Electrochromogenic Detection of Live Bacteria Using Soluble and Insoluble Prussian Blue

Periodic Stratification of Colloids in a Liquid Phase Produced by a Precipitation Reaction and Gel Swelling

Pattern formation is a frequent phenomenon occurring in animate and inanimate systems. The interplay between the mass transport of the chemical species and the underlying chemical reaction networks generates most patterns in chemical systems. Periodic precipitation is an emblematic example of reaction-diffusion patterns, in which the process generates a spatial periodic structure in porous media. Here, we use the dormant reagent method to produce colloidal particles of Prussian blue (PB) and PB analogues at the liquid-gel interface. The generated particles produced a stable periodic stratification pattern in time in the liquid phase placed on top of the solid hydrogel. The phenomenon is governed by periodic swelling of the gel driven by the osmotic stress and stability of the formed particles. To illustrate the phenomenon, we developed an extended reaction-diffusion model, which incorporated the gel swelling and sedimentation effect of the formed colloids and could qualitatively reproduce the pattern formation in the liquid phase.

Rapid Detection and Identification of Vancomycin-Sensitive Bacteria Using an Electrochemical Apta-Sensor

In order to combat the complex and diverse infections caused by bacteria, it is essential to develop efficient diagnostic tools. Current techniques for bacterial detection rely on laborious multistep procedures, with high costs and extended time of analysis. To overcome these limitations, we propose here a novel portable electrochemical biosensor for the rapid detection and identification of Gram-positive bacteria that leverages the recognition capabilities of vancomycin and aptamers. A vancomycin-modified screen-printed carbon electrode was used to selectively capture Gram-positive bacteria susceptible to this antibiotic. Electrochemical impedance spectroscopy and scanning electron microscopy demonstrated that capture was achieved in 10 min, with a limit of detection of only 2 CFU/mL. We then tested the device's potential for aptamer-based bacterial identification using Staphylococcus aureus and Bacillus cereus as the test strains. Specifically, electrodes with captured bacteria were exposed to species-specific aptamers, and the resulting changes in current intensity were analyzed using differential pulse voltammetry. When used directly in untreated milk or serum, the system was able to successfully identify a small amount of S. aureus and B. cereus (100 CFU/mL) in less than 45 min. This novel biosensor has the potential to serve as an invaluable tool that could be used, even by inexperienced staff, in a broad range of settings including clinical diagnostics, food safety analysis, environmental monitoring, and security applications.

Traditional and new proposals for environmental microbial indicators-a review

The continuous increment in world population coupled with the greatest natural resource consumption and waste generation has an enormous impact on the environment. To date, using biological indicators (bioindicators) to evaluate the biological quality of natural environments is very common. Nonetheless, selecting those suitable for each ecosystem or contaminant is one of the most important issues for environmental sciences. Bacteria and helminths are mainly related to fecal contamination, while antibiotic-resistant bacteria, fungi, viruses, and microalgae are organisms used to determine deteriorated ecosystems by diverse contaminants. Nowadays, each bioindicator is used as a specific agent of different contaminant types, but detecting and quantifying these bioindicator microorganisms can be performed from simple microscopy and culture methods up to a complex procedure based on omic sciences. Developing new techniques based on the metabolism and physiological responses of traditional bioindicators is shown in a fast environmental sensitivity analysis. Therefore, the present review focuses on analyzing different bioindicators to facilitate developing suitable monitoring environmental systems according to different pollutant agents. The traditional and new methods proposed to detect and quantify different bioindicators are also discussed. Their vital role is considered in implementing efficient ecosystem bioprospection, restoration, and conservation strategies directed to natural resource management.

Ultrasensitive bacterial sensing using a disposable all-in-one amperometric platform with self-noise cancellation

The early detection of very low bacterial concentrations is key to minimize the healthcare and safety issues associated with microbial infections, food poisoning or water pollution. In amperometric integrated circuits for electrochemical sensors, flicker noise is still the main bottleneck to achieve ultrasensitive detection with small footprint, cost-effective and ultra-low power instrumentation. Current strategies rely on autozeroing or chopper stabilization causing negative impacts on chip size and power consumption. This work presents a 27-μW potentiostatic-amperometric Delta-Sigma modulator able to cancel its own flicker noise and provide a 4-fold improvement in the limit of detection. The 2.3-mm² all-in-one CMOS integrated circuit is glued to an inkjet-printed electrochemical sensor. Measurements show that the limit of detection is 15 pA_rms, the extended dynamic range reaches 110 dB and linearity is R² = 0.998. The disposable device is able to detect, in less than 1h, live bacterial concentrations as low as 10² CFU/mL from a 50-μL droplet sample, which is equivalent to 5 microorganisms.

Portable Prussian Blue-Based Sensor for Bacterial Detection in Urine

Bacterial infections can affect the skin, lungs, blood, and brain, and are among the leading causes of mortality globally. Early infection detection is critical in diagnosis and treatment but is a time- and work-consuming process taking several days, creating a hitherto unmet need to develop simple, rapid, and accurate methods for bacterial detection at the point of care. The most frequent type of bacterial infection is infection of the urinary tract. Here, we present a wireless-enabled, portable, potentiometric sensor for E. coli. E. coli was chosen as a model bacterium since it is the most common cause of urinary tract infections. The sensing principle is based on reduction of Prussian blue by the metabolic activity of the bacteria, detected by monitoring the potential of the sensor, transferring the sensor signal via Bluetooth, and recording the output on a laptop or a mobile phone. In sensing of bacteria in an artificial urine medium, E. coli was detected in ~4 h (237 ± 19 min; n = 4) and in less than 0.5 h (21 ± 7 min, n = 3) using initial E. coli concentrations of ~10³ and 10⁵ cells mL^-1, respectively, which is under or on the limit for classification of a urinary tract infection. Detection of E. coli was also demonstrated in authentic urine samples with bacteria concentration as low as 10⁴ cells mL^-1, with a similar response recorded between urine samples collected from different volunteers as well as from morning and afternoon urine samples.

Determination of W(V) in WO3 Photochromism Using Localized Surface Plasmon Resonance of Ag Nanoparticles

A reversible color change of WO₃ has been widely studied to develop new energy-saving technologies such as smart windows, rewritable paper, and information displays. A blue coloration arises from the intervalence charge transfer between W(VI) and W(V), which is partially formed by the reduction of WO₃ under UV light or an applied voltage. This means that WO₃ has a mixed-valence state of W(V) and W(VI) upon the reduction. However, despite many studies for various applications, how many W(V) atoms are formed and contribute to the intervalence charge transfer (IVCT) transition remains unclear because W(V) formed in WO₃ cannot be determined quantitatively. We determined the amount of the photogenerated W(V) in an aqueous WO₃ colloidal solution containing ethylene glycol (EG) by observing the localized surface plasmon resonance (LSPR) peaks of Ag nanoparticles which were produced by a redox reaction between W(V) and Ag⁺. EG acted as a hole scavenger to suppress the recombination between the photogenerated holes and electrons. First, we explored the reaction condition where only the IVCT transition was observed under UV irradiation, and then it decreased in response to the increase in the LSPR peak in the dark. Under such a condition, the absorbance at 775 nm (A₇₇₅) due to the IVCT transition was observed after the UV irradiation for 30 s, and the absorbance at 410 nm (A₄₁₀) due to the LSPR absorption was obtained when A₇₇₅ completely disappeared in the dark. Experiments were performed at various UV intensities to confirm a proportional relationship between A₇₇₅ and A₄₁₀. Electron spin resonance measurements revealed that A₇₇₅ was proportional to the amount of W(V). Furthermore, Ag nanoparticles were synthesized by a polyol reduction method to obtain the relationship between the LSPR peak intensity and the Ag⁺ concentration, which was consumed for the formation of Ag. On the basis of all of these relationships, A₇₇₅ of 1.669 corresponded to 2.53 × 10^-4 mol dm^-3 W(V), which was estimated to be only 0.21% of 0.12 mol dm^-3 WO₃ used in this study, and the molar absorption coefficient for the IVCT transition between W(V) and W(VI) was evaluated to be 6.85 × 10³ dm³ mol^-1 cm^-1.

Simultaneous Optical Detection of Multiple Bacterial Species Using Nanometer-Scaled Metal-Organic Hybrids

This paper describes a simple strategy to identify bacteria using the optical properties of the nanohybrid structures (NHs) of polymer-coated metal nanoparticles (NPs). NHs, in which many small NPs are encapsulated in polyaniline particles, are useful optical labels because they produce strong scattered light. The light-scattering characteristics of NHs are strongly dependent on the constituent metal elements of NPs. Gold NHs (AuNHs), silver NHs (AgNHs), and copper NHs (CuNHs) produce white, reddish, and bluish scattered light, respectively. Moreover, unlike NPs, the color of the scattered light does not change even when NHs are aggregated. Introducing an antibody into NHs induces antigen-specific binding to cells, enabling the identification of bacteria based on light scattering. Multiple bacterial species adsorbed on the slide can be identified within a single field of view under a dark field microscope based on the color of the scattered light. Therefore, it is a useful development for safety risk assessments at manufacturing sites, such as those for foods, beverages, and drugs, and environmental surveys that require rapid detection of multiple bacteria.