Predicting the early risk of chronic kidney disease in patients with diabetes using real-world data.

Diagnostic procedures, therapeutic recommendations, and medical risk stratifications are based on dedicated, strictly controlled clinical trials. However, a plethora of real-world medical data exists, whereupon the increase in data volume comes at the expense of completeness, uniformity, and control. Here, a case-by-case comparison shows that the predictive power of our real world data-based model for diabetes-related chronic kidney disease outperforms published algorithms, which were derived from clinical study data.

Towards a quantum cascade laser-based implant for the continuous monitoring of glucose.

Continuous glucose monitoring enables an improved disease management for people with diabetes. However, state-of-the-art, enzyme-based, minimally invasive sensors lose their sensitivity over time and have to be replaced periodically. Here, we present the in vitro investigation of a quantum cascade laser-based measurement scheme that conceptually should be applicable over elongated periods of time due to its reagent-free nature and may therefore be considered as an approach towards long-term implantation. The method uses a miniaturized optofluidic interface in transflection geometry to measure the characteristic mid-infrared absorption properties of glucose. A glucose sensitivity of 3.2 mg dL-1 is achieved in aqueous glucose solutions. While this sensitivity drops to 12 mg dL-1 in the presence of biologically plausible, maximum concentrations of other monosaccharides, it is still well within the medically acceptable range according to Parkes error grid analysis. With a response time of less than five minutes, our sensor should be able to react adequately fast to physiological changes in glucose concentration. Finally, no drift or deterioration was found during an extended, 42 days in vitro experiment. These results underline the potential of this technique for its conceivable applicability in vivo as a long-term glucose monitoring implant.

Biomedical applications of mid-infrared quantum cascade lasers - a review.

Mid-infrared spectroscopy has been applied to research in biology and medicine for more than 20 years and conceivable applications have been identified. More recently, these applications have been shown to benefit from the use of quantum cascade lasers due to their specific properties, namely high spectral power density, small beam parameter product, narrow emission spectrum and, if needed, tuning capabilities. This review provides an overview of the achievements and illustrates some applications which benefit from the key characteristics of quantum cascade laser-based mid-infrared spectroscopy using examples such as breath analysis, the investigation of serum, non-invasive glucose monitoring in bulk tissue and the combination of spectroscopy and microscopy of tissue thin sections for rapid histopathology.

On the role of interference in laser-based mid-infrared widefield microspectroscopy.

A laser's high degree of coherence leads to interferences, which-in the absence of precautions-can cause severe image distortions such as fringes and speckles and which thereby strongly hamper a meaningful interpretation of hyperspectral images in laser-based widefield microspectroscopy. While images and spectra of homogenous samples may already suffer from interferences, any structured object such as a tissue thin section will add to these distortions due to wavelength- and, in particular, sample-dependent phase shifts (structure sizes, absorption coefficients, refractive indices). This effect is devastating for the universal applicability of laser-based microspectroscopy especially in the mid-infrared (MIR), where cell sizes are of the same dimension as the wavelength of the illumination source. Here, we show that the impact of interferences is strongly mitigated by reducing the time-averaged spatiotemporal coherence properties of the illumination using a moving plus a stationary scatterer. In this case, the illumination path provides a pseudothermal radiation source and spatially resolved spectra can be obtained at the quality of the reference method, that is, Fourier-transform infrared microspectroscopy, without compromising spectral or spatial resolution.

Optical properties of porcine dermis in the mid-infrared absorption band of glucose.

The optical properties of skin in the mid-infrared range are not known, despite their importance for e.g. non-invasive glucose monitoring. In this paper, transmission, absorption, scattering, and reduced scattering coefficients are quantified using a custom-built goniometer based on a quantum cascade laser operated at the glucose absorption band at a wavelength of around 9.7 µm. The measurements show a strong dominance of absorption and moderate contributions from scattering. The scattered radiation is dominated by single scattering events in the forward direction (g = 0.967) within the range of the investigated dermis layer thicknesses of up to 50 µm, whereby the fraction of multiple scattering is expected to increase with the layer thickness.

Translating vibrational spectroscopy into clinical applications - vision or reality?

The Faraday Discussion meeting "Advanced Vibrational Spectroscopy for Biomedical Applications" provided an excellent opportunity to share and discuss recent research and applications on a highly interdisciplinary level. Spectral pathology, single cell analysis, data handling, clinical spectroscopy, and the spectral analysis of biofluids were among the topics covered during the meeting. The focus on discussion rather than "merely" presentation was highly appreciated and fruitful discussions evolved around the interpretation of the amide-bands, optical resolution, the role of diffraction and data analysis procedure, to name a few. The meeting made clear that the spectroscopy of molecular vibrations in biomolecules has evolved from a purely academic research tool to a technology used in clinical practice in some cases. In this sense, biomedical vibrational spectroscopy has reached a pivotal point at which questions like diagnostic value, therapeutic consequence and financial viability are gaining more and more importance.

Real-time mid-infrared imaging of living microorganisms.

The speed and efficiency of quantum cascade laser-based mid-infrared microspectroscopy are demonstrated using two different model organisms as examples. For the slowly moving Amoeba proteus, a quantum cascade laser is tuned over the wavelength range of 7.6 µm to 8.6 µm (wavenumbers 1320 cm(-1) and 1160 cm(-1) , respectively). The recording of a hyperspectral image takes 11.3 s whereby an average signal-to-noise ratio of 29 is achieved. The limits of time resolution are tested by imaging the fast moving Caenorhabditis elegans at a discrete wavenumber of 1265 cm(-1) . Mid-infrared imaging is performed with the 640 × 480 pixel video graphics array (VGA) standard and at a full-frame time resolution of 0.02 s (i.e. well above the most common frame rate standards). An average signal-to-noise ratio of 16 is obtained. To the best of our knowledge, these findings constitute the first mid-infrared imaging of living organisms at VGA standard and video frame rate.

Surface-enhanced mid-infrared spectroscopy using a quantum cascade laser.

We report on the successful measurement of surface-enhanced infrared vibrational spectra from a few nanometer thick organic semiconductor layers on samples with resonant plasmonic nanoantennas arranged in arrays. For the first time, a setup with a tunable quantum cascade laser as the light source in mid-infrared range is used. The combination of the quantum cascade laser with a microbolometer array for infrared light allows to map an area 2.8 × 3.1 mm(2) with a spatial resolution of about 9 µm, a bandwidth from 1170 to 1300 cm(-1), and a spectral resolution of 2.5 cm(-1) within only five minutes versus 16 hours using a conventional FTIR micro-spectrometer. We present a quantitative comparison of the experimental results from the setup with the quantum cascade laser with those from the FTIR micro-spectrometer.

A fast recoiling silk-like elastomer facilitates nanosecond nematocyst discharge.

BACKGROUND: The discharge of the Cnidarian stinging organelle, the nematocyst, is one of the fastest processes in biology and involves volume changes of the highly pressurised (150 bar) capsule of up to 50%. Hitherto, the molecular basis for the unusual biomechanical properties of nematocysts has been elusive, as their structure was mainly defined as a stress-resistant collagenous matrix. RESULTS: Here, we characterise Cnidoin, a novel elastic protein identified as a structural component of Hydra nematocysts. Cnidoin is expressed in nematocytes of all types and immunostainings revealed incorporation into capsule walls and tubules concomitant with minicollagens. Similar to spider silk proteins, to which it is related at sequence level, Cnidoin possesses high elasticity and fast coiling propensity as predicted by molecular dynamics simulations and quantified by force spectroscopy. Recombinant Cnidoin showed a high tendency for spontaneous aggregation to bundles of fibrillar structures. CONCLUSIONS: Cnidoin represents the molecular factor involved in kinetic energy storage and release during the ultra-fast nematocyst discharge. Furthermore, it implies an early evolutionary origin of protein elastomers in basal metazoans.

A quantitative look inside the body: minimally invasive infrared analysis in vivo.

Today's minimally invasive biosensors are often based on chemical reagents and suffer from, e.g., oxygen dependence, toxic reaction products, excess analyte consumption, and/or degradation of the reagents. Here, we show the first successful analyte quantification by means of a minimally invasive sensor in vivo, which does not use chemical reactions. The concentration of glucose is determined continuously in vivo using transcutaneous, fiber-based mid-infrared laser spectroscopy. When comparing the infrared data measured in vivo with the 127 reference readings of glucose obtained in vitro, an overall standard deviation of 17.5% and a median of the absolute values of the relative deviations of 11.0% are achieved. The encouraging results open up the path toward a reagent-free long-term implant for the continuous surveillance of metabolites. In addition, the high sampling rate facilitates important research in body metabolism as well as its application outside the field of medicine such as real-time analyte sensing during fermentation.

Quantum cascade laser-based hyperspectral imaging of biological tissue.

The spectroscopy of analyte-specific molecular vibrations in tissue thin sections has opened up a path toward histopathology without the need for tissue staining. However, biomedical vibrational imaging has not yet advanced from academic research to routine histopathology due to long acquisition times for the microscopic hyperspectral images and/or cost and availability of the necessary equipment. Here we show that the combination of a fast-tuning quantum cascade laser with a microbolometer array detector allows for a rapid image acquisition and bares the potential for substantial cost reduction. A 3.1 x 2.8 mm2 unstained thin section of mouse jejunum has been imaged in the 9.2 to 9.7 µm wavelength range (spectral resolution ~1 cm(-1)) within 5 min with diffraction limited spatial resolution. The comparison of this hyperspectral imaging approach with standard Fourier transform infrared imaging or mapping of the identical sample shows a reduction in acquisition time per wavenumber interval and image area by more than one or three orders of magnitude, respectively.

Evaporation from open microchannel grooves.

The evaporation of water from open u-shaped microchannel grooves was investigated with particular emphasis on the roles of channel width and air flow conditions. Given the small dimensions of the microchannels, all measurements were conducted in a range where convection and diffusion are of equal importance and known correlations for the calculation of mass transfer coefficients cannot be applied. The evaporation rates were measured using a new optical method and a gravimetric method. Both measurement methods yielded mass transfer coefficients that are in agreement with each other. The observed relation between mass transfer coefficient, air velocity and channel width vastly differs from the predictions obtained from macroscopic structures. With respect to diagnostic devices we conclude that analyte concentration in an open microchannel groove strongly increases even within short times due to the evaporation process and we show that wider channels are more favourable in terms of minimizing the relative evaporation rate.

Fluorescence properties of carba nicotinamide adenine dinucleotide for glucose sensing.

Carba nicotinamide adenine dinucleotide (cNAD) may serve as a stable cofactor for the enzyme-based detection of glucose. Many characteristics of cNAD and its reduced form cNADH resemble those of NAD and NADH, respectively. The fluorescence lifetimes of cNADH are determined to be 0.32(2) ns and 0.66(3) ns compared to 0.28(2) ns and 0.60(3) ns for NADH, and the temperature dependence of these lifetimes hints towards identical processes for quenching. The maximum emission occurs at 464 nm for both cNADH and NADH and absorbance maxima are found at 360 nm and 340 nm, respectively. In contrast to previous suggestions the respective maximum extinction coefficient of cNADH equals that of NADH and amounts to 6.2(2) mM(-1) cm(-1). When changing from NADH to cNADH we observe a ~50% increase in quantum efficiency, which--together with the larger excitation wavelength and the higher stability--should make cNAD a well suited alternative as coenzyme for robust glucose detection.

Effective fragment potential study of the influence of hydration on the vibrational spectrum of glucose.

The standard agent glucose has been the subject of numerous experimental and theoretical studies, especially in the aqueous environments which are present in most biochemical processes. The impact of the solvation process on the vibrational spectra of glucose in the mid-infrared region is investigated in this work. The computational study focused both on the variation of the number of surrounding water molecules from 0 to 229 and on the number of single spectra included in the iterative averaging process. The calculations consisted of a combination of force field methods for the sampling of the configuration space and density functional theory for further geometry optimizations. Effective fragment potentials (EFPs) were employed for the description of the solvent as a compromise between accuracy and computational complexity. A correlation between the experimental data and the number of surrounding water molecules could not be observed for an averaging over a small set of computed single spectra. The inclusion of an additionial polarizable continuum model (PCM) also showed no further impact. However, an increase in the number of underlying single spectra in the averaging process increased the correlation between simulations and the experiment substantially. Especially for 18 explicit EFP water molecules, an inclusion of 80 single spectra delivered a Pearson's correlation coefficient r ≈ 0.94.

Continuous glucose monitoring by means of mid-infrared transmission laser spectroscopy in vitro.

The continuous surveillance of glucose concentration reduces short-term risks and long-term complications for people with diabetes mellitus, a disorder of glucose metabolism. As a first step towards the continuous monitoring of glucose, reagent-free transmission spectroscopy in the mid-infrared region has been carried out in vitro using a quantum cascade laser and an optical silver halide fiber. A 30 µm gap in the fiber allowed for transmission spectroscopy of aqueous glucose solutions at a wavelength of 9.69 µm, which is specific to a molecular vibration of glucose. A noise-equivalent concentration as low as 4 mg/dL was achieved at an average power of 1.8 mW and an integration time of 50 s. This is among the most precise of glucose measurements using mid-infrared spectroscopy. Even with the very low average laser power of 0.07 mW the sensitivity of previous results (using a fiber optical evanescent field analysis) has been improved upon by almost one order of magnitude. Finally, the impact of potentially interfering substances such as other carbohydrates was analyzed.