Methods and devices for signal amplification and/or analyzing a chemical analyte using an electrochemical cell containing colloidal suspension of conductive or redox active nanoparticles in a liquid sample are provided. The liquid sample includes a plurality of electrogenerated chemiluminescent (ECL) moieties and one or more chemical analytes. The colloidal suspension of nanoparticles in the liquid sample are in contact with one or more electrodes of the electrochemical cell. The methods and devices may also employ an optical detection system, which is capable of measuring one or more transient optical properties resulting from redox reactions of the ECL moieties catalyzed by interaction of the nanoparticles with one of the electrodes.