Table 1.

Requisite Design Parameters for Disease-Specific Probes

1. High Stability

physicochemical stability of targeting ligand

optical stability of probe

biological (in vitro) and physiological (in vivo) stability

2. High Sensitivity

high target concentration

high molecular brightness of optical probe

high performance of imaging modality

3. High Specificity

high signal-to-background (noise) ratio (SBR or SNR)

high affinity of ligand to the target (signal)

low nonspecific binding to normal tissue (background)

4. Favorable Delivery to the Target across Biological Barriers

biodistribution (organ delivery with minimum nonspecific uptake)

delivery across cell membranes (intracellular targets)

5. Favorable Pharmacokinetics and Metabolism

rapid accumulation to the target (bound molecules)

sustained retention on the target (bound molecules)

rapid clearance from nonspecific tissues (unbound molecules)

rapid elimination from the body (unbound molecules)

6. Low Toxicity

chemical, biological, physiological toxicity

acute and chronic toxicity

cytotoxicity and in vivo toxicity