A device was developed that uses microfabricated fluidic channels, heaters, temperature sensors, and fluorescence detectors to analyze nanoliter-size DNA samples. The device is capable of measuring aqueous reagent and DNA-containing solutions, mixing the solutions together, amplifying or digesting the DNA to form discrete products, and separating and detecting those products. No external lenses, heaters, or mechanical pumps are necessary for complete sample processing and analysis. Because all of the components are made using conventional photolithographic production techniques, they operate as a single closed system. The components have the potential for assembly into complex, low-power, integrated analysis systems at low unit cost. The availability of portable, reliable instruments may facilitate the use of DNA analysis in applications such as rapid medical diagnostics and point-of-use agricultural testing.

The ability to trap an object-whether a single atom or a macroscopic entity-affects fields as diverse as quantum optics, soft condensed-matter physics, biophysics and clinical medicine. Many sophisticated methodologies have been developed to counter the randomizing effect of Brownian motion in solution, but stable trapping of nanometre-sized objects remains challenging. Optical tweezers are widely used traps, but require sufficiently polarizable objects and thus are unable to manipulate small macromolecules. Confinement of single molecules has been achieved using electrokinetic feedback guided by tracking of a fluorescent label, but photophysical constraints limit the trap stiffness and lifetime. Here we show that a fluidic slit with appropriately tailored topography has a spatially modulated electrostatic potential that can trap and levitate charged objects in solution for up to several hours. We illustrate this principle with gold particles, polymer beads and lipid vesicles with diameters of tens of nanometres, which are all trapped without external intervention and independently of their mass and dielectric function. The stiffness and stability of our electrostatic trap is easily tuned by adjusting the system geometry and the ionic strength of the solution, and it lends itself to integration with other manipulation mechanisms. We anticipate that these features will allow its use for contact-free confinement of single proteins and macromolecules, and the sorting and fractionation of nanometre-sized objects or their assembly into high-density arrays.

An integrated microfluidic device capable of performing a variety of genetic assays has been developed as a step towards building systems for widespread dissemination. The device integrates fluidic and thermal components such as heaters, temperature sensors, and addressable valves to control two nanoliter reactors in series followed by an electrophoretic separation. This combination of components is suitable for a variety of genetic analyses. As an example, we have successfully identified sequence-specific hemagglutinin A subtype for the A/LA/1/87 strain of influenza virus. The device uses a compact design and mass production technologies, making it an attractive platform for a variety of widely disseminated applications.

Mass and electrical charge are fundamental properties of biological macromolecules. Although molecular mass has long been determined with atomic precision, a direct and precise determination of molecular charge remains an outstanding challenge. Here we report high-precision (<1e) measurements of the electrical charge of molecules such as nucleic acids, and globular and disordered proteins in solution. The measurement is based on parallel external field-free trapping of single macromolecules, permits the estimation of a dielectric coefficient of the molecular interior and can be performed in real time. Further, we demonstrate the direct detection of single amino acid substitution and chemical modifications in proteins. As the electrical charge of a macromolecule strongly depends on its three-dimensional conformation, this kind of high-precision electrometry offers an approach to probe the structure, fluctuations and interactions of a single molecule in solution.

Rayleigh-Benard convection is caused by buoyancy-driven instability in a confined fluid layer heated from below (1). The dimensionless Rayleigh number Ra = ga(T -T)h3/VK expresses the interplay between buoyant forces driving the instability and diffusive restoring forces acting in opposition. Here, a is the coefficient of thermal expansion of the fluid, g is the acceleration due to gravity, T, and T2 are the temperatures of the top and bottom surfaces of the cavity, respectively, h is the height of the cavity, v is the kinematic viscosity, and K is the thermal diffusivity.The inherent structure of Rayleigh-Benard convection-steady circulatory flow between surfaces maintained at two fixed temperaturesis ideally suited for performing thermally activated chemical reactions that require temperature cycling. We have developed a device that uses Rayleigh-Benard convection to perform polymerase chain reaction (PCR) amplification of DNA inside a 35-p1l cylindrical cavity. Instead of the external temperature control of conventional thermocyclers, temperature cycling is achieved as the flow field continually shuttles fluid packets vertically through the temperature zones associated with denaturation (-95?C) and annealing/extension (60? to 70?C). The steady circulatory flow field must engage the entire reaction volume yet be slow enough to allow the reaction within each temperature zone to reach completion. The parameters available to control the fluid motion are the Rayleigh number and the aspect ratio hid, where d is the diameter of the cavity. In the case of PCR, the required reaction efficiency constrains the reaction solution and the temperature difference; thus, Ra can only be changed by varying the height of the cavity, leaving geometry as the primary flow control parameter.