A simple and sensitive fluorescence method for detection of telomerase activity using fusion protein bouquets

Research progress of organic fluorescent probes for lung cancer related biomarker detection and bioimaging application

As one of the major public health problems, cancers seriously threaten the human health. Among them, lung cancer is considered to be one of the most life-threatening malignancies. Therefore, developing early diagnosis technology and timely treatment for lung cancer is urgent. Recent research has witnessed that measuring changes of biomarkers expressed in lung cancer has practical significance. Meanwhile, we note that bioimaging with organic fluorescent probes plays an important role for its high sensitivity, real-time analysis and simplicity of operation. In the past years, kinds of organic fluorescent probes targeting lung cancer related biomarker have been developed. Herein, we summarize the research progress of organic fluorescent probes for the detection of lung cancer related biomarkers in this review, along with their design principle, luminescence mechanism and bioimaging application. Additionally, we put forward some challenges and future prospects from our perspective.

Highly selective detection of deoxyribonucleic acid in living cells using RecA-green fluorescent protein-single-stranded deoxyribonucleic acid filament fluorescence resonance energy transfer probe

A fluorescence resonance energy transfer (FRET) method was developed for double-stranded deoxyribonucleic acid (dsDNA) detection in living cells using the RecA-GFP (green fluorescent protein) fusion protein filament. In brief, the thiol-modified single-stranded DNA (ssDNA) was attached to gold nanoparticles (AuNPs); on the contrary, the prepared RecA-GFP fusion protein interacted with ssDNA. Due to the FRET between AuNPs and RecA-GFP, fluorescence of RecA-GFP fusion protein was quenched. In the presence of homologous dsDNA, homologous recombination occurred to release RecA-GFP fusion protein. Thus, the fluorescence of RecA-GFP was recovered. The dsDNA concentration was detected using fluorescence intensity of RecA-GFP. Under optimal conditions, this method could detect dsDNA activity as low as 0.015 optical density (OD) Escherichia coli cells, with a wide linear range from 0.05 to 0.9 OD cells, and the regression equation was ΔF = 342.7c + 78.9, with a linear relationship coefficient of 0.9920. Therefore, it provided a promising approach for the selective detection of dsDNA in living cells for early clinical diagnosis of genetic diseases.

A label- and enzyme-free fluorescence assay based on thioflavin T–induced G-quadruplexes for the detection of telomerase activity

A label- and enzyme-free fluorescence assay based on thioflavin T–induced G-quadruplexes is developed to sensitively and specifically detect telomerase activity. Thioflavin T has a dual role as an efficient inducer and fluorescent probe, and the incorporation of thioflavin T into the thioflavin T–induced G-quadruplexes results in an intense fluorescence enhancement. In the presence of thioflavin T and K+, G-quadruplexes are formed by elongation of the telomerase substrate primer that is catalyzed by telomerase extracted from cancer cells. Thus, the telomerase activity in cancer cell extracts can be evaluated by measuring the thioflavin T fluorescence. More importantly, thioflavin T can specifically recognize and bind to G-quadruplexes, whereas it cannot recognize single- and double-stranded DNAs, which leads to the thioflavin T–based fluorescence assay exhibiting a reduced background and improved signal-to-noise ratio. As a result, the proposed assay has the linear range from 5 to 200 HeLa cells and the detection limit is 34 HeLa cells, which holds great potential for use in the detection of telomerase activity and the diagnosis of cancer.

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.

An ultrasensitive and point-of-care sensor for the telomerase activity detection

Telomerase owns great application potential in diagnosis, therapy, prognosis, and drug screening of cancers. Thus, the ultrasensitive and point-of-care detection of telomerase activity meets the clinical demands extremely. Here, a sensor based on telomerase extends activators to unlock the ssDNase activity of CRISPR/Cas12a was created for the first time to detect the telomerase activity. Based on the fluorescence or CRISPR/Cas12a-based lateral flow assay, we achieve the ultrasensitive and point-of-care detection of telomerase activity in MCF-7 cells low to 57 cells·mL^-1 and 5.7 × 10² cells·mL^-1 in about 1 h, respectively. Besides, the detection of telomerase activity in different subtype breast cancer cells indicates that the proposed sensor possesses potential in the classification of breast cancer cell subtypes.

Gelatin nanoparticles transport DNA probes for detection and imaging of telomerase and microRNA in living cells

Telomerase and microRNA (miRNA) are biomarkers closely related to tumors. Simultaneous detection of both markers can improve accuracy and reliability of early diagnosis. Based on the mechanism of fluorescence resonance energy transfer (FRET), two fluorescent DNA probes were designed for telomerase and miRNA-21. The probes were wrapped by gelatin through electrostatic interaction to form nanoparticles. After that, we synthesized molecularly imprinted coating of transferrin on the surface of gelatin nanoparticles, which can avoid the immune stress response and macrophage phagocytosis to help gelatin nanoparticles enter into the cells smoothly through endocytosis. Following with the degradation of gelatin in the cells, DNA probes were released to react with telomerase and miRNA-21 and lead to the change of the fluorescence signal. Thereby the simultaneous imaging of telomerase and miRNA-21 were successfully achieved in HeLa cells and HepG2 cells. The proposed strategy shows the simultaneous imaging for different biological markers with DNA probes by preventing them from being hydrolyzed with nucleases before the determination and achieves reliable method for early diagnosis of cancer.