Label-free protein detection based on the heat-transfer method-a case study with the peanut allergen Ara h 1 and aptamer-based synthetic receptors

© 2015 American Chemical Society. Aptamers are an emerging class of molecules that, because of the development of the systematic evolution of ligands by exponential enrichment (SELEX) process, can recognize virtually every target ranging from ions, to proteins, and even whole cells. Although there are many techniques capable of detecting template molecules with aptamer-based systems with high specificity and selectivity, they lack the possibility of integrating them into a compact and portable biosensor setup. Therefore, we will present the heat-transfer method (HTM) as an interesting alternative because this offers detection in a fast and low-cost manner and has the possibility of performing experiments with a fully integrated device. This concept has been demonstrated for a variety of applications including DNA mutation analysis and screening of cancer cells. To the best our knowledge, this is the first report on HTM-based detection of proteins, in this case specifically with aptamer-type receptors. For proof-of-principle purposes, measurements will be performed with the peanut allergen Ara h 1 and results indicate detection limits in the lower nanomolar regime in buffer liquid. As a first proof-of-application, spiked Ara h 1 solutions will be studied in a food matrix of dissolved peanut butter. Reference experiments with the quartz-crystal microbalance will allow for an estimate of the areal density of aptamer molecules on the sensor-chip surface

Application of Long Wavelength Ultraviolet Radiation for Modification and Patterning of Protein-Repelling Monolayers

The applicability of long wavelength (390 nm) ultraviolet (UV) light for controlled modification of protein-repelling oligo­(ethylene glycol) terminated alkanethiolate (OEG-AT) monolayers on gold was studied. It was found that these films can be modified in a controlled way even at such a long wavelength, which offers versatile strategies for the design of mixed monomolecular films and chemical lithography. Using the UV treatment, protein affinity of the OEG-AT film could be either directly adjusted for nonspecific adsorption or, in combination with subsequent exchange reactions for molecules bearing a specific receptor, precisely tuned for specific adsorption. The parameters of both procedures were determined, and the results were compared with analogous data for UV light with shorter wavelengths. It occurred that 390 nm UV light is especially well suited for the fabrication of specific protein patterns. In addition, because of the long wavelength, well-developed standard optics and commercial patterning strategies can be potentially utilized

Investigation of the Ionic Hydration in Aqueous Salt Solutions by Soft X ray Emission Spectroscopy

Understanding the molecular structure of the hydration shells and their impact on the hydrogen bond (HB) network of water in aqueous salt solutions is a fundamentally important and technically relevant question. In the present work, such hydration effects were studied for a series of representative salt solutions (NaCl, KCl, CaCl₂, MgCl₂, and KBr) by soft X-ray emission spectroscopy (XES) and resonant inelastic soft X-ray scattering (RIXS). The oxygen <i>K</i>-edge XES spectra could be described with three components, attributed to initial state HB configurations in pure water, water molecules that have undergone an ultrafast dissociation initiated by the X-ray excitation, and water molecules in contact with salt ions. The behavior of the individual components, as well as the spectral shape of the latter component, has been analyzed in detail. In view of the role of ions in such effects as protein denaturation (i.e., the Hofmeister series), we discuss the ion-specific nature of the hydration shells and find that the results point to a predominant role of anions as compared to cations. Furthermore, we observe a concentration-dependent suppression of ultrafast dissociation in all salt solutions, associated with a significant distortion of intact HB configurations of water molecules facilitating such a dissociation