Investigation of Polyurethane Matrix Membranes for Salivary Nitrate ISFETs to Prevent the Drift

Abstract

We have investigated human-stress monitoring by making use of salivary nitrate, which can be a candidate for stress markers, with ion-selective field-effect transistors (ISFETs). ISFETs are suitable for on-site single-drop analysis of salivary nitrate within 10 s. However, when ISFETs are used for salivary nitrate, ISFETs have a problem that is called the initial drift. The initial drift makes accurate nitrate monitoring difficult. Thus, the purpose of this study is to prevent the initial drift and to search for a new, simple polymer to possess a better performance of sensor responses than conventional matrix membranes, such as PVC. In this research, we investigated ISFETs using specific matrix membranes, for example KP-13, Pellethane®­­, and P7281-PU. The initial drift was evaluated from the fluctuations of the response values generated by the ISFETs when immersed in saliva or aqueous solution. As a result, P7281-PU showed a prevention effect on the initial drift, both in the whole saliva and in various solutions. Furthermore, the cause of drift may be H+ diffusion, and the drift prevention effect of P7281-PU may be affected by urethane bond capturing H+ in the ion-selective membrane. This result suggests that a continuous nitrate monitoring is feasible and may be applied to wearable sensors.

Investigation of Drift in Polyurethane Matrices for Salivary Nitrate Ion-selective Field-effect Transistors

“…5, where the x-axis is the logarithm of the nitrate activity and the y-axis is the potential difference. NO 3 − -ISFETs based on PVC, P7276-PU, P7277-PU, P7286-PU, P7293-PU, and P7281-PU showed approximately the same linear response range from 10 −5 to 10 −1 mol/L (M) (29) and had close to the theoretical slope response of 59.2 mV/decade at 25 ℃ according to the Nernst equation. The concentration range of salivary nitrate is approximately 10 −4 to 10 −3 M. (33) Therefore, these ISFETs may be suitable for the determination of salivary nitrate.…”

“…7(e), 7(g), and 7(h), respectively] were considerably different from that of the membrane including PVC [Fig. 7 These results cannot be described in terms of our previous hypothesis (29) that H + or OH − ions are captured in urethane bonds to prevent a pH change in the gate and the membrane interface of We consider that the NO 3 − -ISFETs based on the polyurethane matrix are controlled by the hydrolysis of the urethane bonds. The pH change in the aqueous layer between the gate and the ISM is prevented because the urethane bonds are hydrolyzed by the diffused H + or OH − .…”

“…We previously reported on drift and the hypothesis that the ISM on ISFETs composed of P7281-PU prevents drift. (29) ISFETs based on the reported polyurethane (P7281-PU) showed a more stable response than those based on conventional PVC and other polyurethane-based matrices (Pellethane ® and KP-13).…”

“…(Color) Hypothesized urethane bond capture of H + and OH − by hydrogen bonds (in whole saliva) from our previous report. (29) and P7281-PU) were purchased from Polymer Source (Dorval, QC, Canada). The P72XX-PU series were synthesized from 4,4'-methylenebis(phenyl isocyanate) (MDI), poly(propylene oxide) (PPO), and Bisphenol A ethoxylate (BPAEO).…”

Fully Transparent, Ultrathin Flexible Organic Electrochemical Transistors with Additive Integration for Bioelectronic Applications

“…The drain and gate voltages ( V DS and V GS ) were constantly maintained at −0.8 and 0 V, respectively, while the drain current ( I DS ) was measured by increasing the nitrate ion concentration in deionized water or saline solution (15 m m NaCl aq.). A nitrate‐selective electrode [ 44 ] was used for gate voltage application.…”