Biomedical subjects

Sergio Cova

Publications and source records attributed to Sergio Cova.

5 recordsLinked to original sources

PubMed2006

Microchips and single-photon avalanche diodes for DNA separation with high sensitivity.

Modern techniques for DNA and protein analysis and separation rely on measurements of LIF and face a trend toward employing progressively smaller samples. The currently employed detectors that provide the required ultrahigh sensitivity, e.g. photomultiplier tubes (PMTs), are bulky and/or costly and delicate, whereas a key issue for the development of compact and economical instruments is the availability of miniaturized, inexpensive, and ultrasensitive photodetectors. The planar epitaxial silicon single-photon avalanche diodes (SPADs) combine the typical advantages of microelectronics (miniaturization, ruggedness, low voltage, low power, low cost, etc.) with high sensitivity, even better than that of PMTs. The suitability of such SPADs to microchip CE has been here ascertained by developing a new apparatus with dual-wavelength LIF detection. The apparatus has been experimented in studies on the EOF suppression and on the coating stability and tested in rapid sizing of DNA fragments. The experimental results obtained in the separation of Cy5-labeled oligonucleotide demonstrate sensitivity better than 3 pM, which corresponds to less than 100 fluorescent molecules in the 50 pL illuminated volume.

DNA↗

PubMed2005

Complete single-photon counting and timing module in a microchip.

A complete module for single-photon counting and timing is demonstrated in a single chip. Features comparable with or better than commercially available macroscopic modules are obtained by integration of an active-quenching and active-reset circuit in complementary metal-oxide semiconductor technology together with a single-photon avalanche diode (SPAD). The integrated SPAD has a 12-microm-diameter sensitive area and operates with an overvoltage above breakdown adjustable up to 20 V. With a 5-V overvoltage the photon detection efficiency peaks above 40% around 500 nm, and the dark-counting rate is lower than 600 counts/s at room temperature. The overall counting dead time is 33 ns.

Journal Article↗

PubMed2003

Protein conformational dynamics probed by single-molecule electron transfer.

Electron transfer is used as a probe for angstrom-scale structural changes in single protein molecules. In a flavin reductase, the fluorescence of flavin is quenched by a nearby tyrosine residue by means of photo-induced electron transfer. By probing the fluorescence lifetime of the single flavin on a photon-by-photon basis, we were able to observe the variation of flavin-tyrosine distance over time. We could then determine the potential of mean force between the flavin and the tyrosine, and a correlation analysis revealed conformational fluctuation at multiple time scales spanning from hundreds of microseconds to seconds. This phenomenon suggests the existence of multiple interconverting conformers related to the fluctuating catalytic reactivity.

Amino Acid Substitution↗

PubMed2003

Use of high-molecular-mass polyacrylamides as matrices for microchip electrophoresis of DNA fragments.

DNA fragment analysis requires the use of polymer solutions as sieving matrices. Generally, such matrices are constituted of high-molar-weight polymers employed at a concentration higher than their entanglement threshold concentration. These polymer solutions are highly viscous and difficult to use in the narrow channels of a microchip. Ultralarge polyacrylamides synthesized via a nonconventional method, being the low-temperature plasma-induced polymerization (PIP), were used as DNA sieving matrices for microchip electrophoresis. The distinctive features of these polymers (ultralarge molecular mass and linearity) allow their use at a dilute concentration. Dilute PIP polyacrylamides revealed a constant value of resolution in a broad range of DNA fragment sizes (123 bp-1353 bp), thus proving to be effective in common genotyping applications. Moreover, the low viscosity of the dilute solutions enable it to be easier and faster in filling the channel between runs, thus enhancing the throughput of the microchip devices.

Acrylic Resins↗

PubMed2002

Optical design and evaluation of a three-dimensional imaging and ranging system based on time-correlated single-photon counting.

The design and operation of a noncontact surface profilometry system based on the time-correlated single-photon-counting technique are described. This system has a robust optomechanical design and uses an eye-safe laser that makes it particularly suitable for operation in an uncontrolled industrial environment. The sensitivity of the photon-counting technique permits its use on a variety of target materials, and its mode of operation does not require the continual presence of an operator. The system described has been optimized for a 1-25-m standoff, has a distance repeatability of <30 microm, and has a transverse spatial resolution of approximately 60 microm at a 2-m standoff and approximately 400 microm at a 13-m standoff.

Journal Article↗