Simultaneous Nanoplasmonic and Quartz Crystal Microbalance Sensing: Analysis of Biomolecular Conformational Changes and Quantification of the Bound Molecular Mass

Abstract

This paper presents a study of supported lipid bilayer (SLB) formation and subsequent protein binding using a sensor that combines localized surface plasmon resonance (LSPR) and quartz crystal microbalance with dissipation (QCM-D) monitoring. The LSPR activity arises from silicon oxide (SiO x ) coated nanometric apertures in a thin gold film, which also serves as the active electrode of a QCM-D crystal. Both transducer principles provide signatures for the formation of a SLB upon adsorption and subsequent rupture of adsorbed lipid vesicles. However, the two techniques are sensitive over different regions of the sample: LSPR primarily inside and on the rim of the holes and QCM-D primarily on the planar areas between the holes. Although the dimension of the lipid vesicles is on the same order as the dimension of the nanoholes, it is concluded from the response of the combined system that vesicle rupture in the nanoholes and on the planar region between the holes is synchronized. Furthermore, by determining the thickness of the SLB from the QCM-D response, the characteristic decay length of the LSPR field intensity could be determined. This made it possible not only to determine the mass and refractive index of the homogeneous SLB but also to postulate a generic means to quantify the LSPR response in terms of mass-uptake also for nonhomogeneous films. This is exemplified by measuring the adsorbed lipid mass during vesicle adsorption, yielding the critical lipid vesicle coverage at which spontaneous rupture into a planar bilayer occurs. The generic applicability and versatility of the method is demonstrated from specific protein binding to a functionalized SLB. From the absolute refractive index of the protein, provided from the LSPR data alone, it was possible to determine both the effective thickness of the protein film and the molecular mass (or number) of bound protein.

Nanoplasmonic biosensing with focus on short-range ordered nanoholes in thin metal films (Review)

“…27, 64, and 83͒ as is the decay length of the electromagnetic field ͑tens of nanometers͒. 83,88 To investigate the similarities of the optical properties of short-range ordered nanoholes and nanoparticles we have investigated nanoholes with varying depth and diameter. Figure 6 shows a scanning electron microscopy image of a typical short-range ordered nanohole sample and spectra from four different structures with the same aspect ratio of 1 2 between depth and diameter.…”

“…The fact that the sensing field is localized to the void of short-range ordered nanoholes, together with the decay length being similar to that of nanoparticles, 84,88 suggests that short-range ordered apertures in a thin metal film in most situations provide the same sensing capability as discrete nanoparticles. We therefore refer to sensing with shortrange ordered nanoholes as LSPR sensing.…”

“…Such combinations of sensor concepts are likely to provide the extraction of additional information about the studied systems that is not accessible with the single techniques alone. We recently developed a combination of the LSPR method with the QCM-D monitoring, 88,94 which relied on the fact that a plasmon active short-range ordered nanohole surface can be used as one of the electrodes of a QCM crystal. To form a supported lipid bilayer on the surface, the same structure as described above was used ͑ϳ20 nm SiO x sputtered on the short-range ordered gold nanoholes͒.…”

“…As seen, the separations of the linear extrapolations decrease with increasing refractive index and, consequently, the refractive indices at which the two pairs of curves ͑blue/red and red/ green͒ coincide, correspond to the absolute refractive indices of the SLB and the protein, respectively. 88 The possibility of using this approach to determine the absolute refractive index of the bound molecules originates from the shallow evanescent fields associated with nanoplasmon active substrates, which, in contrast to conventional SPR, means that a thin FIG. 7.…”

Real-time molecular recognition between protein and photosensitizer of photodynamic therapy by quartz crystal microbalance sensor

“…With the development of biotechnology and modern electronics, quartz crystal microbalance (QCM) 1 sensors, due to their low cost and simple operation, have been widely used because they allow the real-time analysis of reactions without labeling requirements and provide quantitative information on the rate and equilibrium association constant [1][2][3][4]. A QCM sensor integrated with a flow injection analysis (FIA) system has the advantage of working continuously and monitoring on-line the binding of the analyte [5][6][7][8].…”