Development and Optimization of a Highly Sensitive Sensor to Quinine-Based Saltiness Enhancement Effect.

The saltiness enhancement effect can be produced by adding specific substances to dietary salt (sodium chloride). This effect has been used in salt-reduced food to help people forge healthy eating habits. Therefore, it is necessary to objectively evaluate the saltiness of food based on this effect. In a previous study, sensor electrodes based on lipid/polymer membrane with Na+ ionophore have been proposed to quantify the saltiness enhanced by branched-chain amino acids (BCAAs), citric acid, and tartaric acid. In this study, we developed a new saltiness sensor with the lipid/polymer membrane to quantify the saltiness enhancement effect of quinine by replacing a lipid that caused an unexpected initial drop in the previous study with another new lipid. As a result, the concentrations of lipid and ionophore were optimized to produce an expected response. Logarithmic responses have been found on both NaCl samples and quinine-added NaCl samples. The findings indicate the usage of lipid/polymer membranes on novel taste sensors to evaluate the saltiness enhancement effect accurately.

Electrical Properties of Two Types of Membrane Component Used in Taste Sensors.

The lipid phosphoric acid di-n-decyl ester (PADE) has played an important role in the development of taste sensors. As previously reported, however, the concentration of PADE and pH of the solution affected the dissociation of H+, which made the measurement results less accurate and stable. In addition, PADE caused deterioration in the response to bitterness because PADE created the acidic environment in the membrane. To solve these problems, our past study tried to replace the PADE with a completely dissociated substance called tetrakis [3,5-bis (trifluoromethyl) phenyl] borate sodium salt dehydrate (TFPB) as lipid. To find out whether the two substances can be effectively replaced, it is necessary to perform an in-depth study on the properties of the two membranes themselves. In this study, we fabricated two types of membrane electrodes, based on PADE or TFPB, respectively, using 2-nitrophenyl octyl ether (NPOE) as a plasticizer. We measured the selectivity to cations such as Cs+, K+, Na+ and Li+, and also the membrane impedance of the membranes comprising PADE or TFPB of the different concentrations. As a result, we found that any concentration of PADE membranes always had low ion selectivity, while the ion selectivity of TFPB membranes was concentration-dependent, showing increasing ion selectivity with the TFPB concentrations. The ion selectivity order was Cs+>K+>Na+>Li+. The hydration of ions was considered to participate in this phenomenon. In addition, the membrane impedance decreased with increasing PADE and TFPB concentrations, while the magnitudes differed, implying that there is a difference in the dissociation of the two substances. The obtained results will contribute to the development of novel receptive membranes of taste sensors.

Pyridone-containing phenalenone-based photosensitizer working both under light and in the dark for photodynamic therapy.

Photosensitizer attracts great attentions and has potential applications in cancer treatment. We developed here a novel pyridone-containing phenalenone-based (PPN-PYR) photosensitizer with excellent singlet oxygen generating ability. Upon light irradiation, PPN-PYR can produce singlet oxygen and transform to its endoperoxide form which in turn release singlet oxygen via thermal cycloreversion at dark. The ability of PPN-PYR to generate reactive oxygen species (ROS) in cell culture and induce corresponding apoptosis both at dark and under light was demonstrated. The efficient PDT performance of PPN-PYR was further verified on cancer cell in vitro. Our study indicate that PPN-PYR can alleviate tumor hypoxia problem and enhance the availability of intermittent photodynamic therapy.