An antifouling polymer for dynamic anti-protein adhesion analysis by a quartz crystal microbalance

Layer-by-layer fabrication of alginate/polyethyleneimine multilayer on magnetic interface with enhanced efficiency in immuno-capturing circulating tumor cells

BACKGROUND

The technology of capturing circulating tumor cells (CTCs) plays a crucial role in the diagnosis, evaluation of therapeutic efficacy, and prediction of prognosis in lung cancer. However, the presence of complex blood environment often results in severe nonspecific protein adsorption and interferences from blood cells, which negatively impacts the specificity of CTCs capture. There is a great need for development of novel nanomaterials for CTCs capture with prominent anti-nonspecific adsorptions from proteins or blood cells.

RESULTS

We present a novel immune magnetic probe Fe3O4@(PEI/AA)4@Apt. The surface of Fe3O4 particles was modified with four layers of PEI/AA composite by layer-by-layer assembly. Furthermore, aptamers targeting epithelial marker EpCAM (SYL3C) and mesenchymal marker CSV (ZY5C) were simultaneously connected on Fe3O4@(PEI/AA)4 to improve the detection of different phenotypic CTCs and reduce false negatives. The results demonstrated that the (PEI/AA)4 coatings not only minimized non-specific protein adsorptions, but also significantly reduced the adsorption rate of red blood cells to a mere 1 %, as a result of which, the Fe3O4@(PEI/AA)4@Apt probe achieved a remarkably high capture efficiency toward CTCs (95.9 %). In the subsequent validation of clinical samples, the probe was also effective in capturing rare CTCs from lung cancer patients.

SIGNIFICANCE AND NOVELTY

A (PEI/AA) polymerized composite with controllable layers was fabricated by layer-by-layer self-assembly technique, which displayed remarkable anti-nonspecific adsorption capabilities toward proteins and cells. Importantly, Fe3O4@(PEI/AA)4@Apt probe significantly improved CTCs capture purity in lung cancer patients to 89.36 %. For the first time, this study combined controllable (PEI/AA) layers with magnetic separation to innovatively build a resistant interface that significantly improves the specific capture performances of CTCs, broadening the application of this polymerized composite.

Unveiling the spatiotemporal dynamics of membrane fouling: A focused review on dynamic fouling characterization techniques and future perspectives

Membrane technology has emerged as a crucial method for obtaining clean water from unconventional sources in the face of water scarcity. It finds wide applications in wastewater treatment, advanced treatment, and desalination of seawater and brackish water. However, membrane fouling poses a huge challenge that limits the development of membrane-based water treatment technologies. Characterizing the dynamics of membrane fouling is crucial for understanding its development, mechanisms, and effective mitigation. Instrumental techniques that enable in situ or real-time characterization of the dynamics of membrane fouling provide insights into the temporal and spatial evolution of fouling, which play a crucial role in understanding the fouling mechanism and the formulation of membrane control strategies. This review consolidates existing knowledge about the principal advanced instrumental analysis technologies employed to characterize the dynamics of membrane fouling, in terms of membrane structure, morphology, and intermolecular forces. Working principles, applications, and limitations of each technique are discussed, enabling researchers to select appropriate methods for their specific studies. Furthermore, prospects for the future development of dynamic characterization techniques for membrane fouling are discussed, underscoring the need for continued research and innovation in this field to overcome the challenges posed by membrane fouling.

Monitoring non-specific adsorption at solid-liquid interfaces by supercritical angle fluorescence microscopy

Supercritical angle fluorescence (SAF) microscopy is a novel imaging tool based on the use of distance-dependent fluorophore emission patterns to provide accurate locations of fluorophores relative to a surface. This technique has been extensively used to construct accurate cellular images and to detect surface phenomena in a static environment. However, the capability of SAF microscopy in monitoring dynamic surface phenomena and changes in millisecond intervals is underexplored in the literature. Here, we report on a hardware add-on for a conventional inverted microscope coupled with a post-processing Python module that extends the capability of SAF microscopy to monitor dynamic surface adsorption in sub-second intervals, thereby greatly expanding the potential of this tool to study surface interactions, such as surface fouling and competitive surface adhesion. The Python module enables researchers to automatically extract SAF profiles from each image. We first assessed the performance of the system by probing the specific binding of biotin-fluorescein conjugates to a neutravidin-coated cover glass in the presence of non-binding fluorescein. The SAF emission was observed to increase with the quantity of bound fluorophore on the cover glass. However, a high concentration of unbound fluorophore also contributed to overall SAF emission, leading to over-estimation in surface-bound fluorescence. To expand the applications of SAF in monitoring surface phenomena, we monitored the non-specific surface adsorption of BSA and non-ionic surfactants on a Teflon-AF surface. Solution mixtures of bovine serum albumin (BSA) and nine Pluronic/Tetronic surfactants were exposed to a Teflon-AF surface. No significant BSA adsorption was observed in all BSA-surfactant solution mixtures with negligible SAF intensity. Finally, we monitored the adsorption dynamics of BSA onto the Teflon-AF surface and observed rapid BSA adsorption on Teflon-AF surface within 10 s of addition. The adsorption rate constant (k_a) and half-life of BSA adsorption on Teflon-AF were determined to be 0.419 ± 0.004 s^-1 and 1.65 ± 0.016 s, respectively, using a pseudo-first-order adsorption equation.

Cell-membrane-inspired polymers for constructing biointerfaces with efficient molecular recognition

Fabrication of devices that accurately recognize, detect, and separate target molecules from mixtures is a crucial aspect of biotechnology for applications in medical, pharmaceutical, and food sciences. This technology has also been recently applied in solving environmental and energy-related problems. In molecular recognition, biomolecules are typically complexed with a substrate, and specific molecules from a mixture are recognized, captured, and reacted. To increase sensitivity and efficiency, the activity of the biomolecules used for capture should be maintained, and non-specific reactions on the surface should be prevented. This review summarizes polymeric materials that are used for constructing biointerfaces. Precise molecular recognition occurring at the surface of cell membranes is fundamental to sustaining life; therefore, materials that mimic the structure and properties of this particular surface are emphasized in this article. The requirements for biointerfaces to eliminate nonspecific interactions of biomolecules are described. In particular, the major issue of protein adsorption on biointerfaces is discussed by focusing on the structure of water near the interface from a thermodynamic viewpoint; moreover, the structure of polymer molecules that control the water structure is considered. Methodologies enabling stable formation of these interfaces on material surfaces are also presented.

Fast and slow EQCM response of zwitterionic weak electrolytes to changes in the electrode potential: a pH-mediated mechanism

Using a fast electrochemical quartz crystal microbalance (EQCM), zwitterionic electrolytes were studied with regard to changes of resonance frequency and resonance bandwidth after the electrode potential was switched. In addition to a fast change of frequency (within milliseconds), a further, slower process with opposite direction is observed. Both the fast and the slow process change sign when the pH is varied across the isoelectric point (pI). The fast process can be attributed to double layer recharging. Its characteristic time is slightly larger than the charge response time (the RC-time) as inferred from electrochemical impedance spectroscopy (EIS). With regard to the slow process, amino acids with moderate concentration behave markedly different from concentrated solutions of proteins. For amino acids, the slow process is larger in amplitude than the fast process and the QCM response is Sauerbrey-like. The shift in half bandwidth is smaller than the shift in frequency and the overtone-normalized frequency shifts agree between overtones (-Δf/n ≈ const. with n the overtone order). This can be explained with a viscosity change in the diffuse double layer. Independent measurements show that the viscosities of these electrolytes are higher than the average in a pH range around the pI. Presumably, the slow process reflects a rearrangement of molecules after the net charge on the molecule has increased or decreased, changing the degree of dipolar coupling and, in consequence, the viscosity. For concentrated solutions of bovine serum albumin (BSA), the QCM response does not follow Sauerbrey behaviour, which can be explained with viscoelasticity and viscoelastic dispersion. The slow process lets the frequency and the bandwidth relax towards a baseline, which is the same for jumps to more positive and to more negative potentials. Presumably, the slow process in this case is caused by a reorientation of molecules inside the Helmholtz layer, such that they screen the electric field more efficiently than immediately after the voltage jump.