A sensitive and innovative detection method for rapid C-reactive proteins analysis based on a micro-fluxgate sensor system

<div><p>A sensitive and innovative assay system based on a micro-MEMS-fluxgate sensor and immunomagnetic beads-labels was developed for the rapid analysis of C-reactive proteins (CRP). The fluxgate sensor presented in this study was fabricated through standard micro-electro-mechanical system technology. A multi-loop magnetic core made of Fe-based amorphous ribbon was employed as the sensing element, and 3-D solenoid copper coils were used to control the sensing core. Antibody-conjugated immunomagnetic microbeads were strategically utilized as signal tags to label the CRP via the specific conjugation of CRP to polyclonal CRP antibodies. Separate Au film substrates were applied as immunoplatforms to immobilize CRP-beads labels through classical sandwich assays. Detection and quantification of the CRP at different concentrations were implemented by detecting the stray field of CRP labeled magnetic beads using the newly-developed micro-fluxgate sensor. The resulting system exhibited the required sensitivity, stability, reproducibility, and selectivity. A detection limit as low as 0.002 μg/mL CRP with a linearity range from 0.002 μg/mL to 10 μg/mL was achieved, and this suggested that the proposed biosystem possesses high sensitivity. In addition to the extremely low detection limit, the proposed method can be easily manipulated and possesses a quick response time. The response time of our sensor was less than 5 s, and the entire detection period for CRP analysis can be completed in less than 30 min using the current method. Given the detection performance and other advantages such as miniaturization, excellent stability and specificity, the proposed biosensor can be considered as a potential candidate for the rapid analysis of CRP, especially for point-of-care platforms.</p></div

Detection sensitivity for CRP.

<p>(A) Full view of the output voltage towards different CRP concentration. (B) The partial enlargement of the field range corresponding to 250–370 μT.</p

Immunoassay and detection method for CRP based on our system.

<p>(A) The immunoassay process of CRP. (B) Illustration of the detection method based on fluxgate sensor (C) The photograph of the fluxgate sensing circuit-system, the inlet shows the illustration of the relative position of the CRP sample in relation to the sensor. (D) CRP-labeled Dynabeads detection mechanism of the proposed system.</p

Photographs of the fabricated micro devices.

<p>(A) The MEMS-fluxgate sensor. (B) The Au film substrates (5×3 mm²).</p

SEM images of immobilized CRP-bead labels of different CRP concentration samples.

<p>(A) 0.002 μg/mL. (B) 0.005 μg/mL. (C) 0.01 μg/mL. (D) 0.1 μg/mL. (E) 1 μg/mL. (F) 10 μg/mL.</p

Specificity investigations of the biosystem.

<p>(A) Blank. (B) AFP (0.02 μg/mL). (C) CEA (0.02 μg/mL). (D) CRP (0.002 μg/mL). (E) CRP (0.002 μg/mL) +AFP (0.02 μg/mL). (F) CRP (0.002 μg/mL) + CEA (0.02 μg/mL).</p

Comparison of different immunosensors for CRP detection.

<p>Comparison of different immunosensors for CRP detection.</p

Linearity analysis.

<p>Linear range for the CRP detection with applied H_e = 330 μT.</p

AFM images and roughness analysis of the modified Au film.

<p>(A) The blank Au film. (B) The Au film after 11-MUA modification. (C) The Au film after antibody modification.</p