Nanoparticle-catalysed electron transfer reactions have been investigated by using an extended version of the theory of electron transfer reactions for the bridge-mediated three-centre process and approximate expressions for various free energy quantities as well as the matrix elements. It is observed that the calculated rates for nanoparticle-catalysed reactions for the reduction of various dyes by standard reducing agents are considerably higher than the rates of direct electron transfer processes and are also found to agree quite well with recently reported experimental results.