Chromatic Biosensor for Detection of Phosphinothricin Acetyltransferase by Use of Polydiacetylene Vesicles Encapsulated within Automatically Generated Immunohydrogel Beads

Evaluation of the Protective Role of Vitamin E against ROS-Driven Lipid Oxidation in Model Cell Membranes

Reactive oxygen species (ROS) are chemically reactive oxygen-containing compounds generated by various factors in the body. Antioxidants mitigate the damaging effects of ROS by playing a critical role in regulating redox balance and signaling. In this study, the interplay between reactive oxygen species (ROS) and antioxidants in the context of lipid dynamics were investigated. The interaction between hydrogen peroxide (H2O2) as an ROS and vitamin E (α-tocopherol) as an antioxidant was examined. Model membranes containing both saturated and unsaturated lipids served as experimental platforms to investigate the influence of H2O2 on phospholipid unsaturation and the role of antioxidants in this process. The results demonstrated that H2O2 has a negative effect on membrane stability and disrupts the lipid membrane structure, whereas the presence of antioxidants protects the lipid membrane from the detrimental effects of ROS. The model membranes used here are a useful tool for understanding ROS-antioxidant interactions at the molecular level in vitro.

Portable Colorimetric Hydrogel Beads for Point-of-Care Antimicrobial Susceptibility Testing

Sepsis is a life-threatening condition with systemic inflammatory responses caused by bacterial infections. Considering the emergence of antibiotic-resistant bacteria such as methicillin-resistant Staphylococcus aureus (MRSA), sepsis is a great threat to public health. The gold standard methods for antimicrobial susceptibility testing (AST), however, take at least approximately 3 days to implement the entire blood culture, pure culture, and AST processes. To overcome the time-consuming nature of conventional AST, a method employing a chromatic biosensor composed of poly(diacetylene), alginate, and LB broth (PAL) is introduced in this study. Compared to the gold standards, AST with PAL biosensors can be completed within a time frame as short as 16 h. Such a significant reduction in time is possible because the consecutive cultures and AST are carried out simultaneously by encapsulating the bacterial nutrients and detection molecules into a single component. The bead-like hydrogel sensors were used in their freeze-dried form, which endows them with portability and stability, thus making them adequate for point-of-care testing. The PAL biosensor yields minimum inhibitory concentrations comparable to those from the Clinical and Laboratory Standards Institute, and the applicability of the biosensor is further shown in MRSA-infected mice.

Recent Developments and Implementations of Conductive Polymer-Based Flexible Devices in Sensing Applications

Flexible sensing devices have attracted significant attention for various applications, such as medical devices, environmental monitoring, and healthcare. Numerous materials have been used to fabricate flexible sensing devices and improve their sensing performance in terms of their electrical and mechanical properties. Among the studied materials, conductive polymers are promising candidates for next-generation flexible, stretchable, and wearable electronic devices because of their outstanding characteristics, such as flexibility, light weight, and non-toxicity. Understanding the interesting properties of conductive polymers and the solution-based deposition processes and patterning technologies used for conductive polymer device fabrication is necessary to develop appropriate and highly effective flexible sensors. The present review provides scientific evidence for promising strategies for fabricating conductive polymer-based flexible sensors. Specifically, the outstanding nature of the structures, conductivity, and synthesis methods of some of the main conductive polymers are discussed. Furthermore, conventional and innovative technologies for preparing conductive polymer thin films in flexible sensors are identified and evaluated, as are the potential applications of these sensors in environmental and human health monitoring.

Bifunctional ligand-mediated amplification of polydiacetylene response to biorecognition of diethylstilbestrol for on-site smartphone detection

Polydiacetylene (PDA) is very suited for sensitively detecting large biomolecules, and its unique chromatic properties enable visual read-out. However, application to the selective detection of small molecules remains challenging. Here, bifunctional ligands are studied to amplify the color change of PDA for biorecognition of small molecules for the smartphone-based detection of diethylstilbestrol (DES). PDA is decorated with streptavidin (PDA-SA, blue), and biotin-modified DES (bio-DES) is prepared as a bifunctional ligand to couple with PDA-SA and DES antibody. Since multiple bio-DES can bind to a single SA, then multiple SAs on PDA lead to an increased surface coverage of the vesicle. In samples without DES, PDA-SA-bio-DES-DES antibody complexes will form, leading to a color transition (blue to red); this color transition is greatly amplified by antibody-induced aggregation of the complexes. When DES is present, aggregation is inhibited due to competition for the antibody and PDA-SA-bio-DES retains its blue color. A linear relationship (0.4-1250 ng mL^-1) is found between the colorimetric response and the logarithmic DES concentration, with adequate selectivity, accuracy (82.24-118.64%), and precision (below 8.24%). Finally, a paper-based DES PDA biosensor is developed with visual and smartphone-based detection limits of 10 ng mL^-1 and 0.85 ng mL^-1 in water, respectively.

Recent advances in the potential applications of luminescence-based, SPR-based, and carbon-based biosensors

Abstract

The need for biosensors has evolved in the detection of molecules, diseases, and pollution from various sources. This requirement has headed to the development of accurate and powerful equipment for analysis using biological sensing component as a biosensor. Biosensors have the advantage of rapid detection that can beat the conventional methods for the detection of the same molecules. Bio-chemiluminescence-based sensors are very sensitive during use in biological immune assay systems. Optical biosensors are emerging with time as they have the advantage that they act with a change in the refractive index. Carbon nanotube-based sensors are another area that has an important role in the biosensor field. Bioluminescence gives much higher quantum yields than classical chemiluminescence. Electro-generated bioluminescence has the advantage of miniature size and can produce a high signal-to-noise ratio and the controlled emission. Recent advances in biological techniques and instrumentation involving fluorescence tag to nanomaterials have increased the sensitivity limit of biosensors. Integrated approaches provided a better perspective for developing specific and sensitive biosensors with high regenerative potentials. This paper mainly focuses on sensors that are important for the detection of multiple molecules related to clinical and environmental applications.

Key points

• The review focusses on the applications of luminescence-based, surface plasmon resonance-based, carbon nanotube-based, and graphene-based biosensors

• Potential clinical, environmental, agricultural, and food industry applications/uses of biosensors have been critically reviewed

• The current limitations in this field are discussed, as well as the prospects for future advancement

Amplifying the Sensitivity of Polydiacetylene Sensors: The Dummy Molecule Approach

There is an increasing need for fast and accurate assessment of various health conditions, where polydiacetylenes (PDA), having unique stress-sensitive optical properties, have great potential. When the conjugated backbone of PDA is disturbed by steric repulsion between the receptor-target complexes formed at the PDA surface via specific recognition events, the bandgap of PDA increases and produces color change and fluorescent emission as a dual sensory signal. However, this detection mechanism suggests an intrinsic sensitivity limit of PDA platform because unless adjacent receptors are occupied by target molecules no signal is anticipated. A novel approach to improve the sensitivity and limit of detection of PDA sensors has been developed by preoccupying the surface of PDA liposomes with an optimized amount of artificial target molecules named as dummy molecules. The sensitivity and limit of detection (LOD) showed large improvement by the surface-bound dummy molecules. In addition, the dummy strategy was synergically integrated with another sensitivity enhancing method with a different working mechanism in a PDA sensor for Neomycin detection. When optimized, the LOD of the PDA sensor was improved to 7 nM from 80 nM of the control and the signal intensity increased consistently throughout the entire tested concentration range of the target Neomycin. Finally, the general applicability of the dummy strategy to other target molecules was successfully confirmed by implementing the dummy strategy in a PDA sensor for Surfactin detection.

Analysis of PDA Dose Curves for the Extraction of Antimicrobial Peptide Properties

A mechanochromic polymer, polydiacetylene, changes color upon ligand binding, being a popular material in biosensing. However, whether it can also detect ligand functions in addition to binding is left understudied. In this work, we report that the polydiacetylene can be used to determine the net charges and the mode of actions (carpet model, toroidal pore model, etc.) of antimicrobial peptides and detergents via EC₅₀ and Hill coefficients from the colorimetric response-dose curves. This opens a potential for high-throughput peptide screening by functions, which is difficult with the conventional methods.

Polydiacetylene Liposome Microarray toward Facile Measurement of Platelet Activation in Whole Blood

The necessity of a simple measurement of platelet activation has been increasing in clinical medicine to regulate the proper dose of the antiplatelet drugs for patients having clinical outcomes in acute situations such as angina pectoris, stroke, or peripheral vascular disease or procedures involving angioplasty or coronary thrombolysis. We developed a self-signaling polydiacetylene (PDA) liposome microarray to detect activated platelets from whole blood samples in a single step. A specific antibody, 9F9 antibody, to platelet-bound fibrinogen was selected and conjugated to the PDA liposome microarray to quantify the fibrinogen-bound platelets. The developed PDA liposome-9F9 microarray generated an intense fluorescence signal when activated platelets in whole blood were introduced and also successfully distinguished the reduced platelet activation in the presence of Tirofiban, a model antiplatelet drug. The results of this single-step benchtop assay incorporates simple, sensitive, and rapid attributes that can detect the extent of platelet activation prior to needed clinical procedures.

Quantitative Analysis of the Membrane Affinity of Local Anesthetics Using a Model Cell Membrane

Local anesthesia is a drug that penetrates the nerve cell membrane and binds to the voltage gate sodium channel, inhibiting the membrane potential and neurotransmission. It is mainly used in clinical uses to address the pain of surgical procedures in the local area. Local anesthetics (LAs), however, can be incorporated into the membrane, reducing the thermal stability of the membrane as well as altering membrane properties such as fluidity, permeability, and lipid packing order. The effects of LAs on the membrane are not yet fully understood, despite a number of previous studies. In particular, it is necessary to analyze which is the more dominant factor, the membrane affinity or the structural perturbation of the membrane. To analyze the effects of LAs on the cell membrane and compare the results with those from model membranes, morphological analysis and 50% inhibitory concentration (IC50) measurement of CCD-1064sk (fibroblast, human skin) membranes were carried out for lidocaine (LDC) and tetracaine (TTC), the most popular LAs in clinical use. Furthermore, the membrane affinity of the LAs was quantitatively analyzed using a colorimetric polydiacetylene assay, where the color shift represents their distribution in the membrane. Further, to confirm the membrane affinity and structural effects of the membranes, we performed an electrophysiological study using a model protein (gramicidin A, gA) and measured the channel lifetime of the model protein on the free-standing lipid bilayer according to the concentration of each LA. Our results show that when LAs interact with cell membranes, membrane affinity is a more dominant factor than steric or conformational effects of the membrane.

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.

Colorimetric biosensing of nopaline synthase terminator using Fe3O4@Au and hemin-functionalized reduced graphene oxide

In this paper, we present a simple and label-free colorimetric biosensor for detection of the nopaline synthase (NOS) terminator in genetically modified (GM) plants. The "signal on" colorimetric biosensor was developed using a nanocomposite consisted of gold nanoparticles doped magnetic Fe₃O₄ nanoparticles (Fe₃O₄@Au NP), capture probe DNA (cDNA), and hemin-functionalized reduced graphene oxide nanosheets (H-GN). The nanocomposite was successfully prepared by means of Au-S bonds and the strong π interactions between cDNA and H-GN. The sensing approach is based on the excellent peroxidase-mimicking activity of H-GN and its different electrostatic interactions with single-stranded DNA (ssDNA) and double-stranded DNA (dsDNA). In presence of the target NOS, the cDNA in the nanocomposite will hybridize with its complementary sequence, and form dsDNA structure. Due to the weak π interactions between dsDNA and H-GN, a portion of H-GN will be released from the surface of Fe₃O₄@Au NPs and transferred into solution. After magnetic separation was performed, the supernatant was incubated with 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of H₂O₂. The released H-GN can catalyze the oxidation reaction of TMB and turn the colorless solution blue. This "signal-on" colorimetric biosensor shows a broad linear range of 0.5-100 nM for the target NOS, with a 0.19 nM detection limit. The application of the biosensor for determination of NOS segments in samples of GM and non-GM tomatoes shows that it can discriminate between GM and non-GM plants. The reliability of the method for samples of NOS-spiked GM tomato suggests satisfactory recoveries in the range of 93.6%-94.2%.

Rhodol-conjugated polymersome sensor for visual and highly-sensitive detection of hydrazine in aqueous media

Hydrazine is a hazardous environmental pollutant, which contaminates land, air and water posturing a severe risk to human health. For the first-hand estimation, a qualitative approach (colorimetric) for recognition of hydrazine could suffice. However, for accurate measurement, under the threshold limit value (TLV), a quantitative technique is desired. We report the polymersome-based sensor for visual detection and quantification of hydrazine in water. The rhodol-functionalized amphiphilic hyperbranched multiarm copolymer (HSP-RDL) was self-assembled into vesicles. The HSP-RDL vesicle probe exhibited high sensitivity and selectivity for hydrazine recognition in presence of various competitive species such as cations, anions, and neutral species. The fast responsive pink color change from colorless could be visualized with naked eye due to spirolactone ring opening by hydrazinolysis triggered strong fluorescence emission. The vesicle probe could detect hydrazine in water with a limit of detection (LOD) value of 2 nM (0.0652 ppb), which is lower than TLV (10 ppb) given by USEPA (United States Environmental Protection Agency). Furthermore, the vesicle probe could quantify hydrazine (recovery ≥ 99 %) in a wastewater sample collected from Huangpu river. The membrane-permeable characteristics of HSP-RDL led hydrazine detection in live cells through confocal fluorescence microscopy.

Nanosensors based on polymer vesicles and planar membranes: a short review

This review aims to summarize the advance in the field of nanosensors based on two particular materials: polymer vesicles (polymersomes) and polymer planar membranes. These two types of polymer-based structural arrangements have been shown to be efficient in the production of sensors as their features allow to adapt to different environment but also to increase the sensitivity and the selectivity of the sensing device. Polymersomes and planar polymer membranes offer a platform of choice for a wide range of chemical functionalization and characteristic structural organization which allows a convenient usage in numerous sensing applications. These materials appear as great candidates for such nanosensors considering the broad variety of polymers. They also enable the confection of robust nanosized architectures providing interesting properties for numerous applications in many domains ranging from pollution to drug monitoring. This report gives an overview of these different sensing strategies whether the nanosensors aim to detect chemicals, biological or physical signals.

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.

Mussel-Inspired Universal Bioconjugation of Polydiacetylene Liposome for Droplet-Array Biosensors

Most solid-state biosensor platforms require a specific immobilization chemistry and a bioconjugation strategy separately to tether sensory molecules to a substrate and attach specific receptors to the sensory unit, respectively. We developed a mussel-inspired universal conjugation method that enables both surface immobilization and bioconjugation at the same time. By incorporating dopamine or catechol moiety into self-signaling polydiacetylene (PDA) liposomes, we demonstrated efficient immobilization of the PDA liposomes to a wide range of substrates, without any substrate modification. Moreover, receptor molecules having a specificity toward a target molecule can also be attached to the immobilized PDA liposome layer without any chemical modification. We applied our mussel-inspired conjugation method to a droplet-array biosensor by exploiting the hydrophilic nature of PDA liposomes coated on a hydrophobic polytetrafluoroethylene surface and demonstrated selective and sensitive detection of vascular endothelial growth factor down to 10 nM.

Crystal polymorphism in polydiacetylene-embedded electrospun polyvinylidene fluoride nanofibers

In this study, polydiacetylene (PDA) is embedded in electrospun polyvinylidene fluoride (PVDF) nanofibers for the preparation of mats with dual colorimetric and piezoelectric responses. The diacetylene monomers are self-assembled during the electrospinning process. The PDA-embedded PVDF nanofibers in the blue phase are obtained via photo-polymerization upon UV-light irradiation. The colorimetric transition of the nanofibers is studied as a function of temperature using a spectrophotometer. The morphology and crystal polymorphism of the nanofibers are investigated. The results show that the addition of PDA increases the diameter of the nanofibers due to the increase in the electrospinning solution viscosity. The results of Fourier transform infrared and wide angle X-ray diffraction demonstrate that PDA has the effect of inhibiting the growth of non-polar α-phase crystals, while promoting the growth of the polar β-phase. However, the red phase of PDA-embedded PVDF exhibits a lower intensity of the β-phase in comparison to that of the blue phase. In fact, the blue-to-red color transition of the PDA-embedded electrospun PVDF nanofibers is accompanied by the variation of piezoelectric signaling caused by variations in the β-phase. This phenomenon creates great potential in commercial detection sensors in addition to their colorimetric detection properties.

Liposomes and lipid bilayers in biosensors

Biosensors for the rapid, specific, and sensitive detection of analytes play a vital role in healthcare, drug discovery, food safety, and environmental monitoring. Although a number of sensing concepts and devices have been developed, many longstanding challenges to obtain inexpensive, easy-to-use, and reliable sensor platforms remain largely unmet. Nanomaterials offer exciting possibilities for enhancing the assay sensitivity and for lowering the detection limits down to single-molecule resolution. In this review, we present an overview of liposomes and lipid bilayers in biosensing applications. Lipid assemblies in the form of spherical liposomes or two-dimensional planar membranes have been widely used in the design of biosensing assays; in particular, we highlight a number of recent promising developments of biosensors based on liposomes in suspension, liposome arrays, and lipid bilayers arrays. Assay sensitivity and specificity are discussed, advantages and drawbacks are reviewed, and possible further developments are outlined.

Polydiacetylene-Coated Sensor Strip for Immunochromatic Detection of Xylella fastidiosa subsp. fastidiosa

This study presents a sensor strip for user-friendly, naked-eye detection of Xylella fasitdiosa, the bacterial causal agent of Pierce's disease in grapevine. This sensor uses anti- X. fastidiosa antibodies conjugated to a polydiacetylene layer on a polyvinylidene fluoride strip to generate specific color transitions and discriminate levels of the pathogen. The detection limit of the sensor is 0.8 × 10⁸ cells/mL, which is similar to bacterial load in grapevine 18 days following bacterial inoculation. This sensor enables equipment-free detection that is highly desirable for in-field diagnostic tools in resource-limited settings.

Polymer Vesicle Sensor for Visual and Sensitive Detection of SO2 in Water

This study reports the first polymer vesicle sensor for the visual detection of SO₂ and its derivatives in water. A strong binding ability between tertiary alkanolamines and SO₂ has been used as the driving force for the detection by the graft of tertiary amine alcohol (TAA) groups onto an amphiphilic hyperbranched multiarm polymer, which can self-assemble into vesicles with enriched TAA groups on the surface. The polymer vesicles will undergo proton exchange with cresol red (CR) to produce CR-immobilized vesicles (CR@vesicles). Subsequently, through competitive binding with the TAA groups between CR and SO₂ or HSO₃^-, the CR@vesicles (purple) can quickly change into SO₂@vesicles (colorless) with the release of protonated CR (yellow). Such a fast purple to yellow transition in the solution allows the visual detection of SO₂ or its derivatives in water by the naked eye. A visual test paper for SO₂ gas has also been demonstrated by the adsorption of CR@vesicles onto paper. Meanwhile, the detection limit of CR@vesicles for HSO₃^- is approximately 25 nM, which is improved by approximately 30 times when compared with that of small molecule-based sensors with a similar structure (0.83 μM). Such an enhanced detection sensitivity should be related to the enrichment of TAA groups as well as the CR in CR@vesicles. In addition, the CR@vesicle sensors also show selectivity and specificity for the detection of SO₂ or HSO₃^- among anions such as F^-, Br^-, Cl^-, SO₄^2-, NO₂^-, C₂O₄^2-, S₂O₃^2-, SCN^-, AcO^-, SO₃^2-, S^2-, and HCO₃^-.

A flexible transparent colorimetric wrist strap sensor

A flexible, transparent, and portable wrist strap sensor device has been well developed from a hierarchical polydiacetylene/MoS₂ nanocomposite (PDA/MoS₂) film. MoS₂ with a nanoflake structure and chelation ability acts as a supporter for PDA films to enhance the porosity as well as the transparency of films, which increases the sensitivity, selectivity, and application potential of a PDA sensor. The PDA/MoS₂ film sensor shows a linear detection range for N,N-dimethylformamide (DMF) vapor from 0.01% to 4% with a visible blue to red color change detected by the naked eye, which is more sensitive than other organic vapors. Exploiting the high transparency, vivid color change, remarkable flexibility and reliability, a wearable wrist strap sensor device with visible DMF sensing ability is fabricated based on PDA/MoS₂ films, indicating their great potential for smart wearable devices.

Fabrication of Polydiacetylene Liposome Chemosensor with Enhanced Fluorescent Self-Amplification and Its Application for Selective Detection of Cationic Surfactants

Polydiacetylene (PDA) materials have been adopted as one of the powerful conjugated polymers for sensing applications due to their unique optical properties. In this paper, we present a new PDA liposome-based sensor system with enhanced fluorescent self-amplification by tuning a fluorophore fluorescence emission. In this system, a 1,8-naphthalimide derivative employed as a highly fluorescent fluorophore was incorporated into a PDA supermolecule. During the formation of blue PDA liposomes, the fluorescence emission of the fluorophore can be directly quenched, while thermal-induced phase transition of PDA liposomes from blue to red can readily restore this fluorescence emission. These phenomena could be ascribed to the tunable Förster energy transfer between the excited fluorophore and PDA conjugated framework. To demonstrate the sensing performance of this newly prepared PDA liposome-based sensor, the sensor with fluorescent self-amplification was successfully applied for the detection of cationic surfactants (CS). The results show that the PDA liposomes displayed a distinct color change and fluorescence restoration in the presence of cationic surfactant species, and allowed detection of cationic surfactants with high sensitivity and selectivity. The limit of detection for target CS, such as cetyltrimethylammonium bromide (CTAB), can reach as low as 184 nM. Compared to the traditional methods based on colorimetric PDA liposomes, this newly fabricated PDA sensor system was superior for sensitivity. Thus, our findings offer an avenue for the design and development of new types of PDA sensors with enhanced sensitivity.

Polydiacetylene-coated polyvinylidene fluoride strip aptasensor for colorimetric detection of zinc(II)

We report a new polydiacetylene (PDA) sensor strip for simple visual detection of zinc ions in aqueous solution. The specificity of this sensor comes from Zn²⁺ DNA aptamer probes conjugated onto PDA. Effects of aptamer length and structure on the sensitivity of PDA's color transition were first investigated. PDA conjugated with the optimal aptamer sequence was then coated onto a strip of polyvinylidene fluoride membrane and photopolymerized by UV exposure. The newly developed sensor successfully exhibited a blue-to-red chromatic change in a semi-quantitative manner in response to zinc ions. No discernable change was observed in solutions containing other common ions. Advantages of this sensor include its ease of fabrication, high specificity, and equipment-free detection, all of which are desirable for in-field applications and use in resource-limited settings.

Recent progress in stimuli-induced polydiacetylenes for sensing temperature, chemical and biological targets

Polydiacetylenes (PDAs) have received increasing attention as smart materials owing to their unique properties. Upon addition of various stimuli, blue PDAs can undergo a colorimetric transition from blue to red along with a change from non-fluorescent to fluorescent. The optical changes can be readily detected by the naked eye and by using absorption and fluorescence spectrometers. These properties make PDAs excellent materials for use in platforms for sensing chemical or biological targets. In recent years, a number of biosensors and chemosensors based on the optical responses of polydiacetylenes have been reported. In this review, recent advances made in this area were discussed following a format based on different cognizing targets, including temperature, metal ions, anions, surfactants, amines, water, gas, sugars, hydrocarbons, neomycin, heparin, virus, enzymes, bacteria, and cancers. Emphasis is given to the methods used to prepare PDA sensing systems as well as their sensing performance.

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.

A Magnetically Responsive Polydiacetylene Precursor for Latent Fingerprint Analysis

A magnetically responsive diacetylene (DA) powder was developed for the visualization of latent fingerprints. A mixture of the DA and magnetite nanoparticles, applied to a surface containing latent fingermarks, becomes immobilized along the ridge patterns of the fingerprints when a magnetic field is applied. Alignment along the ridge structures is a consequence of favorable hydrophobic interactions occurring between the long alkyl chains in the DAs and the lipid-rich, sebaceous latent fingermarks. UV irradiation of the DA-magnetite composite immobilized on the latent fingerprint results in the generation of blue-colored PDAs. Heat treatment of the blue-colored image promotes a blue-to-red transition as well as fluorescence turn-on. A combination of the aligned pale brown-colored monomeric state, UV irradiation generated blue-colored PDA state, as well as the heat treatment generated red-colored and fluorescent PDA state enables efficient visual imaging of a latent fingerprint, which is deposited on various colored solid surfaces.

A biosensor based on electroactive dipyrromethene-Cu(II) layer deposited onto gold electrodes for the detection of antibodies against avian influenza virus type H5N1 in hen sera

This paper describes the development of a biosensor for the detection of anti-hemagglutinin antibodies against the influenza virus hemagglutinin. The steps of biosensor fabrications are as follows: (i) creation of a mixed layer containing the thiol derivative of dipyrromethene and 4-mercapto-1-butanol, (ii) complexation of Cu(II) ions, (iii) oriented immobilization of the recombinant histidine-tagged hemagglutinin, and (iv) filling free spaces with bovine serum albumin. The interactions between recombinants hemagglutinin from the highly pathogenic avian influenza virus type H5N1 and anti-hemagglutinin H5 monoclonal antibodies were explored with Osteryoung square-wave voltammetry. The biosensor displayed a good detection limit of 2.4 pg/mL, quantification limit of 7.2 pg/mL, and dynamic range from 4.0 to 100.0 pg/mL in buffer. In addition, this analytical device was applied for the detection of antibodies in hen sera from individuals vaccinated and non-vaccinated against the avian influenza virus type H5N1. The limit of detection for the assay was the dilution of sera 1: 7 × 10(6), which is about 200 times better than the enzyme-linked immunosorbent assay.