Detecting Gold Biomineralization by Delftia acidovorans Biofilms on a Quartz Crystal Microbalance

Magnetically Modulated Differential Quartz Crystal Microbalances for Rapid, Ultrasensitive, and Direct Probing of Prostate-Specific Antigens Conjugated with Magnetic Beads

The occurrence and development of diseases are closely related to overexpression of specific biomarkers in the serum of patients. Rapid and sensitive biomarker detection is beneficial for early diagnosis and treatment. However, the current laboratory processes and assays for biomarker detection are expensive and time-consuming, and their operation also requires a large number of professionals. We developed a magnetically modulated differential quartz crystal microbalance (MMD-QCM) method combined with magnetic bead (MB) labels for rapid and highly sensitive quantitative detection of prostate-specific antigen (PSA). Because MBs exhibit magnetized rotation motion under an applied AC magnetic field, a pair of QCMs are utilized to measure the difference between the magnetic motion intensities of the MBs and the MB-PSA immune complex to determine the PSA concentration. Experimental results demonstrate that the proposed method can be adopted to determine the PSA concentration in a wide range of 0.01-1000 ng/mL as well as exhibit a low detection limit of 0.065 ng/mL. In addition, the proposed scheme enables fast detection and low sample consumption. The single detection process takes less than 4 h and requires only 113 μL of sample solution. The proposed detection strategy is superior to the existing detection method and can be effectively used in early screening and prognostic diagnosis of cancer and other related diseases owing to its simplicity, low cost, and high speed.

Biological approaches for E-waste management: A green-go to boost circular economy

E-waste is a pressing situation on human due to its complex composition. Although E-waste on one hand has some toxic components but at the same time, it would be a promising business sector. Recycling of E-waste to mine-out valuable metals and other components has opened a chance of business and hence a way towards transformation of linear economy to circular one. Chemical, physical and traditional technologies are holding the position in E-waste recycling sector but sustainability with respect to cost and environmental issues is a major concern associated with these technologies. In order to overcome these gaps, lucrative, environment friendly and sustainable technologies need to be implied. Biological approaches could be a green and clean approach to handle E-waste through sustainable and cost-effective means by considering socio-economic and environmental aspects. This review elaborates biological approaches for E-waste management and advancements in expanse. The novelty covers the environmental and socio-economic impacts of E-waste, solution and further scope of biological approaches, further research and development need in this contour to come up with sustainable recycling process.

Protein-Directed Au(0)-Rich Gold Nanoclusters as Ratiometric Luminescence Sensors for Auric Ions via Comproportionation-Induced Emission Enhancement

Gold nanoclusters (Au NCs) are widely used as fluorescent probes in biomedical sensing and imaging due to their versatile optical properties and low cytotoxicity. Surface engineering of gold nanoclusters (Au NCs) aims to design a surface with versatile physicochemical performances, but previous investigations have primarily focused on the acquisition of the "brightest" species. This has resulted in other types of Au NC being neglected. In the present study, our group prepared a series of Au NCs that were rich in surface Au(0), using the "aged" form of bovine serum albumin (BSA) via controlling the pH during synthesis. We found that slight increases of alkalinity during synthesis over that which produced Au NCs with the most intensive photoluminescence generated the "darkest" Au NCs, which exhibited the strongest absorption. These Au NCs included more Au atoms and had a higher Au(0) content. Furthermore, the addition of Au³⁺ quenched the emission of the "brightest" Au NCs, but increased that of the "darkest" Au NCs. The increased Au(I) proportion observed in the Au³⁺-treated "darkest" Au NCs resulted in a novel comproportionation-induced emission enhancement effect, which we utilized to construct a "turn-on" ratiometric sensor for toxic Au³⁺. The addition of Au³⁺ generated simultaneous, opposite effects on blue-emissive diTyr BSA residues and red-emissive Au NCs. After optimization, we successfully constructed ratiometric sensors for Au³⁺ with high sensitivity, selectivity, and accuracy. This study will inspire a new pathway to redesign the protein-framed Au NCs and analytical methodology via comproportionation chemistry.

Preparation and self-assembly of ionic (PNIPAM-co-VIM) microgels and their adsorption property for phosphate ions

Using N-isopropyl acrylamide (NIPAM) as the main monomer, 1-vinyl imidazole (VIM) containing tertiary amine groups as the functional comonomer, and 1,5-dibromo pentane as the crosslinking agent, ionic P(NIPAM-co-VIM) microgels were prepared by a two-step method. The crosslinking agent was reacted with tertiary amino groups by the quaternary amination. The results of zeta potential and particle size analysis showed that P(NIPAM-co-VIM) microgels were positively charged and had a particle size of about 400 nm, and the microgels with 11 wt% VIM still showed temperature sensitivity with a volume phase transition temperature of approximately 37.5 °C. The effects of VIM content, ambient temperature, and pH on the adsorption properties of the microgels for phosphate anions were explored. The self-assembly of the positively charged P(NIPAM-co-VIM) microgels with polyelectrolytes and the adsorption behavior of the layers for phosphate anions were studied using a quartz crystal microbalance (QCM). It was found that at a phosphate concentration of 0.3 mg mL^-1, VIM mass fraction of 11%, pH of 5, and temperature of 20 °C, the largest adsorption capacity of P(NIPAM-co-VIM) microgel on phosphate ions could reach 346.3 mg g^-1. The frequency responses of the microgel-modified QCM sensor could reach 3.0, 18.8, and 25.9 Hz when exposed to 10^-8, 10^-7, and 10^-6 M phosphate solutions. Therefore, the ionic (PNIPAM-co-VIM) microgels could be promising for fabricating anion-binding materials for separation and sensing applications.

Deposition of polystyrene microplastics on bare or biofilm-coated silica analysed via QCM-D

The mobility of microplastics (MPs) in aqueous media is closely related to their environmental risk. The naturally occurring silica substrate surface in the aquatic environment is easily colonized by microorganisms and forms a biofilm, which may affect the migration and distribution of MPs. Herein, a typical MP, polystyrene (PS), and Pseudomonas fluorescens (P. fluorescens) biofilms were selected to study the deposition and release of pristine or ultraviolet (UV)-aged PS MPs on silica and biofilms under different ionic strengths using a quartz crystal microbalance dissipation (QCM-D) system. Statistical analyses of the deposition experiments revealed a significant impact of P. fluorescens biofilms on deposition (p = 0.0042). The deposition rate of weathered MPs on the biofilms was 4.0 ± 0.1 to 16.3 ± 0.6 times that on silica. A release experiment revealed that the biofilm reduced the release fraction (f_r) of weathered MPs by 34.5 ± 0.3 % compared to bare silica. In addition, the UV-ageing treatment reduced the deposition mass of MPs on the surface of silica by 27.6 ± 0.21 % compared to pristine microspheres. The analysis of the deposition mechanism revealed that the promotion and inhibition of biofilm or UV-ageing treatment on the deposition of microspheres could be attributed to the non-Derjaguin-Landau-Verwey-Overbeek (DLVO) force and the decreased electrostatic repulsion or the increased hydration repulsion, respectively.

Detection and Characterization of Bacterial Biofilms and Biofilm-Based Sensors

Microbial biofilms have caused serious concerns in healthcare, medical, and food industries because of their intrinsic resistance against conventional antibiotics and cleaning procedures and their capability to firmly adhere on surfaces for persistent contamination. These global issues strongly motivate researchers to develop novel methodologies to investigate the kinetics underlying biofilm formation, to understand the response of the biofilm with different chemical and physical treatments, and to identify biofilm-specific drugs with high-throughput screenings. Meanwhile microbial biofilms can also be utilized positively as sensing elements in cell-based sensors due to their strong adhesion on surfaces. In this perspective, we provide an overview on the connections between sensing and microbial biofilms, focusing on tools used to investigate biofilm properties, kinetics, and their response to chemicals or physical agents, and biofilm-based sensors, a type of biosensor using the bacterial biofilm as a biorecognition element to capture the presence of the target of interest by measuring the metabolic activity of the immobilized microbial cells. Finally we discuss possible new research directions for the development of robust and rapid biofilm related sensors with high temporal and spatial resolutions, pertinent to a wide range of applications.

Gold-Specific Biosensor for Monitoring Wastewater Using Genetically Engineered Cupriavidus metallidurans CH34

Transcription factor-based whole-cell biosensors have recently become promising alternatives to conventional analytical methods due to their advantage of simplicity, cost-effectiveness, and environmental friendliness. In this study, we used genetic engineering to develop a whole-cell biosensor based on the activation of promoters by CupR via interactions with gold ions, leading to the expression of reporter genes that yield output signals. Altering the promoter sequences was shown to significantly improve the performance of the biosensor strain in terms of gold-specificity. The detection sensitivity of our engineered strains was 42-fold higher than that of wild-type strains. The linear range of the purposed sensor was 125-1000 nM with a limit of detection at 46.5 nM. The effectiveness of the sensor strain was verified in wastewater samples.

Construction of a Self-Assembled Polyelectrolyte/Graphene Oxide Multilayer Film and Its Interaction with Metal Ions

In this study, a composite multilayer film onto gold was constructed from two charged building blocks, i.e., negatively charged graphene oxide (GO) and a branched polycation (polyethylenimine, PEI) via layer-by-layer (LbL) self-assembly technology, and this process was monitored in situ with quartz crystal microbalance (QCM) under different experimental conditions. This included the differences in frequency (Δf) as well as the changes in dissipation to yield information on the absorbed mass and viscoelastic properties of the formed PEI/GO multilayer films. The experimental conditions were optimized to obtain a high amount of the adsorbed mass of the self-assembled multilayer film. The surface morphology of the PEI/GO multilayer film onto gold was studied with atomic force microscopy (AFM). It was found that the positively charged PEI chains were combined with the oppositely charged GO to form an assembled film on the QCM sensor surface, in a wrapped and curled fashion. Raman and UV-vis spectra also showed that the intensities of the GO-characteristic signals are almost linearly related to the layer number. To explore the films for their use in divalent ion detection, the frequency response of the PEI/GO multilayer-modified QCM sensor to the exposure of aqueous solutions solution of Cu²⁺, Ca²⁺, Zn²⁺, and Sn²⁺ was further studied using QCM. Based on the Sauerbrey equation and the weight of different ions, the number of metal ions adsorbed per unit area on the surface of QCM sensors was calculated. For metal ion concentrations of 40 ppm, the adsorption capacities per unit area of Cu²⁺, Zn²⁺, Sn²⁺, and Ca²⁺ were found to be 1.7, 3.2, 0.7, and 4.9 nmol/cm², respectively. Thus, in terms of the number of adsorbed ions per unit area, the QCM sensor modified by PEI/GO multilayer film shows the largest adsorption capacity of Ca²⁺. This can be rationalized by the relative hydration energies.

Biological Nanofactories: Using Living Forms for Metal Nanoparticle Synthesis

Metal nanoparticles are nanosized entities with dimensions of 1-100 nm that are increasingly in demand due to applications in diverse fields like electronics, sensing, environmental remediation, oil recovery and drug delivery. Metal nanoparticles possess large surface energy and properties different from bulk materials due to their small size, large surface area with free dangling bonds and higher reactivity. High cost and pernicious effects associated with the chemical and physical methods of nanoparticle synthesis are gradually paving the way for biological methods due to their eco-friendly nature. Considering the vast potentiality of microbes and plants as sources, biological synthesis can serve as a green technique for the synthesis of nanoparticles as an alternative to conventional methods. A number of reviews are available on green synthesis of nanoparticles but few have focused on covering the entire biological agents in this process. Therefore present paper describes the use of various living organisms like bacteria, fungi, algae, bryophytes and tracheophytes in the biological synthesis of metal nanoparticles, the mechanisms involved and the advantages associated therein.

Nanohole-boosted electron transport between nanomaterials and bacteria as a concept for nano-bio interactions

Biofilms contribute to bacterial infection and drug resistance and are a serious threat to global human health. Antibacterial nanomaterials have attracted considerable attention, but the inhibition of biofilms remains a major challenge. Herein, we propose a nanohole-boosted electron transport (NBET) antibiofilm concept. Unlike known antibacterial mechanisms (e.g., reactive oxygen species production and cell membrane damage), nanoholes with atomic vacancies and biofilms serve as electronic donors and receptors, respectively, and thus boost the high electron transport capacity between nanomaterials and biofilms. Electron transport effectively destroys the critical components (proteins, intercellularly adhered polysaccharides and extracellular DNA) of biofilms, and the nanoholes also significantly downregulate the expression of genes related to biofilm formation. The anti-infection capacity is thoroughly verified both in vitro (human cells) and in vivo (rat ocular and mouse intestinal infection models), and the nanohole-enabled nanomaterials are found to be highly biocompatible. Importantly, compared with typical antibiotics, nanomaterials are nonresistant and thereby exhibit high potential for use in various applications. As a proof-of-principle demonstration, these findings hold promise for the use of NBET in treatments for pathogenic bacterial infection and antibiotic drug resistance.

Isolation and characterization of an acid and metal tolerant Enterobacter cloacae NZS strain from former mining lake in Selangor, Malaysia

Background

Metal polluted environments have been found to harbor acid and metal tolerant bacterial communities. Metal oxidizing bacteria in particular are industrially important microorganisms that can be utilized for potential applications in biomining and bioremediation. However, some well-characterized strains are not readily culturable as they are obligate and fastidious chemolithotrophs requiring special techniques for their cultivation. Hence, this study was aimed at isolating, identifying, and characterizing indigenous metal tolerant heterotroph(s) from abandoned mines that can potentially be used for biomining or bioremediation processes in the future.

Results

Seventeen bacteria from former mining lakes were isolated and identified using 16S rRNA. Minimal inhibition concentration (MIC) and growth study of isolated bacteria carried out in Luria-Bertani media containing three different metals ions, zinc (II), copper (II), and iron (II), showed that a particular isolate termed Enterobacter cloacae NZS was found to exhibit better growth and tolerance for copper (up to 90 mM), zinc (up to 200 mM), and iron (up to 170 mM). Growth of the strain was notably well in the presence of iron (II). Compared to all the isolates, only E. cloacae NZS was able to be enumerated at pH lower than 5 while other strains were culturable only at pH 7. Its capability in iron (II) oxidation was preliminary assessed based on the pH, cell count, glucose consumption, and amount of iron oxidized throughout incubation in 9K media. E. cloacae NZS strain was found to be capable of oxidizing iron (II) supplied in 9K media to iron (III).

Conclusion

As preliminary investigation showed that E. cloacae NZS was able to oxidize iron (II) in 9K media at pH2, further optimization on the strain, medium, and culture conditions in future may be able to provide a better insight on this strain to be possibly used as an iron oxidizer for various applications.