. 2013 Dec 24;164(2):1059–1067. doi: 10.1104/pp.113.229765

Table I. Algae biosensor and metal-specific FRET ratio responses.

Normalized transgenic algae FRET ratio (527 nm/485 nm) responses for no metal addition and highest metal concentration tested (1.57 mm) and CMY FRET ratio differences are shown. NA, Not applicable; ND, not determined.

Metal Ion	In Vivo YFP/CFP FRET Efficiency Ratio^a	YFP/CFP FRET Ratio with 1.6 mm External Metal Addition	Change in YFP/CFP FRET Ratio	Estimated Internal Metal Concentration (Percentage of External Concentration)
Cd²⁺	0.90	1.15	0.25	60–70 µm (4.0%)
Pb²⁺	0.90	1.64	0.74	240–260 µm (16%)
Cu²⁺	0.90	1.05	0.15	ND
Mg²⁺	0.94	0.88	−0.06	NA
Na⁺	0.88	0.85	−0.03	NA

Determined by extrapolating the FRET ratio changes of algae biosensor FRET responses at 1.6 mm metal ion specified to the FRET response in vitro using purified CMY for each metal indicated.