Cation-Selective Color Sensors Composed of Ionophore−Phospholipid−Polydiacetylene Mixed Vesicles

Supramolecular Optimization of Sensory Function of a Hemicurcuminoid through Its Incorporation into Phospholipid and Polymeric Polydiacetylenic Vesicles: Experimental and Computational Insight

This work presents the synthesis of a new representative of hemicurcuminoids with a nonyloxy substituent (HCur) as a fluorescent amphiphilic structural element of vesicular aggregates based on phosphatidylcholine (PC), phosphatidylserine (PS), and 10,12-pentacosadiynoic acid (PCDA). Both X-ray diffraction analysis of the single crystal and ¹H NMR spectra of HCur in organic solvents indicate the predominance of the enol-tautomer of HCur. DFT calculations show the predominance of the enol tautomer HCur in supramolecular assemblies with PC, PS, and PCDA molecules. The results of the molecular modeling show that HCur molecules are surrounded by PC and PS with a rather weak exposure to water molecules, while an exposure of HCur molecules to water is enhanced under its supramolecular assembly with PCDA molecules. This is in good agreement with the higher loading of HCur into PC(PS) vesicles compared to PCDA vesicles converted into polydiacetylene (PDA) ones by photopolymerization. HCur molecules incorporated into HCur-PDA vesicles exhibit greater planarity distortion and hydration effect in comparison with HCur-PC(PS) ones. HCur-PDA is presented as a dual fluorescence-chromatic nanosensor responsive to a change in pH within 7.5-9.5, heavy metal ions and polylysine, and the concentration-dependent fluorescent response is more sensitive than the chromatic one. Thus, the fluorescent response of HCur-PDA allows for the distinguishing between Cd²⁺ and Pb²⁺ ions in the concentration range 0-0.01 mM, while the chromatic response allows for the selective sensing of Pb²⁺ over Cd²⁺ ions at their concentrations above 0.03 mM.

Polydiacetylene-based colorimetric and fluorometric sensors for lead ion recognition

Development of novel sensors for the detection of lead ions (Pb2+) has attracted increasing interest due to their inherent toxic effects on human health and the environment. In this study, we describe two new polydiacetylene (PDA)-based liposome sensors for the colorimetric and fluorometric recognition of Pb2+ in aqueous solution. In the sensor system, a thymine-1-acetic acid (TAA) or orotic acid (OA) group was reasonably introduced into the diacetylene monomer to work as a strong binding site for Pb2+. The TAA- or OA-functionalized monomer and 10,12-pentacosadiynoic acid (PCDA) were incorporated into PDA liposomes in aqueous solution. After UV light-induced polymerization, deep blue colored liposome solutions were obtained. Upon the addition of a series of transition metal cations into the liposome solutions, only Pb2+ could induce a color change from blue to red observable by the naked eye and a large fluorescence enhancement. The results clearly showed that the PDA-EDEA-TAA and PDA-EDEA-OA liposomes could act as highly selective and sensitive probes to detect Pb2+ in aqueous solution. The detection limits of PDA-EDEA-TAA and PDA-EDEA-OA systems are 38 nM and 25 nM, respectively. The excellent selectivity of PDA liposomes could be attributed to the stronger complexation behavior of Pb2+ with TAA (or OA) and the carboxylic acid at the lipid-solution interface which could perturb the PDA conjugated backbone. In addition, the proposed sensors were successfully applied to detect trace amounts of Pb2+ in real water samples with excellent recovery, indicating that the developed method had a good accuracy and precision for the analysis of trace Pb2+ in practical samples.

Recent progress in polydiacetylene mechanochromism

Polydiacetylenes (PDAs) are a family of mechanochromic polymers that change color from blue to red and emit fluorescence when exposed to external stimuli, making them extremely popular materials in biosensing. Although several informative reviews on PDA biosensing have been reported in the last few years, their mechanochromism, where external forces induce the color transition, has not been reviewed for a long time. This mini review summarizes recent progress in PDA mechanochromism, with a special focus on the quantitative and nanoscopic data that have emerged in recent years.

Structures and strategies for enhanced sensitivity of polydiacetylene(PDA) based biosensor platforms

Polydiacetylene (PDA) is a versatile polymer that has been studied in numerous fields because of its unique optical properties derived from alternating multiple bonds in the polymer backbone. The conjugated structure in the polymer backbone enables PDA to possess the ability of blue-red colorimetric transition when π-π interactions in the PDA backbone chain are disturbed by the external environment. The chromatic property of PDA disturbed by external stimuli can also emit fluorescence in the red region. Owing to the unique characteristics of PDA, it has been widely studied in facile and label-free sensing applications based on colorimetric or fluorescence signals for several decades. Among the various PDA structures, membrane structures assembled by amphiphilic molecules are widely used as a versatile platform because facile modification of the synthetic membrane provides extensive applications, such as receptor-ligand interactions, resulting in potent biosensors. To use PDA as a sensory material, several methods have been studied to endow the specificity to PDA molecules and to amplify the signal from PDA supramolecules. This is because selective and sensitive detection of target materials is required at an appropriate level corresponding to each material for applicable sensor applications. This review focuses on factors that affect the sensitivity of PDA composites and several strategies to enhance the sensitivity of the PDA sensor to various structures. Owing to these strategies, the PDA sensor system has achieved a higher level of sensitivity and selectivity, enabling it to detect multiple target materials for a full field of application.

Rapid evaluation of gold nanoparticle-lipid membrane interactions using a lipid/polydiacetylene vesicle sensor

Surface modification of gold nanoparticles (AuNPs) has significant and complicated effects on their interactions with cell membranes. In this study, we used a lipid/polyacetylene (PDA) vesicle sensor as the lipid membrane model to evaluate AuNP-lipid membrane interactions. Based on the colorimetric response (CR) of PDA vesicles before and after incubation with AuNPs, it was found that the interaction was highly dependent on the surface charge of AuNPs. As compared to the positively charged NPs, neutral and zwitterionic NPs adsorbed much less on the lipid membrane. Negatively charged NPs did not induce any noticeable color changes even at high concentrations. A class of cationic AuNPs with different degrees of surface hydrophobicity was further selected to investigate the role of hydrophobicity in interacting with lipid/PDA vesicles, and log(EC50) was employed as the evaluation index. According to the log(EC50)-NP concentration curve, the hydrophobicity of NPs enhanced the lipid membrane affinity, but electrostatic interactions weakened this effect. Finally, different concentrations of bovine serum albumin (BSA) were used to study the effect of the protein corona on NP-lipid membrane interactions. The formation of a NP-protein corona was found to mask the electrostatic interactions, leading to the decrease of the CR values of cationic NPs, and highly hydrophobic NPs were less affected by a low concentration of BSA due to the strong hydrophobic interactions. Although the effect of NP surface properties on their interactions with cells is far more complicated, our study provides a rapid and effective method for the evaluation of the interactions between surface modified AuNPs and lipid membranes.

Co-functionalization with phosphate and carboxylate on polydiacetylene for colorimetric detection of calcium ions in serum

In this study, co-functionalization with phosphate and carboxylate on polydiacetylene (PDA) was proposed to detect calcium ions in serum, inspired by biologically abundant phosphate-calcium ion and carboxylate-calcium ion binding. The cooperative interaction of calcium ions with phosphate and carboxylate in PDA induced the change of electronic properties in the backbone without aggregation of liposomes, accompanied by blue-to-purple color transition. The cooperative effect through the introduction of mixed ligands facilitated the selective detection of calcium ions over magnesium ions, which was a source of major interference in many calcium ion probes, and in the presence of major serum metal ions. The sensor system exhibited highly sensitive detection of calcium ions with an estimated limit of detection of 0.97 μM. In addition, the detection method was employed to determine the concentration of calcium ions in various serums.

Selective catecholamine detection in living cells by a copper-mediated oxidative bond cleavage

The development of a new triggered-release system for selective detection of catecholamines in biological samples including living cells is reported. Catecholamines are a class of tightly regulated hormones and neurotransmitters in the human body and their dysregulation is implicated in various neurodegenerative diseases. It is highly challenging to selectively sense and detect catecholamines in a complex biological environment due to their small size, non-specific molecular shape and trivial chemical properties. In this study, a copper-based, catecholamine-triggered oxidation that releases a fluorescent reporter is described. The probe is highly sensitive and selective for detecting changes in catecholamine levels in aqueous buffer, human plasma, and cellular models of neuronal differentiation and Parkinson's disease. This new catecholamine sensing strategy features chemical reactivity as part of small molecule recognition as opposed to the conventional use of a well-designed host for reversible binding.

Chemically Engineered Synthetic Lipid Vesicles for Sensing and Visualization of Protein-Bilayer Interactions

From pathogen intrusion to immune response, the cell membrane plays an important role in signal transduction. Such signals are important for cellular proliferation and survival. However, measurement of these subtle signals through the lipid membrane scaffold is challenging. We present a chromatic model membrane vesicle system engineered to covalently bind with lysine residues of protein molecules for investigation of cellular interactions and signaling. We discovered that different protein molecules induced differential spectroscopic signals, which is based on the chemical and physical properties of protein interacting at the vesicle surface. The observed chromatic response (CR) for bound protein molecules with higher molecular weight was much larger (∼5-15×) than those for low molecular weight proteins. Through mass spectrometry (MS), we found that only 6 out of 60 (10%) lysine groups present in bovine serum albumin (BSA) were accessible to the membrane of the vesicles. Finally, a "sphere-shell" model representing the protein-vesicle complex was used for evaluating the contribution of van der Waals interactions between proteins and vesicles. Our analysis points to contributions from van der Waals, hydrophobic, and electrostatic interactions toward observed CR signals resulting from molecular interactions at the vesicle membrane surface. Overall, this study provided a convenient, chromatic, semiquantitative method of detecting biomolecules and their interactions with model membranes at sub-nanomolar concentration.

Measurements of Ion Binding to Lipid-Hosted Ionophores by Affinity Chromatography

The binding affinity between antibiotic ionophores and alkali ions within supported lipid bilayers was evaluated using affinity chromatography. We used zonal elution and frontal analysis methods in nanovolume liquid chromatography to characterize the binding selectivity of the carrier and channel ionophores valinomycin and gramicidin A within different phosphatidylcholine bilayers. Distinct binding sensitivity to the lipid phase, both in affinity and selectivity, is observed for valinomycin, whereas gramicidin is less sensitive to changes in a membrane environment, behavior that is consistent with ion binding occurring within the interior of an established channel. There is good agreement between the chromatographic retention and the reported binding selectivity measured by other techniques. Surface potential near the binding site affects ion retention and the apparent association binding constants, but not the binding selectivity or enthalpy measurements. A model accounting for the surface potential contributions of retained ions during frontal analyses yields values close to intrinsic binding constants for gramicidin A (K_A for K⁺ between 70 and 120 M^-1) using reasonable estimates of the initial potential that is postulated to arise from the underlying silica.

Rapidly Visualizing the Membrane Affinity of Gene Vectors Using Polydiacetylene-Based Allochroic Vesicles

The high-throughput screening of chemically active substances has aroused widespread interest in recent years. The screening of drug carriers is usually ignored, although they interact directly with physiological barriers and target cells, and they determine the fate and efficacy of drugs in vivo. In this work, a series of polydiacetylene (PDA) vesicles (ca. 550 nm) that simulate the cell membrane are constructed to detect the membrane affinity of gene vectors. The surface potentials of vesicles are adjusted by changing the phospholipid composition using different charged compounds. All vesicles show the rapid color changes upon the addition of gene vectors by the naked eye within <5 min. The optimized 1,2-dimyristoyl- sn-glycero-3-phosphocholine (DMPC)-PDA vesicles display the most sensitive discoloration response to the commercially available gene vectors, including Lipofectamine 2000, Entranster-H4000, and polyethylenimine. The logarithm of transfection efficiency for green fluorescent protein plasmid (pGFP) mediated by these three vectors in L02 and HepG2 cells demonstrate an excellent linear correlation with the logarithm of membrane affinity (log K_b) of the gene vectors detected by DMPC-PDA vesicles. This rapid visualization method not only allows the in vitro membrane affinity prediction of gene vectors that greatly contributes to the gene transfection efficiency, but also offers a universal strategy for the potential high-throughput screening of various carrier materials featuring high cell affinity.

Colloidally Stable Monolayer Nanosheets with Colorimetric Responses

Despite the discovery of chromogenic-layered materials for decades of years, fabrication of colloidally stable monolayer organic 2D nanosheets in aqueous media with colorimetric responses is still challenging. Herein reported is the first solution synthesis of chromic monolayer nanosheets via the topochemical polymerization of self-assembled amphiphilic diacetylenes in aqueous media. The polydiacetylene (PDA) nanosheets are ≈3-4 nm thick in solution and only ≈1.9 nm thick in the dried state, while the lateral size can reach several micrometers. Moreover, the aqueous stability endows PDA nanosheets with excellent processability, which can further assemble into films via vacuum filtration or act as an ink for high-resolution inkjet printing. The filtrated films and printed patterns exhibit fully reversible blue-to-red thermochromism, and the film also displays an interesting reversible colorimetric transition in response to near-infrared light, which is not reported for other PDA-only systems. The present colloidal PDA nanosheets should represent a new kind of chromic organic 2D nanomaterials that may be applied as novel building blocks for developing intelligent hybrid materials and may also find diverse sensing, display and/or anticounterfeiting applications.

Topochemical polymerization of hierarchically ordered diacetylene monomers within the block copolymer domains

Effect of annealing conditions on the hierarchical ordering of PCDA monomers within the block copolymer supramolecules and their subsequent topochemical polymerization.

Sphingomyelin and GM1 Influence Huntingtin Binding to, Disruption of, and Aggregation on Lipid Membranes

Huntington disease (HD) is an inherited neurodegenerative disease caused by the expansion beyond a critical threshold of a polyglutamine (polyQ) tract near the N-terminus of the huntingtin (htt) protein. Expanded polyQ promotes the formation of a variety of oligomeric and fibrillar aggregates of htt that accumulate into the hallmark proteinaceous inclusion bodies associated with HD. htt is also highly associated with numerous cellular and subcellular membranes that contain a variety of lipids. As lipid homeostasis and metabolism abnormalities are observed in HD patients, we investigated how varying both the sphingomyelin (SM) and ganglioside (GM1) contents modifies the interactions between htt and lipid membranes. SM composition is altered in HD, and GM1 has been shown to have protective effects in animal models of HD. A combination of Langmuir trough monolayer techniques, vesicle permeability and binding assays, and in situ atomic force microscopy (AFM) were used to directly monitor the interaction of a model, synthetic htt peptide and a full-length htt-exon1 recombinant protein with model membranes comprised of total brain lipid extract (TBLE) and varying amounts of exogenously added SM or GM1. The addition of either SM or GM1 decreased htt insertion into the lipid monolayers. However, TBLE vesicles with an increased SM content were more susceptible to htt-induced permeabilization, whereas GM1 had no effect on permeablization. Pure TBLE bilayers and TBLE bilayers enriched with GM1 developed regions of roughened, granular morphologies upon exposure to htt-exon1, but plateau-like domains with a smoother appearance formed in bilayers enriched with SM. Oligomeric aggregates were observed on all bilayer systems regardless of induced morphology. Collectively, these observations suggest that the lipid composition and its subsequent effects on membrane material properties strongly influence htt binding and aggregation on lipid membranes.

Biomolecule-Functionalized Smart Polydiacetylene for Biomedical and Environmental Sensing

Polydiacetylene (PDA) has attracted interest for use as a sensing platform in biomedical, environmental, and chemical engineering applications owing to its capacity for colorimetric and fluorescent transition in response to external stimuli. Many researchers have attempted to develop a tailor-made PDA sensor via conjugation of chemical or biological substances to PDA. Here, we review smart bio-conjugates of PDA with various biomolecules such as carbohydrates, lipids, nucleic acids, and proteins. In addition, materialization and signal amplification strategies to improve handling and sensitivity are described.

Novel amphiphilic conjugates of p-tert-butylthiacalix[4]arene with 10,12-pentacosadiynoic acid in 1,3-alternate stereoisomeric form. Synthesis and chromatic properties in the presence of metal ions

Functional polydiacetylene vesicles based on thiacalix[4]arene–10,12-pentacosadiynoic acid conjugates showed selective colorimetric response toward lanthanide ions.

Phospholipid/Polydiacetylene Vesicle-Based Colorimetric Assay for High-Throughput Screening of Bacteriocins and Halocins

The colorimetric assay is phospholipid/polydiacetylene vesicle-based assay used for the detection of membrane-acting peptides. Bacteriocins and halocins are antimicrobial peptides known to kill target cells by membrane disruption. Therefore, the assay was applied for high-throughput (HTP) screening of bacteriocins and halocins produced by lactic acid bacteria and haloarchaea, respectively. The assay consisted of vesicles which were synthesized using four different phospholipids: dipalmitoylphosphatydilcholine (DPPC), dimyristoylphosphatidylcholine (DMPC), dimyristoylphosphoethanolamine (DMPE) and dimyristoylphosphatidylglycerol (DMPG) in combination with diacetylene monomer 10,12-tricosadiy noic acid (TRCDA). These vesicles demonstrated blue colour at 640 nm and turned pink/red after interaction with nisin. DMPE/TRCDA vesicles showed pink colour with the highest colorimetric response (CR %) after treatment with nisin and, therefore, selected for the screening of bacteriocins and halocins. The colour of the vesicles was changed within 5 min in the presence of 5 μM nisin suggesting the sensitivity of assay. The assay was applied on 54 strains of lactic acid bacteria (LAB) and 53 haloarchaea for screening of bacteriocins and halocins, respectively. Out of these strains, three strains of LAB and five strains of haloarchaea were found to be bacteriocin and halocin non-producer, respectively. The other strains demonstrated the presence of bacteriocins and halocins. The colorimetric assay was found to be rapid, specific and reliable for HTP screening of antimicrobial peptides such as bacteriocins and halocins from producer strains isolated from various natural resources.

Photopatterned Polydiacetylene Images Using a DNA Bio-Photomask

We describe a novel strategy to fabricate a well-defined polydiacetylene (PDA) supramolecular pattern on polyvinylidene fluoride (PVDF) membrane utilizing a DNA bio-photomask. By focusing on that, the absorption spectrum of DNA molecules having a λmax at 260 nm overlaps with the wavelength at which the photopolymerization of the diacetylene monomer occurs, DNA molecules are used to define specific patterns on PVDF membranes coated with diacetylene lipids by shielding the applied 254 nm UV light and consequently preventing the photopolymerization of the lipids. As a result, the DNA-covered regions retain the original white color on the membrane while the regions uncovered by DNA molecules undergo the color change to blue through the photopolymerization by 254 nm UV irradiation. On the basis of the selective illumination through a DNA photomask, we precisely manufacture specific patterns using a microarray spotting method and also demonstrate the capability of this strategy to achieve a novel colorimetric DNA sensor without any complicated process.

Polydiacetylene Liposomal Aequorin Bioluminescent Device for Detection of Hydrophobic Compounds

In this study, a polydiacetylene liposomal aequorin bioluminescent device (PLABD) that functioned through control of the membrane transport of Ca(2+) ions was developed for detecting hydrophobic compounds. In the PLABD, aequorin was encapsulated in an internal water phase and a calcium ionophore (CI) was contained in a hydrophobic region. Membrane transport of Ca(2+) ions across the CI was suppressed by polymerization between diacetylene molecules. On addition of an analyte, the membrane transport of Ca(2+) ions across the CI increased, and Ca(2+) ions from the external water phase could diffuse into the internal water phase via the CI, which resulted in bioluminescence of the aequorin. Lidocaine, procaine, and procainamide were used as model compounds to test the validity of the detection mechanism of the PLABD. When each analyte was added to a suspension of the PLABD, bioluminescence from the aequorin in the PLABD was observed, and the level of this bioluminescence increased with increasing analyte concentration. There was a linear relationship between the logarithm of the analyte concentration and the bioluminescence for all analytes as follows: R = 0.89 from 10 nmol L(-1) to 10 mmol L(-1) for lidocaine, R = 0.66 from 10 nmol L(-1) to 100 μmol L(-1) for procaine, and R = 0.74 from 100 nmol L(-1) to 100 μmol L(-1) for procainamide. Compared to the traditional colorimetric method using polydiacetylene liposome, the PLABD was superior for both the sensitivity and dynamic range. Thus, PLABD is a valid, simple, and sensitive signal generator for detection of hydrophobic compounds that interact with PLABD membranes.

Molecular Mechanism of Holin Transmembrane Domain I in Pore Formation and Bacterial Cell Death

Bacterial cell lysis during bacteriophage infection is timed by perfect orchestration between components of the holin-endolysin cassette. In bacteria, progressively accumulating holin in the inner membrane, retained in its inactive form by antiholin, is triggered into active hole formation, resulting in the canonical host cell lysis. However, the molecular mechanism of regulation and physical basis of pore formation in the mycobacterial cell membrane by D29 mycobacteriophage holin, particularly in the nonexistence of a known antiholin, is poorly understood. In this study, we report, for the first time, the use of fluorescence resonance transfer measurements to demonstrate that the first transmembrane domain (TM1) of D29 holin undergoes a helix ↔ β-hairpin conformational interconversion. We validate that this structural malleability is mediated by a centrally positioned proline and is responsible for controlled TM1 self-association in membrana, in the presence of a proton gradient across the lipid membrane. We demonstrate that TM1 is sufficient for bacterial growth inhibition. The biological effect of D29 holin structural alteration is presented as a holin self-regulatory mechanism, and its implications are discussed in the context of holin function.

“Clickable” thiacalix[4]arene derivatives bearing polymerizable 1,3-butadiyne fragments: synthesis and incorporation into polydiacetylene vesicles

Thiacalix[4]arene-functionalized polydiacetylene (PDA) vesicles showed selective colorimetric response toward several lanthanide ions. This approach can be a good basis for lanthanide express analysis.

Synthesis of the Stable Ordered Conjugated Polymer Poly(dibromodiacetylene) from an Explosive Monomer

Dibromobutadiyne is an extremely unstable compound that explodes at room temperature, even under inert atmosphere. This instability has limited the studies of dibromobutadiyne almost entirely to spectroscopic characterization. Here we report an approach to control the reactivity of dibromobutadiyne, via topochemical reaction in cocrystals, leading to the ordered polymer poly(dibromodiacetylene), PBDA. At low temperatures (-15 to -18 °C), dibromobutadiyne can form cocrystals with oxalamide host molecules containing either pyridyl or nitrile side groups, in which halogen bonds align the dibromobutadiyne monomers for topochemical polymerization. The cocrystals with the bis(nitrile) oxalamide host undergo complete ordered polymerization to PBDA, demonstrated by solid-state MAS-NMR, Raman, and optical absorption spectroscopy. Once formed, the polymer can be separated from the host; unlike the monomer, PBDA is stable at room temperature.

Chromatic response of polydiacetylene vesicle induced by the permeation of methotrexate

The noble vesicular system of polydiacetylene showed a red shift using two types of detecting systems. One of the systems involves the absorption of target materials from the outer side of the vesicle, and the other system involves the permeation through the vesicular layers from within the vesicle. The chromatic mixed vesicles of N-(2-aminoethyl)pentacosa-10,12-diynamide (AEPCDA) and dimethyldioctadecylammonium chloride (DODAC) were fabricated by sonication, followed by polymerization by UV irradiation. The stability of monomeric vesicles was observed to increase with the polymerization of the vesicles. Methotrexate was used as a target material. The polymerized mixed vesicles having a blue color were exposed to a concentration gradient of methotrexate, and a red shift was observed indicating the adsorption of methotrexate on the polydiacetylene bilayer. In order to check the chromatic change by the permeation of methotrexate, we separated the vesicle portion, which contained methotrexate inside the vesicle, and checked chromatic change during the permeation of methotrexate through the vesicle. The red shift apparently indicates the disturbance in the bilayer induced by the permeation of methotrexate. The maximum contrast of color appeared at the equal molar ratio of AEPCDA and DODAC, indicating that the formation of flexible and deformable vesicular layers is important for red shift. Therefore, it is hypothesized that the system can be applicable for the chromatic detection of the permeation of methotrexate through the polydiacetylene layer.

From molecular modelling to photophysics of neutral oligo- and polyfluorenes incorporated into phospholipid bilayers

The combination of various experimental techniques with theoretical simulations has allowed elucidation of the mode of incorporation of fluorene based derivatives into phospholipid bilayers. Molecular dynamics (MD) simulations on a fully hydrated 1,2-dimyristoyl-sn-glycero-3-phosphatidylcholine (DMPC) bilayer, with benzene (B), biphenyl (BP), fluorene (F) and tri-(9,9-di-n-octylfluorenyl-2,7-diyl), TF, have provided insights into the topography of these molecules when they are present in the phospholipid bilayer, and suggest marked differences between the behavior of the small molecules and the oligomer. Further information on the interaction of neutral fluorenes within the phospholipid bilayer was obtained by an infrared (IR) spectroscopic study of films of DMPC and of the phospholipid with PFO deuterated specifically on its alkyl chains (DMPC-PFO-d34). This was complemented by measurements of the effect of F, TF and two neutral polymers: polyfluorene poly(9,9-di-n-octylfluorenyl-2,7-diyl), PFO, and poly(9,9-di-n-dodecylfluorenyl-2,7-diyl), PFD, on the phospholipid phase transition temperature using differential scanning calorimetry (DSC). Changes in liposome size upon addition of F and PFO were followed by dynamic light scattering. In addition, the spectroscopic properties of F, TF, PFO and PFD solubilised in DMPC liposomes (absorption, steady-state and time-resolved fluorescence) were compared with those of the same probes in typical organic solvents (chloroform, cyclohexane and ethanol). Combining the insight from MD simulations with the results at the molecular level from the various experimental techniques suggests that while the small molecules have a tendency to be located in the phospholipid head group region, the polymers are incorporated within the lipid bilayers, with the backbone predominantly orthogonal to the phospholipid alkyl chains and with interdigitation of them and the PFO alkyl chains.

A polydiacetylene-based fluorescence assay for the measurement of lipid membrane affinity

Polydiacetylene (PDA) is a promising membrane-screening tool because lipid constituents can be incorporated into the PDA framework to form lipid/PDA vesicles used as lipid bilayers.

Janus-compartmental alginate microbeads having polydiacetylene liposomes and magnetic nanoparticles for visual lead(II) detection

Janus-compartmental alginate microbeads having two divided phases of sensory polydiacetylene (PDA) liposomes and magnetic nanoparticles were fabricated for facile sensory applications. The sensory liposomes are composed of PDA for label-free signal generation and 1,2-dipalmitoyl-sn-glycero-3-galloyl (DPGG) lipids whose galloyl headgroup has specific interactions with lead(II). The second phase having magnetic nanoparticles is designed for convenient handling of the microbeads, such as washing, solvent exchange, stirring, and detection, by applying magnetic field. Selective and convenient colorimetric detection of lead(II) and efficient removal of lead(II) by alginate matrix at the same time are demonstrated.

Chemical sensing of neurotransmitters

This review focuses on the chemosensors for neurotransmitters published for the last 12 years, covering biogenic amines (dopamine, epinephrine, norepinephrine, serotonin, histamine and acetylcholine), amino acids (glutamate, aspartate, GABA, glycine and tyrosine), and adenosine.

An easily functionalizable oligo(oxyethylene)- and ester-substituted poly(3,4-propylenedioxythiophene) derivative exhibiting alkali metal ion response

UV-vis spectra of P(ProDOT-EO-ester) in THF in the presence of different cations.