Atomic Force Microscopy Research Articles

Morphology Determination of Luminescent Carbon Nanotubes by Analytical Super-Resolution Microscopy Approaches.

The ability to determine the precise structure of nano-objects is essential for a multitude of applications. This is particularly true of single-walled carbon nanotubes (SWCNTs), which are produced as heterogeneous samples. Current techniques used for their characterization require sophisticated instrumentation, such as atomic force microscopy (AFM), or compromise on accuracy. In this paper, we propose to use super-resolution microscopy (SRM) to accurately determine the morphology (orientation, length, and shape) of individual luminescent SWCNTs. We generate super-resolved images using three recently published SRM analytical software packages (DPR, eSRRF, and MSSR) and metrologically compare their performances to determine the morphological properties of SWCNTs. For this, ground-truth information on nanotube morphologies was obtained using polarization measurements and AFM to directly correlate the results from SRM at the single particle level. We show a more than 4-fold improvement in resolution over standard photoluminescence imaging, revealing hidden morphologies as efficiently as AFM. We finally demonstrate that DPR, and eventually eSRRF, can effectively assess SWCNT length distribution in a much faster and more accessible way than AFM. We believe that this approach can be generalized to other types of luminescent nanostructures and thus become a standard for rapid and accurate characterization of samples.

Experimental and theoretical investigation of Chronic Lymphocytic Leukemia cell's viscoelastic contact mechanics using atomic force microscope

Chronic Lymphocytic Leukemia (CLL) is a type of cancer usually appearing in old age. In this research, a method for detecting CLL cells in young age through the analysis of geometrical and mechanical properties of human Leukocytes has been presented. For this purpose, the CLL cells are cultured and their geometric characteristics, adhesion force, and contact behavior have been examined using an Atomic Force Microscope (AFM) device. Subsequently, the obtained experimental results have been compared with the geometric and mechanical properties of Leukocytes. Furthermore, the manipulation process has been mathematically modeled using different adhesive and non-adhesive contact theories. The results showed that blood cancer cells have up to 8.17% smaller dimensions and up to 23.57% greater elastic modulus compared to leukocytes.

Sensitive determination of hydroquinone and catechol using an electrochemical sensor based on nitrogen-doped malic acid carbon quantum dots

This study introduces an advanced electrochemical sensor fabricated by immobilizing nitrogen-doped malic acid carbon quantum dots (N-MCQDs) onto a glassy carbon electrode (GCE) via microwave-assisted synthesis and electrodeposition. The N-MCQDs were comprehensively characterized using high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and atomic force microscopy (AFM), confirming their successful synthesis and uniform distribution on the GCE surface. The N-MCQDs-modified GCE electrode (N-MCQDs/GCE) sensor displayed a remarkable linear detection range of 1–500 μM for hydroquinone (HQ) and 1–200 μM for catechol (CC), with ultra-low detection limits of 0.18 μM for HQ and 0.13 μM for CC. It also exhibits commendable stability, interference resistance, and the capability to accurately measure in complex real sample. These superior characteristics were attributed to the enhanced electrical conductivity and increased active sites due to nitrogen doping. This study not only broadens the application spectrum of carbon quantum dots but also offers a novel perspective for the design of high-performance electrochemical sensors for environmental analysis.

Antioxidant Activity of Aluminum Oxide Nanoparticles Prepared by Laser Ablation Technique and Evaluating the Toxicity on Blood Human Components (in vitro)

DPPH is one of the most widely used tests with scavenged-free radical effect, in which the color turns to yellow when tested onto a free stable dark-purple tulip, where natural antioxidants are returned by an electron and a proton. The optical, structural properties of Al2O NPs prepared by the pulsed laser ablation (PLA) Nd: YAG laser method at various energies (500,800,1000 mJ) were studied using color absorbance, UV–VIS spectroscopy, scanning electron microscopy (SEM) and atomic force microscopy (AFM). The results showed that the average particle size is less than 41 nm. Spectroscopic analyses were used to study the antioxidant activity of Al2O3 nanoparticles by 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical. The DPPH displacement was shown to be directly proportional to the high energies according to the results. The increased energy of (500, 800 and 1000 mJ) for free radicals are at (64.53 ± 5.487)%, (74.00 ± 2.887)% and (84.67 ± 4.372)% respectively, as compared to ascorbic acid. Furthermore, the toxicity of these nanoparticles on human blood parameters was studied using the complete blood count (CBC) (in vitro) by hematological parameters (PLT), (HGB–Hb), (RBCs), (WBCs), and count type white blood cells, and are compared to control groups. Our results demonstrate no significant changes in levels of (PLT), (HGB–Hb), (RBCs), (WBCs), and count type white blood cells between test and control groups. This data suggests that aluminum oxide nanoparticles have no harmful effect on hematological parameters (in vitro).

Annealing Temperature Effect on TeO2 Thin Films for Optical Detection Devices

Physical vapor deposition method was used for the preparation of nanostructured TeO2. Different morphologies of TeO2 are synthesized using a physical evaporation method with Te powder as the source material and quartz SiO2 as the growth substrates. X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), and ultraviolet-visible (UV–Vis) analyses are used to characterize the structural, morphological, and optical properties of the TeO2 products obtained. By varying the annealing temperature, different morphology of TeO2 structures is investigated. TeO2 nanostructure progress is initiated by the crystallization of particles. Different temperatures have different effects on structures, which are discussed. The films as deposited nature was amorphous; crystallization occurred at a higher annealing temperature (175 oC). With an increase in annealing temperature, the TeO2 films grain size increased. The research also points to the impact of post-deposition thermal annealing temperatures in excess of 100 °C in enhancing TeO2 film characteristics.

Mechanisms of hardness enhancement in CrB2 thin films with varying VB2 concentrations

Transition metal borides are well-known for their high hardness, excellent wear resistance, chemical inertness, and electrical conductivity, making them promising for a wide range of applications. Understanding the interconnections between material structure, composition, and mechanical properties is essential for designing and synthesizing effective coatings. This study systematically investigates the structural and mechanical properties of CrB₂ thin films with varying concentrations of VB₂ (0–10 wt%), focusing on structure, hardness, elastic behavior and deformation characteristics mechanisms through atomic force microscopy and nanoindentation measurements. The results show that increasing VB₂ content leads to the formation of island cluster structures, which significantly strengthens atomic bonds and, in turn, enhances the hardness of the thin films. As particle size decreases, the higher proportion of surface atoms and increased surface energy have a more pronounced effect on the mechanical properties. In particular, the addition of VB₂ up to 10 wt% in CrB₂ thin films results in a marked improvement in superhard properties. 26 % increase in hardness value is also influenced directly by the changes in Young's modulus and Poisson's ratio that depend on the VB₂ concentration.

Synergistic phenotypic adaptations of motile purple sulphur bacteria Chromatium okenii during lake-to-laboratory domestication.

Isolating microorganisms from natural environments for cultivation under optimized laboratory settings has markedly improved our understanding of microbial ecology. Artificial growth conditions often diverge from those in natural ecosystems, forcing wild isolates into distinct selective pressures, resulting in diverse eco-physiological adaptations mediated by modification of key phenotypic traits. For motile microorganisms we still lack a biophysical understanding of the relevant traits emerging during domestication and their mechanistic interplay driving short-to-long-term microbial adaptation under laboratory conditions. Using microfluidics, atomic force microscopy, quantitative imaging, and mathematical modeling, we study phenotypic adaptation of Chromatium okenii, a motile phototrophic purple sulfur bacterium from meromictic Lake Cadagno, grown under laboratory conditions over multiple generations. Our results indicate that naturally planktonic C. okenii leverage shifts in cell-surface adhesive interactions, synergistically with changes in cell morphology, mass density, and distribution of intracellular sulfur globules, to suppress their swimming traits, ultimately switching to a sessile lifeform. A computational model of cell mechanics confirms the role of such phenotypic shifts in suppressing the planktonic lifeform. By investigating key phenotypic traits across different physiological stages of lab-grown C. okenii, we uncover a progressive loss of motility during the early stages of domestication, followed by concomitant deflagellation and enhanced surface attachment, ultimately driving the transition of motile sulfur bacteria to a sessile state. Our results establish a mechanistic link between suppression of motility and surface attachment via phenotypic changes, underscoring the emergence of adaptive fitness under laboratory conditions at the expense of traits tailored for natural environments.

Recent Advances in Zinc Oxide Nanoparticles: Synthesis Methods, Characterization Techniques, and Emerging Applications

Abstract: Zinc oxide (ZnO) is an inorganic compound with unique physicochemical characteris-tics that make it versatile and suitable for various applications, especially in the form of nanoparti-cles (NPs). ZnO nanoparticles (ZnO NPs) exhibit distinct properties and are produced through diverse techniques, making them valuable for applications ranging from consumer goods to medi-cal and catalytic uses. The increasing popularity of ZnO NPs is driven by novel synthesis methods that allow for modification of chemical composition and control over size and shape, thereby en-hancing their properties and expanding their applications. The catalytic activity of ZnO NPs is influenced by parameters such as oxophilicity, large surface area, amphoteric nature, and the zinc cation's ability to approach activated starting material supports, making them viable heterogeneous catalysts for a variety of applications. Various analytical techniques, including X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM) analysis, atomic force microscopy (AFM), and many more, are used to characterize the nanoparticles. This article explores various synthesis methods and characterization techniques and focuses on the catalytic activities of ZnO NPs

Synthesis of group-IV ternary and binary semiconductors using epitaxy of GeH3Cl and SnH4

Ge1−x−ySixSny alloys were grown on Ge buffers via reactions of SnH4 and GeH3Cl. The latter is a new CVD source designed for epitaxial development of group-IV semiconductors under low thermal budgets and CMOS-compatible conditions. The Ge1−x−ySixSny films were produced at very low temperatures between 160 and 200 °C with 3%–5% Si and ∼5%–11% Sn. The films were characterized using an array of structural probes that include Rutherford backscattering, x-ray photoelectron spectroscopy, high-resolution x-ray diffraction, scanning transmission electron microscopy, and atomic force microscopy. These studies indicate that the films are strained to Ge and exhibit defect-free microstructures, flat surfaces, homogeneous compositions, and sharp interfaces. Raman was used to determine the compositional dependence of the vibrational modes indicating atomic distributions indistinguishable from those obtained when using high-order Ge hydrides. For a better understanding of the growth mechanisms, a parallel study was conducted to investigate the GeH3Cl applicability for synthesis of binary Ge1−ySny films. These grew strained to Ge, but with reduced Sn compositions and lower thicknesses relative to Ge1−x−ySixSny. Bypassing the Ge buffers led to Ge1−ySny-on-Si films with compositions and thicknesses comparable to Ge1−ySny-on-Ge; but their strains were mostly relaxed. Efforts to increase the concentration and thickness of Ge1−ySny-on-Si resulted in multiphase materials containing large amounts of interstitial Sn. These outcomes suggest that the incorporation of even small Si amounts in Ge1−x−ySixSny might compensate for the large Ge–Sn mismatch by lowering bond strains. Such an effect reduces strain energy, enhances stability, promotes higher Sn incorporation, and increases critical thickness.

Tubulin-Targeted Therapy in Melanoma Increases the Cell Migration Potential by Activation of the Actomyosin Cytoskeleton─An In Vitro Study.

One of the most dangerous aspects of cancers is their ability to metastasize, which is the leading cause of death. Hence, it holds significance to develop therapies targeting the eradication of cancer cells in parallel, inhibiting metastases in cells surviving the applied therapy. Here, we focused on two melanoma cell lines─WM35 and WM266-4─representing the less and more invasive melanomas. We investigated the mechanisms of cellular processes regulating the activation of actomyosin as an effect of colchicine treatment. Additionally, we investigated the biophysical aspects of supplement therapy using Rho-associated protein kinase (ROCK) inhibitor (Y-27632) and myosin II inhibitor ((-)-blebbistatin), focusing on the microtubules and actin filaments. We analyzed their effect on the proliferation, migration, and invasiveness of melanoma cells, supported by studies on cytoskeletal architecture using confocal fluorescence microscopy and nanomechanics using atomic force microscopy (AFM) and microconstriction channels. Our results showed that colchicine inhibits the migration of most melanoma cells, while for a small cell population, it paradoxically increases their migration and invasiveness. These changes are also accompanied by the formation of stress fibers, compensating for the loss of microtubules. Simultaneous administration of selected agents led to the inhibition of this compensatory effect. Collectively, our results highlighted that colchicine led to actomyosin activation and increased the level of cancer cell invasiveness. We emphasized that a cellular pathway of Rho-ROCK-dependent actomyosin contraction is responsible for the increased invasive potential of melanoma cells in tubulin-targeted therapy.

Unveiling the pore size change in polyamide membrane using aggregation induced emission

Polyamide (PA) membranes play a crucial role in nanofiltration and reverse osmosis separations, while their pore size is primary to determine the separation performance. Current methods for pore size analysis, such as atomic force microscopy (AFM), positron annihilation spectroscopy (PAS), and the filtration experiment of neutral molecules are time-consuming and lack real-time capabilities. This limitation hinders in-situ monitoring of pore size dynamics under various operating conditions. Therefore, a rapid and real-time method is highly desirable for pore size analysis. This work presents a novel approach for real-time detection of pore size variations in PA membranes under different solvent conditions. It utilizes aggregation-induced emission (AIE) with tetraphenylethylene (TPE) groups covalently linked to the PA polymer chain during interfacial polymerization using 1-(4-Aminophenyl)-1,2,2-triphenylethene as a co-monomer. Fluorescence intensity of the PA membrane serves as an indicator of the confined state of the TPE molecules within the polymer network, thereby reflecting pore size changes under various conditions. The accuracy of the AIE-based approach is validated through complementary analyses such as small-angle X-ray scattering (SAXS) and rejection of dye molecules. The observed consistency between fluorescence variations in the PA membrane and pore size changes under different solvent conditions confirms the effectiveness of this method. This work provides a valuable visual tool for in-situ monitoring of pore size dynamics in polyamide membranes.

Multiplex antimicrobial activities of the self-assembled amphiphilic polypeptide β nanofiber KF-5 against vaginal pathogens

BackgroundVaginal infections caused by multidrug-resistant pathogens such as Candida albicans and Gardnerella spp. represent a significant health challenge. Current treatments often fail because of resistance and toxicity. This study aimed to synthesize and characterize a novel amphiphilic polypeptide, KF-5, and evaluate its antibacterial and antifungal activities, biocompatibility, and potential mechanisms of action.ResultsThe KF-5 peptide was synthesized via solid-phase peptide synthesis and self-assembled into nanostructures with filamentous and hydrogel-like configurations. Characterization by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and atomic force microscopy (AFM) confirmed the unique nanostructural properties of KF-5. KF-5 (125, 250, or 500 µg/ml) demonstrated potent antibacterial and antifungal activities, with significant inhibitory effects on drug-resistant Candida albicans and Gardnerella spp. (P < 0.05). In vitro assays revealed that 500 µg/ml KF-5 disrupted microbial cell membranes, increased membrane permeability, and induced lipid oxidation, leading to cell death (P < 0.05). Cytotoxicity tests revealed minimal toxicity in human vaginal epithelial cells, keratinocytes, and macrophages, with over 95% viability at high concentrations. Molecular dynamics simulations indicated that KF-5 interacts with phospholipid bilayers through electrostatic interactions, causing membrane disruption. In vivo studies using a mouse model of vaginal infection revealed that 0.5, 1, and 2 mg/ml KF-5 significantly reduced fungal burden and inflammation, and histological analysis confirmed the restoration of vaginal mucosal integrity (P < 0.01). Compared with conventional antifungal treatments such as miconazole, KF-5 exhibited superior efficacy (P < 0.01).ConclusionsKF-5 demonstrates significant potential as a safe and effective antimicrobial agent for treating vaginal infections. Its ability to disrupt microbial membranes while maintaining biocompatibility with human cells highlights its potential for clinical application. These findings provide a foundation for further development of KF-5 as a therapeutic option for combating drug-resistant infections.

Identification of receptor-binding protein and host receptor of non-lytic dsRNA phage phiNY.

To date, complete genome sequences of 14 double-stranded RNA (dsRNA) phages are available, and studies have shown that the host range of dsRNA phages is limited. The hosts of most dsRNA phages belong to the genus Pseudomonas. However, the dsRNA phage phiNY, which has a non-lytic life cycle, was isolated from Microvirgula aerodenitrificans. Currently, the interaction between dsRNA phage phiNY and its host bacteria is unclear, which is not beneficial to a comprehensive understanding of dsRNA phage biology and the exploitation of dsRNA phage with non-lytic life cycle for biomedical applications and others. Phage adsorption is a crucial step through the interactions between receptor-binding protein (RBP) of the phage and its receptors to initiate the infection process, which dictates host range specificity. Thus, we identified the RBP and host receptor of phiNY. Through homology alignment, amino acid sequence similarity analysis, and the phylogenetic tree analysis, orf11, located in the M-segment of dsRNA phage phiNY, encodes a putative RBP. We further performed the whole-cell enzyme-linked immunosorbent assay (ELISA), western blotting assay, and indirect immunofluorescence assay and demonstrated that this orf11 is an RBP. Finally, using affinity chromatography, ELISA, and dynamic light scattering, we identified lipopolysaccharides (LPSs) on the surface of the host M. aerodenitrificans strain LH9 as host receptors involved in the adsorption of the dsRNA bacteriophage phiNY and observed the state of phiNY RBP after combining with LPS by atomic force microscopy. These results will guide future studies on phage-host interaction in a dsRNA phage with a non-lytic life cycle.IMPORTANCEThe interactions between the lytic dsRNA phages and their host receptors have been clarified in previous studies. However, the interaction between the dsRNA phage phiNY (which has a non-lytic life cycle) and its host receptors during the dsRNA phage adsorption process was unknown. Here, we found that phiNY uses the orf11 protein as a receptor-binding protein (RBP). In addition, we found that this orf11 recognizes lipopolysaccharide from the host bacterium Microvirgula aerodenitrificans strain LH9 as a specific receptor. These results suggest that phiNY, like lytic dsRNA phages, uses an RBP to bind to a similar host receptor (i.e., lipopolysaccharide). Determining the interaction between the dsRNA phage phiNY and its host receptors will help to elucidate the mechanisms underlying the phiNY non-lytic life cycle and enhance our understanding of its infection mechanism.

Effect of waste crab shell powder on matrix asphalt

Abstract In order to solve the problems of depleting petroleum asphalt resources and deteriorating pollution of marine products, a systematic study was carried out on the application prospect of waste crab shell (WS) powder as asphalt modifier. In this study, the physical properties of WS powder modified asphalt (WSA) were tested by blending different contents of WS powder into matrix asphalt; the high and low temperature rheological properties of WS powder modified asphalt were characterized by using Dynamic shear rheometer, Bending beam rheometer, and Multiple stress creep recovery test. In addition, the microscopic chemical properties and modification mechanism were analyzed by Differential scanning calorimetry, Fourier transform infrared spectroscopy, Atomic force microscopy, and Scanning electron microscope. It was shown that the WS powder enhanced the viscoelastic properties, temperature sensitivity properties, and permanent deformation resistance of asphalt. In addition, there was no obvious chemical reaction between the WS powder and the matrix asphalt, and no new chemical substances were generated; at the microscopic level, the WS powder and the matrix asphalt had good compatibility. In conclusion, the use of WS powder as a bio-based asphalt modifier to improve the resources and environmental issues have certain prospects.

Investigation of orientation behavior of nematic liquid crystals on UV-irradiated polyimide films

Abstract The orientation mechanism of liquid crystals (LCs) on surfaces remains unclear, despite several methods for controlling pretilt angles. This study investigates the relationship between the surface condition of polyimide films, whose pretilt angles can be controlled by UV dose, and LC orientation behavior. Absorbance at wavelength of 200 nm and 260 nm significantly decrease, while thickness reduces approximately 4 nm. A rubbing treatment further decreases the thickness by approximately 2 nm. Atomic force microscopy confirmed the change in molecular conformation by UV-irradiation and rubbing treatment. The dispersive and polar components of the surface free energy of UV-irradiated polyimide films are evaluated, it’s found that only the polar component changes with UV dose. Additionally, we confirm that the alignment of LCs transitions from homeotropic to planar with increased UV irradiation, demonstrating that pretilt angle distribution can be spatially controlled. These results contribute to establishing a photoalignment method for pretilt angle control.

Intermolecular Anionic Mixed‐Valence and π‐Dimer Complexes of ortho‐Pentannulated Bisazacoronene Diimide

AbstractThis study reports the serendipitous discovery of intermolecular anionic mixed‐valence (MV) and π‐dimer species in ortho‐pentannulated BisAzaCoroneneDiimides (BACDs) during their electrochemical reduction in a non‐aqueous solvent. A library of nitrogen‐containing extended PDIs was synthesized via an aza‐benzannulation reaction followed by a Pd‐catalysed ortho‐pentannulation reaction. Ortho‐pentannulated BACDs revealed strong aggregation abilities in solution. Concentration‐dependent UV/Vis absorption spectra, variable temperature 1H NMR experiments, and atomic force microscopy coupled to molecular dynamics support their self‐assembly into columnar aggregates. Cyclic voltammetry experiments in dichloromethane reveal prominent splitting of the first reduction wave, attributed to the formation of unprecedented intermolecular anionic MV and π‐dimers in organic solvent. These species were thoroughly characterized by real‐time spectroelectrochemistry, electrochemical simulations and theoretical calculations. Remarkably, this work underscores the tuneable nature of AzaBenzannulatedPerylene Diimides (AzaBPDIs) and BACDs, emphasizing their potential as a promising scaffold for designing supramolecular materials with long‐range radical anion delocalization. The observation of this phenomenon provides insights into the fundamental behaviour of supramolecular organic semiconductors, thereby paving the way for the development of novel electronic devices and electron‐deficient materials.

Intermolecular Anionic Mixed-Valence and π-Dimer Complexes of ortho-Pentannulated Bisazacoronene Diimide.

This study reports the serendipitous discovery of intermolecular anionic mixed-valence (MV) and π-dimer species in ortho-pentannulated BisAzaCoroneneDiimides (BACDs) during their electrochemical reduction in a non-aqueous solvent. A library of nitrogen-containing extended PDIs was synthesized via an aza-benzannulation reaction followed by a Pd-catalysed ortho-pentannulation reaction. Ortho-pentannulated BACDs revealed strong aggregation abilities in solution. Concentration-dependent UV/Vis absorption spectra, variable temperature 1H NMR experiments, and atomic force microscopy coupled to molecular dynamics support their self-assembly into columnar aggregates. Cyclic voltammetry experiments in dichloromethane reveal prominent splitting of the first reduction wave, attributed to the formation of unprecedented intermolecular anionic MV and π-dimers in organic solvent. These species were thoroughly characterized by real-time spectroelectrochemistry, electrochemical simulations and theoretical calculations. Remarkably, this work underscores the tuneable nature of AzaBenzannulatedPerylene Diimides (AzaBPDIs) and BACDs, emphasizing their potential as a promising scaffold for designing supramolecular materials with long-range radical anion delocalization. The observation of this phenomenon provides insights into the fundamental behaviour of supramolecular organic semiconductors, thereby paving the way for the development of novel electronic devices and electron-deficient materials.

The Impact of Metal Ions on MXene Membranes: Critical Role of Titanium Vacancies.

Two-dimensional transition metal carbides and nitrides (MXenes) and MXene-based membranes hold promise for applications including water purification and seawater desalination; however, their environmental behavior and fate in these matrices remain unknown. In this study, we systematically assessed the reaction efficiencies of Ti3C2Tx at varying important environmental conditions. Our experiments revealed that copper and iron ions accelerated the oxidation rate of Ti3C2Tx 55.4 and 33.4 times, respectively. TiO2 and amorphous carbon were identified as the primary solid products. Based on in situ water-phase atomic force microscopy, atomic high-angle annular dark-field scanning transmission electron microscopy, and theoretical results, we postulate that metal ions enhance Ti3C2Tx oxidation by spontaneously migrating and anchoring at Ti vacancies, which then become active sites for this reaction. This process increases the adsorption of H2O and oxygen, making the Ti vacancy-rich surface convex area the most vulnerable site to attack. The findings in this study provide useful information for a comprehensive understanding of the interaction between MXene structural defects and metal ions as well as for the design and modification of MXene membranes resistant to metal ion impact.

On the Parasitic Surface Adsorption of Pyrrolidinium and Phosphonium-based Ionic Liquids Preventing Accurate Differential Capacitance Measurements

Abstract Differential capacitance measurements are known to provide vital information regarding electrical double layer charging as well as interfacial structuring of ionic liquids and ionic liquid-based electrolytes. Several hurdles have prevented these types of measurements from becoming widely used, including the fact that there exists no real consensus as to how the measurement needs to be performed and the results analyzed. To add to the difficulty, some ionic liquids are known to display a hysteresis process, thus inducing measurement variabilities. In this report, we study pyrrolidinium and phosphonium-based ionic liquid electrolytes and show that hysteresis processes indeed exist and that these are mostly the consequence of cationic adsorption on the surface. Atomic force microscopy experiments reveal that pyrrolidinium-based systems display a much denser degree of ionic compaction at the interface, compared to the phosphonium-based systems, a fact that we correlate with the much more intense hysteresis measured in pyrrolidinium-based systems. We further propose a new method for the measurement of differential capacitance and compare it with other methods in use. It is found that the proposed method allows to minimize hysteresis phenomena, thereby leading to better accuracy.

Electrochemical Immunosensors on Laser-Induced Graphene Platforms for Monitoring of Anti-RBD Antibodies After SARS-CoV-2 Infection

The COVID-19 pandemic, caused by the SARS-CoV-2 virus, has posed a major challenge to global health. The development of fast, accurate, and accessible diagnostic methods is essential in controlling the disease and mitigating its impacts. In this context, electrochemical biosensors present themselves as promising tools for the efficient monitoring of SARS-CoV-2 infection. We have developed a highly specific biosensor for the detection of anti-SARS-CoV-2 antibodies in patient sera. The use of the RBD-S region as an antigen, although purified to minimize cross-linking, poses a specific challenge. The structural similarity between SARS-CoV-2 and other respiratory viruses, as well as the complexity of the serum matrix, hinders robust analytical strategies to ensure diagnostic accuracy. This work presents a novel immunosensor for COVID-19 diagnosis using laser-induced graphene (LIG) electrodes subjected to electrochemical reduction with graphene (named rGraphene-LIG). In the present study, we chose an initial approach focused on demonstrating the concept and evaluating the feasibility of the rGraphene-LIG sensor for SARS-CoV-2 detection. The rGraphene-LIG electrodes presented a notable current increase for the redox probe in the aqueous solution of a mixture of 5 mmol L−1 potassium ferricyanide/ferrocyanide ([Fe(CN)6]3−/[Fe(CN)6]4−) in 0.1 mol L−1 KCl (pH set at 7.4). As a proof of concept, the rGraphene-LIG electrode was applied for antibody determination in real samples using cyclic voltammetry, and a limit of detection (LOD) of 0.032 μg L−1 was achieved. When determining antigens in commercial samples, we obtained an LOD of 560 ηg mL−1 and a limit of quantification of 1677 ηg mL−1. The results of the electrochemical experiments were in accordance with the surface roughness obtained from atomic force microscopy images. Based on these results, the rGraphene-LIG electrode is shown to be an excellent platform for immunoglobulin detection when present in individuals after antigenic exposure caused by SARS-CoV-2.