Surface Plasmon Resonance Biosensors with Magnetic Sandwich Hybrids for Signal Amplification

Abstract

The conventional signal amplification strategies for surface plasmon resonance (SPR) biosensors involve the immobilization of receptors, the capture of target analytes and their recognition by signal reporters. Such strategies work at the expense of simplicity, rapidity and real-time measurement of SPR biosensors. Herein, we proposed a one-step, real-time method for the design of SPR biosensors by integrating magnetic preconcentration and separation. The target analytes were captured by the receptor-modified magnetic nanoparticles (MNPs), and then the biotinylated recognition elements were attached to the analyte-bound MNPs to form a sandwich structure. The sandwich hybrids were directly delivered to the neutravidin-modified SPR fluidic channel. The MNPs hybrids were captured by the chip through the neutravidin-biotin interaction, resulting in an enhanced SPR signal. Two SPR biosensors have been constructed for the detection of target DNA and beta-amyloid peptides with high sensitivity and selectivity. This work, integrating the advantages of one-step, real-time detection, multiple signal amplification and magnetic preconcentration, should be valuable for the detection of small molecules and ultra-low concentrations of analytes.

Keywords: biosensors; magnetic preconcentration; signal amplification; surface plasmon resonance.

Scheme 1

Schematic representation of DNA biosensor (A) and immunosensor (B) by directly injecting the sandwich hybrids onto the NA-covered SPR chip.

Figure 1

(A) Fluorescence microscopy images of the FITC–NA/BSA/GSH and BSA/GSH-modified chips. (B) SPR sensorgrams for injection of different hybrids onto the NA/BSA/GSH-modified chip: curve a, bio-DNA/T_DNA/DNA-MNPs; curve b, DNA-MNPs; curve c, T_DNA/DNA-MNPs; curve e, bio-DNA/T_DNA/DNA. Curve d corresponds to that for injection of bio-DNA/T_DNA/DNA-MNPs onto the BSA/GSH-modified chip. The concentration of T_DNA was 1.5 pM.

Figure 2

(A) SPR sensorgrams for the detection of different concentrations of T_DNA (a~i: 1, 10, 100, 500, 1000, 1500, 2000, 2500 and 5000 fM). (B) Dependence of SPR signal on T_DNA concentration. The inset shows the linear portion of the fitting curve.

Figure 2

(A) SPR sensorgrams for the detection of different concentrations of T_DNA (a~i: 1, 10, 100, 500, 1000, 1500, 2000, 2500 and 5000 fM). (B) Dependence of SPR signal on T_DNA concentration. The inset shows the linear portion of the fitting curve.

Figure 3

SPR sensorgrams for injection of Ab₁-MNPs (curve a), Aβ₄₀/Ab₁-MNPs (curve b), bio-Ab₂/Aβ₄₀/Ab₁-MNPs (curve c) and bio-Ab₂/Aβ₄₀/Ab₁ (curve d) into the NA/BSA/GSH-modified chip. The concentration of Aβ₄₀ was 2.5 pM.

Figure 4

(A) SPR sensorgrams for the detection of different concentrations of Aβ₄₀ (a–g: 10, 100, 250, 1000, 2000, 2500 and 5000 fM). (B) Dependence of SPR signal on Aβ₄₀ concentration. The inset shows the linear portion of the fitting curve.

Figure 5

Selectivity of the method toward 1 nM Aβ₁₆ (bar 1), 1 nM Aβ₄₂ (bar 2), 10 ng/mL HSA (bar 3), 1 nM beta-secretase (bar 4), 5 nM avidin (bar 5), 1 pM Aβ₄₀ (bar 6) and the mixture of 1 nM avidin and 1 pM Aβ₄₀ by one-step (bar 7) or two-step (bar 8) magnetic separation.