Alpha particle types: eventually named alpha, beta, and gamma by Rutherford, based on penetration of objects and deflection by a magnetic field. Alpha rays were defined by Rutherford as those having the lowest penetration of ordinary objects. Rutherford's work also included measurements of the ratio of an alpha particle's mass to its charge, which led him to the hypothesis that alpha particles were doubly charged helium ions (later shown to be bare helium nuclei). In 1907, Ernest Rutherford and Thomas Royds finally proved that alpha particles were indeed helium ions. To do this they allowed alpha particles to penetrate a very thin
Janus particles settling, thus enabling these nanoparticles as biocompatible multifunctional probes for bioimaging. Next, by labeling their surfaces and selectively binding them on the membrane of live-tagged Raji and HeLa cells, this demonstrated the nanoparticles as biomarkers and their detection under dark-field illumination was achieved. These new hybrid Janus nanoparticles overcame the individual limitations of FeO (poor particle stability in suspension) and of Ag (toxicity) nanoparticles, while retaining the desired magnetic properties of FeO and the plasmonic optical properties of Ag. The potential application of Janus particles was first demonstrated by Nisisako "et al.", who made use of the electrical anisotropy of