Ghrelin Detection Using Spiegelmer‐Capture Molecules

Mirror-Image Oligonucleotides: History and Emerging Applications

As chiral molecules, naturally occurring d-oligonucleotides have enantiomers, l-DNA and l-RNA, which are comprised of l-(deoxy)ribose sugars. These mirror-image oligonucleotides have the same physical and chemical properties as that of their native d-counterparts, yet are highly orthogonal to the stereospecific environment of biology. Consequently, l-oligonucleotides are resistant to nuclease degradation and many of the off-target interactions that plague traditional d-oligonucleotide-based technologies; thus making them ideal for biomedical applications. Despite a flurry of interest during the early 1990s, the inability of d- and l-oligonucleotides to form contiguous Watson-Crick base pairs with each other has ultimately led to the perception that l-oligonucleotides have only limited utility. Recently, however, scientists have begun to uncover novel strategies to harness the bio-orthogonality of l-oligonucleotides, while overcoming (and even exploiting) their inability to Watson-Crick base pair with the natural polymer. Herein, a brief history of l-oligonucleotide research is presented and emerging l-oligonucleotide-based technologies, as well as their applications in research and therapy, are presented.

Noncompetitive affinity assays of glucagon and amylin using mirror-image aptamers as affinity probes

The ability to detect picomolar concentrations of glucagon and amylin using fluorescently labeled mirror-image aptamers, so-called Spiegelmers, is demonstrated. Spiegelmers rival the specificity of antibodies and overcome the problem of biostability of natural aptamers in a biological matrix. Using Spiegelmers as affinity probes, noncompetitive capillary electrophoresis affinity assays of glucagon and murine amylin were developed and optimized. The detection limit for glucagon was 6 pM and for amylin was 40 pM. Glucagon-like peptide-1 and -2 did not interfere with the glucagon assay, while the amylin assay showed cross-reactivity to calcitonin gene related peptide. The developed assays were combined with a competitive immunoassay for insulin to measure glucagon, amylin, and insulin secretion from batches of islets after incubation with different glucose concentrations. The development of these assays is an important step towards incorporation into an online measurement system for monitoring dynamic secretion from single islets.

Use of RNA in drug design

This is a review of RNA as a target for small molecules (ribosomes, riboswitches, regulatory RNAs) and RNA-derived oligonucleotides as tools (antisense/small interfering RNA, ribozymes, aptamers/decoy RNA and microRNA). This review highlights the present state of research using RNA as a drug target or as a potential drug candidate and explains at which stage and to what extent rational design could eventually be involved. Special attention has been paid to the recent potential clinical applications of RNA either as drugs or drug targets. The review deals mainly with mechanistic approaches rather than with physicochemical or computational aspects of RNA-based drug design.

Aptamer-based silver nanosensor for multiple protein detection

In the present work we design a novel aptamer-based silver nanosensor for one-spot simultaneously detection of multiple proteins. SS-DNA modified AgNPs were immobilized on the aldehyde coated glass slide to form an AgNP array. Then dye-labeled aptamer sequences were allowed to hybridize with their complementary strands assembled on the surface of AgNPs. The target proteins were introduced to associate with the corresponding aptamers to form the aptamer-target complexes. The removal of the aptamer-target complexes resulted in a remarkable decrease in fluorescent signals. This nanosensor is found to be highly sensitive for the detection of proteins. When thrombin was employed as a sample model, the limit of detection of the optimized nanosenor was 0.4 fmol with a linear response of 0.8 fmol to 0.5 pmol. We further demonstrated the multiple protein detection of IgE and thrombin using multicolor silver nanoprobes, which shows effective recognition of the relative protein individually or simultaneously. This silver nanosensor offers a unique heterogeneous approach for protein detection with several advantages, such as high sensitivity, rapidity, high throughput, and miniaturization.

Optical detection systems using immobilized aptamers

Advances in the development and the applications of optical biosensing systems based on immobilized aptamers are presented. These nucleic acid sequences have been used as new molecular recognition elements to develop heterogeneous assays, biosensors and microarrays. Among different detection modes that have been employed, optical ones which are described here are among the most used. Since their first report in 1996, numerous optical detection systems using aptamers and mainly based on fluorescence have been developed. Two main approaches have been used: label-based (using fluorophore, luminophore, enzyme, nanoparticles) or aptamer label-free detection systems (e.g. surface plasmon resonance, optical resonance). Most methods are based on a labeling approach. Some targets can be optically detected using not only colorimetry, chemiluminescence or the most developed fluorescence mode but also more recent non conventional optical methods such as surface plasmon-coupled directional emission (SPCDE). The first SPCDE-based aptasensor for thrombin detection has recently been reported in 2009. Aptasensors based on surface-enhanced Raman scattering spectroscopy (SERS) which presents advantages compared to fluorescence have also been described. Different label-free techniques have recently been shown to be suitable for developing performant aptasensors or aptamer-based microarrays, such as surface plasmon resonance (SPR), diffraction grating, evanescent-field-coupled (EFC) waveguide-mode, optical resonance or Brewster angle straddle interferometry (BASI). Important advances have been realized on optical aptamer-based detection systems that appear as highly efficient devices with enormous potential.