Novel infrared optical probes for process monitoring and analysis based on next-generation silver halide fibers

Mid-infrared spectroscopy has proved to be a powerful method for the study of various samples and chemical media as found in different industrial processes. In general, the analysis of such samples takes advantage of the fact that multiple analytes can be quantified simultaneously and rapidly without the need for additional reagents. When compared to near-infrared spectroscopy, for which quartz fiber probes can be successfully applied, the application of previously used mid-infrared fiber materials was restricted due to deficiencies with regard to their optical transmission and mechanical properties. Progress in the quality of infrared transparent silver halide fibers and their extrusion with different cross-sections enabled us to construct several flexible fiber-optic probes of different geometries which are particularly suitable and inert for process monitoring. Transmission and attenuated total reflection measurement techniques have mainly been employed for the analysis of liquid and gaseous media. One larger field, for which results are reported, is chemical reactor monitoring. Other applications are concerned with bio-reactor monitoring, or quasi-continuous measurements for the food industry. Infrared spectroscopic cosmetic assays for determining the chemical composition of skin-care formulations are a further promising field of application, for which an example is given.     

Application of multivariate data-analysis techniques to biomedical diagnostics based on mid-infrared spectroscopy

The objective of this contribution is to review the application of advanced multivariate data-analysis techniques in the field of mid-infrared (MIR) spectroscopic biomedical diagnosis. MIR spectroscopy is a powerful chemical analysis tool for detecting biomedically relevant constituents such as DNA/RNA, proteins, carbohydrates, lipids, etc., and even diseases or disease progression that may induce changes in the chemical composition or structure of biological systems including cells, tissues, and bio-fluids. However, MIR spectra of multiple constituents are usually characterized by strongly overlapping spectral features reflecting the complexity of biological samples. Consequently, MIR spectra of biological samples are frequently difficult to interpret by simple data-analysis techniques. Hence, with increasing complexity of the sample matrix more sophisticated mathematical and statistical data analysis routines are required for deconvoluting spectroscopic data and for providing useful results from information-rich spectroscopic signals. A large body of work relates to the combination of multivariate data-analysis techniques with MIR spectroscopy, and has been applied by a variety of research groups to biomedically relevant areas such as cancer detection and analysis, artery diseases, biomarkers, and other pathologies. The reported results indeed reveal a promising perspective for more widespread application of multivariate data analysis in assisting MIR spectroscopy as a screening or diagnostic tool in biomedical research and clinical studies. While the authors do not mean to ignore any relevant contributions to biomedical analysis across the entire electromagnetic spectrum, they confine the discussion in this contribution to the mid-infrared spectral range as a potentially very useful, yet underutilized frequency region. Selected representative examples without claiming completeness will demonstrate a range of biomedical diagnostic applications with particular emphasis on the advantageous interaction between multivariate data analysis and MIR spectroscopy.     

Metrology in laboratory medicine – A necessity

 In a recent Letter to the Editor, Dr. B. Neidhart questioned the need to make clinical chemical measurement results traceable to international standards and to incorporate the principles of analytical quality assurance into clinical chemistry. An analysis of the arguments presented shows that modern laboratory medicine has to deliver accurate results, which are comparable over space and time, in order to improve the accuracy of diagnostic tools and minimize cost. The means to achieve accuracy and comparability are metrological traceability and quality assurance as supported by many national and international initiatives.     

Detection and determination of antimalarial drugs and their metabolites in body fluids

This review of methods for determining antimalarial drugs in biological fluids has focused on the various analytical techniques for the assay of chloroquine, quinine, amodiaquine, mefloquine, proguanil, pyrimethamine, sulphadoxine, primaquine and some of their metabolites. The methods for determining antimalarials and their metabolites in biological samples have changed rapidly during the last eight to ten years with the increased use of chromatographic techniques. Chloroquine is still the most used antimalarial drug, and various methods of different complexity exist for the determination of chloroquine and its metabolites in biological fluids. The pharmacokinetics of chloroquine and other antimalarials have been updated using these new methods. The various analytical techniques have been discussed, from simple colorimetric methods of intermediate selectivity and sensitivity to highly sophisticated, selective and sensitive chromatographic methods applied in a modern analytical laboratory. Knowledge concerning the method for a particular study is determined by the type of application and the facilities, equipment and personnel available. Often is it useful to apply various methods when conducting a clinical study in malaria-endemic areas. Field-adapted methods for the analysis of urine samples can be applied at the study site for screening, and corresponding blood samples can be preserved for subsequent analysis in the laboratory. Selecting samples for laboratory analysis is based on clinical, parasitological and field-assay data. The wide array of methods available for chloroquine permit carefully tailored approaches to acquire the necessary analytical information in clinical field studies concerning the use of this drug. The development of additional field-adapted and field-interfaced methods for other commonly used antimalarials will provide similar flexibility in field studies of these drugs.     

Micro- and nano-thermal analysis applied to multi-layered biaxially-oriented polypropylene films

In this paper we compare Wollaston and silicon probes for localized thermal analysis measurements (LTA) on biaxially oriented polypropylene (BOPP) films. Up till now, no real comparison was reported in literature between the different transition temperatures measured using Wollaston and silicon probes. Using different types of probes for studying the same material proves to be very interesting. Using the Wollaston probe, the thermal properties and thickness of a 1 μm thick skin layer can be determined by through-thickness local thermal analysis measurements. The improved resolution of the silicon probes, enables the measurement of thermal properties of individual layers in a cross-sectioned film, even for layers of only 1 μm thickness. Based on the results, the silicon probes seem to be more sensitive toward the start of the melting process, since the silicon probe already penetrates at lower temperature, as compared to the Wollaston probes. This sensitivity can be exploited for studying the effect of variations in thermal history between or within samples.     

New tool for epidermal and cosmetic formulation studies by attenuated total-reflection spectroscopy using a flexible mid-infrared fiber probe

The potential of mid-infrared attenuated total-reflection spectroscopy for dermatology studies has been increased by the development of a flexible fiber-optic probe from silver halide material. Such a tool significantly eases epidermal surface characterization. Spectra of human forearm skin and of bovine udder skin (BUS-model), which is used as a substitute for in-vivo tests on man, were compared, and as an example low concentrations of vitamin E acetate (alpha-tocopherol acetate) in the stratum corneum were measured after topical skin application. Depth profiling was enabled by repeated steps of tape stripping and subsequent skin measurement. The infrared methodology is rapid and can be applied to small areas of skin. It is also sufficiently sensitive for analysis of a large variety of cosmetic formulations and dermatopharmaca. Discrimination of vehicle formulations is possible because of the large information content of mid-infrared spectra.     

Food Analysis on Electrophoretic Microchips

One of the current trends of separation techniques in analytical chemistry is miniaturization. The aim of miniaturization is to attain better performance, shorter analysis time, and reduced reagent consumption. Capillary Electrophoresis (CE) microchips, the first generation of micro-total analysis systems, are the most used microsystems in food analysis. The scope of this review is to gather and discuss the different applications of such miniaturized devices in this field. Various analytes of food significance such as natural antioxidants, amino acids, proteins, dyes, vanilla flavors, DNA probes, heavy metals, toxins, allergens etc. have been successfully monitored using CE-microchips, either to assess food quality or to ensure food safety. Also, to deal with the high complexity of food matrices, the integration of sample preparation steps onto the chip and the use of new tools from nanotechnology for the detection step have been reported.     

Infrared spectroscopic analysis of human interstitial fluid in vitro and in vivo using FT-IR spectroscopy and pulsed quantum cascade lasers (QCL): Establishing a new approach to non invasive glucose measurement

Interstitial fluid, i.e. the liquid present in the outermost layer of living cells of the skin between the Stratum corneum and the Stratum spinosum, was analyzed by Fourier transform infrared spectroscopy and by infrared spectroscopy using pulsed quantum cascade infrared lasers with photoacoustic detection. IR spectra of simulated interstitial fluid samples and of real samples from volunteers in the 850-1800cm(-1) range revealed that the major components of interstitial fluid are albumin and glucose within the physiological range, with only traces of sodium lactate if at all. The IR absorbance of glucose in interstitial fluid in vivo was probed in healthy volunteers using a setup with quantum cascade lasers and photoacoustic detection previously described. A variation of blood glucose between approx. 80mg/dl and 250mg/dl in the volunteers was obtained using the standard oral glucose tolerance test (OGT). At two IR wavelengths, 1054cm(-1) and 1084cm(-1), a reasonable correlation between the photoacoustic signal from the skin and the blood glucose value as determined by conventional glucose test sticks using blood from the finger tip was obtained. The infrared photoacoustic glucose signal (PAGS) may serve as the key for a non-invasive glucose measurement, since the glucose content in interstitial fluid closely follows blood glucose in the time course and in the level (a delay of some minutes and a level of approx. 80-90% of the glucose level in blood). Interstitial fluid is present in skin layers at a depth of only 15-50μm and is thus within the reach of mid-IR energy in an absorbance measurement. A non-invasive glucose measurement for diabetes patients based on mid-infrared quantum cascade lasers and photoacoustic detection could replace the conventional measurement using enzymatic test stripes and a drop of blood from the finger tip, thus reducing pain and being a cost-efficient alternative for millions of diabetes patients.     

Preparation of homogeneous samples of double-labelled protein suitable for single-molecule FRET measurements

Preparation of pure and homogenous site specifically single- and double-labelled biopolymers suitable for spectroscopic determination of structural characteristics is a major current challenge in biopolymers chemistry. In particular, proper analysis of single-molecule Förster resonance energy transfer measurements is based on the spectral characteristics of the probes. Heterogeneity of any of the probes may introduce errors in the analysis, and hence, care must be taken to avoid preparation of inhomogeneous labelled biopolymer samples. When we prepared samples of Escherichia coli adenylate kinase (AK) mutants labelled with either Atto 488 or Atto 647N, the products were spectrally inhomogeneous and the composition of the mixture changed gradually over time. We show here that the inhomogeneity was not a result of variation in the dye interaction with neighbouring side chains. Rather, the slow drift of the spectral characteristics of the probes was a characteristic of an irreversible chemical transformation probably due to the hydrolysis of the succinimide ring of the attached dye into its succinamic acid form. Overnight incubation of the labelled protein in mild basic solution accelerated the interconversion, yielding homogeneous labelled samples. Using this procedure, we obtained stable homogenous AK mutant labelled at residues 142 and 188.     

Selective detection and identification of Se containing compounds--review and recent developments

The complexity of selenium (Se) chemistry in the environment and in living organisms presents broad analytical challenges. The selective qualitative and quantitative determination of particular species of this element is vital in order to understand selenium's metabolism and significance in biology, toxicology, clinical chemistry and nutrition. This calls for state-of-the-art analytical techniques such as hyphenated methods that are reviewed with particular emphasis on interfaced separation with element-selective detection and identification of the detected selenium compounds. Atomic spectral element specific detection for monitoring chromatographic eluent enabled quantitative determination of selenium species in selenized yeast and qualitative measurement for breath samples. Gas chromatography with atomic emission detection (AED) of ethylated species and fluoroacid ion pair HPLC applied to the analysis of currently produced or archived selenized yeast and Brassica juncea have revealed the presence of a previously unrecognised Se-S amino acid, S-(methylseleno)cysteine.     

Reversible Fluorescent Probes for Biological Redox States

The redox chemistry of the cell is key to its function and health, and the development of chemical tools to study redox biology is important. While fluxes in oxidative state are essential for healthy cell function, a chronically elevated oxidative capacity is linked to disease. It is therefore essential that probes of biological redox states distinguish between these two conditions by the reversible sensing of changes over time. In this review, we discuss the current progress towards such probes, and identify key directions for future research in this nascent field of vital biological interest.     

Pushing the band gap envelope: mid-infrared emitting colloidal PbSe quantum dots

Efficient mid-infrared sources are of considerable general interest for gas analysis, remote sensing, and atmospheric monitoring, but existing technologies are limited. Here, we report the synthesis of the first colloidal QDs having photoluminescence (PL) in the mid-infrared. We show particle-size-tunable mid-infrared emission for large (10-17 nm), but quantum-confined, colloidal PbSe QDs, with efficient, narrow-bandwidth PL at energies as low as 0.30 eV (4.1 mum). Applying two new synthetic routes, we have achieved fine control of QD size and size distribution, allowing us to provide the first systematic correlation of QD size with PL energy for PbSe QDs emitting at wavelengths longer than 2 mum, results which are compared with a literature model. For the entire spectral range reported, we provide measured quantum yields in emission, showing a marked decrease with increasing QD size, for which we include a possible explanation. Finally, we present very promising preliminary results for overcoating PbSe with CdSe, a wider-gap semiconductor. We show PL enhanced by approximately 6-fold for such core/shell samples.     

Some practical aspects of the validation of photometric systems for clinical analyses

 It is well known that erroneous data reported to a physician may strongly affect medical decision making. For routine clinical chemistry purposes, different instrumentation can be used to compare measurements of unknown samples with standard reference materials. Currently, acceptable limits of accuracy and precision are poorly defined in the field of clinical chemistry laboratories. In this article, problems associated with spectrophotometric measurements, both manual and automated, are discussed. The task of the validation of photometric systems for clinical analyses is currently of considerable interest. Some practical aspects of this validation and the use of reference materials for this activity in the national area are discussed. Received: 7 November 1996 Accepted: 14 January 1997     

Laboratory intercomparison of the ozone absorption coefficients in the mid-infrared (10 microm) and ultraviolet (300-350 nm) spectral regions

For the measurement of atmospheric ozone concentrations, the mid-infrared and ultraviolet regions are both used by ground-, air-, or satellite-borne instruments. In this study we report the first laboratory intercomparison of the ozone absorption coefficients using simultaneous measurements in these spectral regions. The intercomparison shows good agreement (around 98.5%) between the HITRAN 2000 recommendation for the mid-infrared and the most reference measurements in the ultraviolet regions, whereas systematic differences of about 5.5% are observed when using the recommendation of HITRAN2003 for the mid-infrared. Possible reasons for this discrepancy are discussed. Future measurements are clearly needed to resolve this issue.     

Use of different anticoagulants for HPLC separation and quantification of the free amino acid content of plasma

Amino acid analysis in plasma samples is a very important and difficult task and could represent a useful tool for preventing the occurrence of some diseases (diabetes, cancer, HIV disease). Even though amino acid analysis has been thoroughly investigated, there are still some steps which are not so clear in this analytical procedure, e.g. the coagulation process of the blood to afford plasma and serum. Various anticoagulants are used in clinical chemistry: in this paper we have investigated three commonly used anticoagulants, heparin, EDTA, and sodium citrate. The blood samples have been divided into three portions and each portion treated with a different anticoagulant. The entire analytical procedure (from blood collection to the coagulation all the way to HPLC analysis) has been extensively investigated; the chromatograms and the amino acid recoveries are reported, and the three anticoagulants compared. Finally, the best anticoagulant has been used to analyze glycemic curves of healthy patients: the behavior of essential amino acids in the different blood samples withdrawn has been studied.     

Clinical Chemistry: Challenges for Analytical Chemistry and the Nanosciences from Medicine

Clinical chemistry and laboratory medicine can look back over more than 150 years of eventful history. The subject encompasses all the medicinal disciplines as well as the remaining natural sciences. Clinical chemistry demonstrates how new insights from basic research in biochemical, biological, analytical chemical, engineering, and information technology can be transferred into the daily routine of medicine to improve diagnosis, therapeutic monitoring, and prevention. This Review begins with a presentation of the development of clinical chemistry. Individual steps between the drawing of blood and interpretation of laboratory data are then illustrated; here not only are pitfalls described, but so are quality control systems. The introduction of new methods and trends into medicinal analysis is explored, along with opportunities and problems associated with personalized medicine.     

Ion chromatographic precision measurement procedure for electrolytes in human serum: validation with the aid of primary measurement procedures

In order to make analytical measurement results traceable to the SI units in the field of clinical chemistry, an ion chromatographic (IC) measurement procedure has been developed which allows the amount of substance of the four so-called electrolytes Na, K, Mg and Ca as well as that of Li to be determined efficiently in human serum and with high accuracy. The IC measurement procedure was validated using primary measurement procedures confirmed by international comparison measurements and is proposed for use as a transfer standard when comparing measurements with clinical reference laboratories. The solutions used for calibration were gravimetrically prepared from pure substances (salts). Their chemical compositions had been iteratively fitted to those of the samples. The serum samples were mineralized by microwave-assisted digestion. The following relative expanded uncertainties for the average elemental contents were obtained: Li 0.4%, Na 0.14%, K 0.6%, Mg 0.8% and Ca 0.4%.     

An E1-Catalyzed Chemoenzymatic Strategy to Isopeptide-N-Ethylated Deubiquitylase-Resistant Ubiquitin Probes

Triazole-based deubiquitylase (DUB)-resistant ubiquitin (Ub) probes have recently emerged as effective tools for the discovery of Ub chain-specific interactors in proteomic studies, but their structural diversity is limited. A new family of DUB-resistant Ub probes is reported based on isopeptide-N-ethylated dimeric or polymeric Ub chains, which can be efficiently prepared by a one-pot, ubiquitin-activating enzyme (E1)-catalyzed condensation reaction of recombinant Ub precursors to give various homotypic and even branched Ub probes at multi-milligram scale. Proteomic studies using label-free quantitative (LFQ) MS indicated that the isopeptide-N-ethylated Ub probes may complement the triazole-based probes in the study of Ub interactome. Our study highlights the utility of modern protein synthetic chemistry to develop structurally and new families of tool molecules needed for proteomic studies.     

Analysis of paint cross-sections: a combined multivariate approach for the interpretation of μATR-FTIR hyperspectral data arrays

The present research is aimed at introducing a suitable approach for the exploitation of the hyperspectral data obtained by μATR-FTIR analyses of paint cross-sections. The application of principal component analysis for chemical mapping is well-established, even if a very limited number of applications to μFTIR data have been reported so far in the field of analytical chemistry for cultural heritage. Moreover, in many cases, chemometric tools are under-utilized and the outcomes under-interpreted. As a consequence, results and conclusions may be considerably compromised. In an attempt to overcome such drawbacks, the present work is proposing a comprehensive and efficient procedure based on an interactive brushing approach, which combines the structural information of the score scatter plots and the spatial information of the principal component (PC) score maps. In particular, the study demonstrates not only how the multivariate approach may provide more information than the univariate one, but also how the integration of different chemometric tools may allow a more comprehensive interpretation of the results with respect to the studies up to now reported in the literature. The examination of the average spectral profile of each score cluster, jointly with the loading analysis, is functional to characterize each area investigated on the basis of its spectral features. A multivariate comparison with spectra of standard compounds, projected in the PC score space, helps in supporting the chemical identification. The approach was validated on two real case studies.