Search Results (111)

Accurate biomass quantification is important for evaluating growth kinetics and performance of microalgal and microalgal–bacterial wastewater treatment systems. However, small-scale studies frequently encounter methodological limitations due to low biomass concentrations, limited sampling volumes, and/or interference from non-biotic solids in complex wastewaters. This work adopts a two-fold approach: (i) a concise review of current biomass quantification methods for bench-scale systems, and (ii) an experimental evaluation of a gravimetric protocol for complex wastewaters. The review discusses commonly applied techniques, highlights their strengths and weaknesses, and identifies research gaps in data comparability and reproducibility. The laboratory investigations evaluated the effects of key factors, namely culture volume (250 mL to 1 L), test aliquots (2.5 mL to 10 mL), and the absolute weight of total suspended solids (3.43 g to 14.5 g) on total suspended solids measurements. Aliquots containing <5 mg total suspended solids produced statistically significant variability, whereas reliable and reproducible results were obtained when >8–10 mg absolute total suspended solids per aliquot was present. In complex wastewater matrices, approximately 18% of total suspended solids consisted of non-volatile solids, demonstrating that the method can systematically over-estimate true dry cell weight in microalgal–bacterial systems. The findings emphasized the need for procedural standardization. Finally, a practical gravimetric protocol is proposed for both axenic and consortium-based small-scale studies dealing with complex wastewater, providing an evidence-based roadmap for obtaining more reliable biomass estimations. Full article

Sol–gel phase transitions are complex far-from-equilibrium processes characterized by limited reproducibility, whose origin remains poorly understood and rarely quantified. We investigated the thermally induced sol–gel transition of agar using turbidimetry. A phenomenological model was applied to extract key kinetic parameters (maximum absorbance, maximum rate, and characteristic times) from 96 independent replicates. Variability was quantified and compared with that of an enzymatic reaction exhibiting similar sigmoidal kinetics, allowing for separation of experimental, intrinsic, and nonergodic contributions. Agar gelation displays markedly higher variability. The total variability (CV ≈ 16%) exceeds both the experimental error (1–2%) and the nonergodic contribution (≈2%), demonstrating that it predominantly arises from intrinsic process dynamics. Variability increases sharply during early stages of gelation and then evolves more gradually, indicating that stochastic nucleation and network formation pathways drive divergent kinetic trajectories despite identical initial conditions. Variability in gelation is therefore not a measurement artifact but an intrinsic hallmark of the sol–gel transition. This inherent stochasticity limits the predictive power of deterministic models, particularly at meso- and microscopic scales, and should be considered a fundamental feature of gel-forming systems. Our approach provides a quantitative framework for characterizing variability in phase transitions and may be extended to more complex biological and soft matter systems. Full article

Protein–polyelectrolyte entities (complex, coacervates, flocs, gels, etc.) are of great interest due to their potential applications in biological and medical fields. This study focuses on investigating the interactions between a model protein, human serum albumin (HSA) and a newly synthesized hybrid thermoresponsive copolymer based on chitosan polysaccharide grafted with poly(N-isopropylacrylamide) synthetic polymer chains (Chit-g-PNIPAM), in aqueous media, by mixing the individual component aqueous solutions. Depending on the mixing molar ratio and the order of addition of the two components (protein and copolymer), either stable nanostructured suspension or macrostructures’ phase separation have been observed. Dynamic light scattering (DLS) results reveal that the Chit-g-PNIPAM/HSA_x (molar ratio 5:x, where x = 1, 2, 3, 5, 10 and 15) nanostructures’ and HSA/Chit-g-PNIPAM_x (molar ratio 100:x, where x = 1, 2, 3, 10, 20, 30, 40 and 50) structures’ formation depend on the molar ratio of the two components as well as on the order of addition, with first component amount being kept constant in aqueous solution and second component solution added drop-by-drop in the solution of the first component. Additional information regarding the thermoresponsiveness and stability vs time of the formed (nano)structures were acquired using turbidimetry and DLS measurements. Full article

Listeria monocytogenes (LM) contamination constitutes a paramount global threat to food safety, necessitating the urgent development of advanced, rapid, and non-destructive detection methodologies to ensure food security. This study successfully synthesized Bi₂WO₆ nanoflowers through optimized feed ratios of raw materials and further functionalized them with noble metal Au to construct a high-performance Au-Bi₂WO₆ composite nanomaterial. The composite exhibited high sensing performance toward acetoin, including high sensitivity (R_a/R_g = 36.9@50 ppm), rapid response–recovery kinetics (13/12 s), and excellent selectivity. Through UV-Vis diffuse reflectance spectroscopy (UV-Vis DRS) and X-ray photoelectron spectroscopy (XPS) characterizations, efficient electron exchange between Au and Bi₂WO₆ was confirmed. This electron exchange increased the initial resistance of the material, effectively enhancing the response value toward the target gas. Furthermore, the chemical sensitization effect of Au significantly increased the surface-active oxygen content, promoted gas–solid interfacial reactions, and improved the adsorption capacity for target gases. Compared to conventional turbidimetry, the Au-Bi₂WO₆ nanoflower-based gas sensor demonstrates superior practical potential, offering a novel technological approach for non-destructive and rapid detection of foodborne pathogens. Full article

Tragacanth gum (GT) was mixed with whey protein concentrate (WPC80), whey protein isolate (WPI) or rice protein (RP) across pH 3.0–7.2 in order to clarify the effect of protein type and pH on controlling association and bulk behavior. Turbidimetry at 600 nm by photographic validation, oscillatory and steady-shear rheology, dynamic light scattering (DLS), FTIR spectroscopy, and AutoDock Vina docking were employed and compared. Whey systems reflected a clear, mildly acidic window: low-strain elasticity (G′) reached near pH ~5, with increased A600 and dominant sub-100 nm DLS modes, reflecting associative complexation near the isoelectric region. WPI also reflected a secondary turbidity/viscosity rise at pH 7.2, consistent with segregative aggregationafter the associative window. RP was variable, featuring broadly increased turbidity with viscosity/DLS maxima at pH 6.4, reflecting glutelin-facilitated solubility/aggregation rather than an acid optimum. FTIR changes in the amide band and GT bands (COO⁻ ~1400–1406 cm⁻¹; 1015–1040 cm⁻¹) supplemented enhanced coupling at pH 3–5. Superimposition through docking of multivalent hot-spots (Lys/Arg and H-bonding neighborhoods) corresponded to the phase-level readouts. Together, the data establish protein-dependent, pH-selective windows for GT–protein systems and uncover a mechanistic dichotomy: associative complexation in whey vs. neutral-side, solubility-regulated aggregation in RP. Full article

Thermoresponsive hydrogels that undergo reversible sol-gel transitions near physiological temperatures are highly attractive for biomedical applications, such as injectable drug delivery and embolization therapies. In this study, a library of polyurethane-based hydrogels was synthesized via step-growth polymerization using polyethylene glycol (PEG) of varying molecular weights, different diisocyanates, and a series of functional diols derived from diethanolamine with increasing hydrophobicity. The resulting polymers exhibited sol–gel transition behaviors without the need for external crosslinkers, relying solely on non-covalent interactions. The thermal responsiveness was systematically investigated using UV–Vis turbidimetry, and the cloud point temperature (T_CP) was found to be tunable within a range of 26–49 °C by modulating the monomer composition. Statistical modeling identified PEG molecular weight and diol structure as the primary determinants of T_CP, while diisocyanate type and diol-to-PEG ratio had negligible effects. Only diethanolamine (DEA)-based polymers formed stable hydrogels above a critical gelation temperature (LCGT), attributed to enhanced intermolecular interactions via free amine groups. In vitro degradation assays confirmed good hydrolytic stability under physiological conditions over four weeks, with degradation profiles strongly influenced by the PEG chain length and hydrophobic content. These findings establish a structure–property framework for the rational design of injectable, thermoresponsive polyurethane hydrogels with tailored sol–gel behavior for biomedical applications. Full article

Because of their potential “smart” applications, multifunctional stimuli-responsive polymers are gaining increasing scientific interest. The present work explores the possibility of developing such materials based on the hydrolytically stable N-3-dimethylamino propyl methacrylamide), DMAPMA. To this end, the properties in aqueous solution of the homopolymer PDMAPMA and copolymers P(DMAPMA-co-MMA_x) of DMAPMA with the hydrophobic monomer methyl methacrylate, MMA, were explored. Two copolymers were prepared with a molar content x = 20% and 35%, as determined by Proton Nuclear Magnetic Resonance (¹H NMR). Turbidimetry studies revealed that, in contrast to the homopolymer exhibiting a lower critical solution temperature (LCST) behavior only at pH 14 in the absence of salt, the LCST of the copolymers covers a wider pH range (pH > 8.5) and can be tuned within the whole temperature range studied (from room temperature up to ~70 °C) through the use of salt. The copolymers self-assemble in water above a critical aggregation Concentration (CAC), as determined by Nile Red probing, and form nanostructures with a size of ~15 nm (for P(DMAPMA-co-MMA₃₅)), as revealed by transmission electron microscopy (TEM) and dynamic light scattering (DLS). The combination of turbidimetry with ¹H NMR and automatic total organic carbon/total nitrogen (TOC/TN) results revealed the potential of the copolymers as visual CO₂ sensors. Finally, the alkylation of the copolymers with dodecyl groups lead to cationic amphiphilic materials with an order of magnitude lower CAC (as compared to the unmodified precursor), effectively stabilized in water as larger aggregates (~200 nm) over a wide temperature range, due to their increased ζ potential (+15 mV). Such alkylated products show promising biocidal properties against microorganisms such as Escherichia coli and Staphylococcus aureus. Full article

The fibrin matrix of thrombi is intertwined with neutrophil extracellular traps (NETs) containing histones that render resistance to fibrinolysis. During NET formation, histones are citrullinated. Our study addresses the question of whether citrullination modifies the fibrin-stabilizing effects of histones. We studied the structure and viscoelastic properties of fibrin formed in the presence of native or citrullinated H1 and core histones by scanning electron microscopy, clot permeation, and oscillation rheometry. The kinetics of fibrin formation and its dissolution were followed by turbidimetry and thromboelastometry. Co-polymerizing H1 with fibrin enhanced the mechanical strength of the clots, thickened the fibrin fibers, and enlarged the gel pores. In contrast, the addition of core histones resulted in a reduction in the fiber diameter, and the pores were only slightly larger, whereas the mechanical stability was not modified. Plasmin-mediated fibrinogen degradation was delayed by native and citrullinated core histones, but not by H1, and the action of des-kringle1-4-plasmin was not affected. Plasmin-mediated fibrinolysis was inhibited by native and citrullinated core histones, and this effect was moderated when the kringle domains of plasmin were blocked or deleted. These findings suggest that in NET-containing thrombi that are rich in core histones, alternative fibrinolytic enzymes lacking kringle domains are more efficient lytic agents than the classic plasmin-dependent fibrinolysis. Full article

To mimic the important features of progressing adiposity, in vitro adipose cell culture models must allow gradual intracellular fat accumulation in the three-dimensional (3D) arrangement of adipose-derived stem cells (ASCs) over a long-term culture period. Previously, elastin-like polypeptide (ELP) and polyethyleneimine (PEI) have been used to culture human adipose-derived stem cells (hASCs) as 3D spheroids and to differentiate them to adipocytes over a relatively long culture period of up to 5 weeks. In this study, to further enhance the spheroid adhesion properties, ELP was fused with Arginine–Glycine–Aspartic Acid (RGD) residues, known for their role as cell-attachment sites. This study aimed to assess whether the addition of RGD to the C-or N-terminus of ELP would impact the spheroid-forming ability of ELP-PEI coatings. ELP-RGD conjugates were produced using genetically modified Escherichia coli to express ELP-(RGD)₃ and (RGD)₃-ELP, followed by chemical conjugation with PEI. SDS gel electrophoresis, FTIR spectroscopy, and turbidimetry analyses revealed that ELP was conjugated with RGD without much alteration in the molecular weight, functional groups present, and transition temperature of ELP. The addition of RGD to ELP also did not affect the chemical conjugation capacity of ELP to PEI. We observed that the ELP-PEI coating formed slightly larger spheroids (61.8 ± 3.2 µm) compared to the ELP-(RGD)₃-PEI and (RGD)₃-ELP-PEI coatings (56.6 ± 3.0 and 53.4 ± 2.4 µm, respectively). Despite the size difference, ELP-(RGD)₃-PEI coatings exhibited superior spheroid retention during media changes, with minimal spheroid loss. DNA assay results confirmed a significant decrease in the DNA concentration (p < 0.05) after the 20 media changes for spheroids cultured on the ELP-PEI coating, indicating spheroid loss. However, there was no significant difference in DNA concentration before and after 20 media changes for spheroids cultured on the ELP-(RGD)₃-PEI and (RGD)₃-ELP-PEI coatings (p > 0.05). These findings suggest that RGD incorporation does not hinder the initial spheroid formation ability of the ELP-PEI coating and enhances spheroid retention under dynamic culture conditions. Full article

The accurate detection of Mycobacterium tuberculosis (MTB) is a pressing challenge in the precise prevention and control of tuberculosis. Currently, the efficiency and accuracy of drug resistance detection for MTB are low, and cross-contamination is common, making it inadequate for clinical needs. This study developed a rapid nucleic acid detection method for MTB based on scattering loop-mediated isothermal amplification (LAMP). Specific primers for the MTB-specific gene (Ag85B) were designed, and the LAMP reaction system was optimized using a self-developed scattering LAMP turbidimeter. Experimental results showed that the optimal reaction system included 1.5 µL of 100 mmol/L magnesium ions, 3.5 µL of 10 mmol/L dNTPs, 6 µL of 1.6 mol/L betaine, and a reaction temperature of 65 °C. The minimum detection limit was 12.40 ng/L, with the fastest detection time being approximately 10 min. The reaction exhibited good specificity, with no amplification bands for other pathogens. Twenty culture-positive samples and twenty culture-negative samples were tested in parallel; the accuracy of the positive group was 100%, the detection time was (24.9 ± 13 min), and there was no negative detection. This method features high detection efficiency, low cost, high accuracy, and effectively reduces cross-contamination, providing a new technology for the rapid clinical detection of MTB. Full article

Chronic kidney disease (CKD) continues to pose a critical global health challenge, making ongoing monitoring vital for effective management and preventing its progression to end-stage renal disease. The urinary albumin-to-creatinine ratio (uACR) stands out as a reliable biomarker. MyACR was developed and validated as a novel point-of-care (POC) device for identifying and monitoring the progress of CKD. MyACR device operates using a colorimetric-based spectroscopy to quantify albumin and creatinine levels at 625 nm and 515 nm, respectively. Calculated uACR values were compared with results from the reference turbidimetry method using a dataset of 103 random urine samples from patients at high risk of advanced CKD. The device showed excellent performance in detecting severe nephropathy, with sensitivity, specificity, and accuracy of 100%, 100%, and 100%, respectively. The PPV (positive predictive value) was 100%, indicating perfect identification of patients with severe nephropathy (uACR > 300 mg/g creatinine). The NPV (negative predictive value) was 100%, suggesting a strong ability to rule out severe nephropathy, though a small risk of false negatives remained. Bland–Altman analysis confirmed a high level of agreement, with 96.11% (for all data) and 95.87% (for uACR > 300 mg/g creatinine) of MyACR measurements falling within the 95% confidence interval (−27 to +19). Correlation analysis revealed a significant alignment between MyACR and the reference method (r² 0.9720 to 0.9836). The ROC analysis suggested that combining uACR with the estimated glomerular filtration rate (eGFR) demonstrated strong predictive performance, yielding an area under the curve (AUC) of 0.933 (95% CI: 0.86–1.0). In conclusion, the MyACR device is a robust, affordable, and user-friendly tool for detecting nephropathy, showing performance comparable to the reference method. Its portability and cost-effectiveness make it particularly suitable for use in low-resource environments. Additionally, integrating uACR with eGFR enhances prognostic capabilities, offering a comprehensive approach to assessing kidney function and predicting CKD progression. Full article

Tuning the critical solution temperature (CST) of thermoresponsive polymers is essential to exploit their immense potential in various applications. In the present study, the effect of PEG-methyl ether methacrylate with a higher molecular weight of 1100 g/mol (mPEGMA₁₁₀₀) as a comonomer was investigated for its suitability for the CST adjustment of LCST-type polymers. Accordingly, a library of mPEGMA₁₁₀₀-based copolymers was established with varying compositions (X_mPEGMA1100) using four main comonomers, namely di(ethylene glycol) ethyl ether acrylate, N-isopropyl acrylamide and methacrylamide, and mPEGMA₃₀₀, with different CST values (cloud points, T_CP, and clearing points, T_CL, by turbidimetry). It was found that less than 20 mol% of the mPEGMA₁₁₀₀ in the copolymers is practically sufficient for tuning the CST in the entire measurable temperature range, i.e., up to 100 °C, regardless of the CST of the homopolymer of the main comonomer (CST₀). Moreover, a predictive asymptotic model was developed based on the measured CST values, which strikingly revealed that the CSTs of mPEGMA₁₁₀₀-containing copolymers depend only on the two main parameters of these copolymers, X_mPEGMA1100 and the CST of the homopolymer of the main comonomer (CST₀), that is, CST = f(CST₀, X_mPEGMA1100). The revealed two-parameter relationship defines a surface in 3D plotting, and it is applicable to determine the CST of copolymers in advance for a given composition or to define the suitable composition for a required CST value. These unprecedented results on the dependence of CSTs on two major well-defined parameters enable to design a variety of novel macromolecular structures with tailored thermoresponsive properties. Full article

Background/Objectives: Rheumatoid arthritis (RA) is one of the most prevalent autoimmune diseases, characterized by an articular and extra-articular involvement, where autoantibodies, such as rheumatoid factor (RF) and anti-cyclic citrullinated peptide antibodies (ACPAs), are important biomarkers for the diagnosis. Autoantibody determination can be carried out using different assays. However, the results obtained are usually expressed in arbitrary units that are not comparable. Therefore, the aim of this study is to improve clinical interpretation of RF and ACPA test results using the likelihood ratio (LR). Methods: RF and ACPA titers were analyzed by turbidimetry and chemiluminescence using Optilite and BIO-FLASH systems, respectively, in 781 samples from patients with RA and in 1970 controls. Results: The higher the antibody titer of RF or ACPA, the higher the LR for RA. The definition of test result interval-specific LR based on predefined specificities for antibody levels provides more information than the use of the cut-off set by the manufacturer for each antibody. Conclusions: The LR for RA increased with an increasing antibody level. In addition, the use of test result interval-specific LR allows better clinical interpretation for RF and ACPA assays compared to the traditional idea of interpreting antibody results in a dichotomous manner, such as negative or positive. Full article

Cataracts are diseases characterized by the opacity of the ocular lens and the subsequent deterioration of vision. Metal ions are one of the factors that have been reported to induce crystallin aggregation. For HγS crystallin, several equivalent ratios of Cu(II) promote protein aggregation. However, reports on zinc are contradictory. To characterize the process of metal ion binding and subsequent HγS crystallin aggregation, we performed dynamic light scattering, turbidimetry, isothermal titration calorimetry, fluorescence, and nuclear magnetic resonance experiments. The data show that both metal ions have multiple binding sites and promote aggregation. Zinc interacts mainly with the N-terminal domain, inducing small conformational changes, while copper interacts with both domains and induces unfolding, exposing the tryptophan residues to the solvent. Our work provides insight into the mechanisms of metal-induced aggregation at one of the lowest doses that appreciably promote aggregation over time. Full article

In this work, three carboxymethyl starches (CMS) were obtained by the two-step reaction process of carboxymethylation with different degrees of substitution (0.16, 0.33, and 0.36). From these samples, (bio)polyelectrolyte complexes ((bio)PECs) were obtained with chitosan (Chit) by the mixing of individual solutions of polymers (0.25 wt.%) at different volume ratios. The effect of the biopolymer and ionized groups of z ratios, pH, and degree of substitution of CMS in the formation of PEC were evaluated by turbidimetry and dynamic light scattering. The results showed that increasing the amount of CMS samples (ratio of z) led to an increase in the efficiency of the formation of (bio)PEC using CMS with a high DS value. Using the turbidimetry method for the chitosan and CMS mixtures, it was observed that the formation of (bio)PEC is divided into four transition zones delimited by pH transition points, and the stoichiometric complexation (z = 1) is achieved at a pH that displayed morphological changes “pH_morph”, which is a single point for Chit:CMS 1, and for Chit:CMS 2 and Chit:CMS 3, this is a range of 4.9–6.4 and 4.3–6.4, respectively. Analysis of the structural properties of the structures of (bio)PECs by dynamic light scattering was characterized by monomodal distribution, and the main observed effect was associated with an increase in the value of D_avg with an increase in the ratio of Chit:CMS. Full article