Label free paper sensor and light driven material for the rapid screening of S100P cancer biomarker in saliva

Cancer is one of the main causes of death globally. S100P is a biomarker associated with several types of cancer, including colon, oral, and pancreatic. The sensitive monitoring of S100P in patients is critical for the early detection of the cancer disease. Current detection methods are invasive, expensive and time-consuming. In this work, we present a label-free surface-enhanced Raman spectroscopy (SERS) paper sensor for the sensitive and selective determination of S100P in biological fluids within an hour. A bimetallic material was synthesised by electrodepositing silver (Ag) nanostructures on gold (Au)-coated paper substrate to develop a highly sensitive SERS sensor (EF = 5.21 × 10⁵). The new sensor was used to record the Raman spectrum of S100P, for the first time. The sensor was used for the sensitive quantification of the biomarker in spiked saliva down to 1 ng/mL by direct SERS method (S100P concentration in healthy subjects ∼2.998 ng/mL and in cancer patients ≥28.47 ng/mL). Therefore, the new sensor can be used to monitor the concentration of S100P in cancer patients at the early stage of the disease. To maximise the integrity of the new SERS method and eliminate false positive results, a target-specific extractor chip was developed by functionalising the Ag-Au material with anti S100P antibody molecules that selectively bind and purify the biomarker from complex matrices prior to the SERS measurement. A rapid and inexpensive green synthesis process that uses deep UV LED light was used to functionalise the bimetallic substrate with S100P antibody molecules and develop an S100P-specific extractor chip. The new sensor has strong potential for the rapid determination of the S100P biomarker at points of care (POC), thus supporting the early diagnosis of cancer disease.