Green preparation of fluorescent carbon dots from lychee seeds and their application for the selective detection of methylene blue and imaging in living cells

A green approach was developed for the preparation of fluorescent carbon dots (CDs) by using lychee seeds as precursors. The preparation of CDs was performed by simple pyrolysis. The quantum yield of as-prepared CDs was 10.6% by using quinine sulfate as the reference. The CDs were employed as fluorescence probes for the detection of methylene blue (MB). This sensing system exhibits excellent sensitivity and selectivity toward MB, and a detection limit of 50 mM is achieved. The possible application of as-prepared CDs for imaging in living cells was also explored. The inherent cytotoxicity of CDs was evaluated using HepG2 cell, and the cell viabilities were estimated to be greater than 90% upon addition of the CDs over a wide concentration range of 0-1000 mu g mL(-1). It was then successfully applied for the fluorescence imaging of HepG2 cells.