Clinical assessment of near-infrared spectroscopy for noninvasive diabetes screening

Chip-scale sensor for spectroscopic metrology

Miniaturized spectrometers hold great promise for in situ, in vitro, and even in vivo sensing applications. However, their size reduction imposes vital performance constraints in meeting the rigorous demands of spectroscopy, including fine resolution, high accuracy, and ultra-wide observation window. The prevailing view in the community holds that miniaturized spectrometers are most suitable for coarse identification of signature peaks. Here, we present an integrated reconstructive spectrometer that enables near-infrared (NIR) spectroscopic metrology, and demonstrate a fully packaged sensor with auxiliary electronics. Such a sensor operates over a 520 nm bandwidth together with a resolution below 8 pm, yielding a record-breaking bandwidth-to-resolution ratio of over 65,000. The classification of different types of solid substances and the concentration measurement of aqueous and organic solutions are performed, all achieving approximately 100% accuracy. Notably, the detection limit of our sensor matches that of commercial benchtop counterparts, which is as low as 0.1% (i.e. 100 mg/dL) for identifying the concentration of glucose solution.

Differences in peripheral microcirculatory blood flow regulation in chronic kidney disease based on wavelet analysis of resting near-infrared spectroscopy

Vascular impairment is closely related to increased mortality in chronic kidney disease (CKD). The objective of this study was to assess impairments in the regulation of peripheral microvascular perfusion in patients with CKD based on time-frequency spectral analysis of resting near-infrared spectroscopy (NIRS) signals. Total hemoglobin (tHb) concentration and tissue saturation index (TSI) signals were collected using NIRS for a continuous 5 mins at 10 Hz from the forearm of 55 participants (34 CKD including 5 with end-stage renal disease, and 21 age-matched control). Continuous wavelet transform-based spectral analysis was used to quantify the spectral amplitude within five pre-defined frequency intervals (I, 0.0095-0.021 Hz; II, 0.021-0.052 Hz; III, 0.052-0.145 Hz; IV, 0.145-0.6 Hz and V, 0.6-2.0 Hz), representing endothelial, neurogenic, myogenic, respiratory and heartbeat activity, respectively. CKD patients showed lower tHb average spectral amplitude within the neurogenic frequency interval compared with controls (p = 0.014), consistent with an increased sympathetic outflow observed in CKD. CKD patients also showed lower TSI average spectral amplitude within the endothelial frequency interval compared with controls (p = 0.046), consistent with a reduced endothelial function in CKD. These findings demonstrate the potential of wavelet analysis of NIRS to provide complementary information on peripheral microvascular regulation in CKD.

Advances in cost-effective integrated spectrometers

The proliferation of Internet-of-Things has promoted a wide variety of emerging applications that require compact, lightweight, and low-cost optical spectrometers. While substantial progresses have been made in the miniaturization of spectrometers, most of them are with a major focus on the technical side but tend to feature a lower technology readiness level for manufacturability. More importantly, in spite of the advancement in miniaturized spectrometers, their performance and the metrics of real-life applications have seldomly been connected but are highly important. This review paper shows the market trend for chip-scale spectrometers and analyzes the key metrics that are required to adopt miniaturized spectrometers in real-life applications. Recent progress addressing the challenges of miniaturization of spectrometers is summarized, paying a special attention to the CMOS-compatible fabrication platform that shows a clear pathway to massive production. Insights for ways forward are also presented.

Glucose biosensors in clinical practice: principles, limits and perspectives of currently used devices

The demand of glucose monitoring devices and even of updated guidelines for the management of diabetic patients is dramatically increasing due to the progressive rise in the prevalence of diabetes mellitus and the need to prevent its complications. Even though the introduction of the first glucose sensor occurred decades ago, important advances both from the technological and clinical point of view have contributed to a substantial improvement in quality healthcare. This review aims to bring together purely technological and clinical aspects of interest in the field of glucose devices by proposing a roadmap in glucose monitoring and management of patients with diabetes. Also, it prospects other biological fluids to be examined as further options in diabetes care, and suggests, throughout the technology innovation process, future directions to improve the follow-up, treatment, and clinical outcomes of patients.

An interrelated CataFlower enzyme system for sensitively monitoring sweat glucose

An accurate measurement of sweat glucose is a promising alternative to invasive finger prick blood test, and may provide effective self-monitoring of blood glucose with good patient compliance. Herein, an interrelated catalytic enzyme system has been developed, termed as CataFlower, which is composed of nanoflower MoS₂ (peroxidase) decorated with GOx (glucose oxidase) and MnO₂ (oxygen generator), and exhibits synergistic oxidative capability for sensitively monitoring sweat glucose. CataFlower can not only generate oxygen in situ to maximize GOx activity, but promote peroxidase-triggered H₂O₂ oxidation of methylene blue, resulting in sensitive colorimetric detection of glucose. We identify that CataFlower can precisely detect glucose with a detection limit of 10 μM, allowing for measuring glucose levels in different biological samples, such as blood and urine. Particularly, CataFlower is capable of monitoring dynamic changes in sweat glucose with high sensitivity and accuracy during exercise. Therefore, CataFlower provides a stepping stone to eliminate invasive blood tests, significantly improving the diagnosis and management of diabetes mellitus.

A Novel Luminescent "Nanochip" as a Tandem Catalytic System for Chemiluminescent Detection of Sweat Glucose

Accurate sweat glucose detection is a promising alternative to invasive finger-prick blood tests, allowing for self-monitoring of blood glucose with good patient compliance. In this study, we have developed a tandem catalytic system, termed as a luminescent "nanochip" (LAON), which was composed of gold nanoparticles (AuNPs) and N-(aminobutyl)-N-(ethylisoluminol) (ABEI)-engineered oxygen-doped carbon nitride (O-g-C₃N₄), for chemiluminescent detection of sweat glucose. The LAON exhibits dual catalytic activity of glucose oxidase and peroxidase and can not only oxidize glucose to generate H₂O₂ but catalyze H₂O₂-mediated luminol chemiluminescence, resulting in sensitive detection of glucose. We identify that the LAON can precisely detect glucose with a detection limit of 0.1 μM, enabling us to measure glucose levels in different biological samples. Particularly, the LAON is capable of sensitively and accurately monitoring dynamic changes in sweat glucose during exercise. Therefore, the LAON provides an alternative approach to supersede invasive blood tests and may improve the management of diabetes mellitus.

Enhancing the Accuracy of Non-Invasive Glucose Sensing in Aqueous Solutions Using Combined Millimeter Wave and Near Infrared Transmission

We reported measurement results relating to non-invasive glucose sensing using a novel multiwavelength approach that combines radio frequency and near infrared signals in transmission through aqueous glucose-loaded solutions. Data were collected simultaneously in the 37–39 GHz and 900–1800 nm electromagnetic bands. We successfully detected changes in the glucose solutions with varying glucose concentrations between 80 and 5000 mg/dl. The measurements showed for the first time that, compared to single modality systems, greater accuracy on glucose level prediction can be achieved when combining transmission data from these distinct electromagnetic bands, boosted by machine learning algorithms.

Evaluation of a near-infrared light ultrasound system as a non-invasive blood glucose monitoring device

The aim of this study was to evaluate the newly developed non-invasive blood glucose system NIRLUS® (Near-Infra Red Light Ultra Sound; NIRLUS Engineering AG, Lübeck, Germany) under standardized conditions. Seventeen healthy men of normal weight (body mass index 22.4 ± 1.4 kg/m² ), aged 18 to 45 years, were enrolled in this study. During an intravenous glucose tolerance test, blood glucose profiles were measured simultaneously using the NIRLUS system and a "gold standard" laboratory reference system. Correlation analysis revealed a strong association between NIRLUS and reference values (r = 0.934; P < 0.001). Subsequent Bland-Altman analysis showed a symmetric distribution (r = 0.047; P = 0.395), and 95.5% of the NIRLUS-reference pairs were within the difference (d) of d ± 2 SD. The median deviation of all paired NIRLUS-reference values was 0.5 mmol/L and the mean percent deviation was 11.5%. Error grid analysis showed that 93.6% of NIRLUS-reference pairs are located in the area A, and 6.4% in the area B. No data were allocated in the areas C to E. This proof-of-concept study demonstrates the reproducibility of accurate blood glucose measures obtained by NIRLUS as compared to a gold standard laboratory reference system. The technology of NIRLUS is an important step forward in the development of non-invasive glucose monitoring.

Ex vivo optical measurements of glucose diffusion kinetics in native and diabetic mouse skin

The aim of this study was to estimate the glucose diffusion coefficients ex vivo in skin of mice with diabetes induced in vivo by alloxan in comparison to non-diabetic mice. The temporal dependences of collimated transmittance of tissue samples immersed in glucose solutions were measured in the VIS-NIR spectral range to quantify the glucose diffusion/permeability coefficients and optical clearing efficiency of mouse skin. The average thickness of intact healthy and diabetic skin was 0.023 ± 0.006 cm and 0.019 ± 0.005 cm, respectively. Considerable differences in optical and kinetic properties of diabetic and non-diabetic skin were found: clearing efficiency was 1.5-fold better and glucose diffusivity was 2-fold slower for diabetic skin. Experimental Setup for measuring collimated transmittance spectra of mouse skin samples.

In vivo time-resolved autofluorescence measurements to test for glycation of human skin

We present an evaluation of time-resolved fluorescence measurements on human skin for screening type 2 diabetes. In vivo human skin is excited with a pulse diode at 375 nm and pulse width of 700 ps. Fluorescence decays are recorded at four different emission wavelengths: 442, 460, 478, and 496 nm. Experiments are performed at various locations, including the palms, arms, legs, and cheeks of a healthy Caucasian subject to test single-subject variability. The fluorescence decays obtained are modeled using a three-exponential decay. The variations in the lifetimes and amplitudes from one location to another are minimal, except on the cheek. We compare the fluorescent decays of 38 diabetic subjects and 37 nondiabetic subjects, with different skin complexions and of ages ranging from 6 to 85 yr. The average lifetimes for nondiabetic subjects were 0.5, 2.6, and 9.2 ns with fractional amplitudes of 0.78, 0.18, and 0.03, respectively. The effects of average hemoglobin A1c (HbA1c) from the previous 4 yr and diabetes duration are evaluated. While no significant differences between the fluorescence lifetimes of nondiabetic and diabetic subjects are observed, two of the fractional amplitudes are statistically different. Additionally, none of the six fluorescence parameters correlated with diabetes duration or HbA1c. One of the lifetimes as well as two of the fractional amplitudes differ between diabetic subjects with foot ulcers and nondiabetic subjects.