The previously reported nonreproducibility of the intensity of the OH stretching band of liquid water has been explored. It was found that it can be eliminated in measurements with the Circle® multiple ATR cell by ensuring that the ATR rod is coaxial with the glass liquid holder. It was also found that normal laboratory temperature variations of a few degrees change the intensity by ≤~1% of the peak height. A new imaginary refractive index spectrum of water has been determined between 4000 and 700 cm-1 as the average of spectra calculated from ATR spectra recorded by four workers in our laboratory over the past seven years. It was obtained under experimental and computational conditions superior to those used previously, but is only marginally different from the spectra reported in 1989. In particular, the integrated intensities of the fundamentals are not changed significantly from those reported in 1989. The available imaginary refractive index, k, values between 15,000 and 1 cm-1 have been compared. The values that are judged to be the most reliable have been combined into a recommended k spectrum of H2O(l) at 25°C between 15,000 and 1 cm-1, from which the real refractive index spectrum has been calculated by Kramers-Kronig transformation. The recommended values of the real and imaginary refractive indices and molar absorption coefficients of liquid water at 25 ± 1 °C are presented in graphs and tables. The real and imaginary dielectric constants and the real and imaginary molar polarizabilities in this wavenumber range can be calculated from the tables. Conservatively estimated probable errors of the recommended k values are given. The precision with which the values can be measured in one laboratory and the relative errors between regions are, of course, far smaller than these probable errors. The recommended k values should be of considerable value as interim standard intensities of liquid water, which will facilitate the transfer of intensities between laboratories.

Infrared Intensities of Liquids XX: The Intensity of the OH Stretching Band of Liquid Water Revisited, and the Best Current Values of the Optical Constants of H 2 O(l) at 25°C between 15,000 and 1 cm -1

The process of histopathology, comprising tissue staining and morphological pattern recognition, has remained largely unchanged for over 140 years. Although it is integral to clinical and research activities, histopathologic recognition remains a time-consuming, subjective process to which only limited statistical confidence can be assigned because of inherent operator variability. Although immunohistochemical approaches allow limited molecular detection, significant challenges remain in using them for quantitative, automated pathology. Vibrational spectroscopic approaches, by contrast, directly provide nonperturbing molecular descriptors, but a practical spectroscopic protocol for histopathology is lacking. Here we couple high-throughput Fourier transform infrared (FTIR) spectroscopic imaging of tissue microarrays with statistical pattern recognition of spectra indicative of endogenous molecular composition and demonstrate histopathologic characterization of prostatic tissue. This automated histologic segmentation is applied to routine archival tissue samples, incorporates well-defined tests of statistical significance and eliminates any requirement for dyes or molecular probes. Finally, we differentiate benign from malignant prostatic epithelium by spectroscopic analyses.

Infrared spectroscopic imaging for histopathologic recognition.

Frequent determination of glucose concentrations in diabetic patients is an important tool for diabetes management. This requires repetitive lancing and finger bleeding. Use of noninvasive (NI) detection techniques offers several advantages, such as the absence of pain and exposure to sharp objects and biohazard materials, the potential for increased frequency of testing, and hence, tighter control of the glucose concentrations, and the potential for a closed-loop system including a monitor and an insulin pump. These potential advantages have led to considerable interest in the commercialization of NI glucose monitoring devices. Review of the scientific, patent, and commercial literature indicates that the spectroscopic basis for NI determination of glucose is not yet well established, and attempts at commercialization may be several steps ahead of our understanding the origin and characteristics of an in vivo glucose-specific or glucose-related signal. Several technologies have potential for leading to viable measuring devices, but most of the data are based on in vitro experimentation. Because of the technical complexity of in vivo glucose measurements, this review aims at discussing the gap between the established need and current technology limitations.

Spectroscopic and Clinical Aspects of Noninvasive Glucose Measurements

The aim of this article is to critically discuss the technical and clinical aspects of glucose sensors and to briefly review current technical developments. This includes sensors for spot glucose measurements as well as those used for continuous glucose monitoring. Continuous glucose monitoring in particular should supply the diabetic patient with all the information required to optimize insulin therapy and metabolic control. Such systems should also allow hypo- and hyperglycemic episodes to be avoided. During the last 30 years numerous attempts have been made to develop glucose sensors, and new major breakthroughs have been announced repeatedly. However, up until now no glucose sensor has been available that can be used by diabetic patients in daily life conditions. Also one type of glucose sensor, a glucose electrode, recently received approval by the Food and Drug Administration (USA) and is commercially available. Other glucose sensors employing the transdermal, microdialysis or open tissue microperfusion technique are currently under clinical development and may also become available in the near future. The types of glucose sensors referred to so far are not truly non-invasive, but only minimally invasive. They measure glucose concentration in the interstitial fluid of the skin or the subcutis. Non-invasive optical glucose sensors are designed to monitor glucose changes in the skin by directing light through it. They measure the characteristics of the reflected light that are changed as the result of an interaction with glucose. However, none of the attempts with optical glucose sensors have resulted thus far in the development of a sensor that allows monitoring of glucose with sufficient accuracy and precision within the clinically relevant glucose range in daily life conditions. Nevertheless, more minimal-invasive glucose sensors systems will become available for practical use in the near future, whereas it is still uncertain if this can be said for any non-invasive glucose sensor.

Sensors for glucose monitoring: technical and clinical aspects

We demonstrate the use of Raman spectroscopy to measure the
concentration of many important constituents (analytes) in serum
and whole blood samples at physiological concentration in
vitro across a multipatient data set. A near-infrared
(830-nm) diode laser generates Raman spectra that contain
superpositions of Raman signals from different
analytes. Calibrations for glucose, cholesterol, urea, and other
analytes are developed by use of partial least-squares cross
validation. We predict six analytes in serum with significant
accuracy in a 66-patient data set, using 60-s spectra. The
calibrations are shown to be fairly robust against system drift over
the span of seven weeks. In whole blood, a preliminary analysis
yields accurate predictions of some of the same analytes and also
hematocrit. The results hold promise for potential medical
applications.

/pdf/multicomponent-blood-analysis-by-near-infrared-raman-bu1x7nrias.pdf

Multicomponent blood analysis by near-infrared Raman spectroscopy.

Non-invasive assays for blood glucose can be based on near infrared spectrometry of skin tissue using the diffuse reflectance technique. Using a straightforward spectral variable selection based on choices from the optimum partial least-squares (PLS) regression vector yields better results than using PLS calibration models with full spectrum evaluation previously reported. The pairs of variables are selected from the maxima and minima of the regression weights, respectively, in decreasing order. Substantial improvements in the prediction performance of such calibration models, compared to previous calibrations based on full spectrum evaluation, are obtained. Another aspect is the reduced number of spectral variables needed for robust calibration modeling. In addition, evidence is provided for the physical effect, as manifested by the spectral glucose absorptivities, underlying the individual single-person calibration models. Their regression vector structure shows very similar features as calculated for a glucose calibration experiment based on random human plasma samples. Novel techniques are presented for probing the intravascular fluid space using time-resolved near infrared spectroscopy of oral mucosa. The pulsatile blood spectrum can be derived from these diffuse reflectance lip spectra by Fourier analysis. Future applications and prospects for non-invasive blood analysis are discussed.

Clinical chemistry and near infrared spectroscopy: technology for non-invasive glucose monitoring

Bio-analytical applications of mid-infrared spectroscopy using silver halide fiber-optic probes

The quantitative analysis of biotic fluids can be carried out using attenuated total reflection mid-infrared spectroscopy based on silver halide fibers, because good optical throughput can be achieved especially in the fingerprint region of the mid-infrared spectral range. The advantages and prospects of this technique using biofluids or dry films, obtained from such aqueous solutions, are discussed in the context of developing routine assay methodology for the analysis of biofluids submitted to the clinical laboratory for analysis. Accessories developed from such fibers are simple and less expensive than conventional equipment using classical infrared waveguides. Examples are also given for fiber application in gas analysis.

H.M. Heise

Papers

Clinical chemistry and near infrared spectroscopy: technology for non-invasive glucose monitoring

Bio-analytical applications of mid-infrared spectroscopy using silver halide fiber-optic probes

Attenuated total reflection mid-infrared spectroscopy for clinical chemistry applications using silver halide fibers

Multivariate calibration for protein, cholesterol and triglycerides in human plasma using short-wave near infrared spectrometry

Novel developments in mid-IR fiber-optic spectroscopy for analytical applications