An aptasensor for the detection of Mycobacterium tuberculosis secreted immunogenic protein MPT64 in clinical samples towards tuberculosis detection

This work presents experimental results on detection of Mycobacterium tuberculosis secreted protein MPT64 using an interdigitated electrode (IDE) which acts as a platform for capturing an immunogenic protein and an electrochemical impedance spectroscopy (EIS) as a detection technique. The assay involves a special receptor, single stranded DNA (ssDNA) aptamer, which specifically recognizes MPT64 protein. The ssDNA immobilization on IDE was based on a co-adsorbent immobilization at an optimized ratio of a 1/100 HS-(CH6)(6)-OP(O)(2)O-(CH2CH2O)(6)-5'-TTTTT-aptamer-3'/6-mercaptohexanol. The optimal sample incubation time required for a signal generation on an aptamer modified IDE was found to be at a range of 15-20 min. Atomic Force Microscopy (AFM) results confirmed a possible formation of an aptamer - MPT64 complex with a 20 nm roughness on the IDE surface vs. 4.5 nm roughness for the IDE modified with the aptamer only. A limit of detection for the EIS aptasensor based on an IDE for the detection of MPT64 in measurement buffer was 4.1 fM. The developed EIS aptasensor was evaluated on both serum and sputum clinical samples from the same TB (-) and TB (+) patients having a specificity and sensitivity for the sputum sample analysis 100% and 76.47%, respectively, and for the serum sample analysis 100% and 88.24%, respectively. The developed aptasensor presents a sensitive method for the TB diagnosis with the fast detection time

Insights in the Ionic Conduction inside Nanoporous Metal-Organic Frameworks by Using an Appropriate Equivalent Circuit

The conduction of protons and other ions in nanoporous materials, such as metal-organic frameworks (MOFs), is intensively explored with the aim of enhancing the performance of energy-related electrochemical systems. The ionic conductivity, as a key property of the material, is typically determined by using electrochemical impedance spectroscopy (EIS) in connection with a suitable equivalent circuit. Often, equivalent circuits are used where the physical meaning of each component is debatable. Here, we present an equivalent circuit for the ionic conduction of electrolytes in nanoporous, nonconducting materials between inert and impermeable electrodes without faradaic electrode reactions. We show the equivalent circuit perfectly describes the impedance spectra measured for the ion conduction in MOFs in the form of powders pressed into pellets as well as for MOF thin films. This is demonstrated for the ionic conduction of an aprotic ionic liquid, and of various protic solvents in different MOF structures. Due to the clear physical meaning of each element of the equivalent circuit, further insights into the electrical double layer forming at the MOF-electrode interface can be obtained. As a result, EIS combined with the appropriate reference circuit allows us to make statements of the quality of the MOF-substrate interface of different MOF-film samples

Characterization of printable electrical sensors applied to cellular cultures

Impedance biosensors have turned in a special interest as label-free and low cost platforms for real time detection of biological phenomena. The objective of this study was to characterize a given model of an interdigitated electrode sensor (model 1) manufactured by inkjet printing technology over a flexible substrate (PET). This characterization was applied to HaCaT cellular cultures at different confluences in order to distinguish an impedance response first associated with the cellular presence and then proportional to the cellular confluence of such presence. With this aim in mind, impedance spectroscopy principle was employed as the main analysis method. From the empirical impedance response, electrical equivalent circuits were obtained by fitting the empirical values with theoretical circuit’s elements. In addition, inverted and scanning electron microscopes were used in order to visualize the whole process, as a way of ensuring that the electrical changes recorded had a real and relevant biological meaning. Three different conditions were tested over the sensor: culture medium without cells, HaCaT epithelial cells seeded over the sensor at 40% of confluence and at 80% of confluence. Impedance responses were recorded each 2 h during 36 h. Results obtained showed that at some point the cellular presence changed the equivalent electrical circuit when compared with the control measurements performed without cells. This change in the circuit has been associated with the cellular attachment of the cells on the IDE, which, as it was later confirmed by the visualization of the cellular culture, has been identified to take place from 22 h on and coincides with the presence of an additional time constant in the electrical circuit. Moreover, the constant phase element of such equivalent circuits was compared for the three conditions, obtaining that its variation is inversely proportional to the area covered by the cells on the sensor. The main drawback encountered during the process was the noise coming at low frequencies that compromise the measurement from 0,1 Hz to 10 Hz. In conclusion, this work has been useful to prove that IDEs can provide an impedance response associated to cellular presence. Based on the main findings, another setup to reduce the noise was proposed (solution design: model 2) and tested for the following experiments, reporting good results.Ingeniería Biomédica (Plan 2010

Simulations of Interdigitated Electrode Interactions with Gold Nanoparticles for Impedance-Based Biosensing Applications

In this paper, we describe a point-of-care biosensor design. The uniqueness of our design is in its capability for detecting a wide variety of target biomolecules and the simplicity of nanoparticle enhanced electrical detection. The electrical properties of interdigitated electrodes (IDEs) and the mechanism for gold nanoparticle-enhanced impedance-based biosensor systems based on these electrodes are simulated using COMSOL Multiphysics software. Understanding these properties and how they can be affected is vital in designing effective biosensor devices. Simulations were used to show electrical screening develop over time for IDEs in a salt solution, as well as the electric field between individual digits of electrodes. Using these simulations, it was observed that gold nanoparticles bound closely to IDEs can lower the electric field magnitude between the digits of the electrode. The simulations are also shown to be a useful design tool in optimizing sensor function. Various different conditions, such as electrode dimensions and background ion concentrations, are shown to have a significant impact on the simulations

Simulations of Interdigitated Electrode Interactions with Gold Nanoparticles for Impedance-Based Biosensing Applications

In this paper, we describe a point-of-care biosensor design. The uniqueness of our design is in its capability for detecting a wide variety of target biomolecules and the simplicity of nanoparticle enhanced electrical detection. The electrical properties of interdigitated electrodes (IDEs) and the mechanism for gold nanoparticle-enhanced impedance-based biosensor systems based on these electrodes are simulated using COMSOL Multiphysics software. Understanding these properties and how they can be affected is vital in designing effective biosensor devices. Simulations were used to show electrical screening develop over time for IDEs in a salt solution, as well as the electric field between individual digits of electrodes. Using these simulations, it was observed that gold nanoparticles bound closely to IDEs can lower the electric field magnitude between the digits of the electrode. The simulations are also shown to be a useful design tool in optimizing sensor function. Various different conditions, such as electrode dimensions and background ion concentrations, are shown to have a significant impact on the simulations

Biosensing-inspired Nanostructures:

Thesis advisor: Michael J. NaughtonNanoscale biosensing devices improve and enable detection mechanisms by taking advantage of properties inherent to nanoscale structures. This thesis primarily describes the development, characterization and application of two such nanoscale structures. Namely, these two biosensing devices discussed herein are (1) an extended-core coaxial nanogap electrode array, the ‘ECC’ and (2) a plasmonic resonance optical filter array, the ‘plasmonic halo’. For the former project, I discuss the materials and processing considerations that were involved in the making of the ECC device, including the nanoscale fabrication, experimental apparatuses, and the chemical and biological materials involved. I summarize the ECC sensitivity that was superior to those of conventional detection methods and proof-of-concept bio-functionalization of the sensing device. For the latter project, I discuss the path of designing a biosensing device based on the plasmonic properties observed in the plasmonic halo, including the plasmonic structures, materials, fabrication, experimental equipment, and the biological materials and protocols.Thesis (PhD) — Boston College, 2019.Submitted to: Boston College. Graduate School of Arts and Sciences.Discipline: Physics