A highly sensitive “turn-on” fluorescent probe for bovine serum albumin protein detection and quantification based on AIE-active distyrylanthracene derivative

Recent advances in AIEgen-based chemosensors for small molecule detection, with a focus on ion sensing

Since the aggregation-based emission (AIE) phenomenon emerged in 2001, numerous chemical designs have been built around the AIE concept, displaying its utility for diverse applications, including optics, electronics, energy, and biosciences. The present review critically evaluates the broad applicability of AIEgen-based chemical models towards sensing small analytes and the structural design strategies adjusting the mode of action reported since the last decade. Various AIEgen models have been discussed, providing qualitative and quantitative estimation of cationic metal ions and anionic species, as well as biomolecular, cellular, and organelle-specific probes. A systematic overview of the reported structural design and the underlying working mode will pave the way for designing and developing the next generation of AIEgens for specific applications.

Conjugated Aggregation-Induced Fluorescent Materials for Biofluorescent Probes: A Review

The common fluorescent conjugated materials present weak or quenching luminescent phenomena in the solid or aggregate state (ACQ), which limits their applications in medicine and biology. In the last two decades, certain materials, named aggregation-induced emission (AIE) fluorescent materials, have exhibited strong luminescent properties in the aggregate state, which can overcome the ACQ phenomenon. Due to their intrinsic properties, the AIE materials have been successfully used in biolabeling, where they can not only detect the species of ions and their concentrations in organisms, but can also monitor the organisms' physiological activity. In addition, these kinds of materials often present non-biological toxicity. Thus, AIE materials have become some of the most popular biofluorescent probe materials and are attracting more and more attention. This field is still in its early infancy, and several open challenges urgently need to be addressed, such as the materials' biocompatibility, metabolism, and so on. Designing a high-performance AIE material for biofluorescent probes is still challenging. In this review, based on the molecular design concept, various AIE materials with functional groups in the biofluorescent probes are introduced, including tetrastyrene materials, distilbene anthracene materials, triphenylamine materials, and hexaphenylsilole materials. In addition, according to the molecular system design strategy, the donor-acceptor (D-A) system and hydrogen-bonding AIE materials used as biofluorescent probes are reviewed. Finally, the biofluorescent probe design concept and potential evolution trends are discussed. The final goal is to outline a theoretical scaffold for the design of high-performance AIE biofluorescent probes that can at the same time further the development of the applications of AIE-based biofluorescent probes.

Liposomal OTS964, a TOPK inhibitor: a simple method to estimate OTS964 association with liposomes that relies on enhanced OTS964 fluorescence when bound to albumin

OTS964 is an inhibitor of T-lymphokine-activated killer cell-originated protein kinase (TOPK), a protein kinase important for mitosis and highly expressed in ovarian and lung cancers. This compound demonstrated potent anti-proliferative activity in a panel of cell lines positive for TOPK; however, when administered to mouse xenograft models, adverse hematopoietic toxicities were observed. To overcome this problem, OTS964 was encapsulated into liposomes and a liposomal formulation of OTS964 is now considered a lead candidate for clinical development. To support clinical development of this formulation, it is critically important to define assays that can easily distinguish between free and liposomal OTS964. Here, we develop a new assay to determine liposomal OTS964 encapsulation (percentage of drug associated with the liposomes) and OTS964 that is dissociated from the liposomes (percentage of drug released from liposomes) by monitoring the enhanced OTS964 fluorescence after its binding to albumin. The optical properties of OTS964 were investigated and three absorbance peaks were identified (235 nm, 291 nm, and 352 nm). Fluorescence was observed at 350 nm (excitation) and 470 nm (emission). Interestingly, the fluorescence of OTS964 increased 18-fold in the presence of serum proteins and more specifically albumin. This phenomenon was used to discriminate between the amounts of drug associated with the liposomes or released from the liposomes. Controls consisting of liposomal OTS964 permeabilized with saponins or octyl glucopyranoside served to confirm that drug release could be monitored by albumin-associated increases in fluorescence. The OTS964 liposomal formulation proved to be very stable with less than 10% release after 4 days in phosphate-buffered saline at 37 °C. The quantity of drug associated with the liposomal surface but not inside the liposomes could also be estimated using this approach. These studies present a novel approach to characterize liposomal release of OTS964, in real time and in a non-invasive manner while acquiring additional information about the spatial distribution of liposomal drug.

Polystyrene@poly(ar-vinylbenzyl)trimethylammonium-co-acrylic acid core/shell pH-responsive nanoparticles for active targeting and imaging of cancer cell based on aggregation induced emission

Doubly charged pH-responsive core/shell hydrogel nanoparticles with green fluorescence were prepared and were shown to be viable bioprobes for active targeting tumor tissue and imaging of cancer cells. Via emulsionfree copolymerization hydrogel nanoparticles as VANPs were prepared, the core of which was polystyrene (Ps) and the shell was comprised of strongly positive electrolyte (ar-vinylbenzyl)trimethylammonium (VBTAC) with weak negative electrolyte acrylic acid (AA). Through conventional amidation, the shell was conjugated with cell-specific folic acid (FA), denoted as VANPs-FA. Then, negatively charged sulfonated 9,10-distyrylanthracene derivatives (SDSA) based on aggregation induced emission (AIE), was binding tightly to positively charged VBTAC of VANPs-FA shell. The prepared double charged fluorescent core/shell hydrogel nanoparticles abbreviated as VANPs-FS, showed excitation/emission wavelengths at ~420/528 nm. Dynamic light scattering (DLS) measurements were performed to determine the size and surficial zeta potential of VANPs-FS. Under proper ratio of VBTAC to AA, the VANPs-FS was stable (~ 64.63 nm, -20.2 mV) at high pH (> 7), started to aggregate (~ 683.0 nm, -3.2 mV) at pH around 6, and can redispers at low pH (< 5). The MTT analysis proved that VANPs-FS had good biocompatibility and low cytotoxicity. The targeting effectiveness of VANPs-FS was confirmed by confocal laser scanning microscopy (CLSM). Graphical abstract Detailed synthetic route of VANPs-FS (top) and schematic cancer tumor-target aggregation of pH-sensitive VANPs-FS with enhanced retention and rapid cancer cell imaging (bottom).

A label-free aptasensor for turn-on fluorescent detection of ochratoxin A based on aggregation-induced emission probe

A novel label-free fluorescence aptasensor used for the detection of ochratoxin A (OTA) is presented in this study. When aggregated on the surface of DNA aptamer, aggregation-induced emission (AIE) fluorescence probe presents turn-on fluorescence property. The method proposed in this article was based on an AIE probe, 4, 4-(1E,1E)-2, 2-(anthracene-9, 10-diyl) bis (ethene-2, 1-diyl) bis (N, N, N-trimethylbenzenaminium iodide) (DSAI). With OTA present, the aptamer will combine with OTA and the conformation of the aptamer will switch to an antiparallel G-quadruplex from the initial random coil, which obstructs its digestion by Exo I. After the solution is added with DSAI, DSAI will aggregate on the surface of the aptamer/OTA complex and produces a strong emission. In the range of 5 to 500 ng · ml^-1 OTA concentrations, the fluorescence increases with a linear logarithm relationship. The detection limit is 1.9 ng · ml^-1. This method was used to detect OTA in spiked real samples, with recoveries and RSDs in the range of 92.2% to 106.3%, and 2.7% to 5.2%, respectively.

Specific and Quantitative Detection of Albumin in Biological Fluids by Tetrazolate-Functionalized Water-Soluble AIEgens

The analysis of albumin has clinical significance in diagnostic tests and obvious value to research studies on the albumin-mediated drug delivery and therapeutics. The present immunoassay, instrumental techniques, and colorimetric methods for albumin detection are either expensive, troublesome, or insensitive. Herein, a class of water-soluble tetrazolate-functionalized derivatives with aggregation-induced emission (AIE) characteristics is introduced as novel fluorescent probes for albumin detection. They can be selectively lighted up by site-specific binding with albumin. The resulting albumin fluorescent assay exhibits a low detection limit (0.21 nM), high robustness in aqueous buffer (pH = 6-9), and a broad tunable linear dynamic range (0.02-3000 mg/L) for quantification. The tetrazolate functionality endows the probes with a superior water solubility (>0.01 M) and a high binding affinity to albumin (K_D = 0.25 μM). To explore the detection mechanism, three unique polar binding sites on albumin are computationally identified, where the multivalent tetrazolate-lysine interactions contribute to the tight binding and restriction of the molecular motion of the AIE probes. The key role of lysine residues is verified by the detection of poly-l-lysine. Moreover, we applied the fluorogenic method to quantify urinary albumin in clinical samples and found it a feasible and practical strategy for albumin analysis in complex biological fluids.

A label-free fluorometric aptasensor for adenosine triphosphate (ATP) detection based on aggregation-induced emission probe

Based on Aggregation-Induced Emission (AIE), the development of a label-free, simple and sensitive fluorometric aptasensor for adenosine triphosphate (ATP) detection is described. With ATP present, the aptamers will combine with ATP and the conformation of the aptamer will switch from a random coil to an antiparallel G-quadruplex, which impedes the digestion by exonuclease I (Exo I). Addition of 4,4 -(1E,1E)-2,2-(anthracene-9,10-diyl) bis (ethene-2,1-diyl) bis (N,N, N-trimethyl-benzenaminium iodide) (DSAI) into the solution will cause aggregation of DSAI on the surface of the aptamer/ATP complex and consequently give rise to strong emission. Additionally, a good linear relationship was observed under optimized conditions between the fluorescence intensities and the logarithm of ATP concentrations (R² = 0.9908). The established aptamer sensor was highly sensitive and exhibited a low limit of detection of 32.8 nM, with superior specificity for ATP. It was also used in the quantification of ATP levels in human serum samples and demonstrated satisfactory recoveries in the scope of 93.2%-107.6%. The cellular ATP assay results indicated that the developed method can be used for monitoring ATP concentrations in cell extracts without the interference of other substances in the cells. This method offers several advantages such as simplicity, rapidity, low cost and excellent selectivity, which make it hold great potential for the detection of ATP in bioanalytical and biological studies.

A new approach to developing diagnostics and therapeutics: Aggregation-induced emission-based fluorescence turn-on

Fluorescence imaging is a promising visualization tool and possesses the advantages of in situ response and facile operation; thus, it is widely exploited for bioassays. However, traditional fluorophores suffer from concentration limits because they are always quenched when they aggregate, which impedes applications, especially for trace analysis and real-time monitoring. Recently, novel molecules with aggregation-induced emission (AIE) characteristics were developed to solve the problems encountered when using traditional organic dyes, because these new molecules exhibit weak or even no fluorescence when they are in free movement states but emit intensely upon the restriction of intramolecular motions. Inspired by the excellent performances of AIE molecules, a substantial number of AIE-based probes have been designed, synthesized, and applied to various fields to fulfill diverse detection tasks. According to numerous experiments, AIE probes are more practical than traditional fluorescent probes, especially when used in bioassays. To bridge bioimaging and materials engineering, this review provides a comprehensive understanding of the development of AIE bioprobes. It begins with a summary of mechanisms of the AIE phenomenon. Then, the strategies to realize accurate detection using AIE probes are discussed. In addition, typical examples of AIE-active materials applied in diagnosis, treatment, and nanocarrier tracking are presented. In addition, some challenges are put forward to inspire more ideas in the promising field of AIE-active materials.

Robust organic nanoparticles for noninvasive long-term fluorescence imaging

Organic nanoparticles obtained from fluorophores with aggregation-caused quenching and aggregation-induced emission features for noninvasive long-term bioimaging are summarized and highlighted.

Microwave-assisted facile synthesis of poly(luminol-co-phenylenediamine) copolymers and their potential application in biomedical imaging

Conjugated copolymers have attracted much attention because of their outstanding photo-physical properties. The present work reports for the first time, microwave-assisted copolymerization of o-phenylenediamine with luminol using different weight ratios of the two monomers. The composition of the copolymers was confirmed by Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance spectroscopy (¹H-NMR) while monomer reactivity ratios were determined using the Fineman–Ross method. Ultraviolet-visible spectroscopy revealed the variation in polaronic states upon copolymerization while X-ray diffraction (XRD) and transmission electron microscopy (TEM) analyses showed the morphology of the copolymers to be intermediate between that of the homopolymers. Confocal analysis and fluorescence studies revealed that the copolymers showed composition based blue as well as red emission which could be utilized for in vivo imaging of cancer cells.

Development of bioimaging agents based on poly(o-phenylendiamine and luminol).

Ultrasonic-assisted Kabachnik-Fields reaction for rapid fabrication of AIE-active fluorescent organic nanoparticles

Aggregation-induced emission (AIE)-active fluorescent organic nanoparticles (FNPs) have been extensively explored for fluorescence "turn-on" bio-imaging applications with the unique advantages over conventional FNPs. Transformation of AIE-active molecules into FNPs can greatly expand their biomedical application potential. Here we reported a novel "one-pot" strategy for fabricating AIE-active FNPs through an ultrasonic-assisted, catalysts-free and solvent-free Kabachnik-Fields (KF) reaction for the first time. The KF reaction can be completed within 10min to generate AIE-active PTH-CHO-PEI-DEP FNPs through mixing polyethylenimine and aldehyde group containing AIE dyes and diethyl phosphate. These PTH-CHO-PEI-DEP FNPs were confirmed by proton nuclear magnetic resonance (¹H NMR) spectroscopy, transmission electron microscopy (TEM) and fluorescence spectroscopy etc. The cell uptake behavior as well as cell viability of PTH-CHO-PEI-DEP FNPs was examined to evaluate their potential for biomedical application. We demonstrated that the amphiphilic α-aminophosphonate polymers could self-assemble into PTH-CHO-PEI-DEP FNPs in aqueous solution and showed excellent water dispersibility. TEM image shows the size of PTH-CHO-PEI-DEP FNPs is 100-200nm. More importantly, the PTH-CHO-PEI-DEP FNPs emit strong green fluorescence and desirable biocompatibility, making them very suitable for biomedical applications. Finally, thus smart FNPs design together with their excellent performance will open a new avenue in the development of FNPs for following biological processes such as carcinogenesis.

Marrying multicomponent reactions and aggregation-induced emission (AIE): new directions for fluorescent nanoprobes

Recent development and progress for fabrication and applications of aggregation-induced emission polymers through multicomponent reactions have been summarized in this review.

Fabrication of water dispersible and biocompatible AIE-active fluorescent polymeric nanoparticles through a “one-pot” Mannich reaction

Biocompatible and water dispersible fluorescent polymeric nanoparticles with an aggregation-induced emission feature were fabricated through a facile “one-pot” Mannich reaction and utilized for biological imaging applications.

Tunable Supramolecular Interactions of Aggregation-Induced Emission Probe and Graphene Oxide with Biomolecules: An Approach toward Ultrasensitive Label-Free and "Turn-On" DNA Sensing

Aggregation-induced emission (AIE) probes have shown great potential applications in fluorescent sensing of biomolecules, and the integration of AIE probe and graphene oxide (GO) attracts intense interest in developing new tools for label-free and "turn-on" fluorescent biomolecular analysis. Herein, an ultrasensitive label-free and "turn-on" DNA sensing is realized by tuning the supramolecular interactions of AIE probe and GO with DNA. The investigation of supramolecular interactions of AIE probes and GO with DNA demonstrate that AIE probe with short alkyl chains substitute shows highest binding affinity with DNA strand, and GO with low oxidation degree possesses strong binding interactions to ssDNA and the highest fluorescence quenching efficiency. As a result, the optimized AIE probes and GO-based fluorescent sensor can selectively detect the target DNA sequence and exhibits the detection limitation as low as 0.17 × 10^-9 m. It is believed that the research efforts will provide an efficient approach to improve the performance of DNA sensing assay and an indepth understanding of the supramolecular interactions of AIE probes and GO with DNA, and thus facilitate their extended applications in biosensors and biomedicine.

Solvatochromic fluorescent probes for recognition of human serum albumin in aqueous solution: Insights into structure-property relationship

Human serum albumin (HSA) as the most abundant protein in human blood plasma, serves many physiological functions. The dysregulation of HSA in serum or in urine is associated with various diseases, such as cirrhosis of liver, multiple myeloma, and cardiovascular disease. Therefore, to quantify HSA in body fluids with high selectivity and sensitivity is of great significance for disease diagnosis and preventive medicine. We herein developed a series of amide-functionalized flavonoids probes, 1-3, for recognition of human serum albumin. All flavonoids could be easily prepared by a Claisen-Schmidt condensation and Algar-Flynn-Oyamada reaction, and showed positive solvatochromism on their dual emissions. The chemical structure of flavonoids played an important role on their HSA-sensing abilities. Among three probes, the compound 1 showed the highest sensitivity, the remarkable selectivity, and the quantitive response for HSA in aqueous solution. Together with its high tolerance of environmental pH, anti-interference properties, and time-insensitivity, thus it provides a promising sensing method for HSA.

The analytical and biomedical potential of cytosine-rich oligonucleotides: A review

Polycytosine DNA strands are often found among natural sequences, including the ends of telomeres, centromeres, and introns or in the regulatory regions of genes. A characteristic feature of oligonucleotides that are rich in cytosine (C-rich) is their ability to associate under acidic conditions to form a tetraplex i-motif consisting of two parallel stranded cytosine-hemiprotonated cytosine (C·C+) base-paired duplexes that are mutually intercalated in an antiparallel orientation. Nanotechnology has been exploiting the advantages of i-motif pH-dependent formation to fabricate nanomachines, nanoswitches, electrodes and intelligent nanosurfaces or nanomaterials. Although a few reviews regarding the structure, properties and applications of i-motifs have been published, this review focuses on recently developed biosensors (e.g., to detect pH, glucose or silver ions) and drug-delivery biomaterials. Furthermore, we have included examples of sensors based on parallel C-rich triplexes and silver nanoclusters (AgNCs) fabricated on cytosine-rich DNA strands. The potential diagnostic and therapeutic applications of this type of material are discussed.

A step toward simplified detection of serum albumin on SDS-PAGE using an environment-sensitive flavone sensor

In this study, we report a series of novel flavone-based sensors that exhibit a superior fluorescence response when interacting with serum albumin in real serum samples and in acrylamide gels. The detection limit of probe 4 for serum albumin solution is 0.09 μg mL(-1), and the detectable volume for monkey serum reaches as low as 0.03 μL.

A rapid-response fluorescent probe for the sensitive and selective detection of human albumin in plasma and cell culture supernatants

A rapid-response fluorescent probeACDMwas developed for selective and sensitive detection of human albumin (HA)viabinding on a non-drug binding site.

Quantitation of Albumin in Serum Using "Turn-on" Fluorescent Probe with Aggregation-Enhanced Emission Characteristics

An aggregation-enhanced emission active luminogen named as sodium 4,4'4″-(3,4-diphenyl-1H-pyrrole-1,2,5-triyl)tribenzoate (DP-TPPNa) with propeller construction was synthesized and developed as a "turn on" fluorescent probe for in situ quantitation of albumin in blood serum. The DP-TPPNa fluorescence intensity was linearly correlated with the concentration of two serum albumins, bovine serum albumin (BSA) and human serum albumin (HSA), in pure PBS buffer in the ranges of 2.18-70 and 1.68-100 μg/mL, respectively. The detection limits were as low as 2.18 μg/mL for BSA and 1.68 μg/mL for HSA. The response time of fluorescence to serum albumin (SA) was very short (below 6 s), which achieved real-time detection. It also showed high selectivity to SA because other components in serum barely interfere with the detection of DP-TPPNa to SA, enabling in situ quantitative detection of SA without isolation from serum. DP-TPPNa was successfully applied for the quantitative detection of BSA in fetal bovine serum. The mechanism of fluorescent turn-on behavior was elucidated utilizing an unfolding process induced by guanidine hydrochloride, which revealed a capture process via selective hydrophobic interaction and hydrogen bonding between luminogen and SA.

Polymeric AIE-based nanoprobes for biomedical applications: recent advances and perspectives

The development of polymeric luminescent nanomaterials for biomedical applications has recently attracted a large amount of attention due to the remarkable advantages of these materials compared with small organic dyes and fluorescent inorganic nanomaterials. Among these polymeric luminescent nanomaterials, polymeric luminescent nanomaterials based on dyes with aggregation-induced emission (AIE) properties should be of great research interest due to their unique AIE properties, the designability of polymers and their multifunctional potential. In this review, the recent advances in the design and biomedical applications of polymeric luminescent nanomaterials based on AIE dyes is summarized. Various design strategies for incorporation of these AIE dyes into polymeric systems are included. The potential biomedical applications such as biological imaging, and use in biological sensors and theranostic systems of these polymeric AIE-based nanomaterials have also been highlighted. We trust this review will attract significant interest from scientists from different research fields in chemistry, materials, biology and interdisciplinary areas.

Turn-on sensing for Ag+ based on AIE-active fluorescent probe and cytosine-rich DNA

An aggregation-induced-emission (AIE)-active molecule, 4,4'-(1E,1'E)-2,2'-(anthracene-9,10-diyl) bis (ethene-2,1-diyl) bis (N,N,N-trimethylbenzenaminium iodide) (DSAI), used as a label-free and turn-on fluorescent probe, was developed for Ag(+) sensing. The cytosine-rich DNA (oligo-C) chosen as a base could be induced to form a hairpin structure in the presence of Ag(+). To improve the sensitivity of Ag(+) detection, we selected nuclease S1 to reduce the fluorescence intensity of DSAI via its strong ability to hydrolyze oligo-C. In the solution containing oligo-C, DSAI, and nuclease S1, in the absence of Ag(+), oligo-C was broken into fragments by nuclease S1; this meant DSAI could not aggregate, leading to non-emission of the solution. In the presence of Ag(+), oligo-C was induced to form a hairpin structure via the C-Ag(+)-C base pair and DSAI could aggregate on the surface of the hairpin structure to produce a strong emission. On increasing the amount of Ag(+) in the solution containing oligo-C, DSAI, and nuclease S1, the fluorescence intensity of DSAI gradually increased, and the highest intensity was nearly 16-fold higher than the original intensity. The detection limit at a signal-to-noise ratio (S/N) of 3 was estimated to be 155 nmol L(-1). The new sensing method provides simplicity, easy operation, and good sensitivity and selectivity for Ag(+) detection.

N-type pyrazine and triazole-based luminogens with aggregation-enhanced emission characteristics

N-type pyrazine and triazole-based AIEgens that could readily form red-emissive complexes with triphenylamine in the aggregate state were facilely prepared by click reactions.

Folic acid-functionalized AIE Pdots based on amphiphilic PCL-b-PEG for targeted cell imaging

Folic acid-functionalized polymer dots with aggregation induced emission features (AIE Pdots), which show high fluorescence efficiency and little toxicity to living cells, which possess a good capability for targeted HeLa intracellular imaging.