Permeation-induced chromatic change of a polydiacetylene vesicle with nonionic surfactant

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.

Development of color changing polydiacetylene-based biomimetic nanovesicle platforms for quick detection of membrane permeability across the blood brain barrier

Membrane permeability through passive diffusion is one of the important pathways for passage of drugs across the blood brain barrier (BBB). The present study describes the development of biomimetic unilamellar lipopolymeric nanovesicles of size 268 ± 37 nm, consisting of polar brain lipids in conjunction with polydiacetylene and validation of their application for an abbreviated yet accurate membrane permeability assay with high-throughput and rapid identification of BBB permeability of drugs. The nanovesicle suspension was tested with drugs of known permeability across the BBB to validate the detection of changes in hue, absorbance and fluorescence in response to permeation across the nanovesicles. A simple device was developed based on the nanovesicle sensors along with a mobile application which allowed for the determination of hue corresponding to qualitative identification of whether a drug is BBB permeable (BBB+) or not (BBB-). With respect to determination of a suitable endpoint in this assay, a hue cut off of 275°, reduction in %blueness by less than 59% and a fluorescence intensity of ≥0.22 a.u. at 560 nm accurately differentiated between drugs which are permeable and impermeable across the BBB within 5 minutes. Further quantification of BBB permeability can be done through the concentration at which the above end-points are achieved. For the quantification of the permeability, absorbance and fluorescence measurements were performed. The device thus developed allows the rapid determination of BBB permeability of various agents in drug discovery especially in smaller set-ups with minimal equipment through changes in color, absorbance and fluorescence.

A molecularly imprinted polymer undergoing a color change depending on the concentration of bisphenol A

A molecularly imprinted system is introduced here whose color gradually changes as the analyte becomes rebound. The MIP was prepared from an acryloyl-modified β-cyclodextrin (β-CD), acrylamide (AAm), and N,N'-methylenebisacrylamide (MBAA), and imprinted with bisphenol A (BPA). The sensing capability of the MIP was first tested by potentiometry. A spin-coated gold plate coated with the MIP was used as a working electrode; the electrode can differentiate BPA from phenol or p-cresol, which were used as analogs of BPA. Next, a color-responsive system was fabricated by forming a hydrogel membrane containing the modified β-CD, AAm, and MBAA. A vesicle solution was prepared from N-(2-aminoethyl)pentacosa-10,12-diynamide by sonication and incorporated into the hydrogel. The blue polydiacetylene was formed by UV photopolymerization. In the presence of BPA, this system undergoes a color change from blue to red that is proportional to the degree of BPA rebinding. The color change is due to the contraction of the gel membrane that rebinding causes. The method works to 0.5 mM BPA concentration range. The detection limits for BPA are 0.1 mM on visual assessment and 50 μM on spectrophotometric readout. Graphical AbstractA molecular imprinting system is described whose color changes from blue to red as it binds bisphenol A. The degree of rebinding can be measured by detecting the color change of polydiacetylene vesicle. CD: cyclodextrin, BPA: bisphenol A.

A simple and inexpensive thermal optic nanosensor formed by triblock copolymer and polydiacetylene mixture

Polydiacetylene (PDA) vesicles have been applied as optical sensors in different areas, although there are difficulties in controlling their responses. In this study, we prepared nanoblends of PDA with triblock copolymers (TC) as a better sensor system for detecting temperature change. The influences of diacetylene (DA) monomer, and the TC chemical structure and concentration on the colorimetric response (CR) were examined. The TC/PDA nanoblend was remarkably more sensitive to temperature change, than classical vesicles. A higher L64 concentration of 12.0% (w/w) reduced the chromatic transition temperature (T_tr) to as low as 24°C. When using different TCs, the T_tr values can be ordered as L35<F68<L64<F127<P123, indicating the importance of the hydrophobic environment for the colorimetric transition of nanoblends. The results here demonstrated that the balance of intermolecular interaction between TC-TC, TC-DA, and DA-DA enables the construction of strategic sensor for detecting temperature changes in different applications.

Advances in polydiacetylene development for the design of side chain groups in smart material applications – a mini review

This review focuses on various side chain groups based on PDAs published over the last 3 years, covering urea, melamine, ferriferous oxide and coumarin. Perspectives on the remaining challenges and future developments are also proposed.