Table 1. Targeting of organic biosensors to organelles: Strategies and most used presently available sensors.

Organelle or compartment	Targeting strategy	Measured parameters
Nucleus	NLS, nuclear microinjection	Ca2+ (Allbritton et al., 1994)
ER	Hydrophobicity, alkyl chain	Ca2+ (Hofer et al., 1998; Landolfi et al., 1998)
		pH (Reddy G et al., 2015)
		Cu2+ (Lee et al., 2014)
PM inner surface	Hydrophobic tail	Ca2+ (Vorndran et al., 1995)
		membrane potential (González and Tsien, 1995; Peterka et al., 2011; St-Pierre et al., 2015)
Mitochondrial matrix	Membrane potential	Ca2+ (Hajnóczky et al., 1995)
		Zn2+ (Masanta et al., 2011; Sreenath et al., 2011; Liu et al., 2012b; Chyan et al., 2014)
		thiols (Lim et al., 2011)
		H2O2 (Dickinson and Chang, 2008)
		pH (Sarkar et al., 2016)
		superoxide (Robinson et al., 2006)
		membrane potential (Nicholls, 2012)
Acidic compartments	pH gradient, endocytosis	pH (Zhu et al., 2012; Miao et al., 2013; Lv et al., 2014; Chen et al., 2015; Wang et al., 2015; Yapici et al., 2015)
		thiols (Kand et al., 2015)
		Ca2+ (Gilroy and Jones, 1992; Schlatterer et al., 1992)
		vesicle recycling (Gaffield and Betz, 2007; Li et al., 2009)
		neurotransmitter release (Gubernator et al., 2009)