Cyanobacterial blooms produce hazardous toxins, deplete oxygen, and secrete compounds that confer undesirable organoleptic properties to water. To prevent bloom appearance, the World Health ...Organization has established an alert level between 500 and 2000 cells·mL–1, beyond the capabilities of most optical sensors detecting the cyanobacteria fluorescent pigments. Flow cytometry, cell culturing, and microscopy may reach these detection limits, but they involve both bulky and expensive laboratory equipment or long and tedious protocols. Thus, no current technology allows fast, sensitive, and in situ detection of cyanobacteria. Here, we present a simple, user-friendly, low-cost, and portable photonic system for in situ detection of low cyanobacterial concentrations in water samples. The system integrates high-performance preconcentration elements and optical components for fluorescence measurement of specific cyanobacterial pigments, that is, phycocyanin. Phycocyanin has demonstrated to be more selective to cyanobacteria than other pigments, such as chlorophyll-a, and to present an excellent linear correlation with bacterial concentration from 102 to 104 cell·mL–1 (R 2 = 0.99). Additionally, the high performance of the preconcentration system leads to detection limits below 435 cells·mL–1 after 10 min in aquaponic water samples. Due to its simplicity, compactness, and sensitivity, we envision the current technology as a powerful tool for early warning and detection of low pathogen concentrations in water samples.
There is an increasing demand on alternatives methods to animal testing. Numerous health parameters have been already studied using in vitro devices able to mimic the essential functions of the ...organs, being the real-time monitoring and response to stimuli their main limitations. Regarding the health of the gut, the short chain fatty acids, and particularly acetate, have emerged as key biomarkers to evaluate gut healthiness and disease development, although the number of acetate biosensors is still very low. This article presents a microbial biosensor based on fully biocompatible materials which is able to detect acetate in aerobic conditions in the range between 11 and 50 mM, and without compromising the viability and function of either bacteria (>90% viability) or mammalian cells (>80% viability). The detection mechanism is based on the metabolism of acetate by Escherichia coli bacteria immobilized on the transducer surface. Ferricyanide is used as a redox mediator to transfer electrons from the acetate metabolism in the bacterial cells to the transducer. High bacterial concentrations are immobilized in the transducer surface (109 cfu mL−1) by electrodeposition of conductive alginate hydrogels doped with reduced graphene oxide. The results show successful outcomes to exploit bacteria as a biosensing tool, based on the use of inkjet printed transducers, biocompatible materials and cell entrapment technologies.
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•Escherichia coli uses acetate as carbon source in aerobic conditions.•Stable, biocompatible, conductive alginate hydrogel is electrodeposited on inkjet printed sensor's working electrode.•Immobilization of high bacterial concentrations of E. coli within alginate hydrogel.•Bacterial metabolism oxidizes acetate, enabling amperometric measurement of electron flow via ferricyanide reduction.•Successful proof-of-concept demonstration of bioelectrochemical acetate detection is performed.
Early detection and identification of microbial contaminants is crucial in many sectors, including clinical diagnostics, food quality control and environmental monitoring. Biosensors have recently ...gained attention among other bacterial detection technologies due to their simplicity, rapid response, selectivity, and integration/miniaturization potential in portable microfluidic platforms. However, biosensors are limited to the analysis of small sample volumes, and pre-concentration steps are necessary to reach the low sensitivity levels of few bacteria per mL required in the analysis of real clinical, industrial or environmental samples. Many platforms already exist where bacterial detection and separation/accumulation systems are integrated in a single platform, but they have not been compiled and critically analysed. This review reports on most recent advances in bacterial concentration/detection platforms with emphasis on the concentration strategy. Systems based on five concentration strategies, i.e. centrifugation, filtration, magnetic separation, electric separation or acoustophoresis, are here presented and compared in terms of processed sample volume, concentration efficiency, concentration time, ability to work with different types of samples, and integration potential, among others. The critical evaluation presented in the review is envision to facilitate the development of future platforms for fast, sensitive and in situ bacterial detection in real sample.
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•Biosensors are not sensitive to low bacterial numbers legally established.•Many bacterial concentration strategies exist that are compatible with biosensors.•Strategies have integration, operation and performance advantages/disadvantages.•Current and future tendencies on bacterial concentration are critically discussed.
is a pathogenic bacterium, ubiquitous in freshwater environments and able to colonise man-made water systems from which it can be transmitted to humans during outbreaks. The prevention of such ...outbreaks requires a fast, low cost, automated and often portable detection system. In this work, we present a combination of sample concentration, immunoassay detection, and measurement by chronoamperometry. A nitrocellulose microfiltration membrane is used as support for both the water sample concentration and the
immunodetection. The horseradish peroxidase enzymatic label of the antibodies permits using the redox substrate 3,3',5,5'-Tetramethylbenzidine to generate current changes proportional to the bacterial concentration present in drinking water. Carbon screen-printed electrodes are employed in the chronoamperometric measurements. Our system reduces the detection time: from the 10 days required by the conventional culture-based methods, to 2-3 h, which could be crucial to avoid outbreaks. Additionally, the system shows a linear response (R
value of 0.99), being able to detect a range of
concentrations between 10
and 10
cfu·mL
with a detection limit (LoD) of 4 cfu·mL
.
Waterborne pathogens are a global concern for public health worldwide. Despite continuing efforts to maintain water safety, water quality is still affected by deterioration and pollution. Legionella ...pneumophila colonizes man-made water systems and can infect humans causing Legionnaire's disease (LD), pneumonia. The prevention of LD is a public health issue and requires specific systems to control and detect these microorganisms. Culture plate is the only technique currently approved, but requires more than 10 days to obtain results. A rapid test that inform in hours about the presence of Legionella pneumophila in water samples will improve the control of this pathogen colonization. In order to control colonization by L. pneumophila we developed a membrane filter method to capture and immunodetect this microorganism in water samples. This membrane filter is used to retain the bacteria using a nitrocellulose disc inside a home-made cartridge. Subsequently we perform the immunodetection of the bacteria retained in the nitrocellulose (blocking, antibody incubation, washings and developing). On comparing our test with the gold-standard, the most important finding is the considerably reduction in time maintaining the same detection limit. This rapid test is easily automated for L. pneumophila detection allowing a comprehensive surveillance of L. pneumophila in water facilities and reducing the variability in the analyses due to the low need for manipulation. Moreover, corrective measures may be applied the same day of the analysis.
This method considerably reduces the detection time compared with the conventional, gold-standard detection culture method that requires more than 10 days, being decisive to prevent outbreaks.
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•The prevention of Legionnaire's Disease is a public health issue.•A rapid test to determine the presence of pathogens in water samples is needed.•We developed a membrane filter method to capture and immunodetect this microorganism.•This method reduces the detection time from 10 days to two hours.•Corrective measures may be applied the same day of the analysis, avoiding outbreaks.
Microbial detection is crucial for the control and prevention of infectious diseases, being one of the leading causes of mortality worldwide. Among the techniques developed for bacterial detection, ...those based on metabolic indicators are progressively gaining interest due to their simplicity, adaptability, and, most importantly, their capacity to differentiate between live and dead bacteria. Prussian blue (PB) may act as a metabolic indicator, being reduced by bacterial metabolism, producing a visible color change from blue to colorless. This molecule can be present in two main forms, namely, the soluble and the insoluble, having different properties and structures. In the current work, the bacterial-sensing capacity of soluble and insoluble PB will be tested and compared both in suspensions as PB-NPs and after deposition on transparent indium tin oxide-poly(ethylene terephthalate) (ITO-PET) electrodes. In the presence of live bacteria, PB-NPs are metabolized and completely reduced to the Prussian white state in less than 10 h for soluble and insoluble forms. However, when electrodeposited on ITO-PET substrates, less than 1 h of incubation with bacteria is required for both forms, although the soluble one presents faster metabolic reduction kinetics. This study paves the way to the use of Prussian blue as a metabolic indicator for the early detection of bacterial infection in fields like microbial diagnostics, surface sterilization, food and beverage contamination, and environmental pollution, among others.
A system based on near-infrared (NIR) spectroscopy has been developed for the in-line control of the composition of the milk used as raw material for yoghurt production to control the content of ...protein and fat in the final product, and, therefore, to reduce variability in the production process. Firstly, after selecting the appropriate method for preprocessing NIR data, Partial Least Squares Regression models were built to predict fat and protein content in milk, obtaining good performances. The variance explained of y-block in prediction (R2P) was 0.99 and 0.80, while the Root Mean Square Error of Prediction (RMSEP), was 0.26 and 0.16 for fat and protein, respectively. With those models, it was possible to determine the fat and protein contents in milk in real time, and therefore, the quantity of milk powder and cream added in the manufacturing process of yoghurt could be readjusted. The presented strategy allows the improvement of the homogeneity of the final product, reducing the variability of the nutritional values in more than 70% with respect to the traditional recipe, and also meet the target values according to yoghurt producers for fat and protein content, that is, 10% of fat and 5% of protein.
•Application of NIR spectroscopy to improve in-line manufacture process of yoghurts.•Using PLSR to quantify in-line fat and protein content in milk samples.•New methodology based on NIR and PLSR to act in the production line of yoghurts.
The microbial quality of water is a key aspect to avoid environmental and public health problems. The low pathogen concentration needed to produce a disease outbreak makes it essential to process ...large water volumes and use sensitive and specific methods such as immunoassays for its detection. In the present work, we describe the development of a device based on microfiltration membranes to integrate the concentration and the immunodetection of waterborne bacteria. A microfiltration membrane treatment protocol was designed to reduce the non-specific binding of antibodies, for which different blocking agents were tested. Thus, the proof of concept of the microbial detection system was also carried out using
Escherichia coli
as the bacterial pathogen model.
E. coli
suspensions were filtered through the membranes at 0.5 mL s
−1
, and the
E. coli
concentration measurements were made by absorbance, at 620 nm, of the resultant product of the enzymatic reaction among the horseradish peroxidase (HRP) bonded to the antibody, and the substrate 3,3′,5,5′-tetramethylbenzidine (TMB). The results showed that the homemade concentration system together with the developed membrane treatment protocol is able to detect
E. coli
cells with a limit of detection (LoD) of about 100 CFU in 100 mL.
Graphical abstract
Scheme of the integrated method of concentration and immunodetection of bacteria
Cobalt(III) and chromium(III) salophen chloride complexes were synthesized and tested for the cycloaddition of carbon dioxide (CO2) with epoxides to obtain cyclic carbonates. The cat1, cat2, cat4, ...and cat5 complexes presented high catalytic activity without cocatalysts and are solvent-free at 100 °C, 8 bar, and 9 h. At these conditions, the terminal epoxides (1a–1k) were successfully converted into the corresponding cyclic carbonates with a maximum conversion of ∼99%. Moreover, cat5 was highlighted due to its capability of opening internal epoxides such as limonene oxide (1l) with a 36% conversion to limonene carbonate (2l), and from cyclohexene oxide (1m), cyclic trans-cyclohexene carbonate (2m) and poly(cyclohexene carbonate) were obtained with 15% and 85% selectivity, respectively. A study of the coupling reaction mechanism was proposed with the aid of electrospray ionization mass spectrometry (ESI-MS) analysis, confirming the single-component behavior of the complexes through their ionization due to epoxide coordination. In addition, crystallographic analysis of cat1 single crystals grown in a saturated solution of pyridine helped to demonstrate that the substitution of chloride ion by pyridine ligands to form an octahedral coordination occurs (Py-cat1), supporting the proposed mechanism. Also, a recyclability study was performed for cat5, and a total turnover number of 952 was obtained with only minor losses in catalytic activity after five cycles.
8-Formyl-7-hydroxycoumarin (A) and their derived salophen-type organocatalysts L1, L2, and L3 were used for the synthesis of cyclic carbonates from carbon dioxide (CO2) and epoxides under solvent-, ...halide-, and metal-free conditions. According to previous optimization tests, L1 and L2 had the best catalytic activity presenting 89 and 92% conversion toward the synthesis of 3-chloropropylene carbonate (2c) using 8 bar CO2, 100 °C at 9 h. Therefore, they were used as organocatalysts to complete the catalytic screening with 11 terminal epoxides (1a–k) exhibiting the highest TOF values of 20 and 22 h–1 using 1c and 1b, respectively. Similarly, they were tested with an internal epoxide, such as cyclohexene oxide (1l) exhibiting 72% conversion, becoming the first salophen organocatalyst to obtain cis-cyclohexane carbonate (2l) in the absence of a cocatalyst. In addition, a reaction mechanism was proposed for the formation of cyclic carbonates based on experimental data and computational techniques; these contributed in establishing a probable role of CO2 pressure along the catalysis and the hydrogen bonds that favor the stabilization of the different intermediates of the reaction.
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