The invention concerns an optical component for observing a sample, which includes a substrate and at least one complex index layer of predetermined thickness, designed to show a high intensity or color contrast for optical path variations, reliefs, nanometric thicknesses and diameters when it is observed by incoherent light reflection convergent around the normal incidence under polarization extinction conditions. The upper index layer has specific surface properties providing it with selective affinity relative to at least one characteristic of the sample. An analysis system includes such a component, an analysis method using the component and uses of the method.