Hot electron-induced electrochemiluminescence at cellulose derivatives based composite electrodes

The possibility of using cellulose derivative films as (i) insulating material on metal electrodes or (ii) in composite electrode films on metal to produce hot electron-induced electrochemiluminescence (HECL) was studied. It was shown that the luminophores known to produce HECL at thin insulating film coated cathodes (e.g. Si/SiO2 and Al2O3 electrodes) produced HECL with the present novel electrodes. In the case of composite films consisting of cellulose material doped with conducting carbon particles, the optimal cellulose/carbon black ratios were investigated by measuring the time-resolved HECL (TR-HECL) of an aromatic Tb(III) chelate. In addition to Tb(III) chelate, other well-known labels, fluorescein and Ru(bpy)(3)(2+) chelate, were demonstrated to produce strong HECL at the present composite electrodes, which are more environmental friendly in disposable assay cartridges as the plastic-based composites we have studied previously. Thus, it is now possible on the present basis to manufacture biodegradable paper-based assay cartridges with HECL detection of labels at biodegradable electrodes. It was shown that the present composite films are stable over wide pH range, and also time-resolved detection of Ru(bpy)(3)(2+) chelate is possible although its luminescence lifetime if quite short. The calibration curves were measured for presently used aromatic Tb(III) chelate and for Ru(bpy)(3)(2+). The detection limit (s/n = 3) was 2.10(-10) M for the Tb(III)-chelate and 4.10(-9) M for Ru(bpy)(3)(2+) in time-resolved detection mode. The relative standard deviation for Tb(III)-L1 (n = 5) emission at 10(-5) M concentration was 2%. Wide linear range and low detection limits suggests that cellulose based composite electrodes can be used in HECL bioaffinity assays which was finally demonstrated here by an immunometric immunoassay.