Aptameric sensors based on structural change for diagnosis

Aptamer-enhanced particle aggregation inhibition assay for simple homogeneous protein detection using DNA aptamer and thermo-responsive magnetic nanoparticles

A simple and sensitive homogeneous protein detection system is required for the early detection of biomarkers. Thermo-responsive magnetic particles (TM) have already been developed to achieve easy bound/free separation at the homogeneous protein detection system, but they are still limited owing to the requirement of secondary antibodies and negatively charged polymers, and it is challenging to control the TM aggregation behavior because of the size of the TM. Therefore, at new method to control TM aggregation behavior that is simple, easy, and highly sensitive is required. In this study, we developed a DNA aptamer-based TM assay as a simple protein detection system without additional secondary molecular recognition elements or negatively charged polymer. In the first attempt, a DNA aptamer was modified on the TM surface, and its aggregation behavior was monitored depending on the target molecule concentration. The TM aggregation rate during the heating process decreased depending on the amount of the DNA aptamer and increased depending on the target protein level. This suggests that the DNA aptamer prevented TM aggregation owing to its negative charge and achieved target protein detection owing to the cancellation of repulsion. Capturable aptamers were used in the TM assay to improve the sensitivity and limit of detection. The designed Capture DNA was modified on the TM surface, and the aptamer was captured in the presence of the target protein through a conformational change. Eventually, Capturable aptamer-based TM assay achieved a sub-nanomolar limit of detection and higher sensitivity than that of our initial investigation. Through this study and the ease of the DNA aptamer design, it was shown that the DNA aptamer-modified TM assay enabled the development of a simple and sensitive homogeneous protein detection system.

SELEX Modifications and Bioanalytical Techniques for Aptamer-Target Binding Characterization

The quest to improve the detection of biomolecules and cells in health and life sciences has led to the discovery and characterization of various affinity bioprobes. Libraries of synthetic oligonucleotides (ssDNA/ssRNA) with randomized sequences are employed during Systematic Evolution of Ligands by Exponential Enrichment (SELEX) to select highly specific affinity probes called aptamers. With much focus on the generation of aptamers for a variety of target molecules, conventional SELEX protocols have been modified to develop new and improved SELEX protocols yielding highly specific and stable aptamers. Various techniques have been used to analyze the binding interactions between aptamers and their cognate molecules with associated merits and limitations. This article comprehensively reviews research advancements in the generation of aptamers, analyses physicochemical conditions affecting their binding characteristics to cellular and biomolecular targets, and discusses various field applications of aptameric binding. Biophysical techniques employed in the characterization of the molecular and binding features of aptamers to their cognate targets are also discussed.

Supramolecular electron transfer-based switching involving pyrrolic macrocycles. A new approach to sensor development?

The potential utility of energy transfer in the design of pyrrolic macrocycle-based molecular switches and ability to serve as the readout motif for molecular sensors development is discussed.

Emerging techniques employed in aptamer-based diagnostic tests

Since aptamers were reported in 1990, research into the applications of aptamers, particularly diagnostic applications, has been growing. Aptamers can act as recognition elements instead of antibodies. In this regard, aptamers have unique characteristics because they are composed of nucleic acids. Intra- and intermolecular interactions of nucleic acids can be easily tailored following straightforward hybridization rules. Nucleic acids can be enzymatically replicated and their sequences can be determined using high-throughput methods. Using these properties, ligand-induced structural change-based aptamer sensors for homogeneous assays, polymerase- and/or nuclease-combined aptamer sensors for ultrasensitive assays, and microarray/next-generation sequencing-based aptamer sensors for multiplexed assays have been developed. This article reviews these unique aptamer sensors, demonstrating their great potential for diagnostic applications.

Electrochemical biosensors using aptamers for theranostics

Theranostics, a new term consisting of the words "therapy" and "diagnostics," represents the concept of selecting specific patients for appropriate drug administration using diagnostics. For the development of a molecular targeting drug, the theranostics approach is effective. Therefore, the market for molecular diagnostics is likely to grow at an extraordinary rate over the next 10 years. In this review, we focus on aptamer-based electrochemical biosensors for theranostics. Aptamers are molecular recognition elements that can bind to various target molecules from small compounds to proteins with affinities and specificities comparable to those of antibodies. Inasmuch as various molecules would be targeted for analysis using theranostics, aptamer-based biosensors would be an attractive format because they can be developed for various molecules using the same sensing format. Although a diverse sensing system can be constructed, we focus on electrochemical biosensors in this review because they can measure biomarkers rapidly in a miniaturized sensing system with low cost, such as blood glucose sensors. We summarize the sensing systems of aptamer-based electrochemical biosensors and discuss their advantages for theranostics.

The future: biomarkers, biosensors, neuroinformatics, and e-neuropsychiatry

The emergence of molecular biomarkers for psychological, psychiatric, and neurodegenerative disorders is beginning to change current diagnostic paradigms for this debilitating family of mental illnesses. The development of new genomic, proteomic, and metabolomic tools has created the prospect of sensitive and specific biochemical tests to replace traditional pen-and-paper questionnaires. In the future, the realization of biosensor technologies, point-of-care testing, and the fusion of clinical biomarker data, electroencephalogram, and MRI data with the patient's past medical history, biopatterns, and prognosis may create personalized bioprofiles or fingerprints for brain disorders. Further, the application of mobile communications technology and grid computing to support data-, computation- and knowledge-based tasks will assist disease prediction, diagnosis, prognosis, and compliance monitoring. It is anticipated that, ultimately, mobile devices could become the next generation of personalized pharmacies.

Control of aptamer function using radiofrequency magnetic field

Remote control of aptamer function has allowed us to control protein function in space and time. Here, we propose a novel control system for aptamer function by radiofrequency magnetic field- (RFMF-) induced local heating of a gold nanoparticle conjugated with an aptamer. In this study, we used a 31-mer thrombin-binding aptamer (TBA), which can inhibit thrombin activity, as a model aptamer. We evaluated the RFMF control of the inhibitory activity of a gold nanoparticle-conjugated TBA. To evaluate the effect of RFMF on enzymatic activity, we utilized a complementary DNA strand that maintains the broken structure during the activity assay. We observed a decrease in the inhibitory activity of TBA after RFMF irradiation. It indicates that RFMF is capable of controlling the TBA structure. Because RFMF allows noninvasive control of aptamer function, this strategy is expected to be novel way of controlling aptamer drug activity.