Manifold methods for telomerase activity detection based on various unique probes

Surface-tethered electrochemical biosensor for telomerase detection by integration of homogeneous extension and hybridization reactions

The general electrochemical biosensors for telomerase detection require the immobilization of primers on the electrode surface for telomeric extension and hybridization reactions. However, immobilization of primers may suffer from the challenges of hindrance effect and configuration freedom, thus reducing the extension and hybridization efficiency. Herein, we developed a sensitive electrochemical biosensor for telomerase detection by integration of homogeneous extension and hybridization reactions and surface-tethered detection. In the presence of telomerase, the biotinylated primer (bio-primer) was efficiently elongated with telomeric repeats of (TTAGGG)_n at the 3' end in solution. Then, the extension product (bio-DNA) was hybridized with the signal probe DNA modified on the surface of ferrocene (Fc)-capped gold nanoparticle (AuNP). The bio-DNA/DNA/Fc-AuNP hybrids were then tethered by streptavidin-modified electrodes through the specific avidin-biotin interactions, thus producing strong electrochemical signals from the oxidation of Fc tags. The biosensor was successfully used to determine telomerase in HeLa cells and monitor the inhibition efficiency of inhibitor. A wide linear range for the detection of telomerase extracted from HeLa cells was attained. This method has great potential in clinical diagnosis and anti-cancer drug development, and should be beneficial for the fabrication of novel biosensors by integration of homogeneous catalysis and hybridization reactions.

A simple and smart AND-gate DNA nanoprobe for correlated enzymes tracking and cell-selective imaging

Accurate cancer diagnosis and effective drug therapy entail sensitive and dynamic monitoring of intracellular key enzymes, since their expression level is closely related to disease progression. Simultaneous monitoring of correlated enzymes is promising to help unveiling mystery of cytobiological events during tumor progression and drug response, while is challenged by lacking of a robust and simple simultaneous detection strategy. In order to construct a simple and smart strategy which is complex design-avoided and doesn't need other auxiliary enzyme, here we develop an AND-gate strategy for simultaneously monitoring correlated enzymes which both are upregulated in cancer cells (telomerase and apurinic/apyrimidinic endonuclease 1). An innovative AND-gate DNA nanoprobe has been designed to avoid mutual interference and background noise, guaranteeing an enhanced fluorescent signal output upon catalyzation of dual enzymes. This AND-gate strategy achieves sensitive detection of two enzymes in an individual manner in test tube, through which the diagnostic potential of bladder cancer has been validated by telomerase detection in clinical urine sample. The AND-gate strategy enables specific intracellular imaging of dual enzymes in different cancer cell lines. Importantly, in contrast to traditional single-targeting strategies, AND-gate imaging of dual enzymes significantly improves cancer cell selectivity. Moreover, this strategy dynamically monitors enzymatic activity changes during chemoresistance induced by chemotherapeutic treatment. This simple and smart strategy has foreseeable prospect in the fields of disease diagnosis, drug prognosis evaluation, and precise fluorescence-guided surgery.

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.

Dual biomineralized metal-organic frameworks-mediated conversion of chemical energy to electricity enabling portable PEC sensing of telomerase activity in bladder cancer tissues

In this work, we report on a portable photoelectrochemical (PEC) sensing system for telomerase activity detection based on dual biomineralized ZIF-8 nanoparticles (NPs)-medicated conversion of chemical energy to electricity and terminal deoxynucleoside transferase (TdTase)-catalyzed elongation of Y-junction DNA structure. Two kinds of biomineralized ZIF-8 NPs including glucose oxidase (GOx)-encapsulated ZIF-8 (GZIF) and horseradish peroxidase (HRP)-encapsulated ZIF-8 (HZIF) are involved in this assay system. The recognition of telomerase is started with telomerase-catalyzed elongation of a telomerase substrate (TS) primer, which generates a longer elongation chain to trigger the formation of a Y-junction DNA structure. The Y-junction DNA with abundant 3'-OH terminal and small steric hindrance facilitates the implement of TdTase-catalyzed elongation reaction, in which the branches of Y-junction DNA are elongated and endowed with biotin moiety to capture streptavidin-modified GZIF (SA-GZIF). The signal transduction is then achieved on a luminol/HZIF/CdS-based photoelectrode. Once the H₂O₂ produced from GZIF-catalyzed hydrolysis of glucose is introduced to the photoelectrode, chemiluminescence of HRP-luminol-H₂O₂-p-iodo-phenol (PIP) system confined in HZIF is activated to excite photocurrent of CdS NPs, which is then recorded by a portable digital multimeter (DMM). The developed PEC sensing system possesses a wide calibration range from 50 to 5000 HeLa cells and a low detection limit of 46 cells. Significantly, the sensing platform is successfully applied to evaluate the telomerase activity in resected bladder tumor tissues. This work not only provides a diagnostic tool for telomerase-related diseases but also open a new avenue for establishing PEC assay methods using metal-organic framework (MOF) NPs.

The Red Color of Life Transformed - Synthetic Advances and Emerging Applications of Protoporphyrin IX in Chemical Biology

Protoporphyrin IX (PPIX) is the porphyrin scaffold of heme b, a ubiquitous prosthetic group of proteins responsible for oxygen binding (hemoglobin, myoglobin), electron transfer (cytochrome c) and catalysis (cytochrome P450, catalases, peroxidases). PPIX and its metallated derivatives frequently find application as therapeutic agents, imaging tools, catalysts, sensors and in light harvesting. The vast toolkit of accessible porphyrin functionalization reactions enables easy synthetic modification of PPIX to meet the requirements for its multiple uses. In the past few years, particular interest has arisen in exploiting the interaction of PPIX and its synthetic derivatives with biomolecules such as DNA and heme-binding proteins to evolve molecular devices with new functions as well as to uncover potential therapeutic toeholds. This review strives to shine a light on the most recent developments in the synthetic chemistry of PPIX and its uses in selected fields of chemical biology.

Point-of-Care Strategies for Detection of Waterborne Pathogens

Waterborne diseases that originated due to pathogen microorganisms are emerging as a serious global health concern. Therefore, rapid, accurate, and specific detection of these microorganisms (i.e., bacteria, viruses, protozoa, and parasitic pathogens) in water resources has become a requirement of water quality assessment. Significant research has been conducted to develop rapid, efficient, scalable, and affordable sensing techniques to detect biological contaminants. State-of-the-art technology-assisted smart sensors have improved features (high sensitivity and very low detection limit) and can perform in a real-time manner. However, there is still a need to promote this area of research, keeping global aspects and demand in mind. Keeping this view, this article was designed carefully and critically to explore sensing technologies developed for the detection of biological contaminants. Advancements using paper-based assays, microfluidic platforms, and lateral flow devices are discussed in this report. The emerging recent trends, mainly point-of-care (POC) technologies, of water safety analysis are also discussed here, along with challenges and future prospective applications of these smart sensing technologies for water health diagnostics.

In situ Analysis of Cancer Cells Based on DNA Signal Amplification and DNA Nanodevices

Cancer is a global disease which has been disturbing researchers in medicine and seriously threatens patients' health and lifetime around the world in the past several decades. Due to the characteristics of cancer cells, such as uncontrollable cell proliferation, cell invasion and metastasis to surrounding tissues, lower grade of differentiation, higher telomerase activity and others, it has been one of the most usual lethal factors, next to heart disease in incidence. Cancer mortality can be decreased by early diagnosis, and the people who with treatment at an early stage have an obvious improved survival rate. Consequently, early detection is significant for better understanding the pathogenesis of cancer and improving the prognosis of patients. In situ detection technique is a vital tool for imaging and cellular pathology research, which can provide effective information about tumor markers in the early cancer detection. In view of low expression of most tumor markers in the early stage of cancers, detection techniques based on DNA signal amplification and DNA nanodevices can provide a strong support for the diagnosis and detection of cancers. In this review, we summarize the research progress of different analytical techniques for detecting various tumor markers that have been reported in recent years. We compare different DNA amplification and nanodevices, then provide guidance and suggestions for better understanding in situ analysis of cancer cells.

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.

Telomerase and poly(ADP-ribose) polymerase-1 activity sensing based on the high fluorescence selectivity and sensitivity of TOTO-1 towards G bases in single-stranded DNA and poly(ADP-ribose)

Telomerase and poly(ADP-ribose) polymerase-1 (PARP-1) are two potential cancer biomarkers and are closely related to tumor initiation and malignant progression. TOTO-1 is well-known for differentiating ss-DNA from ds-DNA because it is virtually non-fluorescent without DNA and exhibits very low fluorescence with ss-DNA, while it emits strong fluorescence with ds-DNA. In this paper, for the first time, it was found that TOTO-1 has high fluorescence selectivity and sensitivity towards the G bases in single-stranded DNA and poly(ADP-ribose) (PAR). Poly(dG) was used as the model target to explore its possible mechanism. Molecular dynamics (MD) simulation proved that intramolecular π-π stacking existed in TOTO-1 (in an aqueous solution), while intermolecular π-π stacking formed between TOTO-1 and poly(dG) in a similar way as that observed for dsDNA. Interestingly, telomerase and PARP-1 catalyzed the formation of G-rich DNA and PAR in vivo, respectively. Therefore, TOTO-1 was explored in detecting both of them, obtaining satisfactory results. To the best of our knowledge, no probe has been reported to recognize PAR. It is also the first time where telomerase is detected based on the specific recognition of G bases. Importantly, integrating multiple functions into one probe that can detect not only telomerase but also PARP-1 will significantly raise the specificity of screening cancer and decrease false positive proportion, which make TOTO-1 a promising candidate probe for clinical diagnosis and pharmaceutical screening.

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.

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.