Design, fabrication and development of quantum infrared detectors using graphene are discussed in this paper. By using graphene made from mechanical exfoliation as the sensing element, we observe strong electron-photon coupling effects on the devices. In the presences of two infrared sources with two different wavelengths (830 nm and 1064 nm), we show that the graphene-based devices generates photocurrents at room temperature. The photocurrents induced by electron-hole pair generation are measured on the exfoliated multilayer graphene in uncooled condition. In addition, we found that the photo-carrier generation of the multilayer graphene is higher than that of single-layer graphene and carbon nanotubes which have been studied extensively recently. These results suggest multilayer graphene is suitable for infrared sensing. Besides, a new method of classifying graphene using dielectrophoretic manipulation is presented. Graphene flakes exposed to a non-uniform electric field are expected to behave differently based on the difference in conductivity of graphene. We demonstrate the ability to select and manipulate graphene flakes between electrodes by using the dielectrophoretic manipulation. The infrared responses of the graphene after the different manipulation configuration are investigated. The present study offers a novel classification of graphene for developing high performance nano infrared sensors.