Rapid and accurate detection of Escherichia coli growth by fluorescent pH-sensitive organic nanoparticles for high-throughput screening applications

Injectable pH- and Ultrasound-Responsive Dual-Crosslinked Dextran/Chitosan/TiO2 Nanocomposite Hydrogels for Antibacterial Applications

Combining exogenous and endogenous antibacterial mechanisms has been demonstrated to enhance therapeutic efficacy significantly. This study constructs an innovative type of exogenous and endogenous antibacterial nanocomposite hydrogels with injectable dual-crosslinked networks and dual-stimuli responsiveness. The primary network establishes imine bonds between the functionalized dextran featuring norbornenes and aldehydes (NorAld-Dex) and the quaternized chitosan (QCS). The imine bonds provide self-healing, injectability, and pH-responsiveness to the hydrogel network. The secondary network is established by integrating thiolated mesoporous silica-coated titanium dioxide nanoparticles (TiO2@MS-SH) into the hydrogel network via an ultrasound-activated thiol-norbornene reaction with NorAld-Dex. The microstructures and properties of NorAld-Dex/QCS/TiO2@MS-SH hydrogels can be fine-tuned by adjusting the sonication time to increase the amount of thiol-norbornene crosslinks in the network. Effective antibacterial performance of NorAld-Dex/QCS/TiO2@MS-SH hydrogels at low pH has been demonstrated with the synergistic effect of the acid-induced dissociation of the hydrogel network, protonated QCS, and the reactive oxygen species (ROS) generated by TiO2@MS-SH nanoparticles under ultrasound irradiation. In summary, NorAld-Dex/QCS/TiO2@MS-SH nanocomposite hydrogel is an advanced dual stimuli-responsive antibacterial platform with customizable microstructures and properties, offering great potential for biomedical applications.

Protective Effect of Panax notoginseng Extract Fermented by Four Different Saccharomyces cerevisiae Strains on H2O2 Induced Oxidative Stress in Skin Fibroblasts

Purpose

To produce Panax notoginseng extract as a cosmetic ingredient through Saccharomyces cerevisiae fermentation.

Methods

We first compared the total sugar content, polysaccharide content, reducing sugar content, total phenolic content, total saponin content, DPPH free radical, ABTS free radical, hydroxyl free radical scavenging ability and ferric reducing antioxidant power (FRAP) of Panax notoginseng fermented extract (pnFE) and unfermented extract (pnWE). Their potential correlations were analyzed by Pearson's correlation analysis. Then, the oxidative stress model of H2O2-induced MSFs was used to evaluate the effects of different pnFE on MSF viability, reactive oxygen species (ROS), malondialdehyde (MDA), and the activities of catalase (CAT), glutathione peroxidase (GSH-Px) and superoxide dismutase (SOD) to explore their protective effects on MSFs subjected to H2O2-induced cellular oxidative damage. Finally, their safety and stability were evaluated by using the red blood cell (RBC) test and hen's egg test-chorioallantoic membrane (HET-CAM) assay, and changes in pH and content of soluble solids, respectively.

Results

Compared with pnWE, pnFE has more active substances and stronger antioxidant capacity. In addition, pnFE has a protective effect on H2O2-induced oxidative stress in MSFs with appropriate safety and stability.

Conclusion

PnFE has broad application prospects in the field of cosmetics.

UV-induced oxidase activity of carbon dots in visible UVA dosage, Escherichia coli quantification and bacterial typing

Ultraviolet (UV) light and foodborne pathogenic bacteriais are an important risk to the environment's safety. They endanger human health, and also lead to outbreaks of infectious disease, posing great threats to global public health security, national economy, and social stability. The appearance of carbon dot (CD) nanozymes offers a new perspective to solve the problems of detection of UV light and pathogenic bacteria in environment. This paper reports the preparation of CDs with dual enzyme-like activities (superoxide dismutase activity and UV-induced oxidase activity). The product can catalyze the oxidation of the substrate 3, 3', 5, 5'-tetramethylbenzidine (TMB) under UV light (365 nm) to achieve rapid color development. Based on the excellent fluorescence properties of CDs, the colorimetric-fluorescence dual-channel real-time detection of UVA dose was realized, the mechanism underlying the catalytic oxidation of TMB by UV-induced oxidase CDs was also investigated. Furthermore, a portable CDs-TMB-PA hydrogel was prepared which could realize the real-time monitoring of UV in outdoor environment with the assistance of smartphone. Based on the pH dependency of the CD nanozymes and specific glycolytic response of the pathogenic bacteria Escherichia coli (E. coli) O157:H7, the direct, simple, quick, and sensitive typing and detection have been realized. This research offers new perspectives for studying CD nanozymes and their applications in UV and bacterial detection, demonstrating the remarkable potential of CD nanozymes in detecting environmental hazards.

Turbidimetric flow analysis system for the investigation of microbial growth

The monitoring of life of microbial populations is of the uttermost importance in environmental and food analysis, agriculture, as well as in medicine. The duration of bacteria adaptation to new environmental conditions, its lifetime and the divisions' pace are the key information in many studies. It was found that the fully-mechanized flow analysis system based on solenoid valves and pumps, paired with a dedicated flow-through optoelectronic detector can be successfully applied for monitoring of bacteria growth. The applicability of the designed multicommutated flow analysis (MCFA) system was proved by analysis of solutions containing bacteria cells proceeded by tests of McFarland (McF) standards. The developed setup allowed modelling and simulation of microbial growth, as well as monitoring of the bacteria growth in real-time manner to be carried out. The monitor is useful for the quantitative estimation of the basic parameters of bacteria population like its size, the rate of bacteria multiplication, as well as the times of lag, log and stationary phases of microbial growth.

Automatically showing microbial growth kinetics with a high-performance microbial growth analyzer

It is difficult to show microbial growth kinetics online when they grow in complex matrices. We presented a novel strategy to address this challenge by developing a high-performance microbial growth analyzer (HPMGA), which employed a unique 32-channel capacitively coupled contactless conductivity detector as a sensing element and fixed with a CellStatz software. It was capable of online showing accurate and repeatable growth curves of well-dispersed and bad-dispersed microbes, whether they grew in homogeneous simple culture broth or heterogeneous complex matrices. Moreover, it could automatically report key growth kinetics parameters. In comparison to optical density (OD), plate counting and broth microdilution (BMD) methods, we demonstrated its practicability in five scenarios: 1) the illustration of the growth, growth rate, and acceleration curves of Escherichia coli (E. coli); 2) the antimicrobial susceptibility testing (AST) of Oxacillin against Staphylococcus aureus (S. aureus); 3) the determination of Ag nanoparticle toxicity on Providencia rettgeri (P. rettgeri); 4) the characterization of milk fermentation; and 5) the enumeration of viable pathogenic Vibrio in shrimp body. Results highlighted that the HPMGA method had the advantages of universality and effectivity. This technology would significantly facilitate the routine analysis of microbial growth in many fields (biology, medicine, clinic, life, food, environment, and ecology), paving an avenue for microbiologists to achieve research goals that have been inhibited for years due to a lack of practical analytical methods.

Analytical methods for assessing antimicrobial activity of nanomaterials in complex media: advances, challenges, and perspectives

Assessing the antimicrobial activity of engineered nanomaterials (ENMs), especially in realistic scenarios, is of great significance for both basic research and applications. Multiple analytical methods are available for analysis via off-line or on-line measurements. Real-world samples are often complex with inorganic and organic components, which complicates the measurements of microbial viability and/or metabolic activity. This article highlights the recent advances achieved in analytical methods including typical applications and specifics regarding their accuracy, cost, efficiency, and user-friendliness. Methodological drawbacks, technique gaps, and future perspectives are also discussed. This review aims to help researchers select suitable methods for gaining insight into antimicrobial activities of targeted ENMs in artificial and natural complex matrices.

Nanotechnology Approaches for Rapid Detection and Theranostics of Antimicrobial Resistant Bacterial Infections

As declared by WHO, antimicrobial resistance (AMR) is a high priority issue with a pressing need to develop impactful technologies to curb it. The rampant and inappropriate use of antibiotics due to the lack of adequate and timely diagnosis is a leading cause behind AMR evolution. Unfortunately, populations with poor economic status and those residing in densely populated areas are the most affected ones, frequently leading to emergence of AMR pathogens. Classical approaches for AMR diagnostics like phenotypic methods, biochemical assays, and molecular techniques are cumbersome and resource-intensive and involve a long turnaround time to yield confirmatory results. In contrast, recent emergence of nanotechnology-assisted approaches helps to overcome challenges in classical approaches and offer simpler, more sensitive, faster, and more affordable solutions for AMR diagnostics. Nanomaterial platforms (metallic, quantum-dot, carbon-based, upconversion, etc.), nanoparticle-based rapid point-of-care platforms, nano-biosensors (optical, mechanical, electrochemical), microfluidic-assisted devices, and importantly, nanotheranostic devices for diagnostics with treatment of AMR infections are examples of rapidly growing nanotechnology approaches used for AMR management. This review comprehensively summarizes the past 10 years of research progress on nanotechnology approaches for AMR diagnostics and for estimating antimicrobial susceptibility against commonly used antibiotics. This review also highlights several bottlenecks in nanotechnology approaches that need to be addressed prior to considering their translation to clinics.

Electropolymerised pH Insensitive Salicylic Acid Reference Systems: Utilization in a Novel pH Sensor for Food and Environmental Monitoring

This work summarizes the electrochemical response of a salicylic acid-based carbon electrode for use as a novel solid-state reference electrode in a redox-based pH sensor. This novel reference produces a pH insensitive response over a range of pH 3-10 in solutions with low buffer concentrations, different compositions, conductivities, and ionic strengths is produced. The pH of the local environment is shown to be determined by the chemistry and the electrochemical response of the redox active species on the surface of the electrode; the local pH can be controlled by the electropolymerized salicylic acid moieties due to the acid concentration on the surface, avoiding any perturbation in environmental pH and leading to a stable novel reference system. Sensitivities of -7.1 mV/pH unit, -2.4 mV/pH unit, -0.2 mV/pH unit, and 2.5 mV/pH units were obtained for different food medias, hydroponic solution, seawater, and cell-culture media, respectively, confirming its ability to control the local pH of the electrode. This reference system is paired with a new pH sensing element based on electropolymerized flavanone to provide a calibration free, pH sensitive sensor to effectively and accurately measure the pH of various media with high viscosity, low conductivity, low/high buffer concentration or cell-culture environment, presenting a maximum error of +/-0.03 pH units.

Toward co-design of an AI solution for detection of diarrheal pathogens in drinking water within resource-constrained contexts

Despite successes on the Sustainable Development Goals for access to improved water sources and sanitation, many low and middle-income countries (LMICs) continue to struggle with high rates of diarrheal disease. In Guatemala, 98% of water sources are estimated to have E. coli contamination. This project moves toward a novel low-cost approach to bridge the gap between the microbiologic identification of E. coli and the vast impact that this pathogen has on human health within marginalized communities using co-designed community-based tools, low-cost technology, and AI. An agile co-design process was followed with water quality stakeholders, community staff, and local graphic design artists to develop a community water quality education mobile app. A series of alpha- and beta-testers completed interactive demonstration, feedback, and in-depth interview sessions. A microbiology lab in Guatemala developed and piloted field protocols with lay community workers to collect and process water samples. A preliminary artificial intelligence (AI) algorithm was developed to detect the presence of E. coli in images generated from community-derived water samples. The mobile app emerged as a pictorial and audio-driven community-facing tool. The field protocol for water sampling and testing was successfully implemented by lay community workers. Feedback from the community workers indicated both desire and ability to conduct the water sampling and testing protocol under field conditions. However, images derived from the low-cost $2 microscope in field conditions were not of a suitable quality for AI object detection of E. coli, and additional low-cost technologies are being considered. The preliminary AI object detection algorithm from lab-derived images performed at 94% accuracy in identifying E. coli in comparison to the Chromocult gold-standard.

Compartmentalized Polymeric Nanoparticles Deliver Vancomycin in a pH-Responsive Manner

Vancomycin (VCM) is a last resort antibiotic in the treatment of severe Gram-positive infections. However, its administration is limited by several drawbacks such as: strong pH-dependent charge, tendency to aggregate, low bioavailability, and poor cellular uptake. These drawbacks were circumvented by engineering pH-responsive nanoparticles (NPs) capable to incorporate high VCM payload and deliver it specifically at slightly acidic pH corresponding to infection sites. Taking advantage of peculiar physicochemical properties of VCM, here we show how to incorporate VCM efficiently in biodegradable NPs made of poly(lactic-co-glycolic acid) and polylactic acid (co)polymers. The NPs were prepared by a simple and reproducible method, establishing strong electrostatic interactions between VCM and the (co)polymers’ end groups. VCM payloads reached up to 25 wt%. The drug loading mechanism was investigated by solid state nuclear magnetic resonance spectroscopy. The engineered NPs were characterized by a set of advanced physicochemical methods, which allowed examining their morphology, internal structures, and chemical composition on an individual NP basis. The compartmentalized structure of NPs was evidenced by cryogenic transmission electronic microscopy, whereas the chemical composition of the NPs’ top layers and core was obtained by electron microscopies associated with energy-dispersive X-ray spectroscopy. Noteworthy, atomic force microscopy coupled to infrared spectroscopy allowed mapping the drug location and gave semiquantitative information about the loadings of individual NPs. In addition, the NPs were stable upon storage and did not release the incorporated drug at neutral pH. Interestingly, a slight acidification of the medium induced a rapid VCM release. The compartmentalized NPs could find potential applications for controlled VCM release at an infected site with local acidic pH.

Emerging Antibacterial Strategies with Application of Targeting Drug Delivery System and Combined Treatment

At present, some bacteria have developed significant resistance to almost all available antibiotics. One of the reasons that cannot be ignored is long-term exposure of bacteria to the sub-minimum inhibitory concentration (MIC) of antibiotics. Therefore, it is necessary to develop a targeted antibiotic delivery system to improve drug delivery behavior, in order to delay the generation of bacterial drug resistance. In recent years, with the continuous development of nanotechnology, various types of nanocarriers that respond to the infection microenvironment, targeting specific bacterial targets, and targeting infected cells, and so on, are gradually being used in the delivery of antibacterial agents to increase the concentration of drugs at the site of infection and reduce the side effects of drugs in normal tissues. Here, this article describes in detail the latest research progress on nanocarriers for antimicrobial, and commonly used targeted antimicrobial strategies. The advantages of the combination of nanotechnology and targeting strategies in combating bacterial infections are highlighted in this review, and the upcoming opportunities and remaining challenges in this field are rationally prospected.

Bioanalytical insight into the life of microbial populations: A chemical monitoring of ureolytic bacteria growth

In this publication an alternative approach to investigations of bacterial growth is proposed. Contrary to the conventional physical methods it is based on enzyme activity detection. The procedure for real-time and on-line monitoring of microbial ureolytic activity (applied as a model experimental biosystem) in the flow analysis format is presented. The developed fully-mechanized bioanalytical flow system is composed of solenoid micropumps and microvalves actuated by Arduino microcontroller. The photometric detection based on Nessler reaction is performed using dedicated flow-through optoelectronic detector made of paired light emitting diodes. The developed bioanalytical system allows discrete assaying of microbial urease in the wide range of activity up to 5.4 U mL^-1 with detection limit below 0.44 U mL^-1, a high sensitivity in the linear range of response (up to 200 mV U^-1 mL and relatively high throughput (9 detection per hour). The proposed differential procedure of measurements (i.e. a difference between peaks register for sample with and without external addition of urea is treated as an analytical signal) allows elimination of interfering effects from substrate and products of biocatalysed reaction as well as other components of medium used for microbial growth. The developed bioanalytical system was successfully applied for the control of growth of urease-positive bacteria strains (Proteus vulgaris, Klebsiella pneumoniae and Paracoccus yeei) including examination of effects from various microbial cultivation conditions like temperature, composition of culture medium and amount of substrate required for induction of bacterial enzymatic activity. The developed bioanalytical flow system can be applied for metabolic activity-based estimation of parameters of lag and log phases of microbial growth as well as for detection of decline phase.

Fast detection of E. coli with a novel fluorescent biosensor based on a FRET system between UCNPs and GO@Fe3O4 in urine specimens

Biosensors based on nanomaterials are becoming a research hotspot for the rapid detection of pathogenic bacteria. Herein, a "turn-on" fluorescent biosensor based on a FRET system was constructed for the fast detection of a representative pathogenic microorganism, namely, E. coli, which causes most urinary tract infections. This biosensor was constructed by utilizing synthesized UCNPs as fluorescent donors with stable luminescence performance in complex biological samples and GO@Fe3O4 as a receptor with both excellent adsorption ability and fluorescence quenching ability. A specific ssDNA selected as an aptamer which could recognize E. coli was immobilized on the UCNPs to form UCNP-Apt nanoprobes. The nanoprobes were adsorbed on the surface of GO@Fe3O4 through the π-stacking interactions between aptamers and GO. In the presence of E. coli, UCNP-Apt nanoprobes detached from GO@Fe3O4 due to the specific recognition of aptamers and bacteria, resulting in obvious fluorescence recovery, and the concentration of bacteria was positively correlated with the intensity of the fluorescence signal; such a "turn-on" signal output mode ensures excellent precision. In addition, the easy magnetic separation of GO@Fe3O4 simplifies the operation process, helping the sensor detect bacteria in 30 minutes with a linear range from 103 to 107 CFU mL-1 and a limit of detection of 467 CFU mL-1. Moreover, recovery test results also showed that the sensor has clinical application potential for the rapid detection of pathogenic microorganisms in complex biological samples.

Enabling high-throughput biology with flexible open-source automation

Our understanding of complex living systems is limited by our capacity to perform experiments in high throughput. While robotic systems have automated many traditional hand-pipetting protocols, software limitations have precluded more advanced maneuvers required to manipulate, maintain, and monitor hundreds of experiments in parallel. Here, we present Pyhamilton, an open-source Python platform that can execute complex pipetting patterns required for custom high-throughput experiments such as the simulation of metapopulation dynamics. With an integrated plate reader, we maintain nearly 500 remotely monitored bacterial cultures in log-phase growth for days without user intervention by taking regular density measurements to adjust the robotic method in real-time. Using these capabilities, we systematically optimize bioreactor protein production by monitoring the fluorescent protein expression and growth rates of a hundred different continuous culture conditions in triplicate to comprehensively sample the carbon, nitrogen, and phosphorus fitness landscape. Our results demonstrate that flexible software can empower existing hardware to enable new types and scales of experiments, empowering areas from biomanufacturing to fundamental biology.

Fluorescein Derivatives as Fluorescent Probes for pH Monitoring along Recent Biological Applications

Potential of hydrogen (pH) is one of the most relevant parameters characterizing aqueous solutions. In biology, pH is intrinsically linked to cellular life since all metabolic pathways are implicated into ionic flows. In that way, determination of local pH offers a unique and major opportunity to increase our understanding of biological systems. Whereas the most common technique to obtain these data in analytical chemistry is to directly measure potential between two electrodes, in biological systems, this information has to be recovered in-situ without any physical interaction. Based on their non-invasive optical properties, fluorescent pH-sensitive probe are pertinent tools to develop. One of the most notorious pH-sensitive probes is fluorescein. In addition to excellent photophysical properties, this fluorophore presents a pH-sensitivity around neutral and physiologic domains. This review intends to shed new light on the recent use of fluorescein as pH-sensitive probes for biological applications, including targeted probes for specific imaging, flexible monitoring of bacterial growth, and biomedical applications.

Fluorescent Copolymers for Bacterial Bioimaging and Viability Detection

Novel fluorescent labels with high photostability and high biocompatibility are required for microbiological imaging and detection. Here, we present a green fluorescent polymer chain (GFPC), designed to be nontoxic and water-soluble, for multicolor bioimaging and real-time bacterial viability determination. The copolymer is synthesized using a straightforward one-pot reversible addition-fragmentation chain-transfer (RAFT) polymerization technique. We show that GFPC does not influence bacterial growth and is stable for several hours in a complex growth medium and in the presence of bacteria. GFPC allows the labeling of the bacterial cytoplasm for multicolor bacterial bioimaging applications. It can be used in combination with propidium iodide (PI) to develop a rapid and reliable protocol to distinguish and quantify, in real time, by flow cytometry, live and dead bacteria.

A disposable gold-cellulose nanofibril platform for SERS mapping

In this study, we present a disposable and inexpensive paper-like gold nanoparticle-embedded cellulose nanofibril substrate for the rapid enumeration of Escherichia coli (E. coli) using surface-enhanced Raman scattering (SERS) mapping. A disposable SERS substrate was simply constructed by mixing CNF and gold chloride solution at 120 °C in a water bath. The application of the resulting substrate was carried out by enrichment and SERS detection of E. coli. To this end, the spherical gold nanoparticle-embedded cellulose nanofibril substrate was used as a scavenger for E. coli. After the target bacteria E. coli were separated from the matrix via oriented antibodies, the sandwich assay procedure was carried out using 5,5-dithiobis-(2-nitrobenzoic acid) (DTNB)-coated Au nanorod particles that acted as SERS mapping probes. The distribution density of DTNB was demonstrated visually using SERS mapping, and the assay was completed in one hour. The correlation between the E. coli and SERS mapping signals was found to be linear within the range of 15 cfu mL-1 to 1.5 × 105 cfu mL-1. The limit of detection for the SERS mapping assay was determined to be 2 cfu mL-1. The selectivity of the developed method was examined with Micrococcus luteus (M. luteus), Bacillus subtilis (B. subtilis), and Enterobacter aerogenes (E. aerogenes), which did not produce any significant response. Furthermore, the developed method was evaluated for detecting E. coli in artificially contaminated samples, and the results were compared with those of the plate-counting method.

Fluorimetric Detection of Single Pathogenic Bacterium in Milk and Sewage Water Using pH-Sensitive Fluorescent Carbon Dots and MALDI-TOF MS

The current study is focused on the application of water-soluble, fluorescent, and pH-sensitive carbon dots (CDs) as a nanoprobe for sensitive detection of pathogenic bacteria in milk and sewage water. The CDs were facilely synthesized through the controlled carbonization of sucrose using sulfuric acid and characterized through XRD, FTIR, TEM, UV-Vis Spectroscopy, and fluorescent analysis. The as-synthesized CDs were highly water-soluble, stable, and pH-sensitive fluorescent nanomaterials. The pH-related fluorescence study showed that the ratio of fluorescence intensity (Log[IF410/IF350]) changed linearly in the pH range between 4.9 and 6.9 in the Britton-Robison buffer. By determining the pH variation of the growth medium caused by the released acidic metabolites, the CDs-based ratiometric nanoprobe and MALDI-TOF mass spectrometry (MS) were used for the detection and identification of Escherichia coli O157:H7, respectively. The practical applicability of the pH-sensitive fluorescent CDs-based ratiometric nanoprobe was evaluated to detect Escherichia coli O157:H7 in real samples, i.e., milk and sewage water using agar count plate method with a limit of detection (LOD) up to 1 colony-forming unit per mL (CFU/mL).

Conductometric sensor for viable Escherichia coli and Staphylococcus aureus based on magnetic analyte separation via aptamer

A method is described to determine viable populations of Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). The method employs aptamer-magnetic separation combined with resistivity based detection. The bacteria were separated by means of aptamer-functionalized magnetic beads. They were then quantified by measuring their growth kinetics through time-dependent conductivity changes of culture media. The time-course of growth was logged by real-time and contactless measurements that yielded starting concentrations from the duration of lag intervals prior to the log phase of growth. In pure water samples, the linear ranges for measuring E. coli and S. aureus cells are 2.5 × 10³-2.5 × 10⁸ CFU·mL^-1 and 4.1 × 10³-4.1 × 10⁸ CFU·mL^-1, respectively. In spiked tap water samples, the lower limits of detection are 2.3 × 10⁴ CFU·mL^-1 and 4.0 × 10³ CFU·mL^-1 for E. coli and S. aureus, with recoveries of 87.0-108.7% and 92.5-105.0%, respectively. The relative standard deviation of these measurements (10.0%) is below that of plate counting method (13.9%). The presence of micro/nanoparticles such as magnetic beads or selenium nanoparticles in the culture media does not interfere, unlike in case of automatted optical density monitoring. The E. coli and S. aureus cells captured on the aptamer-functionalized magnetic beads can be directly tested for their susceptibility to antibiotics. The process of magnetic separation and determination of load burden requires neither bulky, sophisticated equipment nor expensive reagents. Graphical abstractAptamer-functionalized magnetic beads are used to selectively capture and separate E. coli and S. aureus cells in aqueous samples. They are directly transferred to a multichannel conductometric sensor for the quantification of viable bacteria via automated monitoring of their growth kinetics.

High-throughput extracellular pH monitoring and antibiotics screening by polymeric fluorescent sensor with LCST property

Monitoring extracellular pH (pHe) is important for biology understanding, since pHe and its homeostasis are closely relevant to cellular metabolism. Hydrogel-based pHe sensors have attracted significant attention and showed wide application, while they are tedious with significant time-cost operation and reproducibility variations for high-throughput application. Herein, we synthesized two polymers for pHe monitoring which are soluble in water at room temperature with easy operations and high reproducibility among various micro-plate wells for high-throughput analysis. P1 (P(OEGMA-co-MEO₂MA-co-pHS)) and P2 (P(OEGMA-co-pHS)) were synthesized via the Reversible Addition Fragmentation Chain Transfer (RAFT) copolymerization of oligo(ethylene glycol) methacrylate (OEGMA), 2-(2'-methoxyethoxy) ethyl methacrylate (MEO₂MA) and the pH sensitive fluorescence moiety N-fluoresceinyl methacrylamide (pHS). P1 is soluble in water at room temperature (25 °C) while insoluble at the temperature above 33 °C, indicating its feature of lower critical solution temperature (LCST) at 33 °C. Further P1 showed higher pH sensitivity and photostability than P2 (without LCST property) when used at physiological temperature (37 °C). Thus, P1 was chosen to in-situ monitor the micro-environmental acidification of E. coli, Hela and Ramos cells during their growth, and the metabolism inhibiting activity of a representative antibiotic, ampicillin. Cell concentration-dependent cellular acidification and drug concentration-dependent inhibition of cellular acidification were observed, demonstrating that the LCST polymer (P1) is suitable for real-time cellular acidification monitoring as well as for high-throughput drug screening. This study firstly demonstrated the use of a LCST polymeric sensor for high-throughput screening of antibiotics and investigation of cell metabolism.

Core–shell polymeric nanoparticles comprising BODIPY and fluorescein as ultra-bright ratiometric fluorescent pH sensors

Ultra-bright pH-sensitive fluorescent nanoparticles, including BODIPY in their core and fluorescein in their shell, are synthesized. They contain more than 2500 fluorophores and exhibit a linear fluorescence response between pH 5.5 and 7.5.

Antibacterial Micelles with Vancomycin-Mediated Targeting and pH/Lipase-Triggered Release of Antibiotics

Antibiotic delivery systems play an important role in increasing the efficacy while reducing the off-target toxicity and antibiotic resistance. Though bacterial infections share pathophysiological pathways similar to tumor tissues, few delivery systems have achieved bacterial targeting and on-demand release of antibiotics. In the current study, amphiphilic poly(ethylene glycol)-poly(ε-caprolactone) (PECL) copolymers are conjugated with vancomycin (VAN) as targeting ligands via pH-cleavable hydrazone bonds to obtain micelle carriers (Van-hyd-PECL). Subsequently, ciprofloxacin (CIP) is encapsulated to obtain Van-hyd-PECL/Cip micelles with an average size of 77 nm and a CIP loading amount of 4.5%. The poly(ethylene glycol) shells and the extension of VAN moieties on the micelle surface enhance the blood circulation and selective recognition of bacteria. The deshielding of VAN shells under acidic conditions disrupts the hydrophobic/hydrophilic balance leading to an increase in micelle sizes, which facilitates the degradation of poly(ε-caprolactone) by lipase overexpressed in the infection site and the release of encapsulated CIP for bacterial destruction. The micelle treatment has improved the survival of Pseudomonas aeruginosa-infected mice and reduced the bacterial burdens and alveolar injuries in lungs, compared with free drugs and micelles without inoculation of VAN moieties. Three doses of Van-hyd-PECL/Cip micelles further extend the animal survival, decrease the bacterial colonization in lungs, and almost restore the normal alveolar microstructure. In this regard, this study has demonstrated a strategy to enhance the bacterial targeting of micelles via an antibiotic (VAN) and to sequentially trigger the release of antibiotics (VAN and CIP) at the infection site.

Detecting Biothreat Agents: From Current Diagnostics to Developing Sensor Technologies

Although a fundamental understanding of the pathogenicity of most biothreat agents has been elucidated and available treatments have increased substantially over the past decades, they still represent a significant public health threat in this age of (bio)terrorism, indiscriminate warfare, pollution, climate change, unchecked population growth, and globalization. The key step to almost all prevention, protection, prophylaxis, post-exposure treatment, and mitigation of any bioagent is early detection. Here, we review available methods for detecting bioagents including pathogenic bacteria and viruses along with their toxins. An introduction placing this subject in the historical context of previous naturally occurring outbreaks and efforts to weaponize selected agents is first provided along with definitions and relevant considerations. An overview of the detection technologies that find use in this endeavor along with how they provide data or transduce signal within a sensing configuration follows. Current "gold" standards for biothreat detection/diagnostics along with a listing of relevant FDA approved in vitro diagnostic devices is then discussed to provide an overview of the current state of the art. Given the 2014 outbreak of Ebola virus in Western Africa and the recent 2016 spread of Zika virus in the Americas, discussion of what constitutes a public health emergency and how new in vitro diagnostic devices are authorized for emergency use in the U.S. are also included. The majority of the Review is then subdivided around the sensing of bacterial, viral, and toxin biothreats with each including an overview of the major agents in that class, a detailed cross-section of different sensing methods in development based on assay format or analytical technique, and some discussion of related microfluidic lab-on-a-chip/point-of-care devices. Finally, an outlook is given on how this field will develop from the perspective of the biosensing technology itself and the new emerging threats they may face.

Advances in online methods for monitoring microbial growth

Understanding the characteristics of microbial growth is of great significance to many fields including in scientific research, the food industry, health care, and agriculture. Many methods have been established to characterize the process of microbial growth. Online and automated methods, in which sample transfer is avoided, are popular because they can facilitate the development of simple, safe, and effective growth monitoring. This review focuses on advances in online monitoring methods over the last decade (2008-2018). We specifically focus on optic- and electrochemistry-based techniques, either through contact measurements or contactless measurement. Strengths and weaknesses of each set of methods are described and we also speculate on forthcoming trends in the field.

Online Monitoring of Bacterial Growth with an Electrical Sensor

Herein, we developed an automatic electrical bacterial growth sensor (EBGS) based on a multichannel capacitively coupled contactless conductivity detector (C⁴D). With the use of the EBGS, up to eight culture samples of E. coli in disposable tubes were online monitored simultaneously in a noninvasive manner. Growth curves with high resolution (on the order of a time scale of seconds) were generated by plotting normalized apparent conductivity value against incubation time. The characteristic data of E. coli growth (e.g., growth rate) obtained here were more accurate than those obtained with optical density and contact conductivity methods. And the correlation coefficient of the regression line ( r) for quantitative determination of viable bacteria was 0.9977. Moreover, it also could be used for other tasks, such as the investigation of toxic/stress effects from chemicals and antimicrobial susceptibility testing. All of these performances required neither auxiliary devices nor additional chemicals and biomaterials. Taken together, this strategy has the advantages of simplicity, accuracy, reproducibility, affordability, versatility, and miniaturization, liberating the users greatly from financial and labor costs.

Optimizing Dual Fluorescent Analysis to Investigate the Toxicity of AgNPs in E. coli

The ever-increasing use of silver nanoparticles (AgNPs) carries potential ecotoxicological risks. For full risk assessment, E. coli cells harboring a plasmid with a constitutively expressed GFP gene under control of lac promoter (lac::GFP) are extensively utilized. Flow cytometry is an advanced technology usually applied to toxicological research for rapid, efficient, multi-parameter analysis of single cells. However, it is difficult to accurately and sensitively detect the toxicity of nanoparticles with flow cytometry due to the interference of aggregated nanoparticles. In this protocol, dual-fluorescence detection with a propidium iodide (PI)-lac::GFP assay is used to determine the toxicity of AgNPs and successfully discriminate the dead or fragilized bacteria from living bacteria and aggregated nanoparticles. © 2017 by John Wiley & Sons, Inc.

Detection of Cronobacter sakazakii in powdered infant formula using an immunoliposome-based immunomagnetic concentration and separation assay

This study aimed to optimize the applicability of an immunoliposome-based immunomagnetic concentration and separation assay to facilitate rapid detection of Cronobacter sakazakii in powdered infant formula (PIF). To determine the detection limit, specificity, and pre-enrichment incubation time (0, 4, 6, and 8 h), assay tests were performed with different cell numbers of C. sakazakii (2 × 10⁰ and 2 × 10¹ CFU/ml) inoculated in 10 g of PIF. The assay was able to detect as few as 2 cells of C. sakazakii/10 g of PIF sample after 6 h of pre-enrichment incubation with an assay time of 2 h 30 min. The assay was assessed for cross-reactivity with other bacterial strains and exhibited strong specificity to C. sakazakii. Moreover, the assay method was applied to the detection of C. sakazakii in PIF without pre-enrichment steps, and the results were compared with INC-ELISA and RT-PCR. The developed method was able to detect C. sakazakii in spiked PIF without pre-enrichment, whereas INC-ELISA failed to detect C. sakazakii. In addition, when compared with the results obtained with RT-PCR, our developed assay required lesser detection time. The developed assay was also not susceptible to any effect of the food matrix or background contaminant microflora.

Recent Progresses in Nanobiosensing for Food Safety Analysis

With increasing adulteration, food safety analysis has become an important research field. Nanomaterials-based biosensing holds great potential in designing highly sensitive and selective detection strategies necessary for food safety analysis. This review summarizes various function types of nanomaterials, the methods of functionalization of nanomaterials, and recent (2014-present) progress in the design and development of nanobiosensing for the detection of food contaminants including pathogens, toxins, pesticides, antibiotics, metal contaminants, and other analytes, which are sub-classified according to various recognition methods of each analyte. The existing shortcomings and future perspectives of the rapidly growing field of nanobiosensing addressing food safety issues are also discussed briefly.

Investigating the environmental factors affecting the toxicity of silver nanoparticles in Escherichia coli with dual fluorescence analysis

Flow cytometric investigation of the toxic effects of nanoparticles on bacteria is highly challenging and not sensitive due to the interference of aggregated nanoparticles: aggregated nanoparticles and bacteria are similar in size. In this study, an optimized dual fluorescence flow cytometric analysis was developed using PI-Lac::GFP (propidium iodide stained Escherichia coli (lac::GFP)) to monitor the toxicity of silver nanoparticles (AgNPs). As compared with single fluorescence analysis, the dual fluorescence analysis enabled more accurate evaluation of the toxic effects of AgNPs. We used this dual fluorescence analysis to investigate how AgNPs toxicity was affected by two typical environmental factors, divalent metal ions and surfactants. Our data revealed that Cu(2+) and SDS significantly enhanced the toxicity of AgNPs in a dose-dependent manner. SDS enhanced the toxicity of both AgNPs and Ag(+) ions, whereas Cu(2+) increased the toxicity of AgNPs but not dissolved Ag(+) ions. Our results suggest that this dual fluorescence analysis can be used to evaluate the toxicity of AgNPs accurately and sensitively.

Stimuli-responsive polymers for antimicrobial therapy: drug targeting, contact-killing surfaces and competitive release

INTRODUCTION

Polymers can be designed to modify their features as a function of the level and nature of the surrounding microorganisms. Such responsive polymers can endow drug delivery systems and drug-medical device combination products with improved performance against intracellular infections and biofilms.

AREAS COVERED

Knowledge on microorganism growth environment outside and inside cells and formation of biofilm communities on biological and synthetic surfaces, together with advances in materials science and drug delivery are prompting strategies with improved efficacy and safety compared to traditional systemic administration of antimicrobial agents. This review deals with antimicrobial strategies that rely on: (i) polymers that disintegrate or undergo phase-transitions in response to changes in enzymes, pH and pO2 associated to microorganism growth; (ii) stimuli-responsive polymers that expose contact-killing groups when microorganisms try to adhere; and (iii) bioinspired polymers that recognize microorganisms for triggered (competitive/affinity-driven) drug release.

EXPERT OPINION

Prophylaxis and treatment of infections may benefit from polymers that are responsive to the unique changes that microbial growth causes in the surrounding environment or that even recognize the microorganism itself or its quorum sensing signals. These polymers may offer novel tools for the design of macrophage-, bacteria- and/or biofilm-targeted nanocarriers as well as of medical devices with switchable antibiofouling properties.

One-step synthesis of amikacin modified fluorescent carbon dots for the detection of Gram-negative bacteria like Escherichia coli

In this paper, we report a one-step strategy to synthesize amikacin modified fluorescent carbon dots (CDs@amikacin) for assaying pathogenic bacteria, Escherichia coli.

Fluorescent core–shell nanoparticles and nanocapsules using comb-like macromolecular RAFT agents: synthesis and functionalization thereof

Ultra-bright fluorescent nanoparticles with comb-like shells based on PEG and acrylic acid were obtained in water using an additive-free miniemulsion polymerization process.