The present disclosure provides a sensor substrate capable of detecting a trace amount of an analyte. This sensor substrate according to the present disclosure is a sensor substrate comprising a metal microstructure that generates surface plasmon when irradiated with excitation light. The metal microstructure is composed of a plurality of protrusions disposed in a planar shape. The plurality of the protrusions are disposed in such a manner that imaginary lines V each passing through a center between adjacent protrusions draw a honeycomb shape in a plan view. Each of the plurality of the protrusions has a substantially hexagonal shape in the plan view. A depth in a thickness direction of the sensor substrate of a gap present between the adjacent protrusions is larger than a radius of an imaginary circle inscribed in a hexagon forming the honeycomb shape.