Shape anisotropy enhanced optomagnetic measurement for prostate-specific antigen detection via magnetic chain formation

- An optomagnetic biosensor for rapid detection of bio-macromolecules is reported.
- Field-induced assembly of magnetic nanoparticle chains enhances the detection.
- Sensitivity in the picomolar range is achieved with a wide dynamic detection range.
- The proposed biosensor holds promise for clinical PSA detection in serum samples.

We demonstrate a homogeneous biosensor for the detection of multivalent targets by combination of magnetic nanoparticle (MNP) chains and a low-cost 405 nm laser-based optomagnetic system. The MNP chains are assembled in a rotating magnetic field and stabilized by multivalent target molecules. The number of chains remaining in zero field is proportional to the target concentration, and can be quantified by optomagnetic measurements. The shape anisotropy of the MNP chains enhances the biosensor system in terms of providing efficient mixing, reduction of depletion effects (via magnetic shape anisotropy), and directly increasing the optomagnetic signal (via optical shape anisotropy). We achieve a limit of detection (LOD) of 5.5 pM (0.82 ng/mL) for the detection of a model multivalent molecule, biotinylated anti-streptavidin, in PBS. For the measurements of prostate-specific antigen (PSA) in 50% serum using the proposed method, we achieve an LOD of 21.6 pM (0.65 ng/mL) and a dynamic detection range up to 66.7 nM (2 µg/mL) with a sample-to-result time of approximately 20 min. The performance for PSA detection therefore well meets the clinical requirements in terms of LOD (the threshold PSA level in blood is 4 ng/mL) and detection range (PSA levels span from < 0.1-104 ng/mL in blood), thus showing great promise for routine PSA diagnostics and for other in-situ applications.