Detection of telomerase activity in high concentration of cell lysates using primer-modified gold nanoparticles

Telomerase: a nexus between cancer nanotherapy and circadian rhythm

Cancer represents a complex disease category defined by the unregulated proliferation and dissemination of anomalous cells within the human body. According to the GLOBOCAN 2020 report, the year 2020 witnessed the diagnosis of approximately 19.3 million new cases of cancer and 10.0 million individuals succumbed to the disease. A typical cell eventually becomes cancerous because of a long-term buildup of genetic instability and replicative immortality. Telomerase is a crucial regulator of cancer progression as it induces replicative immortality. In cancer cells, telomerase inhibits apoptosis by elongating the length of the telomeric region, which usually protects the genome from shortening. Many nanoparticles are documented as being available for detecting the presence of telomerase, and many were used as delivery systems to transport drugs. Furthermore, telomere homeostasis is regulated by the circadian time-keeping machinery, leading to 24-hour rhythms in telomerase activity and TERT mRNA expression in mammals. This review provides a comprehensive discussion of various kinds of nanoparticles used in telomerase detection, inhibition, and multiple drug-related pathways, as well as enlightens an imperative association between circadian rhythm and telomerase activity from the perspective of nanoparticle-based anticancer therapeutics.

A triggered DNA nanomachine with enzyme-free for the rapid detection of telomerase activity in a one-step method

BACKGROUND

Telomerase is considered a biomarker for the early diagnosis and clinical treatment of cancer. The rapid and sensitive detection of telomerase activity is crucial to biological research, clinical diagnosis, and drug development. However, the main obstacles facing the current telomerase activity assay are the cumbersome and time-consuming procedure, the easy degradation of the telomerase RNA template and the need for additional proteases. Therefore, it is necessary to construct a new method for the detection of telomerase activity with easy steps, efficient reaction and strong anti-interference ability.

RESULTS

Herein, an efficient, enzyme-free, economical, sensitive, fluorometric detection method for telomerase activity in one-step, named triggered-DNA (T-DNA) nanomachine, was created based on target-triggered DNAzyme-cleavage activity and catalytic molecular beacon (CMB). Telomerase served as a switch and extended few numbers of (TTAGGG)n repeat sequences to initiate the signal amplification in the T-DNA nanomachine, resulting in a strong fluorescent signal. The reaction was a one-step method with a shortened time of 1 h and a constant temperature of 37 °C, without the addition of any protease. It also sensitively distinguished telomerase activity in various cell lines. The T-DNA nanomachine offered a detection limit of 12 HeLa cells μL-1, 9 SK-Hep-1 cells μL-1 and 3 HuH-7 cells μL-1 with a linear correlation detection range of 0.39 × 102-6.25 × 102 HeLa cells μL-1 for telomerase activity.

SIGNIFICANCE

In conclusion, our study demonstrated that the triggered-DNA nanomachine fulfills the requirements for rapid detection of telomerase activity in one-step under isothermal and enzyme-free conditions with excellent specificity, and its simple and stable structure makes it ideal for complex systems. These findings indicated the application prospect of DNA nanomachines in clinical diagnostics and provided new insights into the field of DNA nanomachine-based bioanalysis.

Measuring telomerase activity using TRAP assays

Telomerase is a reverse transcriptase that consists of the telomerase reverse transcriptase (TERT) protein and the telomerase RNA component TERC which also harbors the template region for telomere synthesis. In its canonical function the enzyme adds single-stranded telomeric hexanucleotides de novo to the ends of linear chromosomes, telomeres, in telomerase-positive cells such as germline, stem- and cancer cells. This potential biochemical activity of telomerase can be measured with the help of a telomerase repeat amplification protocol (TRAP) which often includes a PCR amplification due to the low abundance of telomerase in most cells and tissues. The current chapter describes various TRAP methods to detect telomerase activity (TA) using gel-based methods, its advantages and deficits, how to perform an ELISA-based TRAP assay and how best to interpret its results. Since development of the TRAP assay in 1994, there have been numerous modifications and adaptations of the method from real-time PCR analysis, isothermal amplification and nanotechnology to CRISPR/Cas-based methods which will be briefly mentioned. However, it is not possible to cover all different TRAP methods and thus there is no comprehensiveness claimed by this chapter. Instead, the author describes various aspects of using TRAP assays including required controls, sample preparation, etc. in order to avoid pitfalls and set-backs in applying this rather complex and demanding technique. The TRAP assay is particularly important to support clinical diagnosis of cancer, analyze tumor therapy as well as to evaluate various approaches to inhibit TA as a form of anti-cancer therapy.

Plasmonic Cross-Linking Colorimetric PCR for Simple and Sensitive Nucleic Acid Detection

Simple, low-cost, and accurate nucleic acid assay platforms hold great promise for point-of-care (POC) pathogen detection, disease surveillance, and control. Plasmonic photothermal polymerase chain reaction (PPT-PCR) is a powerful and efficient nucleic acid amplification technique, but it lacks a simple and convenient analysis method for POC applications. Herein, we propose a novel plasmonic cross-linking colorimetric PCR (PPT-ccPCR) assay by integrating plasmonic magnetic nanoparticle (PMN)-based PPT-PCR with gold nanoparticle (AuNP)-based cross-linking colorimetry. AuNPs form assembled structures with the PMNs in the presence of amplicons and collect in a magnetic field, resulting in color changes to the supernatant. Target DNA with concentrations as low as 5 copies/μL can be visually detected within 40 min. The achieved limit of detection was 1.8 copies/μL based on the absorption signals. This simple and sensitive strategy needs no expensive instrumentation and demonstrates high potential for POC detection while enabling further applications in clinical diagnostics.

Sensitive bioanalytical methods for telomerase activity detection: a cancer biomarker

Telomerase is an enzyme that protects the length of telomeres by adding guanine-rich repetitive sequences. In tumors, gametes, and stem cells, telomerase activity is exerted. Telomerase activity can be a cancer biomarker for therapeutic and diagnosis approaches. So, a number of studies concentrating on the discovery of telomerase activity were reported. Bioanalytical devices, in comparison with other tests, have numerous advantages including low expense, simplicity, and excellent sensitivity and specificity. In this article we reviewed recent studies on the subject of various bioanalytical methods based on different nanomaterials. Optical, electrochemical, and quartz crystal microbalance (QCM) are prominent analytical techniques that are mentioned in this paper.

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.

The Integration of Gold Nanoparticles with Polymerase Chain Reaction for Constructing Colorimetric Sensing Platforms for Detection of Health-Related DNA and Proteins

Polymerase chain reaction (PCR) is the standard tool in genetic information analysis, and the desirable detection merits of PCR have been extended to disease-related protein analysis. Recently, the combination of PCR and gold nanoparticles (AuNPs) to construct colorimetric sensing platforms has received considerable attention due to its high sensitivity, visual detection, capability for on-site detection, and low cost. However, it lacks a related review to summarize and discuss the advances in this area. This perspective gives an overview of established methods based on the combination of PCR and AuNPs for the visual detection of health-related DNA and proteins. Moreover, this work also addresses the future trends and perspectives for PCR-AuNP hybrid biosensors.

Fluorescence imaging of intracellular telomerase activity for tumor cell identification by oligonucleotide-functionalized gold nanoparticles

As a specific biological marker for the occurrence and progression of tumor cells, detection of telomerase activity is of great importance for the physiological research of tumors. However, in situ measurement of telomerase activity in living cells still remains a challenge. Herein, we report a precisely designed oligonucleotide-functionalized gold nanoparticle probe that has realized high-efficiency detection of telomerase activity for cellular imaging toward the identification of tumors. Our method has achieved intracellular imaging of telomerase activity and shows good performance towards the distinction of tumor cells from normal ones. Moreover, the method reported here for tracking tumor cells in blood has wide applications in cancer diagnosis. This strategy offers an opportunity for cancer diagnosis, guiding therapy and evaluating prognosis.

Telomerase detection using a DNA-PAINT strategy

Telomerase plays an important role in maintaining the length of telomere during cell division and is recognized as a new kind of biomarkers for cancer diagnosis. In this work, we present a brand new telomerase detection strategy based on a DNA points accumulation for imaging in nanoscale topography (DNA-PAINT) like strategy. With an extraordinary spatial resolution (∼10 nm), the DNA-PAINT based strategy offers several advantages. First, it avoids complicated polymerase chain reaction and electrophoresis procedures. Second, it enables super resolution imaging of the reaction products with a high signal-to-noise ratio and facilitates the location of telomeric elongation sites on the single particle level, which results in a high sensitivity. Third, the detection scheme of the DNA-PAINT strategy allows directin situvisualization of the telomeric elongation process, which has never been achieved before. All these advantages make the DNA-PAINT telomerase detection strategy significant for dynamic investigation of telomerase related physiological processes as well as cancer diagnosis.

Nucleic acid-driven aggregation-induced emission of Au nanoclusters for visualizing telomerase activity in living cells and in vivo

Visual monitoring of telomerase activity in living cancer cells and in vivo is essential for clinical diagnosis and treatment. However, most detection methods were performed in vitro due to the difficulty of probes entering cells and the interferences from complex biological environments. Herein, we developed a novel probe based on Au nanoclusters (AuNCs) with a nucleic acid-driven aggregation-induced emission (AIE) property for the first time. The probe was applied for detection of telomerase with high sensitivity. Importantly, the probe could achieve telomerase imaging in living cells and in solid tumor tissue in vivo. The study provided a specific connection fashion of metal nanoclusters for AIE generation. It holds great potential for the development of AIE-active metal nanoclusters as a diagnostic tool for disease detection in vitro as well as in vivo.

Functionalized nanoprobes for in situ detection of telomerase

Telomerase, a special ribonucleoprotein reverse transcriptase, can maintain the length and stability of telomeres and plays an important role in cell proliferation and differentiation. Due to the distinguishable expression level in normal cells and cancer cells, telomerase has become an important biomarker for cancer diagnosis and prognosis evaluation. Despite major breakthroughs in the field of telomerase detection, the extracts in the cell lysate are still the first choice as the analyte nevertheless, which will bring serious inaccuracies compared with the real intracellular activity. With the development of nanotechnology and nanomaterials, extraordinary progress has been made in telomerase detection by employing different versatile nanoprobes. In this review, we list the superiority of nanoprobes and systematically summarize the applications of nanoprobes in telomerase detection from the aspects of various nanomaterials and discuss the current challenges and potential trends in the future design of nanoprobes.

Confocal Laser Scanning Microscopy and Fluorescence Correlation Methods for the Evaluation of Molecular Interactions

Confocal laser scanning microscopy (CLSM) and related microscopic techniques allow a unique and versatile approach to image and analyze living cells due to their specificity and high sensitivity. Among confocal related techniques, fluorescence correlation methods, such as fluorescence correlation spectroscopy (FCS) and dual-color fluorescence cross-correlation spectroscopy (FCCS), are highly sensitive biophysical methods for analyzing the complex dynamic events of molecular diffusion and interaction change in live cells as well as in solution by exploiting the characteristics of fluorescence signals. Analytical and quantitative information from FCS and FCCS coupled with fluorescence images obtained from CLSM can now be applied in convergence science such as drug delivery and nanomedicine, as well as in basic cell biology. In this chapter, a brief introduction into the physical parameters that can be obtained from FCS and FCCS is first provided. Secondly, experimental examples of the methods for evaluating the parameters is presented. Finally, two potential FCS and FCCS applications for convergence science are introduced in more detail.

Tetrahedral DNA Nanoconjugates for Simultaneous Measurement of Telomerase Activity and miRNA

In this study, a tetrahedral DNA nanostructure was first self-assembled; this was then conjugated with gold nanoparticles (AuNPs) and carbon nanodots (CDs). The fabricated nanocomposites allow simultaneous analysis of telomerase activity and miRNA with dual fluorescence channels. By further introducing an iRGD peptide sequence, the nanoconjuates can be conveniently transferred inside living cells for in situ imaging. The analytical performances and anti-jamming capabilities are excellent. Meanwhile, the materials are highly biocompatible for intracellular applications. Therefore, the proposed biosystem shows great promise as a powerful tool for quantitative analysis of the dual biomarkers. The strategy can also be further exploited as a versatile platform for in situ detection of many other targets for early disease diagnosis.

Dynamic supraparticles for the treatment of age-related diseases

Age-related diseases (ARDs) are arising as a major threat to public health in our fast-aging society. Current development of nanomedicine has sparked much optimism toward ARDs management by improving drug delivery and controlled drug release. However, effective treatments for ARDs, such as cancer and Alzheimer's diseases (AD), are still lacking, due to the complicated pathological features of ARDs including multifactorial pathogenesis, intricate disease microenvironment, and dynamic symptom manifestation. Recently, dynamic supraparticles (DS), which are reversibly self-assembled functional nanoparticles, have provided a novel strategy for combating ARDs. Besides the intrinsic advantages of nanomedicine including multifunctional and multitarget, DS are capable of dynamic structural reconfiguration upon certain stimulation, creating another layer of maneuverability that allows programmed response to the spatiotemporal alterations of ARDs during progression and treatment. In this review, we will overview the challenges faced by ARDs management, and discuss the unique opportunities brought by DS. Then, we will summarize the designed synthesis of DS for ARDs treatment. Finally, we will dissect the therapeutic targets in ARDs that can be exploited by DS, and present the encouraging advances in this field. Hopefully, this review will bridge our knowledge of the design principle of DS and ARDs management, which may inspire the future development of potent theranostic agents to improve the healthcare.

A turn-on graphene quantum dot and graphene oxide based fluorometric aptasensor for the determination of telomerase activity

A turn-on fluorometric assay is described for determination of the activity of enzyme telomerase. For this purpose, graphene quantum dots (GQDs) were first modified with the telomeric sequence (5'-amino-AATCCGTCGAGCAGAGTT-3') via a condensation reaction. Injection of graphene oxide causes instant quenching of the blue fluorescence of the GQDs. Addition of cell extract containing telomerase, triggers the extension of telomer via addition of specific sequence (TTAGGG)n to its 3' end. Fluorescence, best measured at excitation/emission wavelengths of 390/446 nm, is subsequently restored due to folding of the extended telomeric sequence into G-quadruplex structure. The method was applied to the determination of telomerase activity in crude cell extracts of as little as 10 HeLa cells. The linear dynamic range extends from 10 to 6500 cells. Graphical abstractIn this study, a new turn-on graphene quantum dotm and graphene oxide based fluorometric assay is developed for the determination of telomerase activity.

Plasmonic bimetallic nanodisk arrays for DNA conformation sensing

The integration of large-scale 2D bimetallic Ag/Au nanodisk arrays with gold nanoparticles is developed for sensing DNA conformation with the assistance of 3D finite-difference time-domain simulation. The optimized system comprising Ag/Au nanodisk arrays and gold nanoparticles offers a more than 6-fold enhancement in surface plasmon resonance shift, enabling the feasibility for sensitive DNA detection with a detection limit down to 100 femtomolar. Importantly, owing to the distance-dependent nature of the surface plasmon signal, sensitive differentiation of DNA conformations can be achieved with a conventional optical measurement. This platform could provide new exciting capabilities for a reliable, reproducible, and label-free assay analysis for investigating the conformations of DNA and other biological molecules.

Highly sensitive fluorescence biosensor for intracellular telomerase detection based on a single patchy gold/carbon nanosphere via the combination of nanoflare and hybridization chain reaction

How to in situ detect intracellular telomerase activity with high sensitivity still faces many challenges. This paper constructs a new fluorescence biosensing platform for the sensitive detection of intracellular telomerase activity via the combination of nanoflare and hybridization chain reaction (HCR)-based signal amplification on a single patchy gold/carbon nanosphere (PG/CNS), which has two or more distinct parts and allows hybridized-DNA (HS-DNA/Primer-DNA/Flare-DNA) and H1/H2-DNA (a pair of cross complementary DNA hairpins) to bind onto their surfaces via Au-S bond and electrostatic interaction, respectively. In the presence of telomerase, Primer-DNA (telomerase primer) extends at its 3' end to produce a telomeric repeated sequence, resulting in the release of Flare-DNA followed by the recovery of the fluorescence. Subsequently, the released Flare-DNA further initiates cross hybridization of H1 and H2 DNA from mimic-HCR system to amplify the fluorescence signal. The in vivo confocal microscopy studies demonstrate that resulting sensor can enter into the cancer cells such as A549 cells, and lead to the increase in luminescence, which is stronger than the sensor without the HCR-based signal amplification system. A linear relationship between the fluorescence intensity and the amount of A549 cells is observed, and the limit of detection of the sensor reaches about 280 A549 cells.

Non-invasive diagnosis of bladder cancer by detecting telomerase activity in human urine using hybridization chain reaction and dynamic light scattering

Cystoscopy and histology are the gold standards for detection of bladder cancer. However, these methods are highly subjective, expensive, and invasive. We have developed a non-invasive method for the diagnosis of bladder cancer by detecting telomerase activity in human urine. Telomerase substrate (TS) primer is elongated with repeating sequences of (TTAGGG)n in the presence of telomerase. The elongated primer can trigger hybridization chain reaction between two hairpins H1 and H2, result in the aggregation of AuNPs due to the hybridization between the tail sequence on H1 (or H2) and DNA-AuNPs probe, and accompany with the increase of hydrodynamic diameter of AuNPs, which can be measured with dynamic light scattering (DLS). The biosensor displayed a detection limit of 4 MCF-7 cells (a signal-to-noise ratio of 3) and a dynamic range of 10-1000 cells. Moreover, only urine specimens from bladder cancer patients induced a significant change in the average hydrodynamic diameter, indicating its specificity for the non-invasive diagnosis of bladder cancer.

Multi-code magnetic beads based on DNAzyme-mediated double-cycling amplification for a point-of-care assay of telomerase activity

Development of a reliable and facile telomerase activity assay with high specificity and sensitivity is a central challenge to make telomerase testing a routine part of medical care with respect to cancer.

One-pot detection of telomerase activity with high sensitivity and specificity via RNA FRET probes and RNase H-assisted signal cycling amplification

Human telomerase is a universal cancer biomarker and a promising anticancer therapeutic target. Sensitive and specific detection of telomerase activity is of great significance for cancer diagnosis and treatment. Up to now, many methods have been established to detect the activity of telomerase, but most of these methods require complex probe design and tedious experimental steps generally including telomere extension reaction, amplification of the extended products and signal detection. Herein, we propose a one-pot method to detect the telomerase activity via RNA FRET probes and RNase H-assisted signal cycling amplification, and the proposed assay can integrate the telomere extension reaction, signal amplification and readout in one step without requirement of amplification of the extended products, which greatly simplifies the experimental design and operation steps. Additionally, the proposed one-pot method has high sensitivity and can unequivocally detect the telomerase activity in as few as 5 cancer cells, which holds great potential in telomerase-related fundamental and clinical studies.

A one-pot method is developed for the detection of telomerase activity via RNA FRET probes and RNase H-assisted signal cycling amplification.

Multivalent Self-Assembled DNA Polymer for Tumor-Targeted Delivery and Live Cell Imaging of Telomerase Activity

The efficient detection and in situ monitoring of telomerase activity is of great importance for cancer diagnosis and biomedical research. Here we report for the first time that the development of a novel multivalent self-assembled DNA polymer, constructed through telomerase primer sequence (ITS) triggered hybridization chain assembly using two functional hairpin probes (tumor-trageting aptamer modified H1 and signal probe modified H2), for sensitive detection and imaging of telomerase activity in living cells. After internalizing into the tumor cells by multivalent aptamer targeting, the ITS on DNA polymers can be elongated by intracellular telomerase to generate telomere repeat sequences that are complementary with the signal probe, which can proceed along the DNA polymers, and gradually light up the whole DNA polymers, leading to an enhanced fluorescence signal directly correlated with the activity of telomerase. Our results demonstrated that the developed DNA polymer show excellent performance for specifically detecting telomerase activity in cancer cells, dynamically monitoring the activity change of telomerase in response to telomerase-based drugs, and efficiently distinguishing cancer cells from normal cells. The proposed strategy may afford a valuable tool for the monitoring of telomerase activity in living cells and have great implications for biological and diagnostic applications.

Highly sensitive ratiometric fluorescent paper sensor for the urine assay of cancer

Telomerase, as a valuable biomarker, is an important target in cancer diagnosis. Here, we report a ratiometric fluorescent probe for telomerase activity assay in urine and bladder cancer diagnoses based on the color change of Rox-DNA functionalized quantum dots (QDs). The green fluorescence of the QDs was sensitive to H₂O₂, but the red fluorescence of Rox showed no change. An HRP-mimicking hemin/G-quadruplex, which was formed with the help of telomerase activity, catalyzed H₂O₂ into H₂O and O₂. This quadruplex effectively avoided H₂O₂ interference with green fluorescence. In the presence of H₂O₂, the detected color changed from red to yellow-green by increasing the telomerase concentration. The detection limit (LOD) was 10 cells, and response time was within 60 min. More importantly, a paper sensor was developed based on this probe and used for the assay of telomerase activity in urine samples. The results were highly sensitive and reproducible, and visual semi-quantitative detection was realized using the naked eye.

Quantum dot-based electrochemical biosensor for stripping voltammetric detection of telomerase at the single-cell level

Human telomerase is responsible for the maintenance of chromosome end structures and is a valuable biomarker for malignant growth. However, the accurate measurement of telomerase activity at the single-cell level has remained a great challenge. Here we develop a simple quantum dot (QD)-based electrochemical biosensor for stripping voltammetric detection of telomerase activity at the single-cell level. We designed a thiol-modified capture DNA which may be immobilized on the gold electrode by the gold-sulfur bond. The presence of telomerase enables the addition of the telomere repeats of (TTAGGG)_n to the 3' end of the primer, accompanied by the incorporation of abundant biotins in the extension product with the assistance of the biotin-tagged dATP. The subsequent hybridization of extension product with the capture DNA and the addition of streptavidin-coated QDs induce the assembly of large amounts of QDs onto the electrode via specific biotin-streptavidin binding. After the acidic dissolution of QDs, the released Cd (II) can be simply quantified by anodic stripping voltammetry (ASV). Due to the introduction of large amounts of QDs by telomerase-induced primer extension reaction and the synergistic signal amplification induced by the release of Cd (II) from the QDs, this biosensor can detect telomerase activity at the single-cell level without the involvement of any thermal cycling and extra enzymes for signal amplification. Moreover, this assay exhibits a large dynamic range over four orders of magnitude and it is very simple without the involvement of specific hairpin probe design and complicated labelling, holding great potential in point-of-need testing.

Ratiometric Fluorescent Biosensor for Visual Discrimination of Cancer Cells with Different Telomerase Expression Levels

Telomerase is inactive in normal somatic cells but highly activated in tumor cells to maintain their indefinite proliferation and immortal phenotype. As a specific marker for the generation and progress of almost all tumors, the detection of telomerase activity by classical PCR techniques has served in the biological research of tumors. However, the detection of in situ telomerase activity in cell extracts to evaluate the malignancy, progress, and metastasis of tumors remains a daunting challenge. Here, a precisely designed FRET-based ratiometric fluorescent oligonucleotide probe has achieved high-fidelity detection of telomerase activity for accurate discrimination of different cancer cells toward advanced diagnosis of tumors. Our method is superior to other methods in its capabilities to quantify telomerase activity in cell extracts and visualize various tumor cell extracts with different telomerase expression levels by the naked eye for clinical diagnosis. In particular, the ratiometric fluorescent probe used in the assay could exclude other experimental factors influence, and further avoid false positive signal generation. The method reported here could provide a reliable, accurate, and convenient way in medical diagnostics and therapeutic response assessment.

Cross-Platform Cancer Cell Identification Using Telomerase-Specific Spherical Nucleic Acids

Distinguishing tumor cells from normal cells holds the key to precision diagnosis and effective intervention of cancers. The fundamental difficulties, however, are the heterogeneity of tumor cells and the lack of truly specific and ideally universal cancer biomarkers. Here, we report a concept of tumor cell detection, bypassing the specific genotypic and phenotypic features of different tumor cell types and directly going toward the hallmark of cancer, uncontrollable growth. Combining spherical nucleic acids (SNAs) with exquisitely engineered molecular beacons (SNA beacons, dubbed SNAB technology) is capable of identifying tumor cells from normal cells based on the molecular phenotype of telomerase activity, largely bypassing the heterogeneity problem of cancers. Owing to the cell-entry capability of SNAs, the SNAB probe readily achieves tumor cell detection across multiple platforms, ranging from solution-based assay, to single cell imaging and in vivo solid tumor imaging (unlike PCR that is restricted to cell lysates). We envision the SNAB technology will impact cancer diagnosis, therapeutic response assessment, and image-guided surgery.

Determination of the activity of telomerase in cancer cells by using BSA-protected gold nanoclusters as a fluorescent probe

Gold nanoclusters (AuNCs) protected with a bovine serum albumin (BSA) coating are known to emit red fluorescence (peaking at 650 nm) on photoexcitation with ultraviolet light (365 nm). On addition of Cu(II) ions, fluorescence is quenched because Cu(II) complexes certain amino acid units in the BSA chain. Fluorescence is, however, restored if pyrophosphate (PPi) is added because it will chelate Cu(II) and remove it from the BSA coating on the AuNCs. Because PPi is involved in the function of telomerase, the BSA@AuNCs loaded with Cu(II) can act as a fluorescent probe for determination of the activity of telomerase. A fluorescent assay was worked out for telomerase that is highly sensitive and has a wide linear range (10 nU to 10 fM per mL). The fluorescent probe was applied to the determination of telomerase activity in cervix carcinoma cells via imaging. It is shown that tumor cells can be well distinguished from normal cells by monitoring the differences in intracellular telomerase activity. Graphical abstract Gold nanoclusters (AuNCs) protected by bovine serum albumin (BSA) and displaying red photoluminescence were prepared as fluorescent probe for the determination of telomerase activity and used for imaging of cervix carcinoma (HeLa) cells.

A triple-amplification strategy for sensitive detection of telomerase at the single-cell level

We develop a triple-amplification strategy for sensitive detection of telomerase from cancer cells at the single-cell level.

A simple “mix-and-detection” method for the sensitive detection of telomerase from cancer cells under absolutely isothermal conditions

We develop a simple “mix-and-detection” method for the sensitive detection of telomerase from cancer cells under absolutely isothermal conditions.

An AIEgens and exonuclease III aided quadratic amplification assay for detecting and cellular imaging of telomerase activity

Monitoring telomerase activity with high sensitive and reliable is of great importance to cancer analysis. In this paper, we report a sensitive and facile method to detect telomerase activity using AIEgens modified probe (TPE-Py-DNA) as a fluorescence reporter and exonuclease III (Exo III) as a signal amplifier. With the aid of telomerase, repeat units (TTAGGG)n are extended from the end of template substrate oligonucleotides (TS primer) that form duplex DNAs with TPE-Py-DNA. Then, Exo III catalyzes the digestion of duplex DNAs, liberating elongation product and releasing hydrophobic TPE-Py. The released hydrophobic TPE-Py aggregate together and produce a telomerase-activity-related fluorescence signal. The liberated product hybridizes with another TPE-Py-DNA probe, starting the second cycle. Finally, we obtain the target-to-signal amplification ratio of 1:N². This strategy exhibits good performance for detecting clinical urine samples (distinguishing 15 cancer patients' samples from 8 healthy ones) and checking intracellular telomerase activity (differentiating cell lines including HeLa, MDA-MB-231, MCF-7, A375, HLF and MRC-5 from the cells pretreated with telomerase-related drug), which shows its potential in clinical diagnosis as well as therapeutic monitoring of cancer.

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.

Single-molecule imaging of telomerase activity via linear plasmon rulers

A strategy for real-time monitoring of the extension of the telomerase primer based on plasmon rulers was demonstrated for the first time.

DNA-fueled molecular machine for label-free and non-enzymatic ultrasensitive detection of telomerase activity

Herein, a non-enzymatic and label-free strategy based on DNA-fueled molecular machine was developed for ultrasensitive detection of telomerase activity in cancer cell extracts even at the single-cell level.