We have given a brief note on Nanotechnology, Nanoscience, Nanomaterials and their applications in this book. Nanotechnology is a Study of manipulating matter on atomic or molecular scale. It creates many materials and devices with high performance for vast range of applications. Also, Photoelectric effect, Photoelectrons, Hertz effect, Photo-conductivity, Photoconducting materials, Photo-sensitivity, Photo-detectors, Nano Sized Photodetector, Nanowires and UV Photodetecting Nanowires are discussed in this work. An attempt has been made to analyze the activities of Silver nanoparticles on Gram negative and Gram positive Bacteria. Changes in Lattice constant of Silver nanoparticles have been investigated. Some of our guest lecture works, seminar presentations and research works have been compiled. This work will be helpful to acquire a basic knowledge about and nanomaterials and Photoconductivity. We feel that this book will serve as a good survey and act as a good guide for nanotechnology and nanoscience. This work is expected to throw some light on and help further studies.