There are many inventions described and illustrated herein. In one aspect, the present invention is a system, a device and a method for sensing the concentration of an analyte in a fluid (for example, a fluid sample) or matrix. The analyte may be glucose or other chemical of interest. The fluid or matrix may be, for example, the fluid or matrix in the body of an animal (for example, human), or any other suitable fluid or matrix in which it is desired to know the concentration of an analyte. In one embodiment, the invention is a system and/or device that includes one or more layers having a plurality of analyte-equivalents and mobile or fixed receptor molecules with specific binding sites for the analyte-equivalents and analytes under analysis (for example, glucose). The receptor molecules, when exposed to or in the presence of analyte (that resides, for example, in a fluid in an animal), bind with the analyte (or vice versa). As such, some or all (or substantially all) of the receptor molecules within a given layer may bind with the analyte, which results in a change in the optical properties of one or more of the layers. These layer(s) may be examined or interrogated, via optical techniques, whereby the optical response of the layers and/or, in particular, the substance within the layer(s), may be measured, evaluated and/or analyzed.