inorganic chemistry

spores are present on the same focal plane, rendering an accu-
rate enumeration in any single microscopic view impossible.
But, if the dipicolinate released from the germinating spores is
effectively bound to a terbium(macrocycle) complex that is itself
covalently attached to the PDMS coverslip, the PDMS is the only
surface necessary to image. The PDMS could be readily removed
from the agarose following germination, placed on a flat surface
and imaged separately, eliminating the problem of multiple focal
planes.
The second method involves sample concentration to enhance
the current LOD of bacterial spores by taking advantage of the
pH dependence of dipicolinate binding. Chelation of DPA to [Tb
(DO2A)]þis most effective in the pH range 6–10. Above pH 10,
the hydroxide concentration is high enough to compete with the
macrocycle and some lanthanide is lost due to precipitation as
Ln(OH) 3. Below pH 5.5, the macrocycle becomes protonated and
[Tb(DPA)]þdominates (Table VI). The idea of using pH sensitiv-
ity of lanthanide complexes is not new; for instance, a pH sensor
was developed based on the pH dependence of a europium ter-
nary complex containing a b-diketonate as the chromophore.
When the pH shifted out of physiological range, the chromophore
dissociated and sensitization was lost ( 12 ). However, using this
property not as an indicator but as a concentration tool has yet
to be tested.

10

0.8

0.6

Normalized intensity

0.4

0.2

0.0

0 5 10 15 20

Time (h)

25 30 35 40

Aerobic spore

Anaerobic spore

FIG. 17. Germination curves of typical aerobic (Bacillus atrophaeus)
and anaerobic (Clostridium sporogenes) spores. (Data provided by
W.-W. Yang.)

LUMINESCENT LANTHANIDE SENSORS 37