Magnetic Beads in Marine Toxin Detection: A Review

A review on magnetic beads-based SELEX technologies: Applications from small to large target molecules

This review summarizes the stepwise strategy and key points for magnetic beads (MBs)-based aptamer selection which is suitable for isolating aptamers against small and large molecules via systematic evolution of ligands by exponential enrichment (SELEX). Particularities, if any, are discussed according to the target size. Examples targeting small molecules (<1000 Da) such as xenobiotics, toxins, pesticides, herbicides, illegal additives, hormones, and large targets such as proteins (biomarkers, pathogens) are discussed and presented in tabular formats. Of special interest are the latest advances in more efficient alternatives, which are based on novel instrumentation, materials or microelectronics, such as fluorescence MBs-SELEX or microfluidic chip system-assisted MBs-SELEX. Limitations and perspectives of MBs-SELEX are also reviewed. Taken together, this review aims to provide practical insights into MBs-SELEX technologies and their ability to screen multiple potential aptamers against targets from small to large molecules.

Detection of Ciguatoxins and Tetrodotoxins in Seafood with Biosensors and Other Smart Bioanalytical Systems

The emergence of marine toxins such as ciguatoxins (CTXs) and tetrodotoxins (TTXs) in non-endemic regions may pose a serious food safety threat and public health concern if proper control measures are not applied. This article provides an overview of the main biorecognition molecules used for the detection of CTXs and TTXs and the different assay configurations and transduction strategies explored in the development of biosensors and other biotechnological tools for these marine toxins. The advantages and limitations of the systems based on cells, receptors, antibodies, and aptamers are described, and new challenges in marine toxin detection are identified. The validation of these smart bioanalytical systems through analysis of samples and comparison with other techniques is also rationally discussed. These tools have already been demonstrated to be useful in the detection and quantification of CTXs and TTXs, and are, therefore, highly promising for their implementation in research activities and monitoring programs.

Rational design of nonlinear hybridization immunosensor chain reactions for simultaneous ultrasensitive detection of two tumor marker proteins

Sensitive biomarker detection techniques are beneficial for both disease diagnosis and postoperative examinations. The nonlinear hybridization chain reaction (NHCR) is widely used as an output signal amplification technique for biosensor platforms. A novel hairpin-free NHCR was developed in this study as a flow cytometric immunoassay to detect alpha-fetoprotein (AFP) and prostate specific antigen (PSA). First, the target AFP is captured on magnetic beads (MBs) that are modified with capture antibodies. Then, the prepared biotin-streptavidin-biotin (B-S-B) system, which links biotinylated detection antibodies and biotinylated trigger DNA together through the high affinity between biotin-streptavidin interaction, is added to label the target AFP, forming a sandwich complex with three trigger DNA chains. Each trigger DNA chain grows a dendritic DNA nanostructure following a nonlinear hybridization chain reaction. As the substrate flue chains are labeled with fluorophores, the self-assembly process of dendritic DNA is accompanied by the continuous release of fluorophores. Dendrites with strong fluorescence then form on the surface of MBs. Finally, the target AFP is quantified by analyzing the fluorescent MBs using flow cytometry. The proposed immunoassay has a high selectivity along with isothermal, enzyme-free, and exponential amplification efficiency. It shows a limit of detection (LOD) of 1.74 pg mL^-1. The proposed biosensor was also successfully used to quantitatively detect AFP in serum samples. It may be utilized to detect multiple tumor markers simultaneously by changing the size of MBs and antibody-antigen pairs. Most tumor markers are only related to tumor diagnosis but without specificity, so the combined detection of multiple tumor markers can improve the accuracy of early tumor diagnoses.

Overview on the Design of Magnetically Assisted Electrochemical Biosensors

Electrochemical biosensors generally require the immobilization of recognition elements or capture probes on the electrode surface. This may limit their practical applications due to the complex operation procedure and low repeatability and stability. Magnetically assisted biosensors show remarkable advantages in separation and pre-concentration of targets from complex biological samples. More importantly, magnetically assisted sensing systems show high throughput since the magnetic materials can be produced and preserved on a large scale. In this work, we summarized the design of electrochemical biosensors involving magnetic materials as the platforms for recognition reaction and target conversion. The recognition reactions usually include antigen-antibody, DNA hybridization, and aptamer-target interactions. By conjugating an electroactive probe to biomolecules attached to magnetic materials, the complexes can be accumulated near to an electrode surface with the aid of external magnet field, producing an easily measurable redox current. The redox current can be further enhanced by enzymes, nanomaterials, DNA assemblies, and thermal-cycle or isothermal amplification. In magnetically assisted assays, the magnetic substrates are removed by a magnet after the target conversion, and the signal can be monitored through stimuli-response release of signal reporters, enzymatic production of electroactive species, or target-induced generation of messenger DNA.

Nanomaterial-based aptamer biosensors for ochratoxin A detection: a review

Ochratoxin A (OTA) is a widely distributed mycotoxin that often contaminates food, grains and animal feed. It poses a serious threat to human health because of its high toxicity and persistence. Therefore, the development of an inexpensive, highly sensitive, accurate and rapid method for OTA detection is imperative. In recent years, various nanomaterials used in the establishment of aptasensors have attracted great attention due to their large surface-to-volume ratio, good stability and facile preparation. This review summarizes the development of nanomaterial-based aptasensors for OTA determination and sample treatment over the past 5 years. The nanomaterials used in OTA aptasensors include metal, carbon, luminescent, magnetic and other nanomaterials. Finally, the limitations and future challenges in the development of nanomaterial-based OTA aptasensors are reviewed and discussed.

Smartphone-based technology for nanomolecular detection of aflatoxin B1 by aptamer-conjugated magnetic nanoparticles

The need for a healthy market in the rapid and accurate screening of a variety of pathogenic agents and toxins in the environment and food has led to an increase in the development of new biosensors, which have ideal characteristics, such as high sensitivity and specificity with rapid detection and simple preparation of the sample. Among the food contaminants, mycotoxins have been identified as a major challenge for the food industry, and rapid and accurate detection has attracted the attention of food inspection and monitoring organisations. In this study, a nanomolecular detection method is described using aflatoxin B1 (AFB1)-specific aptamers attached to streptavidin-coated magnetic nanoparticles. A prominent feature of the AFB1-specific aptamers is a guanine-rich (G-rich) sequence with a G-quadruplex structure after capturing AFB1 molecules and mimicking peroxidase activity. The enzymatic reaction evaluated in the presence of chromogenic substrate and measurement is done by a smartphone-specific application for colorimetric measurement. The results indicated that the assay could measure AFB1 in rice, flour, seed, maize, and pistachio. In addition, the application of hybrid nanomaterial technology resulting from the binding of biotin-labelled aptamers to the surface of streptavidin-coated magnetic nanoparticles minimises preparation and treatment of samples, improves results, and consequently reduces false negative and positive responses in the detection field. This study may eventually lead to the design and development of a fast, sensitive, specific, and on-site AFB1-based nanomolecular colorimetric detection system via a smartphone-based application that can be readily accessible to all applicants, from professionals to manufacturers of foodstuffs.

High Yield Synthesis and Application of Magnetite Nanoparticles (Fe3O4)

Magnetite nanoparticles (Fe3O4), average particle size of 12.9 nm, were synthesized de novo from ferrous and ferric iron salt solutions (total iron salt concentration of 3.8 mM) using steady-state headspace NH3(g), 3.3% v/v, at room temperature and pressure, without mechanical agitation, resulting in >99.9% yield. Nanoparticles size distributions were based on enumeration of TEM images and chemical compositions analyzed by: XRD, EDXRF, and FT-IR; super-paramagnetic properties were analyzed by magnetization saturation (74 emu/g). Studies included varying headspace [NH3(g)] (1.6, 3.3, 8.4% v/v), and total iron concentrations (1.0 mM, 3.8 mM, 10.0 mM, and >>10 mM). An application of the unmodified synthesized magnetite nanoparticles included analyses of tetracycline’s (50, 100, 200, 300, and 400 ppb) in aqueous, which was compared to the same tetracycline concentrations prepared in aqueous synthesis suspension with >97% extraction, analyzed with LC-MS/MS.

Magnetic Nanoparticles

Magnetic nanoparticles are a class of nanoparticle that can be manipulated using magnetic fields [...]