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.

This study proposes that images of stains from 100-nanolitre drops can be automatically identified as signatures of fluid composition and substrate chemistry, for e.g. rapid biological testing. Two datasets of stain images are produced and made available online, one with consumable fluids, and the other with biological fluids. Classification algorithms are used to identify an unknown stain by measuring its similarity to representative examples of predefined categories. The accuracy ranges from 80 to 94%, compared to an accuracy by random assignment of 3 to 4%. Clustering algorithms are also applied to group unknown stain images into a number of clusters each likely to correspond to similar combinations of fluids and substrates. The clustering accuracy ranges from 62 to 80%, compared to an accuracy by random assignment of 3 or 4%. The algorithms were also remarkably accurate at determining the presence or absence of biotin and streptavidin respectively in the liquid and on the glass, the salt composition, or the pH of the solution.

The microfluidic integration of an entire DNA analysis workflow on a fully integrated miniaturized instrument is reported using lab-on-a-chip automation to perform DNA fingerprinting compatible with CODIS standard relevant to the forensic community. The instrument aims to improve the cost, duration, and ease of use to perform a "sample-to-profile" analysis with no need for human intervention. The present publication describes the operation of the three major components of the system: the electronic control components, the microfluidic cartridge and CE microchip, and the optical excitation/detection module. Experimental details are given to characterize the level of performance, stability, reliability, accuracy, and sensitivity of the prototype system. A typical temperature profile from a PCR amplification process and an electropherogram of a commercial size standard (GeneScan 500™, Applied Biosystems) separation are shown to assess the relevance of the instrument to forensic applications. Finally, we present a profile from an automated integrated run where lysed cells from a buccal swab were introduced in the system and no further human intervention was required to complete the analysis.

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A scanning electrochemical microscopy (SECM) approach for the analysis of heterogeneous catalytic reactions at solid-liquid interfaces is described and applied. In this scheme, reactant, generated at a tip, undergoes a reaction (e.g., disproportionation) at the substrate. The theoretical background for this study, performed by digital simulations using a finite difference method, considers a chemical reaction at the substrate with general stoichiometry. In this case, the fraction of regenerated mediator (nu(S)) may differ with respect to a substrate reaction that is the reverse of the tip reaction, resulting in an asymmetric mediator loop. Simulated tip current transients and approach curves at different values of the kinetic rate constant for reactions where nu(S) < 1 were used to analyze this new SECM situation. This approach was used to study the catalytic decomposition of hydrogen peroxide (HO2- --> 1/2O2 + OH-), where nu(S) = 0.5, on supported catalysts. A gold-mercury amalgam tip was used to quantitatively reduce dissolved O2 (mediator) to HO2-, which was decomposed back to oxygen at the catalyst substrate. Rate constants for the decomposition reaction on immobilized catalase and Pt particles were measured at different pH values by the correlation of experimental approach curves with the theoretical dependencies.