In vivo glucose monitoring using dual-wavelength polarimetry to overcome corneal birefringence in the presence of motion

High-precision non-invasive RBC and HGB detection system based on spectral analysis

Non-invasive blood composition analysis based on dynamic spectrum (DS) theory has gained significant attention due to its non-invasive, simple, and fast performance. However, most of the multi-wavelength photoplethysmography (PPG) detection devices used to obtain DS are composed of halogen light sources and spectrometers and cannot detect effective PPG signals in the visible light short band (400-620 nm), which limits the detection accuracy of blood components with significant absorption spectral differences in that band. Therefore, this paper designs a multi-wavelength spectral acquisition system that can measure high signal-to-noise ratio (SNR > 65 dB) PGG signals at wavelengths of 405, 430, 450, 505, 520, and 570 nm and combines this system with a halogen lamp spectrometer acquisition system for non-invasive blood component detection. Furthermore, this paper collects the DS of 272 subjects with the combined system and establishes a predictive model for DS with the content of red blood cell (RBC) and hemoglobin (HGB) components. The results show that, compared with the halogen lamp spectrometer acquisition system, the correlation coefficient (Rp) of RBC and HGB prediction model established by the combined system has increased by 0.0619 and 0.0489, respectively, and the root mean square error (RMSE) has decreased by 0.08 1e12/L and 0.85 g/L, which confirm the feasibility of the designed multi-wavelength spectrum acquisition system to enhance the accuracy of blood component detection.

Review of Noninvasive Continuous Glucose Monitoring in Diabetics

For diabetics, taking regular blood glucose measurements is crucial. However, traditional blood glucose monitoring methods are invasive and unfriendly to diabetics. Recent studies have proposed a biofluid-based glucose sensing technique that creatively combines wearable devices with noninvasive glucose monitoring technology to enhance diabetes management. This is a revolutionary advance in the diagnosis and management of diabetes, reflects the thoughtful modernization of medicine, and promotes the development of digital medicine. This paper reviews the research progress of noninvasive continuous blood glucose monitoring (CGM), with a focus on the biological liquids that replace blood in monitoring systems, the technical principles of continuous noninvasive glucose detection, and the output and calibration of sensor signals. In addition, the existing limits of noninvasive CGM systems and prospects for the future are discussed. This work serves as a resource for further promoting the development of noninvasive CGM systems.

Noninvasive Glucose Sensing In Vivo

Blood glucose monitoring is an essential aspect of disease management for individuals with diabetes. Unfortunately, traditional methods require collecting a blood sample and thus are invasive and inconvenient. Recent developments in minimally invasive continuous glucose monitors have provided a more convenient alternative for people with diabetes to track their glucose levels 24/7. Despite this progress, many challenges remain to establish a noninvasive monitoring technique that works accurately and reliably in the wild. This review encompasses the current advancements in noninvasive glucose sensing technology in vivo, delves into the common challenges faced by these systems, and offers an insightful outlook on existing and future solutions.

Non-invasive method for blood glucose monitoring using ECG signal

Introduction: Tight glucose monitoring is crucial for diabetic patients by using a Continuous Glucose Monitor (CGM). The existing CGMs measure the Blood Glucose Concentration (BGC) from the interstitial fluid. These technologies are quite expensive, and most of them are invasive. Previous studies have demonstrated that hypoglycemia and hyperglycemia episodes affect the electrophysiology of the heart. However, they did not determine a cohort relationship between BGC and ECG parameters.

Material and method: In this work, we propose a new method for determining the BGC using surface ECG signals. Recurrent Convolutional Neural Networks (RCNN) were applied to segment the ECG signals. Then, the extracted features were employed to determine the BGC using two mathematical equations. This method has been tested on 04 patients over multiple days from the D1namo dataset, using surface ECG signals instead of intracardiac signal.

Results: We were able to segment the ECG signals with an accuracy of 94% using the RCNN algorithm. According to the results, the proposed method was able to estimate the BGC with a Mean Absolute Error (MAE) of 0.0539, and a Mean Squared Error (MSE) of 0.1604. In addition, the linear relationship between BGC and ECG features has been confirmed in this paper.

Conclusion: In this paper, we propose the potential use of ECG features to determine the BGC. Additionally, we confirmed the linear relationship between BGC and ECG features. That fact will open new perspectives for further research, namely physiological models. Furthermore, the findings point to the possible application of ECG wearable devices for non-invasive continuous blood glucose monitoring via machine learning.

Glucose-Sensing Photonic Nanochain Probes with Color Change in Seconds

Glucose-sensing photonic crystals are promising for the significant advance of continuous glucose monitoring systems due to the naked-eye colorimetric readouts and noninvasive detection of diabetes, but the long response time hampers their practical applications. Here, for the first time probes of photonic nanochains (PNCs) are demonstrated that are capable of continuously and reversibly sensing glucose concentration ([glucose]) variation within seconds by color change without power consumption, much faster by 2-3 orders of magnitude than previous ones. They are comprised of 1D equidistant arrays of magnetic nanoparticles enveloped by tens-of-nanometer-thick phenylboronic acid-functionalized hydrogels, and fabricated by developing selective concentration polymerization of monomers in binary microheterogeneous solvents of dimethyl sulfoxide (DMSO) and H₂ O. In this process, both 3-acrylamido phenylboronic acid (AAPBA) and N-2-hydroxyethyl acrylamide (HEAAm) are preferentially dissolved in the small volume of free DMSO concentrated in the vicinity of poly vinylpyrrolidone coated Fe₃ O₄ colloidal nanoparticles (Fe₃ O₄ @PVP), yielding Fe₃ O₄ @PVP@poly(AAPBA-co-HEAAm) PNCs after UV irradiation under magnetic field. The PNCs in phosphate buffered solution have a wavelength-shift range up to 130 nm when [glucose] changes from 0 to 20 × 10^-3 m. The results can facilitate real-time glucose monitoring and provide an alternative to produce functional organic-inorganic nanostructures.

Glucose levels between the anterior chamber of the eye and blood are correlated based on blood glucose dynamics

Glycemic control is essential to manage metabolic diseases such as diabetes. Frequent measurements of systemic glucose levels with prompt managements can prevent organ damages. The eye is a glucose highly demanding organ in our body, and the anterior chamber (AC) in the eye has been suggested for a noninvasive blood glucose monitoring site. However, calculating blood glucose levels from measuring glucose levels in AC has been difficult and unclear. In this study, we aimed to examine glucose levels from AC and find a correlation with blood glucose levels. A total of 30 patients with cataracts (men and women, study 1; 7 and 3, study 2; 9 and 11) who visited Keio University Hospital from 2015 to 2018 and agreed to participate in this study were recruited. Glucose levels from AC and the blood were examined by a UV-hexokinase or H2O2-electrode method before/during the cataract surgery. These values were analyzed with regression analyses depending on the groups (blood glucose-ascending and descending groups). In the blood glucose-descending group, glucose levels from AC were strongly correlated with blood glucose levels (a high R2 value, 0.8636). However, the relatively moderate correlation was seen in the blood glucose-ascending group (a low R2 value, 0.5228). Taken together, we showed different correlation ratios on glucose levels between AC and the blood, based on blood glucose dynamics. Stacking data regarding this issue would enable establishing noninvasive blood glucose monitoring from measuring glucose levels in AC more correctly, which will be helpful for proper and prompt managements for glucose-mediated complications.

Composite polarization systems for independent controlling polarization of two beams with different wavelengths

The usage of independent and simultaneous control of the state of light polarization at different wavelengths can expand the capabilities of polarization methods for biomedical application. Unfortunately, all known methods of polarization conversion cannot convert the state of light polarization at different wavelengths independently. We propose a method and device for independent and simultaneous control of the polarization state at two wavelengths. We have theoretically proved the possibility of maintaining the phase shift at the first wavelength unchanged while simultaneously and independently changing the phase shift at the second wavelength from 0 to 180 degrees. The capabilities of the method were for the first time demonstrated for radiation with wavelengths λ = 632.8 nm and λ = 488 nm. At the wavelength λ = 632.8 nm, the phase shift remained equal to 180° whereas at the wavelength λ = 488 nm, it varied in the range from 121° to 136°.

Label-Free Ultrasensitive Detection of Abnormal Chiral Metabolites in Diabetes

Homochirality is necessary for normal biochemical processes in humans. Abnormal amounts of chiral molecules in biofluids have been found in patients with diabetes. However, the detailed analysis of diabetes-related abnormal chirality in biofluids and its potential use for clinical applications have been hindered by the difficulty in detecting and monitoring the chiral changes in biofluids, due to their low molar mass and trace concentrations. Herein, we demonstrate the label-free detection of chiral molecules using only 10 μL with 107-fold enhancement in sensitivity compared with traditional plasmonic chiral metamaterials. The ultrahigh sensitivity and low sample consumption were enabled by microbubble-induced rapid accumulation of biomolecules on plasmonic chiral sensors. We have applied our technique on mouse and human urine samples, uncovering the previously undetectable diabetes-induced abnormal dextrorotatory shift in chirality of urine metabolites. Furthermore, the accumulation-assisted plasmonic chiral sensing achieved a diagnostic accuracy of 84% on clinical urine samples from human patients. With the ultrahigh sensitivity, ultralow sample consumption, and fast response, our technique will benefit diabetes research and could be developed as point-of-care devices for first-line noninvasive screening and prognosis of prediabetes or diabetes and its complications.

Non-Invasive Blood Glucose Monitoring Technology: A Review

In recent years, with the rise of global diabetes, a growing number of subjects are suffering from pain and infections caused by the invasive nature of mainstream commercial glucose meters. Non-invasive blood glucose monitoring technology has become an international research topic and a new method which could bring relief to a vast number of patients. This paper reviews the research progress and major challenges of non-invasive blood glucose detection technology in recent years, and divides it into three categories: optics, microwave and electrochemistry, based on the detection principle. The technology covers medical, materials, optics, electromagnetic wave, chemistry, biology, computational science and other related fields. The advantages and limitations of non-invasive and invasive technologies as well as electrochemistry and optics in non-invasives are compared horizontally in this paper. In addition, the current research achievements and limitations of non-invasive electrochemical glucose sensing systems in continuous monitoring, point-of-care and clinical settings are highlighted, so as to discuss the development tendency in future research. With the rapid development of wearable technology and transdermal biosensors, non-invasive blood glucose monitoring will become more efficient, affordable, robust, and more competitive on the market.

Is it possible to constantly and accurately monitor blood sugar levels, in people with Type 1 diabetes, with a discrete device (non-invasive or invasive)?

Real-time continuous glucose monitors using subcutaneous needle-type sensors continue to develop. The limitations of currently available systems, however, include time lag behind changes in blood glucose, the invasive nature of such systems, and in some cases, their accuracy. Non-invasive techniques have been developed, but, to date, no commercial device has been successful. A key research priority for people with Type 1 diabetes identified by the James Lind Alliance was to identify ways of monitoring blood glucose constantly and accurately using a discrete device, invasive or non-invasive. Integration of such a sensor is important in the development of a closed-loop system and the technology must be rapid, selective and acceptable for continuous use by individuals. The present review provides an update on existing continuous glucose-sensing technologies, and an overview of emergent techniques, including their accuracy and limitations.

The effect of the glycemic control on the aqueous humor glucose levels in diabetic patients undergoing elective cataract surgery

PURPOSE

Aqueous humor glucose levels play a role in the anterior segment disorders' pathophysiology, mainly in diabetics. Our purpose was to evaluate the ratio of aqueous humor glucose levels to blood glucose levels in diabetics and to evaluate the correlation between this ratio and blood glycated hemoglobin (HbA1c) levels.

METHODS

This prospective study was performed in Sheba Medical Center during 2016-2018. The study included type 2 diabetic patients admitted for elective cataract surgery. Blood glucose levels were measured immediately before surgery. HbA1c was obtained within 3 months preoperatively. At the beginning of surgery, 0.05-0.1 mL aqueous humor was drawn. Main outcome measures were aqueous humor glucose/blood glucose ratio and the correlation between HbA1c and aqueous humor glucose/blood glucose ratio.

RESULTS

Thirty-seven patients (mean age 75.2 ± 11.2 years) were recruited. The average aqueous humor glucose/blood glucose ratio was 0.69 ± 0.20. A significant positive correlation was found between aqueous humor and blood glucose levels, Pearson coefficient constant R = 0.63 (p < 0.01), and specifically stronger among older patients R = 0.89 (p < 0.01), females R = 0.74 (p < 0.01), patients with short-term disease (<10 years) R = 0.80 (p < 0.01), and patients treated with oral anti-diabetic treatment R = 0.74 (p < 0.01). A significant strong positive correlation was found between HbA1c levels and aqueous humor glucose/blood glucose ratio R = 0.62 (p < 0.01), and specifically stronger among older patients R = 0.82 (p < 0.01), males R = 0.70 (p < 0.01), patients with prolonged disease (⩾10 years) R = 0.540 (p < 0.05), and patients treated with oral anti-diabetic treatment R = 0.62 (p < 0.01).

CONCLUSION

A significant strong correlation was found between aqueous humor glucose levels and blood glucose levels. Poor glycemic control was strongly correlated with an increased ratio, reflecting an increased anterior chamber's glucose permeability. Older age group was found to have stronger correlation of poor glycemic control with this ratio.

Hydrogel-Based Colloidal Photonic Crystal Devices for Glucose Sensing

Diabetes, a common epidemic disease, is increasingly hazardous to human health. Monitoring body glucose concentrations for the prevention and therapy of diabetes has become very important. Hydrogel-based responsive photonic crystal (PC) materials are noninvasive options for glucose detection. This article reviews glucose-sensing materials/devices composed of hydrogels and colloidal photonic crystals (CPCs), including the construction of 2D/3D CPCs and 2D/3D hydrogel-based CPCs (HCPCs). The development and mechanisms of glucose-responsive hydrogels and the achieved technologies of HCPC glucose sensors were also concluded. This review concludes by showing a perspective for the future design of CPC glucose biosensors with functional hydrogels.

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.

Real-time compensation method for robust polarimetric determination of glucose in turbid media

Polarimetric determination of glucose is known to be strongly affected by scattering in turbid media. Other effects like fluctuations of light source emission and sample absorption also deteriorate glucose predictability. This work presents a measurement setup using a real-time data processing method to address these problems. The approach uses the frequency-dependent intensity components created when the polarization of the incident light is periodically modulated by a Faraday rotator. The efficacy of the proposed method was verified experimentally for a glucose range of 0 - 500 mg/dl. It was shown that the approach reduces the prediction errors in slightly turbid media from 35.7 mg/dl down to 1.17 mg/dl. In a similar way, the glucose predictability for fluctuating light source emission was improved from ±16.16 mg/dl to ±1 mg/dl and for varying sample absorbance from ±15.69 mg/dl to ±1.23 mg/dl, respectively. Therefore, considerable improvement of robustness and reproducibility of glucose determination was demonstrated.

2D Photonic Crystal Hydrogel Sensor for Tear Glucose Monitoring

Photonic crystal (PC) materials have huge potentials as sensors for noninvasive and real-time monitoring glucose in tears. We developed a glucose-sensitive PC material based on monolayered colloidal crystals (MCCs). Polystyrene nanoparticles were first self-assembled into a highly ordered MCC, and this two-dimensional (2D) template was then coated by a 4-boronobenzaldehyde-functionalized poly(vinyl alcohol) hydrogel. Such a sensor efficiently diffracts visible light, whose structural color could change from red through yellow to green, as the glucose concentration altered from 0 to 20 mM, covering both tears' and bloods' physiological ranges. The sensor also represents a rapid response within 180 s at each titration of glucose, combining the characteristics of high accuracy and sensitivity in detecting the glucose concentration in tears, and this intelligent sensing material presents certain possibility for the frontier point-of-care glucose monitoring.

Dual-modulation, dual-wavelength, optical polarimetry system for glucose monitoring

A dual modulation optical polarimetry system utilizing both laser intensity and polarization modulation was designed, built, and tested. The system was designed to reduce complexity and enhance the speed in order to facilitate the reduction of motion-induced time-varying birefringence, which is one of the major limitations to the realization of polarimetry for glucose monitoring in the eye. The high-speed less complex technique was tested using in vitro phantom studies with and without motion artifact introduced. The glucose concentration ranged from 0 to 600  mg/dl and the glucose measurements demonstrated a standard error of prediction to within 8.1  mg/dl without motion and to within 13.9  mg/dl with motion. Our feedback control systems took less than 10 ms to reach stabilization, which is adequately fast to eliminate the effect of time-varying birefringence. The results indicate that this new optical polarimetric approach has improved the speed and reduced the complexity, showing the potential for it to be used for noninvasive glucose measurements.

Corneal birefringence measured by spectrally resolved Mueller matrix ellipsometry and implications for non-invasive glucose monitoring

A good understanding of the corneal birefringence properties is essential for polarimetric glucose monitoring in the aqueous humor of the eye. Therefore, we have measured complete 16-element Mueller matrices of single-pass transitions through nine porcine corneas in-vitro, spectrally resolved in the range 300…1000 nm. These ellipsometric measurements have been performed at several angles of incidence at the apex and partially at the periphery of the corneas. The Mueller matrices have been decomposed into linear birefringence, circular birefringence (i.e. optical rotation), depolarization, and diattenuation. We found considerable circular birefringence, strongly increasing with decreasing wavelength, for most corneas. Furthermore, the decomposition revealed significant dependence of the linear retardance (in nm) on the wavelength below 500 nm. These findings suggest that uniaxial and biaxial crystals are insufficient models for a general description of the corneal birefringence, especially in the blue and in the UV spectral range. The implications on spectral-polarimetric approaches for glucose monitoring in the eye (for diabetics) are discussed.

Accuracy of Noninvasive Glucose Sensing Based on Near-Infrared Spectroscopy

The noninvasive sensing of the blood glucose concentration is usually based on optical, electrical, or acoustical signals induced by blood glucose; these signals are extremely weak and subject to fluctuations caused by the variation in the body or surroundings. Therefore, it is challenging to detect blood glucose noninvasively with high accuracy, and no successful accurate and noninvasive clinical application has been reported. We found that there are two key measurement issues to be addressed: systematic errors, such as the errors induced by the drifts of devices or by variations in body temperature, among others, are too large to guarantee the trueness of measurement at present; and random disturbances in repeated tests, such as disturbances associated with variations in the human-machine interface, pulses, and the thermal noise of the devices, cause larger repeated measurement errors and compromise precision. Recent novel reference measurements based on differential near-infrared (NIR) spectroscopy are considered promising for solving the systematic error issue by establishing matched references, collected at another detection site or at another time, and subsequently differencing to remove the common systematic errors. However, differencing weakens the signal of interest itself and enlarges the effects of the second issue, random disturbances affecting the precision. It is understood that only reference measurements that can meet the precision requirement will be promising for future applications. Therefore, this study quantitatively evaluates the precision of the main differential NIR spectroscopy measurements considering similar conditions and minimized random disturbances. The precision of the measurements under these conditions should represent their optimal precision levels. After the evaluation, noninvasive glucose-sensing methods that hold promise for future clinical application are proposed. Finally, the evaluation criteria could be a reference for the noninvasive detection of other physiological components.

Design and characterization of a ferromagnetic, air gapped magneto-optic Faraday rotator

A method has been developed to modulate the plane of polarized light through the use of a high permeability ferrite core design. A proof-of-principal, optical Faraday effect device has been constructed and tested. Magnetic fields were generated to provide up to 1 deg of rotation at frequencies of direct current up to 10 kHz using a terbium gallium garnet crystal rod.

Italian contributions to the development of continuous glucose monitoring sensors for diabetes management

Monitoring glucose concentration in the blood is essential in the therapy of diabetes, a pathology which affects about 350 million people around the World (three million in Italy), causes more than four million deaths per year and consumes a significant portion of the budget of national health systems (10% in Italy). In the last 15 years, several sensors with different degree of invasiveness have been proposed to monitor glycemia in a quasi-continuous way (up to 1 sample/min rate) for relatively long intervals (up to 7 consecutive days). These continuous glucose monitoring (CGM) sensors have opened new scenarios to assess, off-line, the effectiveness of individual patient therapeutic plans from the retrospective analysis of glucose time-series, but have also stimulated the development of innovative on-line applications, such as hypo/hyper-glycemia alert systems and artificial pancreas closed-loop control algorithms. In this review, we illustrate some significant Italian contributions, both from industry and academia, to the growth of the CGM sensors research area. In particular, technological, algorithmic and clinical developments performed in Italy will be discussed and put in relation with the advances obtained in the field in the wider international research community.