Ultrafast all-optical switching in a silicon-based plasmonic nanoring resonator.

A silicon-based plasmonic nanoring resonator is proposed for ultrafast, all-optical switching applications. Full-wave numerical simulations demonstrate that the photogeneration of free carriers enables ultrafast switching of the device by shifting the transmission minimum of the resonator with a switching time of 3 ps. The compact 1.00 µm² device footprint demonstrates the potential for high integration density plasmonic circuitry based on this device geometry.

Immunoaffinity sample purification and MALDI-TOF MS analysis of alpha-Solanine and alpha-chaconine in serum.

A sample purification technique was developed for the detection of potato glycoalkaloids (GAs) in blood serum by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). GAs were extracted from spiked serum (5 mL) using a C(18) solid-phase extraction cartridge. The GAs were then selectively captured on antibody-coated agarose beads. The agarose beads were washed with water and the GAs eluted with 25 microL of methanol. MALDI-TOF MS was used to detect the GAs in the methanol eluent. Immunoaffinity sample purification of the GAs effectively reduced the signal suppression observed during the analysis of unpurified samples. alpha-Chaconine and alpha-solanine were detected in serum spiked with 1 ng/mL of each GA.

A capillary electrophoresis laser-induced fluorescence method for analysis of potato glycoalkaloids based on a solution-phase immunoassay. 2. Performance evaluation.

Glycoalkaloids (GAs) occur naturally in potatoes and are toxic to humans and animals. The objective of the present study was to evaluate the performance of a solution-phase immunoassay coupled to capillary electrophoresis with laser-induced fluorescence (CE-LIF) detection for the determination of total glycoalkaloids in potatoes. The immunoassay was based on a competition between potato glycoalkaloids and fluorescently labeled solanidine. Reaction products were separated in the capillary zone electrophoresis mode. A calibration curve of signal vs log[GA] was linear from 50 to 400 nM. The CV for duplicate and day-to-day analyses averaged 5.7% and 12%, respectively. Spike recoveries ranged from 85 to 97% for spike levels ranging from 43 to 170 microg/g fresh potato. Potato samples with GA concentrations ranging from <40 to >200 microg/g were successfully analyzed, indicating that immuno-CE-LIF is a rapid alternative to traditional ELISA and HPLC methods.

A capillary electrophoresis laser-induced fluorescence method for analysis of potato glycoalkaloids based on a solution-phase immunoassay. 1. Separation and quantification of immunoassay products.

Solution-phase immunoassays are typically faster and more precise than ELISAs. This research developed a solution-phase for the immunoassay of potato glycoalkaloids (GAs) based on quantification by capillary electrophoresis (CE) with laser-induced fluorescence (LIF) detection. Solanidine coupled to 4'-(aminomethyl)fluorescein and a polyclonal antibody solution were used as the immunoreagents. Unbound fluorescent solanidine was detected by CE-LIF (excitation 488 nm, emission 520 nm). Optimum resolution of immunoassay products was achieved with a buffer consisting of 50 mM phosphate, 10% (v/v) methanol, and 1.5 mM SDS, pH 7.5. A plot of signal vs log [GA] produced a sigmoidal curve typical of immunoassays. Analysis of extracts of sprouted Yukon Gold potato tubers and nonsprouted Yukon Gold tubers resulted in total [GA] of 98 microg/g (RSD 9%) and 55 microg/g (RSD 9%), respectively. The findings indicated that CE-LIF coupled with a solution-phase immunoassay can be used to quantify total GA in potatoes.

Glycoalkaloid concentration in Alberta potatoes determined by matrix-assisted laser desorption/ionization mass spectrometry.

Matrix-assisted laser desorption and ionization (MALDI) mass spectrometry was used to determine concentrations of individual potato glycoalkaloids in tubers. Samples were extracted with methanol-water and deposited on 2,4,6-trihydroxyacetophenone crystals. Positive ions were analyzed with a MALDI time-of-flight mass spectrometer equipped with a 337 nm laser. Analyte ion intensities relative to an internal standard were used to determine chaconine and solanine concentrations. Calibration curves were prepared by standard additions to potato tuber material. The relative standard deviations (RSDs) of triplicate measurements ranged from 1 to 16%, with an average of 9%. The day-to-day RSD for replicate determinations was 11%. Recoveries of analyst-prepared spikes (50 micrograms/g) averaged 104% for chaconine (RSD, 8%) and 98% for solanine (RSD, 4%). The method limit of detection was estimated to be 2 micrograms/g.

Streptococcus iniae, a human and animal pathogen: specific identification by the chaperonin 60 gene identification method.

It was recently reported that Streptococcus iniae, a bacterial pathogen of aquatic animals, can cause serious disease in humans. Using the chaperonin 60 (Cpn60) gene identification method with reverse checkerboard hybridization and chemiluminescent detection, we identified correctly each of 12 S. iniae samples among 34 aerobic gram-positive isolates from animal and clinical human sources.

Identification of Staphylococcus species and subspecies by the chaperonin 60 gene identification method and reverse checkerboard hybridization.

A previous study (S. H. Goh et al., J. Clin. Microbiol. 34:818-823, 1996) demonstrated that a 600-bp region of the chaperonin 60 (Cpn60) genes from various bacterial isolates could be amplified by PCR with a pair of degenerate primers and that the products could be used as species-specific probes for Staphylococcus aureus, S. epidermidis, S. haemolyticus, S. lugdunensis, S. saprophyticus, and S. schleiferi. To further validate the utility of bacterial Cpn60 genes as universal targets for bacterial identification (ID), reverse checkerboard chemiluminescent hybridization experiments were performed with DNA probes from 34 different Staphylococcus species and subspecies. With the exception of probes from the Cpn60 genes of S. intermedius and S. delphini, which cross hybridized, all were species specific. Two subspecies of both S. capitis and S. cohnii were differentiated from one another, while DNAs from the two S. schleiferi subspecies cross hybridized. When 40 known Staphylococcus isolates were tested in a blind experiment by the Cpn60 gene method, 36 strains, representing six species and one subspecies (S. sciuri, S. caseolyticus, S. hominis, S. warneri, S. hyicus, S. haemolyticus, and S. capitis subsp. ureolyticus), were correctly identified. DNA from the four remaining isolates, known to be S. hyicus bovine strains, failed to hybridize to DNA from the S. hyicus target strain or any other Staphylococcus species. However, DNAs from these S. hyicus isolates did cross hybridize with each other. New DNA sequence data and evidence from previous studies suggest some genetic divergence between the two groups of S. hyicus isolates. Our results demonstrate that this Cpn60 gene-based ID method has the potential to be a basic method for bacterial ID. Studies are in progress to further validate the utility of this Cpn60 gene system for ID of Staphylococcus and other genera, including those of slow-growing microorganisms.