Nobuyasu Hori

An Integrated Glucose Sensor with an All-Solid-State Sodium Ion-Selective Electrode for a Minimally Invasive Glucose Monitoring System

We developed a minimally invasive glucose monitoring system that uses a microneedle to permeate the skin surface and a small hydrogel to accumulate interstitial fluid glucose. The measurement of glucose and sodium ion levels in the hydrogel is required for estimating glucose levels in blood; therefore, we developed a small, enzyme-fixed glucose sensor with a high-selectivity, all-solid-state, sodium ion-selective electrode (ISE) integrated into its design. The glucose sensor immobilized glucose oxidase showed a good correlation between the glucose levels in the hydrogels and the reference glucose levels (r > 0.99), and exhibited a good precision (coefficient of variation = 2.9%, 0.6 mg/dL). In the design of the sodium ISEs, we used the insertion material Na0.33MnO2 as the inner contact layer and DD16C5 exhibiting high Na+/K+ selectivity as the ionophore. The developed sodium ISE exhibited high selectivity (\( \log \,k^{pot}_{Na,K} = -2.8\)) and good potential stability. The sodium ISE could measure 0.4 mM (10−3.4 M) sodium ion levels in the hydrogels containing 268 mM (10−0.57 M) KCl. The small integrated sensor (ϕ < 10 mm) detected glucose and sodium ions in hydrogels simultaneously within 1 min, and it exhibited sufficient performance for use as a minimally invasive glucose monitoring system.

Gold thin layer-assisted DNA immobilization for photoelectrochemical DNA sensor

Electrochemical biosensors have been developed due to its potential to be a compact medical diagnostic devise with high sensitivity. So far we have developed a photoelectrochemical DNA sensor using transparent semiconductor films such as tin-doped indium oxide (ITO), in which probe DNAs that captures fluorescence-labeled target DNAs were immobilized on semiconductor via silane coupling reagent such as aminopropyl triethoxy silane (APTES). Here we aimed to provide an effective DNA immobilization technique using gold thin layer in order to obtain higher photocurrents to noise ratio. Gold thin film (1nm thickness) deposited over semiconductor electrode serves as a substrate to immobilize a thiol-modified DNA (24bases) at its end that can capture fluorescence-labeled target DNA by hybridization. The sensitivity in this method was approximately 4times higher than that in APTES.