In vivo, molecular imaging is prevalent for biology research and therapeutic practice. Among advanced imaging technologies, photoacoustic (PA) imaging and sensing is gaining interest around the globe due its exciting features like high resolution and good (~ few cm) penetration depth. PA imaging is a recent development in ultrasonic technology that generates acoustic waves by absorbing optical energy. However, poor light penetration through tissue continues to be the key obstacle in the field. The NPs as contrast agents can assist in overcoming tissue penetration depth as NPs can produce high signal to noise (SNR) PA signal which aids reconstruction of high resolution of the PA images in deep tissue sights. Subsequently, NPs are very effective in PA based targeted and precise theranostic applications. This article detail about various NPs (organic, inorganic and hybrid) used in PA imaging and spectroscopy applications including various disease diagnosis, therapy and theranostic. It also features optical property, advantages and limitations of various NPs utilised in PA techniques which would comprehend readers about the potential of NPs in evolving PA technique from laboratory to clinical modality in future.