Background: Nanoparticles are now widely gaining popularity in the field of dentistry They are being incorporated into major ingredients in mouthwashes possessing antimicrobial properties and in the treatment of white spot lesions in the field of orthodontics.There is an increased need for alcohol free herbal mouth rinses which are non cytotoxic and biocompatible such that they can be used as an adjunct to mechanical plaque removal techniques in orthodontic patients. Aim:The aim of this study was to evaluate if a novel non alcohol based herbal mouthwash containing selenium nanoparticles(SeNP) and chitosan colloid is safe and biocompatible for use in patients undergoing orthodontic treatment to reduce plaque accumulation. Materials and Methods: 15 gms of brine shrimps were hatched in salt solution after incubating them for 24 hrs. Oral rinse prepared from selenium nanoparticles was added at concentrations 5μL, 10μL, 20μL, 40μL, 80μL in a microtiter plate. 10 Hatched nauplii (brine shrimps) were added in each of these microtiter plates and incubated for 24 - hours. Results: SeNP’s based mouthwash showed excellent compatibility at lower concentrations. Mild toxic effects were elicited at higher concentrations. Conclusion: Oral rinse with 5-10μL of SeNP’s was found to be biocompatible and can be used as a potential adjunct along with mechanical plaque removal techniques in orthodontic patients.