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.

Bioanalytical Application of Peroxidase-Mimicking DNAzymes: Status and Challenges

DNAzymes with peroxidase-mimicking activity are a new class of catalytically active DNA molecules. This system is formed as a complex of hemin and a G-quadruplex structure created by oligonucleotides rich in guanine. Considering catalytic activity, this DNAzyme mimics horseradish peroxidase, the enzyme most commonly used for signal generation in bioassays. Because DNAzymes exhibit many advantages over protein enzymes (thermal stability, easy and cheap synthesis and purification) they can successfully replace HRP in bioanalytical applications. HRP-like DNAzymes have been applied in the detection of several DNA sequences. Many amplification techniques have been conjugated with DNAzyme systems, resulting in ultrasensitive bioassays. On the other hand, the combination of aptamers and DNAzymes has led to the development of aptazymes for specific targets. An up-to-date summary of the most interesting DNAzyme-based assays is presented here. The elaborated systems can be used in medical diagnosis or chemical and biological studies.

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.

Target-controlled in situ formation of G-quadruplex DNAzyme for a sensitive visual assay of telomerase activity

A sensitive visual assay was developed for detecting telomerase activity based on the telomerase-controlled in situ formation of G-quadruplex-hemin DNAzyme. The telomerase activity of 5 HeLa cells per μL was visually detected in human serum.

A facile graphene oxide-based fluorescent nanosensor for the in situ “turn-on” detection of telomerase activity

A graphene oxide-based fluorescent nanosensor has been proposed for the quantitative detection of telomerase and in situ imaging of intracellular telomerase.

An ultra-sensitive colorimetric assay for reliable visual detection of telomerase activity

We proposed a sensitive colorimetric assay for detecting telomerase activity. The telomerase activity of 5 and 20 HeLa cell lysates can be detected via UV-vis spectroscopy and the naked eye, respectively.

Label-free colorimetric assay for T4 polynucleotide kinase/phosphatase activity and its inhibitors based on G-quadruplex/hemin DNAzyme

Here we report a new approach for label-free colorimetric assay of T4 polynucleotide kinase/phosphatase (PNKP) activity based on G-quadruplex/hemin DNAzyme. In the presence of T4 PNKP, the DNA primer with a 3'-phosphate can be dephosphorylated into a 3'-hydroxyl and initiate a primer elongation reaction to open the hairpin probe, and leading to releasing the G-quartets. Under optimal conditions, the proposed method exhibited a considerable performance with a detection limit of 0.01 U/mL. Furthermore, the present assay can be used to study the potential T4 PNKP inhibitor screening, making it promise to be applied in the fields of drug discovery.

Label-free and amplified colorimetric assay of ribonuclease H activity and inhibition based on a novel enzyme-responsive DNAzyme cascade

A simple, label-free and amplified colorimetric assay strategy based on a novel enzyme-responsive DNAzyme cascade is developed for assay of ribonuclease H activity and inhibition. This assay exhibits high sensitivity and selectivity.