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Site-selective protein modification is a key step in facilitating protein functionalization and manipulation. To accomplish this, genetically engineered proteins were previously required, but the procedure was laborious, complex, and technically challenging. Herein we report the development of aptamer-based recognition-then-reaction to guide site-selective protein/DNA conjugation in a single step with outstanding selectivity and efficiency. As models, several proteins, including human thrombin, PDGF-BB, Avidin, and His-tagged recombinant protein, were studied, and the results showed excellent selectivity under mild reaction conditions. Taking advantage of aptamers as recognition elements with extraordinary selectivity and affinity, this simple preparation method can tag a protein in a complex milieu. Thus, with the aptamer obtained from cell-SELEX, real-time modification of live-cell membrane proteins can be achieved in one step without any pre-treatment.

In the past two decades, the study of cancer therapy has gradually advanced to the 'nano' era. Numerous novel nanomaterials armed with unique physical properties have been introduced into biomedical research. At the same time, functional nucleic acid molecules, especially aptamers, have aroused broad attention from the biomedical community. Benefiting from the advancement of molecular engineering strategies, it is now feasible to combine the cancer-specific recognition capability of aptamers with various other special functions of nanomaterials to develop cancer-specific drugs at the nanoscale. Nanodrugs are now offering an unprecedented opportunity to achieve the goal of efficient targeted delivery as well as controlled release. This review highlights some achievements made in multiple aptamer-based nanodrug systems that have emerged in recent years, including studies in the infant stage of 'proof-of-concept'. [ABSTRACT FROM AUTHOR]

Guanine (G)-rich oligonucleotides have attracted considerable interest as therapeutic agents. Two G-rich aptamers were selected against epidermal growth factor receptor (EGFR)-transfected A549 cells, and their G-rich domains (S13 and S50) were identified to account for the binding of parental aptamers. Circular dichroism (CD) spectra showed that S13 and S50 bound to their targets by forming parallel quadruplexes. Their binding, internalization, and antiproliferation activity in cancer and noncancer cells were investigated by flow cytometry and 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2 H-tetrazolium (MTS) assay, and compared with those of nucleolin-binding AS1411 and thrombin-binding aptamer. The two truncated aptamers (S13 and S50) have good binding and internalization in cancer cells and noncancer cells; however, only S50, similar to AS1411, shows potent antiproliferation against cancer cells. Our data suggest that tumor-selective antiproliferation of G-rich oligonucleotides does not directly depend on the binding of the G-rich aptamer to cells. [ABSTRACT FROM AUTHOR]

Fullerene-based photosensitizers exhibit great potential in photodynamic therapy (PDT). Based on the high photodynamic efficacy of trimalonic acid-modified C70 fullerene (TF70), we constructed an aptamer-guided TF70 photosensitizer and investigated its photodynamic effect. Conjugation of the novel aptamer (named R13) could effectively enhance the PDT efficiency of TF70 against A549 lung cancer cells in the presence of serum. The lysosomal location of the TF70-R13 conjugate inside cells facilitates the production of intracellular reactive oxygen species (ROS), which can efficiently kill cells, under light irradiation. The enhanced photodynamic efficiency, along with its good biocompatibility in the dark, makes TF70-R13 a highly promising photosensitizer for tumor-specific PDT. [ABSTRACT FROM AUTHOR]

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In clinical diagnostics, as well as food and environmental safety practices, biosensors are powerful tools for monitoring biological or biochemical processes. Two-dimensional (2D) transition metal nanomaterials, including transition metal chalcogenides (TMCs) and transition metal oxides (TMOs), are receiving growing interest for their use in biosensing applications based on such unique properties as high surface area and fluorescence quenching abilities. Meanwhile, nucleic acid probes based on Watson-Crick base-pairing rules are also being widely applied in biosensing based on their excellent recognition capability. In particular, the emergence of functional nucleic acids in the 1980s, especially aptamers, has substantially extended the recognition capability of nucleic acids to various targets, ranging from small organic molecules and metal ions to proteins and cells. Based on π-π stacking interaction between transition metal nanosheets and nucleic acids, biosensing systems can be easily assembled. Therefore, the combination of 2D transition metal nanomaterials and nucleic acids brings intriguing opportunities in bioanalysis and biomedicine. In this review, we summarize recent advances of nucleic acid-functionalized transition metal nanosheets in biosensing applications. The structure and properties of 2D transition metal nanomaterials are first discussed, emphasizing the interaction between transition metal nanosheets and nucleic acids. Then, the applications of nucleic acid-functionalized transition metal nanosheet-based biosensors are discussed in the context of different signal transducing mechanisms, including optical and electrochemical approaches. Finally, we provide our perspectives on the current challenges and opportunities in this promising field. [ABSTRACT FROM AUTHOR]

We have developed a DNA nanoprobe for adenosine triphosphate (ATP) sensing in living cells, based on the split aptamer and the DNA triangular prism (TP). In which nucleic acid aptamer was split into two fragments, the stem of the split aptamer was respectively labeled donor and acceptor fluorophores that underwent a fluorescence resonance energy transfer if two ATP molecules were bound as target molecule to the recognition module. Hence, ATP as a target induced the self-assembly of split aptamer fragments and thereby brought the dual fluorophores into close proximity for high fluorescence resonance energy transfer (FRET) efficiency. In the in vitro assay, an almost 5-fold increase in FA/FD signal was observed, the fluorescence emission ratio was found to be linear with the concentration of ATP in the range of 0.03-2 mM, and the nanoprobe was highly selective toward ATP. For the strong protecting capability to nucleic acids from enzymatic cleavage and the excellent biocompatibility of the TP, the DNA TP nanoprobe exhibited high cellular permeability, fast response, and successfully realized "FRET-off" to "FRET-on" sensing of ATP in living cells. Moreover, the intracellular imaging experiments indicated that the DNA TP nanoprobe could effectively detect ATP and distinguish among changes of ATP levels in living cells. More importantly, using of the split aptamer and the FRET-off to FRET-on sensing mechanism could efficiently avoid false-positive signals. This design provided a strategy to develop biosensors based on the DNA nanostructures for intracellular molecules analysis. [ABSTRACT FROM AUTHOR]