The diagnosis and treatment of cancerous tumors remains a challenge due to the inherent heterogeneity of the tumors and variation in treatment response between patients. A molecular imaging technique which provides high resolution at a depth of several centimeters could provide important information about the composition of heterogeneous cancerous tissues to aid in the diagnosis and monitoring of the treatment of cancer. Photoacoustic imaging, which can achieve high resolution at a clinically relevant tissue depth, combined with targeted contrast agents whose properties can be tuned to achieve distinct photoacoustic signals, provides a molecular imaging technique which is non-invasive, non-ionizing, and cost-competitive in comparison to existing molecular imaging methods. The research presented here describes combined photoacoustic and ultrasound imaging using tunable gold nanorods which have been targeted to unique cell types or molecular processes, and then distinguished by acquiring photoacoustic images at laser wavelengths spanning the optical absorption spectra of the nanoparticles. The results obtained using tissue models consisting of various cancer cells, overexpressing different receptors, indicate that photoacoustic imaging is capable of identifying multiple molecular targets or cell types within a tissue.