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

Abstract

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.

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

“…The results were separated into two groups: the ones over 4.5 mg and the ones below 4.5 mg showed almost the same response respectively. The response of TFPB membrane is the same as reported [ 37 ]. This result has shown that the Na + ionophore can dramatically improve the sensitivity of NaCl.…”

“…This is because of the partial dissociation property of PADE [ 33 ]. Further investigation on the dissociation property of PADE and tetrakis[3,5-bis(trifluoromethyl)phenyl]borate sodium salt dehydrate (TFPB) has been done in [ 37 ], where membranes made from these two substances have shown differences on ion selectivity; membranes made from PADE had low ion selectivity while high ion selectivity had been found in TFPB membranes.…”

Recent Advances in Bitterness-Sensing Systems

“…Thus, E-tongues can identify and distinguish five basic tastes at the same time. Typically, the selectivity of the working electrodes can be regulated by changing the categories and concentrations of the lipids, polymers, and other materials used [ 49 , 50 , 51 ]. Electrochemical measurements include potentiometry, amperometry, voltammetry, and impedance spectroscopy [ 52 , 53 , 54 ].…”

Construction, Working, and Applications of E-Tongue: A Versatile Tool for All Tastes?

“…The first ever working E-tongue was developed by Hidekazu Ikezaki and Kiyoshi Toko at Kyushu University in Japan in 1989. Since then, this technology has come a long way and with the introduction of deep learning it only continues to grow [3,4].…”