Abstract
Although several researchers had reported on methodologies for surface plasmon resonance (SPR) signal amplification based on the use of nanoparticles (NPs), the majority addressed the sandwich technique and low protein concentration. In this work, a different approach for SPR signal enhancement based on the use of gold NPs was evaluated. The method was used in the detection of two lectins, peanut agglutinin (PNA) and concanavalin A (ConA). Gold NPs were functionalized with antibodies anti-PNA and anti-ConA, and these NPs were used as protein scavengers in a solution. After being incubated with solutions of PNA or ConA, the gold NPs coupled with the collected lectins were injected on the sensor containing the immobilized antibodies. The signal amplification provided by this method was compared to the signal amplification provided by the direct coupling of PNA and ConA to gold NPs. Furthermore, both methods, direct coupling and gold NPs as protein scavengers, were compared to the direct detection of PNA and ConA in solution. Compared to the analysis of free protein, the direct coupling of PNA and ConA to gold NPs resulted in a signal amplification of 10–40-fold and a 13-fold decrease of the limit of detection (LOD), whereas the use of gold NPs as protein scavengers resulted in an SPR signal 40–50-times higher and an LOD 64-times lower.
Highlights
Surface plasmon resonance is a well-established method to study qualitatively and quantitatively the interaction between biomolecules based on the measurement of small variations of the refractive index in the surrounding dielectric medium of a thin metallic film irradiated with light at a certain angle [1]
Another indication that the proteins were linked to the gold NPs was the increase in the hydrodynamic diameter; the size measured by DLS was 60 nm
Gold NPs have been demonstrated as surface plasmon resonance (SPR) signal amplifiers by coating sensor surfaces, as well as by tagging the analytes
Summary
Surface plasmon resonance is a well-established method to study qualitatively and quantitatively the interaction between biomolecules based on the measurement of small variations of the refractive index in the surrounding dielectric medium of a thin metallic film irradiated with light at a certain angle [1]. Most of the recently-developed strategies for the enhancement of SPR sensitivity have been based on nanotechnology for designing a sensor surface with a higher surface area, as well as for employing nanoparticles (NPs) as amplification agents. These strategies have been recently reviewed by several authors [11,12,13,14,15]. The use of metallic NPs, especially gold, has been pointed out as the methodology with the highest SPR sensitivity and lowest limit of detection. The great performance of gold NPs as SPR signal amplifiers has been attributed to the localized surface plasmon coupling
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