TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Materials: The electron acceptor compound may be water, oxygen, a nitrate, an iron(III) compound, a manganese(IV) compound, a sulfate, carbon dioxide, or a chlorinated compound. The electron donor compound may be water or any salt containing sulfide (S2-), selenide (Se2-), sulfite (SO32-), or selenite (SeO32-).    TECHNOLOGY FOCUS - METALLURGY - Preferred Materials: The nanoparticle in the form of a nanorod or nanodumbbell comprises greater than or equal to 2 metal/metal alloy regions separated by semiconductor region(s). The metal/metal alloy region comprises copper (Cu), silver (Ag), gold (Au), platinum (Pt), cobalt (Co), palladium (Pd), nickel (Ni), ruthenium (Ru), rhodium (Rh), manganese (Mn), chromium (Cr), iron (Fe), titanium (Ti), zinc (Zn), iridium (Ir), tungsten (W), molybdenum (Mo), or their alloys. The semiconductor region comprises Group II-VI, Group III-V, Group IV-VI, Group III-VI, and/or Group IV semiconductors. The Group II-VI semiconductor is cadmium selenide (CdSe), cadmium sulfide (CdS), cadmium telluride (CdTe), zinc selenide (ZnSe), zinc sulfide (ZnS), zinc telluride (ZnTe), mercury sulfide (HgS), mercury selenide (HgSe), mercury telluride (HgTe), cadmium zinc selenide (CdZnSe), or their alloys. The Group III-V semiconductor is indium arsenide (InAs), indium phosphide (InP), gallium arsenide (GaAs), gallium phosphide (GaP), indium nitride (InN), gallium nitride (GaN), indium antimonide (InSb), gallium antimonide (GaSb), aluminum phosphide (AlP), aluminum arsenide (AlAs), aluminum antimonide (AlSb), indium arsenide phosphide (InAsP), cadmium selenium telluride (CdSeTe), zinc cadmium selenide (ZnCdSe), indium gallium arsenide (InGaAs), or their alloys. The Group IV-VI semiconductor is lead selenide (PbSe), lead telluride (PbTe), lead sulfide (PbS), or their alloys. The Group III-VI semiconductor is indium selenide (InSe), indium telluride (InTe), indium sulfide (InS), gallium selenide (GaSe), indium gallium selenide (InGaSe), indium selenium sulfide (InSeS), or their alloys. The Group IV semiconductor is silicon (Si), germanium (Ge) or their alloys. The semiconductor region is preferably CdS. CdSe or CdTe and the metal/metal alloy region is preferably gold, platinum, palladium or their alloys.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Materials: The medium may be an aqueous medium or non-aqueous medium. The electron acceptor is a compound having a lowest unoccupied molecular orbital (LUMO) lower than the Fermi level of the nanoparticle. The electron acceptor compound may be tetrachloroethylene, trichloroethylene, dichloroethene, vinyl chloride, alcohol, or any other oxidizing molecule. The electron donor is a compound having highest occupied molecular orbital (HUMO) higher than the Fermi level of region(s) of the nanoparticle. The compound may be an alcohol.    TECHNOLOGY FOCUS - POLYMERS - Preferred Materials: The medium may be a gel, a polymer, a film, an electrode, or a surface.