Influence of macromolecules and electrolytes on heteroaggregation kinetics of polystyrene nanoplastics and goethite nanoparticles in aquatic environments

Fate and transport of nanoplastics in aquatic environments are affected by their heteroaggregation with minerals in the presence of macromolecules. This study investigated the heteroaggregation of polystyrene nanoplastics (PSNPs) with goethite nanoparticles (GNPs) under the influence of macromolecules [humic acid (HA), bovine serum albumin (BSA), and DNA] and electrolytes. Under 1 mg C/L macromolecule, raising electrolyte concentration promoted heteroaggregation via charge screening, except that calcium bridging with HA also enhanced heteroaggregation at CaCl2 concentration above 5 mM. At all NaCl concentrations and CaCl2 concentration below 5 mM, 1 mg C/L macromolecules strongly retarded heteroaggregation, ranking BSA > DNA > HA. Raising macromolecule concentration strengthened such stabilization effect of all macromolecules in NaCl solution and that of DNA and BSA in CaCl2 solution by enhancing steric hindrance. However, 0.1 mg C/L BSA slightly promoted heteroaggregation in CaCl2 solution due to stronger electrostatic attraction than steric hindrance. In CaCl2 solution, raising HA concentration strengthened its destabilization effect via calcium bridging. Macromolecules having more compact globular structure and higher molecular weight may exert greater steric hindrance to inhibit heteroaggregation more effectively. This study provides new insights on the effects of macromolecules and electrolytes on heteroaggregation between nanoplastics and iron minerals in aquatic environments.

Surface Morphology Enriching the Energy Barrier Leads to the Adsorption Characteristic of Nanobubbles

With the emergence of nanobubble research, nanobubble distribution morphology at the interface and its stability control become the bottlenecks of nanobubble resistance reduction applications. In this paper, the evolutionary behavior of nanobubbles on smooth and step HOPG surfaces was compared through molecular dynamics studies. The results show that the surface energy barrier provided by the step HOPG surface restricts diffusion of gas molecules. Then, a method of multisolvent evaporation for preparing hydrophobic nanoindent surfaces was proposed, which can achieve phase separation through different evaporation rates of multisolvents, thus realizing the preparation of surface structures with uniform distribution of nanoindents. In this paper, the nucleation processes of nanobubbles on PS nanoindent hydrophobic surface, HOPG flat hydrophobic surface, and HOPG nanostep hydrophobic surface were compared by using atomic force microscopy in liquid experiment. The evolution of the volume and distribution morphology of nanobubbles on the three nanostructures was observed by 24 h in situ tests, revealing that the energy barrier effect arising from the uneven surface structure can effectively prevent adjacent nanobubbles from merging in close proximity to each other. It is also pointed out that the hydrophobic nanoindents prepared by using the multivariate solvent evaporation method in this paper can cover most of nanobubbles for stable adsorption. It can be seen from the results that the volume drop of the nanobubbles on the HOPG flat hydrophobic surface is 27% and that on the HOPG nanostep and the PS nanoindent hydrophobic surface it is reduced to 19% and 3% under the effect of structural energy barriers, respectively. The density of the nanostructures determines whether the existence of nanobubbles is stable. The coverage of nanobubbles on the HOPG flat hydrophobic surface was 3.313% when the existence of nanobubbles was mostly stable. The HOPG nanostep and PS nanoindent sizes were positively correlated with the morphological size of the nanobubbles, which increased the coverage of the nanobubbles on the hydrophobic surface of the HOPG nanostep and PS nanoindent to 5.229% and 4.437%, respectively, when the existence of nanobubbles was mostly stable.

Global trends and characteristics of nano- and micro-bubbles research in environmental engineering over the past two decades: A scientometric analysis

The present study has two primary goals, the first goal is to investigate a bibliometric analysis and assess the trends to evaluate the global scientific production of microbubbles and nanobubbles from 2000 to 2020. The aim is to elucidate the cornucopia of benefits the two technologies (micro and nanobubbles) can offer in environmental sciences and environmental amelioration such as wastewater treatment, seed germination, separation processes, etc. The second goal is to explicate the reason behind every chart and trend through environmental engineering perspectives, which can confer value to each analysis. The data was acquired from the Web of Science and was delineated by VOS viewer software and GraphPad Prism. Considering 1034 publications in the area of micro-and nanobubbles, this study was conducted on four major aspects, including publication growth trend, countries contribution assessment, categories, journals and productivity, and keywords co-occurrence network analysis. This article revealed a notable growth in microbubbles and nanobubbles-related publications and a general growth trend in published articles in a 20-year period. China had the most significant collaboration with other countries, followed by the USA and Japan. The most dominant categories for microbubbles were environmental sciences and environmental engineering comprising 22.5% of the total publications, while multidisciplinary subjects such as nanotechnology and nanosciences (8%) were among the dominant categories for nanobubbles. Keyword's analysis results showed that microbubbles had reached the apex since their discovery. Consequently, they are being used mostly in water/wastewater treatment or environmental improvement. On the other hand, nanobubbles are still in their infancy, and their pervasive use is yet to be fully materialized. Most of the publications are still striving to understand the nature of nanobubbles and their stability; however, a critical analysis showed that during the past two years, the trend of using nanobubbles as a cost-effective and environmentally friendly approach has already begun.

Proving and interpreting the spontaneous formation of bulk nanobubbles in aqueous organic solvent solutions: effects of solvent type and content

We show that the mixing of organic solvents with pure water leads to the spontaneous formation of suspended nano-entities which exhibit long-term stability on the scale of months. A wide range of solvents representing different functional groups are studied: methanol, ethanol, propanol, acetone, DMSO and formamide. We use various physical and chemical analytical techniques to provide compounded evidence that the nano-entities observed in all these aqueous solvent solutions must be gas-filled nanobubbles as they cannot be attributed to solvent nanodroplets, impurities or contamination. The nanobubble suspensions are characterized in terms of their bubble size distribution, bubble number density and zeta potential. The bubble number density achieved is a function of the type of solvent. It increases sharply with solvent content, reaching a maximum at an intermediate solvent concentration, before falling off to zero. We show that, whilst bulk nanobubbles can exist in pure water, they cannot exist in pure organic solvents and they disappear at some organic solvent-water ratio depending on the type of solvent. The gas solubility of the solvent relative to water as well as the molecular structure of the solvent are determining factors in the formation and stability of bulk nanobubbles. These phenomena are discussed and interpreted in the light of the experimental results obtained.

Surface-Templated Nanobubbles Protect Proteins from Surface-Mediated Denaturation

In this Letter, we report that surface-bound nanobubbles reduce protein denaturation on methylated glass by irreversible protein shell formation. Single-molecule total internal reflection fluorescence (SM-TIRF) microscopy was combined with intramolecular Förster resonance energy transfer (FRET) to study the conformational dynamics of nitroreductase (NfsB) on nanobubble-laden methylated glass surfaces, using reflection brightfield microscopy to register nanobubble locations with NfsB adsorption. First, NfsB adsorbed irreversibly to nanobubbles with no apparent desorption after 5 h. Moreover, virtually all (96%) of the NfsB molecules that interacted with nanobubbles remained folded, whereas less than 50% of NfsB molecules remained folded in the absence of nanobubbles on unmodified silica or methylated glass surfaces. This trend was confirmed by ensemble-average fluorometer TIRF experiments. We hypothesize that nanobubbles reduce protein damage by passivating strongly denaturing topographical surface defects. Thus, nanobubble stabilization on surfaces may have important implications for antifouling surfaces and improving therapeutic protein storage.

Formation and Stability of Bulk Nanobubbles in Different Solutions

The existence of bulk nanobubbles is still controversial in spite of their significance in a large range of applications. Here, we developed a new method of compression-decompression to produce controllably bulk nanobubbles. Then, we further investigated the generation of bulk nanobubbles in pure water, acid, alkaline, and salt solutions using nanoparticle tracking analysis. The results indicated that the concentration of bulk nanobubbles depends on the decompression time and would reach a maximum value when the decompression time is about 30 min for the pure water system. More importantly, we gave a relatively direct evidence of the existence of bulk nanobubbles by measuring the X-ray fluorescence intensity of Kr in acid, alkaline, and salt solutions. It is shown that the decrease tendency in intensity of Kr in alkaline solution is similar to that in the concentration of bulk nanobubbles with the deposited time, indicating that the bulk nanobubbles produced indeed have gas inside. Furthermore, the concentration and stability of bulk nanobubbles in an alkaline solution are greatest compared with other two solutions regardless of gas types. The concentration of bulk nanobubbles will decrease in the order alkaline > acid/pure water > salt solutions. We believe that our results should be very helpful in understanding the formation and stability of bulk nanobubbles in different solutions.

Contact Line Pinning Is Not Required for Nanobubble Stability on Copolymer Brushes

Whereas nanobubble stability on solid surfaces is thought to be based on local surface structure, in this work, we show that nanobubble stability on polymer brushes does not appear to require contact-line pinning. Glass surfaces were functionalized with copolymer brushes containing mixtures of hydrophobic and hydrophilic segments, exhibiting water contact angles ranging from 10 to 75°. On unmodified glass, dissolution and redeposition of nanobubbles resulted in reformation in mostly the same locations, consistent with the contact line pinning hypothesis. However, on polymer brushes, the nucleation sites were random, and nanobubbles formed in new locations upon redeposition. Moreover, the presence of stable nanobubbles was correlated with global surface wettability, as opposed to local structure, when the surface exceeded a critical water contact angle of 50 or 60° for polymers containing carboxyl or sulfobetaine groups, respectively, as hydrophilic side chains. The critical contact angles were insensitive to the identity of the hydrophobic segments.

Probing nanomechanical interaction at the interface between biological membrane and potentially toxic chemical

Various xenobiotics interact with biological membranes, and precise evaluations of the molecular interactions between them are essential to foresee the toxicity and bioavailability of existing or newly synthesized molecules. In this study, surface forces apparatus (SFA) measurement and Langmuir trough based tensiometry are performed to reveal nanomechanical interaction mechanisms between potential toxicants and biological membranes for ex vivo toxicity evaluation. As a toxicant, polyhexamethylene guanidine (PHMG) was selected because PHMG containing humidifier disinfectant and Vodka caused lots of victims in both S. Korea and Russia, respectively, due to the lack of holistic toxicity evaluation of PHMG. Here, we measured strong attraction (Wad ∼4.2 mJ/m²) between PHMG and head group of biological membranes while no detectable adhesion force between the head group and control molecules was measured. Moreover, significant changes in π-A isotherm of 1,2-Dipalmitoyl-sn-glycero-3-phosphatidylcholine (DPPC) monolayers were measured upon PHMG adsorption. These results indicate PHMG strongly binds to hydrophilic group of lipid membranes and alters the structural and phase behavior of them. More importantly, complementary utilization of SFA and Langmuir trough techniques are found to be useful to predict the potential toxicity of a chemical by evaluating the molecular interaction with biological membranes, the primary protective barrier for living organisms.

Direct comparison between subnanometer hydration structures on hydrophilic and hydrophobic surfaces via three-dimensional scanning force microscopy

Hydration layers on heterogeneous substrates are characterized with subnanometer resolution using three-dimensional scanning force microscopy.

Formation and Stability of Bulk Nanobubbles Generated by Ethanol-Water Exchange

Bulk nanobubbles have unique properties and find potential applications in many important processes. However, their stability or long lifetime still needs to be understood and has attracted much attention from researchers. Bulk nanobubbles are generated based on ethanol-water exchange, a method that is generally used in the study of surface nanobubbles. Their formation and stability is further studied by using a new type of dynamic light scattering known as NanoSight. The results show that the concentration of the bulk nanobubbles produced by this method is about five times greater than that in the degassed group, which indicates the existence of bulk gas nanobubbles. The effects of ethanol/water ratios and temperature on the stability of the bulk nanobubbles have also been studied and their numbers reach a maximum at a ratio of about 1:10 (v/v).

Formation of surface nanobubbles on nanostructured substrates

The nucleation and stability of nanoscale gas bubbles located at a solid/liquid interface are attracting significant research interest. It is known that the physical and chemical properties of the solid surface are crucial for the formation and properties of the surface nanobubbles. Herein, we experimentally and numerically investigated the formation of nanobubbles on nanostructured substrates. Two kinds of nanopatterned surfaces, namely, nanotrenches and nanopores, were fabricated using an electron beam lithography technique and used as substrates for the formation of nanobubbles. Atomic force microscopy images showed that all nanobubbles were selectively located on the hydrophobic domains but not on the hydrophilic domains. The sizes and contact angles of the nanobubbles became smaller with a decrease in the size of the hydrophobic domains. The results indicated that the formation and stability of the nanobubbles could be controlled by regulating the sizes and periods of confinement of the hydrophobic nanopatterns. The experimental results were also supported by molecular dynamics simulations. The present study will be very helpful for understanding the effects of surface features on the nucleation and stability of nanobubbles/nanodroplets at a solid/liquid interface.

Interfacial gas nanobubbles or oil nanodroplets?

The force curves on nanobubbles and PDMS nanodroplets are quite different. The peculiar plateaus on nanobubbles can be used to distinguish these two easily confusing objects.

Hidden Nanobubbles in Undersaturated Liquids

Here, we propose theoretically the existence of a new type of nanobubble in undersaturated liquids. These nanobubbles have a concave vapor-liquid interface featured with a negative curvature rather than a positive curvature for nanobubbles in supersaturated liquids, so that they often hide inside of the substrate textures and it might not be easy to characterize them through atomic force microscopy (AFM) measurements. However, these hidden nanobubbles are still stabilized by the contact line pinning effect and stay at the thermodynamically metastable state. We further demonstrate that similar to the nanobubbles in supersaturated liquids the contact angle of the hidden nanobubbles is more sensitive to the nanobubble size rather than the substrate chemistry, and their curvature radius is dependent on the chemical potential but independent of the base radius. Finally, we show several potential situations for the appearance of the hidden nanobubbles.

In situ measurement of contact angles and surface tensions of interfacial nanobubbles in ethanol aqueous solutions

The astonishing long lifetime and large contact angles of interfacial nanobubbles are still in hot debate despite numerous experimental and theoretical studies. One hypothesis to reconcile the two abnormalities of interfacial nanobubbles is that they have low surface tensions. However, few studies have been reported to measure the surface tensions of nanobubbles due to the lack of effective measurements. Herein, we investigate the in situ contact angles and surface tensions of individual interfacial nanobubbles immersed in different ethanol aqueous solutions using quantitative nanomechanical atomic force microscopy (AFM). The results showed that the contact angles of nanobubbles in the studied ethanol solutions were also much larger than the corresponding macroscopic counterparts on the same substrate, and they decreased with increasing ethanol concentrations. More significantly, the surface tensions calculated were much lower than those of the gas-liquid interfaces of the solutions at the macroscopic scale but have similar tendencies with increasing ethanol concentrations. Those results are expected to be helpful in further understanding the stability of interfacial nanobubbles in complex solutions.

Progress on the Surface Nanobubble Story: What is in the bubble? Why does it exist?

Interfaces between aqueous solutions and hydrophobic solid surfaces are important in various areas of science and technology. Many researchers have found that forces between hydrophobic surfaces in aqueous solution are significantly different from the classical DLVO theory. Long-range attractive forces (non-DLVO forces) are thought to be affected by nanoscopic gaseous domains at the interfaces. This is a review of the latest research on nanobubbles at hydrophobic surfaces from experimental and simulation studies. The review focusses on non-intrusive optical view of surface nanobubbles and gas enrichment on solid surfaces by imaging and force mapping. By use of these recent experimental data in conjunction with molecular simulation work, all major theories on surface nanobubble formation and stability are critically reviewed. Even though the current body of research cannot comprehensively explain all properties of surface nanobubbles observed, the fundamental understanding has been significantly improved. Line tension has been shown to be incapable of explaining the contact angle of nanobubbles. Dense gas layer theory provides a new explanation on both large contact angle and long-time stability. The high density of gas in these domains may significantly affect the gas-water interface which is in line with some observation made on bulk nanobubbles. Along this line of inquiry, experimental and simulation effort should be focussed on measuring the density within surface nanobubbles and the properties of the gas water interface which may be the key to explaining the stability of these nanobubbles.

Perspectives on surface nanobubbles

Materials of nanoscale size exhibit properties that macroscopic materials often do not have. The same holds for bubbles on the nanoscale: nanoscale gaseous domains on a solid-liquid interface have surprising properties. These include the shape, the long life time, and even superstability. Such so-called surface nanobubbles may have wide applications. This prospective article covers the basic properties of surface nanobubbles and gives several examples of potential nanobubble applications in nanomaterials and nanodevices. For example, nanobubbles can be used as templates or nanostructures in surface functionalization. The nanobubbles produced in situ in a microfluidic system can even induce an autonomous motion of the nanoparticles on which they form. Their formation also has implications for the fluid transport in narrow channels in which they form.

Spatial organization of surface nanobubbles and its implications in their formation process

We study the size and spatial distribution of surface nanobubbles formed by the solvent exchange method to gain insight into the mechanism of their formation. The analysis of Atomic Force Microscopy (AFM) images of nanobubbles formed on a hydrophobic surface reveals that the nanobubbles are not randomly located, which we attribute to the role of the history of nucleation during the formation. Moreover, the size of each nanobubble is found to be strongly correlated with the area of the bubble-depleted zone around it. The precise correlation suggests that the nanobubbles grow by diffusion of the gas from the bulk rather than by diffusion of the gas adsorbed on the surface. Lastly, the size distribution of the nanobubbles is found to be well described by a log-normal distribution.

Probing the weak interaction of proteins with neutral and zwitterionic antifouling polymers

Protein-polymer interactions are of great interest in a wide range of scientific and technological applications. Neutral poly(ethylene glycol) (PEG) and zwitterionic poly(sulfobetaine methacrylate) (pSBMA) are two well-known nonfouling materials that exhibit strong surface resistance to proteins. However, it still remains unclear or unexplored how PEG and pSBMA interact with proteins in solution. In this work, we examine the interactions between two model proteins (bovine serum albumin and lysozyme) and two typical antifouling polymers of PEG and pSBMA in aqueous solution using fluorescence spectroscopy, atomic force microscopy and nuclear magnetic resonance. The effect of protein:polymer mass ratios on the interactions is also examined. Collective data clearly demonstrate the existence of weak hydrophobic interactions between PEG and proteins, while there are no detectable interactions between pSBMA and proteins. The elimination of protein interaction with pSBMA could be due to an enhanced surface hydration of zwitterionic groups in pSBMA. New evidence is given to demonstrate the interactions between PEG and proteins, which are often neglected in the literature because the PEG-protein interactions are weak and reversible, as well as the structural change caused by hydrophobic interaction. This work provides a better fundamental understanding of the intrinsic structure-activity relationship of polymers underlying polymer-protein interactions, which are important for designing new biomaterials for biosensor, medical diagnostics and drug delivery applications.

A deliberation on nanobubbles at surfaces and in bulk

Surface and bulk nanobubbles are two types of nanoscopic gaseous domain that have recently been discovered in interfacial physics. Both are expected to be unstable to dissolution because of the high internal pressure driving diffusion and the surface tension which squeezes the gas out, but there is a rapidly growing body of experimental evidence that demonstrates both bubble types to be stable. However, the two types of bubbles also differ in many respects: surface nanobubble stability is most probably assisted by the nearby wall, which can repel the water (in the case of hydrophobicity), accept physisorbed gas molecules, and reduce the surface area through which outfluxing can occur; bulk nanobubbles, on the other hand, must stabilise themselves. This is perhaps through ionic shielding, perhaps through diffusive shielding, or perhaps through both. Herein, the features of both bubble types are described individually, their common and disparate features are discussed, and emerging applications are examined.

Bovine serum albumin film as a template for controlled nanopancake and nanobubble formation: in situ atomic force microscopy and nanolithography study

Air nanobubbles and nanopancakes were investigated in situ by both tapping mode atomic force microscopy (TM AFM) and atomic force nanolithography techniques employing bovine serum albumin (BSA) film supported by highly oriented pyrolytic graphite (HOPG). The BSA denaturation induced by the water-to-ethanol exchange served for conservation of nanobubble and nanopancake sites appearing as imprints in BSA film left by gaseous cavities formerly present on the interface in the aqueous environment. Once the BSA film was gently removed by the nanoshaving technique applied in ethanol, a clean basal plane HOPG area with well-defined dimensions was regenerated. The subsequent reverse ethanol-to-water exchange led to the re-formation of nanopancakes specifically at the nanoshaved area. Our approach paves the way for the study of gaseous nanostructures with defined dimensions, formed at solid-liquid interface under controlled conditions.

In situ imaging of multiphase bio-interfaces at the micro-/nanoscale

The multiphase bio-interfacial system constituted by biological surfaces and their surrounding environment is usually considered to be an essential clue for exploring the mysterious relationship between surface architecture and function. As a visualizing method to understand these systems, in situ imaging of multiphase interfaces (e.g., air/liquid/solid and oil/water/solid systems) at the micro-/nanoscale, still remains a huge challenge, as a result of their heterogeneity and complexity. Here, recent progress on real-space micro-/nanoscale imaging of multiphase bio-interfacial systems is reviewed; this includes several techniques and imaging results on bio-interfaces, such as the lotus leaf, fish scale, living cell's surface, and fresh tissue surface. The results evidently show that interfacial structures have a significant impact on the state of the microscopic multiphase interface, further influencing specific functions. Based on this research, technical innovations, some more complicated multiphase interface systems, and structure-function coupling mechanism are proposed.

Removal of nanoparticles from plain and patterned surfaces using nanobubbles

It is the aim of this paper to quantitatively characterize the capability of surface nanobubbles for surface cleaning, i.e., removal of nanodimensioned polystyrene particles from the surface. We adopt two types of substrates: plain and nanopatterned (trench/ridge) silicon wafer. The method used to generate nanobubbles on the surfaces is the so-called alcohol-water exchange process (use water to flush a surface that is already covered by alcohol). It is revealed that nanobubbles are generated on both surfaces, and have a remarkably high coverage on the nanopatterns. In particular, we show that nanoparticles are-in the event of nanobubble occurrence-removed efficiently from both surfaces. The result is compared with other bubble-free wet cleaning techniques, i.e., water rinsing, alcohol rinsing, and water-alcohol exchange process (use alcohol to flush a water-covered surface, generating no nanobubbles) which all cause no or very limited removal of nanoparticles. Scanning electron microscopy (SEM) and helium ion microscopy (HIM) are employed for surface inspection. Nanobubble formation and the following nanoparticle removal are monitored with atomic force microscopy (AFM) operated in liquid, allowing for visualization of the two events.

Principle and applications of microbubble and nanobubble technology for water treatment

In recent years, microbubble and nanobubble technologies have drawn great attention due to their wide applications in many fields of science and technology, such as water treatment, biomedical engineering, and nanomaterials. In this paper, we discuss the physics, methods of generation of microbubbles (MBs) and nanobubbles (NBs), while production of free radicals from MBs and NBs are reviewed with the focuses on degradation of toxic compounds, water disinfection, and cleaning/defouling of solid surfaces including membrane. Due to their ability to produce free radicals, it can be expected that the future prospects of MBs and NBs will be immense and yet more to be explored.

Nanobubbles and micropancakes: gaseous domains on immersed substrates

Surface nanobubbles and micropancakes are two recent discoveries in interfacial physics. They are nanoscopic gaseous domains that form at the solid/liquid interface. The fundamental interest focuses on the fact that they are surprisingly stable to dissolution, lasting for at least 10-11 orders of magnitude longer than the classical expectation. So far, many articles have been published that describe various different nucleation methods and 'ideal' systems and experimental techniques for nanobubble research, and we are now at the stage where we can begin to investigate the fundamental questions in detail. In this topical review, we summarize the current state of research in the field and give an overview of the partial answers that have been proposed or that can be inferred to date. We relate nanobubbles and micropancakes, and we try to build a framework within which nucleation may be understood. We also discuss evidence for and against different aspects of nanobubble stability, as well as suggesting what still needs to be done to obtain a full understanding.

Improved cleaning of hydrophilic protein-coated surfaces using the combination of Nanobubbles and SDS

The use of nanobubbles, the common surfactant sodium dodecyl sulfate (SDS), and nanobubbles in combination with SDS as cleaning agents to remove lysozyme from the solid-liquid interface has been investigated using a quartz crystal microbalance on both hydrophobic and hydrophilic surfaces. On the hydrophobic surface, significant amounts of protein remained on the surface after 10 cycles of nanobubble treatment for 10 s periods in phosphate buffer. The cleaning efficiency of SDS was far superior and was shown to remove approximately 90% of the protein. The use of nanobubbles in combination with SDS failed to improve the cleaning efficiency further. On the other hand, lysozyme on the hydrophilic surface cannot be removed effectively by either 10 cycles of cleaning with nanobubbles or 10 cycles of cleaning with SDS. Nevertheless, the protein can be removed completely after 6 cycles of cleaning with nanobubbles in combination with SDS.

Defouling and cleaning using nanobubbles on stainless steel

The present work demonstrates that nanobubbles can be used as cleaning agents on stainless steel (SS) surfaces. Cleaning efficiency has been quantified. Using an Atomic Force Microscope (AFM), it was demonstrated that nanobubbles can be produced by electrochemical treatment on a SS surface either with or without adsorbed bovine serum albumin (BSA). After allowing adsorption on SS overnight, radio-labeled BSA was removed by electrochemically generated nanobubbles, and then the remaining BSA on the surface was quantified by radioactivity measurement. The results indicate that nanobubbles can remove >10% of the protein in each 3-min electrochemical treatment while in a control group, washing with water and electrolyte resulted in no more than 3% of the protein being removed each time. Cleaning of conducting surfaces by nanobubbles is promising in any system where fouling occurs in biomedia.

Cleaning using nanobubbles: defouling by electrochemical generation of bubbles

Here we demonstrate that nanobubbles can be used as cleaning agents both for the prevention of surface fouling and for defouling surfaces. In particular nanobubbles can be used to remove proteins that are already adsorbed to a surface, as well as for the prevention of nonspecific adsorption of proteins. Nanobubbles were produced on highly oriented pyrolytic graphite (HOPG) surfaces electrochemically and observed by atomic force microscopy (AFM). Nanobubbles produced by electrochemical treatment for 20 s before exposure to bovine serum albumin (BSA) were found to decrease protein coverage by 26-34%. Further, pre-adsorbed protein on a HOPG surface was also removed by formation of electrochemically produced nanobubbles. In AFM images, the coverage of BSA was found to decrease from 100% to 82% after 50 s of electrochemical treatment. The defouling effect of nanobubbles was also investigated using radioactively labeled BSA. The amount of BSA remaining on a stainless steel surface decreased by approximately 20% following 3 min of electrochemical treatment and further cycles of treatment effectively removed more BSA from the surface. In situ observations indicate that the air-water interface of the nanobubble is responsible for the defouling action of nanobubbles.