Evaluation of Antibiotic Penicillin G Activities Based on Electrochemical Measurement of a Tetrazolium Salt

This study focused on the electrochemical properties of tetrazolium salts to develop a simple method for evaluating viable bacterial counts, which are indicators of drug susceptibility. Considering that the oxidized form of tetrazolium, which has excellent cell membrane permeability, changes to the insoluble reduced form formazan inside the cell, the number of viable cells was estimated based on the reduction current of the tetrazolium remaining in the bacterial suspension. Dissolved oxygen is an important component of bacterial activity. However, it interferes with the electrochemical response of tetrazolium. We estimated the number of viable bacteria in the suspension based on potential-selective current responses that were not affected by dissolved oxygen. Based on solubility, cell membrane permeability, and characteristic electrochemical properties of the tetrazolium salt 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium, we developed a method for rapidly measuring viable bacteria within one-fifth of the time required by conventional colorimetric methods for drug susceptibility testing.

Using Stretchable PPy@PVA Composites as a High-Sensitivity Strain Sensor To Monitor Minute Motion

With the rapid development of flexible and wearable electronic devices, research on high-sensitivity strain sensors has been attracting much attention. Here, glutaraldehyde is used as a cross-linking reagent to precross-link poly(vinyl alcohol); then FeCl₃·6H₂O is added into the precross-linked poly(vinyl alcohol) to obtain composite films of FeCl₃@PVA after gelatinization and freeze drying. Elastic conductive films of polypyrrole@poly(vinyl alcohol) (PPy@PVA) are prepared by immersing FeCl₃@PVA into a solution of pyrrole in acetonitrile and water to complete the polymerization in situ. The effects of the concentrations of glutaraldehyde and FeCl₃·6H₂O on the film's structure and properties have been studied in detail; the results show that the strain sensor prepared from the optimized film has excellent stretchability (strain up to 309.5%), mechanical property (tensile strength of 32.8 MPa), and relatively high sensitivity (gauge factor can reach 5.07 under 1.0% strain). It can be used to detect various tiny physiological signals, for example, detecting the number of pulse beats, bending of the knuckles at different frequencies, and recognizing the pronunciation of different words by vocal cord vibration. These good properties mean that this kind of PPy@PVA strain sensor has great application prospects in physiological monitoring.

Combined Blip and Staircase Response of Ascorbic Acid-Stabilized Copper Single Nanoparticle Collision by Electrocatalytic Glucose Oxidation

The current response of the collision of ascorbic acid-stabilized copper (Cu) single nanoparticles (NPs) on a gold (Au) ultramicroelectrode (UME) surface was observed by using an electrocatalytic amplification method. Here, the glucose oxidation electrocatalyzed by oxidized Cu NPs was used as the indicating reaction. In this system, the NP collision signals were obtained simultaneously by both direct particle electrolysis and electrocatalytic amplification. For example, when the applied potential was high enough for Cu NP oxidation, a blip response combined with a staircase response was observed as a current signal. The blip part in the single Cu NP collision signal indicates the self-oxidation of a Cu NP, and the staircase part indicates the steady-state electrocatalytic reaction by oxidized Cu NP.