An optical multimodal detection system for targeted detection of cancer biomarkers in blood serum. The system comprises of a nano-biosensor, a chamber for receiving the nano-biosensor, a localized surface plasmon resonance (LSPR) based detector, a plasmon enhanced fluorescence (PEF) based detector and a surface-enhanced Raman scattering (SERS) based detector. The nano-biosensor comprises of a glass substrate provided with an active site for receiving a sample of blood serum, and is dimensioned to define a flow channel for introducing the sample of blood serum into the nano-biosensor. The nano-biosensor is provided with a layer of amino-silane compound coating over the glass substrate and a plurality of gold nano-urchins (GNU) bound to the layer of silicone compound. The plurality of gold-nano-urchins are functionalized with a hydrazide linker molecule for allowing uniform-oriented conjugation of a Fc region of antibodies to a surface of gold nano-urchins thereby allowing Fab regions of antibodies for binding with cancer biomarkers.