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Raman spectroscopy has developed significantly since its discovery and has become an important analytical vibrational technique for investigating the sample's chemical and structural properties. Today, great emphasis is placed on detecting low-concentrated samples of small volumes, which is a problematic task considering the weak intensity of the Raman signal. To improve the sensitivity significantly, resonance Raman spectroscopy and surface-enhanced Raman spectroscopy were employed. However, they face certain limitations and cannot generally be applied to any molecule. Here, we focus on drop coating deposition Raman (DCDR) spectroscopy that offers a general solution. DCDR lies in a droplet deposition of a liquid sample on an ideally solvophobic substrate where the subsequent drying process results in a preconcentrated deposit. After focusing on the preconcentrated dried parts in the deposit under the Raman micro-spectrometer, this offers high-quality classical Raman spectra even from a low-concentrated sample. Besides the overview of the method, its potential and the applications to biomolecules, biologically significant molecules and contaminants will be discussed. [ABSTRACT FROM AUTHOR]

Drop coating deposition Raman (DCDR) spectroscopy introduces a simple and easily accessible approach to studying biologically important molecules and their mixtures. The method is based on drying a small drop of solution or suspension of studied molecules deposited on a special hydrophobic surface. The drying process efficiently accumulates the molecules in the 'coffee‐ring' or any small pattern from which the Raman spectrum can be measured. In this way, a significant (several orders of magnitude) improvement of the Raman detection sensitivity compared with Raman measurement from solution can be reached. Therefore, a small sample volume (several microliters), as well as a low initial concentration of studied molecules in deposited droplets, are important advantages of the DCDR method over the normal Raman one. Recently, many relevant DCDR applications on biomolecules and related molecules have been reported. The mini‐review covers a brief overview of the DCDR method (principle, short history, suitable hydrophobic surfaces and state‐of‐the‐art). It will be followed by a summary of the studies over the last 15–20 years on different biologically important molecules, including proteins, lipids (in the form of liposomes) and small molecules (e.g., porphyrins, anthrax marker dipicolinic acid and food and environmental contaminants). Finally, the application potential and further perspectives of the DCDR method for biomolecular studies will be discussed. [ABSTRACT FROM AUTHOR]

Microplastics (MPs) and Nanoplastics (NPs) accumulated in the environment have been identified as a major global issue due to their potential harm to wildlife. Current research in the detection of MPs is well established. However, the detection of NPs remains challenging. The aim of this paper is to investigate the detection of polystyrene (PS) NPs on a super-hydrophobic substrate using surface-enhanced Raman spectroscopy (SERS) technology after high-speed centrifugation of PS NPs and AgNPs. The hydrophobic substrate reduces the contact area of droplet, concentrating PS NPs and AgNPs on a small spot, which eliminates the random distribution of nano particles. The condensed PS NPs and AgNPs improve the SERS intensity, reproductivity and detection sensitivity. The results show that SERS measurement on a hydrophobic substrate could significantly improve the detection sensitivity of PS NPs, with the detection limits of PS NPs as low as 0.5 mg/L (500 nm PS NPs) and 1 mg/L (100 nm PS NPs). The study provides an effective and rapid method for the detection of NPs at trace concentration, demonstrating more possibility for the future detection of trace NPs in the aquatic environment. [Display omitted] • High speed centrifugation could enrich PS nanoparticles (NPs) in aqueous samples. • Nano particles can be condensed in a small spot on the hydrophobic substrate. • SERS intensity of PS NPs was improved using the super hydrophobic substrate. • The detection limits of PS NPs could reach as low as 1 mg/L. [ABSTRACT FROM AUTHOR]

Free-standing polyelectrolyte multilayers (PEMs) triggered an intense research effort to develop functional capsules and membranes, nevertheless, the comprehensive understanding of the surface distinctions between the two sides of the free-standing PEMs has been rarely studied. In this paper, we demonstrate the asymmetric surface morphologies, compositions, surface charge and wetting properties of the free-standing PEMs made of alternating deposition of poly(diallyldimethylammonium chloride) (PDDA) and poly(styrenesulfonate) (PSS) on uncharged trimethoxy (octyl) silane modified silicon wafer (TMOS-Si) substrates. The growth behaviors (e.g., linear or exponential growth) of the (PDDA/PSS) n PEMs deposited on TMOS-Si substrates are similar to those deposited on negatively charged substrates except a slower evolution in morphology and thickness, evidenced by atomic force microscopy (AFM) and ellipsometry. The surface charge of the two sides can be tuned as +/+, −/-, and +/− by selecting the first and the terminate layer of the polyelectrolyte during the deposition process, indicated by X-ray photoelectron spectroscopy (XPS) and the surface zeta potential measured by spinning disk method. Further, water contact angle measurements exhibit a strong difference between the back side (the bottom side that was initially contacted with the substrate) (74 ± 4°) and front side (33 ± 2° and 48 ± 3° for PDDA and PSS as the outmost layer, respectively) of the PEMs. The larger water contact angle of the back side is probably resulted from the orientation of the alkyl chains of the polyelectrolytes as the hydrophobic–hydrophobic interactions played significant roles in deposition of a polyelectrolyte onto an uncharged substrate. This paper may gain new insights on understanding surface properties of the PEMs. [ABSTRACT FROM AUTHOR]

Spreading behavior of pure surfactants Triton X-100, Silwet L-77 and Zonyl FSO-100 on hydrophobic substrates was studied using a two-stage regime: (i) the first stage was a spreading at constant humidity (45%) until a quasi-equilibrium state was reached, and (ii) the second stage was a spreading at humidity increasing from 45% to almost saturation. During the first stage surfactants spread until reaching a quasi-equilibrium state, when the droplet diameter and the static advancing contact angle did not vary over time any more. The characteristic time of spreading during the first stage for L-77 and X-100 was a few seconds, whereas for FSO-100 it was tens of seconds. At the second stage, when humidity of the surrounding air was continuously increasing, the droplets of surfactants started to spread again. It was found that at this stage the spreading of all surfactants occurred only above a critical humidity ranged from 70 to 80%. Triton X-100 and Zonyl FSO-100 were found to be more sensitive to increasing humidity compared to Silwet L-77. It is shown that for all three pure surfactants used the radius on time dependencies obeyed a power law, with the power exponents close to either 0.1, which correspond to complete wetting or 0.25, which corresponds to Marangoni driven spreading. It was shown that water adsorption at the surfactant-vapor interface does not play a decisive role in initiation of the further spreading (except for Silwet L-77). Our findings suggested that spreading of surfactant droplets at the second stage was initiated predominantly by adsorption of water molecules from the surrounding air onto the solid substrate in front of the three-phase contract line. [ABSTRACT FROM AUTHOR]

The notion of three-phase (line) tension remains one of the most disputable notions in surface science. A very broad range of its values has been reported. Experts even do not agree on the sign of line tension. The polymer-chain-like model of three-phase (triple) line enables rough estimation of entropic input into the value of line tension, estimated as Γ e n ≅ k B T d m ≅ 10 − 11 N , where d m is the diameter of the liquid molecule. The introduction of the polymer-chain-like model of the triple line is justified by the “water string” model of the liquid state, predicting strong orientation effects for liquid molecules located near hydrophobic moieties. The estimated value of the entropic input into the line tension is close to experimental findings, reported by various groups, and seems to be relevant for the understanding of elastic properties of biological membranes.

In this paper, we have demonstrated the growth of tin oxide (SnO 2 ) thin films composed of nanoparticles on hydrophobic (siliconized) and hydrophilic (non-siliconized) glass substrates by using the spray pyrolysis technique. X-ray diffraction (XRD) analysis confirmed the formation of SnO 2 thin films with tetragonal rutile-phase structure. Average particle size of nanoparticles was determined to be in the range of 3–4 nm measured from the front view images obtained by a field emission gun scanning electron microscope (FESEM), while the size of nanoparticle clusters, when present, were in the range of 11–20 nm. Surface morphology of SnO 2 films grown over hydrophobic substrates revealed larger isolated particles which are less crowded compared to the highly crowded and agglomerated smaller particles in films on hydrophilic substrates. Blue shift in the band gap is observed in samples in which the average particle size is slightly larger than the exciton Bohr radius. Photoluminescence (PL) analysis of samples grown over hydrophobic substrates exhibited an intense defect level emission and a weak near band edge emission. The enhanced visible emission from these SnO 2 thin films is attributed to lattice defects formed during the film growth due to the mismatch between the film and the hydrophobic substrate surface. [ABSTRACT FROM AUTHOR]

[Display omitted] • A superhydrophobic substrate for SERS detection was assembled. • The perfluoropolyether coating enhances the hot spot effect of the SERS substrate. • There is no coffee ring effect during the experiment. • Complete analytical detection of acetamiprid at low concentrations. In this paper, a hydrophobic substrate as concentrators including an inner layer of polytetrafluoroethylene (PTFE) and an outer layer covered a thin layer of perfluoropolyether (PFPE) was constructed to achieve a higher sensitivity for acetamiprid (AC) SERS detection. The condensation effect of the PTFE-PFPE hydrophobic substrate-induced aggregation of gold nanoparticles (Au NPs) result "hot spots" for SERS. The hydrophobic substrate is better reproducibility (RSD < 5%) compared with that on a conventional silicon wafer. A further application of the hydrophobic substrate was demonstrated by the detection of AC in tea samples within a detection range of 0.03 mg/L to 3 mg/L. The hydrophobic substrate eliminates the problem of solution diffusion to avoid the "coffee ring" effect (When a droplet adheres to a solid surface, the suspended molecular particles usually deposit on the edge of the droplet to form a ring). [ABSTRACT FROM AUTHOR]

The energy possibility of the transition of free bubbles A to adherent bubbles M, or the A → M (TAM) transition, is calculated on substrates with different wetting abilities: extremely hydrophilic (Φ), extremely hydrophobic (Γ), and with incomplete wetting ability ( H), where x is the substrate surface fraction covered by a monolayer of collector molecules). Calculations of TAM for bubbles with a diameter ( d) of 2 mm to 20 nm on Φ, Γ, and H substrates showed that the change in specific energy (Δ G/ V) in a bubble in the case of TAM depends on the value of d, substrate wetting ability, and surface area of its contact with the bubble. According to the results of studies, high capillary pressure ( P) in nanobubbles M promotes their instantaneous spreading over the substrate. Herewith, P decreases considerably. The adhesion and spreading processes occur as a single process, irreversibly, one-way, and fast, because they are not complicated by counterprocesses. Upon a decrease in equatorial diameter d and wetting ability of the substrate, the decrease in G/ V reaches several million J/m. The actual simultaneity of the processes of bubble adhesion and spreading is illustrated by microphotographs of larger bubbles with a luminescent apolar reagent eliminating the effect of wetting hysteresis that is easily overcome in nanobubbles in the case of high P values. [ABSTRACT FROM AUTHOR]

Abstract: Spreading of aqueous surfactant solution droplets over hydrophobic substrates proceeds in one slow stage at concentration of surfactants below some critical value and in two stages if the surfactant concentration is above the critical value: the fast and relatively short first stage is followed by a slower second stage. It is shown that the kinetics of a slow spreading at concentrations below the critical value and the second stage at concentrations above the critical value are determined by a transfer of surfactant molecules on a bare hydrophobic substrate in front of the moving three-phase contact line (autophilic phenomenon). The latter process results in an increase of the solid–vapour interfacial tension of the hydrophobic solid surface in front of the moving three-phase contact line and spreading as a result. It is proven that the adsorption of surfactant molecules in front of the moving three-phase contact line results in a decrease of the total free energy of the droplet. Hence, the adsorption of surfactants molecules on a bare hydrophobic substrate in front of the moving three-phase contact line is a spontaneous process in spite of an increase of the local solid–vapour interfacial tension. The duration of the first stage of spreading in the case of the surfactant concentration above the critical value correlates well with the duration of adsorption of surfactant molecules onto a liquid–vapour interface. The latter allows assuming that the adsorption on the liquid–vapour interface is the driving mechanism of spreading during the first fast stage of spreading at surfactant concentrations above the critical value. It is discussed why the first stage of spreading does not take place in the case of surfactant concentrations below the critical concentration in spite of the longer duration of adsorption on liquid–vapour interface in this case. [ABSTRACT FROM AUTHOR]

The influence of the solubility-enhancing fusion proteins glutathione- S-transferase (GST) and NusA on the heterologous expression and in vitro biocatalytic performance of the carotenoid cleavage dioxygenase AtCCD1 from Arabidopsis thaliana was investigated. A micellar dispersion of the water-insoluble model substrate β-apo-8′-carotenal in combination with Triton X-100 was used for the spectrophotometric in vitro assays. Specific activity in the cellular extract was twofold increased by the use of GST as a carrier protein, whereas it was decreased by 70% when fused with NusA. Reduced molar activity of the purified fusion proteins was observed, which could not be regained by proteolytic removal of the carrier protein. The addition of organic solvents in the form of short-chain aliphatic alcohols positively influenced the enzyme activity. Optimization of the reaction medium led to an 18-fold activation, and a clear correlation could be found between the organic solvent concentration required for maximum activation and the log P of the solvent. The results provide a foundation for the development towards the application of carotenoid cleavage dioxygenases as in vitro biocatalysts for the production of norisoprenoids and apocarotenals from carotenoids. [ABSTRACT FROM AUTHOR]

Abstract: In order to get deeper insights into oxidative degradation of the hydrophobic substrates (HS) triglycerides and alkanes by yeasts, tagged mutants affected in these pathways were generated by random insertion of a mutagenesis cassette MTC into the genome of Yarrowia lipolytica. About 9.600 Ura+ transformants were screened in plate tests for utilization of alkanes (C10, C16), oleic acid and tributyrin. HS degradation mutants were recovered as unable to grow on alkane or on intermediates of the pathway (AlkA–AlkE phenotype classes). To identify the disrupted genes, insertion points of the MTC were sequenced using convergent and divergent PCR. Sequence analysis evidenced both known and new genes required for HS utilization, e.g. for AlkD/E mutants MTC insertion had occurred in genes of thioredoxin reductase, peroxines PEX14 and PEX20, succinate-fumarate carrier SFC1, and isocitrate lyase ICL1. Several mutants were affected in alkane utilization depending on chain length. Mutant Z110 (AlkAb: C10− C16+) was shown to be disrupted for ANT1 encoding a peroxisomal membrane localized adenine nucleotide transporter protein, providing ATP for the activation of short-chain fatty acids by acyl-CoA synthetase II in peroxisomes. Mutants N046 and B095 (AlkAc: C10+ C16−) were disrupted for the ABC transporter encoded by ABC1 gene, thus providing first evidence for its participation in chain length dependent alkane transport processes. [Copyright &y& Elsevier]

A gas-phase biofilter inoculated with the fungus Fusarium solani, isolated from a consortium grown on hexane vapors, was used to degrade this compound. The biofilter, packed with perlite and operated with an empty bed residence time of 60 s, was supplied with hexane concentrations between 0.5 g m−3 and 11 g m−3. Biofilter performance was evaluated over 100 days of operation. Several strategies for supplying the nutritive mineral medium were assayed to maintain favorable conditions for the fungal growth and activity. The Fusarium system was able to sustain an average elimination capacity of 90 g m−3 reactor h−1 with a maximum of 130 g m−3 reactor h−1 . The mass transfer limitations due to high biomass development in the biofilter were confirmed in batch experiments. Bacterial contamination was observed, but experiments in the biofilter and in batch reactors using selective inhibitors and controlled pH confirmed the predominant role of the fungus. Results indicate that fungal biofilters can be an effective alternative to conventional abatement technologies for treating hydrophobic compounds. [ABSTRACT FROM AUTHOR]

Abstract: The alkane-assimilating yeast Yarrowia lipolytica degrades very efficiently hydrophobic substrates such as n-alkanes, fatty acids, fats and oils for which it has specific metabolic pathways. An overview of the oxidative degradation pathways for alkanes and triglycerides in Y. lipolytica is given, with new insights arising from the recent genome sequencing of this yeast. This includes the interaction of hydrophobic substrates with yeast cells, their uptake and transport, the primary alkane oxidation to the corresponding fatty alcohols and then by different enzymes to fatty acids, and the subsequent degradation in peroxisomal β-oxidation or storage into lipid bodies. Several enzymes involved in hydrophobic substrate utilisation belong to multigene families, such as lipases/esterases (LIP genes), cytochromes P450 (ALK genes) and peroxisomal acyl-CoA oxidases (POX genes). Examples are presented demonstrating that wild-type and genetically engineered strains of Y. lipolytica can be used for alkane and fatty-acid bioconversion, such as aroma production, for production of SCP and SCO, for citric acid production, in bioremediation, in fine chemistry, for steroid biotransformation, and in food industry. These examples demonstrate distinct advantages of Y. lipolytica for their use in bioconversion reactions of biotechnologically interesting hydrophobic substrates. [Copyright &y& Elsevier]

Dodecanol (1% v/v) and dodecanoic acid (1% w/v) inhibited growth of Yarrowia lipolytica in complex media supplemented with glucose but dodecanedioic acid (1% w/v) was not toxic. Dodecanol-tolerant strains were prepared from the wild type strain H222 as well as the acyl-CoA oxidase deleted (ΔPOX2, POX3, POX5) strain MTLY35. These strains grew in rich media containing up to 10% (v/v) dodecanol. Dodecanol-tolerant strains remained dodecanol tolerant after they had been cultured in rich media without dodecanol. No significant amount of dodecanedioic acid was accumulated by the dodecanol-tolerant strains when grown on glucose in the presence of dodecanol. [ABSTRACT FROM AUTHOR]

The notion of three-phase (line) tension remains one of the most disputable notions in surface science. A very broad range of its values has been reported. Experts even do not agree on the sign of line tension. The polymer-chain-like model of three-phase (triple) line enables rough estimation of entropic input into the value of line tension, estimated as Γ e n ≅ k B T d m ≅ 10 − 11 N , where d m is the diameter of the liquid molecule. The introduction of the polymer-chain-like model of the triple line is justified by the "water string" model of the liquid state, predicting strong orientation effects for liquid molecules located near hydrophobic moieties. The estimated value of the entropic input into the line tension is close to experimental findings, reported by various groups, and seems to be relevant for the understanding of elastic properties of biological membranes. [ABSTRACT FROM AUTHOR]