SPP1 and cervical carcinoma: SERS-based simultaneous detection of squamous cell carcinoma antigen (SCCA) and osteopontin (OPN) in serumDetection limit: 8.628 pg/mL for SCCA and 4.388 pg/mL for OPNSERS intensities at 1593 cm−1 (SCCA) and 1334 cm−1 (OPN) increased in serum from cervical cancer and precancer patients compared to healthy subjectsGood agreement between SCCA and OPN levels measured by SERS and ELISA in serum samples