Bacteria In Aqueous Solution Research Articles

Enhanced ultraviolet driven photocatalytic activity of CTS-SnO2-MWCNTs ternary nanohybrid for photodegradation of methylene blue and bacteria in aqueous solutions

Developing low-cost metal-based photocatalyst with great effectiveness for degradation of organic pollutants is still a serious challenge. In the present study, we suggest a novel “suitable bandgap matching and interfacial engineering” strategy through the synthesis of ternary nanohybrid to attain an effective photocatalytic reaction. The construction synthesized by embedded SnO2 NPs on carbon nanotubes (CNTs) surface homogeneously, that anchored on chitosan (CTS). The synthesized photocatalysts characterized by FT-IR, XRD, FESEM, EDX, elemental mapping, AFM, TEM, BET and UV–Vis DRS spectroscopy. In comparison with SnO2 and CTS-SnO2, the CTS-SnO2-MWCNTs led to increasing photocatalytic degradation (97.59%) and adsorption activity (84.24%) for aqueous methylene blue (MB) dye contaminant under the irradiation of UV light and in the darkness for 30 min. In addition, a feasible reaction mechanism suggested and the scavenger experiment performed in order to find the active radical species role that is responsible for the dye decoloration. The antibacterial reaction of nanostructures against Staphylococcus aureus, Bacillus subtilis and Escherichia coli strains were determined by applying disk diffusion method and showed considerable bactericidal activity against bacteria strains. So, the synthesized ternary nanohybrid could be an effective photocatalyst with antibacterial features. Moreover, the CTS-SnO2-MWCNTs photocatalyst showed great stability even after numerous runs. This research presents promising results for developing an efficient, stable, noble metal-free and UV light-driven photocatalyst.

Highly adsorptive removal of antibiotic and bacteria using lysozyme protein modified nanomaterials

In this paper, we studied adsorption of protein lysozyme on nanosilica and their applications for removal of levofloxacin (LFX) antibiotic and bacteria Escherichiacoli(E.coli) and Bacillus in water environment. Solution pH 10, contact time 120 min, nanosilica dosage 10 mg/mL and 1 mM KCl were the best conditions for lysozyme adsorption on nanosilica to form biomaterial, namely lysozyme modified nanosilica (LMNS). The optimal parameters for the removal of LFX using LMNS were determined to be 90 min of adsorption time, pH 8, and 10 mg/ml of adsorbent. Adsorptive removal of LFX dramatically increased in ideal circumstances, going from 51.51% to 80.63% when using LMNS. Two-step and Freundlich models were used to represent isothermal adsorption of LFX on LMNS at different strengths while a pseudo-second-order achieved the best fit for LFX adsorption kinetic on LMNS. The amount of LFX that adsorbs to LMNS reduced as salt concentration increased, suggesting that electrostatic interaction was primarily responsible for the adsorption. After four regenerations, LFX removal was greater than 60%, proving that LMNS is highly effective in removing LFX. The removal of E.coli and Bacillus were reached greater than 90 % that were much higher than other materials. Both electrostatic and hydrophobic interactions governed the removal of E.coli and Bacillus. Our results indicate that LMNS is an excellent bio-adsorbent for removal of antibiotic and bacteria in aqueous solution.

Phenylalanine stabilized copper nanoclusters for specific destruction of Congo red and bacteria in aqueous solution

A simple preparation method of phenylalanine stabilized copper nanoclusters (Phe-CuNCs) was reported. The Phe-CuNCs were active for specific destruction of Congo red (CR) in aqueous solution under natural light irradiation, showing fast, efficient and stable catalytic activities. The catalytic reaction followed first-order kinetics equation, and a linear relation of ln (At/A0) vs. time was observed. The Phe-CuNCs obtained more electrons to accelerate decolorization of CR in the presence of H2O2. The catalytic efficiency of Phe-CuNCs remained above 70% even after 10 cycles of reactions, showing economy and efficiency. The Phe-CuNCs showed remarkable antibacterial activity against both Escherichia coli and Staphylococcus aureus. Meanwhile, the bacterial damage was visualized by scanning electron microscopy (SEM). In addition, the Phe-CuNCs are not toxic to normal cells (HL-7702) and tumor cells (HepG2) even at high concentrations, whereas Phe-CuNCs can efficiently kill bacteria. Thus, Phe-CuNCs may be a promising nanomaterial for specific degradation of Congo red in aqueous solution as well as an adjuvant for treatment of microbial infections.

Biocomposite based on zirconium and amine-grafted walnut shell with antibacterial properties for the removal of Alizarin red in water: batch and column studies.

Recent progress has been made in the application of novel zirconium-loaded amine-grafted walnut shells as multifunctional adsorbents for the remediation of Alizarin red (AR) and bacteria in aqueous solutions. The morphology and functional groups of ACWNS@Zr were studied using Brunauer-Emmett-Teller (BET) techniques, X-ray diffraction (XRD), pH point of zero charges (pHpzc), scanning electron microscopy (SEM), and Fourier transform infrared (FTIR) spectroscopy. Adsorption and regeneration tests were carried out in batch and column mode. The ACWNS@Zr had a Langmuir maximum capacity of 415.5 ± 6.1mgg-1 at 303K. The spread plate technique was used to evaluate the adsorbent's antimicrobial properties against Staphylococcus aureus and Escherichia coli. ACWNS@Zr exhibited inhibitory potential towards S. aureus and E. coli in the suspensions by 53.3% and 15.0%, respectively. Electrostatic interaction and complexation interaction could be the key mechanisms governing AR dye removal. Equilibrium isotherms fit Langmuir models better for both batch and column studies, while adsorption kinetics to pseudo-second-order and Thomas models for batch and column studies, respectively. Thermodynamic studies indicated that the adsorption process was endothermic and spontaneous. Furthermore, columns' mass transfer capacity (B) increased as the concentration increased due to the enhanced driving force for AR adsorption onto ACWNS@Zr. Regeneration with NaOH solution of AR-loaded ACWNS@Zr was remarkable.

Ammonium continuous removal by zeolite P synthesized using fly ash combined with bacteria in aqueous solution.

The new composite product synthesized by zeolite P and bacteria consisting of nitrobacteria and denitrobacteria can efficiently and continuously remove ammonium in solution through zeolite adsorption and bacteria degradation. In this study, we used fly ash to prepared zeolite P, and then combined bacteria to synthesize the composite product. The adsorption efficiency and mechanism of products for ammonium were further studied by batch and dynamic experiments, and adsorption model. The zeolite P with a relative crystallinity of 84.7% was synthesized using fly ash by an alkali fusion-hydrothermal method. The synthetic zeolite P could combine with bacteria to be prepared an integral adsorption composite that had hierarchical pore structure including macropores, mesopores, and micropores, and its maximum compressive strength reached 106.2 N. The zeolite P could remove ammonium from solution, and Freundlich, Temkin, and Dubinin-Radushkevich models as well as thermodynamic models all showed that the ammonium adsorption by zeolite was mainly physical adsorption. Thus, the adsorbed ammonium was easy to be desorbed and became the nitrogen source for bacteria in composites. By batch experiments, the ammonium adsorption rate of composite product was significantly improved (P < 0.05) compared with zeolite P due to zeolite adsorption and the bacteria degradation. Through dynamic experiments, the composite product could efficiently and continuously remove ammonium from solution than zeolite P and bacteria alone. Therefore, the composite product could form a stable system for the adsorption, desorption, and degradation of ammonium in solution.

Inactivation of biofilm-bound bacterial cells using irradiation across UVC wavelengths

Opportunistic pathogens (OPs), such as Pseudomonas spp., Legionella spp., and mycobacteria, have been detected in biofilms in drinking water distribution systems and water storage tanks and pose potential risks to finished drinking water quality and safety. Emerging UV technologies, such as UV light emitting diodes (LEDs) and krypton chloride (KrCl*) excimers, could provide an alternative to chemical-based secondary disinfection (i.e., chlorine or chloramines) for controlling biofilm-bound OPs. UV systems offer long lifetimes, ability to select wavelength, small size with high power density, and limited-to-no disinfection by-product formation. In this study, inactivation of biofilm-bound Pseudomonas aeruginosa cells across different maturities was investigated using five UVC devices with different peak emission wavelengths, including a KrCl* excimer (222 nm), a low pressure mercury vapor lamp (254 nm), and three UV LEDs (260 nm, 270 nm, and 282 nm). The UV transmittance and absorbance through the biofilm structure was also documented for the first time using a unique approach. Our results show all UVC devices can inactivate biofilm-bound P. aeruginosa cells up to a point, among which the UV LED with peak emission at 270 nm provided the best disinfection performance. UV sensitivities of biofilm-bound cells decreased with biofilm maturity and while initial rates of inactivation were high, no more than 1.5-2.5 log reduction was possible. Re-suspended biofilm bacteria in aqueous solution were highly sensitive to UV, reaching greater than 6 log reduction. UV shielding by biofilm constituents was observed and was likely one of the reasons for UV resistance but did not fully explain the difference in UV sensitivity between biofilm-bound cells versus planktonic cells. This study improves upon fundamental knowledge and provides guidance for innovative designs using emerging UV technologies for biofilm and pathogen control in water distribution systems.

Synthesis and application of g-C3N4/Fe3O4/Ag nanocomposite for the efficient photocatalytic inactivation of Escherichia coli and Bacillus subtilis bacteria in aqueous solutions

Contamination of water with bacteria is one of the main causes of waterborne diseases. The photocatalytic method on the basis of bacterial inactivation seems to be a suitable disinfectant due to the lack of by-products formation. Herein, g-C3N4/Fe3O4/Ag nanocomposite combined with UV-light irradiation was applied for the inactivation two well-known bacteria namely, E. coli and B. subtilis. The nanocomposite was prepared by a hydrothermal method, and subsequently it was characterized by XRD, FT-IR, SEM, EDX and PL analyses. The optimum conditions established for the inactivation of both bacteria were as follows: nanocomposite dosage 3 g/L and bacterial density of 103 CFU/mL. In the meantime, the efficient inactivation of E. coli and B. subtilis took 30 and 150 min, respectively. The results also revealed that inactivation rate dropped with an increase in the bacterial density. It is also pointed out that OH˚ was found out to be the main radical species involved in the inactivation process. Finally, the kinetic results indicated that the inactivation of E. coli and B. subtilis followed the Weibull model. It is concluded that C3N4/Fe3O4/Ag nanocomposite along with UV-light irradiation is highly effective in inactivating E. coli and B. subtilis bacteria in the aqueous solutions.

Efficient chemical hydrophobization of lactic acid bacteria – One-step formation of double emulsion

A novel concept of stabilizing multiple-phase food structure such as emulsion using solely the constitutional bacteria enables an all-natural food grade formulation and thus a clean label declaration. In this paper, we propose an efficient approach to hydrophobically modifying the surface of lactic acid bacteria Lactobacillus rhamnosus (LGG) using lauroyl ahloride (LC) in non-aqueous media. Compared to the unmodified bacteria, cell hydrophobicity was dramatically altered upon modification, according to the higher percentages of microbial adhesion to hexadecane (MATH) and water contact angles (WCA) of LC-modified bacteria. No evident changes were found in bacterial surface charge before and after LC modification. By using one-step homogenization, all the modified bacteria were able to generate stabile water-in-oil-in-water (W/O/W) double emulsions where bacteria were observed on oil–water interfaces of the primary and secondary droplets. Modification using high LC concentrations (10 and 20 w/w%) led to rapid autoaggregation of bacteria in aqueous solution. A long-term lethal effect of modification primarily came from lyophilization and no apparent impact was detected on the instantaneous culturability of modified bacteria.

Simultaneous Ultrasensitive Detection and Elimination of Drug-Resistant Bacteria by Cyclometalated Iridium(III) Complexes.

Antimicrobial resistance has become a major threat to public health due to the rampant and empirical use of antibiotics. Rapid diagnosis of bacteria with the desired sensitivity and selectivity still, however, remains an open challenge. We report a special class of water-soluble metal-based aggregation-induced emission luminogens (AIEgens), namely, cyclometalated iridium(III) polypyridine complexes of the type [Ir(PQ)2(N^N)]Cl (1-3), where PQ = 2-phenylquinoline and N^N = 2,2'-bipyridine derivatives, that demonstrate dual capability for detection and elimination of drug-resistant bacteria in aqueous solutions. These AIEgens exhibit selective and rapid sensing of endotoxins, such as lipopolysaccharides (LPS) and lipoteichoic acid (LTA) released by the bacteria, with a detection limit in the lower nanomolar range. Targeting these naturally amplified biomarkers (approximately 1 million copies per cell) by iridium(III) complexes induces strong AIE in the presence of different Gram-negative and Gram-positive bacteria including carbapenem-resistant A. baumannii (CRAB) and methicillin-resistant S. aureus (MRSA) at concentrations as low as 1.2 CFU/mL within 5 min in spiked water samples. Detection of bacteria by the complexes is also visible to the naked eye at higher (108 CFU/mL) cell concentrations. More notably, complexes 1 and 2 show potent antibacterial activity against drug-resistant bacteria with low minimum inhibitory concentrations (MICs) ≤ 5 μg/mL (1-4 μM) via ROS generation and cell membrane disintegrity. To the best of our knowledge, this work is the "first-in-class" example of a metal-based theranostic system that integrates selective, sensitive, rapid, naked-eye, wash-free, and real-time detection of bacteria using broad-spectrum antibiotics into a single platform. This dual capability of AIEgens makes them ideal scaffolds for monitoring bacterial contamination in aqueous samples and pharmaceutical applications.

Enhanced removal of emerging pharmaceutical contaminant ciprofloxacin and pathogen inactivation using morphologically tuned MgO nanostructures

Abstract The existence of antibiotics like ciprofloxacin in wastewater is a severe threat to human health and it also can leads to the development of antibiotic-resistant pathogens. In the present study, two different morphologies of MgO nanostructures are prepared by using a simple microwave-assisted process to adsorb Ciprofloxacin (CIP) from aqueous solution. The physicochemical properties of the prepared MgO nanostructures are investigated by using X-ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Brunauer-Emmett-Teller (BET) surface analysis and field emission scanning electron microscopy (FESEM) with EDS. The cube and spherical shaped MgO nanostructures demonstrate good adsorption property with the maximum adsorption capacity (Qₒ) of 476 and 528 mg g−1 for CIP. The experimental data have been fitted well with the pseudo second order kinetic model and Langmuir isotherm. The prepared MgO nanostructures show potent antibacterial activity for the gram-positive and gram-negative bacteria. The increased oxidative stress and damaged cell membrane on interaction with MgO nanoparticle ultimately contribute to bacterial death. The prepared MgO nanostructures show high adsorption and antimicrobial activity, which could promise in controlling the threat to humans posed by antibiotics and the development of drug-resistant bacteria in aqueous solution.

Removal of bisphenols A and S by adsorption on activated carbon clothes enhanced by the presence of bacteria

This study investigated the adsorption of two endocrine-disrupting chemicals, bisphenol A (BPA) and S (BPS), from water using activated carbon clothes (ACCs), as-received and oxidized, in the absence and presence of bacteria, analyzing both kinetic and equilibrium adsorption data. Kinetic study of the different systems showed that the adsorption rate was affected both by the oxidation of the adsorbent and by the presence of bacteria. Bisphenol adsorption kinetics followed a second-order kinetic model, with rate constants between 0.0228 and 0.0013 g min−1 mol−1. ACC was a much better adsorbent of E. coli compared to granular activated carbons, achieving 100% adsorption at 24 h. ACC oxidation reduced the adsorption capacity and the adsorbent-adsorbate relative affinity due to the decrease in carbon surface hydrophobicity. Conversely, the presence of bacteria in aqueous solution increased the ACC surface hydrophobicity and therefore enhanced the adsorption capacity of BPA and BPS on ACC, which was 33% and 24%, respectively. In all cases, more BPS than BPA was removed due to the greater dipolar moment of the former. Results found show that activated carbon clothes in the presence of bacteria can be an adequate process to remove bisphenol A and S from different aqueous systems.

Efficient bacteria inactivation by ligand-induced continuous generation of hydroxyl radicals in Fenton-like reaction.

Fenton/Fenton-like reaction is often used as an efficient method to generate hydroxyl radicals (HO) for bacteria inactivation in aqueous solution. However, inactivation efficiency of bacteria in aqueous solution using Fenton/Fenton-like reactions needs to further improve as a result of transient generation of HO. In this paper, we found that the formation of Tris-Co(II) complexes could decrease the redox potential of Co(III)/Co(II), facilitating the transformation of Tris-Co(III) complexes into Tris-Co(II) complexes. Therefore, HO could be generated continuously in the presence of H2O2. Especially, Tris-Co(II) complexes are apt to combine with Escherichia Coli cells by electrostatic interactions, inducing a higher utilization ratio of the generated HO. Therefore, the proposed Tris-Co(II) complex-H2O2 system could be employed as a high-efficiency sterilizing reagent for inactivation of E. Coli. This work provides a promising strategy for bacterial inactivation via an economic and eco-friendly manner.

Construction of novel Z-scheme flower-like Bi2S3/SnIn4S8 heterojunctions with enhanced visible light photodegradation and bactericidal activity

Novel Z-scheme flower-like Bi2S3/SnIn4S8 heterostructures were firstly fabricated through a facile one-step solvothermal method. The Z-scheme Bi2S3/SnIn4S8 heterostructures exhibited excellent sustainable photocatalytic activity of degradation of Rhodamine B (RhB) and disinfection towards bacteria in aqueous solution under visible light irradiation (λ > 420 nm). The Bi2S3/SnIn4S8-2.5% heterostructure displayed the highest photocatalytic performance of decomposition of RhB and disinfection towards gram-negative E.coli and gram-positive S. aureus under visible light irradiation and its degradation constant was about 2 times to that of SnIn4S8, 7.5 times to that of Bi2S3, respectively. The enhanced photocatalytic performance of Bi2S3/SnIn4S8 heterojunctions primarily ascribe to the Z-scheme mechanism which not only promote the separation and migration of photoproduced hole-pairs, but also maintain a superior redox capacity. Additionally, the distinct flower-like architecture of Bi2S3/SnIn4S8 heterojunctions is the another favor factor for the higher photocatalytic activity for providing more contact interface and active sites between the target materials and catalysts and enhancing the visible light harvest. This present work creates an avenue for design and application of Z-scheme SnIn4S8-base photocatalysts in remediation of pathogenic microbes and organic pollutants contaminated water.

Evaluation of Key Antimicrobial Properties of Moringa oleifera in Relation to Its Use as a Hand-Washing Product

Moringa oleifera (M. oleifera) is a fast-growing, drought-resistant plant found throughout tropical and subtropical regions. A previous study found dry M. oleifera leaf powder to be similarly efficacious to non-medicated soap when used as a hand-wash, even without the use of water. These characteristics suggest that M. oleifera could serve as a potential hand-washing product in water and resource-limited contexts, such as humanitarian and emergency settings. The purpose of this study was to assess the efficacy of minimally processed M. oleifera sourced locally in Ghana as a hand-washing and antimicrobial product by assessing whether: (1) different preparations of M. oleifera have antibacterial properties against potential diarrheal pathogens through set-up of die-off studies; (2) M. oleifera is an effective hand-washing product by conducting an in-vivo trial with healthy volunteers; and (3) M. oleifera has antimicrobial properties in potentially reusable aqueous solutions, such as rinse water used for hand-washing. M. oleifera was found to be significantly less effective than non-medicated soap when tested as a hand-washing product and promoted the growth of bacteria in aqueous solution. Moreover, the Moringa used in the study was found to be host to pathogenic bacteria, reinforcing the idea that it is unsuitable to use as a hand-washing product. Accordingly, in its minimally processed form, M. oleifera appears to be an ineffective antimicrobial agent and its use as a hand-washing product in water-scarce and resource-limited settings is not recommended.

The antibacterial effect of G3-poly-amidoamine dendrimer on gram negative and gram positive bacteria in aqueous solutions

Dendrimers are symmetric, round and ramose macromolecules made up of monomers which have a certain structural order. The aim of this study was to evaluate the antibacterial effects of different concentrations of G3-poly-amidoamine dendrimer (G3-PAD) on 7 species of gram-negative and gram-positive bacteria in aqueous solutions. Different concentrations of G3-PAD were prepared and from each bacterial species, a suspension with a different pH was prepared according to the McFarland 0.5 standard. Bacteria were left in a 37 degrees C incubator and shaker from 0 to 60 min, and were cultivated on a Mueller-Hinton Agar plate. The bacteria that grew on each plate were counted and analyzed. The results showed that the antibacterial effect of G3-PAD in aqueous solutions was directly related to dendrimer concentration, contact time and pH. The strongest effect on Salmonella and Bacillus Subtilis was at pH = 6.5 and 7.5 and contact time 45 min, and in pH = 9, contact time 30 min; for Enterococcus faecalis in all three pH, it was 60 min; for Staphylococcus Aureus in pH = 6.5 and 7.5, 60 min and in pH = 9, 30 min; for E. coli in pH = 6.5 and 7.5, 60 min and in pH = 9, 45 min. G3-PAD showed its strongest effect on Shigella bacteria in pH = 6.5, contact time 60 min. In pH = 7.5 there was no optimum condition and in pH = 9, the optimum contact time was 60 min. The strongest effect of G3-PAD on all species was seen in 2000 ppm concentration. These results show a new strategy to improve bacteria elimination from aqueous solutions. However, safely using dendrimers for disinfecting drinking water still needs more research.

Mechanistic investigation of visible light driven novel La2CuO4/CeO2/rGO ternary hybrid nanocomposites for enhanced photocatalytic performance and antibacterial activity

Abstract A facile approach for the synthesis of La 2 CuO 4, CeO 2, La 2 CuO 4 /CeO 2 and novel La 2 CuO 4 /CeO 2 /rGO hybrid nanocomposites were demonstrated via solvothermal assisted homogeneous precipitation method. The surface morphology, phase and crystal structure of the synthesized materials were characterized by field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDX), High resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD). The photocatalytic performance to oxidize a target pollutant RB160 dye and inactivation of bacteria in aqueous solution was investigated under the illumination of visible light. Absorption range and band gap energy were investigated by UV–vis diffuse reflectance spectroscopy (UV–vis DRS). The combination of rGO with La 2 CuO 4 /CeO 2 nanocomposites leads to a better photocatalytic activity than other bare synthesized materials. Typically, 10 mg/l of RB160 could be almost completely oxidized in 150 min and 0.01 g/l of La 2 CuO 4 /CeO 2 /rGO, exhibiting a promising application of the photocatalyst in the degradation of aqueous organic pollutants. The efficiency of RB160 decomposition increased with increasing pH (5–11) and catalyst dosage (0.01–0.03 g/l), but it gets decreased with increasing initial RB160 concentration (10–30 mg/l) and from that the optimum condition for the better photocatalytic performance was identified. Furthermore, the antibacterial activity of La 2 CuO 4 /CeO 2 /rGO hybrid nanocomposite was also investigated by using two different bacteria in typical aqueous medium and the results were showed highly efficient visible light driven photocatalytic antibacterial activity. The enhanced photocatalytic and antibacterial activity of La 2 CuO 4 /CeO 2 /rGO is promising for the further application of visible light driven photocatalyst in polluted water treatment.

Positively charged nanogold label allows the observation of fine cell filopodia and flagella in solution by atmospheric scanning electron microscopy

Optical microscopy is generally the first choice to observe microbes and cells. However, its resolution is not always sufficient to reveal specific target structures, such as flagella and pili, which are only nanometers wide. ASEM is an attractive higher resolution alternative, as the sample is observed in aqueous solution at atmospheric pressure. Sample pretreatment for ASEM only comprises simple tasks including fixation, gold labeling, and reagent exchange, taking less than 1 h in total. The lengthy sample pretreatments often required for more classical electron microscopies, such as embedding and dehydration, are unnecessary, and native morphology is preserved. In this study, positively charged nanogold particles were used to label the surfaces of bacteria and cultured animal cells, exploiting their net negative surface charge. After gold enhancement to increase the size of the nanogold particles, ASEM imaging of the bacteria in aqueous solution revealed pili and delicate spiral flagella. This natural shape contrasts starkly with images of dried flagella recorded by standard SEM. Positively charged nanogold labeled the plasma membrane of cultured COS7 cells, and after enhancement allowed filopodia as thin as 100 nm in diameter to be clearly visualized. Based on these studies, ASEM combined with positively charged nanogold labeling promises to become an important tool for the study of cell morphology and dynamics in the near future.

Presence of bacteria in aqueous solution influences virus adsorption on nanoparticles

Virus contamination in wastewater is usually accompanied by the existence of various bacteria. Nanoparticles (NPs) have been shown to efficiently remove virus. In this study, bacterial cells, supernatants, and cultures were harvested separately from three strains at the culture ages of 6 and 24 h, corresponding to the log and stationary phases, respectively. The aim is to investigate how their presence affects virus adsorption on the three Fe and Al oxide NPs (α-Fe2O3, γ-Fe2O3-B, and Al2O3) and how these effects change with bacterial growth phase. Bacteriophage phiX174 was used as a virus model. Results showed that bacterial cells, supernatants, and cultures harvested at 6 h generally reduced virus adsorption by an average of 0.75±0.84, 7.7±9.0, and 10.3±8.6%, respectively, while those harvested at 24 h reduced virus adsorption by an average of 2.1±0.93, 21.5±6.6, and 24.6±6.9%, respectively. Among the NPs, α-Fe2O3 showed more sensitivity to bacteria than the other two, probably because of its relatively higher value of point of zero charge. It was found that cell-induced and supernatant-induced reductions were combined to achieve added results, in which the supernatants contributed much more than the cells, implying that the bacterial exudates might be more crucial in the reduced virus adsorption than the bacterial cells. These results strongly demonstrated that the bacteria-induced reduction in virus adsorption became more significant with culture age. It is suggested that studies conducted in the absence of bacteria may not accurately evaluate the potential of virus removal efficiency of the NPs in bacteria-containing environments.

Highly Sensitive Detection of Proteins and Bacteria in Aqueous Solution Using Surface-Enhanced Raman Scattering and Optical Fibers

We report the detection of the proteins lysozyme and cytochrome c as well as the live bacterial cells of Shewanella oneidensis MR-1 in aqueous solutions with sensitivities order(s) of magnitude higher than those previously reported. Two highly sensitive surface-enhanced Raman scattering (SERS)-based biosensors using optical fibers have been employed for such label-free macromolecule detections. The first sensor is based on a tip-coated multimode fiber (TCMMF) with a double-substrate "sandwich" structure, and a detection limit of 0.2 μg/mL is achieved in protein detections. The second sensor is based on a liquid core photonic crystal fiber (LCPCF) with a better confinement of light inside the fiber core, and a detection limit of 10(6) cells/mL is achieved for the bacteria detection. Both SERS biosensors show great potential for highly sensitive and molecule-specific detection and identification of biomolecules.

Counting bacteria on a microfluidic chip

This paper reports a lab-on-a-chip device that counts the number of bacteria flowing through a microchannel. The bacteria number counting is realized by a microfluidic differential Resistive Pulse Sensor (RPS). By using a single microfluidic channel with two detecting arm channels placed at the two ends of the sensing section, the microfluidic differential RPS can achieve a high signal-to-noise ratio. This method is applied to detect and count bacteria in aqueous solution. The detected RPS signals amplitude for Pseudomonas aeruginosa ranges from 0.05 V to 0.17 V and the signal-to-noise ratio is 5–17. The number rate of the bacteria flowing through the sensing gate per minute is a linear function of the sample concentration. Using this experimentally obtained correlation curve, the concentration of bacteria in the sample solution can be evaluated within several minutes by measuring the number rate of the bacteria flowing through the sensing gate of this microfluidic differential RPS chip. The method described in this paper is simple and automatic, and have wide applications in determining the bacteria and cell concentrations for microbiological and other biological applications.