Construction of AIEgens-Based Bioprobe with Two Fluorescent Signals for Enhanced Monitor of Extracellular and Intracellular Telomerase Activity

Uncovering the Interaction between Intracellular Telomerase Activity and Hydrogen Peroxide during Cancer Cell Apoptosis Utilizing a Dual-Color Fluorescent Nanoprobe

Uncovering the intrinsic interaction of different bioactive species, i.e., reactive oxygen species (ROS) and telomerase, is of great importance because they play interrelated and interdependent biological roles in living organisms. Nevertheless, exploration of the intracellular ROS/telomerase cross-talk by effective and noninvasive methods remains a great challenge, as it is difficult to simultaneously detect different types of biomolecules (i.e., active small molecules and proteins) in living cells. To address this issue, herein, we report, for the first time, a novel fluorescent nanoprobe for simultaneous determination and in situ imaging of telomerase activity and hydrogen peroxide (H₂O₂) in living cells. With the advantage of high sensitivity and good specificity, this newly fabricated nanoprobe was successfully applied to precisely visualize and monitor the changes in telomerase activity and H₂O₂ concentration in cancer cells. More significantly, by employing the nanoprobe as a one-step incubation tool, it is found that there is a cross-talk between H₂O₂ and telomerase activity in the drug-induced cancer cells' apoptosis process, which provides valuable information for gaining fundamental insights into the relationship between ROS and telomerase activity in cancer treatments. This work affords a promising method for revealing the relevant regulatory mechanisms and roles of ROS and telomerase activity in the occurrence, evolvement, and treatment of diseases.

DNA-Based Nanoprobes for Simultaneous Detection of Telomerase and Correlated Biomolecules

Telomerase (TE), a ribonucleoprotein reverse transcriptase, is enzymatically activated in most tumor cells and is responsible for promoting tumor progression and malignancy by enabling replicative immortality of cancer cells. TE has become an important hallmark for cancer diagnosis and a potential therapy target. Therefore, accurate and in site detection of TE activity, especially the simultaneous imaging of TE activity and its correlated biomolecules, is highly essential to medical diagnostics and therapeutics. DNA-based nanoprobes, with their effective cell penetration capability and programmability, are the most advantageous for detection of intracellular TE activity. This concept article introduces the recent strategies for in situ sensing and imaging of TE activity, with a focus on simultaneous detection of TE and related biomolecules, and provides challenges and perspectives for the development of new strategies for such correlated imaging.

Precisely Detecting the Telomerase Activities by an AIEgen Probe with Dual Signal Outputs after Cell-Cycle Synchronization

By maintaining the telomere lengths, telomerase can make the tumor cells avoid the apoptosis, thus, achieving the cell immortalization. In the past, a series of telomerase detection systems have been developed through utilizing the unique characteristic of telomerase extended primer. However, fluctuation of telomerase activity, along with the cell cycle progression, leads to ambiguous detection results. Here, we reported a dual signal output detection strategy based on cell-cycle synchronization for precisely detecting telomerase activities by using a new AIEgen probe SSNB. Experimental and simulating calculation results demonstrated that positively charged SSNB could interact with DNA through the electrostatic interaction and π-π interaction, as well as the hydrogen bonds. The aggregation of SSNB caused by the extended template strand primer (TP) could be observed in tumor cells, thus, indicating the telomerase activity in various cell lines. Furthermore, after cell cycle synchronization, it was found that the telomerase activity in the S phase was the highest, no matter from the fluorescence intensity or the ROS generation situation. Dual signal outputs of SSNB verified the significance and necessity of cell-cycle synchronization detection for telomerase activity. This strategy could open a new window for the biotargets of which activity is variational in time dimension.

AIE materials for cancer cell detection, bioimaging and theranostics

AIE materials exhibit weakly emissive or non-emissive properties in dilute solutions while emit powerful fluorescence in the aggregated/solid state. Recently, AIE based materials have gained immense attention due to their multifunctional role in cancer cell detection, bioimaging and cancer theranostics. In this present book chapter, we will highlight recent advancements of AIE materials for different cancer theranostics applications.

Sensitive osteosarcoma diagnosis through five-base telomerase product-triggered CRISPR-Cas12a enhanced rolling circle amplification

Osteosarcoma is the most frequent primary malignant bone tumor, composed of mesenchymal cells producing osteoid and immature bone. The sensitive detection of telomerase plays a pivotal role in the early diagnosis and therapeutic treatment of osteosarcoma. We report here an in vitro strategy for sensitive telomerase activity detection through the integration of rolling circle amplification (RCA) and a clustered regularly spaced short palindrome repeats (CRISPR)-Cas12a system. In the proposed strategy, telomerase substrate (TS) primers are easily controlled to extend five bases (GGGTT) to give short telomerase extension products (TEP) with definite lengths without adding dATP. The resulting short TEPs can then cyclize the padlock through hybridizing with its two terminals and thus initiate the following RCA. To obtain an improved sensitivity, the CRISPR-Cas12a system is attached to collaterally cut surrounding DNA reporter probes after recognizing the target single strand DNA sequence in the RCA products. The highlights of this strategy are as follows: (i) the short TEP triggered strategy is excellent at detecting low telomerase activity and thus contributes to the early diagnosis of malignant tumors; (ii) highly sensitive telomerase activity detection which is easy to operate from RCA initiated CRISPR-Cas12a; (iii) opening up of a new avenue for telomerase activity detection with a CRISPR-Cas12a system. Finally, the proposed strategy exhibited sensitive telomerase activity detection under optimized experimental parameters and has great application potential for the clinical diagnosis of malignant tumors and the development of anti-cancer drugs.

A multicolor DNA tetrahedron nanoprobe for analyzing human telomerase in living cells

Herein, we report the in situ analysis of human telomerase by a multicolor DNA tetrahedron nanoprobe. The elongated telomeric repeats can hybridize with settled molecular beacons in order, accompanied by sequentially lighted up fluorescence. Imaging telomerase activity, real-time monitoring telomerase action and determining product length distribution in living cells are realized. It detects multiple information of intracellular telomerase and provides deeper insights into the function of telomerase.

Label-free and enzyme-free fluorescence detection of microRNA based on sulfydryl-functionalized carbon dots via target-initiated hemin/G-quadruplex-catalyzed oxidation

Carbon dots (CDs)-based biosensors have attracted considerable interest in reliable and sensitive detection of microRNA (miRNA) because of their merits of ultra-small size, excellent biosafety and tunable emission, whereas complicated labeling procedure and expensive bioenzyme associated with current strategies significantly limit their practical application. Herein, we developed a label-free and enzyme-free fluorescence strategy based on strand displaced amplification (SDA) for highly sensitive detection of miRNA using sulfydryl-functionalized CDs (CDs-SH) as probe. CDs-SH displayed excellent response to G-quadruplex DNA against other DNAs based on based on the catalytic oxidation of -SH into -S-S- by hemin/G-quadruplex. Further, CDs-SH were employed to detect miRNA, using miRNA-21 as target model, which triggered the SDA reaction of P1 and P2 to generate hemin/G-quadruplex, subsequently making CDs-SH transform from dot to aggresome along with the quenched fluorescence. Therefore, label-free, enzyme-free, and highly sensitive analysis of miRNA-21 was readily acquired with a limit of detection at 0.03 pM. This proposed biosensor couples the advantages of CDs and label-free/enzyme-free strategy, and thus has a significant potential to be used in early and accurate diagnosis of cancer.

Carbon Nanocage/Fe3O4/DNA-Based Magnetically Targeted Intracellular Imaging of Telomerase via Catalyzed Hairpin Assembly and Photodynamic-Photothermal Combination Therapy of Tumor Cells

Human telomerase has been identified as a potential tumor biomarker for early cancer diagnosis and cancer progression monitoring. We construct a novel magnetic targeting carbon nanocage/Fe₃O₄/DNA (CNC/Fe₃O₄/DNA) nanoprobe for intracellular imaging of telomerase via the signal amplification strategy catalyzed hairpin assembly (CHA) and for photodynamic-photothermal therapy of tumor cells. Telomerase primer DNA, trigger DNA, hairpin DNA1 (H1), and hairpin DNA2 (H2) were adsorbed to the surface of CNC/Fe₃O₄ nanoparticles (CNC/Fe₃O₄ NPs), and the fluorescence of (chlorin e6) Ce6 was quenched by CNC/Fe₃O₄ NPs. After entering the living cell through magnetic targeting, the telomerase primer DNA can be extended in the presence of highly activated telomerase, leading to the issue of trigger DNA, which can initiate the CHA cycling process followed by the amplification of the fluorescence intensity. The in vitro detection results justified that the proposed nanoprobe showed good sensitivity and selectivity for telomerase. Confocal microscopy studies indicated that such a nanoprobe can be used to detect the activity of telomerase in living cells and the fluorescence signal was stronger under the guidance of a magnetic field. We successfully employed this nanoprobe to monitor the dynamic activity of telomerase in various types of tumor cells and normal cells and to damage tumor cells by photodynamic-photothermal combination therapy, which evidenced that this is a promising biological method for early cancer diagnosis and tumor cell therapy.

Functional Self-Assembled DNA Nanohydrogels for Specific Telomerase Activity Imaging and Telomerase-Activated Antitumor Gene Therapy

Engineering a functional nanoplatform that integrates dynamic monitoring of endogenous biomarkers and a stimuli-activated therapeutic mode is promising for early diagnosis and treatment of cancers. In this study, we developed an intelligent DNA nanohydrogel with specific targeting capability that can be stimuli-activated for both in vitro telomerase detection and in vivo telomerase-triggered gene therapy. The DNA nanohydrogel was formed simply by the self-assembly of two Y-shaped DNA units and a double-stranded DNA linker labeled with fluorophores and loaded with therapeutic siRNA. When intracellular telomerase was overexpressed, the DNA nanohydrogel collapsed owing to the prolongation of the telomeric primer at the terminal sequence of one of the Y-shaped DNA units. As a result, the quenched fluorescence due to fluorescence resonance energy transfer (FRET) of the DNA nanohydrogel recovered and the trapped siRNA was released, enabling the accurate detection and imaging of intracellular telomerase activity as well as effective gene therapy of tumors. Benefiting from the great biocompatibility, specificity, and stimuli-responsive property, the developed DNA nanoplatform provides a new opportunity for precise cancer diagnosis and treatment as well as other biological applications.

Catalytic Asymmetric trans-Selective Hydrosilylation of Bisalkynes to Access AIE and CPL-Active Silicon-Stereogenic Benzosiloles

Chirality widely exists in a diverse array of biologically active molecules and life forms, and the catalytic constructions of chiral molecules have triggered a heightened interest in the fields of chemistry and materials and pharmaceutical sciences. However, the synthesis of silicon-stereogenic organosilicon compounds is generally recognized as a much more difficult task than that of carbon-stereogenic centers because of no abundant organosilicon-based chiral sources in nature. Herein, we reported a highly enantioselective rhodium-catalyzed trans-selective hydrosilylation of silicon-tethered bisalkynes to access chiral benzosiloles bearing a silicon-stereogenic center. This protocol featured with chiral Ar-BINMOL-Phos bearing hydrogen-bond donors as a privileged P-ligand for catalytic asymmetric hydrosilylation that is operationally simple and has 100% atom-economy with good functional group tolerability as well as high enantioselectivity (up to >99:1 er). Benefiting from the trans-selective hydrosilylation with the aid of Rh/Ar-BINMOL-Phos-based asymmetric catalysis, the Si-stereogenic benzosiloles exhibited pronounced aggregation-induced emission (AIE) and circularly polarized luminescence (CPL) activity.

Target-Driven Nanozyme Growth in TiO2 Nanochannels for Improving Selectivity in Electrochemical Biosensing

Nanozymes have been used in colorimetric and electrochemical sensing because of their low cost and high stability. However, the wide applications of nanozymes in sensing devices are largely limited due to their poor selectivity. In this study, unlike traditional methods using prepared nanozymes for target detection, we designed a target-driven nanozyme growth strategy in TiO₂ nanochannels to detect analytes. Using telomerase as an example, the established recognition event was used to expand the photocatalytic activity of TiO₂ to visible-light region, thus triggering Prussian blue nanoparticle (PBNP) growth in visible light. Benefiting from the peroxidase (POD)-like activity of PBNPs, the uncharged 3,5,3',5'-tetramethylbenzidine (TMB) is oxidized to positively charged oxTMB, which induces significant ionic transport changes in nanochannels, and thus in turn provides information about telomerase activity. Such a nanozyme-triggered sensing system exhibited excellent performance in telomerase detection in urine specimens from patients with bladder cancer. This innovative target-driven signal generation strategy might provide a new method for applying nanozymes in developing sensitive, rapid, and accurate biological sensing systems.

Magnetic bead-enzyme assemble for triple-parameter telomerase detection at single-cell level

In this work, we developed a triple-parameter strategy for the detection of telomerase activity from cancer cells and urine samples. This strategy was developed based on magnetic bead-enzyme hybrids combined with fluorescence analysis, colorimetric assay, or adenosine triphosphate (ATP) meter as readout. The application of magnetic bead-enzyme hybrids has the advantages of magnetic separation and signal amplification. These detection methods can be used individually or in combination to achieve the optimal sensing performance and make the results more convincing. Among them, the ATP meter with portable size had easy operation and low cost, and this response strategy provided a higher sensitivity at the single-cell level. The designed strategy was suitable as naked-eye sensor and point-of-care testing (POCT) for rapid assaying of telomerase activity. Graphical abstract Magnetic bead-enzyme assemble for triple-parameter telomerase detection.

Live-Cell Sensing of Telomerase Activity by Using Hybridization-Sensitive Fluorescent Oligonucleotide Probes

Live-cell sensing of telomerase activity with simple and efficient strategies remains a challenging target. In this work, a strategy for telomerase sensing by using hybridization-sensitive fluorescent oligonucleotide probes is reported. In the presence of telomerase and dNTPs, the designed supporting strand was extended and generated the hairpin structure that catalyzed the next telomerase extending reaction. The special extension mechanism increased the local concentration of another supporting strand and telomerase, which resulted in enhanced telomerase activity. The hybridization-sensitive oligonucleotide probes bound to the hairpin catalyst and generated turn-on fluorescence. This method realized the sensing of telomerase activity in HeLa cell extract with a detection limit below 1.6×10^-6  IU μL^-1 . The real-time in situ observation of telomerase extension was achieved in living HeLa cells. This strategy has been applied to monitor the efficiency of telomerase-targeting anticancer drugs in situ.

Strategies for Tumor Hypoxia Imaging Based on Aggregation-Induced Emission Fluorogens

Hypoxia, as a crucial characteristic of cancer, has become an extremely significant direction for researchers to construct fluorescent probes for early diagnosis of tumors. Aggregation-induced emission fluorogens (AIEgens) possess many superior properties to those of conventional fluorophores due to aggregation-induced emission (AIE) features, such as a linear concentration-dependent increase in brightness, remarkable resistance to photobleaching, and the long-term tracking and imaging of cells. Constructing hypoxic response AIEgen-based probes will be very useful for the early diagnosis of tumors. Herein, several hypoxia-responsive probes based on AIEgens reported in the last three years are reported; these examples may lead to the construction of hypoxia-responsive AIE probes used for tumor hypoxia imaging in the future. In addition, typical, conventional hypoxia-responsive bioprobes are presented to further understand hypoxia-responsive fluorescent probes based on AIEgens.

Modular Design of Peptide- or DNA-Modified AIEgen Probes for Biosensing Applications

Fluorophore probes are widely used for bioimaging in cells, tissues, and animals as well as for monitoring of multiple biological processes in complex environments. Such imaging properties allow scientists to make direct visualizations of pathological events and cellular targets. Conventional fluorescent molecules have been developed for several decades and achieved great successes, but their emissions are often weakened or quenched at high concentrations that might suffer from the aggregation-caused quenching (ACQ) effect, which reduces the efficiencies of their applications. In contrast to the ACQ effect, aggregation-induced emission (AIE) luminogens (AIEgens) display much higher fluorescence in aggregated states and possess various advantages such as low background, long-term tracking ability, and strong resistance to photobleaching. Therefore, AIEgens are employed as unique fluorescence molecules and building blocks for biosensing applications in the fields of ions, amino acids, carbohydrates, DNAs/RNAs, peptides/proteins, cellular organelles, cancer cells, bacteria, and so on. Quite a few of the above biosensing missions are accomplished by modular peptide-modified AIEgen probes (MPAPs) or modular DNA-modified AIEgen probes (MDAPs) because of the multiple capabilities of peptide and DNA modules, including solubility, biocompatibility, and recognition. Meanwhile, both electrostatic interactions and coupling reactions could provide efficient methods to construct different MPAPs and MDAPs, finally resulting in a large variety of biosensing probes. Those probes exhibit leading features of detecting nucleic acids or proteins and imaging mass biomolecules. For example, under modular design, peptide modules possessing versatile recognition abilities enable MPAPs to detect numerous targets, such as integrin α_vβ₃, aminopeptidase N, MMP-2, MPO, H₂O₂, and so forth; MDAP could allow the imaging of mRNA in cells and tissue chips, suggesting the diagnostic functions of MDAP in clinical samples. Modular design offers a novel strategy to generate AIEgen-based probes and expedites functional biomacromolecules research. In this vein, here we review the progress on MPAPs and MDAPs in the most recent 10 years and highlight the modular design strategy as well as their advanced biosensing applications including briefly two aspects: (1) detection and (2) imaging. By the use of MPAPs/MDAPs, multiple bioanalytes can be efficiently analyzed at low concentrations and directly visualized through high-contrast and luminous imaging. Compared with MPAPs, the quantities of MDAPs are limited because of the difficult synthesis of long-length DNA strands. In future work, multifunctional of DNA sequences are needed to explore varieties of MDAPs for diverse biosensing purposes. At the end of this Account, some deficiencies and challenges are mentioned for briging more attention to accelerate the development of AIEgen-based probes.

Label-Free Telomerase Activity Detection via Electrochemical Impedance Spectroscopy

In the last decade, researchers have been searching for innovative platforms, methods, and techniques able to address recurring problems with the current cancer detection methods. Early disease detection, fast results, point-of-care sensing, and cost are among the most prevalent issues that need further exploration in this field. Herein, studies are focused on overcoming these problems by developing an electrochemical device able to detect telomerase as a cancer biomarker. Electrochemical platforms and techniques are more appealing for cancer detection, offering lower costs than the established cancer detection methods, high sensitivity inherent to the technique, rapid signal processing, and their capacity of being miniaturized. Therefore, Au interdigital electrodes and electrochemical impedance spectroscopy were used to detect telomerase activity in acute T cell leukemia. Different cancer cell concentrations were evaluated, and a detection limit of 1.9 × 10⁵ cells/mL was obtained. X-ray photoelectron spectroscopy was used to characterize the telomerase substrate (TS) DNA probe self-assembled monolayer on gold electrode surfaces. Atomic force microscopy displayed three-dimensional images of the surface to establish a height difference of 9.0 nm between the bare electrode and TS-modified Au electrodes. The TS probe is rich in guanines, thus forming secondary structures known as G-quadruplex that can be triggered with a fluorescence probe. Confocal microscopy fluorescence images showed the formation of DNA G-quadruplex because of TS elongation by telomerase on the Au electrode surface. Moreover, electrodes exposed to telomerase containing 2',3'-dideoxyguanosine-5'-triphosphate (ddGTP) did not exhibit high fluorescence, as ddGTP is a telomerase inhibitor, thus making this device suitable for telomerase inhibitors capacity studies. The electrochemical method and Au microchip device may be developed as a biosensor for a point-of-care medical device.

Controlled assembly of AIEgens based on a super-quadruplex scaffold for detection of plasma membrane proteins

Quantification of plasma membrane proteins (PMPs) is crucial for understanding the fundamentals of cellular signaling systems and their related diseases. In this work, a super-quadruplex scaffold was designed to regulate assembly of oligonucleotide-grafted AIEgens for detection of PMPs. The nonfluorescence oligonucleotide-grafted AIEgen (Oligo-AIEgen) was firstly synthesized by attaching the AIEgen to 3'-terminus of the oligonucleotide through click chemistry. Meanwhile, the tetramolecular hairpin-conjugated super-quadruplex (THP-G4) as cleavage element and signal enhancement scaffold composited of three elements: a substrate sequence of DNAzyme in the loop region, partial hybridization region in the stem, and six guanine nucleotides to form G-quadruplex. Once the DNAzyme was anchored on the specific PMPs through aptamer-protein recognition, the substrate sequence on the loop of THP-G4 was cleaved by DNAzyme with the aid of cofactor Mn^II, resulting in the conformation switch of THP-G4 to the activated G-quadruplex scaffold. The latter could assemble Oligo-AIEgens to generate aggregation-induced emission (AIE) enhancement, resulting in a simple and sensitive strategy for detection of membrane proteins. Moreover, the DNAzyme continuously cut the next THP-G4 to achieve recycling amplification. Under the optimized conditions, this AIE-based strategy exhibited good linear relationship with the logarithm of MUC1 concentration from 0.01 to 10 μg mL^-1 with the limit of detection down to 4.3 ng mL^-1. The G4-assembled AIEgens provides a universal platform for detecting various biomolecules and a proof-of concept for AIE biosensing.

A seesaw ratiometric probe for dual-spectrum imaging and detection of telomerase activity in single living cells

Herein, a seesaw ratiometric (SR) probe is designed which integrates fluorescence and surface enhanced Raman scattering (SERS) technology. Fluorescence imaging enables tracking of the spatiotemporal dynamic behaviour of telomerase. Meanwhile, SERS reverse ratiometric measurement can enable sensitive detection of telomerase activity in single living cells.

Biomacromolecule-Functionalized AIEgens for Advanced Biomedical Studies

The advances in bioinformatics and biomedicine have promoted the development of biomedical imaging and theranostic systems to respectively extend the endogenous biomarker imaging with high contrast and enhance the therapeutic effect with high efficiency. The emergence of biomacromolecule-functionalized aggregation-induced emitters (AIEgens), utilizing AIEgens, and biomacromolecules (nucleic acids, peptides, glycans, and lipids), displays specific targeting ability to cancer cell, improved biocompatibility, reduced toxicity, enhanced therapeutic effect, and so forth. This review summarizes the rational design of biomacromolecule-functionalized AIEgens and their biomedical applications in recent ten years, including high-resolution optical imaging of cell, tissue, and small animal model with low background; the biomarker detection for early diagnosis and prognosis; the delivery and monitoring of prodrugs; image-guide photodynamic therapy and its combination with chemotherapy. Through illustrating their functional mechanisms and application, it is hoped that this review would open up a completely new train of research thought for attracted researchers in various fields.

Label-Free Telomerase Detection in Single Cell Using a Five-Base Telomerase Product-Triggered Exponential Rolling Circle Amplification Strategy

Telomerase is a universal biomarker of malignant tumors. Sensitive and reliable analysis for telomerase activity is of vital importance for both early diagnosis and therapy of malignant tumors. Herein, a novel fluorescent strategy was proposed for sensitive and label-free detection of telomerase activity. One highlight of this strategy is that an exponential signal amplification can be triggered by a very short telomerase extension product (TEP). Without adding dATP, the designed telomerase primer can be easily controlled to extend five bases (GGGTT) to give short TEP with definite length. The resulting short TEP can then be constructed as a circular rolling circle amplification (RCA) template and thus initiate a nicking enzyme-mediated exponential RCA, producing G-rich amplification products that can be sensitively probed via specific binding between the fluorescent dye Thioflavin T (ThT) and the nucleic acid G-quadruplexes. Elevated telomerase translocation efficiency, combined with exponential signal amplification and specific probing of RCA products by ThT, endow the sensing platform with extraordinarily high detection sensitivity. The requirement for short TEP increases the possibility to analyze telomerase with low activity. The proposed sensing platform can achieve sensitive telomerase activity detection in individual cells, even with the interference of accumulated normal cells. It was also demonstrated to show excellent capability in screening for the inhibitors of telomerase. Therefore, the proposed sensing platform has great potential for not only clinical diagnosis but also anticancer drug development.

Strand displacement amplification-coupled dynamic light scattering method to detect urinary telomerase for non-invasive detection of bladder cancer

Despite huge successes achieved by strand displacement amplification (SDA) and gold nanoparticles (AuNPs) in biomolecules sensing, the strategy of combination of SDA and AuNPs-based dynamic light scattering (DLS) for a biomolecule sensing is unexplored. Here we developed a non-invasive, SDA-based DLS method for the diagnosis of bladder cancer by detecting telomerase activity in human urine. In the presence of telomerase, the telomerase substrate (TS) primer was elongated with repeating sequences of (TTAGGG)n, and the resulting product triggers SDA between the hairpin deoxyribonucleic acid (DNA) and the Primer. The SDA product can be recognized by the oligonucleotide-modified AuNPs probes, resulting in DLS measurable AuNPs aggregation. The assay displayed a detection limit of 3 MCF-7 cells with a signal-to-noise ratio of 3 in a dynamic range of 5-1000 cells. The method was simple, reliable and has been successfully applied in the detection of telomerase in urine with good accuracy, selectivity and reproducibility. Moreover, only urine samples from bladder cancer patients induced a significant change in the average hydrodynamic diameter, indicating practical applicability of the method for the non-invasive diagnosis of bladder cancer.

Advances in optical assays for detecting telomerase activity

Telomerase uses its RNA as template and its protein unit as reverse transcriptase to synthesize TTAGGG repeats at the ends of the eukaryotic chromosome to maintain the lengths of telomeres. Telomerase activity up-regulates in about 85% of human tumors compared with somatic cells, which indicates that telomerase is a tumor biomarker. Reliable assay of telomerase activity is thus essential in diagnosis and management of malignant tumors. In this review, recent developed optical assays are summarized based on the readout signal, including chemiluminescence assay, colorimetric assay, and fluorescence assay.

AIEgens/Nucleic Acid Nanostructures for Bioanalytical Applications

DNA occupies significant roles in life processes, which include encoding the sequences of proteins and accurately transferring genetic information from generation to generation. Recent discoveries have demonstrated that a variety of biological functions are correlated with DNA's conformational transitions. The non-B form has attained great attention among the diverse forms of DNA over the past several years. The main reason for this is that a large number of studies have shown that the non-B form of DNA is associated with gross deletions, inversions, duplications, translocations as well as simple repeating sequences, which therefore causes human diseases. Consequently, the conformational transition of DNA between the B-form and the non-B form is important for biology. Conventional fluorescence probes based on the conformational transitions of DNA usually need a fluorophore and a quencher group, which suffers from the complex design of the structure and tedious synthetic procedures. Moreover, conventional fluorescence probes are subject to the aggregation-caused quenching (ACQ) effect, which limits their application toward imaging and analyte detection. Fluorogens exhibiting aggregation-induced emission (AIE) have attracted tremendous attention over the past decade. By taking advantage of this unique behavior, plenty of fluorescent switch-on probes without the incorporation of fluorescent quenchers/fluorophore pairs have been widely developed as biosensors for imaging a variety of analytes. Herein, the recent progress in bioanalytical applications on the basis of aggregation-induced emission luminogens (AIEgens)/nucleic acid nanostructures are presented and discussed.

Quartz crystal microbalance for telomerase sensing based on gold nanoparticle induced signal amplification

A mass-sensitive quartz crystal microbalance biosensor was constructed for telomerase sensing based on gold nanoparticle induced signal amplification.

FRET investigation toward DNA tetrahedron-based ratiometric analysis of intracellular telomerase activity

Ratiometric sensing of telomerase activity is realized at a single-cell level based on a novel DNA nanoprobe reconciling an extension primer, a DNA tetrahedron and a flare probe.

A high therapeutic efficacy of polymeric prodrug nano-assembly for a combination of photodynamic therapy and chemotherapy

Combination of photodynamic therapy and chemotherapy has been emerging as a new strategy for cancer treatment. Conventional photosensitizer tends to aggregate in aqueous media, which causes fluorescence quenching, reduces reactive oxygen species (ROS) production, and limits its clinical application to photodynamic therapy. Traditional nanoparticle drug delivery system for chemotherapy also has its disadvantages, such as low drug loading content, drug leakage, and off-target toxicity for normal tissues. Here, we developed a reduction-sensitive co-delivery micelles TB@PMP for combinational therapy, which composed of entrapping a red aggregation-induced emission fluorogen (AIEgen) for photodynamic therapy and PMP that contains a reduction-sensitive paclitaxel polymeric prodrug for chemotherapy. AIEgen photosensitizer illustrates a much improved photostability and ROS production efficiency in aggregate state and PMP loads a high dose of paclitaxel and carries a smart stimuli-triggered drug release property. This co-delivery system provides a better option that replaces AIEgen photosensitizer for cancer diagnosis and therapy.

Xiaoqing Yi et al. report a co-drug delivery micelle system that demonstrates a high therapeutic efficacy for cancer. This system shows a much improved drug load, photostability, and production of reactive oxygen species, compared to traditional photosensitizer-loaded nanoparticles.

Cascaded Electrochemiluminescence Signal Amplifier for the Detection of Telomerase Activity from Tumor Cells and Tissues

Telomerase is closely linked to the physiological transformation of tumor cells and is commonly overexpressed in most types of tumor cells. Therefore, telomerase has become a potential biomarker for the process of tumorigenesis, progression, prognosis and metastasis. Thus, it is important to develop a simple, accurate and reliable method for detecting telomerase activity. As a high signal-to-noise ratio mode, electrochemiluminescence (ECL) has been widely applied in the field of biomedical analysis. Here, our objective was to construct an improved ECL signal amplifier for the detection of telomerase activity. Methods: A cascaded ECL signal amplifier was constructed to detect telomerase activity with high selectivity via controllable construction of a lysine-based dendric Ru(bpy)₃ ²⁺ polymer (DRP). The sensitivity, specificity and performance index were simultaneously evaluated by standard substance and cell and tissue samples. Results: With this cascaded ECL signal amplifier, high sensitivities of 100, 50, and 100 cells for three tumor cell lines (A549, MCF7 and HepG2 cell lines) were simultaneously achieved, and desirable specificity was also obtained. Furthermore, the excellent performance of this platform was also demonstrated in the detection of telomerase in tumor cells and tissues. Conclusion: This cascaded ECL signal amplifier has the potential to be a technological innovation in the field of telomerase activity detection.

In Vivo and in Situ Activated Aggregation-Induced Emission Probes for Sensitive Tumor Imaging Using Tetraphenylethene-Functionalized Trimethincyanines-Encapsulated Liposomes

The design and exploration of fluorescent probes with high-sensitivity and low-background are essential for noninvasive optical molecular imaging. The in vivo and in situ activated aggregation-induced emission (AIE) probes were found to be ideal for achieving higher signal-to-background ratios for tumor detections. We herein developed novel tetraphenylethene-encapsulated liposomes (TPE-LPs) constructed by loading TPE-trimethincyanine into liposomes for the first time, and the probes were applied to tumor bioimaging in vivo. TPE-functionalized trimethincyanines were synthesized with a new and efficient one-pot reaction. In TPE-LPs, TPE-functionalized bicarboxylic acids benzoindole trimethinecyanine (TPE-BICOOH) fluorophores were found to be well dispersed in lipid bilayers (with non-restricted rotation) during the blood circulation, and then aggregated (with restriction of intramolecular rotation) upon liposome rupture in the tumor tissue, achieving a low-background and high-target signal for tumor imaging. The in situ activated AIE probes not only had great accumulation at the tumor site after intravenous injection in 4T1 tumor-bearing mice but also demonstrated excellent signal-to-background ratios, as well as low cytotoxicity and excellent biocompatibility. The proposed strategy is believed to be a simple and powerful tool for the sensitive detection of tumors.

A low background D-A-D type fluorescent probe for imaging of biothiols in living cells

Two probes, structurally symmetric CBFB and asymmetric CBFM, constructed by a D-A-D (donor-acceptor-donor) type curcuminoid as the fluorophore and the DNBS (2,4-dinitrobenzenesulfonyl) group as the biothiol recognition site were designed and synthesized here. The DNBS group can quench the emission of the fluorophore by the PET (photoinduced electron transfer) process, and in the presence of biothiols, the emission of the probe was switched on as a result of the cleavage of the quencher by a nucleophilic aromatic substitution reaction. Experimental analyses and theoretical calculations revealed that two recognition moieties in the molecule can quench the fluorescence more efficiently, therefore, CBFB showed a much higher SNR (signal to noise ratio) than CBFM in biothiol detection with an emission maximum at 610 nm. This "low background" and "turn-on" fluorescent probe, CBFB, was successfully utilized to map endogenous biothiols in living cells.

Enzyme-Responsive Bioprobes Based on the Mechanism of Aggregation-Induced Emission

Enzymes play an indispensable role in maintaining normal life activities. The abnormalities of content and activity in specific enzymes are usually associated with the occurrence and the development of major diseases. Correspondingly, fluorescent bioprobes with distinctive sensing mechanisms and different functionalities have attracted growing attention as convenient tools for optical probing and monitoring the activity of enzymes. Ideally and excitedly, the recently emerged luminogens with an aggregation-induced emission (AIE) feature could perfectly overcome the aggregation-caused quenching (ACQ) effect of conventional bioprobes. Based on the fantastic characteristics of AIE luminogens (AIEgens), specific enzyme bioprobes have been designed through integration with recognition units, demonstrating many advantages including low background interference, a high signal-to-noise ratio (SNR), and superior photostability. In this review, by presenting some typical examples, we summarize the working principle and structural design of specific AIEgen-based bioprobes that are triggered by enzymes and discuss their great potential in biomedical applications, with the aim to promote the future research of fluorescent bioprobes involving enzymes.

Label-Free and Ultrasensitive Biomolecule Detection Based on Aggregation Induced Emission Fluorogen via Target-Triggered Hemin/G-Quadruplex-Catalyzed Oxidation Reaction

Fluorescence biosensing strategy has drawn substantial attention due to their advantages of simplicity, convenience, sensitivity, and selectivity, but unsatisfactory structure stability, low fluorescence quantum yield, high cost of labeling, and strict reaction conditions associated with current fluorescence methods severely prohibit their potential application. To address these challenges, we herein propose an ultrasensitive label-free fluorescence biosensor by integrating hemin/G-quadruplex-catalyzed oxidation reaction with aggregation induced emission (AIE) fluorogen-based system. l-Cysteine/TPE-M, which is carefully and elaborately designed and developed, obviously contributes to strong fluorescence emission. In the presence of G-rich DNA along with K⁺ and hemin, efficient destruction of l-cysteine occurs due to hemin/G-quadruplex-catalyzed oxidation reactions. As a result, highly sensitive fluorescence detection of G-rich DNA is readily realized, with a detection limit down to 33 pM. As a validation for the further development of the proposed strategy, we also successfully construct ultrasensitive platforms for microRNA by incorporating the l-cysteine/TPE-M system with target-triggered cyclic amplification reaction. Thus, this proposed strategy is anticipated to find use in basic biochemical research and clinical diagnosis.

A robust fluorescent probe for detection of telomerase activityin vitroand imaging in living cellsviatelomerase-triggering primer extension to desorb DNA from graphene oxide

A novel strategy for telomerase imaging was developed based on telomerase-triggering primer extension to desorb fluorophore labeled DNA from graphene oxide.

Advances in the detection of telomerase activity using isothermal amplification

Telomerase plays a significantly important role in keeping the telomere length of a chromosome. Telomerase overexpresses in nearly all tumor cells, suggesting that telomerase could be not only a promising biomarker but also a potential therapeutic target for cancers. Therefore, numerous efforts focusing on the detection of telomerase activity have been reported from polymerase chain reaction (PCR)-based telomeric repeat amplification protocol (TRAP) assays to PCR-free assays such as isothermal amplification in recent decade. In this review, we highlight the strategies for the detection of telomerase activity using isothermal amplification and discuss some of the challenges in designing future telomerase assays as well.