Effect of surface parameters on the performance of IgG-arrayed hydrogel chips: a comprehensive study

Analytical Protein Microarrays: Advancements Towards Clinical Applications

Protein microarrays represent a powerful technology with the potential to serve as tools for the detection of a broad range of analytes in numerous applications such as diagnostics, drug development, food safety, and environmental monitoring. Key features of analytical protein microarrays include high throughput and relatively low costs due to minimal reagent consumption, multiplexing, fast kinetics and hence measurements, and the possibility of functional integration. So far, especially fundamental studies in molecular and cell biology have been conducted using protein microarrays, while the potential for clinical, notably point-of-care applications is not yet fully utilized. The question arises what features have to be implemented and what improvements have to be made in order to fully exploit the technology. In the past we have identified various obstacles that have to be overcome in order to promote protein microarray technology in the diagnostic field. Issues that need significant improvement to make the technology more attractive for the diagnostic market are for instance: too low sensitivity and deficiency in reproducibility, inadequate analysis time, lack of high-quality antibodies and validated reagents, lack of automation and portable instruments, and cost of instruments necessary for chip production and read-out. The scope of the paper at hand is to review approaches to solve these problems.

Miniaturized protein arrays: Model and experiment

Nanobiolithography techniques have the ability to fabricate structures of biomolecules as small as ∼40 nm. However, very few examples of working biosensors of these sizes have been demonstrated. These examples use substrates like Gold and Silicon, that are advantageous for fabrication purposes, but present disadvantages as far as signal detection is concerned. The preferred and standard substrates used in microarray research are fabricated on glass. On these surfaces, the binding site density varies between and within individual samples, and is largely not characterized. We report here on the fabrication of a fully functional immunochip with spots of ∼1 μm diameter and a signal to noise ratio (SNR) above 10, using Nano-fountain pen (NFP). To achieve this, we analyze the dominant parameters influencing SNR, develop a model that enables us to compare various types of surfaces and choose the most appropriate ones. We show that a miniaturized immunochip is feasible, yielding detection limit as low as 1.3 ng/ml and dynamic range well above 10(5). Cross-reactivity of two different species is shown to be negligible. In addition, we study the binding mechanism of surfaces, show how to differentiate between 2D and 3D immobilization, and show that a hydrogel surface (using non-covalent immobilization strategy) yields higher intensities for the same target molecule concentrations, and higher dynamic range.

Optical waveguide spectroscopy for the investigation of protein-functionalized hydrogel films

This article reports the implementation of optical waveguide spectroscopy (OWS) for the quantitative time-resolved observation of changes in the swelling behavior and mass density of protein-functionalized hydrogel films. In the experiment, a thin film of an N-isopropylacrylamide (NIPAAm)-based polymer that supported optical waveguide modes is attached to a metallic sensor surface. IgG molecules are in situ immobilized in this gel by using novel coupling chemistry with a charge-attraction scheme based on a tetrafluorophenol sulfonate active ester. The anti-fouling properties of the functionalized hydrogel network and the kinetics of the affinity binding of protein molecules in the gel are investigated.