A voltammetry biosensor based on self-assembled layers of a heteroleptic tris(phthalocyaninato) europium...

A highly efficient enzyme-based sensor was made from a heteroleptic tris(phthalocyaninato) europium triple-decker complex Eu₂(Pc)[Pc(OPh)₈]₂, for the first time. The ITO working electrode was modified by a mixture of hybrid multi-layers consisting of Eu₂(Pc)[Pc(OPh)₈]₂, stearic acid (SA) and tyrosinase (Tyr) (Eu₂(Pc)[Pc(OPh)₈]₂/SA/Tyr-ITO) using the Langmuir-Blodgett (LB) technique. The microstructure and morphology of the resulting LB films can be characterized by their π-A isotherms, UV-vis absorption spectra, X-ray diffraction and atomic force microscopy (AFM) analysis. The experimental results revealed that the triple-decker molecules of Eu₂(Pc)[Pc(OPh)₈]₂ take a H-type molecular stacking mode in both pure and mixed LB film, and the microstructures of films were effectively improved by mixing SA within the triple-decker Eu₂(Pc)[Pc(OPh)₈]₂ molecules. The excellent electrocatalytic effect of the Eu₂(Pc)[Pc(OPh)₈]₂/SA/Tyr LB films, leads to a good linear increase from 5.26 × 10^-7 to 2.1 × 10^-4 M for catechol. It also leads to an excellent sensitivity of 2.19 μA/μM, and a detection limits of 6.29 × 10^-8 M (S/N = 3) of catehol at the oxidation peak, achieving best catechol sensing performance among the phthalocyanine-based biosensing mediators. The reduction peak also showed a good linear increase from 5.26 × 10^-7 to 1.60 × 10^-4 M for catechol with a sensitivity of 0.615 μA/μM, and a detection limit of 1.69 × 10^-7 M (S/N = 3). Moreover, the Eu₂(Pc)[Pc(OPh)₈]₂/SA/Tyr-ITO electrode are easy to reproduce, stable and resistant to interference when it comes to detection for catehol, and this indicates great potential of industrial application of tris(phthalocyaninato) rare earth complexes in ultrasensitive and specific biosensors.