The protein phosphorylation status of exosomes can regulate the activity and function of proteins related to cancer development, and it is highly possible to diagnose cancers through analyzing the protein phosphorylation status. However, monitoring the protein phosphorylation status with a simple and label-free method is still clinically challenging. Here, inspired by beehives, we developed an Au-coated TiO2 macroporous inverse opal (MIO) structure with an engineered "slow light effect" and thus with outstanding surface-enhanced Raman scattering (SERS) performance. The MIO structure can capture and analyze the exosomes from plasma of cancer patients without any labeling processes. It was found that the SERS intensity of exosomes at 1087 cm-1 arising from the P-O bond within the phosphoproteins can be used as a criterion for tumor liquid biopsies. The intensity of the 1087 cm-1 SERS peak from exosomes extracted from the plasma of cancer patients (prostate, lung, liver, and colon) is at least two times of that from healthy people. This indicates the simplicity and versatility of this method in cancer diagnostics. Our method has obvious advantages (noninvasive and time-saving) over currently clinically used tumor liquid biopsy techniques (such as western blot), which has great potentials to make vitro cancer diagnostics/monitoring as simple as diagnostics/monitoring of common diseases.
Keywords: SERS; exosomes; liquid biopsies; protein phosphorylation; slow light effect.