Sensitive and specific detection of E. coli using biomimetic receptors in combination with a modified heat-transfer method

We report on a novel biomimetic sensor that allows sensitive and specific detection of Escherichia colt (E. coli) bacteria in a broad concentration range from 10(2) up to 10(6) CFU/mL in both buffer fluids and relevant food samples (i.e. apple juice). The receptors are surface-imprinted polyurethane layers deposited on stainless-steel chips. Regarding the transducer principle, the sensor measures the increase in thermal resistance between the chip and the liquid due to the presence of bacteria captured on the receptor surface. The low noise level that enables the low detection limit originates from a planar meander element that serves as both a heater and a temperature sensor. Furthermore, the experiments show that the presence of bacteria in a liquid enhances the thermal conductivity of the liquid itself. Reference tests with a set of other representative species of Enterobacteriaceae, closely related to E. coli, indicate a very low cross-sensitivity with a sensor response at or below the noise level

Cell detection by surface imprinted polymers SIPs:A study to unravel the recognition mechanisms

Previous studies have shown that selective synthetic cell receptors can be produced by cell imprinting on polymer layers. However, knowledge on the fundamental detection mechanisms remains limited. In this article, while using yeast cells (Saccharomyces cerevisiae) as model cells, the factors influencing cellular recognition by surface-imprinted polymers (SIPs) are studied by means of spectroscopic and microscopy techniques and a transducer platform based on interfacial thermal transport, the so-called heat-transfer method (HTM). These analyses indicate that cell imprinting creates selective binding sites on the surface of the SIP layer in the form of binding cavities that match the cells in shape and size. Also, we show that phospholipid moieties are incorporated into the SIP cavities during imprinting, while membrane proteins do not seem to be transferred. More importantly, we demonstrate that the incorporated phospholipids significantly enhance cell adhesion to the SIP, and thus play a significant role in the cell-SIP binding mechanism. Furthermore, the hydrophobicity of the SIP layer was found to be considerably higher when compared with a non-imprinted polymer layer (NIP), an effect that could not be attributed to the presence of cavities on the surface of the SIP layer. Therefore, we suggest that the role of phospholipids in the SIP recognition mechanism is mediated by long range hydrophobic forces. (C) 2017 Elsevier B.V. All rights reserved.</p

Direct evidence of ZnO morphology modification via the selective adsorption of ZnO-binding peptides

Biomolecule-mediated ZnO synthesis has great potential for the tailoring of ZnO morphology for specific application in biosensors, window materials for display and solar cells, dye-sensitized solar cells (DSSCs), biomedical materials, and photocatalysts due to its specificity and multi-functionality. In this contribution, the effect of a ZnO-binding peptide (ZnO-BP, G-12: GLHVMHKVAPPR) and its GGGC-tagged derivative (GT-16: GLHVMHKVAPPRGGGC) on the growth of ZnO crystals expressing morphologies dependent on the relative growth rates of (0001) and (10 (1) over bar0) planes of ZnO have been studied. The amount of peptide adsorbed was determined by a depletion method using oriented ZnO films grown by Atomic Layer Deposition (ALD), while the adsorption behavior of G-12 and GT-16 was investigated using XPS and a computational approach. Direct evidence was obtained to show that (i) both the ZnO-BP identified by phage display and its GGGC derivative (GT-16) are able to bind to ZnO and modify crystal growth in a molecule and concentration dependent fashion, (ii) plane selectivity for interaction with the (0001) versus the (10 (1) over bar0) crystal planes is greater for GT-16 than G-12; and (iii) specific peptide residues interact with the crystal surface albeit in the presence of charge compensating anions. To our knowledge, this is the first study to provide unambiguous and direct quantitative experimental evidence of the modification of ZnO morphology via (selective and nonselective) adsorption-growth inhibition mechanisms mediated by a ZnO-BP identified from phage display libraries

Nanocomposite Hydrogels as Functional Extracellular Matrices

Over recent years, nano-engineered materials have become an important component of artificial extracellular matrices. On one hand, these materials enable static enhancement of the bulk properties of cell scaffolds, for instance, they can alter mechanical properties or electrical conductivity, in order to better mimic the in vivo cell environment. Yet, many nanomaterials also exhibit dynamic, remotely tunable optical, electrical, magnetic, or acoustic properties, and therefore, can be used to non-invasively deliver localized, dynamic stimuli to cells cultured in artificial ECMs in three dimensions. Vice versa, the same, functional nanomaterials, can also report changing environmental conditions—whether or not, as a result of a dynamically applied stimulus—and as such provide means for wireless, long-term monitoring of the cell status inside the culture. In this review article, we present an overview of the technological advances regarding the incorporation of functional nanomaterials in artificial extracellular matrices, highlighting both passive and dynamically tunable nano-engineered components

Protein fiber-mediated self-assembly of gold nanoparticle arrays on surfaces

Protein-based scaffolds enable flexible and sustainable approaches to produce and manipulate materials at the nanometer scale1. The underlying self-assembly principles can complement classical top-down fabrication techniques to answer current challenges and needs in applications including biosensing or regenerative medicine. Amyloid protein nanofibres prepared from hen egg white lysozyme have been found to mediate the assembly of gold nanoparticles into 1D-arrays from solutions to silicon oxide surfaces2. The effect of experimental conditions on the self-assembly process is discussed based on atomic force microscopy and UV-visible spectroscopy measurements. The correlation between measured interparticle distances and results of DLVO calculations demonstrates a strong impact of electrostatic interactions on self-assembly. The deposited particles are then used as surface-immobilised seeds for the surfactant-assisted growth of metal structures with a wide range of morphologies. The experimental results are finally correlated with FDTD simulations to understand further the effect of particle spacing and morphology on the optical properties of the surface-deposited biohybrid materials.status: publishe

pH-sensitive quantum dots and rods

Quantum dots and quantum rods are semiconductor nanoparticles with interesting fluorescence properties. These nanoscale particles possess a large surface area, thus their fluorescence is highly sensitive to surface phenomena. Unpassivated surface sites and changes in the surface charges can quench the fluorescence intensity and shift the emission wavelength. In polar solvents, the surface charge and passivation are influenced by environmental factors such as the pH. Therefore, quantum dot fluorescence is in general pH-sensitive [1,2], rendering such particles useful for pH/(bio)sensing applications. We will discuss the pH-sensitivity of CdSe/ZnS quantum dots (QDs) and CdSe/CdS quantum rods (QRs). The dots and rods are initially dispersed in organic solvents. Different strategies exist to obtain water-soluble particles. We use both ligand exchange by thiols and ligand addition of phospholipids. These two water-solubilisation strategies lead to markedly different pH-responses. As generally observed, the fluorescence intensity of the QDs is quenched at acidic pH. The quenching is reversible for phospholipid-encapsulated QDs, but irreversible for thiol-capped QDs. The pH-response of the QRs differs from that of the QDs, showing atypical quenching at alkaline pH. The changes in the fluorescence intensity are often accompanied by small, but consistent shifts of the emission wavelength, the origin of which is not immediately clear [2,3]. Possible sources of spectral shifting are electronic energy transfer and polarization by electric fields. We investigate the source of the spectral shift by measurements of the hydrodynamic size and of the zeta potential, providing information on the particles aggregation state and surface potential , respectively.status: publishe

Hybrid, optically active collagen-QD matrices for read-out and stimulation of neuronal activity

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pH-induced exciton energy shift on water-solubilized CdSe/ZnS quantum dots

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Bioinorganic active cellular matrices: Preparation, mechanical characterization and cellular behaviour

Inorganic nanoparticles (NPs) have the potential to dynamically tune the properties of extracellular matrices. They can be used to modulate cell adhesion, migration or activity1, and to monitor parameters remotely and with a high spatial resolution2,3. In this study, we are producing biofibrillar hybrid matrices from fibre-forming proteins such as lysozyme or collagen, and a range of inorganic materials including gold nanoparticles and quantum dots4. We present 3 approaches for obtaining such bioinorganic scaffolds: where the NPs produced separately are grafted onto the nanofibers, where they are formed on the scaffolds or together with the scaffolds. Each approach leads to specific material dimensions and shapes, phase distribution and mechanical and optical properties as demonstrated by AFM and spectroscopic data. At last the behaviour of living cells is investigated for the different types of matrices.status: publishe

Cell detection by surface imprinted polymers (SIPs) – a study of the sensor surface by optical and dielectric relaxation spectroscopy

Cell imprinting on polymer layers produces synthetic receptors, so called surface imprinted polymers (SIPs) capable of specific and selective cellular recognition. However, their recognition mechanisms are not yet fully understood . Therefore, various factors that influence cell recognition were explored using different spectroscopic techniques. Specifically, the molecular dynamics of surface-imprinted and non-imprinted polyurethane layers was studied with focus on the dielectric relaxation signatures of proteins and lipids by dielectric relaxation spectroscopy (DRS). Furthermore, an alternative detection scheme for the electrical properties of the imprinted polymer layer has been tested . The new idea is to place a patterned thin film interdigitated electrode structure close to the cell recognition layer to obtain local information about the polymer/cell interface.status: publishe