Advances and perspectives in the analytical technology for small peptide hormones analysis: A glimpse to gonadorelin

In the last twenty years, we have witnessed an important evolution of bioanalytical approaches moving from conventional lab bench instrumentation to simpler, easy-to-use techniques to deliver analytical responses on-site, with reduced analysis times and costs. In this frame, affinity reagents production has also jointly advanced from natural receptors to biomimetic, abiotic receptors, animal-free produced. Among biomimetic ones, aptamers, and molecular imprinted polymers (MIPs) play a leading role. Herein, our motivation is to provide insights into the evolution of conventional and innovative analytical approaches based on chromatography, immunochemistry, and affinity sensing referred to as peptide hormones. Indeed, the analysis of peptide hormones represents a current challenge for biomedical, pharmaceutical, and anti-doping analysis. Specifically, as a paradigmatic example, we report the case of gonadorelin, a neuropeptide that in recent years has drawn a lot of attention as a therapeutic drug misused in doping practices during sports competitions.

Highly sensitive detection of lipopolysaccharides using an aptasensor based on hybridization chain reaction

Lipopolysaccharides (LPS), integral components of the outer membrane of all gram-negative bacteria, are closely associated with foodborne diseases such as fever, diarrhea and hypotension, and thus, the early and sensitive detection of LPS is necessary. In this study, an aptasensor assay based on hybridization chain reaction (HCR) was developed to detect LPS. Briefly, two complementary stable species of biotinylated DNA hairpins coexisted in solution until the introduction of a detection probe triggered a hybridization chain reaction cascade. The DNA conjugates specifically reacted with the LPS, which were captured by the ethanolamine aptamer attached to the reaction well surface. After optimizing the key reaction conditions, such as the reaction time of HCR, the amount of the capture probe and detection probes, the increase in the LPS concentration was readily measured by the optical density value, and a relatively low detection limit (1.73 ng/mL) was obtained, with a linear response range of 1–10⁵ng/mL. The approach presented herein introduced the use of an aptasensor for LPS discrimination and HCR for signal amplification, offering a promising option for detecting LPS.

Influences of Probe's Morphology for Metal Ion Detection Based on Light-Addressable Potentiometric Sensors

The sensing mechanism of binding Hg²⁺ into thymine-thymine (T-T) mismatched base pairs was introduced into a light-addressable potentiometric sensor (LAPS) with anti-Hg²⁺ aptamer as the sensing units. Three kinds of T-rich single-strand DNA (ssDNA) chains with different spacer lengths, from 0 to 12 –CH₂ groups, were designed to investigate surface charge and morphological effects on the LAPS’ output. First, by comparing the responding of LAPS modified with three kinds of ssDNA, it was found that the best performance for Hg²⁺ sensing was exhibited by the probe without –CH₂ groups. The detection limit of Hg²⁺ ion was 1 ppt under the optimal condition. Second, the cooperative effects of surface charge and morphology on the output were observed by the controlled experiments. The two effects were the negative charge balanced by metal cations and the morphological changing caused by the formation of T-Hg²⁺-T structure. In conclusion, not only the influences of the aptamer probe’s morphology and surface charge was investigated on the platform of LAPS, but also sensing Hg²⁺ ions was achieved for the first time by the presented aptamer LAPS.

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.

Homogeneous assays using aptamers

Aptamers are DNA or RNA oligonucleotides that can bind with high affinity and specificity to a wide range of targets such as proteins, metal ions or pathogenic microorganisms. Soluble aptamers and aptazymes have been used as sensing elements for developing homogeneous assays in a solution phase, the whole sensing process being carried out in a homogeneous solution. Contrary to most conventional heterogeneous assays that are time-consuming and labor-intensive, aptamer-based homogeneous assays are simple, easy-to-perform, rapid and do not require immobilization nor washing steps. To our knowledge, this review is the first entirely dedicated to aptamer-based homogeneous assays. Optical detection appears as the most developed technique. Colorimetry represents the simplest sensing mode that occupies a very important position among aptamer-based assays, involving gold nanoparticle aggregation (with unmodified or aptamer-modified gold NPs), the formation of HRP-mimicking DNAzyme with hemin, dye displacement or interactions with a cationic polymer. Fluorescence that is highly sensitive offers the most developed detection mode. Aptamers can be labeled or not, to give rise to turn-on or usually less sensitive turn-off fluorescent assays. Newly reported and thus less developed non-conventional magnetic resonance imaging (MRI) and electrochemistry also recently appeared in the literature, thrombin still remains the main detected target. Homogeneous assays based on aptazyme, an aptamer sequence connected to a known ribozyme motif, are also described in this review, involving optical detection, by colorimetry or fluorescence.

Selection of aptamers for signal transduction proteins by capillary electrophoresis

High-affinity aptamers for important signal transduction proteins, i.e. Cdc42-GTP, p21-activated kinase1 (PAK1) and MRCK (myotonic dystrophy kinase-related Cdc42-binding kinase) alpha were successfully selected in the low micro- to nanomolar range using non-systematic evolution of ligands by exponential enrichment (SELEX) with at least three orders of magnitude enhancement from their respective bulk affinity of naïve DNA library. In the non-SELEX procedure, CE was used as a highly efficient affinity method to select aptamers for the desired molecular target through a process that involved repetitive steps of partitioning, known as non-equilibrium CE of equilibrium mixtures with no PCR amplification between successive steps. Various non-SELEX conditions including the type, concentration and pH of the run buffer were optimized. Other considerations such as salt composition of selection buffer, protein concentration and sample injection size were also studied for high stringency during selection. After identifying the best enriched aptamer pool, randomly selected clones from the aptamer pool were sequenced to obtain the individual DNA sequences. The dissociation constants (K(d)) of these sequences were in the low micromolar to nanomolar range, indicating high affinity to the respective proteins. The best binders were also subjected to sequence alignment to generate a phylogenetic tree. No significant consensus region based on approximately 50 sequences for each protein was observed, suggesting the high efficiency of non-SELEX for the selection of numerous unique sequences with high selectivity.

Future aspects of bioprocess monitoring

Nature has the impressive ability to efficiently and precisely control biological processes by applying highly evolved principles and using minimal space and relatively simple building blocks. The challenge is to transfer these principles into technically applicable and precise analytical systems that can be used for many applications. This article summarizes some of the new approaches in sensor technology and control strategies for different bioprocesses such as fermentations, biotransformations, and downstream processes. It focuses on bio- and chemosensors, optical sensors, DNA and protein chip technology, software sensors, and modern aspects of data evaluation for improved process monitoring and control.