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

We demonstrate a homogeneous biosensor for the detection of multivalent targets by combination of magnetic nanoparticle (MNP) chains and a low-cost 405nm 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 5.5pM (0.82ng/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 21.6pM (0.65ng/mL) and a dynamic detection range up to 66.7nM (2µg/mL) with a sample-to-result time of approximately 20min. The performance for PSA detection therefore well meets the clinical requirements in terms of LOD (the threshold PSA level in blood is 4ng/mL) and detection range (PSA levels span from < 0.1-104ng/mL in blood), thus showing great promise for routine PSA diagnostics and for other in-situ applications.

Magnetoresistive sensor for real-time single nucleotide polymorphism genotyping.

We demonstrate a magnetoresistive sensor platform that allows for the real-time detection of point mutations in DNA targets. Specifically, we detect point mutations at two sites in the human beta globin gene. For DNA detection, the present sensor technology has a detection limit of about 160 pM and a dynamic range of about two orders of magnitude. The sensors are based on a new geometry for biological sensing that detects the difference between the amount of beads bound to a sensing pad and a local integrated negative reference pad. The magnetic beads are magnetised by the magnetic field arising from the sensor bias current such that no external magnetic fields are needed. The sensors are integrated in a microfluidic system with temperature control. The local negative reference integrated in the sensor geometry efficiently compensates for sensor offsets, external magnetic fields and a uniform background of magnetic beads, which enables real-time quantification of the specific binding of magnetic beads to the sensor surface under varying experimental conditions.

Improved bacteria detection by coupling magneto-immunocapture and amperometry at flow-channel microband electrodes.

This paper describes the first immunosensing system reported for the detection of bacteria combining immunomagnetic capture and amperometric detection in a one-step sandwich format, and in a microfluidic environment. Detection is based on the electrochemical monitoring of the activity of horseradish peroxidase (HRP), an enzyme label, through its catalysis of hydrogen peroxide (H(2)O(2)) in the presence of the mediator hydroquinone (HQ). The enzymatic reaction takes place in an incubation micro-chamber where the magnetic particles (MPs) are confined, upstream from the working electrode. The enzyme product is then pumped along a microchannel, where it is amperometrically detected by a set of microelectrodes. This design avoids direct contact of the biocomponents with the electrode, which lowers the risk of electrode fouling. The whole assay can be completed in 1h. The experiments performed with Escherichia coli evidenced a linear response for concentrations ranging 10(2)-10(8) cell ml(-1), with a limit of detection of 55 cells ml(-1) in PBS, without pre-enrichment steps. Furthermore, 100 cells ml(-1) could be detected in milk, and with negligible interference by non-target bacteria such as Pseudomonas.