Surface plasmon resonance for water pollutant detection and water process analysis

Electrochemical Impedance Spectroscopy-Based Microfluidic Biosensor Using Cell-Imprinted Polymers for Bacteria Detection

The rapid and sensitive detection of bacterial contaminants using low-cost and portable point-of-need (PoN) biosensors has gained significant interest in water quality monitoring. Cell-imprinted polymers (CIPs) are emerging as effective and inexpensive materials for bacterial detection as they provide specific binding sites designed to capture whole bacterial cells, especially when integrated into PoN microfluidic devices. However, improving the sensitivity and detection limits of these sensors remains challenging. In this study, we integrated CIP-functionalized stainless steel microwires (CIP-MWs) into a microfluidic device for the impedimetric detection of E. coli bacteria. The sensor featured two parallel microchannels with three-electrode configurations that allowed simultaneous control and electrochemical impedance spectroscopy (EIS) measurements. A CIP-MW and a non-imprinted polymer (NIP)-MW suspended perpendicular to the microchannels served as the working electrodes in the test and control channels, respectively. Electrochemical spectra were fitted with equivalent electrical circuits, and the charge transfer resistances of both cells were measured before and after incubation with target bacteria. The charge transfer resistance of the CIP-MWs after 30 min of incubation with bacteria was increased. By normalizing the change in charge transfer resistance and analyzing the dose-response curve for bacterial concentrations ranging from 0 to 107 CFU/mL, we determined the limits of detection and quantification as 2 × 102 CFU/mL and 1.4 × 104 CFU/mL, respectively. The sensor demonstrated a dynamic range of 102 to 107 CFU/mL, where bacterial counts were statistically distinguishable. The proposed sensor offers a sensitive, cost-effective, durable, and rapid solution for on-site identification of waterborne pathogens.

Motility behavior and physiological response mechanisms of aerobic denitrifier, Enterobacter cloacae strain HNR under high salt stress: Insights from individual cells to populations

The motility behaviors at the individual-cell level and the collective physiological responsive behaviors of aerobic denitrifier, Enterobacter cloacae strain HNR under high salt stress were investigated. The results revealed that as salinity increased, electron transport activity and adenosine triphosphate content decreased from 15.75 μg O2/g/min and 593.51 mM/L to 3.27 μg O2/g/min and 5.34 mM/L, respectively, at 40 g/L, leading to a reduction in the rotation velocity and vibration amplitude of strain HNR. High salinity stress (40 g/L) down-regulated genes involved in ABC transporters (amino acids, sugars, metal ions, and inorganic ions) and activated the biofilm-related motility regulation mechanism in strain HNR, resulting in a further decrease in flagellar motility capacity and an increase in extracellular polymeric substances secretion (4.08 mg/g cell of PS and 40.03 mg/g cell of PN at 40 g/L). These responses facilitated biofilm formation and proved effective in countering elevated salt stress in strain HNR. Moreover, the genetic diversity associated with biofilm-related motility regulation in strain HNR enhanced the adaptability and stability of the strain HNR populations to salinity stress. This study enables a deeper understanding of the response mechanism of aerobic denitrifiers to high salt stress.

The Involvement of Lactic Acid Bacteria and Their Exopolysaccharides in the Biosorption and Detoxication of Heavy Metals in the Gut

Heavy metal pollution has become one of the most important global environmental issues. The human health risk posed by heavy metals encountered through the food chain and occupational and environmental exposure is increasing, resulting in a series of serious diseases. Ingested heavy metals might disturb the function of the gut barrier and cause toxicity to organs or tissues in other sites of the body. Probiotics, including some lactic acid bacteria (LAB), can be used as an alternative strategy to detoxify heavy metals in the host body due to their safety and effectiveness. Exopolysaccharides (EPS) produced by LAB possess varied chemical structures and functional properties and take part in the adsorption of heavy metals via keeping the producing cells vigorous. The main objective of this paper was to summarize the roles of LAB and their EPS in the adsorption and detoxification of heavy metals in the gut. Accumulated evidence has demonstrated that microbial EPS play a pivotal role in heavy metal biosorption. Specifically, EPS-producing LAB have been reported to show superior absorption, tolerance, and efficient abatement of the toxicity of heavy metals in vitro and/or in vivo to non-EPS-producing species. The mechanisms underlying EPS-metal binding are mainly related to the negatively charged acidic groups and unique steric structure on the surface of EPS. However, whether the enriched heavy metals on the bacterial cell surface increase toxicity to local mammal cells or tissues in the intestine and whether they are released during excretion remain to be elucidated.

Internal exposure potential of water-soluble organic molecules in urban PM2.5 evaluated by non-covalent adductome of human serum albumin

Water-soluble organic molecules (WSOMs) in inhaled PM2.5 can readily translocate from the lungs into the blood circulation, facilitating their distribution to and health effects on distant organs and tissues in the human body. Human serum albumin (HSA), the most abundant protein carrier in the blood, readily binds exogenous substances to form non-covalent adducts and subsequently transports them throughout the circulatory system, thereby indicating their internal exposure. The direct internal exposure of WSOMs in PM2.5 needs to be understood. In this study, the non-covalent HSA-WSOM adductome was developed as a dosimeter to evaluate the internal exposure potential of WSOMs in urban PM2.5. The WSOM composition was acquired from non-target high-resolution mass spectrometry analysis coupled with multiple ionizations. The binding level of HSA-WSOM non-covalent adducts was obtained from surface plasma resonance. Machine learning combined WSOM composition and the binding level of HSA-WSOM non-covalent adducts to screen bindable (also internalizable) WSOMs. The concentration of WSOM ranged from 4 to 13 μg/m3 during our observation period. Of the 17,513 mass spectral features detected, 9,484 contributed to the non-covalent adductome and possessed the internal exposure potential. 102 major contributors accounted for 90.6 % of the HSA-WSOM binding level. The fraction of internalizable WSOMs in PM2.5 varied from 11.9 % to 61.3 %, averaging 26.2 %. WSOMs that have internal exposure potential were primarily lignin-like and lipid-like substances. The HSA-WSOMs non-covalent adductome represents direct internal exposure potential, which can provide crucial insights into the molecular diagnosis of PM2.5 exposure and precise assessments of PM2.5 health effects.

Biochar amendment combined with partial root-zone drying irrigation alleviates salinity stress and improves root morphology and water use efficiency in cotton plant

An adsorption experiment and a pot experiment were executed in order to explore the mechanisms by which biochar amendment in combination with reduced irrigation affects sodium and potassium uptake, root morphology, water use efficiency, and salinity tolerance of cotton plants. In the adsorption experiment, ten NaCl concentration gradients (0, 50, 100, 150, 200, 250, 300, 350, 400, and 500 mM) were set for testing isotherm adsorption of Na+ by biochar. It was found that the isotherms of Na+ adsorption by wheat straw biochar (WSP) and softwood biochar (SWP) were in accordance with the Langmuir isotherm model, and the Na+ adsorption ability of WSP (55.20 mg g-1) was superior to that of SWP (47.38 mg g-1). The pot experiment consisted three factors, viz., three biochar amendments (no biochar, WSP, and SWP), three irrigation strategies (deficit irrigation, partial root-zone drying irrigation - PRD, full irrigation), and two NaCl concentrations gradients (0 mM and 200 mM). The findings indicated that salinity stress lowered K+ concentration, root length, root surface area, and root volume (RV), but increased Na+ concentration, root average diameter, and root tissue density. However, biochar amendment decreased Na+ concentration, increased K+ concentration, and improved root morphology. In particular, the combination of WSP and PRD increased K+/Na+ ratio, RV, root weight density, root surface area density, water use efficiency, and partial factor productivity under salt stress, which can be a promising strategy to cope with drought and salinity stress in cotton production.

Microfluidic Sensor Based on Cell-Imprinted Polymer-Coated Microwires for Conductometric Detection of Bacteria in Water

The rapid, inexpensive, and on-site detection of bacterial contaminants using highly sensitive and specific microfluidic sensors is attracting substantial attention in water quality monitoring applications. Cell-imprinted polymers (CIPs) have emerged as robust, cost-effective, and versatile recognition materials with selective binding sites for capturing whole bacteria. However, electrochemical transduction of the binding event to a measurable signal within a microfluidic device to develop easy-to-use, compact, portable, durable, and affordable sensors remains a challenge. For this paper, we employed CIP-functionalized microwires (CIP-MWs) with an affinity towards E. coli and integrated them into a low-cost microfluidic sensor to measure the conductometric transduction of CIP-bacteria binding events. The sensor comprised two CIP-MWs suspended perpendicularly to a PDMS microchannel. The inter-wire electrical resistance of the microchannel was measured before, during, and after exposure of CIP-MWs to bacteria. A decline in the inter-wire resistance of the sensor after 30 min of incubation with bacteria was detected. Resistance change normalization and the subsequent analysis of the sensor's dose-response curve between 0 to 109 CFU/mL bacteria revealed the limits of detection and quantification of 2.1 × 105 CFU/mL and 7.3 × 105 CFU/mL, respectively. The dynamic range of the sensor was 104 to 107 CFU/mL where the bacteria counts were statistically distinguishable from each other. A linear fit in this range resulted in a sensitivity of 7.35 μS per CFU/mL. Experiments using competing Sarcina or Listeria cells showed specificity of the sensor towards the imprinted E. coli cells. The reported CIP-MW-based conductometric microfluidic sensor can provide a cost-effective, durable, portable, and real-time solution for the detection of pathogens in water.

Role of Biofilms in Waste Water Treatment

Biofilm cells have a different physiology than planktonic cells, which has been the focus of most research. Biofilms are complex biostructures that form on any surface that comes into contact with water on a regular basis. They are dynamic, structurally complex systems having characteristics of multicellular animals and multiple ecosystems. The three themes covered in this review are biofilm ecology, biofilm reactor technology and design, and biofilm modeling. Membrane-supported biofilm reactors, moving bed biofilm reactors, granular sludge, and integrated fixed-film activated sludge processes are all examples of biofilm reactors used for water treatment. Biofilm control and/or beneficial application in membrane processes are improving. Biofilm models have become critical tools for biofilm foundational research as well as biofilm reactor architecture and design. At the same time, the differences between biofilm modeling and biofilm reactor modeling methods are acknowledged.

Optical Methods for Label-Free Detection of Bacteria

Pathogenic bacteria are the leading causes of food-borne and water-borne infections, and one of the most serious public threats. Traditional bacterial detection techniques, including plate culture, polymerase chain reaction, and enzyme-linked immunosorbent assay are time-consuming, while hindering precise therapy initiation. Thus, rapid detection of bacteria is of vital clinical importance in reducing the misuse of antibiotics. Among the most recently developed methods, the label-free optical approach is one of the most promising methods that is able to address this challenge due to its rapidity, simplicity, and relatively low-cost. This paper reviews optical methods such as surface-enhanced Raman scattering spectroscopy, surface plasmon resonance, and dark-field microscopic imaging techniques for the rapid detection of pathogenic bacteria in a label-free manner. The advantages and disadvantages of these label-free technologies for bacterial detection are summarized in order to promote their application for rapid bacterial detection in source-limited environments and for drug resistance assessments.

Chitosan Micro-Membranes with Integrated Gold Nanoparticles as an LSPR-Based Sensing Platform

Currently, there is an increasing need to develop highly sensitive plasmonic sensors able to provide good biocompatibility, flexibility, and optical stability to detect low levels of analytes in biological media. In this study, gold nanoparticles (Au NPs) were dispersed into chitosan membranes by spin coating. It has been demonstrated that these membranes are particularly stable and can be successfully employed as versatile plasmonic platforms for molecular sensing. The optical response of the chitosan/Au NPs interfaces and their capability to sense the medium's refractive index (RI) changes, either in a liquid or gas media, were investigated by high-resolution localized surface plasmon resonance (HR-LSPR) spectroscopy, as a proof of concept for biosensing applications. The results revealed that the lowest polymer concentration (chitosan (0.5%)/Au-NPs membrane) presented the most suitable plasmonic response. An LSPR band redshift was observed as the RI of the surrounding media was incremented, resulting in a sensitivity value of 28 ± 1 nm/RIU. Furthermore, the plasmonic membrane showed an outstanding performance when tested in gaseous atmospheres, being capable of distinguishing inert gases with only a 10^-5 RI unit difference. The potential of chitosan/Au-NPs membranes was confirmed for application in LSPR-based sensing applications, despite the fact that further materials optimization should be performed to enhance sensitivity.

Research on Tunable SPR Sensors Based on WS2 and Graphene Hybrid Nanosheets

A prismatic excitation-based affinity biosensor consisting of the prism (BK7), WS2/graphene hybrid nanosheets, and silver (Ag) as the active metal for the surface plasmon resonance is proposed in this present research. The introduction of the transition metal WS2/graphene layer protected the silver substrate and enhanced the adsorption of biomolecules, which facilitated the quality and performance of detection. Here, we improved the detection structure by focusing on the metallic materials, graphene and WS2 film layers, and the thickness of the measured medium on the sensing effect. The results show that the silver film had a more desirable resonance effect, and the design of the symmetric detection structure produced a double resonance peak, and it provides a reference for distributed sensing. Changing the thickness of the detection medium can dynamically adjust the wave vector matching conditions, which gives the sensor a certain tunability. In the bilayer WS2 and monolayer graphene (W = 2, G = 1) configuration, the sensitivity was up to 224 deg/RIU with a quality factor of 96.97 RIU−1, which has potential for clinical analytic and biochemical detecting applications.

Smartphone-based Surface Plasmon Resonance Sensors: a Review

The surface plasmon resonance (SPR) is a phenomenon based on the combination of quantum mechanics and electromagnetism, which leads to the creation of charge oscillations on a metal-dielectric interface. The SPR phenomenon creates a signal which measures refractive index change at the metal-dielectric interface. SPR-based sensors are being developed for real-time and label-free detection of water pollutants, toxins, disease biomarkers, etc., which are highly sensitive and selective. Smartphones provide hardware and software capability which can be incorporated into SPR sensors, enabling the possibility of economical and accurate on-site portable sensing. The camera, screen, and LED flashlight of the smartphone can be employed as components of the sensor. The current article explores the recent advances in smartphone-based SPR sensors by studying their principle, components, application, and signal processing. Furthermore, the general theoretical and practical aspects of SPR sensors are discussed.

Design and Optimization of Surface Plasmon Resonance Spectroscopy for Optical Constant Characterization and Potential Sensing Application: Theoretical and Experimental Approaches

The best surface plasmon resonance (SPR) signal can be generated based on several factors that include the excitation wavelength, the type of metal used, and the thickness of the metal layer. In this study, the aforementioned factors have been investigated to obtain the best SPR signal. The excitation wavelength of 633 nm and gold metal with thickness of 50 nm were required to generate the SPR signal before the SPR was used for optical constant characterization by fitting of experimental results to the theoretical data. The employed strategy has good agreement with the theoretical value where the real part refractive index, n value, of the gold thin film was 0.1245 while the value for the imaginary part, k, was 3.6812 with 47.7 nm thickness. Besides that, the optical characterization of nanocrystalline cellulose (NCC)-based thin film has also been demonstrated. The n and k values found for this thin film were 1.4240 and 0.2520, respectively, with optimal thickness of 9.5 nm. Interestingly when the NCC-based thin film was exposed to copper ion solution with n value of 1.3333 and k value of 0.0060 to 0.0070 with various concentrations (0.01–10 ppm), a clear change of the refractive index value was observed. This result suggests that the NCC-based thin film has high potential for copper ion sensing using SPR with a sensitivity of 8.0052°/RIU.

Recent Advances in Biopolymer-Based Dye Removal Technologies

Synthetic dyes have become an integral part of many industries such as textiles, tannin and even food and pharmaceuticals. Industrial dye effluents from various dye utilizing industries are considered harmful to the environment and human health due to their intense color, toxicity and carcinogenic nature. To mitigate environmental and public health related issues, different techniques of dye remediation have been widely investigated. However, efficient and cost-effective methods of dye removal have not been fully established yet. This paper highlights and presents a review of recent literature on the utilization of the most widely available biopolymers, specifically, cellulose, chitin and chitosan-based products for dye removal. The focus has been limited to the three most widely explored technologies: adsorption, advanced oxidation processes and membrane filtration. Due to their high efficiency in dye removal coupled with environmental benignity, scalability, low cost and non-toxicity, biopolymer-based dye removal technologies have the potential to become sustainable alternatives for the remediation of industrial dye effluents as well as contaminated water bodies.

Sensitivity-Enhanced SPR Sensor Based on Graphene and Subwavelength Silver Gratings

A novel surface plasmon resonance (SPR) sensor with graphene and subwavelength gratings is proposed to improve the sensing performance. A series of numerical analyses were performed to investigate the effect of structural parameters on the sensing performance, such as minimum reflectance at resonance (MRR), full width at half maximum (FWHM), and resonance angle. The results indicated that near-zero MRR (2.9 × 10^-6) and narrow FWHM (about 3.5 deg) could be obtained by optimizing the geometrical parameters. Moreover, the influence of the number of graphene layers on sensitivity was also studied. The maximum sensitivity of the designed sensor could reach 192 deg/refractive index unit (RIU), which is a great enhancement compared to the silver-only SPR sensor. In addition, ethylene glycol solutions with different refractive indices were detected. The results showed that the sensitivity of the sensor could reach 220.67 deg/RIU, and the proposed sensor had excellent linearity between the resonance angle and refractive index, enabling extensive potential practical sensing applications.

Molecular Insights into Extracellular Polymeric Substances in Activated Sludge

Extracellular polymeric substances (EPS) are known to crucially affect the properties and performance of activated sludge, but the detailed influential mechanisms and the pertinence to specific compositional, structural properties of EPS are still elusive. Such knowledge gaps have severely limited our ability in optimizing biological wastewater treatment processes, for which long-term robust and efficient sludge performance remains one of the main bottlenecks. Here, we overview the new knowledge on the molecular structure of sludge EPS gained over the past few years and discuss the future challenges and opportunities for further advancing EPS study and engineering. The structural and functional features of several macromolecules in sludge EPS and their important structural roles in granular sludge are analyzed in detail. The EPS-pollutant interactions and environment-dependent regulation machinery on EPS production are deciphered. Lastly, the remaining knowledge gaps are identified, and the future research needs that may lead to molecular-level understanding and precise engineering of sludge EPS are highlighted.

Application of Biosensors for Detection of Pathogenic Food Bacteria: A Review

The use of biosensors is considered a novel approach for the rapid detection of foodborne pathogens in food products. Biosensors, which can convert biological, chemical, or biochemical signals into measurable electrical signals, are systems containing a biological detection material combined with a chemical or physical transducer. The objective of this review was to present the effectiveness of various forms of sensing technologies for the detection of foodborne pathogens in food products, as well as the criteria for industrial use of this technology. In this article, the principle components and requirements for an ideal biosensor, types, and their applications in the food industry are summarized. This review also focuses in detail on the application of the most widely used biosensor types in food safety.

Enhancing the sensitivity of a surface plasmon resonance-based optical sensor for zinc ion detection by the modification of a gold thin film

Surface plasmon resonance (SPR) sensors as novel optical sensors for the detection of a variety of analytes have been receiving increasing attention and their sensitivity has become the research hotspot recently. In this study, the sensitivity of an SPR optical sensor was enhanced by modifying a gold thin film with a nanocrystalline cellulose (NCC)-based material for zinc ion (Zn2+) detection that exists in the environment due to industrial processing. By replacing the gold thin film with a novel modified-gold thin film, Zn2+ can be detected from the range of 0 to 10 ppm using SPR. It is believed that the Zn2+ may interact with the negative charge molecules that exist on the modified-gold thin film, and this was confirmed via X-ray photoelectron spectroscopy (XPS). Moreover, this modified-gold-SPR has a high sensitivity of 1.892° ppm-1 up to 0.1 ppm with an enhanced detection of Zn2+ as low as 0.01 ppm. The SPR results also followed the Langmuir isotherm model with a binding affinity of 1.927 × 103 M-1, which further confirmed the sensitivity of the SPR sensor. In addition, using the modified-gold thin film, SPR has a higher affinity towards Zn2+ compared to other metal ions, i.e. Ni2+, Fe2+, Cr2+, Mn2+, and Co2+.

Recent Advances in Spectroscopy Technology for Trace Analysis of Persistent Organic Pollutants

Persistent organic pollutants (POPs) have attracted significant attention because of their bioaccumulation, persistence, and toxicity. As anthropogenic products, POPs mainly contain polychlorinated biphenyls (PCBs), organochlorine pesticides (OPs), and polycyclic aromatic hydrocarbons (PAHs), and they pose a great threat to human health and the environment. To deal with these toxic contaminants, many different kinds of strategies for sensitively detecting POPs have been developed, such as high performance liquid chromatography (HPLC), surface enhanced Raman spectroscopy (SERS), and fluorescence. This paper mainly summarized the achievements of spectroscopy technologies, which generally consist of SERS, surface plasmon resonance (SPR), and fluorescence, in the detection of low-concentration POPs in different matrices. In addition, a retrospective summary is made on several critical considerations, such as sensitivity, specificity and reproducibility of these spectroscopy technologies in practical applications. Finally, some current challenges and future outlooks for these spectroscopy technologies are provided in regards to environmental analysis.

Detecting Fingerprints of Waterborne Bacteria on a Sensor

Human fecal contamination is a crucial threat that results in difficulties in access to clean water. Enterococcus faecalis is a bacteria which is utilized as an indicator in polluted water. Nevertheless, existing strategies face several challenges, including low affinity and the need for labelling, which limit their access to large scale applications. Herein, a label-free fingerprint of the surface proteins of waterborne bacteria on a sensor was demonstrated for real-time bacteria detection from aqueous and water samples. The kinetic performance of the sensor was evaluated and shown to have a range of detection that spanned five orders of magnitude, having a low detection limit (3.4 × 104 cfu/mL) and a high correlation coefficient (R2 = 0.9957). The sensor also designated a high selectivity while other competitor bacteria were employed. The capability for multiple usage and long shelf-life are superior to other modalities. This is an impressive surface modification method that uses the target itself as a recognition element, ensuring a broad range of variability to replicate others with different structure, size and physical and chemical properties.

Oriented assembly of surface plasmon resonance biosensor through staphylococcal protein A for the chlorpyrifos detection

In this study, we report a direct surface plasmon resonance (SPR) biosensor based on an oriented assembly of antibody for the rapid detection of chlorpyrifos residue in agricultural samples. In this covalent-orientated strategy, staphylococcal protein A (SPA) was first covalently bound to the surface for monitoring chlorpyrifos residue, with subsequent binding of the antibody in an orientated fashion via its fragment crystallizable (Fc) region. Consequently, the SPA-modified biosensor exhibited a satisfactory specificity and a low detection limit of 0.056 ng mL^-1 for chlorpyrifos, with a linear detection range of 0.25-50.0 ng mL^-1. Under optimal conditions, the sensor chip could be regenerated for at least 210 cycles. The results presented here indicate that the SPA-modified sensor chip can successfully improve the sensitivity and obviating the need of the modification of the antibody. The developed SPR biosensor method has the great potential for rapid, sensitive, and specific detection with broad applications in areas of environmental monitoring and food safety. Graphical abstract.

Surface plasmon resonance (SPR) biosensors for food allergen detection in food matrices

Food allergies are recognized as a growing public health concern, with an estimated 3% of adults and 6-8% of children affected by food allergy disorders. Hence, food allergen detection, labeling, and management have become significant priorities within the food industry, and there is an urgent requirement for reliable, sensitive, and user-friendly technologies to trace food allergens in food products. In this critical review, we provide a comprehensive overview of the principles and applications of surface plasmon resonance (SPR) biosensors in the identification and quantification of food allergens (milk, egg, peanut, and seafood), including fiber-optic surface plasmon resonance (FOSPR), surface plasmon resonance imaging (SPRI), localized surface plasmon resonance (LSPR), and transmission surface plasmon resonance (TSPR). Moreover, the characteristics and fitness-for-purpose of each reviewed SPR biosensor is discussed, and the potential of newly developed SPR biosensors for multi-allergen real-time detection in a complex food system is highlighted. Such SPR biosensors are also required to facilitate the reliable, high-throughput, and real-time detection of food allergens by the food control industry and food safety control officials to easily monitor cross-contamination during food processing.

Exploration of surface plasmon resonance for sensing copper ion based on nanocrystalline cellulose-modified thin film

In this research, surface plasmon resonance (SPR) spectroscopy was used for sensing copper ion by combining the SPR with nanocrystalline cellulose modified by hexadecyltrimethylammonium bromide and graphene oxide composite (CTA-NCC/GO) thin film. The binding of Cu²⁺ on CTA-NCC/GO thin film was monitored by using SPR spectroscopy. By using the obtained SPR curve, detection range, binding affinity, sensitivity, full width at half maximum (FWHM), data accuracy (DA), and signal-to-noise ratio (SNR) have been calculated. The results showed that the sensor detection range was 0.01 until 0.5 ppm, and that it reached a saturation value. Moreover, the resonance angle shift followed the Langmuir isotherm model with a binding affinity constant of 4.075 × 10³ M^-1. A high sensitivity of 3.271° ppm^-1 also was obtained for low Cu²⁺ concentration ranged from 0.01 to 0.1 ppm. For the FWHM, the lowest value calculated was at 0.08 and 0.1 ppm, which is 3.35°. The DA of the SPR signal consecutively highest at 0.08 and 0.1 ppm. Besides that, the SNR of the SPR signal increases with the Cu²⁺ concentrations. The CTA-NCC/GO thin film morphological properties were also studied by using atomic force microscopy. The rms roughness values, which were obtained before and after in contact with Cu^2+, were 3.51 nm and 2.46 nm, respectively.

Effects of pharmaceuticals on microbial communities and activity of soil enzymes in mesocosm-scale constructed wetlands

Cyperus alternifolius based mesocosm-scale constructed wetland was employed to remove pharmaceuticals. We investigated the microbial community composition using phosphor lipid fatty acids (PFLAs) analysis and substrate enzyme activity during long-term exposure to pharmaceuticals in mesocosm-scale constructed wetlands. The results showed that there was no visible inhibition effect of pharmaceuticals on CW substrate enzymes activities in the experimental range (0-500 μg/L). Microbial communities, as revealed by PFLAs, were enhanced by the presence of plants, while the PFLAs content was highest when the pharmaceutical concentration was 10 μg/L or 30 μg/L at CWs. Except for anaerobic bacteria and Saturated fatty acids, the maximum PLFAs levels were reached when the pharmaceuticals were 10 μg/L or 30 μg/L, while Bacteria, G (-), fungal bacteria, Aerobic bacteria and Monounsaturated fatty acids were remarkably affected by high pharmaceuticals (100-500 μg/L). However, the main microbial florae were not changed among the treatments. In this study, the removal efficiencies of the studied pharmaceuticals in Planted (30) was greatest, which could be attributed to the higher microbial biomass. These results indicate that C. alternifolius can phytoremediate pharmaceutical-contaminated waters in CWs. Individual fatty acid cannot be used to represent specific species; therefore, more approaches to species identification such as rRNA-based methods must be included in future studies to better understand the metabolic mechanisms of microorganisms involved in the removal of studied pharmaceuticals and improve the performance of CWs.

Imaging the Microprocesses in Biofilm Matrices

Biofilms, which are aggregates of microorganisms and extracellular matrices, widely colonize natural water bodies, wastewater treatment systems, and body tissues, and have vital roles in water purification, biofouling, and infectious diseases. Recently, multiple imaging modalities have been developed to visualize the morphological structure and material distribution within biofilms and to probe the microprocesses in biofilm matrices, including biofilm formation, transfer and metabolism of substrates, and cell-cell communication. These technologies have improved our understanding of biofilm control and the fates of substrates in biofilms. In this review, we describe the principles of various imaging techniques and discuss the advantages and limitations of each approach to characterizing microprocesses in biofilm matrices.

Dynamic Dispersal of Surface Layer Biofilm Induced by Nanosized TiO2 Based on Surface Plasmon Resonance and Waveguide

Pollutant degradation is present mainly in the surface layer of biofilms, and the surface layer is the most vulnerable to impairment by toxic pollutants. In this work, the effects of nanosized TiO₂ (n-TiO₂) on the average thicknesses of Bacillus subtilis biofilm and on bacterial attachment on different surfaces were investigated. The binding mechanism of n-TiO₂ to the cell surface was also probed. The results revealed that n-TiO₂ caused biofilm dispersal and the thicknesses decreased by 2.0 to 2.6 μm after several hours of exposure. The attachment abilities of bacteria with extracellular polymeric substances (EPS) on hydrophilic surfaces were significantly reduced by 31% and 81% under 10 and 100 mg/liter of n-TiO₂, respectively, whereas those of bacteria without EPS were significantly reduced by 43% and 87%, respectively. The attachment abilities of bacteria with and without EPS on hydrophobic surfaces were significantly reduced by 50% and 56%, respectively, under 100 mg/liter of n-TiO₂ The results demonstrated that biofilm dispersal can be attributed to the changes in the cell surface structure and the reduction of microbial attachment ability.IMPORTANCE Nanoparticles can penetrate into the outer layer of biofilm in a relatively short period and can bind onto EPS and bacterial surfaces. The current work probed the effects of nanosized TiO₂ (n-TiO₂) on biofilm thickness, bacterial migration, and surface properties of the cell in the early stage using the surface plasmon resonance waveguide mode. The results demonstrated that n-TiO₂ decreased the adhesive ability of both cell and EPS and induced bacterial migration and biofilm detachment in several hours. The decreased adhesive ability of microbes and EPS worked against microbial aggregation, reducing the effluent quality in the biological wastewater treatment process.

Selective Heavy Element Sensing with a Simple Host-Guest Fluorescent Array

A simple three component array of host-fluorophore complexes is capable of sensitive and selective discrimination of heavy metal ions, including lanthanide and actinide salts in aqueous solution. Instead of applying optical sensors that only use "single-mode" detection, i.e., coordination of the metal to a specific ligand and monitoring the change in emission of an appended fluorophore, we exploit a series of host-fluorophore complexes that are affected by the presence of small amounts of metal ions in aqueous solution in different ways. Variable host-metal and host-guest-metal interactions lead to both turn-on and turn-off fluorescence sensing mechanisms, enhancing the discriminatory properties of the array. The limit of detection for certain metals is as low as 70 nM, and highly similar metals such as lanthanides and actinides can be easily distinguished at low micromolar concentrations in complex salt mixtures.

Thermodynamics of binding interactions between extracellular polymeric substances and heavy metals by isothermal titration microcalorimetry

Extracellular polymeric substances (EPS) play a crucial role in heavy metal bio-adsorption using activated sludge, but the interaction mechanism between heavy metals and EPS remains unclear. Isothermal titration calorimetry was employed to illuminate the mechanism in this study. The results indicate that binding between heavy metals and EPS is spontaneous and driven mainly by enthalpy change. Extracellular proteins in EPS are major participants in the binding process. Environmental conditions have significant impact on the adsorption performance. Divalent and trivalent cations severely impeded the binding of heavy metal ions to EPS. Electrostatic interaction mainly attributed to competition between divalent cations and heavy metal ions; trivalent cations directly competed with heavy metal ions for EPS binding sites. Trivalent cations were more competitive than divalent cations for heavy metal ion binding because they formed complexing bonds. This study facilitates a better understanding about the interaction between heavy metals and EPS in wastewater treatment.