Biomedical subjects

Edgar Diessel

Publications and source records attributed to Edgar Diessel.

4 recordsLinked to original sources

PubMed2005

Nanoliter serum sample analysis by mid-infrared spectroscopy for minimally invasive blood-glucose monitoring.

The aim of this study was to demonstrate that mid-infrared spectroscopy is able to quantify glucose in a serum matrix with sample volumes well below 1 muL. For this, we applied mid-infrared attenuated total reflectance (ATR) or transmission-based spectroscopic methods to glucose quantification in microsamples of dry-film sera, either undiluted or diluted 10 times in distilled water. The sample series spanned physiological glucose concentrations between 50 and 600 mg/dL and volumes of 80, 8, and 1 nL. Calibration was carried out using multivariate partial least-squares (PLS) modeling with spectral data between 1180 and 940 cm(-1). Best performance was achieved in the ATR experiments. For raw ATR spectra, the optimum standard error of prediction (SEP) of 13.3 mg/dL was obtained for the 8 nL sample series with subsequent 10-fold dilution. With respect to the coefficient of variation of the glucose assay, CV(pred), we obtained a value of 3% for the 80 nL volume samples with spectral preprocessing using matrix protein absorption bands as an internal standard, 4% for the 8 nL samples, and 6% for the 1 nL samples with raw data. Spectral standardization resulted in significant improvement, especially for the 80 nL volume sample series. By contrast, the accuracy of the glucose assay for the 1 nL sample volume series could not be improved either by internal standardization or by considering the dry film areas for normalization, which we attribute to varying topographies of the dry films.

Blood Chemical Analysis↗

PubMed2004

Online resistance monitoring during autometallographic enhancement of colloidal Au labels for DNA analysis.

DNA diagnostics at the point-of-care requires biosensors that rely on highly sensitive transducers and are producible at low cost. A promising candidate technology is based on direct electrical detection of autometallographically enhanced Au labeled analytes. We present a substantial improvement to the previously used method by introducing online DC resistance monitoring during the autometallographic enhancement process. Since multi-step enhancement, washing, drying, and measurement cycles are eliminated, our method takes the direct electrical detection method a step further to applicability in a point-of-care environment. The feasibility of the novel method is demonstrated by its application in a simple DNA hybridization assay and the analysis of a single nucleotide polymorphism (SNP) using allele-specific hybridization. Unequivocal discrimination of all possible base pairing combinations in the SNP assay has been achieved. The SNP assay in particular indicates the potential of the method for analyte quantification.

Biosensing Techniques↗

PubMed2004

Single nucleotide polymorphism analysis by chip-based hybridization and direct current electrical detection of gold-labeled DNA.

Single nucleotide polymorphism (SNP) analysis at the point of care requires a low cost detection technology that is capable of miniaturization, multiplexing, and high sensitivity. Direct current electrical detection (DCED) of DNA following nanoparticle labeling and silver enhancement is a promising candidate technology for point-of-care diagnostics. In this work we present, for the first time, SNP analysis in PCR products from patient samples using DCED, taking this platform technology a step closer to practical application. We developed a silane functionalized polymer for coating of biochip surfaces. This polymeric coating is stable under harsh conditions and has exceptionally high binding capacity. Allele-specific oligonucleotide probes were immobilized on chips coated with this polymer. Biotinylated PCR products of the human cholesteryl ester transfer protein gene from different patients were hybridized to the chips, labeled with gold nanoparticles, and autometallographically enhanced. The chips were scanned for DC electrical resistance by applying movable electrodes to the surface. Eighteen of nineteen patient samples were assigned the correct genotype. Our results demonstrate that SNP analysis of patient samples is feasible with DCED.

Affinity Labels↗

PubMed2004

Glucose quantification in dried-down nanoliter samples using mid-infrared attenuated total reflection spectroscopy.

The aim of this study was to determine the feasibility of minimally invasive glucose concentration measurement of a body fluid within the physiologically important range below 100 nL with a number of samples such as interstitial fluid, plasma, or whole blood using mid-infrared spectroscopy, but starting with preliminary measurements on samples of simple aqueous glucose solutions. The Fourier transform infrared spectrometer was equipped with a Golden Gate single reflection diamond attenuated total reflection (ATR) accessory and a room-temperature pyroelectric detector. As the necessary detection limits can be achieved only for dried samples within the spectrometric conditions realized by a commercial instrument, the work focused on the optimization of such ATR measurements. We achieved quantification of samples with volumes as low as 7 nL between 10 and 600 mg/dL. The standard error of prediction (SEP) for the concentration range 10-100 mg/dL is 3.2 mg/dL with full interval data between 1180 and 940 cm(-1). The performance of the prediction is given by a coefficient of variation of prediction (CV(pred) ) of 6.2%. When all samples within the whole concentration range are included, the SEP increases to 20.2 mg/dL, and hence the CV(pred) to 10.6% due to a nonlinear signal dependence on glucose concentration. A detection limit for glucose of 0.7 ng with a signal-to-noise ratio of 10 was obtained.

Glucose↗