Detection and manipulation of biomolecules by magnetic carriers

Fluctuotaxis: Nanoscale directional motion away from regions of fluctuation

Regulating the motion of nanoscale objects on a solid surface is vital for a broad range of technologies such as nanotechnology, biotechnology, and mechanotechnology. In spite of impressive advances achieved in the field, there is still a lack of a robust mechanism which can operate under a wide range of situations and in a controllable manner. Here, we report a mechanism capable of controllably driving directed motion of any nanoobjects (e.g., nanoparticles, biomolecules, etc.) in both solid and liquid forms. We show via molecular dynamics simulations that a nanoobject would move preferentially away from the fluctuating region of an underlying substrate, a phenomenon termed fluctuotaxis-for which the driving force originates from the difference in atomic fluctuations of the substrate behind and ahead of the object. In particular, we find that the driving force can depend quadratically on both the amplitude and frequency of the substrate and can thus be tuned flexibly. The proposed driving mechanism provides a robust and controllable way for nanoscale mass delivery and has potential in various applications including nanomotors, molecular machines, etc.

Magnetic Nanoparticles Mediated Thrombolysis-A Review

Nanoparticles containing thrombolytic medicines have been developed for thrombolysis applications in response to the increasing demand for effective, targeted treatment of thrombosis disease. In recent years, there has been a great deal of interest in nanoparticles that can be navigated and driven by a magnetic field. However, there are few review publications concerning the application of magnetic nanoparticles in thrombolysis. In this study, we examine the current state of magnetic nanoparticles in the application of in vitro and in vivo thrombolysis under a static or dynamic magnetic field, as well as the combination of magnetic nanoparticles with an acoustic field for dual-mode thrombolysis. We also discuss four primary processes of magnetic nanoparticles mediated thrombolysis, including magnetic nanoparticle targeting, magnetic nanoparticle trapping, magnetic drug release, and magnetic rupture of blood clot fibrin networks. This review will offer unique insights for the future study and clinical development of magnetic nanoparticles mediated thrombolysis approaches.

Longitudinal Magneto-Optical Kerr Effect of Nanoporous CoFeB and W/CoFeB/W Thin Films

Nanoporous Co40Fe40B20 (CoFeB) and sandwich tungsten (W)/CoFeB/W thin films were fabricated via an anodic aluminum oxide (AAO) template-assisted magneto sputtering process. Their thickness-dependent magneto-optical Kerr effect (MOKE) hysteresis loops were investigated for enhanced Kerr rotation. Control of the Kerr null points of the polarized reflected light can be realized via the thicknesses of the CoFeB layers and W layers. Simulation of the thickness-dependent phase difference change by the finite element method reveals the existence of the two Kerr null points for W/CoFeB/W thin films, matching the experimental result very well. However, there are two additional Kerr null points for pure CoFeB thin films according to the simulation by comparing with the experimental result (only one). Theoretical analysis indicates that the different Kerr null points between the experimental result and the simulation are mainly due to the enhanced inner magnetization in the ferromagnetic CoFeB layer with the increased thickness, which is usually omitted in the simulation. Clearly, the introduction of non-ferromagnetic W layers can experimentally regulate the Kerr null points of ferromagnetic thin films. Moreover, construction of W/CoFeB/W sandwich thin films can greatly increase the highest magneto-optical susceptibility and the saturated Kerr rotation angle when compared with CoFeB thin films of the same thickness.

A Review on the Role of Nanosensors in Detecting Cellular miRNA Expression in Colorectal Cancer

BACKGROUND

Colorectal cancer (CRC) is one of the leading causes of death across the globe. Early diagnosis with high sensitivity can prevent CRC progression, thereby reducing the condition of metastasis.

OBJECTIVE

The purpose of this review is (i) to discuss miRNA based biomarkers responsible for CRC, (ii) to brief on the different methods used for the detection of miRNA in CRC, (iii) to discuss different nanobiosensors so far found for the accurate detection of miRNAs in CRC using spectrophotometric detection, piezoelectric detection.

METHODS

The keywords for the review like micro RNA detection in inflammation, colorectal cancer, nanotechnology, were searched in PubMed and the relevant papers on the topics of miRNA related to CRC, nanotechnology-based biosensors for miRNA detection were then sorted and used appropriately for writing the review.

RESULTS

The review comprises a general introduction explaining the current scenario of CRC, the biomarkers used for the detection of different cancers, especially CRC and the importance of nanotechnology and a general scheme of a biosensor. The further subsections discuss the mechanism of CRC progression, the role of miRNA in CRC progression and different nanotechnology-based biosensors so far investigated for miRNA detection in other diseases, cancer and CRC. A scheme depicting miRNA detection using gold nanoparticles (AuNPs) is also illustrated.

CONCLUSION

This review may give insight into the different nanostructures, like AuNPs, quantum dots, silver nanoparticles, MoS2derived nanoparticles, etc., based approaches for miRNA detection using biosensors.

Magnetoimpedance Effect in the Ribbon-Based Patterned Soft Ferromagnetic Meander-Shaped Elements for Sensor Application

Amorphous and nanocrystalline soft magnetic materials have attracted much attention in the area of sensor applications. In this work, the magnetoimpedance (MI) effect of patterned soft ferromagnetic meander-shaped sensor elements has been investigated. They were fabricated starting from the cobalt-based amorphous ribbon using the lithography technique and chemical etching. Three-turn (S1: spacing s = 50 μm, width w = 300 μm, length l = 5 mm; S2: spacing s = 50 μm, width w = 400 μm, length l = 5 mm) and six-turn (S3: s = 40 μm, w = 250 μm, length l = 5 mm; S4: s = 40 μm, w = 250 μm and l = 8 mm) meanders were designed. The 'n' shaped meander part was denominated as "one turn". The S4 meander possesses a maximum MI ratio calculated for the total impedance ΔZ/Z ≈ 250% with a sensitivity of about 36%/Oe (for the frequency of about 45 MHz), and an MI ratio calculated for the real part of the total impedance ΔR/R ≈ 250% with the sensitivity of about 32%/Oe (for the frequency of 50 MHz). Chemical etching and the length of the samples had a strong impact on the surface magnetic properties and the magnetoimpedance. A comparative analysis of the surface magnetic properties obtained by the magneto-optical Kerr technique and MI data shows that the designed ferromagnetic meander-shaped sensor elements can be recommended for high frequency sensor applications focused on the large drop analysis. Here we understand a single large drop as the water-based sample to analyze, placed onto the surface of the MI sensor element either by microsyringe (volue range 0.5-500 μL) or automatic dispenser (volume range 0.1-50 mL).

Optimization of sensing performance in an integrated dual sensors system combining microbial fuel cells and upflow anaerobic sludge bed reactor

Two bio-cathode microbial fuel cells (MFCs) with Upflow anaerobic sludge blanket (UASB) are integrated to construct a UASB-MFC dual sensors system, developed to solve the problems of low accuracy and less information about the single sensor system. The bio-cathode MFC is developed as the biosensor for UASB operation performance and online monitoring. Owing to the biosorption of anaerobic microbes, the MFC in the suspended layer is more suitable for effluent chemical oxygen demand (COD) real-time monitoring, and the MFC in the sludge layer is more suitable for total volatile fatty acid (TVFA) real-time monitoring. Electrochemical analysis discovers that the lower electron transfer resistance determines the higher sensitivity of MFC in the suspended layer. The difference in species abundance indicates that TVFA has a stronger inhibitory effect on MFC in the sludge layer. The novel UASB-MFC dual sensors system shows promising potential for COD and TVFA simultaneous online monitoring, which can enhance the reliability of anaerobic reaction.

Magnetic biosensors: Modelling and simulation

In the past few years, magnetoelectronics has emerged as a promising new platform technology in various biosensors for detection, identification, localisation and manipulation of a wide spectrum of biological, physical and chemical agents. The methods are based on the exposure of the magnetic field of a magnetically labelled biomolecule interacting with a complementary biomolecule bound to a magnetic field sensor. This Review presents various schemes of magnetic biosensor techniques from both simulation and modelling as well as analytical and numerical analysis points of view, and the performance variations under magnetic fields at steady and nonstationary states. This is followed by magnetic sensors modelling and simulations using advanced Multiphysics modelling software (e.g. Finite Element Method (FEM) etc.) and home-made developed tools. Furthermore, outlook and future directions of modelling and simulations of magnetic biosensors in different technologies and materials are critically discussed.

Magnetic sensing platform technologies for biomedical applications

Detection and quantification of a variety of micro- and nanoscale entities, e.g. molecules, cells, and particles, are crucial components of modern biomedical research, in which biosensing platform technologies play a vital role. Confronted with the drastic global demographic changes, future biomedical research entails continuous development of new-generation biosensing platforms targeting even lower costs, more compactness, and higher throughput, sensitivity and selectivity. Among a wide choice of fundamental biosensing principles, magnetic sensing technologies enabled by magnetic field sensors and magnetic particles offer attractive advantages. The key features of a magnetic sensing format include the use of commercially available magnetic field sensing elements, e.g. magnetoresistive sensors which bear huge potential for compact integration, a magnetic field sensing mechanism which is free from interference by complex biomedical samples, and an additional degree of freedom for the on-chip handling of biochemical species rendered by magnetic labels. In this review, we highlight the historical basis, routes, recent advances and applications of magnetic biosensing platform technologies based on magnetoresistive sensors.

Performance of a microbial fuel cell-based biosensor for online monitoring in an integrated system combining microbial fuel cell and upflow anaerobic sludge bed reactor

A hybrid system integrating a microbial fuel cell (MFC)-based biosensor with upflow anaerobic sludge blanket (UASB) was investigated for real-time online monitoring of the internal operation of the UASB reactor. The features concerned were its rapidity and steadiness with a constant operation condition. In addition, the signal feedback mechanism was examined by the relationship between voltage and time point of changed COD concentration. The sensitivity of different concentrations was explored by comparing the signal feedback time point between the voltage and pH. Results showed that the electrical signal feedback was more sensitive than pH and the thresholds of sensitivity were S=3×10(-5)V/(mg/L) and S=8×10(-5)V/(mg/L) in different concentration ranges, respectively. Although only 0.94% of the influent COD was translated into electricity and applied for biosensing, this integrated system indicated great potential without additional COD consumption for real-time monitoring.

Giant Magnetoresistance: Basic Concepts, Microstructure, Magnetic Interactions and Applications

The giant magnetoresistance (GMR) effect is a very basic phenomenon that occurs in magnetic materials ranging from nanoparticles over multilayered thin films to permanent magnets. In this contribution, we first focus on the links between effect characteristic and underlying microstructure. Thereafter, we discuss design criteria for GMR-sensor applications covering automotive, biosensors as well as nanoparticular sensors.

Directed transport by surface chemical potential gradients for enhancing analyte collection in nanoscale sensors

Nanoscale detectors hold great promise for single molecule detection and the analysis of small volumes of dilute samples. However, the probability of an analyte reaching the nanosensor in a dilute solution is extremely low due to the sensor's small size. Here, we examine the use of a chemical potential gradient along a surface to accelerate analyte capture by nanoscale sensors. Utilizing a simple model for transport induced by surface binding energy gradients, we study the effect of the gradient on the efficiency of collecting nanoparticles and single and double stranded DNA. The results indicate that chemical potential gradients along a surface can lead to an acceleration of analyte capture by several orders of magnitude compared to direct collection from the solution. The improvement in collection is limited to a relatively narrow window of gradient slopes, and its extent strongly depends on the size of the gradient patch. Our model allows the optimization of gradient layouts and sheds light on the fundamental characteristics of chemical potential gradient induced transport.

Simple and portable magnetic immunoassay for rapid detection and sensitive quantification of plant viruses

Plant pathogens cause major economic losses in the agricultural industry because late detection delays the implementation of measures that can prevent their dissemination. Sensitive and robust procedures for the rapid detection of plant pathogens are therefore required to reduce yield losses and the use of expensive, environmentally damaging chemicals. Here we describe a simple and portable system for the rapid detection of viral pathogens in infected plants based on immunofiltration, subsequent magnetic detection, and the quantification of magnetically labeled virus particles. Grapevine fanleaf virus (GFLV) was chosen as a model pathogen. Monoclonal antibodies recognizing the GFLV capsid protein were immobilized onto immunofiltration columns, and the same antibodies were linked to magnetic nanoparticles. GFLV was quantified by immunofiltration with magnetic labeling in a double-antibody sandwich configuration. A magnetic frequency mixing technique, in which a two-frequency magnetic excitation field was used to induce a sum frequency signal in the resonant detection coil, corresponding to the virus concentration within the immunofiltration column, was used for high-sensitivity quantification. We were able to measure GFLV concentrations in the range of 6 ng/ml to 20 μg/ml in less than 30 min. The magnetic immunoassay could also be adapted to detect other plant viruses, including Potato virus X and Tobacco mosaic virus, with detection limits of 2 to 60 ng/ml.

X-ray phase contrast imaging of cell isolation with super-paramagnetic microbeads

Super-paramagnetic microbeads are widely used for cell isolation. Evaluation of the binding affinity of microbeads to cells using optical microscopy has been limited by its small scope. Here, magnetic property of microbeads was first investigated by using synchrotron radiation (SR) in-line x-ray phase contrast imaging (PCI). The cell line mouse LLC (Lewis lung carcinoma) was selected for cell adhesion studies. Targeted microbeads were prepared by attaching anti-VEGFR2 (vascular endothelial growth factor receptor-2) antibody to the shell of the microbeads. The bound microbeads were found to better adhere to LLC cells than unbound ones. PCI dynamically and clearly showed the magnetization and demagnetization of microbeads in PE-50 tube. The cells incubated with different types of microbeads were imaged by PCI, which provided clear and real-time visualization of the cell isolation. Therefore, PCI might be considered as a novel and efficient tool for further cell isolation studies.

GMR sensors: magnetoresistive behaviour optimization for biological detection by means of superparamagnetic nanoparticles

An immunomagnetic method for the selective and quantitative detection of biological species by means of a magnetoresistive biosensor and superparamagnetic particles has been optimized. In order to achieve this, a giant magnetoresistive [Co (5.10nm)/Cu (2.47 nm)](20) multilayer structure has been chosen as the sensitive material, showing a magnetoresistance of 3.60% at 215 Oe and a sensitivity up to 0.19 Ω/Oe between 145 Oe and 350 Oe. The outward gold surface of the sensor is biofunctionalized with a Self-Assembled Monolayer (SAM). In addition, three different types of magnetic labels have been tested. 2 μm diameter magnetic carriers (7.68 pg ferrite/particle) have shown the best response and they have induced a shift in the magnetoresistive hysteresis loops up to 9% at 175 Oe.

Magnetoresistive Sensors and Magnetic Nanoparticles for Biotechnology

Magnetoresistive Biosensors use a new detection method for molecular recognition reactions based on two recently developed techniques and devices: Magnetic markers and XMR –sensors, where XMR means either GiantMagneto- (GMR) or Tunneling-MagnetoResistance (TMR). The markers are specifically attached to the target molecules, and their magnetic stray field is picked up by the embedded magnetoresistive sensor as a change of the electrical resistance. Compared to established, e.g. fluorescent, detection methods, magnetic biosensors have a number of advantages, including low molecular detection limits, flexibility and the direct availability of an electronic signal suitable for further automated analysis. This makes them a promising choice for the detection units of future widespread and easy to use lab-on-a-chip systems or biochips.

Both the measurement technique using XMR-sensors as well as new developments in the preparation of magnetic carriers are discussed here. Different configurations are discussed and the results for Giant Magnetoresistance sensors are compared to an analysis of the same biological systems marked with fluorescence dyes. Down to a concentration of about 10 pg/μl of, e.g., DNA molecules, the magnetoresistive technique is competitive with nowadays standard analysis methods. The capability of the TMR sensors to detect even single markers is additionally demonstrated by a model experiment using the tip of a magnetic force microscope to meamic the presence of a magnetic particle on top of the sensor surface.

The magnetic carriers (beads) usually detected by the sensors consist of paramagnetic magnetite particles embedded in a polymer matrix with sizes from some μm down to about 100nm. They are linked to, e.g., DNA or proteins (often by a avidin-biotin bond) and thereby enable highly specific detection of complementary molecules. These magnetic particles often suffer from their broad size distribution and the relatively small magnetic moment. With the new colloidal synthesis of superpara- or ferromagnetic Co, CoFe and FePt nanocrystals by, e.g., pyrolythic decomposition of CVD precursor molecules, magnetic markers with superior magnetic moments, smaller size and size distribution can be produced. Here, the question about their potential to replace magnetite is addressed. Starting from a magnetic analysis of the corresponding magnetophoretic mobility of Co and FeCo based alloys their synthesis and resulting microstructural and magnetic properties as function of the underlying particle size distribution and the stability of the oleic acid ligand are discussed.

Moreover, the magnetic particles offer an additional feature: They can be manipulated on chip via currents running through specially designed line patterns. We show, that this manipulation can be performed in a precise and reproducible manner, enabling locally enhanced concentration or even the measurement of binding forces with very low loading rates.

Magnetic nanoparticle biosensors

One of the major challenges in medicine is the rapid and accurate measurement of protein biomarkers, cells, and pathogens in biological samples. A number of new diagnostic platforms have recently been developed to measure biomolecules and cells with high sensitivity that could enable early disease detection or provide valuable insights into biology at the systems level. Most biological samples exhibit negligible magnetic susceptibility; therefore, magnetic nanoparticles have been used for diverse applications including biosensing, magnetic separation, and thermal ablation therapy. This review focuses on the use of magnetic nanoparticles for detection of biomolecules and cells based on magnetic resonance effects using a general detection platform termed diagnostic magnetic resonance (DMR). DMR technology encompasses numerous assay configurations and sensing principles, and to date magnetic nanoparticle biosensors have been designed to detect a wide range of targets including DNA/mRNA, proteins, enzymes, drugs, pathogens, and tumor cells. The core principle behind DMR is the use of magnetic nanoparticles as proximity sensors that modulate the spin-spin relaxation time of neighboring water molecules, which can be quantified using clinical MRI scanners or benchtop nuclear magnetic resonance (NMR) relaxometers. Recently, the capabilities of DMR technology were advanced considerably with the development of miniaturized, chip-based NMR (microNMR) detector systems that are capable of performing highly sensitive measurements on microliter sample volumes and in multiplexed format. With these and future advances in mind, DMR biosensor technology holds considerable promise to provide a high-throughput, low-cost, and portable platform for large scale molecular and cellular screening in clinical and point-of-care settings.

Magnetic nanoparticles for biomedical NMR-based diagnostics

Rapid and accurate measurements of protein biomarkers, pathogens and cells in biological samples could provide useful information for early disease diagnosis, treatment monitoring, and design of personalized medicine. In general, biological samples have only negligible magnetic susceptibility. Thus, using magnetic nanoparticles for biosensing not only enhances sensitivity but also effectively reduces sample preparation needs. This review focuses on the use of magnetic nanoparticles for in vitro detection of biomolecules and cells based on magnetic resonance effects. This detection platform, termed diagnostic magnetic resonance (DMR), exploits magnetic nanoparticles as proximity sensors, which modulate the spin-spin relaxation time of water molecules surrounding molecularly-targeted nanoparticles. By developing more effective magnetic nanoparticle biosensors, DMR detection limits for various target moieties have been considerably improved over the last few years. Already, a library of magnetic nanoparticles has been developed, in which a wide range of targets, including DNA/mRNA, proteins, small molecules/drugs, bacteria, and tumor cells, have been quantified. More recently, the capabilities of DMR technology have been further advanced with new developments such as miniaturized nuclear magnetic resonance detectors, better magnetic nanoparticles and novel conjugational methods. These developments have enabled parallel and sensitive measurements to be made from small volume samples. Thus, the DMR technology is a highly attractive platform for portable, low-cost, and efficient biomolecular detection within a biomedical setting.

Magnetoresistive immunosensor for the detection of Escherichia coli O157:H7 including a microfluidic network

A hand held device has been designed for the immunomagnetic detection and quantification of the pathogen Escherichia coli O157:H7 in food and clinical samples. In this work, a technology to manufacture a Lab on a Chip that integrates a 3D microfluidic network with a microfabricated biosensor has been developed. With this aim, the sensing film optimization, the design of the microfluidic circuitry, the development of the biological protocols involved in the measurements and, finally, the packaging needed to carry out the assays in a safe and straightforward way have been completed. The biosensor is designed to be capable to detect and quantify small magnetic field variations caused by the presence of superparamagnetic beads bound to the antigens previously immobilized on the sensor surface via an antibody-antigen reaction. The giant magnetoresistive multilayer structure implemented as sensing film consists of 20[Cu(5.10nm)/Co(2.47 nm)] with a magnetoresistance of 3.20% at 235Oe and a sensitivity up to 0.06 Omega/Oe between 150Oe and 230Oe. Silicon nitride has been selected as optimum sensor surface coating due to its suitability for antibody immobilization. In order to guide the biological samples towards the sensing area, a microfluidic network made of SU-8 photoresist has been included. Finally, a novel packaging design has been fabricated employing 3D stereolithographic techniques. The microchannels are connected to the outside using standard tubing. Hence, this packaging allows an easy replacement of the used devices.

Magnetic labeling, detection, and system integration

Among the plethora of affinity biosensor systems based on biomolecular recognition and labeling assays, magnetic labeling and detection is emerging as a promising new approach. Magnetic labels can be non-invasively detected by a wide range of methods, are physically and chemically stable, relatively inexpensive to produce, and can be easily made biocompatible. Here we provide an overview of the various approaches developed for magnetic labeling and detection as applied to biosensing. We illustrate the challenges to integrating one such approach into a complete sensing system with a more detailed discussion of the compact Bead Array Sensor System developed at the U.S. Naval Research Laboratory, the first system to use magnetic labels and microchip-based detection.

The Optimization of Magnetosandwich Assays for the Sensitive and Specific Detection of Proteins in Serum

Over the past decade, the use of magnetic particles (MPs) as labels in magnetic biosensors has attracted increasing interest because it provides a highly sensitive platform that can meet the diagnostic needs that are currently not met by existing technologies. However, preparing magnetic biosensors for a specific diagnostic application is a challenging task, and the (bio)chemical aspects are often neglected. Hence, one of the major remaining bottlenecks in the development of magnetic biosensors is the lack of an optimized magnetosandwich assay for the highly sensitive and specific detection of proteins in complex sample matrices. Therefore, in this article, we report on the impact of several different aspects of magnetosandwich assay development, that is, surface chemistry, MP size, rinsing procedure, sample matrix, and blocking procedure on the total-assay performance using quartz crystal microbalance and optical microscopy analysis. The optimization focused on the diagnostically relevant protein S100betabeta, a marker for stroke and minor head injury. It was observed that small MPs in combination with a strong rinsing and a BSA/Tween-20 blocking allows for the most specific and sensitive detection of S100betabeta in serum over a wide concentration range.

CRP determination based on a novel magnetic biosensor

The c-reactive protein (CRP) is a very significant human blood marker for inflammatory processes and is routinely determined for many clinical purposes. The widespread and well established detection method for this approximately 115 kDa hepatic protein is the high-sensitivity ELISA assay (hsCRP-ELISA) in blood serum. New approaches in medical CRP diagnosis (e.g. for CVD, inflammatory bowel disease) require rapid quantification in native matrices. A novel CRP determination method based on magnetic detection is described and tested for human blood serum, saliva and urine. The detection principle is based on two different anti-CRP antibodies (monoclonal, IgG) for CRP trapment and labelling. The linear detection range of this immunosensor ranged from 25 ng/ml to 2.5 microg/ml and is therefore much more sensitive than typical hsCRP-ELISA-assays.

DNA-functionalized MFe2O4 (M = Fe, Co, or Mn) nanoparticles and their hybridization to DNA-functionalized surfaces

Magnetic MFe2O4 (M = Fe, Co, or Mn) nanoparticles with uniform diameters in the 4-20 nm range and with excellent material properties, reported previously, can be rendered soluble in water or aqueous buffers using a combination of alkylphosphonate surfactants and other surfactants such as ethoxylated fatty alcohols or phospholipids. Surfactant-modified oligonucleotides can be incorporated into the particles' organic shell. The particles can withstand salt concentrations up to 0.3 M, temperatures up to 90 degrees C, and various operations such as concentration to dryness, column or membrane separations, and electrophoresis. The particles can be selectively hybridized to DNA-functionalized gold surfaces with high coverages using a two-story monolayer structure. These particles may find valuable applications involving the magnetic detection of small numbers of biomolecules using spin valves, magnetic tunnel junctions, or other sensors.

Sensitive bondforce measurements of ligand–receptor pairs with magnetic beads

The bondforces between biotinylated surfaces and streptavidin or avidin coated beads are investigated by a magnetic field based manipulation system for magnetic microbeads. The magnetic field is generated by currents through a set of conducting lines, and its gradient exerts a force onto the magnetic beads. The force can be increased until the bond between the bead and the surface breaks. Consistent with other groups we found two conformations for both investigated bonds. The measured bondforces for the two conformations are for Streptavidin-Biotin: 55.9 and 244.7 fN and for Avidin-Biotin: 15.9 and 58.4 fN. These very low bondforces (10-100 times smaller than earlier measurements) match to the extremely low loading rate of about 1 fN/s. This new technique thus allows to investigate biomolecular bonds by extremely low forces.

Magnetic techniques for the isolation and purification of proteins and peptides

Isolation and separation of specific molecules is used in almost all areas of biosciences and biotechnology. Diverse procedures can be used to achieve this goal. Recently, increased attention has been paid to the development and application of magnetic separation techniques, which employ small magnetic particles. The purpose of this review paper is to summarize various methodologies, strategies and materials which can be used for the isolation and purification of target proteins and peptides with the help of magnetic field. An extensive list of realised purification procedures documents the efficiency of magnetic separation techniques.