Ambient light assisted spectroscopy

A device for detecting a target substance in a solution, comprising:

• a light source that processes and filters the ambient light to emit substantially monochromatic light;
• a sample container configured to contain the solution that contains one or more types of target substances, said solution having a refractive index different from a refractive index of said one or more types of target substances;
• a reference container containing no substance therein or a reference for the target substances;
• a substantially planar diffraction element optically coupled to the light source to receive the light originating from the light source, the diffraction element having a top surface and a bottom surface and having one or more of openings that are empty or filled with a dielectric to generate plasmon waves upon receipt of the light from the light source, the top surface of the diffraction element being configured to be in contact with the solution in the sample container and with the reference container and configured to be chemically treated to attach surface-immobilized receptors thereon that will bind said one or more types of target substances in the solution so that a change in refractive index occurs in the vicinity of said top surface when the target substance binds to said top surface;
• a two-dimensional image sensor disposed under the diffraction element to detect a first diffraction pattern projected onto the two-dimensional image sensor by the light from the light source that has interacted with a portion of the diffraction element that is in contact with the solution in the sample container and to detect a second diffraction pattern projected onto the two-dimensional image sensor by the light from the light source that has interacted with another portion of the diffraction element that is in contact with the reference container, the two-dimensional image sensor having a plurality of pixels to detect the diffraction patterns;
• and
• a processor connected to the two dimensional image sensor to process signals representing the first diffraction pattern with signals representing the second diffraction pattern, outputted from the two-dimensional image sensor, so as to compensate for fluctuations of said ambient light for determining the presence or absence of the target substance on the diffraction element,
• wherein the diffraction element and the two-dimensional image sensor are configured and arranged such that, upon receipt of the light from the light source, the plasmon waves are generated on the diffraction element so as to generate the diffraction pattern that includes a plurality of distinct diffraction spots or lines on the two-dimensional image sensor, properties of which are dependent on the refractive index in the vicinity of the top surface of the diffraction element.