Lipid Polymer Membrane Research Articles

A microfluidic sensor for continuously measuring membrane potential changes in interactions between taste substances and lipid polymer membranes

To evaluate the taste changes experienced by humans over time, we developed a microfluidic sensor for continuously measuring membrane potential changes in interactions between taste substances and lipid polymer membranes. The performance of the proposed sensing device was evaluated by determining the dependence on concentration using tannic acid (astringency substance) solutions and measuring the selectivity using other taste quality samples. Furthermore, to demonstrate the practicality of the sensor, we measured three samples of red wine. The fabricated microfluidic sensor could measure changes in membrane potential over time and was shown to have high selectivity comparable to that of the commercialized sensor. In addition, measurements were performed on a real sample of red wine, and the membrane potential response over time was measured for several different wines. Thus, it was shown that a new sensor could be realized for objectively quantifying changes in taste perceived by humans over time.

Electrical Properties of Taste Sensors with Positively Charged Lipid Membranes Composed of Amines and Ammonium Salts.

Currently, taste sensors utilizing lipid polymer membranes are utilized to assess the taste of food products quantitatively. During this process, it is crucial to identify and quantify basic tastes, e.g., sourness and sweetness, while ensuring that there is no response to tasteless substances. For instance, suppression of responses to anions, like tasteless NO3- ions contained in vegetables, is essential. However, systematic electrochemical investigations have not been made to achieve this goal. In this study, we fabricated three positively charged lipid polymer membranes containing oleylamine (OAm), trioctylemethylammonium chloride (TOMACl), or tetradodecylammonium bromide (TDAB) as lipids, and sensors that consist of these membranes to investigate the potential change characteristics of these sensors in solutions containing different anions (F-, Cl-, Br-, NO3-, I-). The ability of each anion solution to reduce the positive charge on membranes and shift the membrane potential in the negative direction was in the following order: I- > NO3- > Br- > Cl- > F-. This order well reflected the order of size of the hydrated ions, related to their hydration energy. Additionally, the OAm sensor displayed low ion selectivity, whereas the TOMACl and TDAB sensors showed high ion selectivity related to the OAm sensor. Such features in ion selectivity are suggested to be due to the variation in positive charge with the pH of the environment and packing density of the OAm molecule in the case of the OAm sensor and due to the strong and constant positive charge created by complete ionization of lipids in the case of TOMACl and TDAB sensors. Furthermore, it was revealed that the ion selectivity varies by changing the lipid concentration in each membrane. These results contribute to developing sensor membranes that respond to different anion species selectively and creating taste sensors capable of suppressing responses to tasteless anions.

A basic study of pretreatment method using antibody modified with glucose oxidase for pungent‐taste measurement of taste sensor

AbstractA polyclonal antibody against the analog of piperine, which is a typical pungent taste substance, was produced, and its binding ability to piperine was evaluated using a surface plasmon resonance sensor. The antibody was labeled with glucose oxidase (GOx), and the hydrogen ions produced by the enzymatic reaction were measured at a lipid polymer membrane electrode for sourness in a taste sensor. The results showed that piperine could be detected by that polyclonal antibody; the response of the sourness sensor increased in dependence on the GOx‐labeled antibody concentration when the GOx of GOx‐labeled antibody was reacted with glucose. Thus, it was shown that uncharged pungent compounds can be converted into hydrogen ions. Pungent taste can be measured by the taste sensor using GOx‐labeled antibodies, and GOx‐labeled antibodies can be used as a pretreatment.

味覚センサの辛味測定のためのグルコース酸化酵素標識抗体を用いた前処理法の基礎検討

A polyclonal antibody against the analog of piperine, which is a typical pungent taste substance, was produced, and its binding ability to piperine was evaluated using a surface plasmon resonance sensor. The antibody was labeled with glucose oxidase (GOx), and the hydrogen ions produced by the enzymatic reaction were measured at a lipid polymer membrane electrode for sourness in a taste sensor. The results showed that piperine could be detected by that polyclonal antibody; the response of the sourness sensor increased in dependence on the GOx-labeled antibody concentration when the GOx of GOx-labeled antibody was reacted with glucose. Thus, it was shown that uncharged pungent compounds can be converted into hydrogen ions. Pungent taste can be measured by the taste sensor using GOx-labeled antibodies, and GOx-labeled antibodies can be used as a pretreatment.

Development of a microfluidic-based taste sensor using lipid polymer membrane

This study aims to develop a microfluidic-based taste sensor for detecting time-dependent human taste sensations. Lipid polymer membranes were welded to perforated polycarbonate films with organic solvents to monitor the adsorption and desorption of taste substances to lipid polymer membranes and to physically immobilize lipid polymer membranes to withstand the pressure of a pumped liquid. A polydimethylsiloxane flow channel was bonded chemically to the polycarbonate film with the lipid polymer membrane using 3-aminopropylethoxysilane. A fabricated microfluidic-based taste sensor could measure the membrane potential change with time due to the adsorption and desorption of tannic acid, an astringency substance, onto a lipid polymer membrane. The proposed sensor could be useful as a tool for assessing the time-course changes in human taste.

Tailoring a Solvent-Assisted Method for Solid-Supported Hybrid Lipid-Polymer Membranes.

Combining amphiphilic block copolymers and phospholipids opens new opportunities for the preparation of artificial membranes. The chemical versatility and mechanical robustness of polymers together with the fluidity and biocompatibility of lipids afford hybrid membranes with unique properties that are of great interest in the field of bioengineering. Owing to its straightforwardness, the solvent-assisted method (SA) is particularly attractive for obtaining solid-supported membranes. While the SA method was first developed for lipids and very recently extended to amphiphilic block copolymers, its potential to develop hybrid membranes has not yet been explored. Here, we tailor the SA method to prepare solid-supported polymer–lipid hybrid membranes by combining a small library of amphiphilic diblock copolymers poly(dimethyl siloxane)–poly(2-methyl-2-oxazoline) and poly(butylene oxide)-block–poly(glycidol) with phospholipids commonly found in cell membranes including 1,2-dihexadecanoyl-sn-glycero-3-phosphocholine, 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine, sphingomyelin, and 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine-N-(glutaryl). The optimization of the conditions under which the SA method was applied allowed for the formation of hybrid polymer–lipid solid-supported membranes. The real-time formation and morphology of these hybrid membranes were evaluated using a combination of quartz crystal microbalance and atomic force microscopy. Depending on the type of polymer–lipid combination, significant differences in membrane coverage, formation of domains, and quality of membranes were obtained. The use of the SA method for a rapid and controlled formation of solid-supported hybrid membranes provides the basis for developing customized artificial hybrid membranes.

The possibility of application of the potentiometric sensor with all-solid-state electrodes containing lipid-polymer membranes for classification of tested black leaf teas in terms of their quality

The possibility of application of the potentiometric sensor with all-solid-state electrodes containing lipid-polymer membranes for classification of tested black leaf teas in terms of their quality

Quantification of Pharmaceutical Bitterness Using a Membrane Electrode Based on a Hydrophobic Tetrakis [3,5-Bis (trifluoromethyl) phenyl] Borate

Technologies for quantifying bitterness are essential for classifying medicines. As previously reported, taste sensors with lipid polymer membranes can respond to bitter hydrochloride substances in pharmaceuticals. However, the acid hydrolysis reaction between the lipid phosphoric acid di-n-decyl ester (PADE) and the plasticizer tributyl o-acetylcitrate (TDAB) led to a deterioration in sensor responses during storage. Given the cost of transportation and preservation for commercialization, membrane components that maintain physical and chemical stability during long-term storage are needed. Here we present a membrane electrode based on hydrophobic tetrakis [3,5-bis (trifluoromethyl) phenyl] borate (TFPB) and a plasticizer 2-nitrophenyl octyl ether (NPOE) for the quantification of pharmaceutical bitterness; they maintain a stable response before and after accelerated deterioration, as well as high selectivity and sensitivity. It is a first attempt to use a completely dissociative substance to replace non-completely dissociative lipids. Our work offsets the long-term stability issue of a bitterness sensor with a negatively charged hydrophobic membrane. Meanwhile, we provide the opportunity to select surface charge modifiers for a membrane surface using ester plasticizers containing oppositely charged impurities.

Potentiometric sensor with lipid-polymer membranes for quality assessment of French red wines

Potentiometric sensor with lipid-polymer membranes for quality assessment of French red wines

Reusability Enhancement of Taste Sensor Using Lipid Polymer Membranes by Surfactant Cleaning Treatment

The aim of our study was to enhance the reusability of a taste sensor by increasing the efficiency of the cleaning process. In this paper, we proposed a surfactant cleaning method for two types of bitterness sensor using lipid polymer membranes with high hydrophobicity. To select suitable surfactants for cleaning, the usability of four types of surfactant with different polarities and ionicities was evaluated. Among these surfactants, the anionic surfactant linear alkylbenzene sulfonate (LAS) showed no impact on the initial membrane potential and completely removed residue substances of high-concentration quinine hydrochloride adsorbed on the bitterness sensor used for hydrochloride salts. On the other hand, the amphoteric surfactant lauryl dimethylaminoacetic acid (LDA) showed no impact on the initial membrane potential and almost completely removed residue substances of high-concentration iso- $\alpha $ acid adsorbed on the bitterness sensor used for acidic bitter materials. Moreover, we found that the combined use of the conventional cleaning solution and LDA acid solution in turn greatly improved the reusability of an astringency sensor in multiple measurements of black tea.

Quantification of bitterness of coffee in the presence of high-potency sweeteners using taste sensors

Electronic tongues have been identified as useful tools for quantifying the taste of food and beverages. However, the bitterness evaluation of coffee in the presence of high-potency sweeteners has not been performed yet. In this study, we investigated an approach to quantify the bitterness of coffee with different roasting degrees and the sweetness of acesulfame potassium (Ace K) added to the coffee using taste sensors with lipid polymer membranes. A formula for predicting coffee bitterness with the addition of Ace K was proposed using the responses of a bitterness sensor and a sweetness sensor. We found that the predicted coffee bitterness showed a good correlation with human taste.

A Quantitative Method for Acesulfame K Using the Taste Sensor.

We have developed a method to quantify the sweetness of negatively charged high-potency sweeteners coexisting with other taste substances. This kind of sweetness sensor uses lipid polymer membranes as the taste-sensing part. Two types of outputs have been defined in the measurement of the taste sensor: one is the relative value and the other is the CPA (the change in membrane potential caused by adsorption) value. The CPA value shows a good selectivity for high-potency sweeteners. On the other hand, the relative value is several times higher than the CPA value, but the relative value is influenced by salty substances. In order to obtain both high sensitivity and selectivity, we established a model for predicting the concentration of sweeteners with a nonlinear regression analysis method using the relative values of both the sweetness sensor and the saltiness sensor. The analysis results showed good correlations with the estimated concentration of acesulfame potassium coexisting with salty substances, as represented by R2 = 0.99. This model can correspond well to the prediction of acesulfame K in a concentration of 0.2–0.7 mM, which is commonly used in food and beverages. The results obtained in this paper suggest that this method is useful for the evaluation of acesulfame K using the taste sensors.

Taste Sensor: Electronic Tongue with Lipid Membranes.

Taste is of five basic types, namely, sourness, saltiness, sweetness, bitterness and umami. In this review, we focus on a potentiometric taste sensor that we developed and fabricated using lipid polymer membranes. The taste sensor can measure the taste perceived by humans and is called an electronic tongue with global selectivity, which is the property to discriminate taste qualities and quantify them without discriminating each chemical substance. This property is similar to the gustatory system; hence, the taste sensor is a type of biomimetic device. In this paper, we first explain the sensing mechanism of the taste sensor, its application to beer evaluation and the measurement mechanism. Second, results recently obtained are introduced; i.e., the application of the senor to high-potency sweeteners and the improvement of the bitterness sensor are explained. Last, quantification of the bitterness-masking effect of high-potency sweeteners is explained using a regression analysis based on both the outputs of bitterness and sweetness sensors. The taste sensor provides a biomimetic method different from conventional analytical methods.

Improved Durability and Sensitivity of Bitterness-Sensing Membrane for Medicines.

This paper reports the improvement of a bitterness sensor based on a lipid polymer membrane consisting of phosphoric acid di-n-decyl ester (PADE) as a lipid and bis(1-butylpentyl) adipate (BBPA) and tributyl o-acetylcitrate (TBAC) as plasticizers. Although the commercialized bitterness sensor (BT0) has high sensitivity and selectivity to the bitterness of medicines, the sensor response gradually decreases to almost zero after two years at room temperature and humidity in a laboratory. To reveal the reason for the deterioration of the response, we investigated sensor membranes by measuring the membrane potential, contact angle, and adsorption amount, as well as by performing gas chromatography-mass spectrometry (GC-MS), liquid chromatography-tandem mass spectrometry (LC-MS/MS). We found that the change in the surface charge density caused by the hydrolysis of TBAC led to the deterioration of the response. The acidic environment generated by PADE promoted TBAC hydrolysis. Finally, we succeeded in fabricating a new membrane for sensing the bitterness of medicines with higher durability and sensitivity by adjusting the proportions of the lipid and plasticizers.

Synthesis of ABA Tri-Block Co-Polymer Magnetopolymersomes via Electroporation for Potential Medical Application

The ABA tri-block copolymer poly(2-methyloxazoline)–poly(dimethylsiloxane)–poly(2-methyloxazoline) (PMOXA–PDMS–PMOXA) is known for its capacity to mimic a bilayer membrane in that it is able to form vesicular polymersome structures. For this reason, it is the subject of extensive research and enables the development of more robust, adaptable and biocompatible alternatives to natural liposomes for biomedical applications. However, the poor solubility of this polymer renders published methods for forming vesicles unreproducible, hindering research and development of these polymersomes. Here we present an adapted, simpler method for the production of PMOXA–PDMS–PMOXA polymersomes of a narrow polydispersity (45 ± 5.8 nm), via slow addition of aqueous solution to a new solvent/polymer mixture. We then magnetically functionalise these polymersomes to form magnetopolymersomes via in situ precipitation of iron-oxide magnetic nanoparticles (MNPs) within the PMOXA–PDMS–PMOXA polymersome core and membrane. This is achieved using electroporation to open pores within the membrane and to activate the formation of MNPs. The thick PMOXA–PDMS–PMOXA membrane is well known to be relatively non-permeable when compared to more commonly used di-block polymer membranes due a distinct difference in both size and chemistry and therefore very difficult to penetrate using standard biological methods. This paper presents for the first time the application of electroporation to an ABA tri-block polymersome membrane (PMOXA–PDMS–PMOXA) for intravesicular in situ precipitation of uniform MNPs (2.6 ± 0.5 nm). The electroporation process facilitates the transport of MNP reactants across the membrane yielding in situ precipitation of MNPs. Further to differences in length and chemistry, a tri-block polymersome membrane structure differs from a natural lipid or di-block polymer membrane and as such the application and effects of electroporation on this type of polymersome is entirely novel. A mechanism is hypothesised to explain the final structure and composition of these biomedically applicable tri-block magnetopolymersomes.

Study of the Relationship between Taste Sensor Response and the Amount of Epigallocatechin Gallate Adsorbed Onto a Lipid-Polymer Membrane

A taste sensor using lipid-polymer membranes has been developed to evaluate the taste of foods, beverages and medicines. The response of the taste sensor, measured as a change in the membrane potential caused by adsorption (CPA), corresponds to the aftertaste felt by humans. The relationships between the CPA value and the amount of adsorbed taste substances, quinine and iso-α acid (bitterness), and tannic acid (astringency), have been studied so far. However, that of epigallocatechin gallate (EGCg) has not been clarified, although EGCg is abundantly present in green tea as one of its astringent substances. This study aimed at clarifying the response of the taste sensor to EGCg and its relationship with the amount of EGCg adsorbed onto lipid-polymer membranes. The lipid concentration dependence of the CPA value was similar to that of the amount of adsorbed EGCg, indicating a high correlation between the CPA value and the amount of adsorbed EGCg. The CPA value increased with increasing amount of adsorbed EGCg; however, the CPA value showed a tendency of leveling off when the amount of adsorbed EGCg further increased.

Lipid-Polymer Membranes as Carrier for L-Tryptophan: Molecular and Metabolic Properties

Polymerized liposomes encapsulating L-tryptophan were studied with the aim to characterize them as drug delivery systems for the treatment of several metabolic diseases that need an increased systemic L-tryptophan concentration. polymerized liposomes were obtained by UV irradiation of vesicles containing 1,2-bis(10,12-tricosadiynoyl)-sn-glycero-3-phosphocholine (DC8,9PC) and 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) in a 1:1 molar ratio, in the presence of 10 and 50 mol% of L-tryptophan (respect to total lipid concentration). Polymerization efficiency was studied spectrophotometrically. Also, bilayer packing at the polar head region was followed with the Merocyanine 540 (MC540) and specific interactions in the lipopolymers were studied by FTIR. High L-tryptophan concentrations (50 mol% respect to total lipid concentration) induced a higher amount of six- and nine-unit polymers. This phenomenon was induced because the L-tryptophan located outside the lipid membrane was included in it during the polymerization process and was thus responsible for the better accommodate of the polar head region. This was not possible with the lower amount of L-tryptophan (10 mol%). The stability of lipopolymers with different amounts of L-tryptophan was studied through release profiles. Polymerized liposomes with 50 mol% of L-tryptophan were able to retain around 80% of the amino acid after 24 hours, whereas those with 10 mol % of the amino acid were able to retain 20%. The metabolic activity of the Caco-2 cell line was also studied. Cytotoxic effects were low in the presence of polymerized liposomes, rendering a maximum percentage of cell death of 30%. In summary, this work stresses the relevance of nonspecific drug-polymerized membrane binding on L-tryptophan pharmacological interaction with possible pharmaceutical applications in liposomal drug delivery. Moreover, the absence of significant cytotoxic effects allows the system proposed to be applied in human health.

Lipid-Polymer Membranes as Carriers for L-Tryptophan: Molecular and Metabolic Properties

Polymerized liposomes encapsulating L-tryptophan were studied with the aim to characterize them as drug delivery systems for the treatment of several metabolic diseases that need an increased systemic L-tryptophan concentration. polymerized liposomes were obtained by UV irradiation of vesicles containing 1,2-bis(10,12-tricosadiynoyl)-sn-glycero-3-phosphocholine (DC8,9PC) and 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) in a 1:1 molar ratio, in the presence of 10 and 50 mol% of L-tryptophan (respect to total lipid concentration). Polymerization efficiency was studied spectrophotometrically. Also, bilayer packing at the polar head region was followed with the Merocyanine 540 (MC540) and specific interactions in the lipopolymers were studied by FTIR. High L-tryptophan concentrations (50 mol% respect to total lipid concentration) induced a higher amount of six- and nine-unit polymers. This phenomenon was induced because the L-tryptophan located outside the lipid membrane was included in it during the polymerization process and was thus responsible for the better accommodate of the polar head region. This was not possible with the lower amount of L-tryptophan (10 mol%). The stability of lipopolymers with different amounts of L-tryptophan was studied through release profiles. Polymerized liposomes with 50 mol% of L-tryptophan were able to retain around 80% of the amino acid after 24 hours, whereas those with 10 mol % of the amino acid were able to retain 20%. The metabolic activity of the Caco-2 cell line was also studied. Cytotoxic effects were low in the presence of polymerized liposomes, rendering a maximum percentage of cell death of 30%. In summary, this work stresses the relevance of nonspecific drug-polymerized membrane binding on L-tryptophan pharmacological interaction with possible pharmaceutical applications in liposomal drug delivery. Moreover, the absence of significant cytotoxic effects allows the system proposed to be applied in human health.

Multichannel taste sensors with lipid, lipid like – polymer membranes

The elaboration of a sensitive taste sensor for discrimination of different soft drinks is very important in food industry. The short review of taste sensors described in the literature is presented. Two types of potentiometric taste sensors, one with lipophilic compound-polymer membranes (ISE) and the other with lipid polymer membrane and a conducting polymer film (All solid state electrode, ASSE) were tested in appropriate taste solutions. Five channel ISE sensor was examined in acid, sour and sweet solutions. This sensor was sensitive to bitter and sour substances and not too sensitive to sucrose concentration. It was successfully used for discrimination of different kind of soft drinks. Four channel ASSE sensor was examined in sour solutions. It was found that stability and sensitivity of ASSE are lower than ISE. Therefore, it seems that the previous one cannot be applied in taste sensor.

Investigation of some taste substances using a set of electrodes with lipid-modified membranes

A five-channel taste module based on ion-selective electrodes (ISE) with lipid-polymer membranes was constructed. Five different kinds of lipids or their derivatives were used inPVC membranes as substances transforming taste information into electric signals: benzylcetyldimethylammoniurn chloride monohydrate, hexadecylamine, elaidic acid, 1-dodecanol and oleic acid. The electrode potential in response to sour taste substances — citric, hydrochloric and acetic acids — was examined. It was found that sensitivity of the potential of electrodes containing elaidic acid, 1 -dodecanol or oleic acid in the membrane to citric and hydrochloric acid is very good. Lower sensitivity was observed in the case of acetic acid present in the system. New types of electrodes with conducting PEDT/PSS polymers and oleic acid were tested for sour taste. It was found that stability and reproducibility of electrodes used were very good. The obtained results show that lipid-polymer membranes can be successfully applied as sour taste sensors.