Determination of Low Concentrations of Mercury Based on the Electrodeposition Time.

Soil plays a crucial role in human health through its impact on food and habitation. However, it often contains toxic heavy metals, with mercury being particularly hazardous when methylated. Currently, high-sensitivity, rapid detection of mercury is achievable only through electrochemical measurements. These measurements require pretreatment of the soil sample and the preparation of a calibration curve tailored to the sample's condition. In this study, we developed a method to determine the environmental standard value of mercury content in soil by significantly reducing the pretreatment process. Our approach involves analyzing current peaks from electrodeposition times using specific electrodes and solvent settings. This method demonstrates low error rates under low concentration conditions and can detect mercury levels as low as 0.5 ppb in soil leachate and reagent dilution series. This research facilitates the determination of low mercury concentrations in solutions containing various soil micro-compounds without the need for calibration curves.

Quantification of caffeine in coffee cans using electrochemical measurements, machine learning, and boron-doped diamond electrodes.

Electrochemical measurements, which exhibit high accuracy and sensitivity under low contamination, controlled electrolyte concentration, and pH conditions, have been used in determining various compounds. The electrochemical quantification capability decreases with an increase in the complexity of the measurement object. Therefore, solvent pretreatment and electrolyte addition are crucial in performing electrochemical measurements of specific compounds directly from beverages owing to the poor measurement quality caused by unspecified noise signals from foreign substances and unstable electrolyte concentrations. To prevent such signal disturbances from affecting quantitative analysis, spectral data of voltage-current values from electrochemical measurements must be used for principal component analysis (PCA). Moreover, this method enables highly accurate quantification even though numerical data alone are challenging to analyze. This study utilized boron-doped diamond (BDD) single-chip electrochemical detection to quantify caffeine content in commercial beverages without dilution. By applying PCA, we integrated electrochemical signals with known caffeine contents and subsequently utilized principal component regression to predict the caffeine content in unknown beverages. Consequently, we addressed existing research problems, such as the high quantification cost and the long measurement time required to obtain results after quantification. The average prediction accuracy was 93.8% compared to the actual content values. Electrochemical measurements are helpful in medical care and indirectly support our lives.

Development of an Interactive Touchless Technology Based on Static-Electricity-Induced Luminescence.

Touchless technology has garnered significant interest in recent years because of its effectiveness in combating infectious diseases such as the novel coronavirus (COVID-19). The goal of this study was to develop an inexpensive and high-precision touchless technology. A base substrate was coated with a luminescent material that emitted static-electricity-induced luminescence (SEL), and it was applied at high voltage. An inexpensive web camera was used to verify the relationship between the non-contact distance to a needle and the applied-voltage-triggered luminescence. The SEL was emitted at 20-200 mm from the luminescent device upon voltage application, and the web camera detected the SEL position with an accuracy of less than 1 mm. We used this developed touchless technology to demonstrate a highly accurate real-time detection of the position of a human finger based on SEL.

Demonstration of static electricity induced luminescence.

Can we visualise static electricity, which everyone in the world knows about? Since static electricity is generated by contact or peeling, it may be a source of malfunction of electronic components, whose importance is steadily increasing, and even cause explosion and fire. As static electricity is invisible, makeshift measures of static electricity are taken on various surfaces; there is also a common view that it is hard to take effective measures. Here we present a specific luminescent material, SrAl2O4: Eu2+, which emits light at excitation by an electrostatic charge in the air. Till now, in the interaction between electricity and luminescent materials, it was considered that emission of light is enabled by accelerated particles colliding with the luminescent material in vacuo. There have been no reports on luminescent materials being responsive to low-energy electrostatic charges under atmospheric pressure. Using SrAl2O4: Eu2+ luminescent material discovered by us, we succeeded for the first time in static electricity visualisation in the form of green light. In addition to the fact that such static electricity induced luminescence assists in solving electrostatic-related problems in the industry, it also provides a new measurement method that facilitates the observation of previously invisible electric charges in the air.

Detection of ionized air using a photonic-crystal nanocavity excited by broadband light from a superluminescent diode.

It has been shown that silicon photonic crystal nanocavities excited by spectrally narrow light can be used to detect ionized air. Here, to increase the range of possible applications of nanocavity-based sensing, the use of broadband light is considered. We find that the use of a superluminescent diode (SLD) as an excitation source enables a more reproducible detection of ionized air. When our photonic-crystal nanocavity is exposed to ionized air, carriers are transferred to the cavity and the light emission from the cavity decreases due to free carrier absorption. Owing to the broadband light source, the resonance wavelength shifts caused by the carriers in this system (for example, due to temperature fluctuations) do not influence the emission intensity. SLD-excited cavities could be useful to determine the density of ions in air quantitatively.

System for Visualizing Surface Potential Distribution to Eliminate Electrostatic Charge.

A mixture of positive and negative static charges exists in the same plane on an insulator surface, and this can cause production quality problems at manufacturing sites. This study developed a system with a vibration array sensor to rapidly measure the surface potential distribution of an object in a non-contact and non-destructive manner and with a high spatial resolution of 1 mm. The measurement accuracy differed greatly depending on the scanning speed of the array sensor, and an optimum scanning speed of 10 mm/s enabled rapid measurements (within <3 s) of the surface potential distribution of a charged insulator (area of 30 mm × 30 mm) with an accuracy of 15%. The relationship between charge and dust on the surface was clarified to easily visualize the uneven static charges present on it and thereby eliminate static electricity.

Detection of negatively ionized air by using a Raman silicon nanocavity laser.

The performance of a Raman silicon laser based on a high quality-factor nanocavity depends on the degree of free-carrier absorption, and this characteristic may be useful for certain applications. Here we demonstrate that laser oscillation in a Raman silicon nanocavity laser stops abruptly after an exposure to a weak flux of negatively ionized air for a few seconds. Spectral measurements reveal that the laser interruption is mainly caused by the transfer of extra electrons from the negatively ionized air molecules to the silicon nanocavity. These electrons affect the efficiency of the Raman laser by free carrier absorption. We find that the laser output gradually recovers as the extra electrons escape from the nanocavity and confirm that such a detection of ionized air is repeatable. These results show that a Raman silicon nanocavity laser can be used for the detection of ionized air with a high spatial resolution.