Filter Membrane Research Articles

BACTERIOLOGICAL QUALITY OF DRINKING WATER AND ASSOCIATED FACTORS AT COMMUNITY POINT SOURCES, IN ARUA DISTRICT, UGANDA

Background: Access to ample and safe water is vital, yet many globally lack this essential resource. Each year, 3.4 million individuals die from water-related diseases. Specifically, in Uganda, annual estimates suggest 89,000 cholera cases, resulting in 3,000 deaths. Objective: This study aimed to evaluate the bacteriological quality of drinking water and related factors in Arua Districts community water sources. Method: Utilizing a cross-sectional design and laboratory experiments, 140 samples were analyzed for coliform bacteria presence on filter membranes. Factors relating to contamination risks were identified via a sanitary inspection checklist. Data analysis was conducted using Stata/SE 17.0. Results: About 70.71% of samples contained bacteria, primarily total coliform. Significant risk factors included defective wastewater drainage (aOR: 19.7[5.34-72.72]), malfunctioning appliance parts (aOR: 10.7[2.52-45.92]), and inadequate or absence of fencing (aOR: 9.2[2.43-34.96]), each with a P-value <0.001. Conclusion: Ensuring safe drinking water requires treatment, quality monitoring, maintenance of appliances, and proper fencing to reduce bacterial contamination.

QuEChERS-HPLC-MS for the determination of coronatine residues in paddy field environment and five common fruits and vegetables

The residue of coronatine in the paddy field environment, as well as five common fruits and vegetables, was analyzed using the QuEChERS pre-treatment technique combined with HPLC-MS in this experiment. Acetonitrile was used as the extractant, while C18 and multi-walled carbon nanotubes served as adsorbents for sample extraction and purification. Subsequently, the samples were filtered through a 0.2 μm organic filter membrane before detection on the machine. The limits of detection (LOD) and quantification (LOQ) for coronatine in the paddy field environment and five common fruits and vegetables were determined to be 0.0005–0.0035 mg/kg and 0.0018–0.0118 mg/kg, respectively, exhibiting good linear correlation coefficients (R2≥0.9900) at spiked levels ranging from 0.01 to 1 mg/kg. The average intra-day recoveries ranged from 75.19 % to 107.9 %, with relative standard deviations (RSDs) of 1.24 %-12.66 % at spiked levels of 0.05–0.5 mg/kg.

Optimising microplastics analysis for quantifying and identifying microplastic fibres in laundry wastewater

Current methods for measuring microplastic fibres (MPF) are cumbersome, time consuming and unscalable for routine high throughput analysis. This study reports a method for rapidly extracting, quantifying and analysing MPFs in laundry wastewater with several key improvements which vastly enhance overall efficiency and scalability of analysis. FT-IR surveying is employed as a preliminary step in analysis to quickly determine what polymers are present in a sample prior to fluorescence treatment. Using random quadrating, whole 25 mm filter membranes were surveyed in <30 min with high recovery rates. In industrial laundry wastewater samples, polyester was the most common MPF, however acrylic, nylon, cotton and rayon were all ubiquitous. The study also demonstrates that an excitation wavelength of 365 nm was optimal for fluorescing PET fibres like polyester which were stained with Nile Red, but not 495 nm, which is commonly used in microplastic analysis. Finally, a custom ImageJ macro was written to automatically enumerate and describe MPFs on filter membranes using just a single stitched fluorescence image. In just a few seconds, concentrations of up to 40,000 fibres/L were analysed in industrial laundry wastewater samples with a lower particle size limit of 20 μm. This study highlights the need for more optimised and scalable analysis workflows which maintain high levels of reliability and accuracy.

Interaction between liquid droplets and membrane surfaces

Multi-stage flue gas cleaning systems are used to reduce the pollutant emissions from fuel combustion. A variety of filters have been developed to capture soot particles in flue gases. Such filters are usually based on membranes. Another popular way of reducing the anthropogenic emissions in flue gases is by adding agents or water to fuels. Not much information is available on the impact of vapor produced by the combustion of such fuels on membrane permeability characteristics. Membrane permeability to gas flow should be studied with due consideration of membrane wettability and droplet agglomeration on it. This research focuses on identifying the main patterns of the interaction between liquid droplets and membranes of various types. Using the experimental findings, we have identified two droplet-membrane interaction regimes–spreading and breakup–as well as the interaction phases when each of these two regimes is observed. We have also established that the maximum spreading diameter remains relatively insensitive to the surface wettability at low Weber numbers. The analysis of the experimental findings has shown that an air pocket is formed under a droplet if its impact velocity exceeds 2.5 m/s. The impact with an air pocket triggers droplet breakup and reduces the maximum spreading diameter. This process is a decisive factor in favor of using membranes in flue gas cleaning systems. The findings of this paper can be used to extend the operating life of filtration membranes used in thermal power plants.

Sheep bone powder modified PVDF membrane for highlyefficient oil-in-water emulsion separation

BackgroundThe wetting properties and roughness modification of membrane surfaces are crucial for their application in emulsion separation. However, traditional membrane modification methods suffer from high cost, complex preparation, and secondary pollution. MethodsIn this study, a novel, simple, and economical interfacial engineering method was developed using tannic acid (TA), sodium alginate (SA), and sheep bone powder (BP) as raw materials. Through vacuum filtration, these materials were deposited onto polyvinylidene fluoride (PVDF) membrane to fabricate superhydrophilic/underwater superoleophobic filtration membrane (PDBS). BP induced surface roughness and wetting properties to the membrane, while preserving the porous structure of the substrate membrane. The complex formed by TA and SA encapsulated BP onto the surface of PVDF microfiltration membrane, enhancing its mechanical properties. Significant FindingsThe prepared membrane exhibited a membrane flux of 347 Lm−2h−1 bar−1 and a separation efficiency of 99.9 % for emulsified oil. Furthermore, after soaking in NaCl solution for 30 h, the membrane still showed excellent stability. Therefore, this study developed a new membrane surface modification strategy with promising application prospects in oily wastewater treatment.

Fibrous PVDF membranes modified by anchored g-C3N4@GO composite with enhanced photocatalytic activity

Recently, the development of fibrous membranes for pollutant filtration from air or water has been a topic of great interest. However, these filters’ high and rapid fouling has limited their use. In response, we have prepared photocatalytic active membranes that harness the synergic effect between graphene oxide (GO) and graphitic carbon nitride (g-C3N4). Theresultingcomposite demonstrated the highest photocatalytic activity (kobs = 88 × 10−3 min−1). This g-C3N4@GO composite was then carefully deposited on/in an electrospun polyvinyl difluoride (PVDF) fibrous membrane. The reproducible results of the chemical bonding ofthecomposite to the PVDF matrix were evident during photocatalytic experiments after ten Rhodamine B (Rh B) photocatalytic degradation cycles. Importantly, the fiber structure analysis post-reaction did not reveal any fiber cracks or void formation defects, indicating the excellent chemical stability of the PVDF fibrous matrix. This research offers a promising, sustainable, eco-friendly, and efficient solution for removing pollutants from different environments, inspiring further exploration and development in this field.

Fabrication and performance evaluation of an innovative asymmetric polyethersulfone composite membrane for efficient methyl blue filtration

AbstractGiven the toxicity of wastewater pollutants to both humans and the environment, it is critical to develop a new synthetic membrane with superior permeability and rejection. Herein, a novel asymmetric polyethersulfone (PES) composite filtration membrane was successfully prepared using a simple alternating vacuum‐deposition process with positively charged chitosan and negatively charged cellulose nanofibrils as polycations and polyanions, respectively. As expected, the produced PES composite filtration membranes had a compressed and negatively charged surface, which prevented the anionic dye methyl blue (MB) molecules from infiltrating into the membrane matrix. Consequently, the resulting PES composite filtration membranes exhibited an extremely high MB rejection (99.7%) and a satisfactory flux (37.47 L h−1 m−2 MPa−1). In addition, the composite membrane demonstrated extremely selective removal of anionic dyes in the presence of neutral dyes due to the Donnan effect. Furthermore, the developed PES composite filtration membranes displayed exceptional long‐term stability (99.8% rejection and 36.5 L h−1 m−2 MPa−1 flux after 50 h of filtration) and recycling properties (90.1% flux recovery rate after 3 cycles of running). In conclusion, the PES composite filtration membranes prepared in this study presented great potential in wastewater filtering.

The effect of charge screening for cationic surfactants on the rigidity of interfacial nanoparticle assemblies

HypothesisFunctionalizing colloidal particles with oppositely charged surfactants is crucial for stabilizing emulsions, foams, all-liquid structures, and bijels. However, surfactants can reduce the attachment energy, the driving force for colloidal self-assembly at interfaces. An open question remains on how the inherent interfacial activity of cationic surfactants influences the interfacial rigidity of particle-laden interfaces. We hypothesize that charge screening among cationic surfactants regulates the rigidity of oil/water interfaces by reducing the attachment energy of nanoparticles. ExperimentsWe investigate the interfacial rigidity of cetyltrimethylammonium bromide (CTAB) functionalized silica nanoparticles (Ludox® TMA) by analyzing the shape deformation of 1,4-butanediol diacrylate (BDA) droplets under varying salt and alcohol concentrations. The nanoparticle packing density is assessed using scanning electron microscopy. Attachment energy is characterized through interfacial tension measurements, three-phase contact angle analysis, and CTAB adsorption studies. We also examine the effects of interfacial rigidities on the structure of bijel films formed via roll-to-roll solvent transfer-induced phase separation (R2R-STrIPS) using confocal laser scanning microscopy. FindingsIncreasing salt and alcohol concentrations decrease the interfacial rigidity of CTAB-functionalized nanoparticle films by reducing the interfacial tension. The contact angle has a minor influence on the rigidity. These results indicate that CTAB charge screening weakens the nanoparticle attachment energy to the interface. Controlling the rigidity enables the mass production of bijel sheets with consistent flatness, which is crucial for their potential applications in catalysis, energy storage, tissue engineering, and filtration membranes.

Fast Isolation and Sensitive Multicolor Visual Detection of Small Extracellular Vesicles by Multifunctional Polydopamine Nanospheres.

Small extracellular vesicles (sEVs) assume pivotal roles as vital messengers in intercellular communication, boasting a plethora of biological functions and promising clinical applications. However, efficient isolation and sensitive detection of sEVs continue to present formidable challenges. In this study, we report a novel method for fast isolation and highly sensitive multicolor visual detection of sEVs using aptamer-functionalized polydopamine nanospheres (SIMPLE). In the SIMPLE strategy, aptamer-functionalized polydopamine nanospheres (Apt-PDANS) with 170 nm diameters were synthesized and exhibited a remarkable ability to selectively bind to specific proteins on the surface of sEVs. The binding between sEVs and Apt-PDANS engenders an increase in the overall size of the sEVs, allowing fast isolation of sEVs by filtration (a filter membrane with a pore size of 200 nm). The fast isolation strategy not only circumvents the interference posed by unbound proteins and excessive probes as well as the intricacies associated with conventional ultracentrifugation methods but also expedites the separation of sEVs. Concurrently, the incorporation of Fe3+-doped PDANS permits the multicolor visual detection of sEVs, enabling quantitative analysis by the discernment of visual cues. The proposed strategy achieves a detection limit of 3.2 × 104 sEV mL-1 within 1 h, devoid of any reliance on instrumental apparatus. Furthermore, we showcase the potential application of this methodology in epithelial-mesenchymal transition monitoring and cancer diagnosis, while also envisioning its widespread adoption as a straightforward, rapid, sensitive, and versatile platform for disease monitoring and functional exploration.

Development of quaternized agar-based materials for the coronavirus inactivation

The COVID-19 pandemic has revealed weaknesses in healthcare systems and underscored the need for advanced antimicrobial materials. This study investigates the quaternization of agar, a seaweed-derived polysaccharide, and the development of electrospun membranes for air filtration in facemasks and biomedical applications. Using the betacoronavirus MHV-3 as a model, quaternized agar and membranes achieved a 90–99.99 % reduction in viral load, without associated cytotoxicity. The quaternization process reduced the viscosity of the solution from 1.19 ± 0.005 to 0.64 ± 0.005 Pa.s and consequently the electrospun fiber diameter ranged from 360 to 185 nm. Membranes synthesized based on polyvinyl alcohol and thermally cross-linked with citric acid exhibited lower water permeability. Avoiding organic solvents in the electrospinning technique ensured eco-friendly production. This approach offers a promising way to develop biocompatible and functional materials for healthcare and environmental applications.

Bioinspired Microgel-Loaded Smart Membrane Filtration with the Thermo- and Ion-Dual Responsive Water Gate for Selective Lead(II) Separation.

Lead (Pb2+) is a ubiquitous pollutant. Membrane filtration represents one of the most common water treatment methods, but nanofiltration and ultrafiltration require high transmembrane pressure, while microfiltration has larger pore sizes than ions, making them unfavorable for direct ion removal at low cost. Selective and direct separation of Pb2+ via membrane filtration at high efficiency without sacrificing the flux of clean water still remains challenging. Herein, inspired by the Pb2+-tolerable oleander that enriches and prevents Pb2+ in roots from permeating the plant body, a smart Pb2+-adsorptive filtration membrane with a temperature- and ion-tunable water gate was prepared by loading dual-responsive poly(N-isopropylacrylamido-co-acrylamido-benzo-18-crown-6) (PNB-5-20) microgels onto a commercial membrane. The PNB-5-20 microgel exhibits pronounced temperature-responsive swelling/deswelling (hydrodynamic diameter, 650-330 nm) with a volume phase transition temperature (VPTT) at ∼33 °C. Moreover, the microgel shows a high Pb2+-adsorption capacity (qmax, 85.4 mg/g) and good selectivity (distribution coefficient Kd ∼ 1000 mL/g) thanks to its complexation with the crown ether, as well as good Pb2+ responsiveness, having the VPTT positively shifted to 40 °C in the presence of Pb2+ with enhanced swelling behaviors. Functionalized with PNB-5-20, the smart membrane integrates Pb2+ detection, adsorption, and tunable water drainage in a single device. The membrane selectively recognizes Pb2+ in the polluted water with the gates in membrane pores switching from "open" to "closed", intercepting and adsorbing Pb2+ with water permeation reduced. Once purified, the gates can be "re-opened" by increasing the temperature. Construction of such an intelligent membrane filtration device with a tunable water gate and excellent Pb2+ recognition and adsorption performance will greatly simplify the remediation of Pb2+-polluted water.

Simple and Ultrasensitive Nanozyme-Linked Immunosorbent Assay for SARS-CoV-2 Detection on a Syringe-Driven Filtration Device.

This work proposed a simple and ultrasensitive nanozyme-based immunoassay on a filtration device for the detection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) nucleocapsid protein (NP). Gold core porous platinum shell nanoparticles (Au@Pt NPs) were synthesized with high catalytic activity to oxidize 3,3',5,5'-tetramethylbenzidine, leading to an oblivious color change. The filtration device was designed based on the size difference of magnetic beads, filter membrane pore, and Au@Pt NPs. A simple, rapid, and consistent washing procedure can be performed with the help of a plastic syringe. This detection method could realize the quantitative detection of SARS-CoV-2 NP within 80 min for point-of-care needs. The limit of detection for the SARS-CoV-2 antigen was 0.01 ng/mL in buffer. The coefficients of variation of the assay were 1.78% for 10 ng/mL SARS-CoV-2 antigen, 2.03% for 1 ng/mL SARS-CoV-2 antigen, and 2.34% for the negative sample, respectively. The specificity of the detection platform was verified by the detection of various respiratory viruses. This simple and effective detection system was expected to promote substantial progress in the development and application of virus immunodetection technology.

Synthesis of a Hybrid Membrane of Polysulfone with Zinc Oxide for Cleaning Textile Effluents.

This study aimed to investigate the influence of the ZnO concentration on the structure of a membrane for effluent filtration, varying this concentration from 0% to 3%. To analyze the results, X-ray diffraction tests, Fourier-transform infrared spectroscopy, apparent porosity, atomic force microscopy, and scanning electron microscopy were used, all of which were employed for the characterization of the produced membranes. The solution simulating the effluent was analyzed before and after the filtration process to assess the filtration results. The conducted tests reported results for filtered solution flow, turbidity, pH, dissolved oxygen, and electrical conductivity. All these results indicated that the membrane with the best performance in terms of cleanliness and the amount of filtered effluent was the one produced with a 13% hybrid polysulfone loaded with 1% ZnO in its structure.

Spray-coated PDA-wrapped carboxylic CNT/PES membrane to augment fouling mitigation, organic removal, and membrane stability in electrochemical membrane filtration

This study introduces robust and conductive polydopamine (PDA)-wrapped carboxylic carbon nanotube (C-CNT)-coated polyethersulfone (PES) membrane for electrochemical membrane filtration to treat greywater. Self-polymerized dopamine was prepared directly under oxidative conditions on the CNT strands, followed by their immobilizations on the surface of the PES membrane through a novel spray-coating technique. The spraying coating technique improved both the durability of the coating layer and membrane permeability by 27 % higher than that prepared by the conventional vacuum filtration method. The spraying coating technique enhanced the electroactive properties of the PDA/C-CNT membrane so that the fouling rate was reduced more effectively than the C-CNT membrane or bare PES membrane. Fouling mitigation of the PDA/C-CNT membrane was attributed to the combined effect of electrostatic repulsions between the foulants and the conductive membrane surface along with degradation of organic compounds by electrochemical oxidation. The constant current density profile also confirmed the structural stability of the conductive layer on the membrane under both cathodic and anodic conditions. Furthermore, the fouling layer formed by membrane filtration was removed effectively by in-situ anodic cleaning. Over 80% of water permeability was recovered without losing the membrane integrity up to 3 consecutive anodic cleaning cycles.

Response surface methodology for the production of a filter membrane from the combination of sand, PET and salt as a pore-forming agent

Plastic waste is increasing every day due to urbanization, population growth and in turn, pollutes the environment. These wastes are considered to be a big problem due to their very low biodegradability and presence in large quantities. A large amount of plastic which is being brought by human activities is discarded or burned which leads to the contamination of the environment and air. Therefore, finding alternative methods of disposing of waste by using kind approaches is becoming a major research issue. In this research, polyethene terephthalate waste is used as a binder by burning and mixing with sand and sodium carbonate to investigate the possibility of producing composite material with a plastic sand filter and study the effect of sand, polyethene terephthalate waste and porogen with different design mix ratio on the properties of the product. An experimental design plan was adopted to formulate the materials. To fabricate this material, the melt moulding/particulate leaching technique was used, in which the components are mixed in their respective proportions, moulded, melted and afterwards leached to remove the porogen. We obtained an optimum of 31.0711% porosity for the optimum mixture containing proportions of 0.5, 0.25 and 0.25 plastic sand and porogen respectively. An improved melt/moulding particulate leaching technique was used to improve the permeability and reduce pore sizes of the optimum. This technique involved using a saturated solution of porogen instead of using the porogen in particulate form. The microbial cut-off efficacy of the material was evaluated, in which microbiological analyses were used to enumerate the number of microbes in a lake water sample before and after filtration through the porous material. The results of viable cell counting showed that the material eliminated 92.6% of the water microbes analysed.

Desalination of dye and protein by Ba2+/Ca2+ co-crosslinked alginate filtration membrane loaded on polypropylene non-woven

Calcium alginate hydrogel filtration membranes show excellent fouling resistance, but the poor mechanical properties and instability limit the use of the membranes. In this paper, sodium alginate was co-crosslinked with Ba2+ and Ca2+ to prepare barium alginate/calcium alginate composite hydrogel membrane loaded on polypropylene non-woven (Ba/CaAlg-PP). The morphology, structure, and swelling rate of the composite filtration membrane were characterized. The fracture strength of the Ba/CaAlg membrane reached a maximum value of 2.47 MPa. The rejection rates of Ba/CaAlg-PP membrane for Methyl blue and NaCl were close to 100 % and <8.0 %, respectively. Meanwhile, the flux of the Ba/CaAlg-PP membrane in dye/NaCl mixture was 43.2 L·m−2·h−1 and the selectivity coefficient of dye/NaCl reached 154.6. Ba/CaAlg-PP membranes exhibited excellent permeability, rejection and long-term stability in protein desalination. The results of simultaneous fluorescence spectroscopy and molecular dynamics simulations showed that the Ba2+ in the Ba/CaAlg-PP membrane did not disrupt the helical structure of BSA. The Ba/CaAlg-PP membrane has a wide range of applications prospect in proteins and dyes desalination.

Production and Evaluation of Hydroxypropyl Starch as a Viscosifying Agent for Enhanced Oil Recovery

AbstractIn this study, starch was obtained from rice wastes and the maximum extraction yield was 90.95 %. Chemical modification reactions were carried out by hydroxypropylation to obtain a modified starch extract, named 005A, soluble in synthetic injection brine. Extract 005A had a modified starch concentration of 1.24 %, with a pseudoplastic rheological profile and viscosities of 325.54 cP and 121.03 cP at temperatures of 25 and 60 °C, respectively. The application of extract 005A was evaluated by injectivity/filterability tests, which indicated a good filtration rate and viscosity loss of 3.81 % when passing the fluid through the filtering membrane. Stability tests indicated that the 005A extract had a viscosity loss of 21.35 %, at the temperature of 60 °C, after 60 days. The application of this extract enabled additional mineral oil recovery of 12.19 % in simulated core flooding tests. Therefore, the extract of hydroxypropyl starch is a promising viscosifying agent for Enhanced Oil Recovery (EOR) fluids.

Electrodeposition of WO3 Nanoparticles Onto a Carbon Membrane Surface for the Development of a Hybrid Filtration/Photocatalysis System

This study proposes the development of a photoactive filtration membrane using carbon fiber (CF) modified with an n-type semiconductor (WO3) to create a hybrid filtration/photocatalysis system applied in water treatment for simultaneous retention and degradation of the emerging contaminant (Sertraline - SER). The membrane was prepared through chemical electrodeposition in a three-electrode electrochemical cell, utilizing CF as the working electrode, two-dimensionally stable anode counter electrodes (De Nora), and an Ag/AgCl 4.0 mol L-1 KCl reference electrode. The preparation conditions included: 5.0 mmol L-1 of Na2WO4, 0.075% (v/v) H2O2, pH 1.4, with a potential of -0.5 V applied for 1 h, followed by heat treatment at 450 °C.Characterizations revealed a mesoporous structure, with UV-Vis absorption (300 - 700 nm), a band gap of 3.6 eV, and a BET surface area of 3.1 m2 g-1. Micrographs illustrated the formation of a uniform layer of WO3 on the CF surface, and characteristic peaks of C and WO3 in the monoclinic phase were confirmed. XPS analysis assigned species, including C 1s, O 1s, W (4f, 4f7/2, 4d5/2 4d3/2), with an intense peak at 530 eV related to the metallic bond (W-O).The optimized experimental conditions: SER 2.0 mg L-1, volume 100 mL, flow rate 180 mL min-1, pH 5.6, UV LED irradiation, complete removal of SER was observed in 30 min when applied to real effluents from a water treatment plant before and after the chlorination step. Additionally, complete degradation was achieved after 90 min of the experiment in simulated effluents in Milli-Q water. The photoactive membrane proved effective under various conditions, achieving 1.41 mg L-1 SER degradation after five reuse cycles and complete SER degradation after 40 min under solar irradiation. Experiments with scavenger agents confirmed the participation of species (HO•, O2 •-, 1O2, h+, and H2O2) in the degradation process. Additionally, six degradation products were identified with mass-charge (m/z) of 176, 189, 191, 273, 293, and 322, generated from hydroxylation, demethylation, and dechlorination reactions.The photoactive membrane has shown excellent potential for applications in filtration processes, mitigating issues associated with fouling. It facilitates the rapid removal and effective degradation of pollutants while also allowing for its application under various irradiation conditions. This feature simplifies and enables effective management in the treatment of contaminated waters.

Rapid photothermal assay for ultrasensitive point-of-care detection of tumor markers based on a filter membrane.

Anultrasensitive photothermal assay was designed for point-of-care testing (POCT) of tumor markers based on a filter membrane. Firstly, Cu2-xSe was successfully encapsulated in liposome spheres with biotin on the surface and connected to carcinoembryonic antigen (CEA) aptamer with 3'end modified biotin by streptavidin. Secondly, the CEA antibody was successfully modified on the surface of the nitrocellulose membrane through simple incubation. Finally, the assay process was completed using a disposable syringe, and the temperature was recorded using a handheld infrared temperature detector. In the range 0-50 ng mL-1, the temperature change of the nitrocellulose membrane has a strong linear relationship with CEA concentration, and the detection limit is 0.097 ng mL-1. It is worth noting that the entire testing process can be easily performed in 10 min, much shorter than traditional clinical methods. In addition, this method was successfully applied tothe quantitative determinationof CEA levels in human serum samples with a recovery of 96.2-103.3%. This rapid assay can be performed by "one suction and one push" through a disposable syringe, which is simple to operate, and the excellent sensitivity reveals the great potential of the proposed strategy in the POCT of tumor biomarkers.

Polyamidoamine dendrimer-modified polyvinylidene fluoride microporous membranes for protein separation

The separation efficiency of pressure-driven filtration membranes is primarily dictated by the membrane pore size. Membranes with larger pores typically demonstrate high flux but low or zero rejection when it comes to separating small molecules. In protein separation, ultrafiltration (UF) membranes with pore sizes smaller than the molecular dimensions of target proteins are commonly used for size rejection. Taking inspiration from the separation mechanism of nanofiltration (NF) membranes, we hypothesize that introducing charged groups into membranes of appropriate pore sizes could significantly enhance the electrical interaction between membrane charges and protein charges. This enhancement, occurring at the nanoscale distance when protein molecules approach or pass through charged nanoscale membrane channels, may enable the rejection of proteins substantially smaller than the pore size. Using membranes with relatively large pore sizes could lead to an increase in flux. To test this hypothesis, we conducted experiments involving the modification of polyvinylidene fluoride (PVDF) membranes with suitable pore sizes, using polyamidoamine (PAMAM) dendrimers to introduce negative charges to the membranes. The performance of the PVDF membranes and the modified membranes were investigated in the separation of whey proteins. To evaluate the contribution of steric and electrical hindrance to the solute separation, filtration experiments were performed using polyethylene oxide (PEO) and polyacrylic acid (PAA). The membranes were characterized using techniques such as attenuated total reflectance-Fourier transform infrared (ATR-FTIR), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). The results indicate that the modification enhances the rejection efficiency of whey proteins. The whey protein rejection and permeate flux for PVDF membranes were 58.9% and 15.3 LMH, respectively. Following alkaline treatment or PAMAM-G3.5 dendrimer modification, the whey protein rejection increased to 97.3% and 98.8%, respectively. However, alkaline treatment and PAMAM-G3.5 dendrimer modification resulted in a reduction of permeate flux to 5.6 LMH and 2.3 LMH, respectively. This suggests that increasing membrane charge effectively enhances the separation ability of filtration membranes in charged macromolecule separation.