Sensitive Quantitative Protein Concentration Method Using Luminescent Resonance Energy Transfer on a Layer-by-Layer Europium(III) Chelate Particle Sensor.

A particle-based protein quantification method was developed. The method relies on adsorption of proteins on particles and time-resolved fluorescence resonance energy transfer (TR-FRET). Layer-by-layer (LbL) particles containing europium(III) chelate donor were prepared. A protein labeled with an acceptor was adsorbed onto the particles and near-infrared energy transfer signal was detected in time-gated detection mode. Sample proteins efficiently occupied the particle surface preventing binding of the acceptor-labeled protein leading to a particle sensor with a significant signal change. We detected subnanomolar protein concentration using the rapid and simple mix-and-measure method with a coefficient of variation below 10%. Compared to known protein concentration methods, the developed method required no hazardous substances or elevated temperature to reach the high-sensitivity level.