Advantages Of Aptamers Research Articles

Nucleic acid aptamer-mediated drug delivery for targeted cancer therapy.

Aptamers are emerging as promising therapeutic agents and recognition elements. In particular, cell-SELEX (systematic evolution of ligands by exponential enrichment) allows in vitro selection of aptamers selective to whole cells without prior knowledge of the molecular signatures on the cell surface. The advantage of aptamers is their high affinitiy and binding specificity towards the target. This Minireview focuses on single-stranded (ss) oligonucleotide (DNA or RNA)-based aptamers as cancer therapeutics/theranostics. Specifically, aptamer-nanomaterial conjugates, aptamer-drug conjugates, targeted phototherapy and targeted biotherapy are covered in detail. In reviewing the literature, the potential of aptamers as delivery systems for therapeutic and imaging applications in cancer is clear, however, major challenges remain to be resolved, such as the poorly understood pharmacokinetics, toxicity and off-target effects, before they can be fully exploited in a clinical setting.

A label-free fluorescence assay for thrombin based on aptamer exonuclease protection and exonuclease III-assisted recycling amplification-responsive cascade zinc(ii)-protoporphyrin IX/G-quadruplex supramolecular fluorescent labels

A simple, label-free and sensitive fluorescence protein assay has been developed on the basis of aptamer exonuclease protection and exonuclease III (Exo III)-assisted recycling amplification-responsive cascade ZnPPIX/G-quadruplex supramolecular fluorescent labels. In the sensing system, a special aptamer probe containing the aptamer sequence at the 3'-terminus and the DNAzyme sequence at the 5'-terminus was applied, which has the capacity to recognize a protein target with high affinity and specificity. Exonuclease I (Exo I) can efficiently catalyze the degradation of free single stranded DNA probes in the 3' to 5' direction. In the presence of the target protein, the strong binding between the target protein and its aptamer can protect aptamer probes from degradation. Subsequently, the protected aptamer probes act as catalysators to trigger hybridization with the hairpin DNA probe that contains a partially "caged" G-quadruplex sequence. Upon interaction with the protected aptamer probes, the hairpin opens to yield the active G-quadruplex structure. In the presence of exonuclease III (Exo III), Exo III-assisted recycling amplification occurs generating numerous G-quadruplex supramolecular structures. The zinc(ii)-protoporphyrin IX (ZnPPIX) fluorophore binds to the G-quadruplexes and this results in the enhanced fluorescence of the fluorophore. The resulting fluorescence of the ZnPPIX/G-quadruplex provides the readout signal for the sensing event. Thrombin is used as the model analyte in the current proof-of-concept. The developed method was demonstrated to have very high sensitivity for the detection of proteins with a limit of detection of 0.2 pM without using washes or separations. In addition, this new method for protein detection is simple and inherits all the advantages of aptamers. The mechanism, moreover, may be generalized and used for other forms of protein analysis.

Aptamers as affinity ligands for downstream processing

Aptamers are single‐stranded synthetic oligonucleotides that are able to capture their target molecule with high affinity and specificity. Therefore, they can be thought of as nucleic acid‐based alternative to antibodies, which have several advantages over their amino acid‐based counterparts. Consequently, aptamers can be used in different applications based on molecular recognition including affinity separations. This review will summarize the state‐of‐the‐art in aptamer‐based affinity separations; will discuss the current limitations and will highlight possible future prospects. The first part will point out the advantages of aptamers in downstream processing. Here, the properties of aptamers will be discussed along with their implications on downstream processing from a user's point of view. In the second part, a brief summary of the literature is given with focus on aptamer‐based separation of proteins. Finally, some drawbacks of aptamers will be illustrated and possibilities to overcome these limitations will be suggested. New technologies in the fields of aptamer selection and synthesis are expected to further promote the use of aptamers as affinity ligands in downstream processing.

Aptamer-based assay for prion diseases diagnostic

Abstract Prion diseases is a group of fatal neurodegenerative diseases which cause serious damages in human and animals. Prion diseases-associated isoform (PrPSc), the only marker of these diseases, is abundant in brain only at the late stage which makes the disease diagnostic at the presymptomatic stage difficult. Aptamers owing to their intrinsic advantages such as excellent stability, easy manipulation and reproducible, nontoxic and diagnostic potential, have been applied in protein detection, molecular recognition, cancer diagnostic and cell imaging. Recent years, various aptamers that bind to prion protein (PrP) with high affinity and selectivity were selected by different groups and the application of aptamers to prion diseases diagnostic is arousing more and more attentions as the intrinsic advantages of aptamers. In this context, we will introduce prion diseases, the challenges of prion diseases diagnostic at the presymptomatic stage and aptamers against PrP, and then summarize the latest progress of aptamers-based assay for prion diseases diagnostic.

Sensitive Discrimination and Detection of Prion Disease-Associated Isoform with a Dual-Aptamer Strategy by Developing a Sandwich Structure of Magnetic Microparticles and Quantum Dots

The major challenge of prion disease diagnosis at the presymptomatic stage is how to sensitively or selectively discriminate and detect the minute quantity of disease-associated prion protein isoform (PrP(Res)) in complex biological systems such as serum and brain homogenate. In this contribution, we developed a dual-aptamer strategy by taking the advantages of aptamers, the excellent separation ability of magnetic microparticles (MMPs), and the high fluorescence emission features of quantum dots (QDs). Two aptamers (Apt1 and Apt2), which can recognize their two corresponding distinct epitopes of prion proteins (PrP), were coupled to the surfaces of MMPs and QDs, respectively, to make MMPs-Apt1 and QDs-Apt2 ready at first, which then could be coassociated together through the specific recognitions of the two aptamers with their two corresponding distinct epitopes of PrP, forming a sandwich structure of MMPs-Apt1-PrP-Apt2-QDs and displaying the strong fluorescence of QDs. Owing to the different binding affinities of the two aptamers with PrP(Res) and cellular prion protein (PrP(C)), both of which have distinct denaturing detergent resistance, our dual-aptamer strategy could be applied to discriminate PrP(Res) and PrP(C) successfully in serum. Further identifications showed that the present dual-aptamer assay could be successfully applied to the detection of PrP in 0.01% brain homogenate, about 1000-fold lower than that of commonly applied antibody-mediated assays, which can detect PrP just in 10% brain homogenate, indicating that the present designed dual-aptamer assay is highly sensitive and adequate for clinical diagnosis without isolation of target protein prior to assay.

ChemInform Abstract: Homogeneous Analysis: Label‐Free and Substrate‐Free Aptasensors

AbstractReview: 56 refs.

Homogeneous Analysis: Label‐Free and Substrate‐Free Aptasensors

In this Focus Review, we introduce a kind of "label-free" and "substrate-free" (LFSF) aptasensor that carries out the whole sensing process in a homogeneous solution. This means that commonly used covalent label; separation, and immobilization steps in biosensors are successfully avoided, which simplifies the sensing operations to the greatest degree. After brief description about the advantages of aptamers and "LFSF" aptasensors, the main content of the review is divided into fluorescent aptasenors, calorimetric aptasensors, and hemin-aptamer-DNAzyme "LFSF" aptasensors, which are three most widely developed sensing systems in this field. It is hoped that this review can provide an overall scene about how aptamers function as ideal recognition elements in smart analysis.

Aptamers as molecular recognition elements for electrical nanobiosensors.

Recent advances in nanotechnology have enabled the development of nanoscale sensors that outperform conventional biosensors. This review summarizes the nanoscale biosensors that use aptamers as molecular recognition elements. The advantages of aptamers over antibodies as sensors are highlighted. These advantages are especially apparent with electrical sensors such as electrochemical sensors or those using field-effect transistors.FigureFeeling proteins with aptamer-functionalized carbon nanotubes

Ultrasensitive detection of protein using an aptamer-based exonuclease protection assay.

Currently, methods for protein detection are not as sensitive and specific as methods for detection of specific nucleic acid sequences. Here, we present an analogous technique for detection of proteins using aptamers as ligands for target binding. We have named this method the aptamer-based exonuclease protection assay. We applied a special oligonucleotide probe containing a thrombin aptamer, which has the capacity to recognize thrombin with high affinity and specificity. The aptamer probe is a 22-base-long single-strand oligonucleotide with the thrombin aptamer sequence at the 3'-terminus and 7 additional nucleotides at the 5'-terminus, which is able to bind thrombin with high affinity and specificity. In the exonuclease protection assay, thrombin binds the aptamer and thereby protects it from degradation by exonuclease I, whereas any unbound aptamer probe is degraded by exonuclease I. Subsequently, the aptamer probes that were protected from exonuclease I by thrombin act as linkers to join two free connectors, which contain sequences matching the probe. The joined products, which reflect the identity and amount of the target protein, are amplified by PCR. The exonuclease protection assay is extremely sensitive, since it is based on PCR amplification. This method can detect as few as several hundred molecules of target protein without using washes or separations. In addition, this new method for protein detection is simple and inherits all the advantages of aptamers. The mechanism, moreover, may be generalized and used for other forms of protein analysis.