Europium in Phospholipid Nanoscaffolds for the Photophysical Detection of Antibiotic Traces in Solution

The emissive features of Europium are successfully used to recognize and detect small traces of drugs in solution exploiting an innovative approach where Europium (III) cations are inserted in molecularly organized phospholipid architectures. The weak luminescence of Europium ions in solution is enhanced upon complexation with organic chelants through intramolecular energy transfer: this peculiar emissive property was used to monitor quantitatively the presence of antibiotic residues in solutions in contact with the phospholipids scaffolds. These bioinspired nano-architectures were designed and prepared using phospholipid molecules in monomolecular and multilayer sequences with precise control of the molecular organization. Europium (III) cations were inserted in the outer layer of the nanosystem facing the surrounding aqueous medium containing the drug to be detected. In particular, we focused our studies on a member of the tetracycline family well known to induce strain resistance to antibiotics. Floating monolayers of the phospholipid matrix, i.e. dipalmitoyl phosphatidic acid (DPPA), were prepared and studied by means of surface potential and surface pressure isotherm as a function of Europium concentration, pH and ionic strength. The measurements were repeated in the presence of increasing quantities of Tetracycline (TC) in the subphase and the results correlated to the absorption spectra recorded at water-air interface for different DPPA surface densities. Supported nanoarchitectures of the DPPA matrix were prepared transferring the floating monolayer from the aqueous phase onto solid substrate by means of the Langmuir-Blodgett technique. The resulting multilayers were immersed in the solution containing the TC to be detected and the photophysical properties of Eu (III) in the LB films were studied as a function of Tetracycline concentration, pH and Europium densities in the LB layer. The experimental findings show that excitation, at the wavelength characteristic of TC absorption, results in a sharp emission of the lanthanide ion even for extremely low Tetracycline content and that the emission intensity increases linearly with the antibiotic concentration in solution. These results pave the way to the development of nanosensor devices for the detection of antibiotic residues in fluids and edible materials.