Effect Of pH Research Articles

Polyethylenimine functionalized graphene oxide and cellulose nanofibril composite hydrogels: Synthesis, characterization and water pollutants adsorption

A stable 2,2,6,6-tetramethylpiperidine-1-yl)oxyl (TEMPO)-oxidized cellulose nanofibril (TCNF)/graphene oxide (GO)/polyethylenimine (PEI) composite hydrogel was synthesized by self-assembly instead of chemical crosslinking. Their chemical, morphology, surface, and mechanical properties were characterized and adsorption behavior for methyl blue (–) was systematically investigated in terms of the optimal GO content, pH effect, kinetics, and isotherm models. Additionally, to assess the adsorption capability of the TCNF/GO/PEI hydrogel for various contaminants, its effectiveness was also tested for methylene blue (+), Cu (II), and soybean oils. The maximum adsorption capability for the methyl blue (−) dyes increased from 3125 to 3962 mg/g when 13.3 % of GO was added. The adsorption capability for Cu (II) and soybean oils rose from 205.3 to 218.5 and 2.1 to 7.2 mg/g, respectively. The adsorption capability of optimized TCNF/GO/PEI hydrogel for a variety of contaminants was improved overall based on the increase of surface area, electrostatic interactions, and hydrophobic domains. Moreover, adding GO did not impact the adsorption mechanism but increased the external diffusion rate in the intraparticle diffusion model. This work provides a self-assembling route to TCNF/GO/PEI hydrogels with great potential for the removal of multiple water pollutants.

Cystine crystal nucleation and decay in the context of cystinuria pathogenesis and treatment.

Cystinuria is a rare disease which results in the precipitation of cystine in the renal filtrate, which may cause acute kidney injury due to mechanical trauma. In this work, we attempt to explore the origin of supersaturated cystine in this context to understand disease pathogenesis. This has enabled us to reproduce the clinical habit of cystine following a comprehensive study of cystine nucleation and growth in saline, artificial and human urine. Then, we describe the physical behaviour of these crystals in the presence of: cysteamine, sodium bicarbonate, captopril, tiopronin, penicillamine, glutathione and α-lipoic acid. Surprisingly, we observe that, in vitro, only cysteamine and saturated sodium bicarbonate dissolve crystals at a faster rate than saline, and that when solution pH is adjusted to physiological conditions, crystal dissolution for all agents is reduced to the rate of saline alone. We highlight that the conventional hypothesis of mixed disulphide formation in cysteamine is not the fastest mechanism of cystine dissolution, but rather that cystine dissolution (in the order of hours) is dominated by pH effects. This, combined with cysteamine's ability to take part in disulfide exchange reactions may explain cysteamine's effectiveness in this condition. Overall, our findings not only contribute to an understanding of cystinuria pathogenesis but also offer insights into how we should evaluate emerging treatments.

Preparation of chitosan/cellulose nanofibril composite aerogel and its adsorption performance for Cu(II)-MO binary pollutant

Heavy metals and organic dyes commonly coexist in water, which pose a serious threat to human health. Herein, a functional aerogel for adsorption of Cu(II)-methyl orange binary-polluted system was prepared. Cellulose nanofibril (CNF) was prepared by 2,2,6,6-tetramethylpiperidinyloxy (TEMPO)-NaBr-NaClO system using abandoned pineapple leaves as the main raw material, and chitosan/cellulose nanofibril (CS/CNF) composite aerogel was constructed by sol-gel method combined with freeze-drying. The structure of composite aerogel was characterized by XRD, FTIR, TG and SEM. The fabricated aerogels were ultra-lightweight and exhibited a highly porous 3D network structure. The effects of adsorbent dosage, ionic strength, solution pH, adsorbent concentration, adsorption time, and temperature on the adsorption of Cu(II) and methyl orange (MO) by composite aerogel were studied. The adsorption of composite aerogel towards mono-polluted of Cu(II) and MO reached equilibrium after 100 min with a maximum adsorption capacity of 116.69 and 295.86 mg/g, respectively. The adsorption of Cu(II) and MO by CS/CNF aerogel was mainly achieved through electrostatic attraction, metal chelation and hydrogen bonding interactions. More importantly, the adsorption of Cu(II) by CS/CNF aerogel has an inhibitory effect on its adsorption of MO in Cu(II)-MO binary-polluted system.

Optimization of Copper-Ammonia-Sulfate Electrolyte for Maximizing Cu(I):Cu(II) Ratio Using pH and Copper Solubility

An investigation has been carried out to understand the solution chemistry of the Cu-NH−-SO4−2 system, focusing on the effect of pH on the solubility of copper in the solution and maximizing the Cu(I):Cu(II) ratio. A Pourbaix diagram for the Cu-N-S system has also been created using the HSC Chemistry software for a wide range of Cu-NH3 species, unlike most other studies that focused only on Cu(NH3)42+ and Cu(NH3)52+ (Cu(II)) as the dominant species. The Pourbaix diagram demonstrated that the Cu(I) exists as Cu(NH3)2+, while the Cu(II) species are present in the system as Cu(NH3)42+ and Cu(NH3)52+, depending upon the Eh and pH of the solution. Copper precipitation was observed in the electrolyte at pH values less than 8.0, and the precipitation behavior increased as the pH became acidic. The highest Cu(I):Cu(II) ratio was observed at higher pH values of 10.05 due to the higher solubility of copper at higher alkaline pH. The maximum Cu(II) concentration can be achieved at 4.0 M NH4OH and 0.76 M (NH4)2SO4. In the case of low pH, the highest Cu(I):Cu(II) ratio obtained was 0.91 against the 4.0 M and 0.25 M concentrations of NH4OH and (NH4)2SO4, respectively. Meanwhile, at high pH, the maximum Cu(I):Cu(II) ratio was 15.11 against the 0.25 M (NH4)2SO4 and 4.0 M NH4OH. Furthermore, the low pH experiments showed the equilibrium constant (K) K < 1, and the high pH experiments demonstrated K > 1, which justified the lower and higher copper concentrations in the solution, respectively.

Segment-Based Peptide Design Reveals the Importance of N-Terminal High Cationicity for Antimicrobial Activity Against Gram-Negative Pathogens.

Host defense antimicrobial peptides (AMPs) are recognized candidates to develop a new generation of peptide antibiotics. While high hydrophobicity can be deployed in peptides for eliminating Gram-positive bacteria, high cationicity is usually observed in AMPs against Gram-negative pathogen. This study investigates how the sequence distribution of basic amino acids affects peptide activity. For this purpose, we utilized human cathelicidin LL-37 as a template and designed four highly selective ultrashort peptides with similar length, net charge, and hydrophobic content. LL-10 + , RK-9 + , KR-8 + , and RIK-10 + showed similar activity against methicillin-resistant Staphylococcus aureus in vitro and comparable antibiofilm efficacy in a murine wound model. However, these peptides showed clear activity differences against Gram-negative pathogens with RIK-10 + (i.e., LL-37mini2) being the strongest and LL-10 + the weakest. To understand this activity difference, we characterized peptide toxicity; the effects of salts, pH, and serum on peptide activity; and the mechanism of action and determined the membrane-bound helical structure for RIK-10 + by two-dimensional NMR spectroscopy. By writing an R program, we generated charge density plots for these peptides and uncovered the importance of the N-terminal high-density basic charges for antimicrobial potency. To validate this finding, we reversed the sequences of two peptides. Interestingly, sequence reversal weakened the activity of RIK-10 + but increased the activity of LL-10 + especially against Escherichia coli, Pseudomonas aeruginosa, and Acinetobacter baumannii. Those more active peptides with high cationicity at the N-terminus are also more hydrophobic based on HPLC retention times. A database search found numerous natural sequences that arrange basic amino acids primarily at the N-terminus. Combined, this study not only obtained novel peptide leads but also discovered one useful strategy for designing novel antimicrobials to control drug-resistant Gram-negative pathogens.

Water vapor responsiveness of chitosan: An experimental and simulation analysis.

Stimuli-responsive polymers have gained significant research interest in recent years owing to their potential applications in diverse areas. Here, we present a study on the actuation characteristics of chitosan-based free-standing films that exhibit full reversibility and repeatability in response to water vapor exposure. The effect of pH of the water and the degree of cross-linking of the chitosan films on the actuation performance is studied. In the case of free-standing polymer film-based actuators, the primary driving force behind actuation is understood to be the differential strain induced by the gradient in volume changes across the thickness of the film. To understand it further, we conducted full atomistic molecular dynamics simulation studies to explore water absorption and adsorption into the chitosan matrix. Our simulations revealed an accumulation of water molecules in the surface layer that rapidly desorb when shielded from water vapor. Furthermore, estimates of the energy gain resulting from the adsorption of water on the surface suggest that it is adequate to drive the shape change of the actuator when subjected to asymmetric exposure to water vapor. This finding supports the fact that the adsorbed layer of water on the surface of the chitosan film plays a role in actuation.

A Detailed Reaction Mechanism for Thiosulfate Oxidation by Ozone in Aqueous Environments.

The ozone oxidation, or ozonation, of thiosulfate is an important reaction for wastewater processing, where it is used for remediation of mining effluents, and for studying aerosol chemistry, where its fast reaction rate makes it an excellent model reaction. Although thiosulfate ozonation has been studied since the 1950s, challenges remain in developing a realistic reaction mechanism that can satisfactorily account for all observed products with a sequence of elementary reaction steps. Here, we present novel measurements using trapped microdroplets to study the pH-dependent thiosulfate ozonation kinetics. We detect known products and intermediates, including SO32-, SO42-, S3O62-, and S4O62-, establishing agreement with the literature. However, we identify S2O42- as a new reaction intermediate and find that the currently accepted mechanism does not directly explain observed pH effects. Thus, we develop a new mechanism, which incorporates S2O42- as an intermediate and uses elementary steps to explain the pH dependence of thiosulfate ozonation. The proposed mechanism is tested using a kinetic model benchmarked to the experiments presented here, then compared to literature data. We demonstrate good agreement between the proposed thiosulfate ozonation mechanism and experiments, suggesting that the insights in this paper can be leveraged in wastewater treatment and in understanding potential climate impacts.

Harnessing Moringa oleifera root powder (MORP) for the sustainable remediation of heavy metal contaminated water.

Heavy metal environmental pollution is rapidly increasing due to the increase in industrialization and urbanization. Industrial processes, such as paint production, mining, and raw materials producing industries release effluents rich in heavy metals, like Pb2+, Cd2+, Cu2+, and Cr3+. These heavy metals are dangerous because they persist in nature, are non-biodegradable and they have high tendency to accumulate in the environment and in living organisms who are exposed to them. This work studied the removal of heavy metals (Cu, Pb, Cr, and Cd) from aqueous solution using Moringa oleifera root powder (MORP) as the adsorbent. The MORP was characterized by SEM, FTIR, BET, and XRD. Batch adsorption experiments carried out investigated the effects of adsorbate concentration, adsorbent dosage, agitation time, pH and temperature on adsorption. The optimum parameters are: contact time (90 min); pH (9); adsorbent dose (0.6); metal ion concentration (30 mg L-1) for Cr and 40 mg L-1 for the rest; and temperature (50 °C) for Cu and Pb, and 70 °C for Cr and Cd. These experimental data were analyzed with 5 isotherm models (Temkin, Flory-Huggins, Langmuir, D-R and Freundlich). The result obtained fitted best to Temkin isotherm in comparison to others. Kinetic studies revealed that the pseudo-second order kinetic model best described the adsorption (with high R2 values ranging from 0.9810-0.9976) compared to pseudo-first order and intra-particle diffusion kinetics model. Results of the thermodynamic study showed that the sorption process was endothermic for Cu and Pb, but exothermic for Cd and Cr. The adsorbent showed good adsorptive tendencies toward the ions studied, and could be applied on an industrial scale for the remediation of metal contaminated water.

The Combined Effects of Temperature and pH to the Toxicity of the Water-Soluble Fraction of Gasoline (WSFG) to the Neotropical Yellow-Tail Tetra, Astyanax altiparanae.

Continental aquatic environments have undergone chemical pollution due to increased anthropogenic activities. Among those substances, petroleum hydrocarbons are a potential hazard for the aquatic animals. Additionally, alterations in the abiotic characteristics of the water, such as temperature and pH, can impose additional stress when those substances are present. We evaluate how alterations in water temperature and pH modified the acute (96h) toxicity of the water-soluble fraction of gasoline (WSFG) to Astyanax altiparanae through physiological analysis. We also investigated the physiological responses after the fish recovery from exposure (96h) in clean water. Both isolated and combined exposures to WSFG resulted in significant physiological changes. Alone, WSFG altered energetic metabolism and haematopoietic functions, potentially due to metabolic hypoxia. When combined with changes in water temperature (30°C) and pH (4.0), A. altiparanae activated additional physiological mechanisms to counterbalance osmoregulatory and acid-base imbalances, likely exacerbated by severe metabolic hypoxia. In both isolated and combined exposure scenarios, A. altiparanae maintained cellular hydration, suggesting a robust capacity to uphold homeostasis under environmental stress conditions. Following a recovery in clean water, energetic metabolism returned to control levels. Nevertheless, plasmatic Na+ and Cl- levels and haematological parameters remained affected by WSFG exposure. Our findings underscore the impact of interactions between WSFG contaminants, temperature and pH, leading to additional biological damage in A. altiparanae.

Optimization, characterization and biosafety of carotenoids produced from whey using Micrococcus luteus

This study aimed to optimize the production of carotenoid pigments from Micrococcus luteus (ATCC 9341) through the statistical screening of media components and the characterization of antimicrobial, antioxidant, cytogenetic and cytotoxic activities. A BOX-Behnken design was used to assess the effects of whey concentration, inoculum size, pH, temperature, and agitation speed on carotenoid yield. The optimum combination increased production to 2.19 g/L, with a productivity of 0.045 g L-1 h−1 and a productivity yield of 0.644 g/g, as confirmed by an observed carotene production of 2.19 g/L. The final response surface model fitting the data had an R2 of 0.9461. High-performance liquid chromatography (HPLC) analysis identified 12 carotenoid pigment compounds produced by M. luteus. The extracts displayed moderate antimicrobial efficacy against Gram-positive bacteria such as Bacillus cereus (ATCC 11778), Staphylococcus aureus (ATCC 6538), and E. faecalis (ATCC 19433), with inhibition zone diameters (IZD) of 29.0, 14.0, and 37.0 mm, respectively, at 1000 μg/mL. However, its effectiveness against Gram-negative bacteria is limited. In comparison, tetracycline exhibited greater antimicrobial potency. The IC50 value of carotenoids was used to indicate the antioxidant activity. IC50 value from the DPPH assay was 152.80 mg/100mL. An IC50 cytotoxicity value greater than 300 μg/mL was found against normal mouse liver cells, with over 68% cell viability even at 300 μg/mL, indicating low toxicity. Histological structure studies revealed normal myocardial muscle tissue, lung tissue, and kidney tissue sections, whereas liver tissue sections revealed ballooning degeneration of hepatocytes and disorganization of hepatic cords. Cytogenetic parameters revealed that the carotene treatment group had a mitotic index (70%) lower than that of the control but higher than that of the positive control, mitomycin, and did not substantially increase numerical (1.2%) or structural aberrations compared with those of the control, suggesting a lack of genotoxic effects under the experimental conditions. In conclusion, optimized culture conditions enhanced carotenoid yields from M. luteus, and the extracts displayed promising bioactivity as moderate antibiotics against certain gram-positive bacteria and as antioxidants. The high IC50 values demonstrate biosafety. Overall, this bioprocess for enhanced carotenoid production coupled with bioactivity profiling and low cytotoxicity support the application of M. luteus carotenoids.

Study on Preparation and Properties of Pickering Emulsions Prepared by Carboxymethyl Starch‐Xanthan Gum Nanoparticles

AbstractIn this work, carboxymethyl starch‐xanthan gum nanoparticles (CXN) with different ratios are prepared by ethanol precipitation method. The effects of different ratios, NaCl content, and pH on the particle size and zeta potential of the nanoparticles are investigated, as well as the rheological properties and stability of the CXN emulsions. The results show that with the increase of xanthan gum (XG), the particle size, and zeta potential of the nanoparticles decrease and the prepared emulsions have higher shear stress and viscosity, as well as greater thermal and storage stability. Changes in pH and NaCl concentration significantly affect the particle size and zeta potential values of the nanoparticles. Excess acids or bases increase the viscosity of the emulsions. At low salt concentrations (0.05 M), the emulsion viscosity increases significantly, after which the emulsion viscosity decreases with increasing salt concentration. Neutral pH conditions at room temperature are not conducive to the stability of the emulsions. At high temperatures (100 °C), high salt concentrations, excessive acids or bases can destabilize emulsions. This study provides a new way to reduce the particle size of nanoparticles and a feasible strategy for developing long‐term stable Pickering emulsion.

Effect of pH on the surface charges of permanently/variably charged soils and clay minerals.

Traditionally, the surface charge number (SCN) of permanently charged soils/clay minerals is believed to be unaffected by environmental pH. However, recent studies have revealed the occurrence of polarization-induced covalent bonding between H+ and the surface O atoms of permanently charged clay minerals. This discovery challenges the traditional notions of "permanently charged soil" and "permanently charged clay mineral". The purpose of this study is to confirm that there are no true "permanently charged clay" or "permanently charged soil". In this study, the SCNs of two permanently charged clay minerals, two variably charged clay minerals, five permanently charged soils (temperate soils), and four variably charged soils (tropical or subtropical soils) were measured at different pH values using the universal determination method of SCN. The results showed that: (1) The SCNs of the permanently/variably charged soils and clay minerals decreased significantly with decreasing pH; (2) the SCN of montmorillonite decreased less with decreasing pH than the SCNs of variably charged minerals, whereas the SCN of illite decreased to nearly the same extent, indicating strong polarization-induced covalent bonding between H+ and the surface O atoms of illite; (3) the SCNs of permanently charged soils decreased to a similar extent as those of variably charged soils with decreasing pH. This study demonstrated that the concepts, "permanently charged clay mineral" or "permanently charged soil", are questionable because of the polarization-induced covalent bonding between H+ and the surface O atoms of clay minerals.

Effect of pH of Synthetic Solution on the Performance of the Fluid Loss Control Additive Used in Oil Well Cement

Effect of pH of Synthetic Solution on the Performance of the Fluid Loss Control Additive Used in Oil Well Cement

Corrosion behavior of Laves precipitates in FeCrAl-1Nb alloy at 290 °C and 7 MPa: The size effect and critical role of pH

The corrosion behavior of Laves precipitates in FeCrAl-1Nb alloy was investigated in four different deoxygenated solutions at 290 °C and 7 MPa. The Laves precipitates exhibit potential size effect during corrosion in a weak alkaline solution: the microscale precipitates undergo oxidation with amorphization and element dissolution, and these phenomena are not observed in nanoscale precipitates. The corrosion of nanoscale precipitates is less insensitive to slight changes in pH; however, micro-galvanic corrosion was observed between some nanoscale precipitates and the ferrite phase. Deuterium isotope labeling experiments observed hydrogen enrichment in some oxidized precipitates.

Effect of pH, acid catalyst, and aging time on pore characteristics of dried silica xerogel

ABSTRACT This study investigates the impact of pH and ageing time on silica xerogel pore characteristics prepared via the sol-gel method. Using tetraethyl orthosilicate (TEOS) and HCl as a precursor and acid catalyst, respectively, tailored pore size distributions in the meso- and macroporous range were achieved. Field emission scanning electron microscopy (FESEM) revealed interconnected porous structures, with pore size increasing linearly with ageing time. pH variation yielded average pore sizes ranging from ~ 31 nm (mesoporous) to ~ 59 nm (macroporous). Higher acid catalyst concentration accelerated gelation, resulting in smaller pores. Elemental analysis confirmed silicon and oxygen as primary constituents, while X-ray diffraction (XRD) confirmed amorphous nature. Sol-gel synthesis provides versatile control over microstructure and properties, enabling customisation for applications such as liquid filters, batteries, sensors, and bio-scaffolds. It offers a cost-effective, direct synthesis of high-purity multi-component materials, emphasising its potential for functional material development.

Effect of Nutrient Solution pH on the Growth and Quality of Lactuca sativa Grown in a Static Hydroponic System

Lettuce is an easy-to-grow and nutrient-rich leafy vegetable. It grows well using a static hydroponic system, which saves space and is easy to maintain. However, understanding pH’s impact on lettuce growth in static hydroponic systems is limited. Hence, this study was conducted to determine the effect of pH nutrient solution on the growth performance and eating quality of lettuce grown in a static hydroponic system. Lettuce was grown in pH 5.2, 6.2, and 7.2 nutrient solutions. Its growth performance was collected weekly, including plant height, root length, number of leaves, leaf area, leaf chlorophyll content, total dry weight, and total moisture content. The harvested lettuce was analyzed for firmness, soluble solids concentration, titratable acidity, pH, and ascorbic acid content by the fourth week after transplanting. The plant height, root length, number of leaves, leaf area, and total dry weight of lettuce were affected by the interaction between nutrient solution pH and weeks after transplanting. By the third week after transplanting, lettuce grown in pH 6.2 was 11.12 and 18.67% taller than those grown in pH 7.2 and 5.2 nutrient solutions, respectively. By the fourth week after transplanting, the firmness of lettuce grown in pH 6.2 was significantly higher than those grown in pH 5.2 and 7.2 nutrient solutions by 2.34 and 7.32%, respectively. It is concluded that lettuce should be grown in a pH 6.2 nutrient solution when using a static hydroponic system.

Eliminating the effect of pH: Dual-matrix modulation adsorbent enables efficient lithium extraction from concentrated seawater

Lithium ion sieve adsorbents frequently extract liquid lithium resources due to their adsorption effect and cost advantages. However, the adsorption effect is significantly influenced by the ambient pH. The pH effects on the adsorption process can be categorized into two main areas: the competition adsorption of impurity ions and the difference in surface zeta potential. A dual-matrix modulation adsorbent was prepared, comprising a carrier matrix modified with zwitterionic quaternary ammonium bases and an adsorption matrix modified with carboxylation. The zwitterionic quaternary ammonium base groups were employed to mitigate the competitive adsorption of impurity ions by acid-base neutralization. Furthermore, the negative charge of carboxyl groups was employed to diminish the discrepancy in surface zeta potential. The adsorption effect of the ion sieve adsorbent under natural conditions appeared to be significantly enhanced by the dual-matrix modulation, with the saturated adsorption capacity (28 mg/g) and adsorption selectivity (α(Li+/Mg2+)=24.23) being 6.3 and 7.8 times higher than that of the manganese-based adsorbent (HMO) under the same conditions, respectively. Moreover, the adsorption effect was found to be consistent with HMO under alkaline conditions. The results demonstrate that by optimizing the adsorption conditions of the adsorbent, the detrimental impact of pH on the adsorption process of lithium ion sieves can be eliminated.

Visible Light-Triggered Catalytic Performance of Reduced Graphene Oxide Decorated With Copper Oxide Nanocomposite for Degradation of Rhodamine B Dye and Kinetics Studies.

Herein, novel nanocomposites based on reduced graphene oxide decorated copper oxide nanoparticles (rGO/CuO) were prepared by the in situ co-precipitation method. The structural, morphological, and optical characterization of as-prepared nanocomposites was performed by powdered x-ray diffraction (p-XRD), scanning electron microscopy (SEM), and Fourier-transform infrared (FTIR), Raman, and ultraviolet-visible (UV-Vis) spectroscopy, respectively. The as-prepared nanocomposites exhibited better photocatalytic activity of rhodamine B dye with maximum ~94% degradation in 120 min with a rate constant of 0.2353 min-1 under optimized conditions. Furthermore, the effects of solution pH and catalyst loading are studied on the degradation process. Therefore, this state-of-the-art strategy for the decoration of CuO nanoparticles onto the surface of rGO nanosheets could be an ideal platform for fabricating highly efficient photocatalysts.

Light increases resistance of thylakoid membranes to thermal inactivation.

In the region of slightly acidic pH (рН 5.7), the manganese cluster in oxygen-evolving complex of photosystem II (PSII) is more resistant to exogenous reductants. The effect of such pH on the heat inactivation efficiency of the electron transport chain (O2 evolution and 2,6-dichlorophenolindophenol reduction) in PSII membranes and thylakoid membranes was investigated. Under thylakoid membranes illumination accompanied by lumen acidification, their resistance to heat inactivation increases. In the presence of protonophores, the rate of heat inactivation increases, which seems to be associated not with the protonophore mechanism, but with structural and/or functional changes in membranes. In PSII membrane preparations, the efficiency of the oxygen evolution inhibition at pH 5.7 is also lower than at pH 6.5. The role of reactive oxygen species in thermal inactivation of photosynthetic membranes was investigated using a lipophilic cyclic hydroxylamine ESR spin probe.

B-064 Bovine Serum Albumin Coats Silicon Dioxide More Uniformly Near its Isoelectric Point Based on Atomic Force Microscopy Analysis

Abstract Background Bovine serum albumin (BSA) serves as a blocking agent in in-vitro diagnostic (IVD) applications, with fatty acid stabilized (FAS) and fatty acid free (FAF) BSA as common options. The presence of fatty acids and pH influence the conformation of BSA. While previous studies have explored the individual effects of fatty acids or pH on BSA blocking, limited data exists on their combined impact. This study employs atomic force microscopy (AFM) to investigate how pH and fatty acids jointly affect BSA adsorption onto silica, a surface relevant within diagnostics. Methods AFM, a sensitive microscopic technique, provides topographic images of surfaces with superior resolution compared to optical microscopy. We conducted experiments to assess the adsorption of 1% FAS and FAF BSA on a silica surface at pH 5.2 and pH 7. Evaluation of the coatings involved scratching to assess overall thickness, and roughness, indicating thickness variability. Results Results revealed that both fatty acids and pH play significant roles in shaping the BSA coating characteristics on silica surfaces. In three out of four experimental conditions, the average thickness of the BSA coating ranged between 3-4 nm, except for FAS BSA at pH 7, which exhibited a thicker average coating measuring 5.6 nm. The pH impacted the roughness of the BSA coating. Coatings prepared at pH 5.2 displayed smoother surfaces compared to those at pH 7. Utilizing the root mean square average height variability analysis, there is 95% confidence that the FAF and FAS BSA surfaces at pH 5.2 had a height range between 2.4-4.3 nm and 2.0-4.9 nm, respectively, indicating complete coverage of the silica surface without much height variation. In contrast, the FAF and FAS BSA coatings at pH 7 exhibited a wider range of heights, with 95% confidence intervals spanning from -1.5-8.6 nm and 0.0-11.2 nm, respectively. This variability suggests potential issues including incomplete BSA coverage at the lower range, and steric hindrance at the higher end, highlighting the importance of pH in optimizing BSA coatings for various applications. Conclusions Silica is commonly used in IVD assays, with BSA frequently employed to coat and passivate the surface. Our AFM experiments highlight the impact of pH and fatty acid presence on coating thickness and uniformity. Notably, FAS BSA at pH 7 exhibited the thickest coating; however, its increased roughness may pose challenges in IVD applications due to steric hindrance blocking antibody-antigen interactions. Alternatively, FAF BSA at pH 7 displayed an adequate thickness but also considerable roughness, suggesting potential insufficiencies in surface coverage and passivation. FAS and FAF BSA coatings at pH 5.2 showed relatively consistent thickness, indicating a more uniform surface which may be ideal for IVD coating applications. These AFM experiments were conducted on pure silica surfaces, which may differ from surfaces engineered for IVD. Additionally, both FAF and FAS BSA grades are proven to be effective in IVD applications. Further research employing AFM and other biophysical techniques is warranted to deepen our understanding of pH and fatty acid effects on BSA-surface interactions, aiming to enhance blocking strategies in IVD.