A self-sampling-and-flow biosensor for continuous monitoring

A self-sampling-and-flow biosensor was fabricated by sandwiching a nitrocellulose strip on the working electrode side of the double-sided microporous gold electrodes and a wicking pad on the counter electrode side. The double-sided microporous electrodes were formed by plasma sputtering of gold on a porous nylon substrate. Sample was taken up to the enzyme-immobilized working electrode by the capillary action of the front nitrocellulose strip dipped into the sample solution, analyzed electrochemically at the enzyme-immobilized electrode, and diffuses out to the backside wicking pad through the micropores of the electrodes, constituting a complete flow cell device with no mechanical liquid-transporting device. Biosensor was formed by co-immobilizing the glucose oxidase and electron transfer mediator (ferrocene acetic acid) on the thioctic acid self-assembled monolayer-modified working electrode. A typical response time of the biosensor was about 5 min with the sensitivity of 2.98 nA/mM glucose, providing linear response up to 22.5 mM. To demonstrate the use of self-sampling-and-flow biosensor, the consumption rate of glucose in the presence of yeast was monitored for five days.