Optical short-wave infrared sensor for biomedical applications

Abstract

The present invention relates to an optical sensor and a wearable device comprising the same for non-invasively determining a concentration of blood components, for example, blood glucose and glycated hemoglobin levels. The optical sensor comprises an emitter configured to emit short-wave infrared (SWIR) radiation, an insulator with a channel transparent to the SWIR radiation, the emitter being disposed on top of the insulator and configured to emit the radiation into a biological tissue through the transparent channel, an optical concentrator made from a material with a refractive index of 1.7 or more, and a photodetector disposed in an upper part of the optical concentrator. The invention provides the possibility of non-invasive, instant or continuously monitoring of blood glucose and glycated hemoglobin levels. 2 indep. claims and 13 dep. claims, 15 figs., 2 tables.

Description

OPTICAL SHORT-WAVE INFRARED SENSOR FOR BIOMEDICAL APPLICATIONS

[0001] The present invention relates to optical short-wave infrared (SWIR) sensors for biomedical applications, namely for non-invasive monitoring of blood parameters with a low concentration of the studied component, for example, glucose and glycated hemoglobin levels. The optical short-wave infrared (SWIR) sensors according to the present invention are intended to be used in wearable devices such as modern smartwatches and fitness bracelets.

[0002] The present invention is made taking into account the propagation effect of SWIR radiation in a human skin and is aimed at transmitting, collecting from an extended area of the skin and receiving the SWIR radiation in order to determine a concentration of blood components, for example, glucose and glycated hemoglobin levels in blood.

[0003] The average life expectancy in the world is gradually increasing due to the development of medicine. The increase in the average life expectancy is affected not only by the development of medicine, but also by the growing interest of the population in checking and managing its health. According to the World Health Organization (WHO), in 2010, the number of diabetic patients was more than 284.6 million people, which is 6% of the population in the age of 20 to 79 years. Despite progress in medicine, the number of diabetes mellitus patients is constantly growing. Every 12-15 years, the number of diabetic patients doubles on average. Nowadays, diabetes mellitus ranks third among the causes of high disability and mortality of patients after cardiovascular diseases and cancer. Almost half of diabetes deaths occur among people under the age of 70. More than 50% of people with diabetes mellitus are unaware of their condition, and in some countries, the percentage of unawareness is as high as 80%. Diabetes care and treatment have shown that more frequent control of blood glucose and insulin can prevent many of the long-term complications of diabetes mellitus. Diabetes mellitus patients are recommended to self-monitor blood sugar (glucose) daily several times a day (at least before the main meals and before bedtime, as well as periodically after meals). Diabetes mellitus patients are forced to test a blood glucose level at home because without this information it is difficult for them to adjust their food ration, physical activity, the use of insulin and other hypoglycemic drugs. Most often, a glucose measurement is made by pricking a finger and extracting a blood drop that is applied to a test strip consisting of chemicals that are sensitive to glucose in a blood sample. An optical meter (glucometer) is used to analyze the blood sample and provides a numerical value for a glucose content.

[0004] Concentrations of various blood components are markers of human health and their timely control contributes to the prevention, timely detection of diseases and control of their course, as well as other disorders in body. Therefore, it is necessary to constant monitor blood parameters, in particular glucose and glycated hemoglobin levels.

[0005] Glucose is a simple carbohydrate, a universal source of energy for body. Having entered inside a cell, glucose serves as a source of energy, undergoing the process of glycolysis. But with metabolic pathologies, glucose can accumulate in blood and exert a toxic effect on heart and blood vessels. Glucose, which does not circulate in blood, accumulates in skeletal muscle and liver cells as glycogen. Glucose metabolism is regulated by two hormones, i.e., insulin and glucagon. Insulin is produced in pancreas in response to rising a blood glucose level and helps glucose from a blood flow to enter into cells that need energy. Due to insulin, there is no excess glucose in blood in a norm. Glucagon is also produced in pancreas, but it acts exactly contrary: it "tracks" that there is not too little sugar in blood. In a norm, the “glucose - insulin - glucagon” system is in a dynamic balance: after meal the glucose level rises, and in response to this, insulin is produced. If glucose becomes too low due to hunger or the action of insulin, then glucagon is produced, which increases the glucose level by enhancing the catabolism of the liver deposited glycogen. Due to insufficient production of insulin or glucagon, or owing to other disorders, hyperglycemia (a high blood glucose content) or, contrary, hypoglycemia (a lowered blood glucose concentration) develops. Analysis of a glucose level allows diabetes mellitus and other metabolic disorders to be timely detected.

[0006] As an example, for a person weighing 70 kilograms, about four grams of dissolved glucose (also called "blood glucose") are permanently in a blood plasma. The normal blood glucose level is necessary for normal functionality of a number of tissues, including brain which consumes about 60% of a blood contained glucose for people who follows a sedentary lifestyle and has not meal. The blood glucose level is usually lowest in the morning, before the first eating for a day, and rises after the meal for hour or two hours by a few millimoles. The normal blood glucose level (in fasting state) for people who has no diabetes should be 3.9 to 5.5 mmol / L (70 to 100 mg / dL). For diabetic persons, according to the American Diabetes Association, the target fasting blood glucose range should be 3.9 to 7.2 mmol / L (70 to 130 mg / dL) and less than 10 mmol / L (180 mg / dL) two hours after eating. Despite significant differences in the intervals between meals or the occasional consumption of high-carbohydrate foods, a human’s blood glucose level tends to remain generally within the norm. However shortly after eating in people who has no diabetes, the blood glucose level may temporarily rise to 7.8 mmol / L (140 mg / dL).

[0007] Hemoglobin (Hb) is the main respiratory pigment and the main component of red blood cells, performing important functions in a human body: transfer of inhaled oxygen from lungs to biological tissues and organs, and transfer of carbon dioxide from the tissues and organs to the lungs, where it is exhaled. This occurs due to that oxygen is able to be reversibly bound by iron whose atoms are “built-into” hemoglobin. Hemoglobin also plays a significant role in maintaining the acid-base balance of blood, the buffer system created by hemoglobin facilitates pH of blood to be maintained within certain limits. Erythrocytes or red blood cells are highly specialized blood cells whose main function is to participate in the gas exchange due to the ability of erythrocytes to bind oxygen and carbon dioxide and transport them within a blood flow. Oxygen binding is ensured by the high content of hemoglobin in erythrocytes. Erythrocytes are involved in hemostasis, maintaining the acid-base balance, immune reactions and represent the largest population of blood cells.

[0008] Glycated (glycosylated) hemoglobin (reference designation: hemoglobin A1c, HbA1c) is a biochemical indicator of blood that reflects an average content of blood sugar over a long time period (two to three months), in contrast to a blood glucose measurement result, which provides an idea of the blood glucose level only at the time of test.

[0009] Glycated hemoglobin reflects the percentage of blood hemoglobin irreversibly bound to glucose molecules. Glycated hemoglobin is produced by the Maillard reaction between hemoglobin and glucose in blood, this glycosylation reaction is irreversible. Increasing a blood glucose level in diabetes mellitus significantly accelerates this reaction, which results to increasing a blood glycated hemoglobin level. In other words, glycated hemoglobin is an integral indicator of glycemia over about two to three months. The higher the glycated hemoglobin level, the more often there was glycemia, that is, the elevated glucose level over the past three months and, accordingly, the greater the risk of developing complications of diabetes mellitus. Thus, the glycated hemoglobin level is currently a generally accepted indicator of the severity and degree of compensation of carbohydrate metabolism disorders.

[0010] In arterial blood, substantially all (93-95%) hemoglobin HbA is bound to oxygen, i.e. it is in oxygenated form, and serves to transfer oxygen. The rest of HbA (5-7%) is glycated hemoglobin and there are at least three options thereof: HbA1a, HbA1b, HbA1c, but only the HbA1c option, which is hemoglobin A modified by covalent addition of glucose thereto prevails quantitatively (4-6% of total hemoglobin) and provides a closer correlation with the severity of diabetes mellitus.

[0011] HbA1c values of 4% to 5.7% are considered to be normal, and values between 5.7% and 6.4% signal a predisposition to diabetes. In diabetes, the HbA1c level is 6.5% or higher, which indicates a greater risk of development of retinopathy, nephropathy and other complications. The International Diabetes Federation recommends to maintain the HbA1c level below 6.5%, and the HbA1c value being above 8% means that diabetes is not well controlled and therapy should be altered.

[0012] Summarizing the above, the HbA1c level is proportional to the average blood glucose level over the past 6-12 weeks and constantly monitoring of this level is necessary to prevent the development of complications and to predict the development and phase of microvascular complications associated with diabetes. It should also be noted that the HbA1c content is 4-6% of the total amount of blood hemoglobin, and therefore, a very high sensitivity of the device used for the HbA1c measurement method is necessary. In addition, in optical measurement methods in the visible and near-infrared range, it should be taken into account that the absorption / reflection spectra of oxygenated, glycated and total hemoglobin overlap to each other, and therefore they are difficult to be separated.

[0013] The total hemoglobin concentration exceeds the glucose concentration by about 140 times, and exceeds the glycated hemoglobin concentration by about 15-25 times. Accordingly, the signal quality (signal-to-noise ratio) of the optical sensor should be sufficient to effectively detect a level of glucose or glycated hemoglobin that have low concentrations relative to other blood components. Hence, an optical sensor of a new type is necessary to be developed, which has high sensitivity and is able to detect change in the concentration of components such as glucose and glycated hemoglobin.

[0014] Nowadays, a plurality of personal medical devices have been developed that allow people to check their health without visiting the hospitals. As an example, many diabetic patients often check their blood sugar level with a compact tester without visiting the hospitals. Diabetic patients can check their blood sugar level several times a day to make sure they have enough insulin level.

[0015] Nowadays, a plurality of devices with built-in multi-wavelength optical sensors operating in the visible-near-infrared (VIS-NIR range) range and designed to detect blood components with high concentration such as hemoglobin are known. For example, a hemoglobin level can be determined by using a smartwatch with a built-in photoplethysmographic (PPG) sensor. Most often, in prior art, Fresnel lenses are used to collect signals from a skin surface, which allow most of the signals to be collected and focused into a photodetector. All non-invasive optoelectronic devices use a broadband pulsed radiation source with subsequent analysis of light absorption at a specific wavelength by narrowband interference filters and separate photodetectors.

[0016] The main problems of prior art are:

[0017] - a low signal-to-noise ratio (SNR) in the SWIR range, which is caused by materials used to provide this range;

[0018] - increasing the SNR with the sensor size, so the photodetector size should not be increased, and therefore it is necessary to use one photodetector;

[0019] - the necessity to develop a compact and large-scale production suitable SWIR sensor that can be built into a wearable device.

[0020] The present invention provides the possibility to measure blood parameters with a low concentration of the studied component, such as glucose or glycated hemoglobin, by using SWIR radiation. As noted above, blood contains both components with a high concentration, for example, hemoglobin, and components with a low concentration, for example, glucose.

[0021] Invasive, minimally invasive and non-invasive methods are used to determine blood glucose and glycated hemoglobin levels.

[0022] Invasive methods are laboratory techniques that require the patient’s blood to be sampled from a finger or from a peripheral vein. Meanwhile, it should be noted that regular blood sampling may be painful and create psychological stress. In addition, since frequent blood samplings are able to cause a potential risk of infection to a person, frequent blood sugar testing is undesirable. With laboratory techniques, qualified personnel and expensive laboratory equipment are required for blood testing, and also waste should be disposed. Moreover, laboratory techniques are not suitable for continuously monitoring a glucose level, and patients cannot perform them self-acting.

[0023] Electrophoresis, as well as methods that use an electrochemical biosensor, an implanted microsystem relate to minimally invasive methods. In particular, in recent years, a method for continuously monitoring of a blood glucose concentration (Continuous Glucose Monitoring, CGM) was appeared and actively used. The gist of the method consists in constantly automatically measuring a blood glucose level by using a CGM system for several days according to indirect data acquired regarding an intracellular (interstitial) fluid. Such a system is composed of three modules:

[0024] - a highly sensitive platinum sensor;

[0025] - a transmitting device and a monitoring device (sensing device);

[0026] - a device for exporting data from the transmitting device to a computer.

[0027] The sensor is an individual disposable device that senses the sugar level in the interstitial fluid, and is installed subcutaneously on a patient’s shoulder by using a special device with almost no pain. After installation, the transmitting device is attached to the sensor, which is used to transmit a signal from the sensor to the monitoring device by using the Bluetooth technology. The monitoring device is suspended on a patient’s waist and is there throughout the entire period of study. The monitoring device automatically measures blood sugar every 10 seconds and records the average value according to the collected readings once every 5 minutes. During the study, it is necessary to calibrate the monitoring device for blood sugar from a finger several times. This requires parallel self-monitoring of sugar on a glucose meter. The monitoring device allows an information about events in the patient’s life such as male or medication intake, physical activity, etc. to be inputted therein. This helps to improve the quality of interpretation of the collected data. After the study is completed, the full acquired digital information is transferred to the computer and analyzed by an attending doctor. At the same time, such a system is well suitable for dynamics of monitoring for a long period of time, for example, several days, but it is not suitable for dynamics of monitoring for a short period of time, when, for example, diabetic patients should measure instant glucose values before meals, during meals and immediately after one, since the principle of indirect measurement by the interstitial fluid implies some delay in distribution of sugar from blood into the interstitial liquid after meals. Conventional glucose meters are more suitable for such purposes. In addition, the necessity to use a glucose meter for control measurements and to wear the entire CGM system for several days is inconvenient for a user.

[0028] Polarimetric analysis, Raman spectroscopy, optical coherence tomography, photoacoustic spectroscopy, as well as IR spectroscopy relate to non-invasive methods.

[0029] In the large-scale arsenal of modern methods of laboratory and functional diagnostics based on estimation of morphological, functional, biochemical and genetic parameters of a body, non-invasive methods still occupy a rather modest place. However, in the medicine of future, the role of non-invasive diagnostics will steadily increase, since non-invasive methods:

[0030] - exclude the introduction of pathogenic viruses and bacteria, foreign substances (xenobiotics) into a body;

[0031] - allow eliminating the radiation exposure to a body, for example, when performing X-ray, radioisotope and ultrasound diagnostic study methods;

[0032] - free a patient from a complex of pain sense modality and sense of discomfort;

[0033] - non-invasive methods based on the use of sensory and signal transmitting devices allow the main blood parameters, for example, glucose and glycated hemoglobin to be monitored and remote alarm systems to be developed. The latter can be very useful as a means of constantly tracking from a center, for example, from a hospital or clinic, for specific groups of patients (patients with the danger of sudden cardiac death, hypertension, diabetes mellitus, etc.), and providing timely assistance in critical states.

[0034] In non-invasive methods of monitoring glucose and glycated hemoglobin levels, the passage of a signal through the patient’s blood, tissue fluid, eye fluid, saliva, urine, and sweat is studied.

[0035] One of the modern devices is a non-invasive glucose meter Glucowise which includes a sensor that measures painlessly a glucose level, and a communication means for communicating with a smartphone app for tracking data and a “smart cloud” for storing and managing the data. The device allows determining quickly (within 10 seconds) and painlessly a blood glucose level at the capillary level by using a non-invasive method. High-frequency, low-power radio waves (about 65 GHz) pass through a skin area with sufficient capillary blood supply, usually an earlobe or an area between the thumb and index finger. The signals acquired by the sensor on the opposite side of the device are then recorded and analyzed. In addition, special nanocomposite films are embedded (built) into the sensor, that enhance the skin’s sensitivity to radio waves exposure at the time of measurement, so the measurement accuracy does not depend on age, skin color or type. The device displays the measurement result in real time on the sensor screen. The data acquired by the glucose meter is transmitted to a mobile app on a smartphone or tablet to allow blood glucose levels to be tracked over a long period and other indicators that affect carbohydrate metabolism to be taken into account. It should be noted that this device has not yet entered large-scale production, since it does not provide sufficient measurement accuracy compared to reference laboratory techniques.

[0036] Optical measurement methods that are most suitable to be used in wearable devices suppose the use of optical radiation to probe the patient’s biological tissues and organs in order to acquire diagnostic information on the biochemical composition and morphological structure of the studied area of the patient's body tissues from the radiation reflected (scattered) or passed through the tissue. The magnitude of the signal recorded in this case depends on both the radiation absorbance and scattering coefficient by the patient’s tissue, including blood. The main contribution to absorption is defined by water (H2O), proteins, lipids, various forms of hemoglobin, skin melanin and glucose.

[0037] The radiation transmission at each wavelength is a function of thickness, color, and structure of skin, bones, blood, and other tissues through which the radiation passes. Thus, the glucose concentration can be determined by analyzing the change in the electromagnetic signal by wavelength, polarization or light intensity.

[0038] Optical methods for determining blood parameters are based on the phenomenon of absorption of electromagnetic radiations by groups of atoms of the tested object, generally in the IR range. The absorption is associated with the excitation of molecular vibrations by quanta of the IR radiation. When molecules are irradiated with the IR radiation, only those quanta are absorbed whose frequencies correspond to the frequencies of valence (stretching), deformation vibrations and vibrations of the molecules. Glucose produces one of the weakest electromagnetic radiation absorption signals in the IR range among most main components of biological tissues. In addition, in optical measurement methods in the VIS-NIR radiation range, it should be taken into account that the absorption / reflection spectra of some blood components overlap to each other, and therefore they are difficult to be separated.

[0039] However, the use of the short-wave IR (SWIR) radiation is promising for measuring a blood glucose level. The previously existing restrictions on the use of SWIR radiation have now been eliminated and it has become possible to use materials that ensure the operation of devices in the SWIR range. Glucose measurement in the case of the IR radiation is possible at a tissue depth in the range from 1 to 100 mm, wherein the penetration depth decreases when the radiation wavelength is increased, so the signal in the SWIR range is collected from a shallower tissue depth than in the NIR range.

[0040] The SWIR radiation is the publicly accepted name for the short-wave IR radiation of electromagnetic waves in the range of 0.9-2.5 μm. The SWIR radiation receivers are based on elements made from silicon whose sensitivity limit corresponds to about 1.0 μm. Other typical SWIR receivers are created on the basis of indium gallium arsenide (InGaAs), which is sensitive in the range from 550 nm to 2.5 μm, as well as on the basis of cadmium mercury telluride (HgCdTe) and indium antimonide (InSb), which are also very sensitive in the SWIR range. Meanwhile, for example, InGaAs-based sensors have a higher level of electrical noise compared to silicon sensors with the same total detection area (active surface of a sensor).

[0041] In contrast with the mid- and long-IR range radiation, which emits from the objects themselves, the SWIR radiation is similar to the visible range in that photons are either reflected or absorbed by the objects, and this property provides the wide dynamic range required for high-resolution images. Due to the SWIR radiation passes through glass, lenses / objective lenses and other optical components such as optical filters and windows designed for the SWIR range can be manufactured on the same technologies those used for visible range components, which reduces manufacturing costs and makes it possible to use the filters and windows within a single optical system.

[0042] One of the factors that define the advantage of operating in the SWIR range is caused by the clear difference in the radiation wavelengths at which the absorption peaks of the main biological components of the tissue such as glucose, water and fats, are located, the data on which are shown in Table 1.

[0043] Table 1. Particulars of absorption spectra of various biological components

[0044] Biological componentHighest absorption peaks, nmGlucose1408, 1536, 1688, 2261Water1450, 1787, 1934Fats2299, 2342

[0045] Thus, the absorption peaks of the SWIR radiation by glucose, water and fats can be clearly identified, and therefore a blood glucose level can be measured.

[0046] It should be noted that constantly monitoring of a blood glucose level is necessary to prevent the development of complications and to predict the development and phase of microvascular complications associated with diabetes. It has been proven that hyperglycemia contributes to the development and progression of micro-, macroangiopathy, polyneuropathy with damage, dysfunction and subsequent insufficiency of body vital organs and systems. Retinal vascular lesions with rapid vision loss, glomerulosclerosis with the development of chronic renal failure, diabetic foot, arterial hypertension, acute / chronic coronary disease of heart, brain and their consequences (myocardial infarction, heart failure, stroke, atrophy of the cerebral cortex with decreased cognitive function and the development of dementia) - this is far from a complete list of diseases and syndromes associated with diabetes mellitus.

[0047] Thus, the following target groups can be identified for which monitoring of a blood glucose / glycated hemoglobin level is necessary:

[0048] - healthy people for the purpose of preventive control;

[0049] - children with diabetes;

[0050] - diabetic patients with abnormal renal glucose threshold;

[0051] - patients with type I diabetes mellitus, insulin-dependent;

[0052] - pregnant women with type II diabetes;

[0053] - other people when food ration or other habits are altered.

[0054] Hence, the blood glucose and glycated hemoglobin levels are an important and significant indicator of human health and require to be continuously monitored.

[0055] Differences in measurements of blood components in the VIS-NIR and SWIR ranges and advantages provided by measurements in the SWIR range will be described below.

[0056] The graphs of Figs. 1A, B illustrate dependences of interpolated absorption coefficients of key skin tissues chromophores such as melanin, oxyhemoglobin, deoxyhemoglobin, water, baseline-collagen, and absorbances of hemoglobin (Hb), glucose and glycated hemoglobin (HbA1c), respectively, on a radiation wavelength. From the graph of Fig. 1B illustrating overtone (first overtone) and combinational (compound) bands, which is taken from the article by Kaiwen Guo et al., High SNR Glucose Monitoring using a SWIR Super-Continuum Light Source, https: / islam.engin.umich.edu / wp-content / uploads / sites / 57 / 2017 / 12 / glucose.pdf, it can be seen that in the SWIR range, glucose has clearly distinguishable absorption peaks, which are not affected by the absorption of Hb and HbA1c. In addition, in the range from about 2000 nm to about 2400 nm, the effect of such a highly absorbing background as water on glucose absorption is minimized since in this range the radiation absorption by water is minimal. Moreover, as can be seen from the graph of Fig. 1B, glycated hemoglobin has a wide combinational absorption band with a maximum at a wavelength of about 2200 nm, while total hemoglobin and water have no pronounced absorption peaks in the range of 2100-2400 nm. This creates the basis for measuring glycated hemoglobin in the SWIR range as well. It should be noted that the measurement of glycated hemoglobin in the VIS-NIR range is difficult due to the overlap of absorption peaks of glycated and total hemoglobin.

[0057] Thus, SWIR devices are promising for measuring glucose and glycated hemoglobin levels. Meanwhile, the measurements are not interfered with high concentration of other blood components, for example, hemoglobin. The SWIR devices present a high-performance option for photosensitive applications, taking advantages of the short-wave infrared spectrum, with ultra-high sensitivity, resolution and stability.

[0058] The use of the SWIR radiation is a potential solution for the development of an optical sensor for non-invasively monitoring of glucose and glycated hemoglobin. The main reasons to select the SWIR range (900-2500 nm) for measuring by a non-invasive method are:

[0059] - less interference due to low absorption by skin chromophores (hemoglobin, melanin) and water;

[0060] - high absorption by glucose and glycated hemoglobin.

[0061] Photo-receiving devices (photodetectors) are actively used in various spheres of human activity, and their usage depends on a radiation spectrum to be recorded. This radiation spectrum can be divided into sub-bands, in a broad sense, these are the ranges of radiation visible to a human eye, ultraviolet (UV) radiation and infrared (IR) radiation. The IR radiation range, as illustrated in Fig. 2, is located between the visible and microwave regions of the electromagnetic spectrum and can be divided into 4 sub-bands: Near Infrared (NIR) radiation with a wavelength of 0.75-1 μm, Short-Wave Infrared (SWIR) radiation with a wavelength of 1-2.5 μm, Medium-Wave Infrared (MWIR) radiation with a wavelength of 3-5 μm and Long-Wave Infrared (LWIR) radiation with a wavelength of 8-12 μm. As known, when a wavelength of electromagnetic radiation increases, an energy decreases, which causes some differences in applications of the NIR and SWIR radiations.

[0062] The NIR range is used in food testing, remote control, agriculture, and biomedical instrumentation applications. For example, pulse oximeters that measure blood oxygen saturation often use a combination of red (700 nm) and IR (900 nm) LEDs to determine the optical absorption of oxy- and deoxyhemoglobin. Self-driving cars use an infrared light detecting and ranging (LIDAR) locator to map their surroundings. LIDAR infrared optics typically operate at wavelengths of 905 or 940 nm. Night vision goggles and electro-optical converters also operate in the NIR range. Remote control devices also operate in this range, typically using 940 nm LEDs for communicating with devices.

[0063] Silicon, which has sensitivity (responsivity) in the range of 400-1100 nm, is most often used as an optical material for NIR detectors. Many of materials for the IR region operate in the NIR range, which also operate in the UV and visible band of the electromagnetic spectrum. Glasses and ceramics such as BK7 (optical borosilicate crown glass), UV and IR fused silica, quartz and sapphire are used for optical windows, lenses, and other components due to excellent transmission in this spectral range.

[0064] SWIR spectroscopy is used in food and drug testing, SWIR cameras are used to examine printed circuit boards (PCBs), to non-destructive test artworks, packaged goods, and to test counterfeit. Recently, SWIR cameras are increasingly used in medical research, small animal imaging, and brain imaging. Most of the SWIR spectral range is inexpediently to be used due to the intense absorption by water and carbon dioxide. However, this range provides operating windows for optical coupling at some wavelengths, as shown in Fig. 1B, where low transmission loss and low dispersion are observed.

[0065] Since silicon does not absorb the SWIR radiation, other materials, for example, germanium (Ge), indium gallium arsenide (InGaAs), and indium gallium arsenide phosphide (InGaAsP) are used in the detectors. Germanium has sensitivity from 0.8 μm to 1.6 μm, whereas InGaAs can operate over a wider range from 0.8 μm to 1.8 μm.

[0066] In addition to the previously mentioned NIR materials such as IR fused silica, IR transparent materials include zinc selenide (ZnSe), zinc sulfide (ZnS), calcium fluoride (CaF2), and magnesium fluoride (MgF2). All of them operate in the range from the visible spectrum up to 8-10 μm. As an example of a material for optical windows and lenses operating in the SWIR range, Corning HPFS® 7979 IR (fused quartz glass) can be presented.

[0067] The main advantage of operating in the NIR range is that the NIR radiation penetrates deeper into a biological tissue compared to the SWIR radiation, so it can easily reach the dermis layer of skin with capillaries and even large vessels such as arteries and interact with blood components. At the same time, strong scattering of the NIR radiation by the surface skin layers, low possibility of glucose detection, a smaller bandwidth that does not correlate well with a blood glucose level, since the glucose reflection peaks in this band overlap with the reflection peaks of other blood components and biological tissue, relate to the drawbacks. Thus, the NIR range is not optimal for monitoring a blood glucose level by a non-invasive method.

[0068] Operation in the SWIR range provides the following main advantages:

[0069] - materials for a SWIR light emitter provide a high level of power efficiency and thermal stability;

[0070] - less interference due to low absorption by skin chromophores (hemoglobin, melanin);

[0071] - high possibility of glucose detection, since there are absorption peaks that do not overlap with absorption peaks of other blood components.

[0072] At the same time, a smaller depth of penetration of the SWIR radiation compared to the NIR radiation and a higher level of electrical noise of the SWIR detectors compared to the NIR detectors relate to the drawbacks. In addition, as noted earlier, it is necessary to use a compact detector that can be built in a wearable device, such as a smartwatch or fitness bracelet, since when its size increases, the signal-to-noise ratio decreases.

[0073] Fig. 3 illustrates a simulated graph showing a penetration depth of the SWIR photons into a human skin at a radiation wavelength of 2200 nm. It can be seen from Fig. 3 that a signal is collected from the two upper skin layers, i.e., epidermis and dermis with capillaries from a depth of 0.02-2.00 mm, preferably 0.2-2.0 mm, which encompasses the range of the population-average total thickness of the two upper skin layers, in which the glucose content alters. In dermis, the glucose content alters faster because it contains more blood capillaries.

[0074] Thus, the following main problems can be identified when operating in the SWIR range:

[0075] 1. The SWIR radiation has a smaller depth of penetration into a biological tissue compared to the NIR radiation, whereby signals are collected from a smaller depth, and therefore a set of collected signals is less informative. When light is emitted to skin, a significant part thereof is reflected from the upper skin layers and returns to the photodetector, whereby it will be powerful in value, but a harmful signal that does not carry any information about the studied object (weakly correlates with a glucose level). This problem is illustrated in Fig. 4.

[0076] 2. SWIR detectors have a higher level of electrical noise compared to NIR detectors.

[0077] Hence, the signal quality (signal-to-noise ratio) could not be enough for effective detection of biological objects, in particular for determination of a glucose level.

[0078] Taking into account the above-mentioned main problems, it is necessary to ensure selectivity of detection within the depth of skin, that is, to acquire a signal from the required depth of the skin layers, as well as to prevent signals associated with the radiation reflection and scatter from the upper skin layers from being entered into the photodetector. In addition, taking into account a high noise level and a compact size of the photodetector, it is necessary to provide an optical concentrator for collecting a larger number of photons from the larger area into the photodetector.

[0079] The solution according to the present disclosure, which uses the SWIR radiation, provides selectivity of glucose detection in the depth of skin and isolation of the photodetector from radiation reflected and scattered by the upper skin layers. In addition, since SWIR detectors have a high noise level, the claimed solution provides the collection of photons from a large area into a photodetector having a small aperture through the use of an optical concentrator. These and other particulars of the present disclosure will be described in more detail below.

[0080] Nowadays, a number of devices for non-invasively measuring a blood sugar level have been developed that reduce discomfort for patients. However, they are not always applicable for continuously monitoring and are not suitable for operation in the SWIR range. Moreover, there are no wearable devices on the market, such as smartwatches or fitness bracelets designed to determine glucose and glycated hemoglobin levels by a non-invasive method, with which it is easier for the user to monitor unassisted.

[0081] A patent application US2023 / 0204506 A1, “Multiple light paths architecture and obscuration methods for signal and perfusion index optimization” (Apple Inc.), discloses a photoplethysmographic (PPG) device built in a smartwatch that includes one or more light emitters and one or more photodetectors to generate the multiple light paths for measuring a PPG signal and perfusion indices of a user. The multiple light paths between each pair of the light emitters and photodetectors can include different separation distances to measure both an accurate PPG signal and a perfusion index value in different users under different conditions of use.

[0082] The PPG device can further include one or more lenses and / or reflectors to increase the signal strength and / or to obscure the optical components and associated wiring from being visible to a user's eye. The solution allows various biological objects to be detected.

[0083] The drawbacks of such solution are: use of several photodetectors, the lack of light collecting elements except for widely used Fresnel lens. In addition, the solution is not suitable for the SWIR range.

[0084] A patent US11,553,851 B2, “Method for detection biometric information by using spatial light modulation, electronic device, and storage medium” (Samsung Electronics Co., Ltd.), discloses an electronic device in the form of a smartwatch, that may comprise... at least one light-emitting element mounted on the support structure;… a spatial light modulator (SLM) disposed between the transparent plate and the LED while being spaced apart from the light-emitting element; a light-receiving element (photodetector) mounted on the support structure...; and a processing circuit comprising at least one electrical path electrically connected to the SLM, the processing circuit being operatively coupled to the light-receiving element and being configured to generate photoplethysmogram (PPG) data by using the light-emitting element. The solution allows various biological objects to be detected.

[0085] The drawbacks of this solution are: use of several photodetectors, a poor collected signal due to use of Fresnel lens. In addition, the solution is not suitable for the SWIR range.

[0086] A patent US10,799,128 B2, “Optical vital signs sensor” (Koninklijke Philips N.V.), discloses an optical sensor configured to measure or determine vital signs of a user and comprising a light source configured to generate a light beam having an angular range of angles of incidence. A photodetector is provided to detect light which is indicative of reflection of the light beam of the light source in or from the user’s skin. A light shaping unit is configured to shape the light beam from the light source before the light beam enters the skin by limiting the angular range of an angle of incidence to less than 20°.

[0087] The drawbacks of this solution are the use of optical concentrators only at a transmit side, that is, only to enter radiation into the skin, as well as a low signal-to-noise ratio. In order to increase the signal-to-noise ratio, it is better to use a concentrator at a receive side.

[0088] An international application publication WO2015 / 108508 A1, “Optical measurement system having a concentrator” (Avolonte Health LLC), discloses an optical system that directs light along an optical path, with a variable propagation direction, from a collimated light source into an internal reflection element, onto an interface between the internal reflection element and a measured sample (breakdown), out of the internal reflection element, through a concentrator, and onto a detector. The concentrator is shaped so that the light is directed from an incident face of the concentrator, via total internal reflection, to an exiting face of the concentrator. The exiting face has a smaller area than the incident face.

[0089] The drawback of this solution is that the light source and detector are located at a long distance from each other, whereby this arrangement is bulky and cannot be used in a wearable device.

[0090] A patent application US2021 / 0381958 A1, “Spectroscopic Measurements With Parallel Array Detector” (Nueon Inc.), discloses optical components arranged to provide parallel measurements of a biological sample. The parallel sample measurements provide improved accuracy with lower detection limit and may comprise one or more of Raman spectroscopy measurements or infrared spectroscopy measurements. The parallel measurements can be combined with a light source in various ways. The light source emits radiation of one or more wavelengths corresponding to resonance frequencies of one or more molecules of the sample, such as wavelengths of ultraviolet light. The parallel array optical arrangement can be combined with wavelengths of light corresponding to the resonance frequencies.

[0091] The drawbacks of this solution are the use of a hollow reflector filled with air having reflectance equal to 1, the lack of optical matching and an insulating channel.

[0092] The advantages of monitoring of blood parameters, in particular glucose and glycated hemoglobin levels by using wearable devices such as modern smartwatches or fitness bracelets, are instant or continuous measurement, ease of use, the capability for long-term monitoring of blood parameters. At the same time, the estimation of blood parameters by using wearable devices is not accurate enough, especially for the studied components having a low concentration.

[0093] Thus, the main problem of this technical field consists in the lack of an optical sensor to be built in a wearable device and allowing a blood parameter with a low concentration, such as glucose or glycated hemoglobin, to be monitored instantly or continuously.

[0094] Hence, there is demand for an optical sensor to be built in a wearable device and a method for non-invasively measuring blood parameters with a low concentration of the studied component such as glucose or glycated hemoglobin with high accuracy implemented by using the same. In other words, a device for non-invasively, instantly or continuously monitoring of glucose and glycated hemoglobin levels is required.

[0095] Possible products in which the method according to the invention is used are wearable devices such as smartwatches or smart bracelets, stationary diagnostic tools, household appliances and gadgets for personal medical monitoring.

[0096] Taking into account the above technical problems, hereinafter the proposed invention will be described as an example with reference to the description and the drawings presented below, but not as a limitation.

[0097] This summary of the invention essence precedes the detailed description of specific exemplary embodiments in order to give a general idea of aspects of the claimed invention that will be further explained below, and is in no way intended to define or limit the scope of the present invention.

[0098] An object of the present invention is to provide an optical SWIR sensor to be built in a wearable device such as a smartwatch and capable of providing high accuracy of measurement of blood components with a low concentration, for example, blood glucose or glycated hemoglobin levels. Meanwhile, the use of the optical SWIR sensor built in smartwatches render possible to significantly reduce a cost of measurement, eliminate the use of consumables, provide the capability of convenient measurement, etc.

[0099] Within the scope of the present invention, an extensive study of particulars of interaction of the SWIR radiation with a biological tissue, its reception and processing has been performed, and an optical sensor operating in the SWIR range and designed to measure glucose and glycated hemoglobin levels has been developed.

[0100] The proposed invention is an optical sensor for determining a concentration of blood components, the optical sensor comprising: an emitter configured to emit short-wave infrared (SWIR) radiation, an insulator with a channel transparent to the SWIR radiation, wherein the emitter is disposed on top of the insulator and is configured to emit the SWIR radiation into a biological tissue through said transparent channel, an optical concentrator made from a material with a refractive index of 1.7 or more, and a photodetector disposed in an upper part of the optical concentrator, wherein the concentrator and the insulator are arranged such that the concentrator covers the insulator, and a ring-shaped gap is formed between an outer surface of the insulator and a surface of the concentrator to form a ring-shaped detection region for radiation scattered from the biological tissue, the concentrator is made in a rotation figure shape for collecting and focusing the radiation, scattered from the biological tissue and entering from the ring-shaped detection region into the ring-shaped gap, into the photodetector, the insulator and the concentrator are configured to contact with the biological tissue during operation of the optical sensor, and the photodetector is optically matched with the upper part of the concentrator.

[0101] According to an embodiment, the optical concentrator further has a coating whose inner surface is reflective, wherein there is no coating on a part of the optical concentrator being in contact with the biological tissue during operation.

[0102] According to an embodiment, the optical concentrator is made in the form of a spherical segment, a spherical layer, an ellipsoid segment or a flattened circular cone.

[0103] According to an embodiment, the optical concentrator is made of at least two parts disposed on top of each other, each of which represents a rotation figure, wherein a rotation axis of all the parts is a rotation axis of the concentrator.

[0104] According to an embodiment, the material of the optical concentrator is silicon, a chalcogenide glass, or zinc sulfide.

[0105] According to an embodiment, the material of each of the at least two parts of the optical concentrator is silicon, a chalcogenide glass, or zinc sulfide.

[0106] According to an embodiment, the emitter is a light emitting diode (LED) or a laser diode and is configured to emit radiation with a wavelength in the range of 0.9-2.5 μm.

[0107] According to an embodiment, the insulator is made in the form of a cylinder having a cylindrical channel.

[0108] According to an embodiment, the photodetector is made on the basis of indium gallium arsenide (InGaAs), cadmium mercury telluride (HgCdTe), or indium antimonide (InSb).

[0109] According to an embodiment, a working surface of the photodetector is in a focal plane of the optical concentrator, the rotation axis of the optical concentrator passes through the center of a focal spot, and is perpendicular to the working surface of the photodetector.

[0110] According to an embodiment, the photodetector is adhered to the upper part of the optical concentrator with an optical glue.

[0111] According to an embodiment, the optical glue is a Master Bond EP30, MasterSil 151, MB600, or UV15 epoxy resin adhesive.

[0112] According to an embodiment, an antireflection coating is further applied between the upper part of the optical concentrator and the optical glue.

[0113] According to an embodiment, the refractive index of the optical concentrator material is preferably greater than 2.0, more preferably greater than 3.0.

[0114] According to an embodiment, the blood components are glucose and glycated hemoglobin.

[0115] The proposed invention also relates to a wearable device comprising the optical sensor for determining a concentration of blood components according to any one of the above embodiments.

[0116] According to an embodiment, the wearable device further comprises a housing, a processor, a battery, a memory device, an input and output device and a communication module housed in the housing.

[0117] According to an embodiment of the wearable device, the memory device is configured to store an information, the input and output device is configured to display the concentration of a blood component, the communication module is configured to communicate with a remote server and / or a cloud storage.

[0118] According to an embodiment, the wearable device is configured to be placed on a wrist.

[0119] According to an embodiment, the wearable device is a smart device, preferably a smartwatch or a fitness bracelet.

[0120] The technical effects provided by the optical SWIR sensor for biomedical applications according to the present invention:

[0121] - increasing a signal-to-noise ratio of a SWIR signal while maintaining a compact structure of the sensor;

[0122] - the capability to detect blood components with a low concentration, for example, glucose or glycated hemoglobin.

[0123] The proposed optical SWIR sensor and the wearable device comprising the same for determining a concentration of blood components provide the capability of personal, instant or continuous non-invasive monitoring of blood parameters with a low concentration of a studied component, for example, blood glucose or glycated hemoglobin levels.

[0124] Features and advantages of the present invention, as well as its background will be explained in the following description with reference to the accompanying drawings. The provided specific exemplary embodiments of the claimed invention considered in conjunction with the drawings are not intended to limit the scope of the invention. Based on study of the presented description, additional embodiments, modifications, or equivalents of the present invention will be apparent to those skilled in the art, and all such embodiments, modifications, and equivalents are deemed to be included in the present invention.

[0125] The drawings are provided merely to assist in understanding the description and they should in no way be construed as limiting the scope of the invention. The drawings depict the following:

[0126] FIGS. 1A, B illustrate graphs of a dependence of interpolated absorption coefficients of key skin tissues chromophores such as melanin, oxyhemoglobin, deoxyhemoglobin, water, baseline-collagen, and absorbances of hemoglobin (Hb), glucose and glycated hemoglobin (HbA1c) on a radiation wavelength.

[0127] FIG. 2 schematically illustrates a scale of electromagnetic radiation and the locality of near-infrared (NIR) radiation and short-wave infrared (SWIR) radiation ranges on this scale.

[0128] FIG. 3 illustrates a simulated graph showing a penetration depth of SWIR photons with a wavelength of 2200 nm into a human skin.

[0129] FIG. 4 schematically illustrates the problem in collecting of skin-reflected and skin-scattered photons in prior art.

[0130] FIG. 5 schematically illustrates an exemplary arrangement of an optical sensor according to the present invention.

[0131] FIG. 6 illustrates a first key particular (KP1) of the present invention in comparison with a prior art solution.

[0132] FIG. 7 illustrates a second key particular (KP2) of the present invention in comparison with a prior art solution.

[0133] FIG. 8A illustrates examples of optical concentrators made from materials with different refractive indices, and propagation paths of photons therein.

[0134] FIG. 8B illustrates the efficiency of radiation input into a photodetector depending on square of a refractive index of the optical concentrator material.

[0135] FIG. 9 illustrates particulars of optical matching the photodetector and concentrator.

[0136] FIGS. 10A, B illustrate simulation results showing propagation paths of photons in optical sensors of various structures according to embodiments of the present invention.

[0137] FIGS. 11A, B illustrate KP1 and KP2 of the present invention.

[0138] FIGS. 12, 13 illustrate embodiments of the optical sensor according to the present invention.

[0139] FIG. 14 illustrates the possibility of using various high refractive index materials for the optical concentrator according to the present invention.

[0140] FIG. 15A schematically illustrates options of exemplary displaying of 24-hour glucose level measurement results and variance of multi-month glucose measurement results on a screen of a wearable device according to the invention in the S-Health app. Fig. 15B schematically illustrates a graph displayed on a screen of the wearable device in the S-Health app and allowing the variance of the glucose level from the target value to be monitored.

[0141] Fig. 5 illustrates an example arrangement of an optical sensor according to the present invention, which is configured to be built in a wearable device such as a smartwatch. The optical sensor has small dimensions, approximately 2×2×2 mm, and includes an emitter, an insulating channel (insulator), an optical concentrator and a photodetector. The emitter is configured to emit radiation through the insulating channel onto a user’s skin (a biological tissue). The insulating channel is made from such a material and is configured such as to prevent, firstly, radiation from directly entering from the emitter to the photodetector, and, secondly, radiation reflected and scattered from the upper skin layers from entering into the photodetector. The insulating channel is generally made in the form of a hollow cylinder, but not limited to. Its shape can be a polygonal prism, a truncated polygonal or circular cone, a parallelepiped, a cube, etc. having a through hole passing through the parallel faces of the mentioned figures. If the optical sensor according to the present invention is built in a wearable device such as a smartwatch, when the user wears the smartwatch, the lower part of the insulating channel is in close contact with the user’s skin to prevent parasitic illumination of the photodetector. Here, "the parasitic illumination of the photodector" may refer to the light emitted from the emitter being directly incident on the photodector rather than on the user's skin. In an embodiment, "the parasitic illumination of the photodector" may refer to the light reflected from the skin surface and upper skin layers being directly incident on the photodector rather than on the user's biological tissues. That is, “to prevent parasitic illumination of the photodetector” may refer that the insulator or the insulating channel is configured to suppress the light emitted from the emitter being directly incident on the photodector rather than on the user's biological tissues. And / or to prevent parasitic illumination of the photodetector” may refer that the insulator or the insulating channel is configured to suppress the light reflected from the skin surface and upper skin layers being incident on the photodector rather than on the user's biological tissues.

[0142] The through hole or cavity of the insulating channel is usually filled with a material that provides the effective passage of radiation therethrough and entering the radiation into the skin. Ideally, the cavity should be filled with air, however, in order to prevent foreign substances, for example, dust, skin particles, etc., from entering the cavity, it is filled with a material transparent to the SWIR radiation, in particular a suitable polymer selected from polyolefins, for example, but not limited to. The walls of the insulating channel are made from a material that absorbs the SWIR radiation, such as polymers - polymethyl methacrylate (PMMA) or polycarbonate (PC), but not limited to. In particular, PMMA can be modified, for example, dyed in a suitable way in order to absorb the SWIR radiation. The arrangement of the optical sensor is such that there is a gap between the outer surface of the insulating channel and the surface of the optical concentrator. In an embodiment, radiation reflected and scattered by the epidermis and dermis layers of the user’s skin enters within the concentrator through the gap between the outer surface of the insulating channel and the surface of the optical concentrator. Radiation photons passed through the skin and entered the optical concentrator are refracted by the material of the concentrator, reflected from its surface and focused (concentrated) into a small size photodetector. In addition, optically matching of the optical concentrator and the photodetector is provided to more efficient input light to the photodetector. The optical concentrator can be made, for example, in the form of a spherical segment, but not limited to. High refractive index materials are used for manufacturing the optical concentrator. Summarizing the above, the optical sensor according to the present invention is configured such that radiation is inputted into skin through the insulating channel, and then the radiation reflected from and scattered in the skin enters the concentrator through the gap between the walls (outer surface) of the insulating channel and the surface of the optical concentrator and focuses into the photodetector.

[0143] In the left part of Fig. 5, detection areas are shown in comparison, i.e. the skin portions from which radiation reflected from and scattered in the patient’s skin is collected by the traditional sensor and the optical sensor according to the present invention. With the optical sensor according to the present invention, radiation is recorded from a portion whose area is several times larger than an area provided with the traditional sensor. For example, as illustrated in Fig. 5, the area of the radiation record portion by the traditional sensor, without the use of a concentrator, is about πR^2, and the area of the a ring shaped radiation record portion by the sensor according to the invention is about π(R2^2-R1^2).

[0144] A first key particular (KP1) of the present invention is to provide optical isolation of the photodetector from the emitter within the optical skin interface. For this purpose, a laser or LED radiation guiding optical insulating channel is provided.

[0145] The effect of KP1 is to isolate the photodetector from radiation reflected from the skin surface and upper skin layers.

[0146] A second key particular (KP2) of the present invention is that the optical concentrator is made from a material with a high refractive index and has optical contact with the photodetector. The optical concentrator made from a material with a high refractive index (n≥1.7) focuses the radiation to the photodetector. The optical contact is necessary to prevent photons from reflecting off the interface between the optical concentrator and photodetector and to effectively input the photons into the photodetector.

[0147] The effect of KP2 is to collect photons from the skin and focus them into a photodetector having a small aperture (less than the detection region), which is necessary for biomedical SWIR sensors operating on skin, due to the high noise level of the SWIR radiation detectors.

[0148] The selection of the shape and material of the concentrator (instead of the conventional type) allows the size of the optical sensor to be reduced so that it is suitable to be built in a smartwatch.

[0149] The proposed optical sensor and the wearable device comprising the same provide the capability of non-invasive, accurate instant or continuous determination of a concentration of blood components such as blood glucose and glycated hemoglobin and are suitable for non-professional use.

[0150] Hereinafter, particulars and exemplary embodiments of the present invention will be described with reference to the drawings. Persons skilled in the art will be understood that various exemplary embodiments should in no way be construed as limiting the scope of the claimed invention, and that other tangible and technical means equivalent to or similar to those listed below may be used by skilled persons to perform various components of the optical sensor, functions, method steps, etc., described below. The present detailed description is not intended to limit the scope of the claimed invention, which is defined only by the appended claims.

[0151] The optical sensor according to the present disclosure, designed in particular for measuring a blood glucose level, comprises a SWIR emitter, a photodetector, an optical concentrator, and an insulating channel. As used herein, the terms “radiation receiver”, “receiver”, “photoreceiver”, “photodiode”, “detector”, “photodetector”; “SWIR emitter,” “emitter”, “radiation source”, “LED / laser diode”; “insulating channel”, “insulator”, as well as “optical concentrator”, “concentrator” can be used interchangeably.

[0152] The radiation sources used in the optical sensor according to the present disclosure are semiconductor microlasers and light-emitting diodes (LEDs). Their main advantages are miniature dimensions and low power consumption, high speed (fast response time), which allow them to be used in electronic circuits with high-speed microprocessors, high conversion factor of electrical power into a useful electromagnetic signal. Among the wide variety of structures of semiconductor LEDs and lasers of the SWIR range, two main classes can be identified: injection and optically-pumped ones. The used radiation source, for example, a semiconductor laser, generally comprises a multilayer semiconductor structure as a heterostructure with layers having specified thicknesses and bandgap energies, and a semiconductor electromagnetic pump source. The thickness of the semiconductor layers is selected on the basis of properties of the used semiconductor materials and the specified requirements for the spectrum and output power of the SWIR radiation. A LED or a semiconductor microlaser with a radiation wavelength of 0.9-2.5 μm is used as an electromagnetic pump source. Meanwhile, various optical and electronic components allowing the radiation wavelength to be shifted to the required region can be additionally used. InAsSb / InAsP, InAsSb / InAs, GaInSb heterostructure-based LEDs, Nd:YAG laser can be used as the radiation sources, but not limited to. The use of a microlaser is reasonable in cases where it is necessary to obtain the maximally high conversion factor of electric power into light energy, as well as when it is required to obtain a radiation source as close as possible to a point one (the technologically achievable size of the luminescence region for an LED pump source is 1×1 mm, and for a laser one is 0.1×0.1 mm). This is especially important when it is necessary to interface an infrared radiation source with optical components.

[0153] The optical concentrator is made in the form of a rotation body, optionally with a coating, the inner surface of the coating being reflective. Meanwhile, no coating is applied to the surface (portion) of the optical concentrator, which will be in contact with a user’s skin during operation. Such a surface is usually referred to as a bottom surface. In an embodiment, the coating is configured to reflect or guide the radiation input into the optical concentrator into the photodector. In the optical sensor according to the present disclosure, the photodetector is disposed on top of the concentrator. The optical concentrator can be made in the form of one of the following rotation bodies: a spherical segment, a spherical layer, a truncated circular cone, an ellipsoid or paraboloid segment. The optical concentrator can also be composed and include at least two parts located on top of each other, each of which is one of the above-mentioned rotation bodies, wherein the coating, if any, includes at least two portions: the first (lower) portion, which is a coating of the lower rotation body, and the second (upper) portion, which is a coating of the upper rotation body. In addition, the bottom part of the optical concentrator may be a cylinder, optionally with a coating, and the upper part may be any of the above-mentioned rotation bodies or be composed. A rotation axis of the concentrator passes through the center of a focal spot, which is formed by photons focused into the photodetector, perpendicular to it, and is the rotation axis of all the parts of the concentrator. The shape and manufacturing material of the optical concentrator are selected such that the photons entering therein can be focused on the working surface of the photodetector.

[0154] The photodetector is positioned so that the working surface of the photodetector is in the focal plane of the concentrator. For example, the photodetector is a planar single-sided photoelectric cell with a circular shape, and the working surface of the photoelectric cell is in the focal plane and coincides with the focal spot of the concentrator.

[0155] The optical concentrator provides uniform illumination of the focal spot in line with the concentrator shape. The presence of the reflective surface in combination with the concentrator shape provides a more effective steep incidence of rays on the focal spot and, accordingly, on the working surface of the photodetector located therein while decreasing the angles of incidence, and also provides the entry of reflected rays to each point of the focal spot, which results to an increase in conversion efficiency by reducing the coefficient of reflection of the rays from the working surface of the photodetector and increasing the concentration ratio.

[0156] The optical concentrator for the optical sensor according to the present disclosure is made from a material with a refractive index n≥1.7. In one embodiment, the optical concentrator may preferably have a refractive index of 2.0 or more. More preferably, as illustrated in Table 2, the optical concentrator may have a refractive index of 3.0 or more. Components made from silicon, which is one of the hardest optical materials, are preferably used for this. Silicon optical components are widely used in a variety of infrared applications operating in the wavelength range from about 1 μm to 7 μm. Silicon in optical components is generally slightly doped (resistivity is 5-40 Ω / cm) in order to prevent absorption bands and provide better transmission. The low density of silicon (2.329 g / cm3) is ideally suitable for weight-sensitive applications. Si has Knoop hardness of 1150, which makes silicon optical components harder, less brittle alternatives to similar optical components, for example, made from germanium. High thermal conductivity and low weight of silicon are attractive characteristics in IR applications. Its transmittance is about 50% within from 1 μm to 6 μm, which means that non-glare (antireflection) coatings are usually required to improve transmission. The usually required thickness of the antireflection coating in the IR range is from 1 / 2 wave to 2 waves and is selected depending on the application. The parameters of the antireflection coating are selected for a specific optical system and photodetector material. The refractive index of Si is about 3.4-3.5 over the entire SWIR range. Specific values of the refractive index of silicon for different wavelengths are shown in Table 2 below.

[0157] Table 2. Refractive index of Silicon

[0158] Wavelength, μmRefractive index n1,3573,49751,3673,49621,3953,49291,52953,47951,6603,46961,7093,46641,8133,46081,9703,45372,1533,44762,3253,4430

[0159] The manufacture of SWIR radiation receivers is an extremely complex process problem and has only recently been adopted. The photodetectors used in the optical sensor according to the present disclosure are made similarly to the silicon-based charge coupled device (CCD) sensors or complementary metal-oxide-semiconductor (CMOS) sensors, they convert incident photons into electrons, so they are also often referred as quantum detectors. Germanium (Ge), gallium indium arsenide (InGaAs), gallium indium arsenide phosphide (InGaAsP), indium antimonide (InSb) or cadmium mercury telluride (HgCdTe; HCT) - based photodetectors can be used for operation in the radiation range of 0.9-2.5 μm. For example, Ge is used in the range of 0.8-1.6 μm, whereas InGaAs is used in the range of 0.8-1.8 μm. Meanwhile, depending on the material composition, whose chemical structure is variable and selected taking into account the detection problems, these photodetectors are sensitive to wavelengths of different ranges.

[0160] At the moment, the vast majority of scale-produced photodetectors are hybrid assemblies based on the phenomenon of internal photoelectric effect. Thus, the short-wave IR sensitive element is coupled (bonding process) with an integrated reading circuit based on CMOS sensors. Despite the high values of quantum efficiency, a low noise and power consumption level, this type devices have a number of drawbacks. First of all, this is the high cost of technological production, the limitation of the form factor associated with the technological limit of the bonding process, the non-uniformity of sensitivity and defectiveness of pixels, as well as the impossibility of implementing an active-pulse mode with a short strobe duration (less than 200 μs). The above-listed drawbacks are absent in the case of building photo-receiving systems based on a hybrid photoelectronic device (HFP) having a photocathode heterostructure InP / InGaAs / InP and an electronically sensitive element, which are in the same vacuum volume. At the output of such a device, an electrical signal corresponding to the converted photon radiation is generated. This makes it possible to implement a scheme for accumulating and transmitting signals in a digital form. In this case, the elements of electronic optics used to record the IR range and the visible range are identical, which significantly reduces the cost of their production.

[0161] Thus, the InGaAs-based photodetectors are the most efficient to be used due to their high quantum efficiency and low dark current at room temperature.

[0162] As an example, the InGaAs-based photodetector consists of several layers:

[0163] 1. An InP substrate, optionally with an antireflection coating.

[0164] 2. A photosensitive layer InGaAs grown by epitaxial methods on the InP substrate.

[0165] 3. Indium bumps.

[0166] 4. A reading integrated circuit.

[0167] The principle of operation is simple: photons scattered / reflected from objects of interest enter the photodetector through a lens (objective lens), for which the same optics can be used as in cameras operating in the visible or near-IR ranges, then the photons are absorbed in the indium-gallium arsenide layer, and as a result of the internal photoelectric effect, photoelectrons are generated, which are then transmitted, by means of the indium bumps, to the sensitive area of the silicon detector, i.e., the reading integrated circuit (RIC) organized according to the principle of a CCD or CMOS logic.

[0168] The optical sensor according to the present disclosure can be built in a wearable device. The wearable device according to the present disclosure may comprise a housing, a processor (for example, a microprocessor), a battery or secondary cell, an input device and an output device, a display device, a memory device, a communication module including a wireless communication module and a wired communication module, etc. The input device and the output device may be configured as a single input and output device. The wearable device may comprise additional sensors, for example, inertial movement sensors, gyroscopes, accelerometers, an electrocardiogram (EKG) measurement sensor, an atmospheric pressure sensor, a humidity sensor, a Hall sensor, an ambient light sensor, photoplethysmographic (PPG) sensors, and bio-impedance (BIA) sensors, etc. In embodiments, the wearable device may be a smart device, in particular a smartwatch or fitness bracelet, a medical health monitoring wearable device with function of determining a level of glucose, glycated hemoglobin, etc. The wearable device is an electronic wearable device and can be configured to establish a wired or wireless communication channel with external devices such as smartphones, wearable fitness bracelets, voice assistants, smart TVs, smartwatches, etc., or with a server and can be configured to transmit data via a network or a cloud storage.

[0169] Fig. 6 illustrates the first key particular (KP1) of the present invention consisting in providing optical isolation of the photodetector from the emitter within an optical skin interface.

[0170] In the left part of Fig. 6, an interface between an optical sensor and skin according to a prior art solution is schematically shown. In general, in the optical sensor built in the wearable device such as a smartwatch, the photodetector and the emitter are configured on the same PCB, which is caused by convenience of manufacture. A part of the back cover of the smartwatch is a glass window. In the operating position of the smartwatch, the back cover is pressed against the user’s wrist through the use of the watch strap, wherein the light from the emitter passes through the glass window and penetrates the skin, then it is reflected and scattered by the skin and passes through the glass window to the photodetector again. The emitter in such optical sensor can be isolated from the photodetector by a shutter (blind), which usually does not contact directly with the skin, but prevents photons from entering the photodetector directly from the emitter. However, such a shutter does not prevent photons back-reflected and back-scattered from the upper skin layers and from the skin surface from entering the photodetector, which negatively affects the measurement result since at this time the signal-to-noise ratio reduces.

[0171] Thus, the contact with the skin through a glass optical window and the lack of optical isolation of the photodetector from the emitter may be related to the drawbacks of the traditional solution since the optical window without an optical insulator does not provide the capability to cut off a non-useful signal from the upper skin layers.

[0172] The result of the above drawbacks is the negative affect of the reflection from the upper skin layers on the measurement results.

[0173] In the right part of Fig. 6, a portion of the optical sensor according to the present invention, that provides the input of radiation into skin, is schematically shown. One of its particulars is the presence of an isolating optical channel (insulator), which is made as a hollow cylinder in one of the embodiments. The wall of this cylinder is made from a material that absorbs electromagnetic radiation from the emitter, while the cavity of the cylinder should be filled with air in the ideal case, but, in practice, it is filled with a material that is transparent to the radiation used and prevents dust, skin flakes and other foreign substances from entering the cavity. The radiation emitted by the emitter passes through the material in the cylinder cavity and enters the skin. The insulating channel is in close contact with the skin and prevents, firstly, the radiation from directly entering the photodetector, and, secondly, the radiation scattered in and reflected from the upper skin layers, including the skin surface, from entering the photodetector. Thus, the background signal power from the skin upper layers decreases and the signal-to-noise ratio increases. It should be noted that biological tissues are relatively transparent to the NIR and SWIR radiation, which makes non-invasive measurement at a depth of a few millimeters being safe for human. In addition, a passage trajectory of photons through the tissues resembles a parabola, which is sometimes described by the term “banana-shape”. Therefore, due to the emitter and photodetector location and the use of the appropriate radiation wavelengths, an area of interest can be accurately defined, that is, the area for collecting signals from the required skin layers by depth.

[0174] Thus, the optical sensor according to the present invention provides:

[0175] - direct contact with skin, that is, direct input of radiation emitted from the emitter into the skin without an intermediate component as a glass window;

[0176] - optical isolation of the photodetector from the emitter.

[0177] As a result, the reflection from the upper skin layers does not affect the measurement results.

[0178] The optical sensor according to the present invention comprises an isolating optical channel configured to completely optically isolate the photodetector from the emitter in order to selectively detect the radiation reflection and diffusion (scattering) from the deep skin layers. The isolating optical channel isolates the photodetector from radiation reflected from the skin surface and partially isolates the photodetector from radiation that has passed through the upper skin layers.

[0179] As a result, the effect of selectivity of radiation detection from the deep skin layers is provided. The optical interface i.e., the isolator, allows radiation from the emitter to penetrate into the deep skin layers with selective detection of the radiation reflected and scattered by the deep skin layers.

[0180] Fig. 7 illustrates the second key particular (KP2) of the present invention consisting in provision of the optical concentrator made from a material with a high refractive index and having optical contact with the photodetector.

[0181] In the left part of Fig. 7, an arrangement of an optical sensor according to a prior art solution is schematically shown. In prior art solutions, in order to provide the collection of a signal from a predetermined depth of tissues, a wavelength of radiation is selected and a distance between the emitter and the photodetector is set taking into account the propagation of photons in the tissue along the “banana-shape” trajectory. When the emitter and the photodetector are located on the same PCB adjacent to each other, the signal detection (collection) area has an area of πR^2, where R is an approximate radius of the photodetector with a round-shaped sensitive element when viewed from above, that is, the signal collection area increases when the size of the photodetector itself increases, which, as noted earlier, results to decreasing the signal-to-noise ratio, and therefore to the difficulty of extraction of the signal informative part. The above signal is not sufficient to solve the problem of the present invention consisting in providing of measuring blood components with a low concentration.

[0182] In the right part of Fig. 7, a portion of the optical sensor according to the present invention, that provides the collection of radiation into the photodetector, is schematically shown. Use of the optical concentrator provides the capability to collect photons from a larger area than in the solutions used in the optical sensors of smartwatches at present. In the bottom part of Fig. 7, the detection regions of the sensor according to the present invention and the prior art sensor are illustrated in comparison. A large ring-shaped detection region for the optical sensor according to the present invention provides an increase in the signal-to-noise ratio due to a larger photon collection area.

[0183] Thus, the optical sensor according to the present invention uses the optical concentrator made from a material with a high refractive index to collect photons from the region around the emitter and efficiently focus them into the photodetector. The specially designed optical concentrator provides the collection of photons from a ring-shaped region on the skin and the effectively focusing them into the photodetector. To that end, the optical concentrator made from a material with a high refractive index n≥1.7 concentrates this radiation to its top side. In one embodiment, the optical concentrator may preferably have a refractive index of 2.0 or more. More preferably, as illustrated in Table 2, the optical concentrator may have a refractive index of 3.0 or more. In addition, optical contact (matching) is provided, for which the optical antireflection coating and / or optical glue are used, which prevents photons from being reflected from the photodetector and guides photons to the photodetector.

[0184] As a result, the effect of collecting photons from a larger area of the skin and the effective input of radiation reflected from the deep skin layers into the photodetector are provided.

[0185] Figs. 8A and B illustrate in detail the reasons that cause the use of a material with a high refractive index n≥1.7 for manufacturing the optical concentrator. The present inventors have studied a plurality of potential materials for manufacturing the optical concentrator, which can be used in the SWIR range, but collect radiation with different efficiency. Fig. 8A illustrates optical concentrators made from air (n=1.0), a glass (n=1.5), zirconium oxide (n=2.2), and silicon (n=3.48). The optical concentrator made from air is a reflective rotation surface that limits the space filled with air (“flask”). Under each of the optical concentrators, propagation paths of photons therein and optical efficiency Cfosprovided by such concentrator, which is the ratio of the intensity of the detected photons, that is, the photons entering the photodetector, and the intensity of the photons passing through the skin and entering the optical concentrator, are shown. The optical efficiency for the optical concentrator made from air is 10%, a glass is 17%, ZrO2is 33% and Si is 47%.

[0186] Fig. 8B schematically shows a graph of dependence of the optical efficiency Cfos on square of a refractive index (n^2) of a material used for manufacturing the optical concentrator. It can be seen from the graph that the optical system efficiency increases significantly in the value range of n from about 1.5 to more than 3 to reach a value of about 50%. Hence, a material with a refractive index equal to or greater than 1.7, preferably greater than 2.0, and most preferably greater than 3.0, is used as the material for manufacturing the optical concentrator.

[0187] Fig. 9 illustrates the problem of optical matching of the concentrator and the photodetector or creating an effective optical contact therebetween.

[0188] It is necessary to select a material for creating an optical contact that allows radiation to be effectively inputted into the photodetector. To that end, an optical glue and a special coating are used.

[0189] In the top graph of Fig. 9, results of study of dependence of electromagnetic radiation transmission by various materials used as an optical glue on the radiation wavelength are shown. An optical glue is used to fix the photodetector on the optical concentrator, prevent photons from reflecting off the photodetector and guide photons into the photodetector. Thus, the refractive indices of the optical glue, concentrator and photodetector are to be matched to provide efficient radiation input into the photodetector. In addition, it is important to properly select the thickness of the optical glue to provide efficient radiation input into the photodetector. The thickness of the optical glue just as the parameters of the antireflection coating is selected for a specific optical system and a photodetector material. The present inventors had been simulated the human skin layers and the optical paths of SWIR photons in skin using the Monte Carlo Simulation by using a model of biological tissues of human skin, and, after the reflected and scattered radiation data are acquired, used RayTracing (for example, Comsol modeling) technology to simulate the tracing of SWIR photons in optical components such as the concentrator, optical glue, photodetector. With the mentioned technologies, a plurality of optical sensor structures have been modeled and their effectiveness has been studied, including the use of different materials for manufacturing the optical concentrator, different shapes of the optical concentrator, different optical glues for the SWIR range, etc.

[0190] The following materials manufactured by Master Bond® had been studied as an optical glue: Master Bond EP30, MasterSil 151, MB600, UV15, whose transmission in a spectrum range of 500-2500 nm is almost 100%. Master Bond EP30 is preferred from these materials, i.e., a very low viscosity, two-component epoxy resin designed for high-performance bonding, coating, sealing, potting and encapsulation. It readily cures at room temperature and does not contain any solvents or diluents. EP30 possesses very good optical clarity along with superior transmission when compared to many other epoxy resins. EP30 bonds well to a variety of materials, including metals, a glass, and ceramics, as well as many plastics and rubber materials. EP30 forms high strength, rigid bonds that are resistant to chemicals, including water, oil, acids, bases, and many solvents. At the same time, the optical glue that can be used in the optical sensor according to the present disclosure is not limited to the above.

[0191] An antireflection coating can be used to optically match the high-refractive index material, for example, Si, from which the concentrator is made, with a next layer, for example, the optical glue. As a result of the antireflection coating usage, the reflection of photons from the photodetector decreases.

[0192] In the graphs below of Fig. 9, the transmission of a silicon lens is shown as a function of the radiation wavelength in the absence of an antireflection (AR) coating and when such a coating is used. As can be seen from the graphs, the presence of the antireflection coating significantly increases the transmission of the silicon lens.

[0193] Figs. 10A and B show the results of simulation by using the above-mentioned technologies, that demonstrate the propagation of electromagnetic radiation (photons) in the optical sensors of various structures. The inventors have conducted a plurality of simulation experiments, including the selection of different materials for manufacturing the optical concentrator, the selection of different shapes of the concentrator, etc. Generally, the concentrator shape is a spherical segment or spherical layer, but not limited to and can be made in the form of another rotation figure. The optical efficiency of the concentrator depends on the shape and material from which it is made. Thus, by changing various parameters, the optical efficiency of the optical system can be altered.

[0194] A simulation experiment illustrated in Fig. 10A has been performed regarding a structure of an optical sensor, in which an emitter and a photodetector are located at opposite sides of the same PCB, and an optical concentrator is made in the form of a spherical segment. The arrows show the propagation paths of photons from the emitter into skin, their reflection by various skin layers, collection and guiding to the photodetector by using the optical concentrator. The graph below shows the distribution of photon intensity, taking into account the distance between the emitter and the photodetector, wherein the axis of ordinates on the left shows the penetration depth of photons into the skin, the axis of ordinates on the right shows the signal intensity, the axis of abscissa shows the coordinate along the emitter-photodetector axis (the emitter is in coordinate 0, the center of the photodetector is in coordinate 1.0 mm). According to the experiment, the optical efficiency of this system is 53%.

[0195] A simulation experiment illustrated in Fig. 10B has been performed regarding a structure of an optical sensor, in which an optical concentrator is made in the form of a truncated circular cone, or rather, two truncated cones with different inclination of the side surface, located one above the other, and the radiation source and photodetector are located on different PCBs at opposite parallel sides of the concentrator. As an example, the approximate dimensions of the optical sensor according to the present invention are shown in section view - 1 mm × 2 mm. According to the experiment, the optical efficiency of this system is 47%.

[0196] The bottom part of Fig. 10B illustrates a cross-section side view of an optical sensor structure according to an embodiment of the invention. The optical sensor includes a SWIR LED, a SWIR photodetector, an optical concentrator, an optical (transmission) window, an insulating channel. The optical window is designed to contact with a user’s skin and is configured to transmit the SWIR radiation. The LED and optical concentrator are adhered to the optical window with an optical glue. The optical glue is an epoxy resin transparent in the SWIR range, whose examples were provided earlier, and is designed to decrease optical contrast and to reduce reflection from the optical interface. The insulating channel in this embodiment is configured as two ring-shaped radiation absorbing diaphragms located at two opposite surfaces of the optical window, and is designed to guide radiation into a user’s skin at a specific angle and to prevent radiation reflected from the skin surface and upper skin layers from entering the photodetector. The optical concentrator has a truncated circular cone shape, optionally with a mirror-reflecting surface, and is an optical element, for example, a silicon lens configured to collect and focus the radiation passed through the skin into the photodetector. Here, “the radiation passed through the skin” may be understood as the radiation is scattered from the biological tissue and enters from the detection region into the ring-shaped gap. The SWIR photodetector is attached to the upper part of the optical concentrator by using the same optical glue or other mentioned glue. The upper part here means the surface furthest from the optical window, wherein the optical window contacts with the skin during operation.

[0197] Thus, the possibility to measure blood components with a low concentration, for example, blood glucose or glycated hemoglobin levels, is realized by using the following key particulars of the present invention, which are illustrated in Figs. 11A, B:

[0198] KP1. The use of the ring-shaped optical skin interface with optical isolation of the photodetector from the emitter.

[0199] 1. Provision of optical isolation by the optical laser / LED input channel or insulating channel that completely isolates the photodetector from radiation reflected from the skin surface and partially isolates the photodetector from radiation passed through the upper skin layers, as shown in the upper part of Fig. 11A.

[0200] 2. Increased area of collecting radiation since the entire area around the emitter is used as shown in the bottom part of Fig. 11A. In case if the intensity is non-uniform (has a gradient along the radius R), the geometric factor further increases.

[0201] KP2. Use of the optical concentrator made from a material with a high refractive index (n≥1.7) and having optical contact with the photodetector.

[0202] 3. The optical concentrator concentrates the radiation passed through the upper skin layers to the upper part, where the photodetector is disposed.

[0203] 4. Provision of optical contact between the concentrator upper part and the photodetector by using the optical glue that prevents the reflection of photons from the photodetector and guides the radiation into the photodetector.

[0204] The technical result of the present invention is to provide an optical SWIR sensor for biomedical applications, that has a compact structure, provides an improved signal-to-noise ratio of detected SWIR radiation, and therefore the capability to detect blood components with a low concentration, for example, glucose and glycated hemoglobin.

[0205] Figs. 12, 13 show embodiments of the present invention. Embodiments differ mainly in the optical concentrator shape and the different positional relationship of the emitter and photodetector.

[0206] In a first embodiment, the emitter and the photodetector, in this case a LED and a photodiode, are on the same PCB but are disposed at opposite sides thereof. This is a suitable option for solving the power supply problem in a smartwatch since with this arrangement (layout) there is no necessity for an additional wiring, and both the emitter and the photodetector are powered directly through said PCB. Accordingly, this is the easiest option of the optical sensor for manufacture. However, the optical efficiency, when a single PCB is used in the arrangement, is generally lower than when the emitter and photodetector are arranged on different PCBs. It should be noted that in the first embodiment, optical matching of the concentrator and the photodetector is not required because they do not contact to each other.

[0207] In a second embodiment, one emitter and two photodetectors arranged coaxially are used. In addition, in this embodiment, the arrangement includes two optical concentrators, in this case lenses, one nested within the other. Meanwhile, a part of the radiation passed through the skin enters the internal concentrator and is focused into the first photodetector, and a part of the radiation enters the external concentrator and focuses into the second photodetector. In this arrangement, the emitter and photodetectors are located on different PCBs. This embodiment is more sensitive for detecting blood components, but also more difficult to manufacture.

[0208] In the first and second embodiments, the optical concentrators are configured as a segment of a rotation ellipsoid.

[0209] In a third embodiment, the optical concentrator is in the form of a truncated circular cone. The optical sensor according to this embodiment can be more easily adapted to a target device structure and / or technological restrictions since it has a reduced volume as compared to the sensor according to the previous embodiments. The optical sensor according to the third embodiment and the sensors having similar arrangements provide the greatest optical efficiency.

[0210] In fourth and fifth embodiments, the emitter and the photodetector are disposed non-coaxially relative to each other on a single PCB.

[0211] In the fourth embodiment, the emitter and the photodetector are located on the same side of the PCB, and the optical sensor structure further includes a set of reflectors to guide the radiation through the insulating channel into skin. This is a suitable option for solving the problem of supplying a power in a smartwatch. The optical sensor according to this embodiment is difficult to manufacture, but it has the advantage of being built in a wearable device.

[0212] The fifth embodiment is characterized by the use of a flexible PCB with the emitter and the photodetector located on the same side thereof. The optical sensor structure further includes a reflector to guide radiation through the insulating channel into skin. This is a suitable option for solving the problem of supplying a power in a smartwatch, characterized by better matching of the emitter and the concentrator. The optical sensor according to this embodiment is the most difficult to manufacture.

[0213] Fig. 14 illustrates different materials that are used to manufacture the optical concentrator. Meanwhile, the optical concentrator of the same structure, but manufactured from different materials, provides different optical efficiency (Cfos). As discussed earlier, it is reasonable to build the optical system using a material with a refractive index n≥1.7, more preferably with n≥2, and most preferably with n≥3.

[0214] Suitable materials for manufacturing the optical concentrator are silicon (n=3.48), various chalcogenides, for example, a chalcogenide glass (n=2.8), ZnS (n=2.5). In particular, a chalcogenide glass provides a wide transmission window (1-20 μm) depending on a composition, has high refractive indices that allow most of the light to be concentrated outside a core material, making them suitable for sensitive detection in medical or environmental applications. For example, a chalcogenide glass of the Te-As-Se (TAS) family is characterized by a high refractive index n=2.8 for a wavelength range of 2 to 12 μm (see the article by Marie-Laure Anne et al., Chalcogenide Glass Optical Waveguides for Infrared Biosensing, https: / www.mdpi.com / 1424-8220 / 9 / 9 / 7398).

[0215] It should be noted that according to an embodiment, several materials may be used to manufacture the optical concentrator. For example, as shown in the drawing in the middle of Fig. 14, a part of the optical concentrator in the form of a spherical segment is made from one material, and a part of the concentrator in the form of a hollow cylinder is made from another material.

[0216] Thus, the present invention provides improved quality of a received signal (increased signal-to-noise ratio) and provides the possibility to detect blood components with a low concentration, for example, such a complex component to measure as glucose or glycated hemoglobin. This is achieved through the key particulars of the present disclosure, consisting in:

[0217] - isolation of the photodetector from radiation reflected from the upper skin layers and skin surface (KP1),

[0218] - collecting and focusing the radiation passed through the skin to the photodetector having a small aperture less than the detection area, which is necessary for biomedical SWIR sensors applied to the skin due to the high noise level of SWIR detectors,

[0219] - selection of the concentrator shape and material (instead of a conventional concentrator), which allow the sensor dimensions to be reduced so that it is suitable for a smartwatch.

[0220] Worldwide, about 0.5 billion people suffer from diabetes mellitus. It is forecast that their numbers will rise to more than double to 1.3 billion in the near 30 years. This disease can affect men, women and children of all ages in all countries. The following target groups are necessary to control the disease course of the predisposition to diabetes:

[0221] - healthy people for the purpose of preventive control;

[0222] - children with diabetes;

[0223] - diabetic patients with abnormal renal glucose threshold;

[0224] - patients with type I diabetes mellitus, insulin-dependent;

[0225] - pregnant women with type II diabetes;

[0226] - people over 45 years of age;

[0227] - people with a familiar risk of disease;

[0228] - other people when food ration or other habits are altered.

[0229] Also, people are at a risk group who have:

[0230] - a high blood pressure;

[0231] - vision problems;

[0232] - disease of the cardiovascular system and / or stroke incident;

[0233] - kidney disease.

[0234] In order to prevent the risk to disease type II diabetes, it is necessary to follow a healthy diet, lose excess weight, and exercise regularly. Patients who exercise regularly can reduce their risk to disease diabetes in half. Patients who lose at least 5% of their body weight can significantly reduce risk of diabetes development.

[0235] As known, a blood glucose level is tracked by using two indicators: a glycated hemoglobin (HbA1c) level and an instant glucose level. HbA1c represents a long-term glucose indicator over the last 1-3 months and is not affected by short-term changes in a blood glucose level caused by meal, exercising, etc. at the day of testing. An instant glucose level is a short-term indicator of glucose at a particular time of testing, for example, a fasting or post-meal blood sugar level, and is prone to fluctuations due to eating and stress.

[0236] The wearable device with the built optical sensor according to the present invention is configured to both instant and continuous non-invasive measure blood glucose and glycated hemoglobin levels, wherein a blood sugar can be measured both in a fasting state and after eating. Therefore, a wearable device such as a smartwatch can be used in proactively monitoring a glucose level and receiving feedback on user's treatment results.

[0237] An instant glucose level measurement is possible even when the user puts on the smartwatch for the first time. A continuous level measurement is possible when the smartwatch is constantly worn by the user. Meanwhile, the smartwatch equipped with the optical SWIR sensor according to the present invention provides an accurate estimation of both an instant glucose level and dynamics of glucose level over a long period.

[0238] The wearable device with the integrated optical sensor according to the present invention provides advanced functionality for health monitoring and is necessary for continuous control of glucose and glycated hemoglobin levels since there is a direct relationship between poor control and the development of complications. In addition, by glucose control, the development and phase of diabetes-related complications can be predicted.

[0239] Fig. 15A schematically illustrates options of exemplary depiction of 24-hour glucose level measurement results and variances (deviations) of multi-month glucose measurement results on a screen of the wearable device according to the invention in the S-Health app. As illustrated in Fig. 15A, a user of the wearable device can see on the screen of the wearable device various data with glucose measurement results for different periods of time, including, for example, specific results of single measurements and average values for a day, for a month, for a year, etc. By using the S-Health app, glucose control can be performed as follows:

[0240] - to track the average blood glucose level,

[0241] - to track how many peaks there are per day and the time of their occurrence,

[0242] - to track whether blood glucose rises quickly or normally,

[0243] - to determine a normal or abnormal level, that is, whether the blood glucose level is within the norm or above the norm.

[0244] Fig. 15B schematically illustrates a graph displayed on a screen of the wearable device in the S-Health app and allowing the variance of the glucose level from the target value to be monitored. With long-term glucose monitoring, for example, over several months, variance from the target zone of the normal glucose level, as well as crossing high and low level alert thresholds can be monitored. It is important to monitor any variances of said level from the target zone. Meanwhile, when a glucose level is monitored, the following situations are possible. When a high or low blood glucose level outside the target zone is determined, the device user is informed about the result obtained and about the preliminary diagnosis, for example, state of predisposition to diabetes and general recommendations can be displayed on the screen: altering in diet, an increase in physical activity, walks in fresh air or a recommendation to visit a doctor.

[0245] Meanwhile, short-term variances in a blood glucose level from the norm are not critical and can be corrected by the device user by using recommendations displayed on the display screen. In contrast, long-term variances in a blood glucose level from the norm can mean serious health problems and recommendations for obligatory visit to a doctor are displayed on the display screen. In addition, the data of the acquired glucose level monitoring results can be sent to a doctor directly from the measuring device.

[0246] Similarly, a glycated hemoglobin level can be monitored.

[0247] The advantages of such monitoring are relatively low studying expenses, provision of a long-term period of continuous tracking of blood parameters, that provides the acquiring of reliable measurement data and the establishing a more accurate diagnosis of a person based on the acquired data.

[0248] The advantageous effects of the present invention are:

[0249] - providing the user with a blood condition estimation, in particular information on blood glucose and glycated hemoglobin levels;

[0250] - the possibility of use to monitor other vital signs, such as heart rate;

[0251] - the possibility of use in telemedicine.

[0252] Thus, as is foreseen, the optical sensor and the wearable device comprising the same according to the present invention, configured to non-invasive, continuous and / or on-demand determine a concentration of blood components, in particular glucose / glycated hemoglobin levels, and able for non-professional use, will be demand in the market.

[0253] The possibility to determine blood glucose / glycated hemoglobin levels expands the functionality of the S-Health app in a smartwatch, while providing additional parameters for a comprehensive analysis of the user’s health status. The smartwatch can provide daily variations, current values, a continuous glucose estimation result for a predetermined period of time.

[0254] As noted earlier, the target groups for which glucose level control is necessary are:

[0255] - healthy people for the purpose of preventive control;

[0256] - diabetic children;

[0257] - diabetic patients with abnormal renal glucose threshold;

[0258] - patients with type I diabetes mellitus, insulin-dependent;

[0259] - pregnant women with type II diabetes;

[0260] - other people when food ration or other habits are altered.

[0261] Continuously monitoring of glucose and / or glycated hemoglobin levels provides an estimate of an average glucose outcome for a certain period of time, allows a direct relationship between poor monitoring and the development of complications to be determined, as well as the development and phase of microvascular complications associated with diabetes to be predicted. Hence, preventive control of glycemia and feedback in the diabetes mellitus treatment can be provided. The determination of glucose and / or glycated hemoglobin levels using the wearable device disclosed herein is performed in an easy-to-use manner for a user.

[0262] Thus, the technical result of the present invention is to provide a wearable device capable of performing an automatic non-invasive estimation of, for example, a blood glucose level, while acquiring both an instant value and an average value for a certain period of time.

[0263] The blood glucose level has diagnostic value in determining diabetes mellitus. The glucose level in the range of 3.3-5.5 mmol / L is considered normal (normoglycemia), less than 3.3 mmol / L is low (hypoglycemia), elevated levels are 5.5-8.3 mmol / L (hyperglycemia) and more than 8.3 mmol / L (diabetes). With age, the normal glucose level shifts to the range of 4.1-6.0 mmol / L. Normoglycemia indicates that there is currently no likelihood of diabetes mellitus development. With hyperglycemia, there is a predisposition to diabetes (prediabetes). The risk of general mortality and case fatality from stroke and myocardial infarction increases. The glucose concentration of more than 8.3 mmol / l indicates the necessity to rule out or confirm insulin-dependent (type I) or non-insulin-dependent (type II) diabetes mellitus and indicates the necessity for additional studying methods.

[0264] Symptoms of the high blood glucose level (hyperglycemia) include:

[0265] - frequent urination;

[0266] - thirst;

[0267] - blurred vision;

[0268] - fatigue;

[0269] - slow healing of wounds.

[0270] Symptoms of the high blood glucose level (hyperglycemia) include:

[0271] - anxiety;

[0272] - heart palpitations;

[0273] - sweating;

[0274] - trembling;

[0275] - gnawing hunger;

[0276] - confusion mental state.

[0277] Possible causes of a physiological increase in a blood glucose level:

[0278] - sedentary lifestyle;

[0279] - high-carbohydrate food ration;

[0280] - drinking of insufficient amount of water;

[0281] - inflammatory process in body;

[0282] - intake of certain medications (neuroleptics, steroids);

[0283] - a women menstrual period.

[0284] In patients with non-insulin-dependent diabetes mellitus, mortality from malignancies (cancer), especially of the colorectal region, increases with the elevated glucose level. An increase in the blood glucose level always indicates the presence of a long period of hyperglycemia and an increased risk of complications in the form of retinopathy, nephropathy, polyneuropathy, micro- and macroangiopathy. A patient suffering from hyperglycemia should strive to achieve the normal glucose level of 3.3-5.5 mmol / L. However, this is not always possible. In such cases, a goal object of therapy is considered to reduce the glucose level to 6-7 mmol / L. If this goal object has been achieved, then it can be stated that sugar disease is well enough compensated, the likelihood of the consequences of hyperglycemia in the form of all kinds of complications is reduced to a minimum level.

[0285] Blood glucose testing is also performed on women with diabetes when planning pregnancy. It has been established that a high glucose level in six months before the onset of gestation and during the first trimester is directly dependent on the likelihood of various complications of pregnancy course. Strict control of a blood glucose concentration reduces the incidence of fetal malformations from 30-40% to 2%.

[0286] A low glucose level (less than 3.3 mmol / L) can be detected in an insulin-producing pancreatic tumor (insulinoma). The reason for the decrease is frequent hypoglycemic conditions. A low glucose level is detected in adrenal insufficiency and some rare hereditary diseases (Gers and Forbes diseases, hereditary fructose intolerance). In addition, the following relate to possible causes of the physiological decrease in a blood glucose level:

[0287] - excessive physical activity;

[0288] - abstinence from food (starvasion);

[0289] - long-term diet;

[0290] - use of alcoholic beverages.

[0291] Thus, the capability to accurately estimate blood glucose and glycated hemoglobin levels by using the wearable device according to the present invention facilitates monitoring a user’s health state.

[0292] Although the invention has been described with some illustrative embodiments, it should be understood that the invention essence is not limited to these specific embodiments. In contrary, the invention essence is intended to include all alternatives, modifications, and equivalents that can be included within the spirit and scope of the claims.

[0293] In addition, the invention includes all equivalents of the claimed invention, even if the claims will be modified in a process of consideration.

Claims

1.An optical sensor for determining a concentration of blood components, the optical sensor comprising:an emitter configured to emit short-wave infrared (SWIR) radiation,an insulator with a transparent channel transparent to the SWIR radiation, wherein the emitter is disposed on top of the insulator such that the SWIR radiation is emitted into a biological tissue through the transparent channel,an optical concentrator made from a material with a refractive index of 1.7 or more, anda photodetector disposed in an upper part of the optical concentrator, whereinthe optical concentrator and the insulator are arranged such that the optical concentrator covers the insulator, and a ring-shaped gap is formed between an outer surface of the insulator and a surface of the optical concentrator to form a detection region for radiation scattered from the biological tissue,the optical concentrator is made in a rotation figure shape and is configured to collect and to focus the radiation, which is scattered from the biological tissue and enters from the detection region into the ring-shaped gap, into the photodetector,the insulator and the optical concentrator are configured to contact with the biological tissue during operation of the optical sensor, andthe photodetector is optically matched with the upper part of the optical concentrator.2.The optical sensor according to claim 1, wherein the optical concentrator further includes a coating of which inner surface is reflective, wherein none of the coating is on a part of the optical concentrator being in contact with the biological tissue during the operation.3.The optical sensor according to claim 1 or 2, wherein the optical concentrator is made in a form of a spherical segment, a spherical layer, an ellipsoid segment or a flattened circular cone.4.The optical sensor according to claim 1 or 2, wherein the optical concentrator is made of at least two parts disposed on top of each other, each of which represents a rotation figure, wherein a rotation axis of all the parts is a rotation axis of the optical concentrator.5.The optical sensor according to any one of claims 1 to 4, wherein a material of the optical concentrator is silicon, a chalcogenide glass, or zinc sulfide.6.The optical sensor according to any one of claims 1 to 5, wherein the emitter is a light emitting diode (LED) or a laser diode and is configured to emit radiation with a wavelength in a range of 0.9-2.5 μm.7.The optical sensor according to any one of claims 1 to 6, wherein the insulator is made in a form of a cylinder having a cylindrical channel.8.The optical sensor according to any one of claims 1 to 7, wherein the photodetector is made on a basis of indium gallium arsenide (InGaAs), cadmium mercury telluride (HgCdTe), or indium antimonide (InSb).9.The optical sensor according to any one of claims 1 to 8, wherein a working surface of the photodetector is in a focal plane of the optical concentrator, andwherein the rotation axis of the optical concentrator passes through a center of a focal spot, and is perpendicular to the working surface of the photodetector.10.The optical sensor according to any one of claims 1 to 9, wherein the photodetector is adhered to the upper part of the optical concentrator with an optical glue.11.The optical sensor according to claim 10, wherein an antireflection coating is applied between the upper part of the optical concentrator and the optical glue.12.The optical sensor according to any one of claims 1 to 11, wherein the refractive index of the optical concentrator material is greater than 2.0.13.The optical sensor according to any one of claims 1 to 12, wherein the blood components are glucose and / or glycated hemoglobin.14.A wearable device comprising the optical sensor for determining a concentration of blood components according to any one of claims 1 to 13.15.The wearable device according to claim 14, further comprising a housing, a processor, a battery, a memory device, an input and output device and a communication module housed in the housing,wherein the memory device is configured to store an information, the input and output device is configured to display the concentration of a blood components, andwherein the communication module is configured to communicate with a remote server and / or a cloud storage.

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