The present disclosure describes the identification and use of aptamers and photoaptamers having slower dissociation rate constants than those obtained using previously described methods. Specifically, the present disclosure describes methods for the identification and use of aptamers to one or more targets within a histological or cytological sample, which have slow rates of dissociation. The aptamers may be used to assess localization, relative density, and presence or absence of one or more targets in cytological and histological samples. Targets may be selected that are specific and diagnostic of a given disease state for which the sample was collected. The aptamers may also be used to introduce target specific signal moieties. In addition to target identification, the aptamers may be used to amplify signal generation through a variety of methods.