Figure 6.

(a) The core of this sensor for calcium dipicolinate (CaDPA) consists of silica doped with fluorescein isothiocyanate (FITC). The surface is functionalized with ethylenediaminetetraacetic acid dianhydride (EDTAD), which chelates Eu³⁺. While the FITC emission dominates in the absence of CaDPA, the red Eu³⁺ emission becomes visible upon addition of the analyte. (b) Increase in the intensity of the spectral features associated with Eu³⁺ emission results from the increase in CaDPA concentrations. (c) The addition of CaDPA to the NPs changes emission from green, arising from the FITC, to red, originating with the Eu³⁺. Vials shown contain concentrations of CaDPA, from left to right, of 0 μM, 25 μM, 50 μM, and 100 μM. Reproduced from [48].