A highly integrated monolithic device was developed that automatically carries out a complex series of molecular processes on multiple samples. The device is capable of extracting and concentrating nucleic acids from milliliter aqueous samples and performing microliter chemical amplification, serial enzymatic reactions, metering, mixing and nucleic acid hybridization. The device, which is smaller than a credit card, can manipulate over 10 reagents in more than 60 sequential operations and was tested for the detection of mutations in a 1.6 kb region of the HIV genome from serum samples containing as few as 500 copies of the RNA. The elements in this device are readily linked into complex, flexible and highly parallel analysis networks for high throughput sample preparation or, conversely, for low cost portable DNA analysis instruments in point-of-care medical diagnostics, environmental testing and defensive biological agent detection.

Resistance to room temperature oxidation and control over wetting properties can be achieved by chemical modification of a porous-silicon surface. Fourier transform infrared spectroscopy was used in the transmission mode to monitor the surface chemistry of both treated and untreated porous-silicon samples before and after exposure to humid air at room temperature. Surface modification methods investigated include: (i) vapor-phase silation using either hexamethyldisilazane or trimethylchlorosilane, and (if) rapid thermal annealing in nitrogen, ammonia, or argon ambients. The silation treatments, carried out in the presence of trace moisture, were successful both in creating surface trimethylsilyl groups and in suppressing room temperature oxidation. Rapid thermal annealing at temperatures as low as 500~ for 30 s eliminates all silicon hydrides. Nitrided porous-silicon layers are formed at 1100~ in either ammonia or nitrogen; in both cases the silicon nitride infrared absorption peaks scale with the porous layer thickness, indicating that the compounds are distributed throughout the porous layer.Electrochemical etching of silicon in hydrofluoric acid forms a high-surface-area material commonly called porous silicon. The physical characteristics: pore size, porosity, and specific surface area are determined by the processing conditions such as hydrofluoric-acid concentration, current density, dopant type, and dopant density. ~' 2 After the porous silicon is formed, its large exposed surface area will typically oxidize even in air at room temperature. This spontaneous oxidation is enhanced by the presence of moisture in the air. The growth of a native oxide layer (typically 1.5 to 4 nm thick) 3 significantly alters the structure and chemical activity of the porous silicon. For many sensor or optoelectronic users of porous silicon, the surface must be stabilized. In the following, some methods to passivate the surface of porous silicon from continued room temperature oxidation are described. 4

Plastic microchannels (4.5 cm long) fabricated from an etched glass master were tested for high-resolution single-stranded DNA analysis. Using replaceable denaturing linear polyacrylamide as sieving matrix, one-color separation of a fragment sizing standard with single-base resolution (R > 0.5) was achieved up to 275 bases. Two-color sizing analysis of four loci short tandem repeat (STR) allelic ladder (CSF1PO, TPOX, TH01, vWA) with single-base resolution (R = 0.62) on TH01 alleles 9.3 (198 bp) and 10 (199 bp) was demonstrated. An average standard deviation of +/- 0.06 bp and +/-0.11 bp in sizing 32 alleles of the CTTv ladder was attained between runs and between channels, respectively. Four-color sequencing separation of a terminator sequencing standard showed a base-calling accuracy of 99.1% out to 320 bases in 13 min.

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We report capacitance and current-voltage measurements of porous silicon in contact with sputter-deposited aluminum. Three different substrates: 30-50 ~-cm boron-doped (p--type), 0.01-0.03 t~-cm boron-doped (p+-type), and 0.003-0.005 gt-cm phosphorus-doped (n § silicon, are used as starting material. Porous silicon formed from p--and p%type substrates exhibits full-and partial-carrier depletion, respectively. The electric field, potential distribution, and capacitance for full depletion are derived and shown to compare qualitatively with measured capacitance as a function of porous layer thickness for p--type porous silicon. Impedance variation with porous layer thickness was used to determine the resistivity of p--type porous silicon as 1.6 • 107 gt-cm. A three-dimen~ional space-charge region accounting for the observed partial depletion in p+-type porous silicon is described in detail. Capacitance with bias was used to measure the effective interface area of p+-type porous silicon. This reduced interface area can be explained in terms of a lateral depletion region surrounding each pore, with an average of 0.8 times the pore radius. Current-voltage measurements indicate a blocking contact between sputtered aluminum and both p--and p+-type porous silicon, in contrast to ohmic contacts between sputtered aluminum and nonporous p--and p+-type silicon. Capacitance-and current-voltage dependences of n § silicon indicate that in this material conversion to porous silicon has a relatively small effect.

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