Background: DNA melting analysis for genotyping and mutation scanning of PCR products by use of highresolution instruments with special "saturation" dyes has recently been reported. The comparative performance of other instruments and dyes has not been evaluated.

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An on-line solid phase extraction method has been developed for the determination of 238U and 232Th biological certified reference material using inductively coupled plasma mass spectrometry (ICP-MS ). Absolute detection limits were 2.7 pg and 3.1 pg for the determination of 238U and 232Th respectively, both being blank limited. The result for the determination of 238U in NASS-4 Open Ocean Sea Water was 2.13±0.28 ng ml−1 compared with a certified value of 2.68±0.12 ng ml−1. The results for the determination of 238U in SLRS-3 River Water was 0.043±0.002 ng ml−1 compared with an indicative value of 0.045 ng ml−1. Results for the determination of 238U and 232Th in NIST 1575 Pine Needles were 14.6±3.4 ng g−1 and 28.3±4.5 ng g−1 respectively compared with certified values of 20±4 ng g−1 and 37±3 ng g−1, using a dry and wet ashing sample preparation method. Results for the determination of 238U and 232Th in NIST 1566a oyster tissue were 121±21 ng g−1 and 29±8 ng g−1 for 238U and 232Th compared to certified and indicative values of 132±12 ng g−1 and 40 ng g−1, using the same method. When a lithium metaborate fusion method was used, results for 238U and 232Th were 23.3±2.0 ng g−1 and 36.2±5.6 ng g−1 respectively in NIST 1575 Pine Needles. The application of electrothermal vaporisation ICP-MS ( ETV-ICP-MS) to NASS-4 Open Ocean Sea Water gave 2.81±0.54 ng ml−1 and SLRS-3 River Water 0.045±0.004 ng ml−1 for 238U. When the fused NIST 1575 samples were analysed using ETV-ICP-MS, results for 238U and 232Th were 19.5±1.7 ng g−1 and 38.8±2.2 ng g−1 respectively. Absolute detection limits for ETV-ICP-MS were 30 fg and 9 fg for 238U and 232Th respectively, both being blank limited. cluded that results for the determination of 239Pu in urine were

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Background: Unlabeled probe detection with a doublestranded DNA (dsDNA) binding dye is one method to detect and confirm target amplification after PCR. Unlabeled probes and amplicon melting have been used to detect small deletions and single-nucleotide polymorphisms in assays where template is in abundance. Unlabeled probes have not been applied to low-level target detection, however. Methods: Herpes simplex virus (HSV) was chosen as a model to compare the unlabeled probe method to an in-house reference assay using dual-labeled, minor groove binding probes. A saturating dsDNA dye (LCGreen ® Plus) was used for real-time PCR. HSV-1, HSV-2, and an internal control were differentiated by PCR amplicon and unlabeled probe melting analysis after PCR. Results: The unlabeled probe technique displayed 98% concordance with the reference assay for the detection of HSV from a variety of archived clinical samples (n ‫؍‬ 182). HSV typing using unlabeled probes was 99% concordant (n ‫؍‬ 104) to sequenced clinical samples and allowed for the detection of sequence polymorphisms in the amplicon and under the probe. Conclusions: Unlabeled probes and amplicon melting can be used to detect and genotype as few as 10 copies of target per reaction, restricted only by stochastic limitations. The use of unlabeled probes provides an attractive alternative to conventional fluorescence-labeled, probe-based assays for genotyping and detection of HSV and might be useful for other low-copy targets where typing is informative.