Insight into diacetylene photopolymerization in Langmuir-Blodgett films using simultaneous AFM and fluorescence microscopy imaging

Paper Doped with Polyacrylonitrile Fibres Modified with 10,12-Pentacosadiynoic Acid

This work reports a modification of a fibrous cellulose material (paper) by the addition of polyacrylonitrile (PAN) fibres doped with 10,12–pentacosadiynoic acid (PDA). The fibres are sensitive to ultraviolet (UV) light. When the paper containing PAN–PDA is irradiated with UV light it changes colour to blue as a consequence of interaction of the light with PDA. The colour intensity is related to the absorbed dose, content of PAN–PDA fibres in the paper and the wavelength of UV radiation. The features of the paper are summarised after reflectance spectrophotometry and scanning microscopy analyses. All the properties of the modified paper were tested in accordance with adequate ISO standards. Moreover, a unique method for assessing the unevenness of the paper surface and the quality of printing was proposed by using a Python script (RGBreader) for the analysis of RGB colour channels. The modification applied to the paper can serve as a paper security system. The modified paper can act also as a UV radiation indicator.

Alkali Metal Salts of 10,12-Pentacosadiynoic Acid and Their Dosimetry Applications

Wide-dose-range 2D radiochromic films for radiotherapy, such as GAFchromic EBT, are based on the lithium salt of 10,12-pentacosadiynoic acid (Li-PCDA) as the photosensitive component. We show that there are two solid forms of Li-PCDA-a monohydrated form A and an anhydrous form B. The form used in commercial GAFchromic films is form A due to its short needle-shaped crystals, which provide favorable coating properties. Form B provides an enhanced photoresponse compared to that of form A, but adopts a long needle crystal morphology, which is difficult to process. The two forms were characterized by powder X-ray diffraction, Fourier transform infrared spectroscopy, CP-MAS ¹³C solid-state NMR spectroscopy, and thermogravimetric analysis. In sum, these data suggest a chelating bridging bidentate coordination mode for the lithium ions. The sodium salt of PCDA (Na-PCDA) is also reported, which is an ionic cocrystal with a formula of Na⁺PCDA^-·3PCDA. The PCDA and PCDA^- ligands display monodentate and bridging bidentate coordination to the sodium ion in contrast to the coordination sphere of the Li-PCDA forms. In contrast to its lithium analogues, Na-PCDA is photostable.

Highly Sensitive Polydiacetylene Ensembles for Biosensing and Bioimaging

Polydiacetylenes are prepared from amphiphilic diacetylenes first through self-assembly and then polymerization. Different from common supramolecular assemblies, polydiacetylenes have stable structure and very special optical properties such as absorption, fluorescence, and Raman. The hydrophilic head of PDAs is easy to be chemically modified with functional groups for detection and imaging applications. PDAs will undergo a specific color change from blue to red, fluorescence enhancement and Raman spectrum changes in the presence of receptor ligands. These properties allow PDA-based sensors to have high sensitivity and specificity during analysis. Therefore, the PDAs have been widely used for detection of viruses, bacteria, proteins, antibiotics, hormones, sialic acid, metal ions and as probes for bioimaging in recent years. In this review, the preparation, polymerization, and detection mechanisms of PDAs are discussed, and some representative research advances in the field of bio-detection and bioimaging are highlighted.

Synchronous, Crosstalk-free Correlative AFM and Confocal Microscopies/Spectroscopies

Microscopies have become pillars of our characterization tools to observe biological systems and assemblies. Correlative and synchronous use of different microscopies relies on the fundamental assumption of non-interference during images acquisitions. In this work, by exploring the correlative use of Atomic Force Microscopy and confocal-Fluorescence-Lifetime Imaging Microscopy (AFM-FLIM), we quantify cross-talk effects occurring during synchronous acquisition. We characterize and minimize optomechanical forces on different AFM cantilevers interfering with normal AFM operation as well as spurious luminescence from the tip and cantilever affecting time-resolved fluorescence detection. By defining non-interfering experimental imaging parameters, we show accurate real-time acquisition and two-dimensional mapping of interaction force, fluorescence lifetime and intensity characterizing morphology (AFM) and local viscosity (FLIM) of gel and fluid phases separation of supported lipid model membranes. Finally, as proof of principle by means of synchronous force and fluorescence spectroscopies, we precisely tune the lifetime of a fluorescent nanodiamond positioned on the AFM tip by controlling its distance from a metallic surface. This opens up a novel pathway of quench sensing to image soft biological samples such as membranes since it does not require tip-sample mechanical contact in contrast with conventional AFM in liquid.

Fluorescence anisotropy imaging of a polydiacetylene photopolymer film

UV-illumination of phase-separated surfactant films prepared from mixtures of photopolymerizable 10,12-pentacosadiynoic acid and perfluorotetradecanoic acid results in the formation of fluorescent polydiacetylene fibers and aggregates. In this work, the orientation of polymer strands that comprise the resulting photopolymer structures has been probed using fluorescence anisotropy imaging in combination with defocused single-molecule fluorescence imaging. Imaging experiments indicate the presence of significant fiber-to-fiber heterogeneity, as well as anisotropy within each fiber (or aggregate), with both of these properties changing as a function of film preparation conditions. This anisotropy can be attributed to various alignments of the constituent polymer strands that comprise the larger fibers and aggregates. Intriguingly, when using defocused imaging, fiber images consisted of a series of discrete “doughnut” fluorescence emission patterns, which exhibited intermittent on–off blinking behavior; both of these properties are characteristic of individual emission transition dipoles (single molecules). Further, all of the individual emission transition dipoles had a uniform orientation with respect to the axis of the fiber, indicating a common orientation of discrete emitters in the larger polymer fiber. The implications of these results for future studies of the electronic properties of conjugated polymers in larger macroscopic systems are noted.