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

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

Substrate Topography Determines Neuronal Polarization and Growth In Vitro

The establishment of neuronal connectivity depends on the correct initial polarization of the young neurons. In vivo, developing neurons sense a multitude of inputs and a great number of molecules are described that affect their outgrowth. In vitro, many studies have shown the possibility to influence neuronal morphology and growth by biophysical, i.e. topographic, signaling. In this work we have taken this approach one step further and investigated the impact of substrate topography in the very early differentiation stages of developing neurons, i.e. when the cell is still at the round stage and when the first neurite is forming. For this purpose we fabricated micron sized pillar structures with highly reproducible feature sizes, and analyzed neurons on the interface of flat and topographic surfaces. We found that topographic signaling was able to attract the polarization markers of mouse embryonic neurons -N-cadherin, Golgi-centrosome complex and the first bud were oriented towards topographic stimuli. Consecutively, the axon was also preferentially extending along the pillars. These events seemed to occur regardless of pillar dimensions in the range we examined. However, we found differences in neurite length that depended on pillar dimensions. This study is one of the first to describe in detail the very early response of hippocampal neurons to topographic stimuli. © 2013 Micholt et al.Flanders Fund for Scientific Research; the Federal Office for Scientific Affairs (IUAP p6/43); Flemish Government Methusalem; Spanish Ministry of Science and Innovation Ingenio-Consolider (CSD2010-00064, SAF2010-14906)Peer Reviewe

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

Ta2O5 as gate dielectric material for low-voltage organic thin-film transistors

In this paper we report the use of Ta2O5 as gate dielectric material for organic thin-film transistors. Ta2O5 has already attracted a lot of attention as insulating material for VLSI applications. We have deposited Ta2O5 thin-films with different thickness by means of electron-beam evaporation. Being a relatively low-temperature process, this method is particularly suitable for organic thin-film transistor fabrication on plastic substrates. Deposition and patterning are achieved in one step by the use of shadow masks. The dielectric can be evaporated on top of the semiconducting layer. In this way a large variety of structures can be realized. Poly(3-hexylthiophene) was used as semiconducting material in the transistor structure. Such transistors are operating at voltages smaller than −3 V. Having a high dielectric constant (r=21), Ta2O5 facilitates the charge carrier accumulation in the transistor channel at much lower electrical fields. The properties of the dielectric material as well as the operation of the organic transistors with a Ta2O5 gate dielectric are discussed

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

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

status: publishe

Improving SERS uniformity by isolating hot spots in gold rod-in-shell nanoparticles

© 2016, Springer Science+Business Media Dordrecht. Surface-enhanced Raman scattering (SERS) tags show ultrasensitivity and multiplexing abilities due to strong and characteristic Raman signals and therefore can be utilized as optical labeling agents similar to fluorescent dyes and quantum dots for biosensing and bioimaging. However, SERS tags have the difficulty to realize quantitative analysis due to the uniformity and reproducibility issue. In this work, we have reported on a new type of SERS tag called Au rod-in-shell (RIS) gap-enhanced Raman tag (GERT). With the high-resolution transmission electron microscopy (TEM) and optical absorbance measurements, we have demonstrated the subnanometer sized gap junctions inside the RIS GERTs. SERS measurements and FDTD calculations show that the core–shell subnanometer gap geometry in the RIS GERTs not only generates strong SERS hot spots but also isolates SERS hot spots by Au shells to avoid the influence when the particle aggregates form, therefore showing better SERS uniformity and stronger SERS intensity than normal Au nanorods. Those RIS NPs exhibit great potential as the labeling agents for SERS-based bioimaging and biosensing applications.status: publishe