Patent ID: 8735170

Claim:
A method for measuring a concentration of a first antigen contained in a test solution, by using an apparatus for measuring a concentration of a biogenic substance, the method comprising the following steps (a) to (h): step (a) of preparing the apparatus, the apparatus comprising: a cell comprising therein a first region, a second region, and a space for retaining the test solution; a light source emitting a polarized light to the cell; a photoreceiver for receiving light which has passed through the cell along an optical axis that intersects the first region, the second region, and the space for retaining the test solution, wherein a plurality of first metallic nanorods each having a first antibody on a surface thereof are immobilized on the first region, a plurality of second metallic nanorods each having a blocking substance on a surface thereof are immobilized on the second region, the long axes of the plurality of first metallic nanorods are aligned in the same direction, the long axes of the plurality of second metallic nanorods are aligned in the same direction, the long-axis direction of the first metallic nanorods is orthogonal to the long-axis direction of the second metallic nanorods, and at least either one of the light source or the cell is rotatable about the optical axis; step (b) of supplying the test solution to the space for retaining the test solution to allow the first antigen to be bound to the first antibody and not to allow the first antigen to be bound to the blocking substance; step (c) of allowing polarized light parallel to the long-axis direction of the plurality of first metallic nanorods to pass through the cell along the optical axis to receive resultant first light with the photoreceiver; step (d) of calculating an amount Δλa of shift of a localized surface plasmon resonant wavelength caused by binding the first antigen to the antibody, on the basis of the first light; step (e) of rotating at least either one of the light source or the cell such that the polarized light is parallel to the long-axis direction of the plurality of second metallic nanorods; step (f) of allowing polarized light parallel to the long-axis direction of the plurality of second metallic nanorods to pass through the cell along the optical axis to receive resultant second light with the photoreceiver; step (g) of calculating an amount Δλb of shift of the localized surface plasmon resonant wavelength caused by supplying the test solution to the space for retaining the test solution, on the basis of the second light; and step (h) of calculating the concentration of the first antigen on the basis of a calibration curve and a difference represented by the following equation: the difference=Δλ a−Δλb.