Plasmonic biosensors fabricated by galvanic displacement reactions for monitoring biomolecular interactions in real time

Abstract

Optical sensors are prepared by reduction of gold ions using freshly etched hydride-terminated porous silicon, and their ability to specifically detect binding between protein A/rabbit IgG and asialofetuin/Erythrina cristagalli lectin is studied. The fabrication process is simple, fast, and reproducible, and does not require complicated lab equipment. The resulting nanostructured gold layer on silicon shows an optical response in the visible range based on the excitation of localized surface plasmon resonance. Variations in the refractive index of the surrounding medium result in a color change of the sensor which can be observed by the naked eye. By monitoring the spectral position of the localized surface plasmon resonance using reflectance spectroscopy, a bulk sensitivity of 296 nm ± 3 nm/RIU is determined. Furthermore, selectivity to target analytes is conferred to the sensor through functionalization of its surface with appropriate capture probes. For this purpose, biomolecules are deposited either by physical adsorption or by covalent coupling. Both strategies are successfully tested, i.e., the optical response of the sensor is dependent on the concentration of respective target analyte in the solution facilitating the determination of equilibrium dissociation constants for protein A/rabbit IgG as well as asialofetuin/Erythrina cristagalli lectin which are in accordance with reported values in literature. These results demonstrate the potential of the developed optical sensor for cost-efficient biosensor applications.

Plasmonic Nanohole Arrays on Top of Porous Silicon Sensors: A Win–Win Situation

“…Protein A has a strong affinity to surfaces made of gold and cannot be easily detached. 32,33 In contrast, PSi functionalized with APTES has a positive charge in acidic media, and its electrostatic repulsive interaction with protein A, which is also positively charged (at this pH value), facilitates the removal of protein A from the PSi layer. Similar observations have already been described for BSA.…”

“…Upon exposure of the sensor to PBS (from ∼61 to ∼72 min) and 0.1 M acetic acid solutions (from ∼72 to ∼81 min), the protein A was successfully removed from the PSi layer but remained adsorbed on the gold surface. Protein A has a strong affinity to surfaces made of gold and cannot be easily detached. , In contrast, PSi functionalized with APTES has a positive charge in acidic media, and its electrostatic repulsive interaction with protein A, which is also positively charged (at this pH value), facilitates the removal of protein A from the PSi layer. Similar observations have already been described for BSA .…”

Surface Plasmon Photodetectors Based on Noble Metals

“…Plasmonic materials, when properly illuminated with visible or near infrared wavelengths, exhibit unique and interesting characteristics that can be exploited to tailor and adjust the radiation and propagation properties of light to nanoscale dimensions [1][2][3][4][5][6][7][8]. Various plasmonic structures have been exploited for optical signal filtering [9,10], switches [11,12], transport [13,14], modulation [15,16] and detection [17,18].…”