Fibril growth captured by electrical properties of amyloid-β and human islet amyloid polypeptide

Impedance Spectroscopy Unveiled the Surfactant-Induced Unfolding and Subsequent Refolding of Human Serum Albumin

Protein-surfactant interaction is a dynamic interplay of electrostatic and hydrophobic forces that ensues from the folding of a protein. We employ impedance spectroscopy (IS), a label-free method, to investigate the unfolding and refolding of human serum albumin (HSA), a globular plasma protein, in the presence of two surfactants: polysorbate-20 (Tween-20), a nonionic surfactant, and sodium dodecyl sulfate (SDS), an anionic surfactant. The equivalent electrical analog circuit was predicted from impedance spectra of HSA in an aqueous solution at physiological pH and room temperature, focusing on varying the concentration of codissolved surfactants. A change in the dielectric constant (ε') and ionic conductivity (κ) is observed by comparing the surfactant-treated protein samples to the bare surfactant solutions to assess the conformational changes induced by surfactants in HSA. Far-UV circular dichroism analysis revealed a decrease in α-helices and an increase in β-sheets and random coils upon SDS addition, which were reversed by Tween-20. Dynamic light scattering supported the findings by measuring changes in the hydrodynamic diameter (dh) of HSA. Unfolding and refolding of HSA with surfactants were also observed through photoluminescence spectroscopy by examining the microenvironment surrounding the single tryptophan (W) within the protein, and the thermodynamic parameters were obtained using the modified Stern-Volmer equation. Our research explores the intriguing domain of protein-surfactant interactions, offering insights with promising applications across diverse biological processes and IS as a suitable alternative technique for investigating protein conformational changes by studying the electrical response of the samples.

Probing silver nanoparticle mediated mitigation of UV-photolysis in proteins by electrical impedance analysis

The dynamic equilibrium between an array of molecular forces precisely organizes the native structure of the protein. The charge on the protein, an interconnected network continuum, is crucial in determining its secondary and tertiary structure. The photolysis of the protein by ultraviolet (UV) light occurs by generating reactive oxygen intermediates from the interaction of matter and light. Herein, we have investigated the photolysis of the protein and its prevention by the pre-treatment with silver nanoparticle (AgNP) using non-faradaic electrical impedance spectroscopy (Nf-EIS). Five microliters of protein solution are used to measure its impedimetric parameters via Nf-EIS. The photoionization process sparks off an altered surface charge continuum of the protein molecules in tandem with the genesis of solvated electrons and protons, spurring an upward shift in conductivity. The AgNP pre-treatment has reduced the damaging effects of the UV radiation, which is reflected as lesser conductivity in contrast to the photolyzed protein solution. Raman Spectroscopy and circular dichroism tests affirm the trend of Nf-EIS results. These results show that Nf-EIS can evaluate protein structure analysis utilized in quality assurance and toxicity analysis for biologics.

Bio-inspired microfluidics: A review

Biomicrofluidics, a subdomain of microfluidics, has been inspired by several ideas from nature. However, while the basic inspiration for the same may be drawn from the living world, the translation of all relevant essential functionalities to an artificially engineered framework does not remain trivial. Here, we review the recent progress in bio-inspired microfluidic systems via harnessing the integration of experimental and simulation tools delving into the interface of engineering and biology. Development of "on-chip" technologies as well as their multifarious applications is subsequently discussed, accompanying the relevant advancements in materials and fabrication technology. Pointers toward new directions in research, including an amalgamated fusion of data-driven modeling (such as artificial intelligence and machine learning) and physics-based paradigm, to come up with a human physiological replica on a synthetic bio-chip with due accounting of personalized features, are suggested. These are likely to facilitate physiologically replicating disease modeling on an artificially engineered biochip as well as advance drug development and screening in an expedited route with the minimization of animal and human trials.

Supramolecular organization of Cytochrome-C into quantum-dot decorated macromolecular network under pH and thermal stress

The holo form of Cytochrome-C which is involved in the electron transfer chain of aerobic and anaerobic respiration remains structurally intact by its complex with heme. However, when a prolonged thermal and pH stress was applied, heme was found to abruptly dissociate from the holo protein, resulting in complete collapse of the three-dimensional functional structure. Interestingly, two distinct structures were formed as the consequence of the dissociation event: (i) A macromolecular amyloid-network formed by the collapsed protein fragments, generated by self-oxidation, and (ii) Fe-containing Quantum-Dots (FeQDs) with 2-3 nm diameter formed by heme reorganization. Further adding to intrigue, the FeQDs were re-adsorbed on the surface of the amyloid network leading to FeQD-decorated macromolecular amyloid matrix. The heme-interactant Met80, constituting the amyloidogenic region, initiates the amylogenic cascade, and gradual exposure of Trp59 synergistically emit intrinsic fluorescence alongside FeQDs. The development of the aforementioned events were probed through a multitude of biophysical, chemical and computational analyses like ThT/ANS/intrinsic fluorescence assays, CD-spectroscopy, FETEM/STEM/elemental mapping, Foldamyloid/Foldunfold/Isunstruct/H-protection/LIGplot analyses, etc. The FeQD-decorated amyloid-network was found to exhibit gel-like property, which supported the growth of BHK-21 fibroblast without cytotoxicity. Further studies on FeQD-decorated Cytochrome C amyloid network might open possibilities to design advanced biomaterial for diverse biological applications.

Kinetics of protein aggregation at a temperature gradient condition

The unconventional multi-sigmoidal kinetic behaviour of protein aggregation at a temperature gradient condition is reported in this study. To establish a feasible theory for protein aggregation kinetics at a temperature gradient condition, the spatial height of the protein solution is divided into hypothetical layers and the kinetic equations in those layers are solved. Furthermore, we endeavour to study numerically the effect of the temperature gradient on the kinetics of oligomer-mediated protein aggregation and protein inhibition.

Microfluidic Integrated Organic Electrochemical Transistor with a Nanoporous Membrane for Amyloid-β Detection

Alzheimer's disease (AD) is a neurodegenerative disorder associated with a severe loss in thinking, learning, and memory functions of the brain. To date, no specific treatment has been proven to cure AD, with the early diagnosis being vital for mitigating symptoms. A common pathological change found in AD-affected brains is the accumulation of a protein named amyloid-β (Aβ) into plaques. In this work, we developed a micron-scale organic electrochemical transistor (OECT) integrated with a microfluidic platform for the label-free detection of Aβ aggregates in human serum. The OECT channel-electrolyte interface was covered with a nanoporous membrane functionalized with Congo red (CR) molecules showing a strong affinity for Aβ aggregates. Each aggregate binding to the CR-membrane modulated the vertical ion flow toward the channel, changing the transistor characteristics. Thus, the device performance was not limited by the solution ionic strength nor did it rely on Faradaic reactions or conformational changes of bioreceptors. The high transconductance of the OECT, the precise porosity of the membrane, and the compactness endowed by the microfluidic enabled the Aβ aggregate detection over eight orders of magnitude wide concentration range (femtomolar-nanomolar) in 1 μL of human serum samples. We expanded the operation modes of our transistors using different channel materials and found that the accumulation-mode OECTs displayed the lowest power consumption and highest sensitivities. Ultimately, these robust, low-power, sensitive, and miniaturized microfluidic sensors helped to develop point-of-care tools for the early diagnosis of AD.