The present invention provides method and compositions for detecting target molecules present on cells and tissues. In particular, the methods involve adding primary antibodies such as scFv-targeted lactamase that are directed against a target of interest (e.g., cancer markers) to a tissue sample, followed by adding a lactam-containing compound and finally a lactamase reporter system. In some preferred embodiments, the lactamase reporters are fluorescent reporters that bind to the test tissue. In some particularly preferred embodiments, the test tissue contains at least once cancer cell and/or at least one cancer-associated marker.
