Langmuir-Blodgett Research Articles

Circularly Polarized Luminescence and SHG Chiral Signals of Helical TPE Macrocycles

Main observation and conclusionOne pair of new enantiomers of helical tetraphenylethylene (TPE) tetracycle tetradodecylurea, which show aggregation‐induced emission (AIE) enhancement effect, were synthesized by attaching four dodecyl chains to a helical TPE tetracycle tetramine through urea linkage. These two TPE helicates bearing long alkyl chains could display strong circular dichroism (CD) and circularly polarized luminescence (CPL) signals not only in solution but also in solid state. Due to strong van der Waals interactions between the alkyl chains, the absolute dissymmetrical factor |glum| was up to 6.6 × 10‐3 , which was 2—3 fold larger than that of the helical TPE tetracycle tetramine (TPETA) without long alkyl chains in solution. Due to bearing hydrophilic urea units and hydrophobic long dodecyl chains, the helical TPE tetracycle could form chiral Langmuir‐Blodgett (LB) monolayers at air/water interface and showed a strong and stable second harmonic generation (SHG) chiral signals. The degree of chiral excess (DCE) for P‐isomer monolayer was up to ‐0.682 ± 0.0014. This is the first example to detect chirality at the air/water interface for chiral AIE molecules. It provides a new access to the application of chiral AIE compounds in nonlinear optical activity.

Efficient quantum dot light-emitting diodes with ultra-homogeneous and highly ordered quantum dot monolayer

Regarding conventional quantum dot light-emitting diodes (QLEDs) fabricated by using the spin-coating (SC) technique, voids and interstitial spaces are inevitable due to unordered quantum dots (QDs) stacking, generating device leakage current under an external bias. In the present study, we fabricated an ultra-homogeneous and highly ordered QD monolayer by adopting the Langmuir-Blodgett (LB) technique. The QD monolayer was transferred as a emissive layer with a horizontal lifting (HL) method to a red QLED, which exhibited high performance with an external quantum efficiency (EQE) of 19.0% and lifetime (T95@100 cd m−2) of 13,324 h. When compared with the SC-based device, the EQE and lifetime were improved by 15% and 183% due to the compact and ordered QD monolayer that lowered the leakage current. Moreover, white QLEDs with stacked QD monolayers could be obtained at a low voltage of 4 V because LB technique is an organic-solvent-free approach avoiding interlayer mixing and controlling the QD layer thickness precisely. In addition, we successfully fabricated an ultra-homogeneous large-area QD monolayer on a rectangular substrate with a size of 9 cm × 5 cm, indicating the promising size scalability of the LB-HL strategy.

Fluorescent sensing of free bilirubin at nanomolar level using a Langmuir-Blodgett film of glucuronic acid-functionalized gold nanoclusters.

Serum bilirubin is an important indicator to assess liver function and diagnose various types of liver diseases. The level of serum bilirubin is also negatively correlated with the risk of cardiovascular disease and cancer. We had fabricated a fluorescent film sensor aiming at free bilirubin detection at the nanomolar level. Gold nanoclusters capped by human serum albumin (HSA-AuNCs) were utilized as a fluorescent platform for bilirubin biorecognition. HSA-AuNCs were functionalized with glucuronic acid to increase the binding sites for bilirubin. An ultrathin film of glucuronic acid-functionalized gold nanoclusters was obtained by the Langmuir-Blodgett (LB) technique. When exposed to bilirubin, the interaction between free bilirubin and the functionalized AuNCs resulted in fluorescent quenching of the film. Good linearity could be achieved for the quenching efficiency versus the logarithm of free bilirubin concentration over a concentration range of 1.00nM~5.00μM. The limit of detection (LOD) was calculated to be (2.70 ± 0.14) × 10-1nM (S/N = 3). The film sensor presents a good anti-interference capability towards common substances coexisting with bilirubin in serum. Satisfactory results achieved in the tests of real serum samples indicate that the LB film sensor can be used for bilirubin determination in nanomolar concentration.

Supramolecular Reorientation During Deposition Onto Metal Surfaces of Quasi-Two-Dimensional Langmuir Monolayers Composed of Bifunctional Amphiphilic, Twisted Perylenes.

Supramolecular dye structures, which are often ruled by π-π interactions between planar chromophores, crucially determine the optoelectronic properties of layers and interfaces. Here, we present the interfacial assembly of perylene monoanhydride and monoimide that do not feature a planar chromophore but contain chlorine substituents in the bay positions to yield twisted chromophores and hence modified π-stacking. The assembly of the twisted perylene monoanhydride and monoimide is driven by their amphiphilicity that ensures proper Langmuir layer formation. The shielding of the hydrophilic segment upon attaching an alkyl chain to the imide moiety yielded a more rigid Langmuir layer, even though the degrees of freedom were increased due to this modification. For the characterization of the Langmuir layer's supramolecular structure, the layers were deposited onto glass, silver, and gold substrates via Langmuir-Blodgett (LB) and Langmuir-Schaefer (LS) techniques and were investigated with atomic force microscopy and surface-enhanced resonance Raman spectroscopy (SERRS). From the similarity between all SERR spectra of the LS and LB layers, we concluded that the perylenes have changed their orientation upon LB deposition to bind to the silver surface of the SERRS substrate via sulfur atoms. In the Langmuir layer, the perylenes, which are π-stacked with half of the twisted chromophores, must already be inclined and cannot achieve full parallel alignment because of the twisting-induced steric hindrance. However, upon rotation, the energetically most favorable antiparallel aligned structures can be formed and bind to the SERRS substrate. Thus, we present, to the best of our knowledge, the first fabrication of quasi-two-dimensional films from twisted amphiphilic perylene monoimides and their reassembly during LB deposition. The relation between the molecular structure, supramolecular interfacial assembly, and its adoption during adsorption revealed here is crucial for the fabrication of defined functionalizations of metal surfaces, which is key to the development of organic (opto)electronic devices.

Laponite elementary sheets assisted fluorescence resonance energy transfer: A demonstration by Langmuir-Blodgett technique

The fluorescence resonance energy transfer (FRET) between donor-acceptor molecules of fluorescein (FL) and rhodamine B (RhB) was enhanced by clay sheets of laponite. This enhancement was implemented by the Langmuir-Blodgett (LB) technique. Hybrid films were prepared by incorporating elementary clay sheets into dye molecules (FL and RhB for different molar ratios) at the air/water interface. The spectroscopic measurements (UV–Vis absorption and photoluminescence) of these mixture systems (FL, RhB and clay mineral) were analyzed both in colloidal dispersion and LB films. A high efficiency (92%) of FRET from FL to RhB was achieved with presence of laponite. Characterizations such as surface pressure versus area (π-A) isotherms, atomic force microscopy (AFM) and contact angle measurements were used to confirm the successful incorporation of clay sheets in hybrid films with loaded dye molecules. The clay incorporation were indicated to shorten the distance between donor and acceptor chromophores (Förster radius), which was realized by the tightly bounded dye molecules on clay sheets and self-assembly of dye molecule pairs.

Dynamic Control of the Interparticle Distance in a Self-Assembled Ag Nanocube Monolayer for Plasmonic Color Modulation

We experimentally demonstrated plasmonic color modulation by dynamically controlling the plasmon resonance excited in an assembled Ag nanocube (AgNC) monolayer. The plasmon resonance wavelength of the hybridization plasmon mode of the local plasmon and collective oscillation plasmon in the Ag nanocube monolayer is sensitive to the interparticle distances. The interparticle distances were continuously controlled with a stretchable and transparent polydimethylsiloxane (PDMS) substrate. Crystalline Ag nanocubes were synthesized through a polyol process. The nanocube shape provides a narrower plasmon resonance band as a result of the small dispersion of electron vibrations. The synthesized nanocubes were densely assembled in a monolayer on the PDMS substrate using the Langmuir–Blodgett (LB) method. The interparticle distance of the Ag nanocube monolayer was controlled from 5.8 to 24.8 nm through biaxial stretching of the substrate from 0 to 20%. The transmitted light color of the Ag nanocube monolayer was actively tuned from magenta to orange to yellow by stretching the substrate up to 20% under random polarization incidence. This color modulation was generated by the plasmon resonance transition from the collective oscillation mode between particles to the local oscillation mode in the isolated nanocubes. Such a plasmonic color modulation is expected to enable a multispectral image sensor with compact and high light utilization efficiency.

PEGylated DPPC/Anti-SNAP25 Antibody Targeted Liposomes from Langmuir Monolayer Study to Formulations

Background: Molecule compatibility is an important factor to be considered before preparing antibody-targeted liposomes, stealth-liposomes, and stealth antibody-targeted liposomes. Objective: To determine the intermolecular interaction of 1,2-dioleoyl-sn-glycero-3-phosphoethanolamide- N-[methoxy(polyethyleneglycol)-2000] (ammonium salt), DOPE PEG2000 and Anti-SNAP25 (AS25) in 1,2-dipalmitoyl-sn-glycero-3-phosphorylcholine (DPPC) monolayer, and their liposomes. Methods: In this study, DPPC was used to create a monolayer mimicking the half membrane of liposomes to investigate its interactions with a polyclonal antibody, AS25, and DOPE PEG2000, which are based on Langmuir-Blodgett (LB) techniques. The surface morphology of DPPC-AS25 and DPPC-DOPE PEG2000-AS25 bilayers were also imaged and analyzed by using atomic force microscopy (AFM) to support the LB findings. The LB findings were then utilized as a reference to prepare DPPC liposomes in this work. Results: The best mole ratio of DPPC-DOPE PEG2000, determined to be 50 to 1, was used to study the interaction with the polyclonal antibody AS25. The free energy of mixing (ΔGmix) of DPPC- DOPE PEG2000-AS25 was more negative than DPPC-AS25 in the entire investigated ranges, indicating that the ternary mixture of DPPC-DOPE PEG2000-AS25 was more compatible than the binary mixture of DPPC-AS25. The presence of DOPE PEG2000 in DPPC-AS25 increased the fluidity of the membrane, which resulted in a greater interaction of AS25 with DPPC. Conclusion: The constant values of particle size and zeta potential measurements of DPPC-DOPE PEG2000-AS25 liposomes showed agreement with the LB findings, indicating that LB is a good technique to predict precise liposomal formulations.

Adhesion-Shielding based synthesis of interfacially active magnetic Janus nanoparticles

HypothesisA unique adhesion-shielding (AS)-based method could be used to manufacture magnetic Janus nanoparticles (IM-JNPs) of promising interfacial activities, asymmetric surface wettability, and great performance on deoiling from oily wastewater under the external magnetic field. ExperimentsThe IM-JNPs were characterized using scanning electron microscope (SEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA), and Fourier-transform infrared spectroscopy (FTIR). The interfacial properties of IM-JNPs were investigated by the measurements of interfacial pressure-area isotherms (π-A), oil–water interfacial tension, and the related crumpling ratio. The Langmuir-Blodgett (L-B) technique was used to determine the asymmetric surface wettability of the IM-JNPs. The performance and recyclability of IM-JNPs for treating oily wastewater were also investigated. FindingsUsing the proposed AS-based method, 17.9 g IM-JNPs were synthesized at a time and exhibited excellent interfacial properties, as indicated by decreasing oil–water interfacial tension from 38 to 27 mN/m. The crumpling behavior of the oil droplet further demonstrated the irreversible deposition of IM-JNPs at the oil droplet surfaces. The L-B technique and water contact angle measurement confirmed the asymmetric surface wettability of the IM-JNPs. The IM-JNPs were applied to successful removal of > 90% emulsified oil droplets from the household-produced oily wastewater under the external magnetic field while realizing facile recyclability and regeneration.

Langmuir-Blodgett Films of Diketopyrrolopyrroles with Tunable Amphiphilicity.

In this work, we present the formation of H- and J-aggregates of amphiphilic centrosymmetric diketopyrrolopyrroles containing aliphatic or aromatic amino groups. The inherent amphiphilicity of these dyes predestines their assembly at interfaces to form ordered supramolecular structures. In this work, we employed the Langmuir-Blodgett (LB) technique to generate, manipulate, and deposit such supramolecular structures. The aforementioned amines provide an additional means to control the formation of the supramolecular assemblies. In the resulting LB films, both H- and J-aggregates of the dyes can be realized, leading to very broad absorption spectra. In contrast to many reports on H- and J-aggregates, the interactions between the symmetric diketopyrrolopyrroles are controlled via interface assembly and π-stacking and not by dipolar interactions. We show that in the case of the aliphatic, but not for the aromatic amine functionalization, the usage of an acidic subphase enables the transition from H- to J-aggregate-dominated LB films via an increase in the surface pressure during deposition.

Stearic acid mediated growth of edge-on oriented bilayer poly(3-hexylthiophene) Langmuir films

The growth and structural evolution of stearic acid (SA) blended poly(3-hexylthiophene) [P3HT] Langmuir and Langmuir–Blodgett (LB) films were studied using complimentary surface and interface sensitive techniques to understand the possibility of ordering and layering of promising charge carrier mobility polymers, at the air–water interface and on the transferred solid substrate. SA-induced and subsequent compression-induced transitions in P3HT structure, from aggregated-3D to soft-2D and from in-plane mixed to unmixed layer, are evident at low and high pressures, respectively. The blending of SA molecules enhances the amphiphilic character of P3HT, which reduces the extent of the out-of-plane aggregation to form edge-on oriented (EO) bottom side-chain folded-bilayer (f-BL) islands (of size ~60 nm) within SA monolayer (ML), of commensurate thickness (~2.6 nm). Further compression, gradually rejects the less hydrophilic f-BL islands from the mixed layer to form EO P3HT BL islands (of coverage in-tune with starting composition) on top of SA ML. The formation of nearly covered P3HT(BL)/SA(ML) structured film on solid substrate is evident for the first time, which (even of limited P3HT thickness) has immense importance in the device properties, as the current in the bottom-gated organic thin-film transistors is known to travel only within few ML region near gate-dielectric.

Interactions of Microorganisms with Lipid Langmuir Layers.

Preventing microbial contamination of aquatic environments is crucial for the proper supply of drinking water. Hence, understanding the interactions that govern bacterial and virus adsorption to surfaces is crucial to prevent infection transmittance. Here, we describe a new approach for studying the organization and interactions of various microorganisms, namely, Escherichia coli (E. coli) bacteria, E. coli-specific bacteriophage T4, and plant cucumber green mottle mosaic viruses (CGMMV), at the air/water interface using the Langmuir-Blodgett (LB) technique. CGMMV were found as applicable candidates for further studying their interactions with Langmuir lipid monolayers. The zwitterionic, positively, and negatively charged LB lipid monolayers with adsorbed viruses were deposited onto solid supports and characterized by atomic force microscopy. Using polymerase chain reaction, we indicated that the adsorption of CGMMV onto the LB monolayer is a result of electrostatic interactions. These insights are useful in engineering membrane filters that prevent biofouling for efficient purification systems.

Synthesis, characterization and chemical sensor properties of a novel Zn(II) phthalocyanine containing 15-membered dioxa-dithia macrocycle moiety

The issue of utilizing organic materials in chemical sensing devices has recently received considerable critical attention. Phthalocyanines (Pcs) and metal phthalocyanines (MPcs) have been identified as promising materials thanks to their outstanding properties reported in this study. A novel zinc(II) phthalocyanine containing four 15-membered dioxa-dithia macrocyclic moieties was synthesized via the reaction of anhydrous Zn(II) acetate and 13,14-dihydro-6H,12H,20H-tribenzo[f,j,n][1,5]dioxa[9,12] dithiacyclopenta-decine-2,3-dicarbonitrile which was prepared from 1,3-di(2-thio-methylphenoxy) propane and 4,5-dichloropthalonitrile. In order to synthesize and characterize this novel compound, elemental analysis, MS, FT-IR, 1H, 13C NMR, and UV–vis spectral techniques were utilized. To create a Quartz Crystal Microbalance (QCM) sensor, zinc(II) phthalocyanine-based macrocyclic molecules were deposited onto a quartz crystal using the Langmuir-Blodgett (LB) thin film technique. The sensing ability of this chemical sensor was examined by recording the interaction between this novel material as a QCM-sensor and selected chemical vapors such as carbon tetrachloride, chloroform, benzene and toluene. The interaction results for this zinc(II) phthalocyanine based macrocyclic material indicated that this material can be used as a QCM chemical sensor element for chloroform sensing devices with a low detection limit, fast response and recovery times, selectivity, and high sensitivity.

Nanoscale Chemical Imaging of Supported Lipid Monolayers using Tip‐Enhanced Raman Spectroscopy

AbstractVisualizing the molecular organization of lipid membranes is essential to comprehend their biological functions. However, current analytical techniques fail to provide a non‐destructive and label‐free characterization of lipid films under ambient conditions at nanometer length scales. In this work, we demonstrate the capability of tip‐enhanced Raman spectroscopy (TERS) to probe the molecular organization of supported DPPC monolayers on Au (111), prepared using the Langmuir–Blodgett (LB) technique. High‐quality TERS spectra were obtained, that permitted a direct correlation of the topography of the lipid monolayer with its TERS image for the first time. Furthermore, hyperspectral TERS imaging revealed the presence of nanometer‐sized holes within a continuous DPPC monolayer structure. This shows that a homogeneously transferred LB monolayer is heterogeneous at the nanoscale. Finally, the high sensitivity and spatial resolution down to 20 nm of TERS imaging enabled reproducible, hyperspectral visualization of molecular disorder in the DPPC monolayers, demonstrating that TERS is a promising nanoanalytical tool to investigate the molecular organization of lipid membranes.

Preparation of Zinc (II) phthalocyanine-based LB thin film: Experimental characterization, the determination of some optical properties and the investigation of the optical sensing ability

Zinc(II) phthalocyanine (Zn(II)Pc) molecule was the first time prepared onto three different substrates utilizing Langmuir-Blodgett (LB) deposition technique to investigate its vapor sensing abilities and some optical properties. We utilized five different and well-known techniques to control monolayer quality of Zn(II)Pc LB film. The obtained the thickness and refractive index values for Zn(II)Pc LB film with coated at different layers vary from 3.2 to 10.9 nm and from 1.42 to 1.71, respectively. The sensing properties were investigated by exposing the Zn(II)Pc-based mass or optical sensor to some organic vapors. Kinetic results presented that this Zn(II)Pc material is a good candidate as a sensor element with a fast and reversible response for dichloromethane sensing devices.

Vanadium Dioxide–Iridium Composite Development: Specific Near Infrared Surface Plasmon Resonance

This work serves as a roadmap for the development of a Vanadium dioxide (VO2)–Iridium composite based on the self-assembly of closely packed colloidal polystyrene microspheres (P-spheres) coupled with a Pulsed Laser Deposition (PLD) process. The self-assembly of a monolayer of PS is performed on an Al2O3-c substrate, using an adapted Langmuir–Blodgett (LB) process. Then, on the substrate covered with P-spheres, a 50-nanometer Iridium layer is deposited by PLD. The Iridium deposition is followed by the removal of PS with acetone, revealing an array of triangular shaped metallic elements formed on the underlaying substrate. In a last deposition step, 50-, 100- and 200-nanometer thin films of VO2 are deposited by PLD on top of the substrates covered with the Iridium quasi-triangles, forming a composite. Adapting the size of the P-spheres leads to control of both the size of the Iridium micro-triangle and, consequently, the optical transmittance of the composite. Owing to their shape and size the Iridium micro-triangles exhibit localized surface plasmon resonance (LSPR) characterized by a selective absorption of light. Due to the temperature dependent properties of VO2, the LSPR properties of the composite can be changeable and tunable.

Ultrasensitive Immunosensor Based on Langmuir-Blodgett Deposited Ordered Graphene Assemblies for Dengue Detection.

In this manuscript partially reduced graphene oxide (RGO) nanosheet-based electrodes have been utilized for quantification of the NS1 protein and subsequently for dengue detection. NS1 is the biomarker found circulating in the body of dengue-infected persons on or after first day of the appearance of disease symptoms. Graphene oxide (GO) has been synthesized using a modified Hummer's method, and its ordered nanostructured films have been electrophoretically deposited on indium tin oxide (ITO)-coated glass substrates using Langmuir-Blodgett (LB) deposition. Deposited LB films of GO have been reduced with hydrazine vapors to obtain RGO-coated ITO electrodes. NS1 antibodies have been grafted onto the ordered thin films using covalent linking, and the bioelectrodes have been utilized for the specific detection of NS1 antigen. The electrochemical performance of the fabricated bioelectrodes for NS1 antigen detection has been explored in standard and spiked sera samples. The limit of detection for the standard samples and spiked serum samples is found to be 0.069 ng mL-1 and 0.081 ng mL-1, respectively, with a sensitivity of 8.41 and 36.75 Ω per ng mL, respectively, in the detection range of 101 to 107 ng mL-1.

Polarized Electroluminescence Emission in High-Performance Quantum Rod Light-Emitting Diodes via the Langmuir-Blodgett Technique.

Due to their anisotropic structure, quantum rods (QRs) feature unique properties that differ from quantum dots, such as suppression of non-radiative Auger recombination and linearly polarized light emission. Despite many potential advantages, the progress of QR-based light-emitting diodes (QR-LEDs) is left behind due to the difficulty in aligning QRs. In this study, polarized electroluminescence emission is reported in high-performance QR-LEDs by employing the Langmuir-Blodgett (LB) technique. The adoption of the LB technique successfully produces a highly dense and smooth QR film with a high degree of alignment. As a result, the aligned QR films exhibit polarized photoluminescence emission with a degree of linear polarization of 2.1. Advantageous features of the LB technique, such as nondestructiveness, precise thickness control, and the nonnecessity of an additional matrix material, allow to fabricate QR-LEDs with the same procedure as the standard spin coating-based scheme. The device is fabricated via the LB technique, which shows excellent device performance, such as the low turn-on voltage of 1.8V, peak luminance of 56287 cd m-2 , and peak external quantum efficiency (EQE) of 10.33%. Furthermore, these devices clearly exhibit an indication of polarized electroluminescence emission, which opens new opportunities for QRs in display technologies.

Construction of Multifunctional and Adjustable Langmuir-Blodgett Composite Films Containing Black Phosphorus with High Stability for Optically Electrical Applications.

Fabrication of composite thin-film materials based on black phosphorus (BP) will greatly broaden the applications of BP in various areas. However, it is still a challenge to prepare a BP-based composite film with good stability and controllable structure. In this work, a series of BP-based composite Langmuir-Blodgett (LB) films are prepared by the self-assembly of polyethyleneimine (PEI)-modified BP nanosheets (BPNSs) (BPNS-PEI) and dye molecules. The presence of PEI greatly improves the stability of BPNSs. As for BPNS-PEI and dye molecules, the electrostatic interactions or π-π stacking interactions ensure the formation of stable composite LB films. Due to the protonation and deprotonation of amino groups, the synthesized BPNS-PEI/dye composite films show a sensitive response to acid and alkali gases, which shows wide application prospects as a highly sensitive gas sensor. Furthermore, surface-enhanced Raman scattering (SERS) proves that the prepared LB films exhibit good reproducibility and obvious Raman enhancement effect on rhodamine 6G molecules. In addition, due to the high carrier transfer rate of the obtained composite films, they possess enhanced photocurrent generation performance than pure BPNS-PEI and pure dye films. The current work demonstrates an effective method for preparing the ordered self-assembled BP-based composite LB films with good SERS and photoelectric conversion performance.

Ultraflat Langmuir–Blodgett assembled graphene oxide saturable-absorber films for pulsed near-infrared laser generation

Large-scale production of ultraflat broadband saturable-absorber films is highly desired for passive mode-locked solid-state lasers. However, the current vapour deposition and spin coating routes for fabricating saturable absorbers (SAs) are suffering from the limited flexibility in substrate choice and complexity of mass production processes. Here, we demonstrate an ultraflat carboxyl-functionalized graphene oxide (GO-COOH) SA film via Langmuir–Blodgett (LB) assembly for solid state laser mode-locking. Hydrophilic carboxyl groups from GO sheets weaken the aggregation effect thus contribute to the uniform and stable dispersion of GO sheets in water. Such GO suspensions are made into an ultrathin large-area graphene-based SA film by a LB assembly process ensuring high surface uniformity. The room-temperature and highly repeated operation for GO LB films avoids the thermal damage of GO sheets and improves the membrane repeatability. Consequently, the ultrathin GO-COOH SA shows the modulation depth (2.3%) and low saturation intensity (24.7 KW cm−2) under 1064 nm laser irradiation. By inserting the GO SA into a Nd:GdVO4 laser, both passive Q-switched (QS) and passive Q-switched mode-locked (QML) operations are also attained. The slope efficiency of QS laser is up to 35.6% and the maximum single pulse energy is 1.48 μJ. In particular, the QML pulses can be achieved stably and repeatedly with an average output power of 1.33 W and a pulse energy of 13.2 nJ. Our strategy provides a new concept for improving the modulation stability of graphene-based SAs and promoting their industrial application in pulsed solid-state lasers.

Surface Chemistry Studies on the Formation of Mixed Stearic Acid/Phenylalanine Dehydrogenase Langmuir and Langmuir-Blodgett Films.

This work investigates the physicochemical properties of mixed stearic acid (HSt)/phenylalanine dehydrogenase enzyme (PheDH) Langmuir films and their immobilization onto solid supports as Langmuir-Blodgett (LB) films. PheDH from the aqueous subphase enters the surfactant matrix up to an exclusion surface pressure of 25.3 mN/m, leading to the formation of stable and highly condensed mixed Langmuir monolayers. Hydrophobic interactions between the enzyme and HSt nonpolar groups tuned the secondary structure of PheDH, evidenced by the presence of β-sheet structures as demonstrated by infrared and circular dichroism spectra. The floating monolayers were successfully transferred to solid quartz supports, yielding Y-type LB films, and then characterized employing fluorescence, circular dichroism, and microscopic techniques, which indicated that PheDH was co-immobilized with HSt proportionally to the number of transferred layers. The enzyme fluidized the HSt monolayers, reducing their maximum dipoles when condensed to their maximum, and disorganized the alkyl chains of the fatty acid, as detected with infrared spectroscopy. The stability of the mixed floating monolayers enabled their transfer to solid supports as LB films, which is important for producing optical and electrochemical sensors for phenylalanine whose molecular architecture can be controlled with precision.