We present a study of thermal noise of commercially available atomic force microscopy (AFM) cantilevers in air and in water. The purpose of this work is to investigate the oscillation behavior of a clamped AFM microlever in liquids. Up to eight vibration modes are recorded. The experimental results are compared to theoretical predictions from the hydrodynamic functions corresponding to rigid transverse oscillations of an infinitely long rectangular beam. Except for the low-frequency modes, the known hydrodynamic functions cannot describe the amount of dissipated energy due to the liquid motion induced by the cantilever oscillation. The observed variation of the damping coefficient is smaller than the one predicted. The difference at higher modes between the mentioned theoretical description and experimental results is discussed with the help of numerical solutions of the three-dimensional Navier–Stokes equation.

We demonstrate a conduit for the delivery of a step change in the DNA analysis process: A fully integrated instrument for the analysis of multiplex short tandem repeat DNA profiles from reference buccal samples is described and is suitable for the processing of such samples within a forensic environment such as a police custody suite or booking office. The instrument is loaded with a DNA processing cartridge which incorporates on-board pumps and valves which direct the delivery of sample and reagents to the various reaction chambers to allow DNA purification, amplification of the DNA by PCR, and collection of the amplified product for delivery to an integral CE chip. The fluorescently labeled product is separated using micro capillary electrophoresis with a resolution of 1.2 base pairs (bp) allowing laser induced fluorescence-based detection of the amplified short tandem repeat fragments and subsequent analysis of data to produce a DNA profile which is compatible with the data format of the UK DNA database. The entire process from taking the sample from a suspect, to database compatible DNA profile production can currently be achieved in less than 4 h. By integrating such an instrument and microfluidic cartridge with the forensic process, we believe it will be possible in the near future to process a DNA sample taken from an individual in police custody and compare the profile with the DNA profiles held on a DNA Database in as little as 3 h.

Articles you may be interested inMeasurement of fluid properties using an acoustically excited atomic force microscope micro-cantilever J. Rheol. 54, 959 (2010); 10.1122/1.3460907 Frequency response of cantilever beams immersed in compressible fluids with applications to the atomic force microscope

We report the direct experimental measurement of electrical double layer profiles on metallic (Pt foil) and insulator (SiO 2 on Si) surfaces in a dilute electrolyte with no added redox mediator by scanning electrochemical potential microscopy (SECPM). An important consideration in these measurements is fabrication of the probe (tip), and experimental details are given for the reproducible preparation of suitable polyethylene-coated PtIr nanoelectrodes. A small amount of silver was electrodeposited on these tips to stabilize them for sensitive potentiometric measurements. A Pt foil surface and an oxide-grown Si(100) wafer in 10 µM KCl were approached to record the potential distribution in the vicinity of the surface. The advantages and limitations of SECPM are compared to conventional current-sensing techniques.