A PCR-free fluorescence strategy for detecting telomerase activity via double amplification strategy

Amplification-free detection of telomerase activity at the single-cell level via Cas12a-lighting-up single microbeads (Cas12a-LSMBs)

Telomerase overexpresses in almost all cancer cells and has been deemed a universal biomarker for cancer diagnosis and therapy. However, simple and ultrasensitive detection of telomerase activity in single-cells is still a huge challenge. Herein, we wish to report Cas12a-lighting up single microbeads (Cas12a-LSMBs) for ultrasensitive detection of telomerase activity without nucleic acid amplification. In this platform, single-strand DNA reporter (ssDNA reporter)-functionalized single-microbeads (functionalized-SMBs) are employed as a reactor for the trans-cleavage of telomerase-activated CRISPR/Cas12a as well as a reporting unit for fluorescence signal enrichment and visualization. Due to the space-confined effect and signal enrichment mechanism on the surface of the functionalized SMBs, the Cas12a-LSMBs can accurately detect telomerase activity in crude cell lysates with high specificity. Importantly, we have demonstrated that the Cas12a-LSMBs are a reliable and practical tool to detect telomerase activity in single cells and investigate cellular heterogeneity of telomerase activity from cell-to-cell variations.

Ultrasensitive fluorescent detection of telomerase activity based on tetrahedral DNA nanostructures as carriers for DNA-templated silver nanoclusters

Precise evaluation of telomerase activity is essential for the clinical diagnosis of early tumors. Herein, we have ingeniously designed a tetrahedral DNA nanostructure, with hairpin-shaped DNA probes rich in cytosine bases at four vertices for telomerase detection. The DNA-templated silver nanoclusters can be formed after the addition of Ag. Then the introduction of telomerase adds the single-strand TTAGGG extension, which can "turn on" the fluorescence of silver nanoclusters quickly by the proximity of the resulting guanine-rich sequences to silver nanoclusters and realize accurate detection of telomerase activity. In this study, integration of high stability tetrahedral DNA nanostructure and fluorescence signal amplification of four DNA-templated silver nanoclusters offers the advantage of high sensitivity, with a low detection limit of 1 cell. More than that, this method is low-cost, facile, and feasible for practical clinical applications.

Portable and sensitive detection of cancer cells via a handheld luminometer

A simple and sensitive chemiluminescent method for portable detection of cancer cells via a handheld luminometer.

Cost-Effective Trap qPCR Approach to Evaluate Telomerase Activity: an Important Tool for Aging, Cancer, and Chronic Disease Research

OBJECTIVES

Telomeres are a terminal "DNA cap" that prevent chromosomal fusion and degradation. However, aging is inherent to life, and so is the loss of terminal sequences. Telomerase is a specialized reverse transcriptase encoded by self-splicing introns that counteract chromosome erosion. Telomerase activity is observed during early embryonic development, but after the blastocyst stage, the expression of telomerase reduces. The consequences of either insufficient or unrestrained telomerase activity underscore the importance of ongoing studies aimed at elucidating the regulation of telomerase activity in humans. In the present study, we aimed to standardize a simplified telomerase repeat-amplification protocol (TRAP) assay to detect telomerase activity in unstimulated and PHA-stimulated mononuclear cells.

METHODS AND RESULTS

Our optimized qPCR-based can efficiently evaluate telomerase activity. Quantification of protein and DNA between unstimulated and PHA-stimulated peripheral blood mononuclear cells revealed cellular activation and cell-cycle entry. The assay also showed that relative telomerase activity is significantly different between these two conditions, supporting the applicability of the assay. Furthermore, our findings corroborated that telomerase activity decreases with age.

CONCLUSIONS

Telomeres and telomerase are implicated in aging and development of chronic diseases and cancer; however, difficulty in accessing commercial kits to investigate these aspects is a critical constraint in health surveillance studies. Our optimized assay was successfully used to differentiate telomerase activity between unstimulated and stimulated cells, clearly showing the reactivation of telomerase upon cell activation. This assay is affordable, reproducible, and can be executed in resource-limited settings.

Sensitive detection of intracellular telomerase activity via double signal amplification and ratiometric fluorescence resonance energy transfer

As an important and universal tumor marker, the reliable and in situ detection of intracellular telomerase activity is crucial for cancer diagnosis. Herein, a ratiometric fluorescence resonance energy transfer (FRET) method was developed for detecting intracellular telomerase activity. It takes full advantage of manganese dioxide nanosheets (MnO2NS) that can carry DNA probes with different conformations into cells and then completely release the DNA probes via decomposition of MnO2NS by intracellular reduced glutathione (GSH). In the presence of telomerase, a telomere substrate (TS) could be extended to form long telomerase extension products (TEPs), which trigger the cycling strand displacement reaction (SDR) between two fluorophore-labeled hairpin DNA probes to form lots of DNA duplexes. The close contact of two fluorophores led to an effective ratiometric FRET for reliable detection of telomerase activity. Fluorescence confocal imaging demonstrated that the activity of telomerase in tumor cells was reliably detected. The inhibition of telomerase activity by an inhibitor resulted in a decrease in FRET signal. For extracellular detection, the FRET ratio (FA/FD) shows a good linear relationship with the number of HeLa cells in the range of 20-1000 cells. Therefore, it offers a more facile method for reliable and sensitive detection of intracellular telomerase activity.

Capping Ligand Size-Dependent LSPR Property Based on DNA Nanostructure-Mediated Morphological Evolution of Gold Nanorods for Ultrasensitive Visualization of Target DNA

Systematically tuning the structures and properties of noble-metal nanoparticles through biomolecule-mediated overgrowth is of significant importance for their applications in biosensing and imaging. Herein thiolated biomolecules with different concentrations and sizes (molecular weight and spatial structure) were used as a class of capping ligands to control the longitudinal surface plasmon resonance (LSPR) property of gold nanorods (GNRs). The LSPR peaks were red-shifted by increasing the capping agent concentration. The size effect could be divided to two aspects: (1) When the ligands are small molecules, the LSPR peak is blue-shifted as the size of the capping ligand increases. (2) When the ligands are macromolecular proteins, the LSPR property is similar to that of the overgrown nanoparticle (Au@gap@GNR) without thiolated biomolecules as capping agents. Interestingly, thiol-free and nonhomooligomeric DNA strands as capping agents present a similar influence in shaping the overgrowth of GNRs by varying their concentrations and sizes. In addition, the size effect of a DNA nanostructure was used to construct a Δλ_LSPR-based catalytic nucleic acid biosensor using a DNA dendritic nanostructure as a capping agent combined with LSPR signals generated from the Au@gap@GNRs with morphological evolution. More importantly, the Δλ_LSPR-based biosensor possesses three advantages in nucleic acid biosensing: (1) It is completely label- and wash-free, (2) it has an ultrahigh sensitivity and signal-to-noise ratio, and (3) it can be visualized without any instrumental aid, indicating a significant potential for ultrasensitive biosensing.

Visual and sensitive detection of telomerase activity via hydrogen peroxide test strip

The point of care testing (POCT) of telomerase activity is critical for early diagnosis of cancer. Herein, a colorimetric method was developed for visual detection of telomerase activity via hydrogen peroxide test strip. It is based on the telomerase-controlled in-situ formation of hydrogen peroxide. Firstly, biotinylated telomerase substrate (TS) primer was attached on the surface of magnetic beads (MBs) via the streptavidin-biotin reaction to form MB-TS complex. Then, TS primers were elongated by telomerase to form long telomere elongated products (TEP) which contains TTAGGG repeat units. The in-situ formed MB-TEP complex specifically hybridized with glucose oxidase modified cDNA (GOD-cDNA). After magnetic separation and washing, the MB-TEP/GOD-cDNA complex incubated with glucose solution to in-situ produce hydrogen peroxide which was detected by hydrogen peroxide test strip. One long TEP hybridized with multiple GOD-cDNAs, which enriched GOD to highly efficiently catalyze glucose for generating hydrogen peroxide. Thus, the visual assay achieved sensitive detection of telomerase activity, and the limit of detection (LOD) reached as low as 10 HeLa cells/μL by naked eyes and 4.5 HeLa cells/μL by absorbance measurements. Therefore, it offers a sensitive and low-cost method for visual detection of telomerase activity, which also, widens the application of commercial hydrogen peroxide test strip in the development of non-H₂O₂ biosensors.

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.

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.

Ultrasensitive fluorescent detection of HTLV-II DNA based on magnetic nanoparticles and atom transfer radical polymerization signal amplification

Human T-lymphotropic virus type II (HTLV-II) is a crucial retrovirus that is closely associated with a variety of human diseases. Herein, an ultrasensitive fluorescent HTLV-II DNA detection strategy was developed for the first time based on magnetic nanoparticles (MNPs) and atom transfer radical polymerization (ATRP) amplification. In this approach, hairpin DNA probes (pDNA) labelled with 5' thiol and 3' azide group terminally were immobilized on amino group modified MNPs surface through sulfo-N-succinimidyl-4-maleimidobutyrate sodium salt (sulfo-GMBS) cross-linkers. In the presence of target DNAs (tDNA), pDNA hybridized with tDNA to form double-stranded DNA, and therefore its azide group was away from the MNPs surface. Subsequently, to initiate ATRP reaction, initiators were introduced into the pDNA by a Cu (I)-catalyzed alkyne-azide cycloaddition (CuAAC). Then, large numbers of 9-anthracenylmethyl methacrylate polymer (pAMMA) were successfully labelled on the MNPs surface, resulting in significant amplification of the fluorescence signal. Under optimized conditions, the fluorescence signal was proportional to the logarithm of the concentration of tDNA over the range from 1 fM to 1 nM, with a detection limit of 0.22 fM. Moreover, this strategy was capable of discriminating mismatched bases and detecting HTLV-II DNA in human serum samples. By virtue of the high sensitivity, selectivity, simplicity and economy, this ultrasensitive biosensor demonstrates great potential for biomedical research and early clinical diagnosis.

Electrocatalysis of cerium metal-organic frameworks for ratiometric electrochemical detection of telomerase activity

A ratiometric electrochemical biosensor was constructed to detect telomerase activity based on electrocatalysis of cerium-based metal-organic frameworks (CeMOFs) and conformation switch of hairpin DNA. First, the CeMOFs were synthesized using Ce as nodes and 1,3,5-benzenetricarboxylic acid as linker in a green method, and then functionalized with gold nanoparticles. The resulted Au@CeMOF tags demonstrated an excellent electrocatalysis toward hydroquinone oxidation. Meanwhile, a methylene blue (MB) modified hairpin probe was designed with telomerase primer (TP) hybridized "stem" and immobilized on the electrode surface via Au-S chemistry. In the presence of the dNTPs and telomerase, the extended TP can open the hairpin DNA and keep the MB away from the electrode surface, resulting in a decrease of electrochemical signal. In the meantime, the TP-extended part could capture the Au@CeMOF-cDNA tags on the electrode surface via hybridization, leading to the increase electrochemical signal of hydroquinone oxidation catalyzed by Au@CeMOF-cDNA tags. Thus, a ratiometric signal output mode was developed for the electrochemical detection of telomerase activity. This biosensor showed wide dynamic correlation of telomerase activity from 2 × 10² to 2 × 10⁶ cells mL^-1 with the limit of detection of 27 cells mL^-1, and was applied to evaluate telomerase activity in single cell. The ratiometric electrochemical strategy based on the catalysis of MOFs provides a new avenue on signal transduction in telomerase detection.

Molecular machine and gold/graphene quantum dot hybrid based dual amplification strategy for voltammetric detection of VEGF165

Graphene quantum dots (GQDs) were prepared via pyrolysis of citric acid and glutamic acid, then reacted with chlorauric acid to form a gold/graphene quantum dot hybrid (Au/GQD), and finally connected with hairpin DNA probe 1 (H1) and thionine (Thi). The H1-Au/GQD-Thi composite is found to be a viable redox probe for electrochemical and aptamer-based determination of vascular endothelial growth factor VEGF165. A dual amplification strategy is employed based on the use of molecular machine and the Au/GQD. Each single VEGF165 molecule can bind two DNA probes via specific aptamer-target recognition to produce a molecular machine. Surface-tethered hairpin DNA 2 (H2) hybridizes with the molecular machine through proximity effect, and the prelocked toehold domain of H2 becomes exposed. This part binds to H1-Au/GQD-Thi to release the molecular machine which then moves to the neighboring H2 upon which a surface programmatic chain reaction is initiated. By continuous molecular machine travel, many H1-Au/GQD-Thi probes are present on the gold electrode surface. This implies an efficient signal amplification capability. The Au/GQD based redox probes in-situ catalyzes the redox activity of thionine and further enhances the detection signal. The aptasensor exhibits ultrahigh sensitivity and selectivity for VEGF165. The square wave voltammetric signal, best measured at -0.18 V vs. Ag/AgCl, increases linearly in the 1.0 fM to 120 pM VEGF165 concentration range, and the detection limit is 0.3 fM. Conceivably, the method may be applied to other target proteins if the corresponding high-affinity aptamers are available. Graphical abstract This study report one dual amplification strategy for ultrasensitive electrochemical detection of VEGF165 based on gold-graphene quantum dot hybrid (Au/GQD) and bipedal molecular machine (BMM) powered surface programmatic chain reaction (SPCR).

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.

High-Discrimination Factor Nanosensor Based on Tetrahedral DNA Nanostructures and Gold Nanoparticles for Detection of MiRNA-21 in Live Cells

While detection of microRNA with or without signal amplification is highly informative, nanosensors with high specificity for cell-specific RNA detection are rare. Methods: In this study, a tetrahedral DNA nanostructure (TDN) with a specific function was combined with gold nanoparticles (Au-NP) possessing fluorescence quenching effects and a large surface area to fabricate a fluorescence resonance energy transfer based nanosensor (Au-TDNN). The presence of miR-21 (target) can separate the fluorescent dye-labeled detection probe on Au-TDNNs from Au-NPs, which separates the donor and acceptor, thus inducing an intensive fluorescence signal. High specificity for discerning point mutation targets was achieved by rationally designing the nucleic acid strand displacement reaction to occur spontaneously with ΔG⁰ ≈ 0 based on thermodynamic parameters; under this condition, slight thermodynamic changes caused by base mismatch exert significant effects on hybridization yield. Results: Chemically synthesized DNA of three single-base-changed analogues of target, let-7d, and miR-200b were tested. A discrimination factor (DF) of 15.4 was produced by the expected detection probe on Au-NPs for proximal single-base mismatch. As the control group, the DF produced by an ordinary detection probe on Au-NPs only reached 2.4. The feasibility of the proposed strategy was also confirmed using hepatocyte cancer cells (HepG2). Conclusion: This improved nanosensor opens a new avenue for the specific and easy detection of microRNA in live cells.

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 PCR-free colorimetric strategy for visualized assay of telomerase activity

A simple yet powerful polymerase chain reaction (PCR)-free strategy for visualized assay of human telomerase activity was reported in this work. Gold nanoparticles (AuNPs) based colorimetric strategy was applied with well-designed enzyme-aided cyclic amplification. Briefly, the detection relies on the elongated primers of telomerase substrate (TS) induced by telomerase, which open the hairpin DNA and hybridize with linker DNA, the trigger of AuNPs aggregation. Nicking endonuclease was added in the sensing system, which cleaved linker DNA after hybridization and released complimentary strand for cyclic hybridization with linker DNA, resulted in high sensitivity for the detection of telomerase. Down to 25 HeLa cells with high expression of telomerase could be recognized. The proposed strategy provides a good platform for the determination of telomerase activity, differentiation of cancer cell lines from normal cell line and screening of telomerase-targeted anticancer drugs.

Polyamidoamine starburst dendrimer-activated chromatography paper-based assay for sensitive detection of telomerase activity

Telomerase is extensively expressed in various cancer cells and recognized as a target for cancer drug discovery. In the present study, a simple and amplification-free fluorescence assay based on polyamidoamine starburst dendrimer (PAMAM dendrimer)-activated paper device is proposed for sensitive detection of telomerase activity through hybridization of Cy5 modified single strand DNA probes with telomerase extension products. The paper substrate is fabricated by hand drawing according to a template, which is low cost, instrument free and easy operation. PAMAM is rich in amino groups on its surface and employed to immobilize the telomerase substrate (TS) primer. Highly sensitive detection of telomerase activity in HeLa cell lysate of 10 cells is achieved since the PAMAM dendrimer-activated paper surface can provide high density of binding sites for immobilization of TS primer. The experimental results also demonstrate that the assay can be employed to evaluate telomerase activity levels of various cell lines and screen telomerase inhibitors.

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.

Joint quantitative measurement of hTERT mRNA in both peripheral blood and circulating tumor cells of patients with nasopharyngeal carcinoma and its clinical significance

Background

The study was aimed to quantitatively detect mRNA levels of the catalytic subunit of telomerase (hTERT) in both peripheral blood and circulating tumor cells (CTCs) of patients with nasopharyngeal carcinoma (NPC) and explore its significance in early diagnosis and treatment of NPC.

Methods

hTERT mRNA levels in peripheral blood and CTCs of 33 NPC patients before and after treatment with intensity-modulated radiation therapy (IMRT) or/and chemotherapy and 24 healthy controls were measured using real-time quantitative PCR (qPCR) and their correlations to clinic pathological factors of NPC were analyzed.

Results

Peripheral hTERT mRNA content was 10.75 ± 4.29 in NPC patients and 0.95 ± 0.37 in control subjects (P < 0.05), and had a significant correlation with patients’ clinical stage, T stage, and N stage (P < 0.05). Treatment of NPC patients at stages I and II with simple IMRT significantly reduced hTERT mRNA level from 5.60 ± 2.33 to 3.43 ± 1.42 (P < 0.05) and treatment of patients at advanced stage (III and IV) with induction chemotherapy followed by IMRT significantly reduced hTERT mRNA levels from 12.68 ± 3.08 to 10.68 ± 2.48 to 3.13 ± 1.69 (P < 0.05), respectively. In addition, the study also showed that hTERT mRNA content in CTCs of NPC patients was 10.65 ± 4.28, evidently higher than that of 1.09 ± 0.40 in control subjects (P < 0.05) and hTERT mRNA level in CTCs of NPC patients was obviously correlated to patients’ clinical stage, T stage and N stage (P < 0.05). After treatment, hTERT mRNA level in CTCs of NPC patients lowered from 10.65 ± 4.28 to 5.59 ± 2.32 (P < 0.05). The correlation analysis found that hTERT mRNA level in peripheral blood and CTCs of NPC patients were highly correlated with a correlation coefficient of 0.981.

Conclusions

hTERT mRNA levels in peripheral blood and CTCs of NPC patients were significantly enhanced compared to that in healthy controls and highly correlated. Changes in hTERT mRNA level was closely correlated to patients’ clinical stage and T stage. Radiochemotherapy could effectively reduce hTERT mRNA level in peripheral blood and CTCs. Thus, it is possible using the joint detection of hTERT mRNA level in peripheral blood and CTCs as a new biomarker for early diagnosis, treatment efficacy and prognosis of NPC.

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.

High-throughput identification of telomere-binding ligands based on the fluorescence regulation of DNA-copper nanoparticles

Formation of the G-quadruplex in the human telomeric DNA is an effective way to inhibit telomerase activity. Therefore, screening ligands of G-quadruplex has potential applications in the treatment of cancer by inhibit telomerase activity. Although several techniques have been explored for screening of telomeric G-quadruplexes ligands, high-throughput screening method for fast screening telomere-binding ligands from the large compound library is still urgently needed. Herein, a label-free fluorescence strategy has been proposed for high-throughput screening telomere-binding ligands by using DNA-copper nanoparticles (DNA-CuNPs) as a signal probe. In the absence of ligands, human telomeric DNA (GDNA) hybridized with its complementary DNA (cDNA) to form double stranded DNA (dsDNA) which can act as an efficient template for the formation of DNA-CuNPs, leading to the high fluorescence of DNA-CuNPs. In the presence of ligands, GDNA folded into G-quadruplex. Single-strdanded cDNA does not support the formation of DNA-CuNP, resulting in low fluorescence of DNA-CuNPs. Therefore, telomere-binding ligands can be high-throughput screened by monitoring the change in the fluorescence of DNA-CuNPs. Thirteen traditional chinese medicines were screened. Circular dichroism (CD) measurements demonstrated that the selected ligands could induce single-stranded telomeric DNA to form G-quadruplex. The telomere repeat amplification protocol (TRAP) assay demonstrated that the selected ligands can effectively inhibit telomerase activity. Therefore, it offers a cost-effective, label-free and reliable high-throughput way to identify G-quadruplex ligands, which holds great potential in discovering telomerase-targeted anticancer drugs.

Nanoparticle-Aided Amplification of Fluorescence Polarization for Ultrasensitively Monitoring Activity of Telomerase

To realize facile and reliable analyzing telomerase activity in homogeneous, herein, for the first time, a fluorescent polarization (FP) strategy was developed for polymerase chain reaction (PCR) free monitoring activity of human telomerase at single-cell level ground on gold nanoparticle (GNP) enhancement of FP. First, thiolated telomerase substrate (TS) primer is modified to the surface of GNP via Au-S bond. In the presence of telomerase, TS primer was extended via adding hexamer repeats (GGGTTA), leading to the formation of a long elongation DNA. Several short carboxyfluorescein (FAM)-modified complementary DNA (F-cDNA) can hybridize with the hexamer repeats, resulting in a sharp increase in FP value. Because of the GNP enhancement and self-amplification of telomerase, telomerase activity accounting to one HeLa cell can be rapidly detected in homogeneous solution. Telomerase activities of various cell lines were also favorably estimated. Meanwhile, the inhibition efficiency of telomerase inhibitor was studied, which holds great potential in screening telomerase-targeted anticancer drugs as well. So, a facile method was put forward to reliably and ultrasensitively detect telomerase activity.

Specific Magnetic Isolation of E6 HPV16 Modified Magnetizable Particles Coupled with PCR and Electrochemical Detection

The majority of carcinomas that were developed due to the infection with human papillomavirus (HPV) are caused by high-risk HPV types, HPV16 and HPV18. These HPV types contain the E6 and E7 oncogenes, so the fast detection of these oncogenes is an important point to avoid the development of cancer. Many different HPV tests are available to detect the presence of HPV in biological samples. The aim of this study was to design a fast and low cost method for HPV identification employing magnetic isolation, polymerase chain reaction (PCR) and electrochemical detection. These assays were developed to detect the interactions between E6-HPV16 oncogene and magnetizable particles (MPs) using commercial Dynabeads M-280 Streptavidin particles and laboratory-synthesized “homemade” particles called MANs (MAN-37, MAN-127 and MAN-164). The yields of PCR amplification of E6-HPV16 oncogene bound on the particles and after the elution from the particles were compared. A highest yield of E6-HPV16 DNA isolation was obtained with both MPs particles commercial M-280 Streptavidin and MAN-37 due to reducing of the interferents compared with the standard PCR method. A biosensor employing the isolation of E6-HPV16 oncogene with MPs particles followed by its electrochemical detection can be a very effective technique for HPV identification, providing simple, sensitive and cost-effective analysis.

High-throughout identification of telomere-binding ligands based on photo-induced electron transfer

A fast and cost-effective method is developed for high-throughout screening G-quadruplex-binding ligands based on the photo-induced electron transfer.