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This study presents a biosensor working at a frequency of 3.5 GHz, which is designed as a square ring metamaterial resonator. This study aimed to evaluate the impact of blood amount on the metamaterial-based resonator sensor's sensitivity. The structure was constructed using Rogers-RT5880 material, with an overall area of 85.71 mm × 85.71 mm2. The simulation of the design involved modelling the blood samples using Debye 1st-order equations. The empirical results observed a noticeable shift towards a lower frequency range in the response and changes in the magnitude, corresponding to an increase in the blood sample's glucose concentration and thickness. Following this, the experiment was designed to corroborate the simulated results. The sensor achieved the highest sensitivity of 0.23 dB per 100 mg/dl change in glucose level when the thickness of blood was 0.1 mm. It was concluded from the results that the increase in the volume of blood increases the sensor's sensitivity. However, a trade-off mark is necessary in which an optimum sensitivity is achieved with blood volume as minimum as possible so that a noninvasive biosensor can be designed. [ABSTRACT FROM AUTHOR]

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

Non-invasive glucose determination provides major advantages in health monitoring and protection. It enables widespread point-of-care testing, which is affordable, sensitive, specific, rapid and equipment-free. This work reports on the development and analytical performance of a colorimetric biosensor in detecting glucose in human urine. Highly porous polyamide microparticles were synthesized as the support for the glucose oxidase (GOx) and horseradish peroxidase (HRP) dyad, which was immobilized randomly or consecutively—first HRP and then GOx. The latter system was superior, as GH@PA-C showed much higher activity than the random system, and it was used to prepare the biosensor, along with the 3,3′,5,5′-tetramethylbenzidine chromogen. When in contact with urine, the biosensor displayed a strict linear correlation between the color difference and the glucose concentration in urine in the range of 0.01–3.0 mM, as established by the CIELab image processing algorithm and UV-VIS measurements. The biosensor acted in 20 s and had a detection limit of 30.7 µM in urine, high operational activity at pH = 4–8 and unchanged detection performance after 30 days of storage. Its unique feature is the possibility of multiple consecutive uses without the serious deterioration of the recovery and dispersion values. These characteristics can open the way for new routines in non-invasive personal diabetes detection. [ABSTRACT FROM AUTHOR]

The spectral properties of the molecules depend on the matrix in which the interactions with other molecules inside the matrix affect the vibrational and rotational modes of the molecule. In this study, an absorption-based system was designed to show how the absorbance properties of the glucose change in polyacrylamide (PAAm) hydrogel when compared with water. The measurements were performed at different wavelengths; 960 nm, 1450 nm, 1550 nm, and 1950 nm and it was observed that the system is sensitive to glucose at the wavelengths of 1450 and 1950 nm in PAAm hydrogel, whereas it is only sensitive at 1450 nm in water which is due to the high absorbance of water at 1950 nm. In PAAm hydrogel, water molecules mostly gather around the polymer chains via electrostatic interactions and the absorbance of water decreases which results in an increasing absorbance of glucose. According to the results, the responsivity of the system at 960 and 1550 nm, which are the wavelengths commonly used in LED-based systems for measuring glucose in literature, is not high enough for reliable glucose measurements when compared with 1450 and 1950 nm. [ABSTRACT FROM AUTHOR]

Conventional glucose testing methods require the analysis of a droplet of blood from the patient's finger, which is painful and inconvenient. Such a one-time method carries an infectious risk and is not suitable for the long-term, daily continuous glucose monitoring often required today. Continuous glucose monitoring can provide timely information about the success of therapy during treatment and make appropriate adjustments. Currently, there is no single method of continuous monitoring. Currently, there is no single method of continuous monitoring. Glucose concentrations, although different kinds of non-invasive sensors have been developed for such monitoring on different physical principles. Such devices can provide painless, risk-free, inexpensive and frequent testing. This article discusses recent advances in non-invasive glucose control techniques. [ABSTRACT FROM AUTHOR]

Diabetes is a serious health condition that requires patients to regularly monitor their blood glucose level, making the development of practical, compact, and non-invasive techniques essential. Optical glucose sensors—and, specifically, NIR sensors—have the advantages of being non-invasive, compact, inexpensive, and user-friendly devices. However, these sensors have low accuracy and are yet to be adopted by healthcare providers. In our previous work, we introduced a non-invasive dual-channel technique for NIR sensors, in which a long channel is utilized to measure the glucose level in the inner skin (dermis) layer, while a short channel is used to measure the noise signal of the superficial skin (epidermis) layer. In this work, we investigated the use of dual-NIR channels for patients with different skin colors (i.e., having different melanin concentrations). We also adopted a Monte Carlo simulation model that takes into consideration the differences between different skin layers, in terms of blood content, water content, melanin concentration in the epidermis layer, and skin optical proprieties. On the basis of the signal-to-noise ratio, as well as the sensitivities of both the epidermis and dermis layers, we suggest the selection of wavelengths and source-to-detector separation for optimal NIR channels under different skin melanin concentrations. This work facilitates the improved design of a compact and non-invasive NIR glucose sensor that can be utilized by patients with different skin colors. [ABSTRACT FROM AUTHOR]

Electromagnetic waves still show a great interest in non-invasive blood glucose detection (BGD). Near infrared (NIR), which is heavily used for this purpose, suffers due to cost, low absorption in biological chromospheres, and stratum corneum, and accuracy. One of the candidates that has not been widely investigated for BGD is visible laser light. Compared to NIR, the refractive index of red laser light is more sensitive to the variations in glucose level concentration resulting in faster response times. Red laser light also demonstrates both higher linearity and accuracy for BGD. On the other hand, a visible laser source is essential to realize low-cost sensor devices. The difficulty in using red laser for BGD is its low penetration depth. Long range surface plasmon resonance (LRSPR) can considerably improve the penetration depth. In this paper we designed and simulated with finite difference time domain (FDTD) a fingertip touch based non-invasive glucose sensor with LRSPR using a visible laser diode (LD) in an insulator-metal-insulator (IMI) structure coated onto a glass prism employing the matrix method. The results show that a symmetric design of SiO2-Au-SiO2 (420 nm - 50 nm - 420 nm) is necessary for achieving better sensitivity. Besides, a considerable improvement in the SPR dip for sensing application was observed when BK7 is used as a glass material. The detection limit and the sensitivity of detection of the proposed sensor are calculated and found to be 3.1 mM and 0.0139 o/mg/dl, respectively. The simulated model concludes a great potential towards the fabrication of a low cost, non-invasive glucose sensor based on visible laser light. [ABSTRACT FROM AUTHOR]

Due to the poor conductivity of Fe based, Cu based and Co based electrode materials commonly used in the electrochemical detection of glucose, and the uneven stirring and poor conductivity of the traditional preparation method based on glassy carbon electrode. In order to solve the above problems, in this work, CdIn2O4 with high electrical conductivity was directly grown on three-dimensional (3D) Ni foam to prepare electrode materials for non-enzymatic glucose sensors. CdIn2O4 nanoparticles is prepared from cadmium acetate and indium nitrate hydrate in benzyl alcohol by non-aqueous sol–gel method. The electrocatalytic oxidation performances of CdIn2O4 electrode material for non-enzymatic glucose are studied. The results show that the proposed CdIn2O4 electrode material has good electrochemical properties and sensing performance for glucose detection. The electrochemical response of CdIn2O4 electrode material to glucose is recorded that calibration plot for glucose concentrations ranging from 1.0 μM to 1.0 mM (R2 = 0.99), a limit detection of 0.08 μM, an excellent sensitivity of 3.2925 mA.mM−1.cm−2, a rapid response time of 1.58 s, a good selectivity and a good long-term stability. These demonstrate the significant potential of CdIn2O4 electrode material based on 3D Ni foam as non-enzymatic glucose sensors, which makes it possible to use it as a practical glucose detector. This work could introduce a new concept of nanoparticles modified electrode material grown directly on 3D Ni foam, thus a simple and reliable electrochemical glucose sensor platform is realized. This study was completed in 2019 in the school of materials and energy, Yunnan University. [ABSTRACT FROM AUTHOR]

A unique vapour transport cum glancing angle deposition (VT-GLAD) technique was employed to fabricate titanium dioxide (TiO2) nanowires (NWs). The NWs were grown and assembled to form the clusters. Both brookite (412) and rutile (002) phase for TiO2 was obtained from X-ray diffraction (XRD). The d spacing of ~ 1.37 Å was calculated from the transmission electron microscopy (TEM) of TiO2 NWs, which corresponds to (002) crystal plane. The silver (Ag) nanoparticles (NPs) on TiO2 NWs were grown using thermal evaporation cum GLAD technique. The presence of Ag NPs on the TiO2 NWs enhanced the photoconduction as compared to bare TiO2 NWs device. The maximum photosensitivity of the Ag NPs/TiO2 NWs based device was recorded ~ 1.6 times compared to the bare TiO2 NWs based device at − 2.5 V. The Ag NPs containing device was highly UV sensitive and maximum responsivity for the device was calculated to be ~ 2.3 A/W at 370 nm. The device also possessed high responsivity rejection (RR) ratio of ~ 6.5 between UV (370 nm) and visible (450 nm) light. The Ag NPs decorated TiO2 NWs based detector also showed response to white light. The different concentration of glucose into deionised (DI) water-based solution was detected precisely under white light illumination. The normalised (light/dark) detector current/glucose concentration value was decreased from ~ 0.19 to ~ 0.05 at − 2.5 V, with an increase in glucose concentration into the solution from 40 mg/dl to 200 mg/dl. [ABSTRACT FROM AUTHOR]

The prevalence of diabetes is increasing globally. More than 690 million cases of diabetes are expected worldwide by 2045. Continuous blood glucose monitoring is essential to control the disease and avoid long-term complications. Diabetics suffer on a daily basis with the traditional glucose monitors currently in use, which are invasive, painful, and cost-intensive. Therefore, the demand for non-invasive, painless, economical, and reliable approaches to monitor glucose levels is increasing. Since the last decades, many glucose sensing technologies have been developed. Researchers and scientists have been working on the enhancement of these technologies to achieve better results. This paper provides an updated review of some of the pioneering non-invasive optical techniques for monitoring blood glucose levels that have been proposed in the last six years, including a summary of state-of-the-art error analysis and validation techniques. [ABSTRACT FROM AUTHOR]

In this article, a biosensor composed of a single metamaterial asymmetric resonator is specifically designed for sensing the glucose level of 1 µL of solution. The resonator has two gaps, and one of them ends with a semicircle shape on which the glucose solution is placed. This design helps in confining the drops of glucose solutions in a specific area where the field is maximally confined in order to enhance the electromagnetic wave-matter interaction. Six samples of glucose solutions with concentrations that cover hypoglycemia, normal and hyperglycemia conditions that vary from around 41 to 312 mg/dL were prepared and examined by this biosensor. The resonance frequency redshift was used as a measure of the changes in the glucose level of the solutions. Without glucose solution, an excellent agreement between the measured and simulated transmission amplitude was observed. The increase in glucose concentrations exhibited clear and noticeable redshifts in the resonance frequency. This biosensor revealed a 0.9997 coefficient of determination, which implies an excellent prediction fitting model. More importantly, a sensitivity of 438 kHz/(mg/dL) was observed over the range of concentrations of the aqueous solution. [ABSTRACT FROM AUTHOR]