Biochemical sensors. Adapting to nanoscale events

CHEMICAL DESIGN OF COMPLEX NANOSTRUCTURED METAL OXIDES IN SOLUTION

Nanostructured materials with controlled architectures are desirable for many applications, among which, metal oxides are especially important in optics, electronics, biology, catalysis, and energy conversions. Various chemical routes have been widely investigated for the synthesis of nanostructured metal oxide particles and films. More recently, deliberately designed chemical strategies have been used to produce particles and films composed of more complex crystal structures. In this paper, we discuss some recent progresses in the design of complex nanostructures through chemical routes, emphasize particularly on metal oxides. We first review some basic concepts involved in the fabrication of complex nanostructures, including crystal nucleation and growth, shape controlling and ripening process. We then describe more recent work on the use of different methods to synthesize a wide range of complex nanostructures, including hierarchical structures, heterostructures, as well as oriented nanowires and nanotubes. Such purposely built materials are designed, and engineered to match the physical, chemical, and structural requirements of their applications.

Controlling DNA capture and propagation through artificial nanopores

Electrophorescing biopolymers across nanopores modulates the ionic current through the pore, revealing the polymer's diameter, length, and conformation. The rapidity of polymer translocation ( approximately 30,000 bp/ms) in this geometry greatly limits the information that can be obtained for each base. Here we show that the translocation speed of lambda-DNA through artificial nanopores can be reduced using optical tweezers. DNAs coupled to optically trapped beads were presented to nanopores. DNAs initially placed up to several micrometers from the pore could be captured. Subsequently, the optical tweezers reduced translocation speeds to 150 bp/ms, about 200-fold slower than free DNA. Moreover, the optical tweezers allowed us to "floss" single polymers back and forth through the pore. The combination of controlled sample presentation, greatly slowed translocation speeds, and repeated electrophoresis of single DNAs removes several barriers to using artificial nanopores for sequencing, haplotyping, and characterization of protein-DNA interactions.

Advances in sequencing technology

Faster sequencing methods will undoubtedly lead to faster single nucleotide polymorphism (SNP) discovery. The Sanger method has served as the cornerstone for genome sequence production since 1977, close to almost 30 years of tremendous utility [Sanger, F., Nicklen, S., Coulson, A.R, DNA sequencing with chain-terminating inhibitors, Proc. Natl. Acad. Sci. U.S.A. 74 (1977) 5463-5467]. With the completion of the human genome sequence [Venter, J.C. et al., The sequence of the human genome, Science 291 (2001) 1304-1351; Lander, E.S. et al., Initial sequencing and analysis of the human genome, Nature 409 (2001) 860-921], there is now a focus on developing new sequencing methodologies that will enable "personal genomics", or the routine study of our individual genomes. Technologies that will lead us to this lofty goal are those that can provide improvements in three areas: read length, throughput, and cost. As progress is made in this field, large sections of genomes and then whole genomes of individuals will become increasingly more facile to sequence. SNP discovery efforts will be enhanced lock-step with these improvements. Here, the breadth of new sequencing approaches will be summarized including their status and prospects for enabling personal genomics.

A functional assay for paralytic shellfish toxins that uses recombinant sodium channels

Saxitoxin (STX) and its derivatives are highly toxic natural compounds produced by dinoflagellates commonly present in marine phytoplankton. During algal blooms ("red tides"), shellfish accumulate saxitoxins leading to paralytic shellfish poisoning (PSP) in human consumers. PSP is a consequence of the high-affinity block of voltage-dependent Na channels in neuronal and muscle cells. PSP poses a significant public health threat and an enormous economic challenge to the shellfish industry worldwide. The standard screening method for marine toxins is the mouse mortality bioassay that is ethically problematic, costly and time-consuming. We report here an alternative, functional assay based on electrical recordings in cultured cells stably expressing a PSP target molecule, the STX-sensitive skeletal muscle Na channel. STX-equivalent concentration in the extracts was calibrated by comparison with purified STX, yielding a highly significant correlation (R=0.95; N=30) between electrophysiological determinations and the values obtained by conventional methods. This simple, economical, and reproducible assay obviates the need to sacrifice millions of animals in mandatory paralytic shellfish toxin screening programs.