Rensselaer inventors created a hybrid fiber UV photodetector with a completely new internal gain mechanism which can achieve extremely high external quantum efficiency for ultrasensitive UV sensing while at the same time only require low voltage supply. The new photodetector has a high potential for system integration; the size of hybrid fiber UV photodetector is comparable to a 2 cm long human hair, with negligible weight. It is highly flexible, can bend to any angle with a great flexibility and potential for smart system integration, such as Micro Robot, Lab on a Chip, etc. The invention has a wide range of applications, including, but not limited to: missile tracking, medical imaging, advanced space-to-space communication, and pollution monitoring. The backbone of this UV photodetector is a graphene fiber (can be any flexible highly conductive organic/inorganic materials). The photoactive layer is made of blends of nanoparticles (of any wide band gap semiconductor nanomaterial). The carbon nanotubes network (can be mono/bi-layer graphene or any transparent electrode) is deposited to cover the hybrid fiber as outer electrode for the UV photodetector. The material is available through low-cost solution synthesis method. The (visible-blind) detector fabrication is based on a simple and low-cost dip coating process, enabling extremely high photoresponsivity and a fast-transient response (~μs).