Organic Nanoparticles: Mechanism of Electron Transfer to Indigo Nanoparticles

Organic nanoparticles are attracting many significant applications in bio-imaging and nanomedicine. However, in comparison with intensive studies of metal and inorganic nanoparticles, the research of organic nanoparticles is still at a very early stage due to their complex physical and chemical properties. Most recently, there are increasingly significant interests in developing nano-capacitors and nano-scale energy storage and sensor devices based on organic materials. Herein, we report for the first time the kinetics and mechanism of electron transfer to individual organic nanoparticles, using indigo nanoparticles as a model system, via analysis of the charge transferred in the reduction of individual organic nanoparticles. We conclude the indigo nanoparticles display irreversible (slow) electron transfer kinetics and that the charge transfer is the rate-determining step in the reductive dissolution of the nanoparticles; protonation and detachment of molecules from the nanoparticles occurs after this rate-determining step. The transfer coefficient, a, of the electron transfer is found to be 0.25 +/- 0.05, whilst the rate constant (k(0)) is determined as the composite parameter k(0) exp(0.25F/RT E-f(theta)) where E-f(theta) is the formal potential, which is found to have the value of 1.7 x 10(-8) ms(-1). Given the high importance of the electron transfer mechanism for organic nanomaterials, this report may have great significance on future research of organic nanomaterials for diverse applications.