In vitro glucose measurement using tunable mid-infrared laser spectroscopy combined with fiber-optic sensor

Evanescent wave quartz-enhanced photoacoustic spectroscopy employing a side-polished fiber for methane sensing

We present an all-fiber-based laser gas analyzer (LGA) employing quartz-enhanced photoacoustic spectroscopy (QEPAS) and a side-polished fiber (SPF). The LGA comprises a custom quartz tuning fork (QTF) with 0.8 mm prong spacing, two acoustic micro-resonators (mR) located on either side of the prong spacing, and a single-mode fiber containing a 17 mm polished section passing through both mRs and QTF. The SPF polished face is positioned to enable the evanescent wave (EW) to create a photoacoustic wave and excite the fundamental flexural mode of the QTF. Sensor performance was demonstrated using methane in nitrogen gas mixtures, with CH4 mixing ratios ranging from 75 ppmv to 1% (by volume), measured with an accumulation time of 300 ms, and a minimum detection limit of 34 ppmv subsequently determined. The EW-QEPAS sensor is ideal for miniaturization, as it does not contain any free-space optics and is suitable for gas sensing in harsh environments and where mobility is required.

Detection of blood glucose with hemoglobin content using compact photonic crystal fiber

We have proposed Twin Elliptical Core Photonic Crystal Fiber (TEC-PCF) sensor for the detection of blood glucose level under the influence of hemoglobin components. The main featuring of the proposed biosensor is to detect the wide range of blood glucose content with enhanced sensitivity, by utilizing small length of the fiber. In order to achieve this, we have constructed asymmetric TEC-PCF where the elliptical core is filled by blood sample. The numerical sensing characteristics are evaluated using Finite Element Method (FEM). By varying hemoglobin concentrations as 120 g/L, 140 g/L and 160 g/L, we realize enhanced blood glucose sensing with detection range from 0 g/L to 100 g/L. The sensing performance of the proposed biosensor is studied through the coupling length and transmission power spectrum by calculation of effective index of the coupling mode. The obtained maximum wavelength sensitivity under the influence of 160 g/L hemoglobin content is 2.4 nm/(g/L) and 2.42 nm/(g/L) with fiber length of 0.245 mm and 0.215 mm for X and Y polarization, respectively. Further, limit of detection (LOD) is calculated under the influence of 160 g/L hemoglobin content is 0.375 mg/L and 0.372 mg/L for X and Y polarization, respectively. The proposed miniaturized sensing device can be integrated with microfluidic systems for the development of next-generation biosensor applications as point of-care and lab-on-a-chip.

Blood glucose monitoring- an overview of current and future non-invasive devices

BACKGROUND AND AIMS

Blood glucose monitoring is very important for individuals with diabetes due to its rate determining role in medication strength adjustment and observation of possible life-threatening hypoglycemia. Possible non-invasive devices can overcome some of these burdens and could increase adherence towards checking blood glucose.

METHODS

Data extraction methods were primarily based through various PubMed scholarly articles for real-world examples of non-invasive approaches. Additional articles were used in adjust as supplementary to the PubMed articles.

RESULTS

Non-invasive technology is being heavily researched and could create a new market that could offer novel options for blood glucose monitoring at home. The lack of adherence for blood glucose monitoring may be tied to current blood glucose monitoring devices, which require invasive procedures that are often painful and expensive to acquire. Certain non-invasive devices have and are being developed for accurately assessing the blood glucose levels of individuals when compared to current blood glucose monitoring devices.

CONCLUSION

Blood glucose monitoring is very important for the health and safety of individuals with diabetes. It is important to consider the direct problems that may occur from the lack of adherence to blood glucose monitoring and propose options to help reduce the issues associated with current devices. Different non-invasive technologies can tailor to the needs of patients with diabetes based on the body target that is used for detection. Further research may be needed to help improve the specificity and sensitivity of certain technologies.

Broadband polarimetric glucose determination in protein containing media using characteristic optical rotatory dispersion

One of the major challenges during polarimetric determination of glucose concentration is the spectral superposition with other optically active molecules, especially proteins like albumin. Since each of those substances has a characteristic optical rotatory dispersion (ORD), we developed a broadband polarimeter setup to distinguish between glucose and albumin. A partial least squares (PLS) regression with 5 components was applied to the polarimeter signal in the wavelength range of 380 - 680 nm . To verify the efficacy of the proposed method, different glucose levels of 0 - 500 mg/dl were spiked with varying albumin concentrations up to 1000 mg/dl . A standard error of prediction of ± 16.0 mg/dl was achieved compared to ± 128.3 mg/dl using a two-wavelength system with 532 nm and 635 nm under the same conditions.

Infrared Spectroscopy with a Fiber-Coupled Quantum Cascade Laser for Attenuated Total Reflection Measurements Towards Biomedical Applications

The development of rapid and accurate biomedical laser spectroscopy systems in the mid-infrared has been enabled by the commercial availability of external-cavity quantum cascade lasers (EC-QCLs). EC-QCLs are a preferable alternative to benchtop instruments such as Fourier transform infrared spectrometers for sensor development as they are small and have high spectral power density. They also allow for the investigation of multiple analytes due to their broad tuneability and through the use of multivariate analysis. This article presents an in vitro investigation with two fiber-coupled measurement setups based on attenuated total reflection spectroscopy and direct transmission spectroscopy for sensing. A pulsed EC-QCL (1200–900 cm−1) was used for measurements of glucose and albumin in aqueous solutions, with lactate and urea as interferents. This analyte composition was chosen as an example of a complex aqueous solution with relevance for biomedical sensors. Glucose concentrations were determined in both setup types with root-mean-square error of cross-validation (RMSECV) of less than 20 mg/dL using partial least-squares (PLS) regression. These results demonstrate accurate analyte measurements, and are promising for further development of fiber-coupled, miniaturised in vivo sensors based on mid-infrared spectroscopy.

Non-invasive, transdermal, path-selective and specific glucose monitoring via a graphene-based platform

Currently, there is no available needle-free approach for diabetics to monitor glucose levels in the interstitial fluid. Here, we report a path-selective, non-invasive, transdermal glucose monitoring system based on a miniaturized pixel array platform (realized either by graphene-based thin-film technology, or screen-printing). The system samples glucose from the interstitial fluid via electroosmotic extraction through individual, privileged, follicular pathways in the skin, accessible via the pixels of the array. A proof of principle using mammalian skin ex vivo is demonstrated for specific and 'quantized' glucose extraction/detection via follicular pathways, and across the hypo- to hyper-glycaemic range in humans. Furthermore, the quantification of follicular and non-follicular glucose extraction fluxes is clearly shown. In vivo continuous monitoring of interstitial fluid-borne glucose with the pixel array was able to track blood sugar in healthy human subjects. This approach paves the way to clinically relevant glucose detection in diabetics without the need for invasive, finger-stick blood sampling.

Hollow optical-fiber based infrared spectroscopy for measurement of blood glucose level by using multi-reflection prism

A mid-infrared attenuated total reflection (ATR) spectroscopy system employing hollow optical fibers and a trapezoidal multi-reflection ATR prism has been developed to measure blood glucose levels. Using a multi-reflection prism brought about higher sensitivity, and the flat and wide contact surface of the prism resulted in higher measurement reproducibility. An analysis of in vivo measurements of human inner lip mucosa revealed clear signatures of glucose in the difference spectra between ones taken during the fasting state and ones taken after ingestion of glucose solutions. A calibration plot based on the absorption peak at 1155 cm(-1) that originates from the pyranose ring structure of glucose gave measurement errors less than 20%.

In vitro evaluation of fluorescence glucose biosensor response

Rapid, accurate, and minimally-invasive glucose biosensors based on Förster Resonance Energy Transfer (FRET) for glucose measurement have the potential to enhance diabetes control. However, a standard set of in vitro approaches for evaluating optical glucose biosensor response under controlled conditions would facilitate technological innovation and clinical translation. Towards this end, we have identified key characteristics and response test methods, fabricated FRET-based glucose biosensors, and characterized biosensor performance using these test methods. The biosensors were based on competitive binding between dextran and glucose to concanavalin A and incorporated long-wavelength fluorescence dye pairs. Testing characteristics included spectral response, linearity, sensitivity, limit of detection, kinetic response, reversibility, stability, precision, and accuracy. The biosensor demonstrated a fluorescence change of 45% in the presence of 400 mg/dL glucose, a mean absolute relative difference of less than 11%, a limit of detection of 25 mg/dL, a response time of 15 min, and a decay in fluorescence intensity of 72% over 30 days. The battery of tests presented here for objective, quantitative in vitro evaluation of FRET glucose biosensors performance have the potential to form the basis of future consensus standards. By implementing these test methods for a long-visible-wavelength biosensor, we were able to demonstrate strengths and weaknesses with a new level of thoroughness and rigor.

Blood glucose measurement by using hollow optical fiber-based attenuated total reflection probe

A noninvasive glucose monitoring system based on mid-infrared, attenuated total reflection spectroscopy using a hollow optical fiber probe is developed. Owing to the flexible fiber probe, measurement of oral mucosa, where blood capillaries are near the skin surface, is possible. Blood glucose levels are measured by detecting the peak intensity of glucose absorption bands, and the experimental results showed that the reproducibility of the measurement is high enough for monitoring blood glucose.