In this study, electrochemical detection of viable bacterial cells was performed using a tetrazolium salt, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), which was converted to an insoluble and redox active formazan compound in viable microbial cells. The insolubility of this formazan was effectively exploited as a surface-confined redox event. An indium-tin-oxide electrode was applied to a microbial suspension that had been incubated with MTT and was heated to dry for the extraction and adsorption of formazan. Drying led to the appearance of a distinctive voltammetric oxidation peak at +0.1 V vs Ag|AgCl, the magnitude of which was successfully correlated to the number of viable microbes in the suspension. Thus, the electrochemical detection of formazan was effectively coupled with the thermal lysis of microbes. It is also noteworthy that this lysis-adsorption technique was highly selective to the hydrophobic formazan molecule due to the removal of hydrophilic cell components during equilibration in a phosphate buffer before voltammetric measurement. This technique was capable of detecting microbes above 2.8 × 10 CFU mL and required only a 1 h incubation. The results of this study indicate that the sensitivity of the present technique is up to 10 000-fold higher than that of MTT colorimetry. The higher sensitivity was mainly ascribed to the concentration of the microbially produced formazan on the electrode by thorough desiccation of the bacterial suspension.

Shewanella oneidensis MR-1 is a facultative anaerobic bacterium that is known to transfer electrons generated during metabolism to various metal ions and produce nanoparticles on the bacterial surface. In this study, we tracked the formation of gold nanoparticles (Au NPs) on the S. oneidensis cell surfaces and investigated the roles of membrane proteins and extracellular polysaccharides in this process by spectrometry, zeta potential analysis, and electron microscopy.

Specific identification of enterohemorrhagic Escherichia coli was achieved using microspheres coated with overoxidized polypyrrole. The microspheres are well dispersed in aqueous media, and they specifically, spontaneously, and efficiently bind E. coli O157:H7 through surface area effects. In addition, we found that light-scattering by a single microsphere depended linearly on the number of bound cells.

Background Clinicians, researchers, and patients alike would greatly benefit from more accessible and inexpensive biomarkers for neural β-amyloid (Aβ). We aimed to assess the performance of fully automated plasma Aβ immunoassays, which correlate significantly with immunoprecipitation mass spectrometry assays, in predicting brain Aβ status as determined by visual read assessment of amyloid positron emission tomography (PET). Methods The plasma Aβ42/Aβ40 ratio was measured using a fully automated immunoassay platform (HISCL series) in two clinical studies (discovery and validation studies). The discovery and validation sample sets were retrospectively and randomly selected from participants with early Alzheimer’s disease (AD) identified during screening for the elenbecestat Phase 3 program. Results We included 197 participants in the discovery study (mean [SD] age 71.1 [8.5] years; 112 females) and 200 in the validation study (age 70.8 [7.9] years; 99 females). The plasma Aβ42/Aβ40 ratio predicted amyloid PET visual read status with areas under the receiver operating characteristic curves of 0.941 (95% confidence interval [CI] 0.910–0.973) and 0.868 (95% CI 0.816–0.920) in the discovery and validation studies, respectively. In the discovery study, a cutoff value of 0.102 was determined based on maximizing the Youden Index, and the sensitivity and specificity were calculated to be 96.0% (95% CI 90.1–98.9%) and 83.5% (95% CI 74.6–90.3%), respectively. Using the same cutoff value, the sensitivity and specificity in the validation study were calculated to be 88.0% (95% CI 80.0–93.6%) and 72.0% (95% CI 62.1–80.5%), respectively. Conclusions The plasma Aβ42/Aβ40 ratio measured using the HISCL series achieved high accuracy in predicting amyloid PET status. Since our blood-based immunoassay system is less invasive and more accessible than amyloid PET and cerebrospinal fluid testing, it may contribute to the diagnosis of AD in routine clinical practice.

Bacterial cells possessing a certain zeta potential are immobilized by electrochemical deposition within conducting polymers such as poly­(3,4-ethylenedioxythiophene) (PEDOT) and polypyrrole (PPy). These conducting polymers serve as a biocompatible matrix for trapping bacteria on an indium–tin–oxide (ITO)-coated glass substrate. The biological functions of bacteria were not affected by the chemical structure and electrical conductivity of the matrix. The viability of the bacteria on the ITO glass was monitored by dark-field microscopy. The cell density of Escherichia coli increased logarithmically during incubation in nutrient broth medium, leading to definitive formation of a biofilm on PPy. The facultative E. coli anaerobe sustains metabolism under aerobic and anaerobic conditions, but proliferates more extensively in the presence of oxygen. The conducting PPy film also facilitates electrochemical evaluation of the respiratory activity of bacterial cells and establishes that facultative anaerobic and aerobic bacteria exhibit similar respiratory activities under aerobic conditions.