multifunctional antimicrobial peptide (AMP) that is a part of the innate immune response. Details of the LL-37 direct activity against pathogens are not well understood at the molecular level. Here, we present research on the mechanism of interaction between LL-37 and a model multicomponent bilayer lipid membrane (BLM), mimicking microbial cell membrane. Electrochemical impedance spectroscopy (EIS), high-resolution atomic force microscopy (AFM) imaging, and polarization-modulation infrared reflection–absorption spectroscopy (PM-IRRAS) were applied to study the peptide influence on a model microbial-like membrane. We show that LL-37 causes changes in the phospholipid molecules conformation and orientation, leading to membrane disintegration, significantly affecting the membrane electrical parameters, such as capacitance and resistance. High-resolution AFM imaging shows topographical and mechanical effects of such disintegration, while PM-IRRAS data indicates that introduction of LL-37 causes changes in the phospholipid acyl chains from all-trans to gauche conformations. Moreover, the presence of LL-37 significantly alters the value of the phospholipid tilt angle. Altogether, our results suggest a “carpet” membrane dissolution followed by a detergent-like membrane disruption mechanism upon LL-37 activity. This research gives a novel insight into the understanding of LL-37 influence on multicomponent model membranes and a promising contribution to the development of LL-37-derived therapeutic agents against drug-resistant bacteria.

Consequences of the exposure to bisphenol A in cell membrane models at the molecular level and hamster ovary cells viability

The inadequate disposal and the difficulty in its removal from water treatment systems have made the endocrine disruptor bisphenol A (BPA) a significant hazard for humans and animals. The molecular-level mechanisms of BPA action are not known in detail, which calls for systematic investigations using cell membrane models. This paper shows that BPA affects Langmuir monolayers and giant unilamellar vesicles (GUVs) of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) used as membrane models, in a concentration-dependent manner and with effects that depend on BPA aggregation. BPA increases DPPC monolayer fluidity in surface pressure isotherms upon interacting with the headgroups through hydrogen bonding, according to polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS). In DPPC GUVs, BPA induced wrinkling and distortion in the spherical shape of the vesicles, but this was only observed for fresh solutions where it is not aggregated. BPA also decreased the viability of hamster ovary cells (CHO) in in vitro experiments. In contrast, aged, aggregated BPA solutions did not affect the GUVs and even increased CHO viability. These results may be rationalized in terms of size-dependent effects of BPA, which may be relevant for its endocrine-disrupting effects.

Effects of insecticide acephate on membrane mimetic systems: The role played by electrostatic interactions with lipid polar headgroups

Pesticides are important agrochemicals to yield high crop productivity but their indiscriminate use may harm the environment and human health. In order to seek a compromise between effectiveness as insecticide and safety for humans, it is essential to correlate their physiological action with molecular-level interaction with cell membranes. In this study, we found that acephate interacts preferentially with positively charged Langmuir monolayers that represent simplified cell membranes. This was proven by comparing surface pressure-molecular area (π-A) isotherms and polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS) data on monolayers of the zwitterionic 1,2-dipalmitoyl-sn-glycerol-3-phosphocholine (DPPC) and 1-palmitoyl-2-oleoyl-glycero-3-phosphocholine (POPC), the cationic dimethyldioctadecyl ammonium bromide (DODAB) and 1,2-dipalmitoyl-3-trimethylammonium-propane (DPTAP), and the anionic dihexadecyl phosphate (DHP) and 1,2-dipalmitoyl-sn-glycero-3-phosphate (DPPA). While acephate induced a closer packing of DODAB and DPTAP monolayers upon binding to their quaternary ammonium and choline groups, respectively, almost no effects were observed in the π-A isotherms of the other lipids. Such preferred interaction between acephate and the positively-charged groups was confirmed with density-functional theory (DFT) calculations. Acephate also changed the size and zeta potential of large unilamellar vesicles (LUVs) formed with cationic lipids. Taken together these results point to a physiological action related to acephate binding to positively charged groups owing to its negative character, which may help establish conditions for the safe use of this insecticide.

How the replacement of cholesterol by 25-hydroxycholesterol affects the interactions with sphingolipids: The Langmuir Monolayer Study complemented with theoretical calculations.

In this paper, a representative of chain-oxidized sterols, 25-hydroxycholesterol (25-OH), has been studied in Langmuir monolayers mixed with the sphingolipids sphingomyelin (SM) and ganglioside (GM1) to build lipid rafts. A classical Langmuir monolayer approach based on thermodynamic analysis of interactions was complemented with microscopic visualization of films (Brewster angle microscopy), surface-sensitive spectroscopy (polarization modulation-infrared reflection-absorption spectroscopy) and theoretical calculations (density functional theory modelling and molecular dynamics simulations). Strong interactions between 25-OH and both investigated sphingolipids enabled the formation of surface complexes. As known from previous studies, 25-OH in pure monolayers can be anchored to the water surface with a hydroxyl group at either C(3) or C(25). In this study, we investigated how the presence of additional strong interactions with sphingolipids modifies the surface arrangement of 25-OH. Results have shown that, in the 25-OH/GM1 system, there are no preferences regarding the orientation of the 25-OH molecule in surface complexes and two types of complexes are formed. On the other hand, SM enforces one specific orientation of 25-OH: being anchored with the C(3)-OH group to the water. The strength of interactions between the studied sphingolipids and 25-OH versus cholesterol is similar, which indicates that cholesterol may well be replaced by oxysterol in the lipid raft system. In this way, the composition of lipid rafts can be modified, changing their rheological properties and, as a consequence, influencing their proper functioning.

Ion transport mechanism in gramicidin A channels formed in floating bilayer lipid membranes supported on gold electrodes

The ion channel properties of gramicidin A (gA) in a model floating bilayer lipid membrane were studied by electrochemical impedance spectroscopy (EIS) and polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS). To determine if the transport of Na+ across the membrane is coupled with the transport of the counterion, fluoride and perchlorate anions were explored due to their large differences in hydration energy. The combined EIS and IR experiments demonstrated that in contrast to valinomycin, the mechanism of Na+ transfer through the gA channel is independent of the accompanying anion present in the supporting electrolyte. These studies also demonstrated that the conductivity of the gA sodium channel depends on the transmembrane potential and the IR measurements indicated that more gA molecules insert into the bilayer with the decrease of the transmembrane potential. The results of this present study demonstrate that the fBLM system is a suitable model bilayer for the in situ investigations of membrane-active peptides.

In Situ Spectroelectrochemical Investigations of Electrode-Confined Electron-Transferring Proteins and Redox Enzymes.

This perspective analyzes recent advances in the spectroelectrochemical investigation of redox proteins and enzymes immobilized on biocompatible or biomimetic electrode surfaces. Specifically, the article highlights new insights obtained by surface-enhanced resonance Raman (SERR), surface-enhanced infrared absorption (SEIRA), protein film infrared electrochemistry (PFIRE), polarization modulation infrared reflection–absorption spectroscopy (PMIRRAS), Förster resonance energy transfer (FRET), X-ray absorption spectroscopy (XAS), electron paramagnetic resonance (EPR), and differential electrochemical mass spectrometry (DMES)-based spectroelectrochemical methods on the structure, orientation, dynamics, and reaction mechanisms for a variety of immobilized species. This includes small heme and copper electron shuttling proteins, large respiratory complexes, hydrogenases, multicopper oxidases, alcohol dehydrogenases, endonucleases, NO-reductases, and dye decolorizing peroxidases, among other enzymes. Finally, I discuss the challenges and foreseeable future developments toward a better understanding of the functioning of these complex macromolecules and their exploitation in technological devices.

Lipid-matrix effects on tyrosinase immobilization in Langmuir and Langmuir-Blodgett films.

The immobilization of the enzyme tyrosinase (Tyr) in lipid matrices can be explored to produce biosensors for detecting polyphenols, which is relevant for the food industry. Herein, we shall demonstrate the importance of the lipid composition to immobilize the enzyme tyrosinase in Langmuir-Blodgett (LB) films. Tyr could be incorporated into Langmuir monolayers of arachidic acid (AA), 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and 1,2-dipalmitoyl-sn-glycero-3-phospho-(1'-rac-glycerol) (sodium salt) (DPPG), having as the main effect an expansion in the monolayers. Results from polarization-modulated infrared reflection-absorption spectroscopy (PM-IRRAS) pointed to electrostatic interactions between the charged residues of Try and the lipid headgroups, in addition to changes in the order of lipid chains. The interaction between Tyr and DPPC in Langmuir monolayers can be correlated with the superior performance of DPPC/Tyr LB films used as biosensors to detect catechol by cyclic voltammetry. The molecular-level interactions assessed via PM-IRRAS are therefore believed to drive an immobilization process for Tyr in the lipid LB matrix and may serve as a general criterion to identify matrices that preserve enzyme activity.

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 240 pM 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.