Direct electrical control of IgG conformation and functional activity at surfaces

Electric Field-Assisted Molecularly Imprinted Polymer-Modified QCM Sensor for Enhanced Detection of Immunoglobulin

In this study, an electric-field-assisted molecularly imprinted polymer (EFAMIP) as an enhanced form of MIP was developed to improve the MIP-modified quartz crystal microbalance (QCM) biosensors. While exerting a vertical electric field, polymerization of methacrylic acid in the presence of immunoglobulin G (IgG) as the template was initiated, and later, after the template removal process, the EFAMIPs were obtained. The polymer surface characterization was conducted by using a scanning electron microscope. The impact of electric field direction on IgG binding sites, forming either EFAMIP-Fab or EFAMIP-Fc, was assessed. Next, the static measurement results in liquid for EFAMIP-modified QCM and MIP-modified QCM were compared. While encompassing IgG, EFAMIP-modified QCMs exhibited up to a 113.5% higher frequency shift than typical MIP in time-limited detection. The final frequency shift of EFAMIP, which determines the detection limit of IgG, was improved up to 12.5% compared to typical MIP. Moreover, the EFAMIP-Fab performance was promising for the selective detection of IgG in a solution containing different types of immunoglobulins.

Electric-Field-Mediated In-Sensor Alignment of Antibody's Orientation to Enhance the Antibody-Antigen Binding for Ultrahigh Sensitivity Sensors

Applying an electric-field (E-field) during antibody immobilization aligns the orientation of the antibody on the biosensor surface, thereby enhancing the binding probability between the antibody and antigen and maximizing the sensitivity of the biosensor. In this study, a biosensor with enhanced antibody-antigen binding probability was developed using the alignment of polar antibodies (immunoglobulin G [IgG]) under an E-field applied inside the interdigitated electrodes. The optimal alignment condition was first theoretically calculated and then experimentally confirmed by comparing the impedance change before and after the alignment of IgG (a purified anti-β-amyloid antibody). With the optimized condition, the impedance change of the biosensor was maximized because of the alignment of IgG orientation on the sensor surface; the detection sensitivity of the antigen amyloid-beta 1-42 was also maximized. The E-field-based in-sensor alignment of antibodies is an easy and effective method for enhancing biosensor sensitivity.

Predicting the Orientation of Adsorbed Proteins Steered with Electric Fields Using a Simple Electrostatic Model

Under the most common experimental conditions, the adsorption of proteins to solid surfaces is a spontaneous process that leads to a rather compact layer of randomly oriented molecules. However, controlling such orientation is critically important for the development of catalytic surfaces. In this regard, the use of electric fields is one of the most promising alternatives. Our work is motivated by experimental observations that show important differences in catalytic activity of a trypsin-covered surface, which depended on the applied potential during the adsorption. Even though adsorption results from the combination of several processes, we were able to determine that (under the selected conditions) mean-field electrostatics play a dominant role, determining the orientation and yielding a difference in catalytic activity. We simulated the electrostatic potential numerically, using an implicit-solvent model based on the linearized Poisson-Boltzmann equation. This was implemented in an extension of the code PyGBe that included an external electric field, and rendered the electrostatic component of the solvation free energy. Our model (extensions available at the Github repository) allowed estimating the overall affinity of the protein with the surface, and their most likely orientation as a function of the potential applied. Our results show that the active sites of trypsin are, on average, more exposed when the electric field is negative, which agrees with the experimental results of catalytic activity, and confirm the premise that electrostatic interactions can be used to control the orientation of adsorbed proteins.

Biosensors based on zinc oxide thin-film transistors using recyclable plastic substrates as an alternative for real-time pathogen detection

The fabrication of biosensors has different future applications mainly from the perspective of eco-friendly technologies. Label-free strategies, recyclable materials and low-temperature processing are parameters to consider for the development of a new generation of biosensor devices. In this work, Zinc oxide (ZnO) Thin-film Transistors (TFTs) using recyclable plastic substrates were used for real-time enteropathogenic Escherichia coli detection as an approach for biosensing (bio-TFTs). Fourier Transform Infrared Spectroscopy was used to verify the characteristic absorption peaks at the different steps of the bio-TFT assembly process. The bio-TFTs are ready to observe the bacterial detection by electrical characterization. Finally, detection was validated by a coupled strategy that fuses the genomic DNA extraction from bacteria attached in situ over bio-TFTs surface and, the development of the Polymerase Chain Reaction to amplify specific genes from enteropathogenic Escherichia coli.

Engineering an Enzyme for Direct Electrical Monitoring of Activity

Proteins have been shown to be electrically conductive if tethered to an electrode by means of a specific binding agent, allowing single molecules to be wired into an electrical sensing circuit. Such circuits allow enzymes to be used as sensors, detectors, and sequencing devices. We have engineered contact points into a Φ29 polymerase by introducing biotinylatable peptide sequences. The modified enzyme was bound to electrodes functionalized with streptavidin. Φ29 connected by one biotinylated contact, and a second nonspecific contact showed rapid small fluctuations in current when activated. Signals were greatly enhanced with two specific contacts. Features in the distributions of DC conductance increased by a factor 2 or more over the open to closed conformational transition of the polymerase. Polymerase activity is manifested by a rapid (millisecond) large (25% of background) current fluctuations imposed on the DC conductance.

Curvature-dependent effects of nanotopography on classical immune complement activation

The aim of this study was to investigate how the size of nanosized surface features affect classical immune complement activation through adsorption of IgG and the following binding of C1q. By using model surfaces with immobilized SiO₂ nanoparticles of different sizes (8, 32 and 68 nm in diameter), three different curvatures with the same chemistry was systematically studied and analyzed using the acoustic sensing technique; Quartz Crystal Microbalance with Dissipation Monitoring (QCM-D). Circular Dichroism (CD) was employed to study any changes in the secondary structure of IgG using a methodology with stacked functionalized substrates. Our results show that the amount of IgG adsorption increased slightly with nanoparticle size, but also showed a strong size/curvature-dependent effect on the following C1q binding, with the highest binding to IgG adsorbed on the largest nanoparticles and a smooth control surface, indicating that classical immune complement activation possibly increase with decreasing curvature. We conclude that the difference in C1q binding was not due to changes in the secondary structure of IgG, suggesting that geometrical arrangement of adsorbed IgG is the determining factor.

STATEMENT OF SIGNIFICANCE

We have shown that small changes at the topographical nanoscale can give large effects on the initiation of the classical immune complement cascade, an important immunological reaction that take place when a foreign material is inserted in the body. By developing a methodology using silicon dioxide nanoparticles with three different sizes, to systematically study their impact on the secondary structure and binding of human immunoglobulin G (IgG) to the initiator protein C1q of the classical complement cascade, we have shown that the initiation of the classical immune complement is hampered by the sharp curvature of the smaller nanoparticles. We conclude that this is not mediated by changes in the secondary structure of the adsorbed proteins, but rather an effect of curvature-induced spatial mismatch. The results provide a possible mechanistic explanation on how nanotopography may effect protein adsorption and protein cascade events.

MoS2 Nanoparticles as Electrocatalytic Labels in Magneto-Immunoassays

Ability to detect biomolecules with a simple and cost-effective approach has been very demanding in today's medicine. The nanoparticles and two-dimensional materials have been extensively used within this field in devices with high selectivity and sensitivity. Here, we report the use of MoS₂ nanoparticles (MoS₂ NPs) as a signal-enhancing label in a standard immunoassay test. MoS₂ NPs were prepared by a bipolar electrochemistry method. The current response during the hydrogen evolution reaction catalyzed by MoS₂ was measured. This current was directly proportional to the amount of the MoS₂ NPs and thus also to the concentration of desired protein. The immunoassay containing the MoS₂ NPs displays extraordinary low limit of detection (1.94 pg mL^-1), good selectivity, and reproducibility. This MoS₂ NP detection system could have profound implication for analytical applications.