Recent advances in the development of polydiacetylene-based biosensors

Polydiacetylene-based aptasensors for rapid and specific colorimetric detection of malignant exosomes

Exosomes (50-150 nm) play significant biological functions in intercellular communication and transportation of diverse biomolecules, including proteins and nucleic acids. In particular, malignant exosomes have received a great deal of attention as possible indicators for cancer detection and treatment. To swiftly and precisely identify malignant exosomes from normal exosomes in diverse bodily fluids, we developed polydiacetylene (PDA)-based aptasensors with distinct optical features exhibiting color shift in response to biological recognition. To identify epithelial cell adhesion molecules (EpCAM) overexpressed on the surface of malignant exosomes, anti-EpCAM aptamer-conjugated diacetylene monomer (TCDA-Apt) was synthesized and used to create anti-EpCAM aptamer-conjugated PDA (anti-EpCAM Apt-PDA) vesicles. In just 15 min following the reaction with malignant exosomes, the anti-EpCAM Apt-PDA vesicles underwent a visible color change from blue to purple. They showed high specificity to EpCAM-positive malignant exosomes over non-malignant exosomes, bovine serum albumin (BSA), and fibrinogen. Moreover, its effectiveness in the point-of-care (POC) detection of malignant exosomes was evaluated using human sera. Therefore, our PDA-based aptasensors have tremendous potential for on-site cancer diagnosis.

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.

A mitochondria targetable near-infrared fluorescence probe for glutathione visual biological detection

Glutathione (GSH), an abundant non-protein thiol, plays a crucial role in numerous biotic processes. Herein, a mitochondria-targeted near-infrared GSH probe (JGP) was synthesized, which displayed desired properties with high specificity and sensitivity, appreciable water solubility, and rapid response time. In the presence of GSH, nearly a 13-fold fluorescence emission growth appeared at 730 nm and the solvent color changed from blue to cyan. The sensing mechanism of JGP and GSH was confirmed by a high-resolution mass spectroscopy analysis. Moreover, good cell penetration enabled JGP to be successfully used for imaging biological samples such as HeLa cells, C. elegans, and especially rat brain slices. Imaging experiments showed that JGP could monitor the GSH concentration changes with a dose-dependent direct ratio in all the tested samples. The successful application of JGP in brain imaging indicates that JGP is a suitable GSH optical probe, which may have wide application value in fields of brain imaging. It also lays a theoretical and practical foundation for the further application of fluorescent probes in brain sciences.

Polydiacetylene vesicles acting as colorimetric sensor for the detection of plantaricin LD1

The interaction of antimicrobial peptides with membrane lipids plays a major role in numerous physiological processes. In this study, polydiacetylene (PDA) vesicles were synthesized using 10, 12-tricosadiynoic acid (TRCDA) and 1, 2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC). These vesicles were applied as artificial membrane biosensor for the detection of plantaricin LD1 purified from Lactobacillus plantarum LD1. Plantaricin LD1 (200 μg/mL) was able to interact with PDA vesicles by changing the color from blue to red with colorimetric response 30.26 ± 0.59. Nisin (200 μg/mL), used as control, also changed the color of the vesicles with CR% 50.56 ± 0.98 validating the assay. The vesicles treated with nisin and plantaricin LD1 showed increased infrared absorbance at 1411.46 and 1000-1150 cm^-1 indicated the interaction of bacteriocins with phospholipids and fatty acids, respectively suggesting membrane-acting nature of these bacteriocins. Further, microscopic observation of bacteriocin-treated vesicles showed several damages indicating the interaction of bacteriocins. These findings suggest that the PDA vesicles may be used as bio-mimetic sensor for the detection of bacteriocins produced by several probiotics in food and therapeutic applications.

An ICT-based fluorescent probe guided by theoretical calculation for selectively mapping endogenous GSH in living cells

Glutathione (GSH) is one of the most essential bio-thiols to maintain the redox balance of organisms which is strongly associated with many physiological processes. Detecting the concentration and mapping the distribution of GSH in the living system is significant to study many related diseases. In this work, we have successfully constructed an ICT-based model to guide the design and synthesis of GSH specific fluorescent probe CF1. A serials spectroscopy test demonstrated that the response of CF1 towards GSH owned large stokes shift (~167 nm) and an excellent linear relationship (0-120 μM, R² = 0.9961). Furthermore, CF1 was successfully applied to image endogenous GSH in different cell lines with high sensitivity. This work is instructive for the oriented synthesis of ICT-based functional fluorescent probe and the further visualization of intracellular targets in the living system.

A pyridine-Si-rhodamine-based near-infrared fluorescent probe for visualizing reactive oxygen species in living cells

A lysosomal-targeted near infrared (NIR) fluorescent probe for reactive oxygen species (ROS) was developed with highly sensitive ability. The different responding activity toward H₂O₂, OH, and HClO were investigated. Meanwhile, the probe has been successfully applied in detecting and imaging reactive oxygen species both in cells and in vivo.

A reaction-based ratiometric fluorescent probe for mercury ion detection in aqueous solution

Mercury ions are crucially harmful to ecosystem and human being due to their characters of bioaccumulation and difficulty of biochemical degradation. Therefore, development of mercury ion detection methods has attracted increasing interests recently. In this study, we successfully synthesized a hydroxyphenylbenzothiazole (HBT)-based fluorescent probe HBT-Hg in an extremely simple manner for mercuric ions detection. The spectral studies revealed that the probe HBT-Hg could react with Hg²⁺ selectively and sensitively in PBS buffer (10 mM, pH = 7.40), showing ratiometric fluorescent changes from blue to light green. The response mechanism of the probe HBT-Hg and Hg²⁺ was finally confirmed by HPLC analysis, viz., the probe HBT-Hg converted to its precursor compound 1. Finally, the probe HBT-Hg was successfully applied in monitoring Hg²⁺ in living A549 cells.

A DCM-based NIR sensor for selective and sensitive detection of Zn2+ in living cells

Zinc ion is the 2nd abundant transition metal element in human's body. It is responsible for many physiological and biological functioning in the body, such as growth of people, immunity, endocrine, etc. The deficiency of zinc could result in an increasing risk for growth retardation, neurological disorder and infectious disease. Thus, developing a nondestructive method for detecting Zn²⁺ in living systems is important. Here we reported a 2-(2-methyl-4H-ylidene)- malononitrile (DCM)-based NIR probe DF-Zn for selective and sensitive detection of Zn²⁺. The probe DF-Zn is cell-permeable and stable at broad pH range. DF-Zn showed a fast response to Zn²⁺, big stock's shift, and "nude-eye" recognition for Zn²⁺. Moreover, the selective binding of probe DF-Zn to Zn²⁺ was reversible. With the addition of EDTA in buffer solution, reversible response of probe to Zn²⁺ could be observed in MCF-7 cells imaging.

Visual Simultaneous Detection and Real-Time Monitoring of Cadmium Ions Based on Conjugated Polydiacetylenes

We prepared the monomer PCDA-HP composed of 5-hydroxy-N ¹,N ³-bis(pyridin-2-ylmethyl)isophthalamide (HP) as a cadmium ion tweezer and then polymerized them to form a polydiacetylene (PDA)-based sensor (PDA-HP), which displayed selective and sensitive colorimetric and fluorometric change upon addition of a cadmium ion (Cd²⁺) at both pH 7.4 and 6.8. The PDA-HP polymer was highly selective for Cd²⁺ over other metal ions with colorimetric change. In addition, the PDA-HP chemosensor also showed a red fluorescence change in the presence of Cd²⁺ at both pH 7.4 and 6.8. Naked-eye detection of Cd²⁺ was accomplished in an aqueous solution through a PDA-based sensor system. Finally, the lowest energy structure of an HP chelator was obtained by the crystal structure and density functional theory (DFT) calculations.

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.

Chemical sensors for selective and quantitative heparin sensing

In this review article, chemical sensors for selective and quantitative heparin sensing are discussed with detailed examples.

Construction and bioimaging application of novel indole heptamethine cyanines containing functionalized tetrahydropyridine rings

IR780 as a commercially available dye with near-infrared emission has been extensively applied in fluorescent probes and bioimaging.