Combined small and large magnetic nanoparticle extraction and concentration from biofluids for non-toxic detection of biomarkers.

We propose a novel non-toxic method of diagnostic biomarker extraction and concentration from biofluids. The method is based on the usage of (1) magnetic nanoparticles of a few nanometres in size bearing molecular traps for biomarkers on their surface and (2) additional larger (several tens of nanometres) magnetic nanoparticles for catching smaller magnetic nanoparticles in a strong magnetic field gradient with their consequent concentration into the detection area. It is shown that the interference of an external permanent gradient magnetic field with the magnetic field of large magnetic nanoparticles allows one to catch small magnetic nanoparticles from their trajectories in a fluid at a distance around ten radii of the large nanoparticles. Theoretical analysis and mathematical simulation show the validity of the proposed non-toxic method for fast and robust biomarker extraction and concentration for increasing the sensitivity of biomarker detection. We believe that the results presented herein can serve as a starting point in the development of a new subclass of biosensors and a human body diagnostic approach with enhanced sensitivity and selectivity.