Plant leaves store digital information
ages collected. In mature leaf tissues, the image lasts ~ 8 min. It fades more quickly in leaves in the early stages of aging. Move over semiconductors, here come . . . plant leaves? Semiconducting elecRemarkably, the leaves stored and retronic device manufacturers need not covered an image of Botticelli's Birth of worry about the competition, but Larry S. Venus. The bess image waa sbtained db Daley and co-workers at Oregon State plotting estimated quantum yield. They University, Gerald E. Edwards of Washalso stored a binary representation of n to ington State University, and James B. Cal- 100 digits, but the system's resolution was lis of the University of Washington deminsufficient to store a decimal representaonstrated that the photosynthetic apparation of n. The images generated by the tus in tobacco (Nicottana tabacum L.) ana leaves were discernible to the human eye; Gingko biloba leaves cac briefly store digi- to facilitate the computer reading of the tal information. image, however, the authors corrected uneven intensities caused by variations in Images were generated by placing colored transparent masks of the selected the physiology of leaf regions, in the sensitivity of individual CCD pixels, and in image over a leaf, which was then illumileaf illumination. nated through the mask with a fluorometer lamp for 0.5-3.5 min. The exact duraThe authors do not expect the immedition of illumination depended on the parate use of leaves as memory storage deticular leafs germplasm, age, and history vices, although they do not rule out the of light exposure. The mask was then reeventual possibility. They do expect, howmoved and a series of fluorescence imever, that their method will allow the in
Dual-microcolumn immunoassay for insulin Dual-column immunoassays (DCIAs), in which the immunoaffinity column is followed by a reversed-phase column, offer better selectivity and detection limits than one-column immunoassays by reconcentrating and providing another separation dimension. Robert T. Kennedy and coworkers at the University of Florida have developed a DCIA with packed capillary
DMIA of500-mL serum samples. (A) Serum blank (no insulin added)) (B) serum wiih 200 pM human insulin added; ;C) Serum sample with 1 nM human insulin added. (Adapted with permission from Elsevier Science.)
An image of Botticelli's Birth of Venus stored in a tobacco leaf by fluorescence estimated quantum yield. .Adapted with permission from the Society for Applied Spectroscopy..
vivo selection of the best plant germplasm for a given bioelectronic purpose. (Appl. Spectrosc. 1997, 51,1-9)
columns (called a dual-microcolumn immu- AFM comes through noassay, or DMIA) that provided higher in the stretch mass sensitivity and better compatibility In recent years, there has been a wealth of with MS and consumed less material than measurements of single molecules. One DCIAs using conventional HPLC columns. interesting approach to collecting this The multiple stages of preconcentration type of data has been to chemically link allowed lower concentration detection limmolecules between the tip of an atomic its for antigens, even with a UV absorbance force microscope (AFM) cantilever and a detector. support structure, then measure the force They applied the assay to insulin deterneeded to pull the molecule loose, like mination in serum and insulin secretion stretching chewing gum between two from ssngle rat islets so Langerhans, which fingers. are responsible for insulin secretion in the Matthias Rief and colleagues at Ludwigpancreas. Rat islets are interesting because Maximillians-Universtat (Germany) used the rodents use two variants of insulin; this approach to probe the elastic propermost radioimmunoassays (the usual way of ties of dextranfilamentslinked to a gold measuring islet secretion) do not distinsurface through an epoxy-alkanethiol guish between the types. The DMIA showed that the rat islets released rat insulin I and II differentially, but the ratio did not vary with glucose concentration. Insulin analysis in serum proved to be more difficult because of nonspecific adsorption in the immunoaffinity column that interfered with the insulin retention time. However, it was still possible to clearly observe an insulin peak at 200 pM. They calculated a detection limit of 100 pM; basal insulin levels in serum tend to fall between 47 and 150 pM. DMIA may be used for samples as complex as serum but trace-level substances Dextran strands are bound to a gold surface and picked up by an AFM tip will be difficult to determine without opthrough a bond between streptavidin (half timization of either the separation or the circle) and biotin (full circle) (Adapted with detection. (J. Chromatogr. B 1997, 689, permission from the American Association 295-303) for the Advancement of Science.) Analytical Chemistry News & Features, May 1, 1997 2 7 9 A
News
LABORATORY PROFILE LGC steps out on its own In the smoggy streets of London, mid19th century, shady deals took place at every turn, and an unscrupulous tradesman might make himself a nice living stretching his cache of tobacco a little bit further with tea leaves and other vegetable matter. By the 1840s, Her Majesty's Customs decided that it had had enough of poor-quality tobacco and was under pressure from its paymasters who saw rapidly dwindling revenues from tobacco imports. The government passed the Pure Tobacco Act, which forbade additions to tobacco. Excise Officer George Phillips offered to sniff out the bad tobacco. As the sole member of the staff he established a lab now known as the Laboratory of the Government Chemist (LGC) and in October 1842 he began analyzing tobacco consignments for adulteration and hounded the miscreants involved In 1989, almost 150 years later, LGC had become the U.K. government's focal point for analytical chemistry, acting as the expert nose for numerous government departments, such as the Ministry of Agriculture, Fisheries, and Food; the Department of the Environment; and, of course, Customs and Excise. At this time, the governing Conservative Party decided that LGC should become an agency wholly answerable to the Department of Trade and Industry and that its future should depend on its ability to compete in the commercial marketplace "Granting agency status was part of a general trend in government to encourage individual departments to pursue more commercial attitudes," explains Richard Worswick, Government Chemist and LGC Chief Executive. LGC became more flexible, rather than
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answering directly to government and functioning solely for the benefit of its departments. "Other departments, our customers, were under increasing pressure to seek and demonstrate value for money, and agency status allowed us to expand our customer base into areas at home and abroad," adds Worswick. In 1994, a review by accountancy and management consultants led to the recommendation that the government laboratories should be privatized. This move, the report claimed, would offer the best opportunity for the laboratories to maintain and develop the expertise and facilities for the changing needs of government and industry. By November 1994, the government found its preferred bidder for the LGC buyout. Ownership would be split equally between LGC's own management, the Royal Society of Chemistry, and the investment group 3i Fiona Sloman, national officer of the trade union Institute of Professional Managers and Specialists, commented to the journal Chemistry & Industry that tht announcement was something of a "doubleedged sword, with this particular bid always likely to win." Sloman's prediction proved to be accurate, and on April 1,1996, LGC became an independent company. Since then, many developments have been encouraging, according to Ray Ah-Sun, head of Business Development. LGC has broadened its expertise into geochemistry and se-
The private LGC, getting very busy.
Analytical Chemistry News & Features, May 1, 1997
cured a major contract with petroleum giant BP, acquiring technical staff directly from the company. LGC's work is now divided into three core areas. Its food service spans the chain from nutritional, vitamin, and trace-metal analysis to testing for fungal contaminants and pesticides. Its forensics section covers illegal drugs and employee screening. Its environmental service looks at contaminated land and water. Among its clients are the U.K.'s national and local governments, the legal profession, the armed forces, food retailers and manufacturers, jewelry manufacturers, toy manufacturers, and even architects. For contractual reasons, LGC is unable to disclose exactly what it does for specific customers, but the range of analytical skills is used to study everything from the sex of tinned meat to the purity of extra virgin olive oil to building materials and precious metals. Since dealing with 19th-century tobacco touts LGC has grown to a 300-member staff occupying almost 100 000 square feet more than twothirds of which is dedicated laboraspace in its west London premises Meanwhile, the top brass is pleased that, free from government ties, the laboratory is progressing. "As an independent company, LGC is able to build and strengthen its reputation as an impartial center for analytical science, and we are looking forward to more exciting developments in the future, such as DNA testing," says ^Vorswick. LGC recently acquired University Diagnostics Ltd a pioneer in the commercial applications of DNA testing Worswick adds that this is "an important step in our strategy to become a European leader in the provision oftop-qualirv analytical and diagnostic services " David Bradley
bond. The dextran was modified with streptavidin which, in turn, complexes on the "other" side of the polymer to the biotin bound to the AFM tip. The researchers carefully brought the tip in and out, as in fly fishing, until a single molecule was bound to the cantilever. Segment elasticity and Kuhn length were virtually identical for all measured dextran strands, confirming that the experiments dealt with individual filaments and that the deformation caused by the couplers was negligible. The researchers report that, at low forces, deformation of dextran was dominated by entropic forces; at high forces, strand elongation was governed by a twist of bond angles; and at still higher forces, the polymer underwent a conformational change as it stiffened and segment elasticity was controlled by the bending of bond angles. The last change was reversible and was corroborated by molecular dynamics calculations. (Science e997,275, 1295-97)
Dendrimer-solute interactions One of the hottest fields in synthetic organic chemistry is the synthesis of large snowflake-like dendritic polymers. These huge polymers could have a wide range of applications, including the sequestration and stabilization of small molecules for agricultural, pharmaceutical, or fragrance applications. As the size and complexity of these dendrimers increase, the data from many traditional
Possible reaction pathways for the thermolysis of a substituted cyclobutane. (Adapted with permission from the National Academy of Sciences.)
Finding the needle Just because a reaction product is thermodynamically highly disfavored doesn't mean that none of it is made. The question is how to find the disfavored product in an excess of the major product. James J. La Clair of the Scripps Research Institute used confocally adjusted fluorescence correlation spectroscopy to detect the reaction products of the thermolysis of a substituted cyclobutane, which could cleave along either the xory axis or un-
analytical tools become increasingly difficult to interpret. Curtis A Monnig and colleagues from the University of California-Riverside and the University of South Florida introduced a clever approach for generating analytical data on dendrimers that is easy to analyze. They used polyacid cascade dendrimers as a pseudostationary phase in electrokinetic capillary chromatography. By investigating the separation of a homologous series of molecules, they can calculate capacity factors and distribution coefficients which in turn yield thermodynamic para. meters for the dendrimer-solute interactions For example the researchers found that as the size of the oolvacid dendrimer in-
dergo a vinylcyclobutane rearrangement. The dye labeled number 2 (*-axis cleavage) is the minor product; its production is disfavored by ~ 8.7 kcal/mol relative to y-axis fragmentation. Of the possible products, the dye was the only one that autocorrelated, a fact that was used to verify its formation. La Clair detected this unfavored product at a concentration of 2.3 x 10""1 M in the presence of ~ 5 x 10"7 M of fhe major products. (Proc. Natl. Acad. Sci. USA 1997.94,1623-28)
A new UV Raman microspectrometer UV resonance Raman spectroscopy (UVRSS) is an excellent technique for studying materials with electronic transitions in the 180- to 300-nm region, but the combination of UVRSS with the sampling ease of an optical microscope has proven difficult because the typical sources easily caused sample breakdown and saturation. Sanford A Asher and colleagues at the University of Pittsburgh have described a system that exploits the benefits but avoids the pitfalls normally associated with this technique. Their system, based on an optical microscope, uses a continuous-wave intracavity frequency-doubled argon-ion laser and prism to focus light on the sample inde-
entronv becomes the driving force for solubilization and enthalnv is disfavored
The procedure can be run with commercially •1 1.1
4.
J
available equipment and •J
Structure of a polyacid dendrimer.
• \ -
r
1
in a wide variety of solutions. (I. Am. Chem. Soc. i y y 7 , ny, ZZDD—oi)
Schematic of the UV Raman microspectrometer. .Adapted with permission from the Society for Applied Spectroscopy.)
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