Fluorescence detection of DNA hybridization based on the aggregation-induced emission of a perylene-functionalized polymer

AIE active polymers for biological applications

The discovery of aggregation-induced emission (AIE) phenomenon, significantly altered the understanding of the scientific world about the luminophore aggregation. Polymers with AIE features have recently emerged as promising materials with wide range of applications in optoelectronics devices, chemosensors, bioimaging, cancer theranostics and drug delivery. By introducing the AIE active molecule into the polymer structure, novel materials encompassing the characteristics properties of both the functional materials such as excellent brightness, versatile structure modification, high biocompatibility, exceptional stability and facile processability are achieved. This chapter presents the advances in synthetic design as well as potential biological applications of AIE active polymers, beginning with a brief introduction to the AIE phenomenon. The versatile synthetic route, easier functionalization, and light up feature of the AIE active polymers offer direct visualization of the physiological processes within or outside the living organisms. This chapter also precisely describes the photodynamic therapy/photothermal therapy (PDT/PTT) with up-to-date advancement of AIE active polymer and their emerging applications in biomedical field. The AIE active Photosensitizers (PSs) are much more efficient in singlet oxygen (¹O₂) production than their small molecule AIE active PSs due to their enhanced inter system crossing (ISC) process and improved light-harvesting ability. Additionally, the present chapter aims to focus on all recent AIE active polymers for drug screening and drug delivery. The AIE active polymer often shows decent drug loading capacity, high stability and good biocompatibility comprising image guided drug monitoring features. Lastly, the concluding discussion reveals the future prospective of the AIE active polymers.

Functional Polymer Systems with Aggregation-Induced Emission and Stimuli Responses

Functional polymer systems with stimuli responses have attracted great attention over the years due to their diverse range of applications. Such polymers are capable of altering their chemical and/or physical properties, such as chemical structures, chain conformation, solubility, shape, morphologies, and optical properties, in response to single or multiple stimuli. Among various stimuli-responsive polymers, those with aggregation-induced emission (AIE) properties possess the advantages of high sensitivity, fast response, large contrast, excellent photostability, and low background noise. The changes in fluorescence signal can be conveniently detected and monitored using portable instruments. The integration of AIE and stimuli responses into one polymer system provides a feasible and effective strategy for the development of smart polymers with high sensitivity to environmental variations. Here, we review the recent advances in the design, preparation, performance, and applications of functional synthetic polymer systems with AIE and stimuli responses. Various AIE-based polymer systems with responsiveness toward single physical or chemical stimuli as well as multiple stimuli are summarized with specific examples. The current challenges and perspectives on the future development of this research area will also be discussed at the end of this review.

Enantiomeric selectivity of ruthenium (II) chiral complexes with antitumor activity, in vitro and in vivo

Different enantiomers of chiral drugs show distinctive activities. Here, a pair of chiral ruthenium Λ-[Ru(phen)₂(TPEPIP)]²⁺ (Λ-Ru), and Δ-[Ru(phen)₂(TPEPIP)]²⁺ (Δ-Ru) (phen = 1,10-phenanthroline; TPEPIP = 2-(4'-(1,2,2-triphenylvinyl)-[1,1'-biphenyl]-4-yl)-1H-imidazo[4,5-f][1,10]phenanthroline) compounds have been prepared and characterized. Both have aggregation-induced emission characteristics, although Λ-Ru exhibits much higher activity, towards duplex DNA extracted from SGC-7901 cancer cells. In vitro experiments demonstrate that both Λ-Ru and Δ-Ru can induce the apoptosis of tumor cells with Λ-Ru showing greater activity than Δ-Ru. Λ-Ru aggregates in the cell nucleus of SGC-7901 within 5 h which shows that nucleic acids may be the effective target of Λ-Ru. In vivo experiments with nude mice showed that Λ-Ru can inhibit the growth and proliferation of a tumor, in tumor-bearing mice as well as targeting the tumor site, as demonstrated by fluorescence. These results demonstrate the dual-function of Λ-Ru, which could be used for real-time visualization of a chemotherapeutic agent.

Lighting up forensic science by aggregation-induced emission: A review

Forensic science requires a fast, sensitive, and anti-interfering imaging tool for on-site investigation and bio-analysis. The aggregation-induced emission (AIE) phenomenon exhibits remarkable luminescence properties (large Stokes shift, diverse molecular structures, and high photo-stability), which can provide a viable solution for on-site analysis, while at the same time overcoming the problem of aggregation-caused quenching (ACQ). Based on the outstanding performance in chemical analysis and bio-sensing, AIE materials have great prospects in the field of forensic science. Therefore, the application of AIE in forensic science has been summarized for the first time in this article. After a brief introduction to the concept and development of AIE, its applications in the determination of toxic or hazardous substances, based on data on poisoning deaths, has been summarized. Subsequently, besides the bio-imaging function, other applications of AIE in analyzing markers related to forensic genetics, forensic pathology, (focusing on the corpse) and clinical forensics (focusing on the living) have been discussed. In addition, applications of AIE molecules in criminal investigations, including recognition of fingerprints and blood stains, detection of explosives and chemical warfare agents, and anti-counterfeiting have also been presented. It is hoped that this review will light up the future of forensic science by stimulating more research work on the suitability of AIE materials in advancing forensic science.

Synthesis, Photophysics, and Solvatochromic Studies of an Aggregated-Induced-Emission Luminogen Useful in Bioimaging

Biological samples are a complex and heterogeneous matrix where different macromolecules with different physicochemical parameters cohabit in reduced spaces. The introduction of fluorophores into these samples, such as in the interior of cells, can produce changes in the fluorescence emission properties of these dyes, caused by the specific physicochemical properties of cells. This effect can be especially intense with solvatofluorochromic dyes, where changes in the polarity environment surrounding the dye can drastically change the fluorescence emission. In this article, we studied the photophysical behavior of a new dye and confirmed the aggregation-induced emission (AIE) phenomenon with different approaches, such as by using different solvent proportions, increasing the viscosity, forming micelles, and adding bovine serum albumin (BSA), through analysis of the absorption and steady-state and time-resolved fluorescence. Our results show the preferences of the dye for nonpolar media, exhibiting AIE under specific conditions through immobilization. Additionally, this approach offers the possibility of easily determining the critical micelle concentration (CMC). Finally, we studied the rate of spontaneous incorporation of the dye into cells by fluorescence lifetime imaging and observed the intracellular pattern produced by the AIE. Interestingly, different intracellular compartments present strong differences in fluorescence intensity and fluorescence lifetime. We used this difference to isolate different intracellular regions to selectively study these regions. Interestingly, the fluorescence lifetime shows a strong difference in different intracellular compartments, facilitating selective isolation for a detailed study of specific organelles.

Advances in luminescent materials with aggregation-induced emission (AIE) properties for biomedical applications

Fluorescent materials have recently received great attention in biomedical research because of their good optical properties, species diversity and high sensitivity. However, most of the traditional fluorophores suffer from the aggregation-caused quenching (ACQ) effect at high concentration or in the aggregated state, which has greatly limited their biomedical applications. Fluorescent materials with the AIE effect show exactly the opposite effect to the ACQ effect, and have exhibited significant advantages in terms of tunable emission, excellent photostability and biocompatibility. In this review, we summarize current advances of AIE-based materials for biomedical applications. In particular, AIE-active biosensors for detecting biomolecules, such as hydrogen peroxide, hydrogen sulfide, biothiols and enzymes, have been summarized. Moreover, AIE-based materials applied for bioimaging, drug delivery and cancer theranostics have also been described in detail. In the last section, the future prospects and possible challenges in the development of AIE-based materials are discussed briefly.

Unveiling the Different Emission Behavior of Polytriazoles Constructed from Pyrazine-Based AIE Monomers by Click Polymerization

Polymers with aggregation-induced emission (AIE) characteristics have aroused tremendous interest because of their potential applications in large-area flexible display and luminescent self-assembling, and as stimuli-responsive and porous materials. However, the design of AIE-active polymers is always not as easy as that of small molecules because their properties are hard to predict. In some cases, the polymers prepared from the AIE-active monomers show the aggregation-caused quenching (ACQ) instead of AIE effect. To understand the structure-property relationship of the polymers constructed from the AIE monomers, in this paper, two pyrazine-containing AIE monomers were utilized to construct luminescent polymers by click polymerization. The photophysical property investigation indicates that the polytriazole containing tetraphenylpyrazine units is AIE-active, whereas that bearing 2,3-dicyano-5,6-diphenylpyrazine units suffers from the ACQ effect. Through systematical investigation, the cause for such difference was unveiled. Thus, this work provides a useful guidance for further design of AIE-active polymers.

A novel pyridinium modified tetraphenylethene: AIE-activity, mechanochromism, DNA detection and mitochondrial imaging

A cationic AIE-gen demonstrates multiple functions including mechanoluminochromic and solvatochromic effects, fluorescence turn-on responses to DNA-binding and mitochondria-specific living cell imaging.

In situ polymerization of supramolecular nanorods assembled from polymerizable perylene bisimide

Dimethacryl amide functionalized perylene bisimide monomer was synthesized, in-situ free radical polymerization was then performed in the organized state to maintain the assembly structures.

Label-free DNA-based biosensors using structure-selective light-up dyes

Label-free biosensors (LFBs) have demonstrated great potential in cost-effective applications. This review collected the latest reported works which employed structure-selective nucleic acid dyes for the development of DNA-based LFBs.

Stitching of tyrosine and 10H-acridin-9-one: turn-ON fluorescence in the narrow pH range 7.4–8.5 and intracellular labelling of cancer cells

We tailored 10H-acridin-9-one and (S)-tyrosine into 3-(4-hydroxyphenyl)-2-[(9-oxo-9,10-dihydroacridine-4-carbonyl) amino]propionic acid (2).

Dual-emission fluorescent sensor based on AIE organic nanoparticles and Au nanoclusters for the detection of mercury and melamine

A novel dual-emission ratiometric fluorescence probe is designed and developed by linking two parts, positively charged aggregation-induced emission (AIE) organic fluorescence nanoparticles (OFNs) as the reference and negatively charged Au nanoclusters (Au NCs) as the response, by electrostatic attraction for the first time. This probe can be used for not only visual but quantitative determination of Hg(2+) as well as melamine, because red fluorescence of Au NCs can be quenched by mercury ions and recovered by melamine, due to the strong affinity metallophilic Hg(2+)-Au interaction and stronger affinity Hg(2+)-N. During this process, the green fluorescence of AIE-OFNs remains constant owing to the protection of ε-polylysine (ε-Ply). In addition, the prepared dual-emission ratiometric fluorescence probe has good biocompatibility, indicating the potential of the probe in applications of biological imaging and detection. The results revealed that this dual-emission ratiometric fluorescence probe broadens the application of AIE-based organic fluorescent nanoparticles, and presents a new method to prepare more sensitive, biocompatible, and visual ratiometric fluorescent probes.

Phosphorescent quantum dots/ethidium bromide nanohybrids based on photoinduced electron transfer for DNA detection

Mercaptopropionic acid-capped Mn-doped ZnS quantum dots/ethidium bromide (EB) nanohybrids were constructed for photoinduced electron transfer (PIET) and then used as a room-temperature phosphorescence (RTP) probe for DNA detection. EB could quench the RTP of Mn-doped ZnS QDs by PIET, thereby forming Mn-doped ZnS QDs/EB nanohybrids and storing RTP. Meanwhile, EB could be inserted into DNA and EB could be competitively desorbed from the surface of Mn-doped ZnS QDs by DNA, thereby releasing the RTP of Mn-doped ZnS QDs. Based on this mechanism, a RTP sensor for DNA detection was developed. Under optimal conditions, the detection limit for DNA was 0.045 mg L(-1), the relative standard deviation was 1.7%, and the method linear ranged from 0.2 to 20 mg L(-1). The proposed method was applied to biological fluids, in which satisfactory results were obtained.

Chemiluminescent labels released from long spacer arm-functionalized magnetic particles: a novel strategy for ultrasensitive and highly selective detection of pathogen infections

Previously, the unique advantages provided by chemiluminescence (CL) and magnetic particles (MPs) have resulted in the development of many useful nucleic acid detection methods. CL is highly sensitive, but when applied to MPs, its intensity is limited by the inner filter-like effect arising from excess dark MPs. Herein, we describe a modified strategy whereby CL labels are released from MPs to eliminate this negative effect. This approach relies on (1) the magnetic capture of target molecules on long spacer arm-functionalized magnetic particles (LSA-MPs), (2) the conjugation of streptavidin-alkaline phosphatase (SA-AP) to biotinylated amplicons of target pathogens, (3) the release of CL labels (specifically, AP tags), and (4) the detection of the released labels. CL labels were released from LSA-MPs through LSA ultrasonication or DNA enzymolysis, which proved to be the superior method. In contrast to conventional MPs, LSA-MPs exhibited significantly improved CL detection, because of the introduction of LSA, which was made of water-soluble carboxymethylated β-1,3-glucan. Detection of hepatitis B virus with this technique revealed a low detection limit of 50 fM, high selectivity, and excellent reproducibility. Thus, this approach may hold great potential for early stage clinical diagnosis of infectious diseases.

Label-free detection of Pb2+ based on aggregation-induced emission enhancement of Au-nanoclusters

The luminescence intensity of the glutathione capped Au-nanoclusters could be enhanced due to the formation of aggregates, and was employed for the visual detection of Pb²⁺.

Water-soluble nano-fluorogens fabricated by self-assembly of bolaamphiphiles bearing AIE moieties: towards application in cell imaging

Water-soluble nano-fluorogens with AIE properties are fabricated by self-assembly of a bolaamphiphile, and successfully applied in cell imaging.