Disposable biosensor using biochemo-mechanical gel
We developed a disposable biosensor which works by converting the volume change of a biochemo-mechanical gel into the change in liquid column length. It consists of a small compartment for incorporating the gel, a flow channel with a filled dye solution, and a polydimethylsiloxane (PDMS) diaphragm by which the gel and the dye solution were separated. A lightly cross-linked N-isopropylacrylamide (NIPAAm)/acrylic acid (AA) copolymer gel with immobilized glucose oxidase was used as a sensing element. It was found that a change in the gel volume caused by the immobilized enzyme reaction was accurately converted into a change of the column length (?l) with the help of the PDMS diaphragm. By use of a cylindrical gel (diameter ~2 and thickness ~1 mm), time curve of ?l varied depending upon glucose concentration over a range of 0.2 - 50 mM; in particular, it is of importance that semi-logarithmic plots of ?l (in mm) against glucose concentration (in mM) can be used as a calibration curve. For glucose solutions of mM order, 1 min was enough to determine the concentrations, while 10 min was required for concentrations of μM order. When the measurement time was limited within 10 min, the lower detection limit was 200 μM. The response was affected by buffering capacity of samples, but this was controllable through reduction of the sample volume.
Fig. 1 Outline of our glucose sensing device. Construction of the device is shown in (a). Also shown in (b) and (c) is a change of column liquid length caused by the shrinking of gel. The dimensions of the device are 8 mm X 28 mm X 1.6 mm.
Fig. 2 Calibration curves for our glucose sensor. Each ?l was obtained as a function of glucose concentration at 37 °C and at measuring times indicated in the figure. Buffer-free glucose solutions were used as the standard sample. The curves are drawn by the least squares fitting for the data points.