Unraveling the liquid gliding on vibrating solid liquid interfaces with dynamic nanoslip enactment

Plasmonic Geometry-Induced Viscoelastic Biocomplex Formation with Optical Concealment, Liquid Slips, and Soundscapes in Bioassays

Plasmonic nanoparticles (NPs), typically made up of gold or silver, are widely used in point-of-care bio- and chemical sensing due to their role in enhancing detection sensitivity. Key NP properties influencing sensing performance include the material type, NP size, and geometry. While much research has focused on material and size optimization, less attention has been given to understand NP geometry effects and interactions with biomolecules involved in the bioassay. In this context, we investigate the interfacial properties of the biocomplex formed by spherical-shaped gold nanoparticles (AuNPs) and gold nanostars (AuNSts) during a sandwich assay using localized surface plasmon resonance (LSPR) and quartz crystal microbalance with dissipation (QCM-D). The chosen model to study the biocomplex specifically detects interleukin-6 (IL-6). Our results show that AuNSts, with their anisotropic shape and higher surface area, form antibody-antigen complexes more effectively than AuNPs. AuNSts also create a softer, more hydrated layer due to their complex geometry, which leads to larger liquid slips. Lastly, we showed that AuNSts avoid optical concealment at high IL-6 concentrations, unlike AuNPs, making them more reliable for detecting a wider range of concentrations. These findings highlight the importance of optimizing NP geometry for improved bio/chemical sensor performance.

Dynamic Monitoring of Biomolecular Hydrodynamic Dimensions by Magnetization Motion on Quartz Crystal Microbalance

Hydrodynamic dimension (HD) is the primary indicator of the size of bioconjugated particles and biomolecules. It is an important parameter in the study of solid-liquid two-phase dynamics. HD dynamic monitoring is crucial for precise and customized medical research as it enables the investigation of the continuous changes in the physicochemical characteristics of biomolecules in response to external stimuli. However, current HD measurements based on Brownian motion, such as dynamic light scattering (DLS), are inadequate for meeting the polydisperse sample demands of dynamic monitoring. In this paper, we propose MMQCM method samples of various types and HD dynamic monitoring. An alternating magnetic field of frequency ωm excites biomolecule-magnetic bead particles (bioMBs) to generate magnetization motion, and the quartz crystal microbalance (QCM) senses this motion to provide HD dynamic monitoring. Specifically, the magnetization motion is modulated onto the thickness-shear oscillation of the QCM at the frequency ωq. By analysis of the frequency spectrum of the QCM output signal, the ratio of the magnitudes of the real and imaginary parts of the components at frequency ωq ± 2ωm is extracted to characterize the particle size. Using the MMQCM approach, we successfully evaluated the size of bioMBs with different biomolecule concentrations. The 30 min HD dynamic monitoring was implemented. An increase of ∼10 nm in size was observed upon biomolecular structural stretching. Subsequently, the size of bioMBs gradually reduced due to the continuous dissociation of biomolecules, with a total reduction of 20∼40 nm. This HD dynamic monitoring demonstrates that the release of biomolecules can be regulated by controlling the duration of magnetic stimulation, providing valuable insights and guidance for controlled drug release in personalized precision medicine.

Coverage Effects in Quartz Crystal Microbalance Measurements with Suspended and Adsorbed Nanoparticles

Quartz crystal microbalance (QCM) biosensors often deal with nanoparticles suspended in the solvent at tens of nanometers above the resonator while being linked to some molecular receptor (DNA, antibody, etc.). This work presents a numerical analysis based on the immersed boundary method for the flow and QCM impedance created by an ensemble of spherical particles of radius R at varying surface coverage Θ and particle-surface gap distance Δ. The trends for the frequency Δf and dissipation ΔD shifts against Θ and Δ are shown to be determined by modifications in the structure of the perturbative flow created by the analytes. Simulations are in good agreement with a relatively large experimental database collected from the literature. Qualitative differences between the adsorbed (Δ ≈ 0) and suspended states (Δ > 0) are highlighted. In the case of adsorbed particles, deviations from the linear scaling Δf ∝ Θ are observed above Θ > 0.05 and largely depend on the specific analyte-substrate combination. Moreover, in general, ΔD(Θ) is not monotonous and usually presents a maximum around Θ ∼ 0.2. In the case of suspended analytes, the agreement with the numerical results is quantitative, indicating that the predicted scalings are universal and determined by hydrodynamics. Up to high coverage, the suspended particles present Δf ∼ Θ and ΔD ∼ Θβ, where β ≈ 0.85 is not largely dependent on R. The present findings should help forecast molecular configurations from QCM signals and have implications on QCM analyses, e.g., in the case of suspended ligands (Δf ∝ Θ), it is safe to use Δf to build Langmuir isotherms and estimate equilibrium constants. Open questions on the transition from the suspended-to-adsorbed state are discussed.

Rapid and Label-Free Analysis of Antigen-Antibody Dynamic Binding of Tumor Markers Using Piezoelectric Quartz Crystal Biosensor

Quantitative biomacromolecular diagnosis is rapidly developing in molecular oncology. In this study, we developed a continuous flow immunoassay device based on a piezoelectric (PZ) quartz crystal biosensor fabricated with whole-electrode occupation for the quantitative molecular diagnosis of tumor markers such as alpha-fetoprotein (AFP). Only one face of the crystal was in contact with the serum sample during the assays. First, the characteristics of AFP and anti-AFP binding kinetics, such as the optimal time for immune response, the average antigen binding rate, the kinetic constants and the optimal standard curve, were investigated. The overall immunoreaction time was only 12 min, the average antigen binding rate of AFP was 45.9 ng/min, the concentration range of AFP detection was 18.8-1100 ng/mL and the association rate constant (kon), dissociation rate constant (koff) and equilibrium dissociation constant (KD) were 5.58×104 M-1s-1,1.79×10-5 s-1 and 3.21×10-10 M, respectively. This sensing system was further validated by detecting AFP values from clinical serum samples, which were obtained from pregnant women, liver and lung cancer patients and those undergoing liver cancer screening. No cross-reactivity with lung cancer markers were found, and the detection results were in good agreement with the radioimmunoassay (RIA) results, with a relative deviation of no more than 3.7% and correlation coefficient r of 0.9998. Therefore, the developed immunoassay device has the potential to be used in large-scale screening for cancers, as well as in novel high-affinity binding drug development.

Recognizing the Less Explored "Active Solid"-"Moving Liquid" Interfaces in Bio/Chemical Sensors

Bio/chemical sensors possess a plethora of advantageous features that have proven to be invaluable tools in detecting and monitoring biomolecules, facilitating advancements in healthcare, environmental monitoring, food safety, and more. However, when it comes to their routine use in continuous fluid flow conditions, an intricate web of solid-liquid interfacial phenomena emerges, which requires a deep understanding of the sensor surface and fluid interations. These interfacial phenomena encompass a broad spectrum of physical, chemical, and biological processes, other than the actual detection, that influence the sensor's response. In this context, perhaps exploring a new theme "active solid"-"moving liquid" interface will unleash the full potential of bio/chemical sensors in any flow-based application.

Modeling and Analysis of the Capillary Force for Interactions of Different Tip/Substrate in AFM Based on the Energy Method

This paper presents a simple and robust model to describe the wet adhesion of the AFM tip and substrate joined by a liquid bridge. The effects of contact angles, wetting circle radius, the volume of a liquid bridge, the gap between the AFM tip and substrate, environmental humidity, and tip geometry on the capillary force are studied. To model capillary forces, while a circular approximation for the meniscus of the bridge is assumed, the combination of the capillary adhesion due to the pressure difference across the free surface and the vertical component of the surface tension forces acting tangentially to the interface along the contact line is utilized. Finally, the validity of the proposed theoretical model is verified using numerical analysis and available experimental measurements. The results of this study can provide a basis to model the hydrophobic and hydrophilic tip/surfaces and study their effect on adhesion force between the AFM tip and the substrate.