Significant Fouling Research Articles

Electrochemical detection of amine neurotransmitters is drastically different in buffer solutions, in vivo, and cell culture systems

Detection of neurotransmitters requires high sensitivity and temporal resolution, favoring electrochemical techniques for the sensing mechanism. However, electrochemical detection of amine neurotransmitters is highly dependent on electrode surface condition and thus, results obtained in clean buffer solutions are not directly applicable to the real measurement environment in vivo or in vitro. In these more complex electrolyte solutions, the presence of antioxidants and surface-adsorbing molecules drastically alters the redox characteristics of amine neurotransmitters, their precursors and metabolites. Accordingly, we surveyed their redox characteristics in the phosphate buffered saline (PBS), cerebrospinal fluid (CSF) and cell culture medium, with high-sensitivity electrodes made of single-walled carbon nanotube network.The concentration of surface-fouling molecules was lowest in the PBS and highest in the culture medium. Accordingly, electrochemical reaction kinetics were facile in the PBS and sluggish in the culture medium. Surprisingly, analyte molecular structure had much more importance in the CSF compared to other electrolytes, however the reaction kinetics remained to be generally slower in the CSF compared to when measured in the PBS.Whereas the CSF also contains L-Ascorbic acid and uric acid that are electrochemically active interfering molecules, they are either completely absent or can be omitted in the in vitro setting. On the contrast, the culture medium contains substantially higher concentration of surface-adsorbing molecules that causes more significant fouling of electrode and thus loss of sensitivity. As the in vitro brain-on-a-chip applications are rapidly being adopted, direct comparison of these different experimental settings was essential to understand their implications for electrochemical sensors.

Improving separation efficiency of various micropollutants from water by polymer-enhanced ultrafiltration using oxidized alginate featuring less viscous and low filtration resistance

Polymer-enhanced ultrafiltration (PEUF) is an economical and energy-efficient alternative using a versatile water-soluble polymer (WSP) to remove micropollutants by electrostatic interactions, allowing size exclusion through ultrafiltration (UF) membranes due to the WSP being bigger than the pores of UF membranes. However, the WSP used in PEUF is so viscous that it inevitably causes significant filtration resistance and membrane fouling, reducing filtration and energy efficiency. To overcome this problem, in this study, sodium alginate (Alg), which significantly performs in removing cationic pollutants, was oxidized using sodium periodate to produce oxidized alginate (OxAlg). The retention and water flux profiles of OxAlg for three micropollutants, methylene blue (MB), ciprofloxacin, and tetramethylammonium hydroxide, using the PEUF method were investigated in terms of pH, ionic strength, polymer and pollutant amount. A comparison between Alg and OxAlg demonstrated 1.19% to 1.8% higher MB retention rates (99.31%-99.97%) and up to 4.07 times higher water flux depending on the amount of polymer added. Furthermore, OxAlg displayed excellent retention rates of the NF level and 20-60 times higher water flux than typical NF. This outstanding OxAlg performance was mainly due to OxAlg’s properties, such as the low viscosity, flexibility and the resulting accessibility, and appropriate size from the perspective of filtration. Lastly, OxAlg was found to have the potential to surpass the existing WSP in that it showed a higher maximum retention capacity than about 560 to 1250mg/g in the real-world pH enrichment test even before the saturation.

Analysis of Tubular NF Plants in Scotland Indicates That Summer Temperatures and Redox-Sensitive Elements Are Correlated with Membrane Biofouling and Shortened Useful Life.

We investigate the effects of seasonal variations in water composition and temperature on the performance of two full-scale drinking water treatment plants in Scotland, equipped with tubular cellulose acetate nanofiltration membranes. Multiple environmental and water quality parameters, recorded over a 4.5-year period, were correlated against membrane permeance, cleaning frequency, and useful life. Membrane autopsies enabled the characterization of the foulant composition. Temporal variations in temperature at plant X led to significant biofouling (manifested by permeance losses of 30-50%, and bacteria detected on the membrane surface) during the summer months, when water temperatures exceeded 20 °C and microbiological activity was highest. Plant Y, in contrast, displayed smaller seasonal variations and was operationally stable without significant fouling. A pronounced increase in manganese and iron (up to 200 and 600 μg/L, respectively) in the lake water at plant X in summer was accompanied by elevated content (∼60 mg/m2) of those metals on the membrane surface, which was consistent with lake thermal stratification and metal input from the sediment into the water column. Our work shows that membrane plants in regions supplied by standing surface water bodies, such as plant X, are more vulnerable to biofouling, especially during warmer months.

Advanced absorption-storage water molecules strategy reinforces antifouling property for stable oil/water emulsions separation

Constructing membranes with extraordinary resistance to oil contamination under high permeation flux is a considerable challenge. Herein, an advanced absorption-storage water molecules strategy is proposed for constructing the robust hydration layers to achieve effective anti-oil fouling and stable oily wastewater purification. Specifically, metal–organic framework (MOF, UiO-66-NH2) nanoparticles with powerful water-absorbing characteristics are preferentially adsorbed to collect water in oil/surfactant/water systems. Combining excellent water retention, the micro-/ nano-networks formed by attapulgite (APT) could store the water molecules captured by MOF. The synergistic effect of the water-absorbing/water-retaining interactions between the MOF and APT created robust hydration layers defense barriers, which enhanced the resistance of membrane to oil contamination. Furthermore, the abundant hydrophilic groups (e.g., –OH, –NH2 and –CONH2) of chitosan (CS) further improved the membrane surface hydrophilic coverage, permeability and hydration ability. As a result, the developed CS/APT@MOF composite membrane exhibited significant anti-oil fouling capability and realized superior purification property towards various oil-in-water emulsions stabilized by surfactants. The CS/APT@MOF composite membrane demonstrated outstanding oil repellency (flux recovery ratio > 99.6 %, total flux decline ratio < 3.8 %) over 10 cycles under large permeability (>660 L m-2h−1 bar−1). Meanwhile, the constructed CS/APT@MOF composite membrane exhibited stable separation cycle capability (10 cycles) and continuous purification performance (60 min) for different oil/water emulsions. Therefore, this advanced strategy based on absorption-storage water molecules to construct robust hydration layers provides a promising insight for the development of superior antifouling and operationally stable oil/water emulsions separation membranes.

Dual defense against membrane fouling for efficient and sustainable oil/water separation on a novel super-hydrophilic/underwater superoleophobic and catalytic nanofibrous membrane

Membrane separation technology is widely recognized as an efficient method for treating organically polluted wastewater in virtue of high performance and straightforward operation. However, the practical application of membranes is inevitably confronted with contamination issues, presenting a major challenge in terms of fouling resistance. To address this issue, a defensive-offensive dual-defense strategy based on wettability and catalytic ability control is proposed. With this concept, a novel nanofibrous membrane with a unique structure was successfully prepared through polyacrylonitrile (PAN) electrospinning, pre-oxidation, CoFe Prussian blue analogue (PBA) and polypyrrole (PPy) modification, and calcination processes. For the passive defense mode, the as-prepared membrane has shown good underwater-superoleophobicity for various types of oils, good separation capability for corresponding oil–water emulsions with retention ratios of above 99 % and fluxes ranging from 231.5 to 1524.2 L·m−2·h−1·bar−1, as well as organic solvent (dimethylformamide, DMF) resistance. For the offensive defense mode, this membrane exhibits well catalytic degradation performance for refractory pollutants with the assistance of peroxymonosulfate (PMS), which is due to the membrane being decorated with catalytic nanoparticles that contain abundant encapsulated ultra-small Fe doped Co3O4 (∼2.28 nm), and that is much smaller than the size of the pristine PBA (∼33.8 nm). Notably, the surfactants present in oil-in-water emulsions are found to be the main cause of membrane fouling, where the cationic surfactants exhibit the most significant fouling effect, while the introduction of photo-Fenton-like catalysis can endow the membrane with excellent antifouling performance and extended service life, and nearly a fully recover of emulsion separation performance was achieved. Overall, this work paves pathways to the design of advanced membranes for sustainable wastewater treatment.

Molecular weight insight into critical component contributing to reverse osmosis membrane fouling in wastewater reclamation

Molecular weight (MW) of organics was one of the important factors influencing membrane fouling propensity. This study identified critical foulants of reverse osmosis (RO) membranes in reclaimed water by MW fractionation. MW > 10 kDa component was identified as the critical fouling contributor (CFC) in secondary effluent (SE), which accounted for only 13 ± 5% of dissolved organic carbon (DOC) but contributed to 86 ± 11% of flux decline. Throughout 12-month monitoring, SE and MW > 10 kDa component showed a similar fouling variation tendency: apparently higher fouling potential in winter and lower in summer, while MW < 10 kDa component presented minor fouling changes. Morphology of membrane fouled by CFC characterized a smooth and thick foulant layer on membrane surface. CFC was mainly composed of proteins and polysaccharides, and a protein-polysaccharide-protein “sandwich” fouling layer structure was preferentially formed on membrane surface. extended Derjaguin–Landau-Verwey–Overbeek (xDLVO) analysis demonstrated that strong attractive interactions between CFC and membrane surface dominated the fouling process. Furthermore, computational fluid dynamics (CFD) simulation revealed strong filtration resistance of CFC, confirming its significant fouling potential. Dual effects including attractive interactions and advantageous ridge-and-valley surface appearance accounted for the significant fouling propensity of MW > 10 kDa component and glean valuable insights into RO fouling mechanisms of reclaimed water in practical application.

Novel CNT/MXene composite membranes with superior electrocatalytic efficiency and durability for sustainable wastewater treatment

Self-assembled composite membranes are increasingly acknowledged for their potential in wastewater treatment due to their superior selectivity, high operational efficiency, and environmental sustainability. Nonetheless, challenges such as inadequate removal efficiencies for low molecular weight dyes and significant membrane fouling restrict their broader industrial application. To address these challenges, a structurally stable composite membrane of sodium lignosulfonate carbon nanotubes/alkalized MXene (SLS-CNT/alk-MXene) has been engineered. This membrane employs a polyethersulfone substrate pretreated with dopamine for uniform nanoparticle assembly through a layer-by-layer self-assembly technique. The manufacturing process includes hydrophilic modification of carbon nanotubes with lignosulfonate, followed by alkalization of MXene using sodium hydroxide. Performance evaluation of the M2 composite membrane, with a content ratio of SLS-CNT to alk-MXene of 4:2 by weight, revealed outstanding membrane properties. It achieved high selective permeability, with over 99 % retention efficiency for Methyl Blue and Congo Red, and a permeation flux of 51.6 L m-2h−1 bar−1. This membrane efficiently degraded various organic dyes within 1h, including Methyl Orange, Methylene Blue, Malachite Green, and Rhodamine B, and thanks to the integration of electrocatalysis with membrane separation, while maintaining a low membrane resistance of only 813 Ω. After environmentally sustainable testing, the membrane displayed excellent stability and 80 % recovery capacity, presenting a novel approach and design blueprint for enhancing clean water resources and environmental protection.

Membrane fouling control and contaminant removal during direct nanofiltration of surface water

Direct nanofiltration (NF) is an attractive separation process that produces high-quality drinking water without pretreatment. However, the propensity for membrane fouling is a considerable challenge. This study evaluated the potential of direct NF treatment of surface water using submerged flat-sheet (polyamide composite) NF membranes to achieve stable operation and high-quality water production. Direct NF treatment at a constant permeate flux of 5.0 L/m2h (NF270) and 2.5 L/m2h (NF90) was successfully continued for over 100 d with a monthly one-wipe sponge cleaning. Sponge cleaning eliminated the foulants on the NF270 membrane surface, thereby recovering the membrane permeability. Contrastingly, tight NF90 membranes did not exhibit significant changes in membrane permeability. The rejection of odorous compounds and other dissolved organic matter by the NF90 membrane was significant (>95 %), whereas those by the NF270 membrane considerably varied with the feed temperature. Further investigation suggested that the visible foulant on the membrane surface could be a porous cake layer mainly composed of constituents with a molecular weight of >300 Da, resulting in low hydraulic resistance. One-wipe sponge cleaning can readily detach fluffy cake layers. The results of this study suggest the viability of direct NF treatment as a low-energy advanced drinking water treatment system.

Membrane biofouling control by D-ribose in membrane bioreactor

BackgroundMembrane biofouling is still one major obstacle in the application of membrane bioreactor (MBR). Because of similar chemical structure to quorum sensing (QS) signaling molecule autoinducer-2 (AI-2), D-ribose might be an ideal QS inhibitor to inhibit membrane biofouling. Methods100 μM of D-ribose were periodically added to MBR to investigate the effect of D-ribose on membrane biofouling in MBR. Significant findingsThe fouling cycle was prolonged significantly, and the membrane was covered with larger and looser foulants with the addition of D-ribose. The soluble microbial products (SMP) content were reduced slightly and the secretions of extracellular polymeric substances (EPS) in activated sludge were effectively inhibited by the addition of D-ribose. Moreover, D-ribose could promote catalase (CAT) and superoxide dismutase (SOD) activity of activated sludge, and reduce the accumulation of malondialdehyde (MDA). Furthermore, long-term addition of D-ribose could increase the abundance of quorum-sensing quenching (QQ) bacteria, strengthen the quenching ability of the system and effectively inhibit membrane biofouling.

Ultrasonic and conversion-based inline fouling measurements for continuous emulsion copolymerisation of vinyl acetate in a tubular reactor.

One of the serious challenges for the implementation of continuous emulsion polymerisation is their significant fouling. The elucidation of time-dependent fouling processes and the development of inline analysis methods for fouling mass quantification are crucial to making progress in this area. Inline-sensor concepts based on ultrasonic measurements as well as residence time and conversion analysis were investigated regarding their suitability for the detection of time-dependent fouling formation and compared with gravimetrical results in order to validate their precision. Both a set-up using a turnover analysis for determination of losses in reaction volume by fouling and an ultrasound-based measurement system detecting deposit-caused changes by evaluating the average sound velocity could be used as suitable sensor concepts. The accuracies of both sensors are below 10% deviation to fouling references.

The pre-coated photocatalytic ceramic membrane with Bi2O3–TiO2/powdered activated carbon nanoparticles to alleviate ultrafiltration fouling caused by intracellular organic matter of Microcystis aeruginosa

Algal intracellular organic matter (IOM), released during algae's normal growth phase and water treatment processes, has long been a source of significant membrane fouling, considerably limiting the effective use of ultrafiltration(UF) technology. In this study, a Bi-doped TiO2 composite with powdered activated carbon (Bi2O3–TiO2/PAC) was loaded on ceramic UF membranes by vacuum filtration, and the prepared photocatalytic modified ceramic membranes (MCMs) were investigated for the removal of IOM and the mitigation of membrane fouling at different loading levels and under three operating conditions: Dark, Dark-UV, and UV. The results showed that the photocatalytic MCMs were able to remove the protein and humic acid fluorescent components of IOM and decompose or mineralize organic matter with molecular weights of 10–50 kDa. Under the Dark, Dark-UV, and UV conditions, the final normalized flux of MCM-2.88 was significantly increased by 22.6 %, 82.1 %, and 108.0 %, respectively. The hydrophilicity of MCMs not only transformed the interactions between IOM and the membrane into repulsive forces, but also the composite material on the membrane surface transforms the membrane fouling mechanism from intermediate blocking model to cake layer formation. Furthermore, the application of photocatalytic oxidation under the Dark-UV and UV conditions yielded a reduction in both reversible and irreversible fouling. This action led to an increased hydrophilicity and elevated free energy of adhesion with IOM during the filtration process. Moreover, the main fouling mechanism changed into complete or intermediate blocking. These outcomes collectively underscore the capability of MCMs to alleviate membrane fouling induced by IOM. This advancement holds substantial promise for the advancement and widespread implementation of photocatalytic ceramic membrane filtration techniques.

Assessment of denitrification efficiency and membrane fouling potential in a sulfur-driven membrane bioreactor treating effluent from biological treatment

In this study, any remaining nitrate not eliminated during a biological treatment process with a low C/N ratio was effectively removed using sulfur powder in an autotrophic denitrification membrane bioreactor. Moreover, particular attention was given to investigating the potential for membrane fouling in a sulfur-based denitrification reactor, with a comparative analysis to conventional activated sludge in an aerobic membrane bioreactor. At an influent nitrate concentration of 320 mg/L, the removal efficiency reached 94–98 % within a 4-hour hydraulic retention time and at a reactor temperature of 30 °C. The sulfur-based denitrification reactor exhibited soluble microbial products concentration and specific cake resistance values of 38.3 mg/L and 1.4 × 1013 m/kg, respectively, which were 5.47 and 2.26 times higher than those of conventional activated sludge. Furthermore, it was observed that the supernatant from the sulfur-based denitrification reactor resulted in more significant fouling within the membrane surface.

Photocatalytic hydrogel film assisted forward osmosis (PFO) for water treatment: Sustainable performance and contaminant control

The integration of catalytic oxidation with forward osmosis (FO) holds promising potential to address two crucial challenges encountered by FO: fouling and unsustainable performance, but suitable approaches are still rare. Herein, we have successfully developed a photocatalysis-assisted forward osmosis (PFO) system. In the PFO, a self-made porous carbon nitride doped functional carbon nanotube photocatalytic hydrogel film (PCN@CNTM) was engaged in the FO process in an inventive way by simply sticking to the commercial FO membrane surface, preventing damage to the membrane from the catalyst's direct insertion and delaying the assault from the oxidation groups. PFO allowed organic pollutants to decompose in the feed solution (90%) and on the membrane surface, regulating the water chemical potential and giving the FO membrane antifouling properties. This resulted in sustainable water flux (11.8 LMH) with no significant membrane fouling in PFO, whereas in FO alone there was a significant fouling and flux drop (from 12.73 to 7.23 LMH in 4 h). Moreover, the expensive FO membrane was protected while the hydrogel film can be replaced on demand. The PFO exemplifies the concept of synergistic technology integration, presenting a new perspective on harnessing the strengths of distinct technologies in a mutually beneficial manner.

Understanding Protein and Polysaccharide Fouling with Silicon Dioxide and Aluminum Oxide in Low-Pressure Membranes.

Humic, protein, and polysaccharide substances have been recognized as significant types of foulants in membrane systems. Despite the remarkable amount of research that has been performed on the interaction of these foulants, particularly humic and polysaccharide substances, with inorganic colloids in RO systems, little attention has been paid to the fouling and cleaning behavior of proteins with inorganic colloids in UF membranes. This research examined the fouling and cleaning behavior of bovine serum albumin (BSA) and sodium alginate (SA) with silicon dioxide (SiO2) and α-aluminum oxide (Al2O3) in individual and combined solutions during dead-end UF filtration. The results showed that the presence of SiO2 or Al2O3 in water alone did not cause significant fouling or a flux decline in the UF system. However, the combination of BSA and SA with inorganics was observed to have a synergistic effect on membrane fouling, in which the combined foulants caused higher irreversibility than individual foulants. Analysis of blocking laws demonstrated that the fouling mechanism shifted from cake filtration to complete pore blocking when the combined organics and inorganics were present in water, which resulted in higher BSA and SA fouling irreversibility. The results suggest that membrane backwash needs to be carefully designed and adjusted for better control of BSA and SA fouling with SiO2 and Al2O3.

Removal of per- and polyfluoroalkyl substances by nanofiltration: Effect of molecular structure and coexisting natural organic matter

This study investigates the removal efficiency of anionic, cationic, and zwitterionic per- and polyfluoroalkyl substances (PFAS) by nanofiltration (NF) in the presence of three representative natural organic matter (NOM) types: bovine serum albumin (BSA), humic acid (HA), and sodium alginate (SA). In particular, effects of PFAS molecular structure and coexisting NOM on the transmission and adsorption efficiency of PFAS during NF treatment were analyzed. The results indicate that NOM types dominate membrane fouling behavior despite the coexistence of PFAS. SA exhibits the most significant fouling propensity, resulting in maximum water flux decline. NF effectively removed both ether and precursor PFAS. The effects of the three typical NOM on the membrane-passing behavior of PFAS were consistent for all PFAS investigated. Generally, PFAS transmission decreased in the order of SA-fouled > pristine > HA-fouled > BSA-fouled, indicating that the presence of HA and BSA enhanced PFAS removal while SA declined. Furthermore, reduced PFAS transmission was observed with increased perfluorocarbon chain length or molecular weight (MW), regardless of the presence or type of the NOM. The impacts of NOM on PFAS filtration diminished when the PFAS van der Waals radius was > 4.0 Å, MW > 500 Da, polarization > 20 Å, or LogKow > 3. These findings suggest that both steric repulsion and hydrophobic interactions, especially the former, play important roles in PFAS rejection by NF. This study provides insights into the specific applicability and performance of membrane-based processes for eliminating PFAS during drinking and wastewater treatments, and highlighting the importance of coexisting NOM.

Progress towards Stable and High-Performance Polyelectrolyte Multilayer Nanofiltration Membranes for Future Wastewater Treatment Applications

The increasing demand for nanofiltration processes in drinking water treatment, industrial separation and wastewater treatment processes has highlighted several shortcomings of current state-of-the-art thin film composite (TFC NF) membranes, including limitations in chemical resistance, fouling resistance and selectivity. Polyelectrolyte multilayer (PEM) membranes provide a viable, industrially applicable alternative, providing significant improvements in these limitations. Laboratory experiments using artificial feedwaters have demonstrated selectivity an order of magnitude higher than polyamide NF, significantly higher fouling resistance and excellent chemical resistance (e.g., 200,000 ppmh chlorine resistance and stability over the 0-14 pH range). This review provides a brief overview of the various parameters that can be modified during the layer-by-layer procedure to determine and fine-tune the properties of the resulting NF membrane. The different parameters that can be adjusted during the layer-by-layer process are presented, which are used to optimize the properties of the resulting nanofiltration membrane. Substantial progress in PEM membrane development is presented, particularly selectivity improvements, of which the most promising route seems to be asymmetric PEM NF membranes, offering a breakthrough in active layer thickness and organic/salt selectivity: an average of 98% micropollutant rejection coupled with a NaCl rejection below 15%. Advantages for wastewater treatment are highlighted, including high selectivity, fouling resistance, chemical stability and a wide range of cleaning methods. Additionally, disadvantages of the current PEM NF membranes are also outlined; while these may impede their use in some industrial wastewater applications, they are largely not restrictive. The effect of realistic feeds (wastewaters and challenging surface waters) on PEM NF membrane performance is also presented: pilot studies conducted for up to 12 months show stable rejection values and no significant irreversible fouling. We close our review by identifying research areas where further studies are needed to facilitate the adoption of this notable technology.

Maillard reaction products between whey powder and water-soluble tempeh protein extract: membrane-based fractionation

Whey powder, an industrial by-product, has the potential to be transformed into functional ingredients using the Maillard reaction. In this study, this chemical reaction occurred between whey powder and tempeh protein extract, resulting in increased antioxidant activity. This study aimed to isolate the Maillard reaction products (MRP) with the best antioxidant capacity using an ultrafiltration (UF) membrane by considering the fouling phenomenon that occurred on the membrane surface and critical flux for the filtration. MRP exhibited an antioxidant capacity of 0.09 mg ascorbic acid equivalent antioxidant capacity/mL, and the fractionation using a 5 kDa MWCO PES membrane showed the highest antioxidant capacity in terms of free radical reduction and metal chelating mechanisms. During MRP filtration, fouling on the membrane surface was observed, which could be attributed to the cake filtration model. The critical flux value was determined to be 4.23 LMH with a corresponding pressure of 0.75 bar. A long-term filtration below the critical flux showed stable performance, but filtration above the critical flux resulted in significant fouling. The permeate antioxidant IC50 value was 4.25 mg/mL. Based on the LC-MS analysis, 1,4-dihydroxy-2-methyl-anthraquinone and ilexin II were found as the potential contributors to the antioxidant activity of MRP. In summary, our study demonstrates that fractionating MRP using UF membrane-based filtration is an effective method for isolating MRP with high antioxidant capacity. Our findings also shed light on the critical flux value and fouling phenomenon during MRP filtration, which are important considerations for scaling up the production process.

Galvanic Redox Potentiometry for Fouling‐Free and Stable Serotonin Sensing in a Living Animal Brain

AbstractSerotonin (5‐HT) is a major neurotransmitter broadly involved in many aspects of feeling and behavior. Although its electro‐activity makes it a promising candidate for electrochemical sensing, the persistent generation of fouling layers on the electrode by its oxidation products presents a hurdle for reliable sensing. Here, we present a fouling‐free 5‐HT sensor based on galvanic redox potentiometry. The sensor efficiently minimizes electrode fouling as revealed by in situ Raman spectroscopy, ensuring a less than 3 % signal change in a 2 hour continuous experiment, whereas amperometric sensors losing 90 % within 30 min. Most importantly, the sensor is highly amenable for in vivo studies, permitting real‐time 5‐HT monitoring, and supporting the mechanism associated with serotonin release in brain. Our system offers an effective way for sensing different neurochemicals having significant fouling issues, thus facilitating the molecular‐level understanding of brain function.

Galvanic Redox Potentiometry for Fouling-Free and Stable Serotonin Sensing in a Living Animal Brain.

Serotonin (5-HT) is a major neurotransmitter broadly involved in many aspects of feeling and behavior. Although its electro-active feature renders the electrochemical sensor promising, the persistent generation of fouling layers on electrode by its oxidation products presents a hurdle for reliable sensing. Here, we present a fouling-free 5-HT sensor based on galvanic redox potentiometry. The sensor efficiently minimizes electrode fouling as revealed by in situ Raman spectroscopy, ensuring a less than 3% signal change in a 2-hour continuous experiment, whereas amperometric sensors losing 90% within 30 min. Most importantly, the sensor is highly amenable for in vivo studies, permitting real-time 5-HT monitoring, and supporting the mechanism associated with serotonin release in brain. Our system offers an effective way to sensing different neurochemicals having significant fouling issues, thus facilitating the molecular-level understanding of brain function.

Flexible surfaces prepared through direct ink writing with drag reduction and antifouling

The riblet structure on the surface of the shark skin provides significant drag reduction and fouling protection. Inspired by the structure of the shark skin, we present a direct ink writing protocol by modifying the rheological properties of polydimethylsiloxane to make it printable, and a series of flexible surfaces have been created with drag reduction and antifouling. The shear stress transport k–omega model was used as a suitable turbulence model for the numerical study to compare with results of drag reduction tests. Simulations and tests proved that printed non-smooth surfaces effectively reduced water drag, where the maximum drag reduction rate reached 18.16 % at 0.06 m/s. Through the analysis of the characteristics of the flow field near the wall, the drag reduction mechanism of the riblet surface was examined. Moreover, the antifouling tests revealed that the printed surface exhibited excellent fouling resistance and inhibited the spread of dirt on the surface. Our findings may provide a new surface skinning strategy for ships, underwater vehicles and wearable devices to reduce drag and contaminant adhesion and improve navigation efficiency and longevity.