Highly Sensitive Fluorometric Turn-On Detection of Lysozyme Based on a Graphene Oxide/ssDNA Assembly

Lysozyme, acts as a natural 'drug,' plays crucial role in the innate immune system. Sensitive detection of lysozyme in saliva, serum, and urine has considerable clinical importance. We report a fluorometric 'turn-on' strategy for the highly sensitive detection of lysozyme based on a graphene oxide/ssDNA assembly. The anti-lysozyme DNA aptamer labeled with fluorescein (FAM) was used as a probe to recognize target and transduce fluorescence signal. Graphene oxide (GO) was used as an efficient nanoquencher to turn off the fluorescence of FAM. In the absence of target, the FAM-labeled aptamer adsorbs on the surface of GO via weak π - π stacking interactions. However, in the presence of target, a turn-on fluorescence signal was observed due to the specific binding of aptamer and lysozyme followed by a subsequent separation from the surface of GO. Compared to the previously reported fluorometric turn-on methods for lysozyme, we obtained the highest sensitivity, and the limit of detection for lysozyme in saliva was estimated to be as low as 21.8 pM. Moreover, the method is convenient and rapid, because there is no need for amplification, washing, and extra procedure of bioconjugation.