Synthesis of nanoparticles using biodegradable source is safer and echo-friendly. Here we describe the synthesis of polycrystalline silver nanocrystals using Citrus sinensis acting both as reducing and capping agent. After exposing the silver ions to orange extract, rapid reduction of silver ions led to the formation of stable silver nanocrystals due to the reducing and stabilizing properties of orange fruit juice. The synthesized silver nanocrystals were characterized using various analytical techniques like UV-Vis spectroscopy, XRD, Dynamic Light Scattering (DLS), SEM and TEM. The biochemical activity of the synthesized nanocrystals was studied in the light of affinity to Bovine Serum Albumin using several biophysical methods like absorbance, fluorescence and circular dichroism spectroscopy. Cytotoxic activity of these nanocrystals was also studied against Hep-2 cell line using fluorescence microscopy. It was also found that the synthesized nanocrystals can sense mercuric ion down to 50 µM in presence of a number of cations. Furthermore, we established that the silver nanoparticles can effectively catalyze the reduction of methylene blue by ascorbic acid. The present study will enrich our knowledge on the chemical and biochemical activity of green-synthesized silver nanocrystals.