Beyond traditional needs of biosensors such as high sensitivity and selectivity for analyte detection, newly emerging requirements including a real-time detection ability and in-field applicability have been gradually emphasized to address clinical and environmental availability. Highly programmable, synthetic aptamers that can specifically recognize a broad range of targets have the potential to fulfill these requirements; cooperative binding to target molecules achieves a significant increase in sensitivity, and binding-induced structure-switching enables target detection even in complex mixtures. Due to the availability of chemical synthesis and functional modifications, these artificial ligand materials are easily installed in many devices, and the amenability to modularization allows the aptamer-based biosensors to diversify detectable targets and signaling processes. In this review, we highlight current progress in the development of aptamer-based, next-generation biosensors including new types of field-effect transistors, electrochemical detectors, and microfluidic devices. As the nucleic acid aptamers have been rapidly generated by various in vitro selection techniques, the use of the versatile nanostructures is expected to expand further to include in-field and real-time biosensors.

We describe the integration of microfluidic selection with high-throughput DNA sequencing technology for rapid and efficient discovery of nucleic acid aptamers. The Quantitative Selection of Aptamers through Sequencing method tracks the copy number and enrichment-fold of more than 10 million individual sequences through multiple selection rounds, enabling the identification of high-affinity aptamers without the need for the pool to fully converge to a small number of sequences. Importantly, this method allows the discrimination of sequences that arise from experimental biases rather than true high-affinity target binding. As a demonstration, we have identified aptamers that specifically bind to PDGF-BB protein with K _d < 3 nM within 3 rounds. Furthermore, we show that the aptamers identified by Quantitative Selection of Aptamers through Sequencing have ∼3–8-fold higher affinity and ∼2–4-fold higher specificity relative to those discovered through conventional cloning methods. Given that many biocombinatorial libraries are encoded with nucleic acids, we extrapolate that our method may be extended to other types of libraries for a range of molecular functions.

We present a one-photon visible light-responsive micellar system for efficient, on-demand delivery of small molecules.

Significance: The comprehensive functional mapping of the human proteome will require access to high-quality affinity reagents that specifically bind to their respective proteins with high affinities. Unfortunately, currently available antibodies can only target a small fraction of the proteome, and their affinity and specificity can vary considerably for each protein. Thus there is an urgent need for novel technologies capable of generating alternative, synthetic affinity reagents in a scalable and economical manner. Toward this end, we report a unique screening system (termed the “Quantitative Parallel Aptamer Selection System”) that can accelerate discovery of high-quality aptamer reagents by enabling simultaneous measurements of binding affinity ( K _d ) and specificity for thousands of aptamers in parallel.

We describe an innovative selection approach to generate self-reporting aptamers (SRAs) capable of converting target-binding events into fluorescence readout without requiring additional modification, optimization, or the use of DNA helper strands. These aptamers contain a DNAzyme moiety that is initially maintained in an inactive conformation. Upon binding to their target, the aptamers undergo a structural switch that activates the DNAzyme, such that the binding event can be reported through significantly enhanced fluorescence produced by a specific stacking interaction between the active-conformation DNAzyme and a small molecule dye, N -methylmesoporphyrin IX. We demonstrate a purely in vitro selection-based approach for obtaining SRAs that function in both buffer and complex mixtures such as blood serum; after 15 rounds of selection with a structured DNA library, we were able to isolate SRAs that possess low nanomolar affinity and strong specificity for thrombin. Given ongoing progress in the engineering and characterization of functional DNA/RNA molecules, strategies such as ours have the potential to enable rapid, efficient, and economical isolation of nucleic acid molecules with diverse functionalities.