Search

DNA amplification reactions are often used for nucleic acid analysis on lab-on-chip devices. In view of point of care testing e.g. for pathogen detection in emergency stations, such an analysis must be fast and simple to be performed. As an alternative to fluorescence based measurements the method presented here is based on detecting the change in the rheological properties of the assay. For the first time, on chip DNA amplification with real time viscometric detection is shown, with first results already being available after less than 20 min. The change of the sample's viscosity during the polymerization employing the rolling circle amplification (RCA) is detected using a micromachined vibrating cantilever. The RCA was chosen, as it is isothermal and produces very long strands resulting in a high change of the fluid's rheological properties. As the reaction proceeds, an increase of the cantilever's damping and required excitation power to keep its amplitude constant is observed in real-time. Evaluating the slope of these two parameters e.g. 27 min after starting the reaction, samples where polymerization takes place and samples without reaction can perfectly be distinguished. The described approach works without explicit functionalization of the sensor surface or labeling of reaction components.

When measuring the properties of fluids from biological sources, sample volumes in the micro-liter range are often desired as higher volumes may not be available or are very expensive. Miniaturized viscosity and density sensors based on a vibrating cantilever fulfill this requirement. In this paper, the possibility of measuring viscosity and density of DNA solutions at the same time using such a sensor is shown. The sensor requires a sample volume of 10 μl. By doing a titration of a solution containing 110 bp long strands of DNA in the diluted, Newtonian regime, the intrinsic viscosity can be determined to be 0.047 ml mg(-1) using the cantilever sensor. The cantilever is also tested with solutions of 10 kbp long strands with concentrations in the semi-dilute, non-Newtonian regime. The comparably small change in resonance frequency and damping observed using these solutions at 12.5 kHz is attributed to shear thinning, which is expected when extrapolating results from other groups.

This paper proposes a novel method for an inductive readout of vibrating MEMS cantilever structures submerged in a liquid. The excitation of the system is separated in time from the detection of the cantilever oscillation. With this strategy the resonance frequency and damping are quantified overcoming the problem of measuring a small amplitude signal while applying a large amplitude signal for the excitation at the same time. An application to loop and plate shaped viscosity and density sensors is shown. Measurements with mixtures of glycerol, ethylene glycol and water are presented. The sensors exhibit very high sensitivity while requiring simple instrumentation.

A chip-based viscosity and density sensor which requires a sample volume of less than 10 colonl is presented. A resistive heater and a temperature sensor are provided for accurate and fast temperature dependent measurements. An inductive readout of the resonance frequency and the damping further facilitates the measurement procedure. Thereby high resolution measurements of fluid properties are easily made in view of their analysis in the context of thermorheologically simple materials., Procedia Engineering, 25, Eurosensors XXV

This paper describes a hybrid silicon/plastic chip which is used to analyze DNA samples without the need of fluorescence or surface functionalization. The viscosity and density of the solutions to be tested are measured using a vibrating silicon beam immersed in the fluid. The sensitivity of the chip with respect to DNA concentration and length is analyzed, yielding a limit of detection of 0.5 μg/μl. We show that the sensitivity of the chip is statistically significant for PCR end-point detection. State-of-the-art on-chip detection methods of DNA solutions need optical devices or specially designed reactions. With the viscometric method proposed in this paper, these drawbacks are avoided., Procedia Engineering, 47, 26th European Conference on Solid-State Transducers, EUROSENSOR 2012