Surface Pressure Of Monolayers Research Articles

Degradation Behavior of Poly(Lactide-Co-Glycolide) Monolayers Investigated by Langmuir Technique: Accelerating Effect.

Among biodegradable polymers, polylactides (PLAs) have attracted considerable interest because the monomer can be produced from renewable resources. Since their initial degradability strongly affects commercial application fields, it is necessary to manage the degradation properties of PLAs to make them more commercially attractive. To control their degradability, poly(lactide-co-glycolide) (PLGA) copolymers of glycolide and isomer lactides (LAs) were synthesized, and their enzymatic and alkaline degradation rates of PLGA monolayers as functions of glycolide acid (GA) composition were systematically investigated by the Langmuir technique. The results showed that the alkaline and enzymatic degradations of PLGA monolayers were faster than those of l-polylactide (l-PLA), even though proteinase K is selectively effective in the l-lactide (l-LA) unit. Alkaline hydrolysis was strongly affected by their hydrophilicity, while the surface pressure of monolayers for enzymatic degradations was a major factor.

Tyrosine-derived polymeric surfactant nanospheres insert cholesterol in cell membranes

HypothesisThe design of biodegradable tyrosine-derived polymeric surfactants (TyPS) through the use of calculated thermodynamic parameters could lead to phospholipid membrane surface modifiers capable of controlling cellular properties such as viability. Delivery of cholesterol by TyPS nanospheres into membrane phospholipid domains could provide further controlled modulation of membrane physical and biological properties. ExperimentCalculated Hansen solubility parameters (∂T) and hydrophile:lipophile balances (HLB) were applied to design and synthesize a small family of diblock and triblock TyPS with different hydrophobic blocks and PEG hydrophilic blocks. Self-assembled TyPS/cholesterol nanospheres were prepared in aqueous media via co-precipitation. Cholesterol loading and Langmuir film balance surface pressures of phospholipid monolayers were obtained. TyPS and TyPS/cholesterol nanosphere effects on human dermal cell viability were evaluated by cell culture using poly(ethylene glycol) (PEG) and Poloxamer 188 as controls. FindingsStable TyPS nanospheres incorporated between 1% and 5% cholesterol. Triblock TyPS formed nanosphere with dimensions significantly smaller than diblock TyPS nanospheres. In accord calculated thermodynamic parameters, cholesterol binding increased with increasing TyPS hydrophobicity. TyPS inserted into phospholipid monolayer films in a manner consistent with their thermodynamic properties and TyPS/cholesterol nanospheres delivered cholesterol into the films. Triblock TyPS/cholesterol nanospheres increased human dermal cell viability, which was indicative of potentially beneficial TyPS effects on cell membrane surface properties.

Dilatational and shear rheology of soluble and insoluble monolayers with a Langmuir trough

HypothesisThe surface dilatational and shear moduli of surfactant and protein interfacial layers can be derived from surface pressures measured with a Wilhelmy plate parallel, ΔΠpar and perpendicular ΔΠperp to the barriers in a Langmuir trough. ExperimentalApplying area oscillations, A0+ ΔAeiωt, in a rectangular Langmuir trough induces changes in surface pressure, ΔΠpar and ΔΠperp for monolayers of soluble palmitoyl-lysophosphatidylcholine (LysoPC), insoluble dipalmitoylphosphatidylcholine (DPPC), and the protein β-lactoglobulin to evaluate Es∗+Gs∗=A0ΔΠparΔA and Es∗-Gs∗=A0ΔΠperpΔA. Gs∗ was independently measured with a double-wall ring apparatus (DWR) and Es∗ by area oscillations of hemispherical bubbles in a capillary pressure microtensiometer (CPM) and the results were compared to the trough measurements. FindingsFor LysoPC and DPPC, A0ΔΠparΔA≅A0ΔΠperpΔA meaning Es∗≫Gs∗ and Es∗≅A0ΔΠparΔA≅A0ΔΠperpΔA. Trough values for Es∗ were quantitatively similar to CPM when corrected for interfacial curvature. DWR showed G∗ was 4 orders of magnitude smaller than Es∗ for both LysoPC and DPPC. For β-lactoglobulin films, A0ΔΠparΔA>A0ΔΠperpΔA and Es∗ and Gs∗ were in qualitative agreement with independent CPM and DWR measurements. For β-lactoglobulin, both Es∗ and Gs∗ varied with film age and history on the trough, suggesting the evolution of the protein structure.

Osmotic Method for Calculating Surface Pressure of Monolayers in Molecular Dynamics Simulations.

Surface pressure is a fundamental thermodynamic property related to the activity of molecules at interfaces. In molecular simulations, it is typically calculated from its definition: the difference between the surface tension of the air-water and air-surfactant interfaces. In this Letter, we show how to connect the surface pressure with a two-dimensional osmotic pressure and how to take advantage of this analogy to obtain a practical method of calculating surface pressure-area isotherms in molecular simulation. As a proof-of-concept, compression curves of zwitterionic and ionic surfactant monolayers were obtained using the osmotic approach and the curves were compared with the ones from the traditional pressure tensor-based scheme. The results shown an excellent agreement between both alternatives. Advantageously, the osmotic approach is simple to use and allows to obtain the surface pressure-area isotherm on the fly with a single simulation using equilibration stages.

DNA penetration into a monolayer of amphiphilic polyelectrolyte

Using infrared reflection–absorption spectroscopy, surface tensiometry and atomic force microscopy it is demonstrated that a network of fibrous aggregates of DNA–cationic polyelectrolyte complexes is formed at the water–air interface, the mechanism of the network generation depending on the initial surface pressure of the polyelectrolyte monolayer.

Masking of a malodorous substance on 1,2-dioleoyl-sn-glycero-3-phosphocholine molecular layer

The performance of a trans-2-nonenal (NE)-including 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) molecular layer as a model of epithelial cellular membrane damaged by malodorous substance was investigated to understand the masking effect of odorants (benzaldehyde (BA), cyclohexanecarboxyaldehyde (CA), 4-anisaldehyde (AA), and 4-methoxycyclohexanecarbaldehyde (MA)). The surface pressure of the DOPC monolayer increased upon the addition of NE, and the surface pressure–area isotherm of the DOPC-NE mixture was characteristically responsive to the odorants (BA, CA, AA, and MA). Differential scanning calorimetry, Fourier-transform infrared spectroscopy, and ultraviolet absorption spectrophotometry were conducted to evaluate the interactions among DOPC, NE, and the odorants. The results suggested that odorants with an aromatic ring form a complex with NE and were eliminated from the DOPC membrane. We found that odorants with an aromatic ring play an important role in inducing the masking effect on the DOPC-NE mixed monolayer because of the characteristic interactions between NE and odorant.

Lipid exchanges between dioctadecyldimethylammonium bromide monolayer and vesicles in the subphase

AbstractStudies on the interaction of lipid monolayer with bilayer structures, such as vesicles, are relatively scarce in the literature. In order to ascertain whether these structures interact for cationic dioctadecyldimethylammonium bromide (DODAB) monolayers at the aqueous surfaces of 0, 0.05, and 0.5 mmol L−1 DODAB vesicle dispersions, differential scanning calorimetry (DSC) and surface film balance experiments were carried out. DSC results confirmed the presence of unilamellar vesicles in the subphase, while changes in the monolayer surface pressure–area per molecule (π–A) isotherm profile yielded by the presence of DODAB vesicle in the subphase revealed monolayer‐vesicle interactions as a result of monomer exchanges between the monolayer and the vesicles with stronger effects at the higher vesicle concentration investigated.

Unmodified Clay Nanosheets at the Air-Water Interface.

Quasi-two-dimensional (2D) nanolayers, such as graphene oxide or clay layers, adhere to gas–liquid or liquid–liquid interfaces. Particularly, clays are of wide general interest in this context because of their extensive and crucial use as Pickering emulsion stabilizers, as well as for their ability to provide colloidosome capsules. So far, clays could only be localized at oil–water or air–saline-water interfaces in aggregated states, while our results now show that clay nanosheets without any modification can be located at air–deionized-water interfaces. The clay mineral used in the present work is synthetic fluorohectorite with a very high aspect ratio and superior quality in homogeneity and charge distribution compared to other clay minerals. This clay mineral is more suitable for achieving unmodified clay anchoring to fluid interfaces compared to other clay minerals used in previous works. In this context, we studied clay nanosheet organization at the air–water interface by combining different experimental methods: Langmuir–Blodgett trough studies, scanning electron microscopy (SEM) studies of film deposits, grazing-incidence X-ray off-specular scattering (GIXOS), and Brewster angle microscopy (BAM). Clay films formed at the air–water interface could be transferred to solid substrates by the Langmuir–Schaefer method. The BAM results indicate a dynamic equilibrium between clay sheets on the interface and in the subphase. Because of this dynamic equilibrium, the Langmuir monolayer surface pressure does not change significantly when pure clay sheets are spread on the liquid surface. However, also, GIXOS results confirm that there are clay nanosheets at the air–water interface. In addition, we find that clay sheets modified by a branched polymer are much more likely to be confined to the interface.

Interfacial complex of α-lactalbumin with oleic acid: effect of protein concentration and PM-IRRAS study

We used the Langmuir technique to investigate the binding of the bovine α-lactalbumin (BLA III) to the oleic acid (OA) monolayer in gastric conditions (pH 2.0 and 36.6 °C). Both substances are components of the BAMLET complex, which is beneficial to human health. The monolayer studies have been completed with BAM imaging and PM-IRRAS spectra. This paper explores the interfacial behavior of the lipid monolayer in the presence of the protein. It proves that the higher the concentration of protein in the subphase, the higher the increase in the relative surface pressure of the OA monolayer is, until the additional amount of protein affects the maximmum film response. We also discussed the MIP (maximum insertion pressure) value and analyzed the infrared spectra to prove that BLA III interacts with OA at the interface. We focused on the kinetics of the interaction between these components. We noticed that after protein adsorption at the interface (which rate depends on BLA III concentration), the protein penetrates the lipid monolayer, followed by film rearrangement (the protein forces on fatty acid molecules to change their orientation) until finally a stable lipid-protein complex is formed at the air-water interface. This multi-stage process is relevant to the course of a relaxation curve, which demonstrates the monolayer response on protein injection. This paper explores the physicochemical phenomena which fully recognized may open the door to numerous applications of these lipid-protein system.

Precise and instrumental measurement of thermodynamics and kinetics of froth flotation by langmuir-blodgett technique

Froth flotation is most common means in mineral separation, and the in-situ measurement of flotation is of significance. However there were no instrumental means of measuring kinetics and thermodynamics for this process up to date. Herein, for the first time a facile method was developed by using Langmuir-Blodgett (LB) technique to get precise recording of kinetics and thermodynamics for adsorption process of Langmuir hybrid layer at the air/water interface. The formation of hybrid Langmuir monolayer was assumed to simulate the adsorption of mineral particles by frother/collector bubbles in the micro-flotation although this was a semi-static adsorption process. The kinetic parameters including time constant (τ1/e, 32.0∼139.0 s) and adsorption rate constant (k, 0.0315∼0.00718 s−1) were precisely determined according to surface pressure vs. time (π-t) plots of Langmuir monolayer which consisted of floated minerals particles and collector molecules. The thermodynamic data such as partition coefficient (Kd, 0.221−0.339), Gibbs free energy of adsorption ΔG (2.68∼3.74 kJ mol−1), and minimum dosages of collector molecules (potassium butylxanthate) were derived from the surface pressure vs. molecular area (π-A) isotherms. Taking the major mineral of pyrite with minor of dolomite and quartz as a froth flotation model, the recovery yield of concentrate pyrite obtained from LB technique was found in good agreement with the common tests used micro-flotation, suggesting the consistency of the new-developed LB method in predicting kinetics and thermodynamics for froth flotation.

Can simple physicochemical studies predict the effects of molecules on epidermal water‐impermeable barrier function?

Improvement of the water-impermeable barrier function of skin is clinically important, because barrier abnormality is associated with various skin diseases, such as psoriasis or atopic dermatitis. We have shown that topical application of fatty acids, sex hormones, hexoses, polyols and polymers influences barrier homeostasis, but the effects are highly dependent on even small variations of molecular structure. Moreover, the effects appear within one hour after application and thus are likely to be non-genomic (physicochemical) phenomena. Secretion of lipids from lamellar bodies into the intercellular space between stratum granulosum and stratum corneum is a crucial step in epidermal water-impermeable barrier homeostasis, especially at the early stage of barrier recovery after damage, and phase transition of the lipid lamellar structure in the epidermis is an important part of this process. Therefore, we evaluated the effects of the above molecules on the physicochemical properties of phospholipid monolayers and liposomes as models of the lamellar body membrane and cell membrane. Molecules that influenced the barrier recovery process also altered the stability of liposomes and the air-water surface pressure of phospholipid monolayers. Studies using attenuated total reflection Fourier-transform infrared spectroscopy (ATR FT-IR), differential scanning calorimetry (DSC) and 13 C nuclear magnetic resonance (NMR) spectrometry suggested that molecules influencing barrier recovery interact specifically with phospholipids. The idea that molecules interacting with phospholipids may influence barrier homeostasis should open up new approaches to the treatment of a variety of skin diseases.

Physicochemical characterization of novel 3-carboxymethyl-bile salts, as permeability and solubility enhancers

New bile acid derivatives are synthesized: 3-(carboxymethyl)-5β-chol-3-ene-7α,12α,24-triol (ND-1) and 3α-(carboxymethyl)-5β-cholan-7α,12α,24-triol (ND-2). The derivative ND-1 has more hydrophobic convex surface than deoxycholic acid (D), but its partition coefficient in 1-octanol-aqueous phase is lower than one of ursodeoxycholic acid (UD), which means that ND-1 has smaller total hydrophobic surface in comparison to UD. The anion D shows greater increase in DPPC monolayer surface pressure than it can be derived from the size of its hydrophobic surface at the β side of steroid skeleton. Membrane toxicity of ND-1 and ND-2 is lower than the one of D. The derivative ND-1 has lower value of the critical micellar concentration (cmc) than the anion D. At cmc ND-1 and ND-2 build Small primary micelles, while at the concentrations several times higher than cmc they form secondary micelles. The equilibrium constant of nitrazepane incorporation into the ND-1 and the ND-2 micelles implies that these micelles have larger hydrophobic nuclei than the micelles of natural dihydroxy bile acid derivative anions.

Alteration of surface pressure of macromolecular monolayer at the air-water interface and electrochemical impedance characteristics

Proteins are very important biological macromolecules, specific in their functions essential for many biological activities. Proteins are among the most vital components of all living matters with thousands of different types, and they are very specific in their nature which makes them important for usage in many biotechnological, biomedical, and food processing applications. Langmuir monolayer studies provide the characteristics of monolayer at the air-liquid interface. Langmuir monolayer of protein is affected by the molecular weight, macromolecular structure, denaturation and its purity. The interaction of the protein with other molecules greatly affects the behaviour of monolayer. Coconut oil layer at the air-water interface was prepared with different sub-phases including casein protein and whey protein. Wilhelmy plate measurement technique has been used to measure the surface pressure of the monolayer at the air-liquid interface. Experiments were carried out to study the stability using electrochemical impedance measurements. The electrostatic forces dominated the coconut oil - protein interaction, and the interface of macromolecules were controlled by expansion and compression. The macromolecules were adsorbed with a preferential orientation at the interface, and the stability of colloidal dispersions was governed by the intermolecular interactions. The stability using electrochemical impedance spectroscopy on the selected protein macromolecules along with other analysis were performed by varying various parameters.

Preparation of Non-Surface-Active Langmuir Trough Subphases from Milk.

Milk polar lipid interfacial behavior continues to be analyzed using Langmuir trough experiments, but the reported Langmuir trough subphases commonly used are not fully representative of milk. A method to transform liquids of biological origin, such as milk, into appropriate Langmuir trough subphases does not currently exist, which hinders the applicability of Langmuir trough experiments to nature. Here, a procedure to manufacture milk-derived Langmuir trough subphases with insignificant amounts of surfactants from bovine milk is presented. Ultrafiltration is used to remove the bulk of protein surfactants from milk followed by the creation of solvent-induced emulsions that remove trace proteins and lipids from collected skim milk permeates. Change in surface tension upon compression of resulting washed permeates from the surfactant removal process was ≤0.1 mN/m, terming the permeates non-surface-active (NSA). NSA permeates (72.4 ± 0.2 mN/m) had a surface tension similar to that of ultrapure water (72.6 ± 0.1 mN/m), but their pH, conductivity, percent total solids, Brix percentage, alkalinity, and hardness were not the same, with NSA permeates being more compositionally similar to skim milk than water. The lift-off points of milk ganglioside GM3 monolayer surface pressure–area isotherms spread on NSA permeates and ultrapure water subphases were significantly different when compared for the same sample, indicating that surface tension measurements obtained on ultrapure water are not the same as with NSA milk permeate. Overall, surfactants were removed from bovine milk without the addition of exogenous compounds, allowing for the production of a NSA solution derived from milk that can be used in the Langmuir trough experiment to more realistically resemble the natural environment of milk polar lipids. The procedure described here was able to produce NSA solutions for other dairy beverages aside from milk, indicating that it can be applicable to other biological fluids.

Kinetics of interaction between antimicrobial peptide nisin and Langmuir monolayers of DPPC and DPPG molecules.

We have studied the kinetics of the interaction between antimicrobial peptide nisin and Langmuir monolayers of phospholipids DPPC and DPPG at the air-water interface using the surface manometry technique. The charge on the nisin and the lipid molecules is controlled by varying the pH of the subphase, and the interactions between them are studied by measuring the surface pressure of the lipid monolayer as a function of time after injecting the nisin in the subphase. A model based on the diffusion of particles under the influence of a constant force is developed to obtain an analytical expression for surface pressure as a function of time. The expression was found to fit well with the experimental data. The average hydrodynamic radius and the translational diffusion constant of the nisin molecules are calculated from the fit parameters for the different subphase pH solutions.

Alterations in the surface properties of sea spray aerosols introduced by the presence of sterols

The mixed stearic acid (SA)/sterol systems were used as sea spray aerosol mimics to get more insights into the alterations in surface properties of aerosols induced by sterols. By means of surface pressure (π)–area (A) isotherms and polarization modulation-infrared reflection absorption spectroscopy (PM-IRRAS), the effect of cholesterol (chol), stigmasterol (stig) and ergosterol (erg) on the lateral packing and chain conformation of SA monolayer was explored. The fact that the excess areas of mixing of the mixed monolayers exhibit significant deviations from ideally mixed film proves that, the sterols are miscible with SA throughout all the monolayer compositions and surface pressures examined. The lift-off areas in π–A isotherms were found to increase with increasing mole fraction of sterols, indicating that expulsive interactions exist between SA and sterols, which are more pronounced when the mole fraction of sterols is 0.7. In addition, the peak intensities of νa(CH2) and νs(CH2) in IRRAS spectra decrease with increasing sterols levels, which is consistent with our findings in the π–A isotherms, that the addition of sterols leads to a looser chain packing in SA monolayer. The proportion of gauche defects in SA monolayer induced by the sterols follows the order cholesterol < stigmasterol < ergosterol at a certain sterol level, as reflected by the decreasing peak intensities of νa(CH2) and νs(CH2). Consequently, the sterols generally give rise to considerable expanding effects on SA monolayer, which are particularly pronounced for stigmasterol and ergosterol, suggesting that the additional alkyl side chains and double bonds of the sterols play a role on disordering SA monolayer. The present study is likely to shed light on many boundary processes take place at the interface of SSAs, in particular, transport processes of water and trace gases across the interface.

Folded Structure and Membrane Affinity of the N-Terminal Domain of the Three Human Isoforms of the Mitochondrial Voltage-Dependent Anion-Selective Channel.

Voltage-dependent anion-selective channels (VDACs) are primarily located in the mitochondrial outer membrane (MOM). They are essential for the regulation of ion and metabolite exchanges. In particular, their role in energy-related nucleotide exchange has many implications in apoptosis, cancer, and neurodegenerative diseases. It has been proposed that VDACs’ functions are regulated by mobility of the N-terminal helical domain, which is bound to the inner wall of the main β-barrel domain but exists in equilibrium between the bound-folded and the unbound-unfolded state. When the N-terminal domain detaches from the channel’s wall and eventually leaves the lumen, it can either stay exposed to the cytosolic environment or interact with the outer leaflet of the MOM; then, it may also interact with other protein partners. In humans, three different VDAC isoforms are expressed at different tissue-specific levels with evidence of distinct roles. Although the N-terminal domains share high sequence similarity, important differences do exist, with the functionality of the entire protein mostly attributed to them. In this work, the three-dimensional structure and membrane affinity of the three isolated hVDAC N-terminal peptides have been compared through Fourier-transform infrared and NMR spectroscopy in combination with molecular dynamics simulations, and measurement of the surface pressure of lipid monolayers. Although peptides were studied as isolated from the β-barrel domain, the observed differences are relevant for those whole protein’s functions in which a protein–protein interaction is mediated by the N-terminal domain.

Molecular-Level Structure and Packing in Phase-Separated Arachidic Acid-Perfluorotetradecanoic Acid Monolayer Films.

Synchrotron-based X-ray scattering measurements of phase-separated surfactant monolayers at the air-water interface provide molecular-level structural information about the packing and ordering of film components. In this work, grazing incidence X-ray diffraction (GIXD) and X-ray reflectivity (XR) measurements were used to collect crystallographic structural information for binary mixed monolayers of arachidic acid (AA, C19H39COOH) with perfluorotetradecanoic acid (PA, C13F27COOH), a system that has previously been investigated using a variety of thermodynamic and micron-scale structural characterization methods. GIXD measurements at surface pressures of π = 5, 15, and 30 mN/m indicated that AA in pure and mixed films forms a rectangular lattice at π = 5 and 15 mN/m but a hexagonal lattice at π = 30 mN/m. PA formed hexagonal lattices under all conditions, with films being highly ordered and crystalline (as determined by Bragg peak width) at even the lowest surface pressures investigated. Phase separation occurred for all mixed monolayer film compositions and surface pressures, manifesting as diffraction peaks characteristic of the individual components appearing at different in-plane scattering vector qxy. For both pure and mixed films, the molecular tilt angle of the AA hydrocarbon chain toward the nearest-neighbor was substantial at low pressures but decreased with increasing pressure. The PA fluorocarbon chain showed negligible molecular tilt under all conditions, and was oriented normal to the subphase surface regardless of surface pressure or the presence of AA in the films. In all cases, the two components in the mixed film behaved entirely independently of film composition, which is exactly the expected result for a fully phase-separated, immiscible system. XR measurements of film thickness at the air-water interface supported these results; overall film thickness approached the calculated ideal surfactant tail lengths with increasing surface pressure, indicating nearly normal oriented surfactants. The overall surfactant packing and crystallographic features of the mixed monolayers are discussed in terms of the lipophobic nature of the perfluorinated surfactant as well as in context of thermodynamic miscibility and domain structure formation reported elsewhere in the literature for these mixed monolayer systems.

Highly sensitive gas sensor using hierarchically self-assembled thin films of graphene oxide and gold nanoparticles

In this study, we fabricated hierarchically self-assembled thin films composed of graphene oxide (GO) sheets and gold nanoparticles (Au NPs) using the Langmuir–Blodgett (LB) and Langmuir–Schaefer (LS) techniques and investigated their gas-sensing performance. First, a thermally oxidized silicon wafer (Si/SiO2) was hydrophobized by depositing the LB films of cadmium arachidate. Thin films of ligand-capped Au NPs and GO sheets of the appropriate size were then sequentially transferred onto the hydrophobic silicon wafer using the LB and the LS techniques, respectively. Several different films were prepared by varying the ligand type, film composition, and surface pressure of the spread monolayer at the air/water interface. Their structures were observed by scanning electron microscopy (SEM) and atomic force microscopy (AFM), and their gas-sensing performance for NH3 and CO2 was assessed. The thin films of dodecanethiol-capped Au NPs and medium-sized GO sheets had a better hierarchical structure with higher uniformity and exhibited better gas-sensing performance.

Tailoring plasmonic response by Langmuir–Blodgett gold nanoparticle templating for the fabrication of SERS substrates

Nanoparticle self-assembly is a robust and versatile strategy for the development of functional nanostructured materials, offering low-cost and scalable methods that can be fine-tuned for many different specific application. In this work, we demonstrate a pathway for the fabrication of tailorable quasi-two-dimensional lattices of gold nanoparticles to be used in Surface Enhanced Raman Scattering (SERS) detection of biomolecules. As a first step, nanoparticles are spread as a monolayer at the water/air interface, compressed to a target lateral density in a Langmuir–Blodgett technique, and transferred to a properly functionalized substrate surface. Once firmly adhered to the substrate, the lattice of nanoparticles can be directly used or be further processed using electroless gold deposition to let the nanoparticle grow thus tuning the plasmonic response and SERS enhancement. Compared to direct deposition or self-assembly methods, our protocol enables to obtain consistent results and much higher coverage of Au nanoparticles thanks to the active control of the surface pressure of the spread monolayer.