Studies on the Biotin-Avidin Multilayer Adsorption by Spectroscopic Ellipsometry

Isotropic three-dimensional dual-color super-resolution microscopy with metal-induced energy transfer

Over the past two decades, super-resolution microscopy has seen a tremendous development in speed and resolution, but for most of its methods, there exists a remarkable gap between lateral and axial resolution, which is by a factor of 2 to 3 worse. One recently developed method to close this gap is metal-induced energy transfer (MIET) imaging, which achieves an axial resolution down to nanometers. It exploits the distance-dependent quenching of fluorescence when a fluorescent molecule is brought close to a metal surface. In the present manuscript, we combine the extreme axial resolution of MIET imaging with the extraordinary lateral resolution of single-molecule localization microscopy, in particular with direct stochastic optical reconstruction microscopy (dSTORM). This combination allows us to achieve isotropic three-dimensional super-resolution imaging of subcellular structures. Moreover, we used spectral demixing for implementing dual-color MIET-dSTORM that allows us to image and colocalize, in three dimensions, two different cellular structures simultaneously.

Dynamic ellipsometry measurement based on a simplified phase-stable dual-comb system

Spectroscopic ellipsometry is a powerful tool for characterizing thin film, polarization optics, semiconductors, and others. Conventional approaches are subject to restrictions of mechanical instability and measurement speed. The complex locking scheme of previous dual-comb spectroscopic ellipsometry belies its practicability. We present and demonstrate here dynamic spectroscopic ellipsometry based on a simplified phase-stable dual-comb system, which could realize the online dynamic measurement of optical properties of materials. A precision of 1.31 nm and a combined uncertainty of 13.80 nm (k = 2) in the thickness measurement of thin-film samples has been achieved. Moreover, the dynamic performance of the system is investigated under a high data acquisition rate (1 kHz) with a dynamic resolution of ellipsometric parameter better than 0.1 rad.

On the control of dispersion interactions between biological membranes and protein coated biointerfaces

HYPOTHESIS

Interaction of cellular membranes with biointerfaces is of vital importance for a number of medical devices and implants. Adhesiveness of these surfaces and cells is often regulated by depositing a layer of bovine serum albumin (BSA) or other protein coatings. However, anomalously large separations between phospholipid membranes and the biointerfaces in various conditions and buffers have been observed, which could not be understood using available theoretical arguments.

METHODS

Using the Lifshitz theory, we here evaluate the distance-dependent Hamaker coefficient describing the dispersion interaction between a biointerface and a membrane to understand the relative positioning of two surfaces. Our theoretical modeling is supported by experiments where the biointerface is represented by a glass substrate with deposited BSA and protein layers. These biointerfaces are allowed to interact with giant unilamellar vesicles decorated with polyethylene glycol (PEG) using PEG lipids to mimic cellular membranes and their pericellular coat.

RESULTS

We demonstrate that careful treatment of the van der Waals interactions is critical for explaining the lack of adhesiveness of the membranes with protein-decorated biointerfaces. We show that BSA alone indeed passivates the glass, but depositing an additional protein layer on the surface BSA, or producing multiple layers of proteins and BSA results in repulsive dispersion forces responsible for 100 nm large equilibrium separations between the two surfaces.

Dynamic characterization of polarization property in liquid-crystal-on-silicon spatial light modulator using dual-comb spectroscopic polarimetry

Spectroscopic polarimetry (SP) is a powerful tool for characterization of thin film, polarization optics, semiconductor, and others. However, mechanical polarization modulation of broadband light hampers its application for dynamic monitoring of a sample. In this article, we demonstrate the dynamic SP with features of polarization-modulation-free polarimetry and spectrometer-free spectroscopy benefiting from dual-comb spectroscopy (DCS) using a pair of optical frequency combs (OFCs). DCS enables the direct determination of polarization without the need for polarization modulation by using mode-resolved OFC spectra of amplitude and phase for two orthogonally linear-polarized lights while securing rapid, high-precision, broadband spectroscopy without the need for spectrometer. Effectiveness of the proposed system is highlighted by visualizing the hysteresis property of dynamic response in a liquid-crystal-on-silicon spatial light modulator at a sampling rate of 105 Hz.

Adsorption properties of BSA and DsRed proteins deposited on thin SiO2 layers: optically non-absorbing versus absorbing proteins

Protein adsorption on solid surfaces is of interest for many industrial and biomedical applications, where it represents the conditioning step for micro-organism adhesion and biofilm formation. To understand the driving forces of such an interaction we focus in this paper on the investigation of the adsorption of bovine serum albumin (BSA) (optically non-absorbing, model protein) and DsRed (optically absorbing, naturally fluorescent protein) on silica surfaces. Specifically, we propose synthesis of thin protein layers by means of dip coating of the dielectric surface in protein solutions with different concentrations (0.01-5.0 g l^-1). We employed spectroscopic ellipsometry as the most suitable and non-destructive technique for evaluation of the protein layers' thickness and optical properties (refractive index and extinction coefficient) after dehydration, using two different optical models, Cauchy for BSA and Lorentz for DsRed. We demonstrate that the thickness, the optical properties and the wettability of the thin protein layers can be finely controlled by proper tuning of the protein concentration in the solution. These results are correlated with the thin layer morphology, investigated by AFM, FTIR and PL analyses. It is shown that the proteins do not undergo denaturation after dehydration on the silica surface. The proteins arrange themselves in a lace-like network for BSA and in a rod-like structure for DsRed to form mono- and multi-layers, due to different mechanisms driving the organization stage.

Dual-comb spectroscopic ellipsometry

Spectroscopic ellipsometry is a means of investigating optical and dielectric material responses. Conventional spectroscopic ellipsometry is subject to trade-offs between spectral accuracy, resolution, and measurement time. Polarization modulation has afforded poor performance because of its sensitivity to mechanical vibrational noise, thermal instability, and polarization-wavelength dependency. We combine spectroscopic ellipsometry with dual-comb spectroscopy, namely, dual-comb spectroscopic ellipsometry. Dual-comb spectroscopic ellipsometry (DCSE). DCSE directly and simultaneously obtains the ellipsometric parameters of the amplitude ratio and phase difference between s-polarized and p-polarized light signals with ultra-high spectral resolution and no polarization modulation, beyond the conventional limit. Ellipsometric evaluation without polarization modulation also enhances the stability and robustness of the system. In this study, we construct a polarization-modulation-free DCSE system with a spectral resolution of up to 1.2 × 10-5 nm throughout the spectral range of 1514-1595 nm and achieved an accuracy of 38.4 nm and a precision of 3.3 nm in the measurement of thin-film samples.Spectroscopic ellipsometry is an established technique to characterize the optical properties of a material. Here, Minamikawa et al. combine the method with dual-comb spectroscopy, which allows them to obtain ellipsometric parameters including the phase difference between s-polarized and p-polarized light.

A Review of Techniques to Measure Protein Sorption to Soft Contact Lenses

PURPOSE

To compare and critically evaluate a variety of techniques to measure the quantity and biological activity of protein sorption to contact lenses over short time periods.

METHODS

A literature review was undertaken investigating the major techniques to measure protein sorption to soft contact lens materials, with specific reference to measuring protein directly on lenses using in situ, ex situ, protein structural, and biological activity techniques.

RESULTS

The use of in situ techniques to measure protein quantity provides excellent sensitivity, but many are not directly applicable to contact lenses. Many ex situ techniques struggle to measure all sorbed proteins, and these measurements can have significant signal interference from the lens materials themselves. Techniques measuring the secondary and tertiary structures of sorbed proteins have exhibited only limited success.

CONCLUSIONS

There are a wide variety of techniques to measure both the amount of protein and the biological activity of protein sorbed to soft contact lens materials. To measure the mass of protein sorbed to soft contact lenses (not just thin films) over short time periods, the method of choice should be I radiolabeling. This technique is sensitive enough to measure small amounts of deposited protein, provided steps are taken to limit and measure any interaction of the iodine tracer with the materials. To measure the protein activity over short time periods, the method of choice should be to measure the biological function of sorbed proteins. This may require new methods or adaptations of existing ones.

Multiplexed cancer biomarker detection using chip-integrated silicon photonic sensor arrays

The analysis of disease-specific biomarker panels holds promise for the early detection of a range of diseases, including cancer. Blood-based biomarkers, in particular, are attractive targets for minimally-invasive disease diagnosis. Specifically, a panel of organ-specific biomarkers could find utility as a general disease surveillance tool enabling earlier detection or prognostic monitoring. Using arrays of chip-integrated silicon photonic sensors, we describe the simultaneous detection of eight cancer biomarkers in serum in a relatively rapid (1 hour) and fully automated antibody-based sandwich assay. Biomarkers were chosen for their applicability to a range of organ-specific cancers, including disease of the pancreas, liver, ovary, breast, lung, colorectum, and prostate. Importantly, we demonstrate that selected patient samples reveal biomarker "fingerprints" that may be useful for a personalized cancer diagnosis. More generally, we show that the silicon photonic technology is capable of measuring multiplexed panels of protein biomarkers that may have broad utility in clinical diagnostics.

Kinetics of Competitive Adsorption between Lysozyme and Lactoferrin on Silicone Hydrogel Contact Lenses and the Effect on Lysozyme Activity

PURPOSE

To determine the effect of competitive adsorption between lysozyme and lactoferrin on silicone hydrogel contact lenses and the effect on lysozyme activity.

METHODS

Three commercially available silicone hydrogel contact lens materials (senofilcon A, lotrafilcon B and balafilcon A) were examined, for time points ranging from 10 s to 2 h. Total protein deposition was determined by I(125) radiolabeling of lysozyme and lactoferrin, while the activity of lysozyme was determined by a micrococcal activity assay.

RESULTS

Senofilcon A and balafilcon A did not show any relevant competitive adsorption between lysozyme and lactoferrin. Lotrafilcon B showed reduced protein deposition due to competitive adsorption for lactoferrin at all time points and lysozyme after 7.5 min. Co-adsorption of lactoferrin and lysozyme decreased the activity of lysozyme in solution for senofilcon A and lotrafilcon B, but co-adsorption had no effect on the surface activity of lysozyme for all lens types investigated.

CONCLUSIONS

Competition between lysozyme and lactoferrin is material specific. Co-adsorption of lysozyme and lactoferrin does not affect the activity of surface-bound lysozyme but can reduce the activity of subsequently desorbed lysozyme.

Real-time label-free detection of complement activation products in human serum by white light reflectance spectroscopy

We present a label-free, real-time sensor based on white light reflectance spectroscopy for quantitating the complement activation product C3b and its metabolites as a biomarker in human serum. Our novel sensor allows real-time monitoring of biomolecular reactions (in this case, antigen-antibody reactions) taking place on a reflective surface within a flow cell. Detection was based on monitoring the increase in film thickness caused by its immunoreaction with a specific antibody; this reaction was seen as a shift in the wavelength at which constructive interference was observed. Quantitation of C3b was achieved by immobilizing a specific mouse monoclonal antibody onto the refractive surface and monitoring the rate of the signal changes occurring during the first 60s of the immunoreaction between the antibody and known concentrations of purified C3b or dilutions of complement-activated human serum. The lowest detectable concentration of purified C3b was 20 ng/mL, and complement activation products in human serum samples could be detected at dilutions as high as 6000-fold. The advantages of the method include its relatively low cost, short analysis time, and high assay sensitivity and reliability. Thus, this novel assay method can be used to monitor serum C3b produced as a result of complement activation in a variety of normal and pathologic conditions.

Investigating Protein Adsorption via Spectroscopic Ellipsometry

In this chapter, the basic concepts behind ellipsometry and spectroscopic ellipsometry are discussed along with some instrument details. Ellipsometry is an optical technique that measures changes in the reflectance and phase difference between the parallel (R_P) and perpendicular (R_S) components of a polarized light beam upon reflection from a surface. Aside from providing a simple, sensitive, and nondestructive way to analyze thin films, ellipsometry allows dynamic studies of film growth (thickness and optical constants) with a time resolution that is relevant to biomedical research. The present chapter intends to introduce ellipsometry as an emerging but highly promising technique, that is useful to elucidate the interactions of proteins with solid surfaces. In this regard, particular emphasis is placed on experimental details related to the development of biomedically relevant conjugated surfaces. Results from our group related to adsorption of proteins to nanostructured materials, as well as results published by other research groups, are discussed to illustrate the advantages and limitations of the technique.

Cantilever biosensors

This review will provide a general introduction to the field of cantilever biosensors by discussing the basic principles and the basic technical background necessary to understand and evaluate this class of sensors. Microfabricated cantilever sensors respond to changes in their environment or changes on their surface with a mechanical bending in the order of nanometers which can easily be detected. They are able to detect pH and temperature changes, the formation of self-assembled monolayers, DNA hybridization, antibody-antigen interactions, or the adsorption of bacteria. The review will focus on the surface stress mode of microfabricated cantilever arrays and their application as biosensors in molecular life science. A general background on biosensors, an overview of the different modes of operation of cantilever sensors and some details on sensor functionalization will be given. Finally, key experiments and current theoretical efforts to describe the surface stress mode of cantilever sensors will be discussed.

A streptavidin surface on planar glass substrates for the detection of biomolecular interaction

Based on the requirements of biomolecular interaction analysis on direct optical transducers, a streptavidin surface is examined. A general protocol was developed allowing the immobilization of biotinylated compounds using the rife biotin-streptavidin system. This type of surface modification can be applied to all biosensors using glass surfaces as sensor devices. Reflectometric interference spectroscopy (RIfS), a label-free, direct optical method was used to demonstrate the quality of the transducer surfaces. The surface modification is based on an aminofunctionalized polyethylene glycol layer covalently bound to the silica surface of the transducer and shows very little nonspecific binding. Biotin molecules can be easily coupled on such layers. Streptavidin followed by a biotinylated estrone derivative was immobilized by incubation of the biotinylated transducer surface. For the streptavidin layer we obtained interference signals corresponding to a protein monolayer. Finally, using a surface prepared as described above, biomolecular interaction experiments with an antibody against estrone were carried out to show the quality of the transducer surface. With RIfS all of the affinity-based surface modifications can be detected online and time resolved.

Quartz crystal microbalances for quantitative biosensing and characterizing protein multilayers

The use of quartz crystal microbalances (QCMs) for quantitative biosensing and characterization of protein multilayers is demonstrated in three case studies. Monolayers of QCM-based affinity biosensors were investigated first. Layers of a thiol-containing synthetic peptide constituting an epitope of the foot-and-mouse-disease virus were formed on gold electrodes via self-assembly. The binding of specific antibodies to epitope-modified gold electrodes was detected for different concentrations of antibody solutions. Oligolayers were studied in a second set of experiments. Dextran hydrogels were modified by thrombin inhibitors. The QCM response was used in a competitive binding assay to identify inhibitors for thrombin at different concentrations. Multilayers of proteins formed by self-assembly of a biotin-conjugate and streptavidin were investigated next. The QCM frequency response was monitored as a function of layer thickness up to 20 protein layers. A linear frequency decay was observed with increasing thickness. The decay per layer remained constant, thus indicating perfect mass coupling to the substrate. Frequency changes a factor of four higher were obtained in buffer solution as compared to measurements in dry air. This indicates a significant incorporation of water (75% weight) in the protein layers. This water behaves like a solid concerning the shear mode coupling to the substrate. The outlook discusses briefly the need for controlled molecular engineering of overlayers for subsequent QCM analysis, and the importance of an additional multiparameter analysis with other transducer principles and with additional techniques of interface analysis to characterize the mechanical coupling of overlayers as biosensor coatings. A promising trend concerns the use of QCM-arrays for screening experiments.