The only amino acid that exists is cysteineamong the 20 non-essential amino acids in the human system that contains the thiol group [1, 2]. Its found in keratin the primary protein that builds up nails, skin, and hair contain it aids in the production of collagen, which keeps skin supple and smooth [3, 4]. Cysteine also protects liver parenchymal cells, improves hematopoietic function, boosts leukocyte production, and speeds up skin cell turnover. A shortage of cysteine can lead to hair loss, psoriasis, swelling, tiredness, liver damage, decreased hematopoietic white blood cell loss, and other problems [5, 6]. As a consequence, it plays a crucial role in protein synthesis.
Congenital metabolic abnormalities and cystinuria may be linked to abnormal cysteine concentrations in the body . The measurement of cysteine is critical for precise pre-diagnosis of a variety of diseases. Capillary electrophoresis , high-performance liquid chromatography , mass spectrometry , fluorescence analysis , and electrochemical voltammetry are among the sensitive and selective methods being developed for the detection and measurement of cysteine in environmental, pharmaceutical, and biological samples or precursors .These processes depend on redox chemistry or derivative products of chromo pore/fluorescent groups, and they necessitate high temperatures, specialized instruments, and the use of powerful and harmful reagents to improve the detection of trace components and the removal of basic disruptions in a cost-effective manner. Therefore, colorimetric sensing differs from earlier approaches in that it relies on a colour shift in the nanoparticles that can be observed and analyzed with the naked eye and a basic UV-vis spectrometer . Its more convenient to use, but it’s also less expensive.
Because of the advancement of nanotechnology, colorimetric detection based on silver nanoparticles has recently been recognized a promising strategy for detecting cysteine [13, 14]. Due to their high valueabsorption coefficient and range dependent optical features. Silver nanoparticles are substantially less expensive compared to other metal nanoparticles and have a high affinity for nitrogen and sulfur-containing molecules . AgNPs bind strongly to the biomolecules accessible thiol groups.The aim of green nanoparticles synthesize is to reduce waste and establish a long-term procedure. In recent years, the development of nanotechnology has prioritized green processes that use mild reaction conditions and nontoxic precursors to promote environmental sustainability . As biological agents, such as plants or microbiological sources, are used as reducing and capping agents in an environmentally friendly method . Green synthesized silver nanoparticles are a novel and promising alternative to nanoparticles producingchemically produced. Due to its unique antibacterial capabilities , larvicidal activity , anticancer activity , and Metabolites detection  green silver nanoparticles have gotten a lot of interest.
As shown in Scheme 1, the purpose of this study was to use CCB extract to synthesize AgNPs for cysteine detection. Initially, CCB extract was extracted from the husk. Then, utilizing Tollens reagent [Ag (NH3)2OH] and CCB, well dispersed Ag-NPs were produced at 80°C under magnetic stirring.CCB extract was used as a reducing and stabilizing agent during the synthesis, rather than some other synthetic reducing or stabilizing chemical, resulting in the development of a synthesize mechanism from metal nanoparticles from agriculture wastes. Finally, employing the naked eye and UV-vis spectra, the generated Ag-NPs were used in a sensitive and selective colorimetric manner. Inaddition, the detection of cystine inhuman serum was also discussed in order to evaluate the potential direct implementation of the generated Ag-NPs.