We have developed a green, facile and economical route to synthesise luminescent carbon quantum dots from pulp free juice of Citrus limon in ethylene glycol. The obtained graphitic carbon dots with an average size of 3 nm exhibits strong UV absorption. Dependence of excitation wavelength on blue emitting carbon dots is investigated. This spectral behaviour remains unchanged with sulphur doping in carbon dots. They show good biocompatibility while inhibiting the growth of DLA cancerous cells. Moreover optical properties of S-doped carbon quantum dots are utilised to detect hydrogen peroxide with a detection limit of 0.49 mM. GRAPHICAL ABSTRACT

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