Surface plasmons are incompressible oscillations of conduction band electrons in metallic nanostructures and have provided a promising route for light-harvesting and light-driven catalysis. Energetic electron-hole pairs, known as hot carriers, are created when plasmons decay through a non-radiative channel and hold extraordinary potential for boosting the efficiency of both photocurrent generation in photovoltaic devices and plasmon-enhanced photocatalysis. In this thesis, the fundamentals and mechanisms of plasmon-induced hot carrier generation were firstly introduced. Then we demonstrated how hot carrier generation could facilitate chemical reactions with the antenna-reactor concept. In this picture, we showed that by directly combining plasmonic and catalytic nanoparticles, the plasmonic nanoantenna could couple strongly with light and induce a forced plasmon in the catalytic reactor, enabling significantly enhanced generation of hot carriers within the catalyst nanoparticles and dramatically increased chemical reaction rates consequently. This could overcome the weak light coupling of traditional transition metal catalysts and provide independent control of chemical and light-harvesting properties of the catalysts by modular design. This approach is investigated and demonstrated by various heterometallic antenna-reactor complexes, including Pd islands decorated Al nanocrystals, Al-Pd heterodimers and Al-Cu2O nanoshell structures. In the second part of the thesis, a novel device for Mid-infrared photodetection was introduced based on efficient collections of hot holes. Apart from its high responsivity rivalling commercially available IR detectors, this photodetector could work on room temperature, which is significantly advantageous over conventional IR detector that requires cryogenic cooling. The devices consists of a plasmonic Al grating that operates both as an electric contact and optical filter, and a p-doped silicon substrates acting as a MIR absorber through free carrier absorption, generally regarded as detrimental in IR detection. The photodetector achieves its high performance through a modulation of the carrier mobility in silicon. Direct electrical read-outs of the absorption spectra of two molecules were performed using this detector, demonstrating its great potential for on-chip molecular vibrational spectroscopy.