Biomedical subjects

Christoph Gerber

Publications and source records attributed to Christoph Gerber.

8 recordsLinked to original sources

PubMed2007

Investigating the molecular mechanisms of in-plane mechanochemistry on cantilever arrays.

Free-standing cantilevers, which directly translate specific biochemical reactions into micromechanical motion, have recently attracted much attention as label-free biosensors and micro/nano robotic devices. To exploit this mechanochemical sensing technology, it is essential to develop a fundamental understanding of the origins of surface stress. Here we report a detailed study into the molecular basis of stress generation in aqueous environments focusing on the pH titration of model mercaptohexadecanoic acid self-assembled monolayers (SAMs), using in situ reference cantilevers coated with nonionizable hexadecanethiol SAMs. Semiautomated data analysis and a statistical model were developed to quantify cyclic deprotonation/protonation reactions on multiple arrays. In-plane force titrations were found to have the sensitivity to detect ionic hydrogen bond formation between protonated and nonprotonated carboxylic acid groups in the proximity of the surface pK1/2, which generated a mean tensile differential surface stress of +1.2 +/- 0.3 mN/m at pH 6.0, corresponding to 1 pN attractive force between two adjacent MHA molecules. Conversely, the magnitude of compressive differential surface stress was found to increase progressively with pH >/= 7.0, reaching a maximum of -14.5 +/- 0.5 mN/m at pH 9.0, attributed to enhanced electrostatic repulsion between deprotonated carboxylic acid groups. However, striking differences were observed in the micromechanical responses to different ionic strength and ion species present in the aqueous environment, highlighting the critical role of counter- and co-ions on surface stress. Our findings provide fundamental insights into the molecular mechanisms of in-plane mechanochemistry, which may be exploited for biosensing and nanoactuation applications.

Biosensing Techniques↗

PubMed2006

Conformational change of bacteriorhodopsin quantitatively monitored by microcantilever sensors.

Bacteriorhodopsin proteoliposomes were used as a model system to explore the applicability of micromechanical cantilever arrays to detect conformational changes in membrane protein patches. The three main results of our study concern: 1), reliable functionalization of micromechanical cantilever arrays with proteoliposomes using ink jet spotting; 2), successful detection of the prosthetic retinal removal (bleaching) from the bacteriorhodopsin protein by measuring the induced nanomechanical surface stress change; and 3), the quantitative response thereof, which depends linearly on the amount of removed retinal. Our results show this technique to be a potential tool to measure membrane protein-based receptor-ligand interactions and conformational changes.

Bacteriorhodopsins↗

PubMed2005

A label-free immunosensor array using single-chain antibody fragments.

We report a microcantilever-based immunosensor operated in static deflection mode with a performance comparable with surface plasmon resonance, using single-chain Fv (scFv) antibody fragments as receptor molecules. As a model system scFv fragments with specificity to two different antigens were applied. We introduced a cysteine residue at the C terminus of each scFv construct to allow covalent attachment to gold-coated sensor interfaces in directed orientation. Application of an array enabled simultaneous deflection measurements of sensing and reference cantilevers. The differential deflection signal revealed specific antigen binding and was proportional to the antigen concentration in solution. Using small, oriented scFv fragments as receptor molecules we increased the sensitivity of microcantilevers to approximately 1 nM.

Antigens↗

PubMed2005

Micromechanical mass sensors for biomolecular detection in a physiological environment.

Micromechanical cantilever arrays are used to measure time-resolved adsorption of tiny masses based on protein-ligand interactions. Here, streptavidin-biotin interactions are investigated in a physiological environment. A measurement method is introduced using higher flexural modes of a silicon cantilever in order to enhance the sensitivity of mass detection. Modeling the cantilever vibration in liquid allows the measurement of absolute mass changes. We show time-resolved mass adsorption of final 7+/-0.7 ng biotinylated latex beads. The sensitivity obtained is about 2.5 pg/Hz measuring at a center frequency of 750 kHz.

Biomechanical Phenomena↗

PubMed2005

Label free analysis of transcription factors using microcantilever arrays.

We report the measurement of protein interaction with double-stranded DNA oligonucleotides using cantilever microarray technology. We investigated two different DNA-binding proteins, the transcription factors SP1 and NF-kappaB, using cantilever arrays as they allow label-free measurement of different biomolecular interactions in parallel. Double-stranded DNA oligonucleotides containing a specific binding site for a transcription factor were sensitized on gold-coated cantilevers. The binding of the transcription factor creates a surface stress, resulting in a bending of the cantilevers. Both transcription factors could be detected independently at concentrations of 80-100 nM. A concentration dependence of the bending signal was measured using concentrations from 100 to 400 nM of NF-kappaB. The experiments show that the recognition sequence of one transcription factor can serve as a reference for the other, highlighting the sequence specificity of transcription factor binding.

DNA↗

PubMed2004

Inkjet deposition of alkanethiolate monolayers and DNA oligonucleotides on gold: evaluation of spot uniformity by wet etching.

Inkjet printing allows localized, contact-free deposition of liquids onto arbitrary substrates. In this article we demonstrate the fast formation of high-quality self-assembled monolayers (SAMs) on gold surfaces. Using a selective etch process, we verify the uniformity of the deposited spots. A direct comparison with microcontact-printed SAMs on Au revealed similar resist quality as inkjet-deposited alkanethiolate SAMs. Likewise, inkjet printing of thiol-functionalized and non-thiolated single-stranded DNA oligomers formed molecular layers protecting Au from etchants. For all compounds used, we achieved etched patterns that were homogeneous and free of defects. These results indicate that an inkjet is a convenient tool for surface functionalization and the direct writing of molecular films and resists.

Alkanes↗

PubMed2003

["Esthetic plus"-ITI-implants (TPS): a prospective clinical study].

The purpose of this prospective study was to examine the influence of a 1 mm lengthening of the rough surface (TPS) of "esthetic plus"-ITI-implants on the periimplant soft and hard tissues. Twenty-one "esthetic plus" ITI-implants were inserted into the maxilla in an esthetically critical zone of 12 patients with sufficient alveolar bone. Clinical and radiographic examinations were performed after ten and 32 months. The mean DIB-score (DIB = distance between implant shoulder and first implant-bone contact) was 2.19 mm after 32 month. The average DIB-score of implant sites adjacent to natural teeth was 1.90 mm, there only 0.1 mm of the rough surface did not have bone contact. However, the average DIB-scores of implant sites adjacent to other implants (2.63 mm) or distal extension situations (2.79 mm) were much higher. This means that the coronal part of the rough surface had no radiographic bone contact with 0.83 mm (to other implants) and with 0.99 mm (to distal extension situations), what should be taken into consideration when using an "esthetic plus"-ITI-implant. As a consequence a standard ITI-implant with a smooth neck of 2.8 mm would be indicated. The results of the present study indicate, that not only the shortening of the smooth implant neck to 1.8 mm but also the adjacent structures influence the periimplant soft and hard tissues.

Adult↗

PubMed2002

Multiple label-free biodetection and quantitative DNA-binding assays on a nanomechanical cantilever array.

We report a microarray of cantilevers to detect multiple unlabeled biomolecules simultaneously at nanomolar concentrations within minutes. Ligand-receptor binding interactions such as DNA hybridization or protein recognition occurring on microfabricated silicon cantilevers generate nanomechanical bending, which is detected optically in situ. Differential measurements including reference cantilevers on an array of eight sensors can sequence-specifically detect unlabeled DNA targets in 80-fold excess of nonmatching DNA as a background and discriminate 3' and 5' overhangs. Our experiments suggest that the nanomechanical motion originates from predominantly steric hindrance effects and depends on the concentration of DNA molecules in solution. We show that cantilever arrays can be used to investigate the thermodynamics of biomolecular interactions mechanically, and we have found that the specificity of the reaction on a cantilever is consistent with solution data. Hence cantilever arrays permit multiple binding assays in parallel and can detect femtomoles of DNA on the cantilever at a DNA concentration in solution of 75 nM.

Base Sequence↗