A conjugate comprising a dye-labeled microporous crystal, a stop-cock moiety, and covalently bound thereto an affinity binding agent is disclosed. The dye-labeled microporous crystal is a zeolite crystal, such as a zeolite L crystal, having a large number of channels in its interior into which the dye is loaded. The stop-cock moiety can be functionalized with an amino group to which a carboxyester group can be attached. The affinity binding agent allows for the binding to a biological moiety. The conjugate of the moiety can be used in in-vivo and/or in-vitro imaging applications.