binding motif and sensitization. Carboxylate oxygens are strong
donors but appear to be made even stronger with the help of a prox-
imal nitrogen donor. It follows that analytes with additional nitro-
gen donors can in principle be detected using lanthanide optical
sensors, and work in this area should be undertaken.
IV. Looking to the FutureThe future of lanthanide-based sensing technologies is limit-
less, owing in part to dramatic recent advancements in receptor
design. Improvements in the sensitivity, stability, and selectivity
of lanthanide receptors will encourage use of such sensors over a
wider range of conditions, including bothin situ and in vivo
situations. Enhancements in binding affinities will result in bet-
ter limits of detection, thereby increasing the number and
variety of analytes that can be monitored by such systems.
We anticipate further development of lanthanide binary
complexes as receptors for aromatic ions, with the ultimate goal
of generating highly specific devices capable of sensitive detec-
tion in matrices such as environmental samples or biological
fluids. The possibility of using several lanthanide sensors
FIG. 16 Emission spectra (lex¼278 nm) of various terbium
complexes, 10.0mM in 50 mM MOPS buffer, pH 7.5. (a) DPA; (b) 3,5-
DPA; (c) Pic; and (d) 2,4-DPA.
LUMINESCENT LANTHANIDE SENSORS 35