TABLE 4.

Examples of stimuli responsive strategies

Response to	Target	Examples
pH	Acidic compartments found at pathological tissues (tumor sites) or within cells in the endosomes.	Gao et al., 2005; Bae et al., 2007; Cohen et al., 2008, 2009; Lee et al., 2008
Thermal	Heat applied external or from physiologically changes	De et al., 2008; Rahimi et al., 2008; Peng et al., 2011
Light	Externally applied light	Suzuki and Tanaka, 1990; Goodwin et al., 2005; Jiang et al., 2006; Fomina et al., 2010
Redox	Regions where reactive oxidative and reductive species are abundant (inflammation and tumor sites)	Napoli et al., 2004; Rehor et al., 2005; Reddy et al., 2006; Wilson et al., 2010; Mahmoud et al., 2011
Enzyme	Regions of high protease expression such as cancerous tissue	Olson et al., 2009; Andresen et al., 2010; Whitney et al., 2010; van Duijnhoven et al., 2011; Wong et al., 2011