Gold nanomaterials for the selective capturing and SERS diagnosis of toxins in aqueous and biological fluids

Highlights - Combined extraction and detection of protein from biological fluid within the hour. - A highly efficient approach to the oriented immobilization of antibody fragments onto nanomaterial. - Facile recycle of functionalized nanoparticles for repeated extraction of biomolecules. - Facile synthesis of new paper-based substrate for cost effective SERS screening. - Highly portable rapid protein nanosensing methodology for biomedical and environmental applications. Abstract A highly sensitive nanosensing method for the combined selective capture and SERS detection of Microcystin-LR (MC-LR) in blood plasma has been developed. The new method utilizes gold coated magnetic nanoparticles that are functionalized with anti MC-LR antibody Fab' fragments for the selective capture of MC-LR from aqueous media and blood plasma. Using an oriented immobilization approach, the Fab' fragments are covalently attached to gold surface to form a monolayer with high capture efficiency towards the toxin. After the selective capture, the purified MC-LR molecules were released from the extractor nanoparticles within 5 min by manipulating the pH environment of the nanoparticles. The regenerated extractor nanoparticles maintained their capture efficiency and, therefore, were re-used to capture of MC-LR from successive samples. The released purified toxin was screened within 10 min on gold coated silicon nanopillars and a new paper-based SERS substrate by handheld Raman spectrometer. The SERS enhancement factors of the nanopillars and the new paper-based substrate were 2.5×106 and 3×105 respectively. The lower limit of quantification (LOQ) of MC-LR by SERS on the nanopillar substrate was 10 fM (R2=0.9975) which is well below the clinically required detection limit of the toxin. The SERS determination of MC-LR was cross validated against ELISA. By using antibody fragments that are specific to the target biomolecule, the new methodology can be extended to the rapid extraction and detection of other toxins and proteins.