Fluorescence based penicillin

Scheme 117 Fluorescence-based penicillin structure having a 7-hydroxy-4-methylcoumarin as releasable group...

Attachment of 7-hydroxy-4-methylcoumarin as the releasable group of this side chain generated a penicillin structure that can function as a fluorescence-based reporter substance/diagnostic for the presence of low levels of (3-lactamase enzyme in solution (Scheme 117), [320]. 

It must be underlined that, for the development of a successful FILA based on the use of non-related tracers, the latter should also show sufficient affinity for the specific binding sites of the imprinted polymer otherwise the assay will not be selective. For instance, in order to facilitate the competition between the labeled derivative and the analyte, Moreno-Bondi et al. have developed a FILA for the analysis of penicillins [34, 36] using novel fluorescently labeled [5-lactam antibiotics with a close resemblance to the analyte (Fig. 12) [95]. 

Of particular relevance to the current section, //-lactamase is a bacterial enzyme that normally cleaves //-lactam antibiotics such as the penicillins and cephalosporins. CCF4 is a FRET-based fluorescent substrate of //-lactamase that contains two fluorophores, coumarin and fluorescein, that are linked by a cephalosporin backbone. When CCF4 is intact, the coumarin and fluorescein are in close proximity and excitation of coumarin by light at wavelength 409 nm results in efficient transfer of energy to fluorescein, leading to emission of green fluorescence (peak at 520 nm). When the... 

Other fluorescent colorants can be used to produce pH, pNHs, and pCX)2 optical sensors. One example is the trisodium salt of 8-hydroxy 1,3,6-pyrenetrisulfonic acid (called HOPS A or HPTS) whose basic form can be excited at 470 nm to emit fluorescence at 510 nm [203, 204]. The CX)2 optical sensor requires a silicone membrane to contain a bicarbonate solution, just like potentiometric pC02 electrodes. A further similarity with potentiometric electrodes is that the pH, pNHs and pC02 optical sensors serve as the bases for enzyme sensors. The appropriate enzymatic membrane is simply attached. The optical sensor for penicillin uses penicillinase to catalyse the transformation of penicillin into penicilloic acid. The acid is detectable with a pH optical sensor that uses fluorescein isothiocyanate (FITC) as a colored indicator [205]. 

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