**7. Conclusion**

This chapter summarizes the fundamental introduction of NMs and NPs, the significance of colloidal metal NPs for range of applications, diverse physicochemical and biological pathways for synthesis of colloidal NPs and the parameters affecting the synthesis of NPs. Colloidal metal NPs, notably noble metal NPs such as gold, are being utilized since ancient times for multiple applications due to eminent and unique properties which make them superior compared with molecules or fellow bulk materials. Further, these NPs are preferred for biomedical applications due to their effectiveness to attenuate the shortcomings of traditional provisions, as it can be manipulated to deal healthily with the *in vivo* biological environment. Alongside,

the size of NPs compliments them with access through cells and tissues which helps not only to diagnose the disease proficiently but also aids for site specific treatment. Such prospective usages encourage the production of NPs in massive quantity. The colloidal metal NPs have been synthesized dominantly by using chemical and physical methods for many years, but the shortfalls of the methods confine their practice in biological fields. Hence researchers have opted a biological friendly way to synthesize NPs from natural environmental sources. Even though the mechanism of green production of NPs from microorganisms and plants is not yet entirely revealed, the synthesizing parameters, namely pH, temperature, time, concentration of metal salt affect the synthesis of NPs to a great extent and their optimization is very much necessary to yield the NPs in bulk quantity with desired properties. Besides the ongoing research on colloidal metal NPs from last few decades, its actual implementation in clinical field is at primary stage and many aspects such as distribution of NPs inside body, their accumulation and clearance from the body after treatment etc. need to be addressed for better involvement of NPs in biomedical applications.
