Glucose Water Solution Research Articles

Near-infrared spectroscopy for glucose detection in aqueous solution

This work presents a near-infrared spectroscopy-based technique to measure the glucose concentration in an aqueous solution. A near-infrared light source sends optical energy through a glucose-water solution. The energy transmitted through the aqueous solution is received by a photodetector and a conditioning circuit that includes an operational amplifier and a low-pass filter to remove high-frequency noise. The received light intensity converted to DC voltage is found to be inversely proportional to the glucose concentration in the aqueous solution. The experimental results for glucose concentration in the range of 0–4000 mg/dL confirm the expected theoretical behavior. The sensitivity of the system is 26.25 μV/mgdL-1. The proposed glucose detection system is a promising tool for monitoring glucose levels in various industries, including food and beverage quality and healthcare.

EFFECT OF MOLECULAR ENVIRONMENT ON PROTEIN RUBBER PROPERTIES

ABSTRACTMany natural organisms use “protein rubbers” to store and release an imposed strain energy with high efficiency to make motion easier. Protein rubbers exist in a complicated environment surrounded by water and other molecules such as sugars, implying that amino acid composition and its environment are important in protein rubber behavior. Gelatin, the hydrolysis product of animal collagen, is hydrated or “plasticized” with water, ethylene glycol, glycerol, corn syrup, and aqueous solutions of sorbitol, glucose, and fructose. The rubber formed is “dry”, that is, is not fully immersed in liquid, and has the appearance and feel of a soft rubber band. The mechanical and thermodynamic behavior of each rubber is characterized with low strain dynamic and high strain tensile experiments with good agreement between the two. Plasticized gelatin rubbers are incompressible and follow the neo-Hookean model for rubber elasticity up to moderate extension ratios. Higher molecular weight polyols with more hydrogen bond donors and acceptors create gelatin networks with lower crosslink density. Ethylene glycol–, glycerol-, sorbitol syrup–, and fructose syrup–plasticized gelatin rubbers have similar molecular relaxation mechanisms and are the most efficient rubbers when probed in the rubbery plateau region prior to approaching the glass transition. The other plasticizers have different molecular relaxation mechanisms that detract from the efficiency of energy storage and return that is not related to network formation but perhaps the individual solvation ability of each plasticizer.

Design and Experimental Validation of a Noninvasive Glucose Monitoring System Using RF Antenna-Based Biosensor

This article presents an end-to-end microwave-based system to detect the glucose level in aqueous solutions through a noninvasive scheme. A microwave signal is generated and transmitted through the sample under test (i.e., glucose–water solution). The received signal is then conditioned using a low-noise amplifier (LNA), a bandpass filter (BPF), and an RF detector. The change in the dc output voltage on the receiver side is used as a new way to detect the glucose level. The proposed glucose sensor is implemented using two RF microstrip patch antennas that resonate at 5.7 GHz and are fabricated using an FR-4 substrate. The design specifications of the sensing antennas are thoroughly studied and presented. The system is verified experimentally using glucose–water testing samples. The experimental results confirm the correlation between the glucose concentration and the dc output voltage for a concentration range of 0–5000 mg/dL. The effect of the transmitted power level on the system performance is also investigated. Finally, the proposed system is compared with the state-of-the-art systems reported in the literature.

High Sensitivity Detection Method for Liquid Concentrations Based on Coupled Microwave Resonators

This paper presents a new measurement method for liquid concentrations based on two inductively coupled resonators with enhanced sensitivity compared with traditional methods in microwave frequency ranges. The equivalent circuit of the coupled resonators is proposed with its eigenequation having three eigenfrequencies derived. We demonstrate that, compared to a single resonator, the sensitivity of the center eigenfrequency shift to the changed capacitance increases by an order of magnitude if the product of the coupling coefficient and Q-factor of the second resonator is close to unity. In addition, that the reflection magnitude changes with the varied capacitance is also giant under impedance matching condition at the down and up eigenfrequencies. Based on the proposed method, a sensor composed of an open quarter-wavelength microstrip-line resonator (OQMR) and a split ring resonator (SRR) for detecting concentrations of water-glucose solutions is designed. By adjusting the sample volume and the distance between two resonators, different coupling coefficients and Q-factors can be attained, enabling marked increases in the sensitivity. Experimental and simulated results show that the sensitivity of the center eigenfrequency shift and of the reflection magnitude change to the concentration are as high as 9.4 MHz/(mg/mL) and 5.41 dB/(mg/mL), respectively, both of which are excellent compared to other sensors.

A Highly Sensitive Molecularly Imprinted Polymer (MIP)-Coated Microwave Glucose Sensor.

A novel, low-cost, sensitive microwave microfluidic glucose detecting biosensor incorporating molecularly imprinted polymer (MIP) is presented. The sensing device is based on a stub resonator to characterize water glucose solutions. The tip of one of the stubs is coated with MIP to increase the selectivity of the sensor and hence the sensitivity compared to the uncoated or to the coated with non-imprinted polymer (NIP) sensor. The sensor was fabricated on a FR4 substrate for low-cost purposes. In the presence of the MIP, the sensor loaded with a glucose solution ranging from 50 mg/dL to 400 mg/dL is observed to experience an absorption frequency shift of 73 MHz when the solutions flow in a microfluidic channel passing sensing area, while the lower limit of detection (LLD) of the sensor is discovered to be 2.4 ng/dL. The experimental results show a high sensitivity of 1.3 MHz/(mg/dL) in terms of absorption frequency.

Novel Microwave Frequency-Locked-Loop-Based Sensor for Complex Permittivity Measurement of Liquid Solutions

In this article, a new microwave frequency-locked-loop (FLL)-based sensor is proposed for complex permittivity measurement of liquid solutions. An interdigitated electrode split-ring resonator (IDESRR) is embedded in the FLL and used as a sensing device to distribute electric field in the near-field region and sense the permittivities of the liquid solutions with different concentrations. When the test liquid is placed on the IDESRR, a deviation will be introduced to the resonance frequency based on the perturbation theory. This frequency deviation accompanies a corresponding phase shift in the FLL operating frequency. The phase-shifted signal then leads the FLL to output a frequency-modulated (FM) signal, whose frequency deviation depends on the concentration level of the test liquid. The quadrature frequency discriminator is used to demodulate this FM signal and transfer it into dc voltages, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$V_{I}$ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$V_{Q}$ </tex-math></inline-formula> . Reference liquids with known permittivities are used to calibrate the proposed sensor and relate the measured voltages to the dielectric constant and loss tangent. In this article, the water–ethanol mixtures and water–glucose solutions are used as the test liquids to evaluate the measurement performance of the proposed FLL-based permittivity sensor. The measured results obtained using the proposed sensor agree very well with those obtained using the commercial dielectric probe. Moreover, since the proposed permittivity sensor has the benefits of a simple system architecture, high sensitivity, and not requiring a vector network analyzer (VNA), it has great potential to be developed as a new type of biomedical sample sensor.

Optical Identification of Parenteral Nutrition Solutions Exploiting Refractive Index Sensing

Parenteral artificial nutrition (PAN) is a lifesaving treatment for a large population of patients affected by different diseases, and it consists of intravenous injection of nutritive fluids by means of infusion pumps. Wrong PAN solutions are, unfortunately, often administered, thus threatening the patients’ well-being. Here, we report an optofluidic label-free sensor that can distinguish PAN solutions on the basis of their volumetric refractive index (RI). In our system, a monochromatic light beam, generated by a laser diode, travels obliquely through a transparent, square-section polystyrene channel, is then back-reflected by a mirror, and finally exits the channel in a position that depends on the filling fluid RI. The displacement of the output light spot ΔXexperim is easily detected with a linear, 1-D position sensitive detector (PSD). We initially calibrated the sensor with water-glucose solutions demonstrating a sensitivity S = ΔXexperim/Δn = 13,960 µm/RIU. We then clearly distinguished six commercial PAN solutions, commonly administered to patients. To the best of our knowledge, this is the first reported healthcare sensing platform for remote contactless recognition of PAN fluids, which could be inserted into infusion pumps to improve treatment safety, by checking the compliance to the prescription of the fluid actually delivered to the patient.

I-design terahertz microfluidic chip for attomole-level sensing

We developed a nonlinear optical crystal-based compact terahertz (THz)-microfluidic chip with several I-design meta-atoms for attomole (amol)-level sensing of trace amounts of solution samples. The I-design meta-atom consists of a metallic strip with a micometer-sized gap sandwiched by other metallic strips. It is periodically arrayed in a row of 1 × 5 units. A point THz source locally generated by optical rectification at the irradiation spot of a femtosecond-pulse laser beam induces a tightly confined electric-field mode at the gap regions and modifies the resonance frequency when a microchannel fabricated along the space between the metallic strips is filled with solutions. Using this chip, we could detect minute changes in the concentration of trace amounts of ethanol- and glucose-water solutions and mineral water by measuring the shift in the resonance frequencies. We succeeded in detecting 472 amols of solutes in solutions less than 100 picoliters using an effective sensing area of 0.10 λ THz × 0.57 λ THz, which indicates an improvement of approximately one order of magnitude compared to the performance of existing chips. This technique compactifies THz-microfluidic chips with high sensitivity and would accelerate the development of microfluidics integrated with THz technology, such as lab-on-a-chip devices and THz micro total analysis systems.

Spectral Methods for Response Enhancement of Microwave Resonant Sensors in Continuous Non-Invasive Blood Glucose Monitoring.

In this paper, the performance of three recent algorithms for the frequency-response enhancement of microwave resonant sensors are compared. The first one, a single-step algorithm, is based on a couple of direct-inverse Fourier transforms, giving a densely sampled response as a result. The second algorithm exploits an iterative procedure to progressively restricts the frequency response. The final one is based on the super-resolution MUSIC algorithm. The comparison is carried out through a Monte Carlo analysis. In particular, synthetic signals are firstly exploited to mimic the frequency response of a resonant microwave sensor. Then, experimental data collected from water-glucose solutions are adopted as validation test for potential applications in noninvasive blood-glucose monitoring.

A Forward-Backward Iterative Procedure for Improving the Resolution of Resonant Microwave Sensors

This paper sets out a method for improving the resolution of resonant microwave sensors. Usually, the frequency response of these devices is associated with a low quality factor, and consequently with a low resolution in terms of tracking capacity of the resonance frequency shift. Furthermore, since only a finite number of samples can be acquired during the measurement process, the “true” resonance frequency may not be included in the set of acquired data. In order to have an accurate estimate of the resonance frequency, high performance systems with very fine frequency sampling are thus required. To limit these drawbacks, an iterative algorithm is presented which aims to refine the response of resonant microwave sensors by means of a suitable post-processing. The algorithm evaluation is first carried out on synthetic data, and then applied on experimental data referring to a practical scenario, which is inherent to return loss measurements performed by a microwave patch antenna immersed in a water-glucose solution with different concentrations.

Whispering Gallery Mode Resonator Temperature Compensation and Refractive Index Sensing in Glucose Droplets.

Among the different types of photonic sensor devices, optical whispering gallery mode resonators (WGMRs) have attracted interest due to their high level of sensitivity, small size, and ability to perform real-time temperature measurements. Here we demonstrate the applicability of temperature measurements using WGMR in both air and liquid environments. We also show that WGMR allowed measurements of the refractive index variations in an evaporating glucose–water solution droplet. The thermal tuning of WGMR can be reduced by coating WGMRs with a thin layer of polymethyl methacrylate (PMMA). Dip-coating the silica microsphere multiple times significantly reduced the resonance shift, partially compensating for the positive thermo-optical coefficient of silica. The shift direction changed the sign eventually.

Phase sensitive optical rotation measurement using the common-path heterodyne interferometry and a half-wave plate at a specific azimuth angle

We proposed a new method for small optical rotation measurement. The method is based on the use of a half-wave plate and the high-stability common-path heterodyne interferometry. When the azimuth angle is at 22.5° of a half-wave plate, the phase has a distinct change caused by the small polarization rotation of the test beam. The optical rotation can be obtained from the relationship between the phase and the azimuth angle of the wave plate. The resolution of polarization rotation measurement can achieve 1.6 × 10−5 degree/mm and the detection sensitivity on circular birefringence of glucose-water solution can be up to δ|nr − nl | = 5.6 × 10−11.

Study of Qᵤ-Based Resonant Microwave Sensors and Design of 3-D-Printed Devices Dedicated to Glucose Monitoring

A low-cost, additively manufactured, biocompatible glucose sensor based on the changes in the unloaded quality factor ( $Q_{\mathbf {u}}$ ) with a single split-ring resonator is presented. An exposition of the fundamentals for the use of the $Q_{\mathbf {u}}$ as sensing parameter with microwave planar resonant sensors is shown. The convenience of this sensing parameter is analyzed from the theoretical point of view, and practical design and optimization guidelines are inferred with a special focus on the optimization of $Q_{\mathbf {u}}$ sensitivity to glucose concentration. For practical demonstration and experimental assessment, a novel inverted microstrip configuration is considered, built upon a customized structure made with a certified biocompatible material thanks to 3-D printing techniques, which is aimed to provide for a stronger interaction between the electromagnetic fields and the sample. Two metallization solutions are investigated, yielding devices operating at 4.50 and 4.62 GHz, with operating $Q_{\mathbf {u}}$ of 16.36 and 22.00, relative $Q_{\mathbf {u}}$ sensitivities of 1.377 and 2.727, $Q_{\mathbf {u}}$ sensitivities to glucose content within the physiological range of $0.3\times 10^{-3}$ per mg/dL and $0.6\times 10^{-3}$ per mg/dL, sensing areas of approximately $11.7\times8.8$ mm2 and total structure sizes of 950.0 $\times 35.0\times3.5$ mm3. The devices show good performance with water–glucose solutions covering a wide range of concentrations, involving physiological as well as industry-related ones.

Surface Plasmonic Feature Microwave Sensor With Highly Confined Fields for Aqueous-Glucose and Blood-Glucose Measurements

This article proposes a method of using a highly efficient spoof surface plasmon polariton (SSPP) endfire sensor for monitoring of aqueous glucose solutions and on-body glucose measurements. Occupying an area of around (52 mm $\times24$ mm), the proposed sensor radiates an endfire beam into a glucose water solution with a substantially reduced effective aperture. At the coplanar waveguide (CPW) port of the sensor, a pair of triangular ground planes was added to suppress the sidelobes, which have been proven to be counter-productive in glucose sensing. The slow-wave nature of the proposed SSPP endfire sensor has further advantageously enabled the glucose concentrations to be measured with an increased sensitivity. The guiding body of the sensor was designed to simulate an electromagnetic beam propagating in a dense dielectric medium with a group velocity comparable to the phase velocity of light propagating in a glucose solution. Consistent with the results of our analysis, the experimental results of this work revealed that the gradual transition of slow electromagnetic wave from the SSPP endfire sensor to the glucose water solution has successfully enabled the glucose concentrations of a solution to be measured and displayed in the form of highly observable resonant frequency shifts in S 11 parameters. The proposed design has achieved a high sensitivity of 150 MHz/mgmL−1 during on-body measurements.

Precise Noninvasive Estimation of Glucose Using UWB Microwave With Improved Neural Networks and Hybrid Optimization

A precise noninvasive estimation method for blood glucose concentration is proposed using an improved neural network model and hybrid optimization (INNHO) method. This method consists of a modified back propagation neural network model and a hybrid least squares-random sample consensus algorithm for accuracy optimization. The S-parameter and frequency data measured by ultrawide band (UWB) microwave are employed as the input data for glucose concentration estimation. Before model training, a preprocess technique is put forward to select the data range and generate relative S-parameters from a reference baseline. In this study, a three-layer earlobe model is built to theoretically analyze the wave propagation and elucidate the relationship between the S-parameters and the glucose concentration. Based on the model, the sensitivity and uncertainty of the system are investigated and the suitable frequency range is determined. During the measurement, the S-parameters of UWB signals in the 0.2-4 GHz range are measured and the concentration of glucose water solutions from 20 to 500 mg/dL is investigated. The results show that using the proposed preprocessing method and neural networks, the estimation accuracy can be significantly improved. Then, the hybrid optimization algorithm is able to further enhance the estimation accuracy. The final estimations for solutions of unknown concentrations agree well with the true concentration values. The relative error ranges from 0.31% to 4.64% and the root-mean-square error of the final results is 5.5237 mg/dL, demonstrating that the proposed method is effective and precise for glucose concentration estimation.

A Tunable High-Q Microwave Detector for On-Column Capillary Liquid Chromatography

We report a novel approach to ultrahigh quality factor ( $Q$ ) in the split-ring resonator with an active feedback loop, which utilizes a phase shifter to tune equivalent negative resistance for accurate loss compensation. Based on the proposed technique, a microwave detector is designed for on-column liquid chromatography. With lossy solvents loaded, the measured $Q$ is as high as $4.0\times 10^{6}$ at ~ 3.89 GHz. We demonstrate the highly sensitive and contactless measurement of glucose–water solution in a capillary tube under stop–flow and plug–unplug modes, respectively. With the stop–flow mode, different concentrations between 40 and 150 mg/dL are measured, which covers the normal blood-glucose levels. The minimum detectable quantity of glucose is ~18.8 ng with an effective sample volume of ~47 nL. The plug–unplug mode provides fast and flexible sampling and analysis. Further investigations are required for quantification of material-under-test permittivity and promotion of sensitivity.

An In-Vitro Study of Wireless Passive Inductor Integrated Cavity for Future long-term Implantable resonator-based Glucose Monitoring.

In this paper, a label-free biosensor is developed for monitoring the glucose level in the solution. A wireless passive inductor integrated cavity (IIC)-based biosensor is studied. The proposed IIC consists of a passive spiral inductor integrated cavity resonator for continuous monitoring of capillary blood glucose. The proposed method is based on the cavity perturbation theory, where the solution with different glucose levels perturbs and interacts with the passive IIC-based biosensor. The variation in the effective permittivity εeff and permeability μeff of the cavity resonator due to different glucose levels changes the equivalent capacitance and inductance of the proposed IIC. In turn, the corresponding resonance frequency changes. The in-vitro measurements are performed on deionized water glucose solutions of various glucose concentrations within the range of 75 mg/dL to 250 mg/dL. The results demonstrate that the sensor's resonant frequency increases with the increase in glucose level in the solution with a sensitivity of 32 kHz/mgdL-1.

Electrical Properties of Porous Silicon as a Biosensor Material

The electrical properties of porous silicon nanocomposites with various glucose solutions were studied. The current-voltage characteristics (I–V) of glucose solutions in water and tear fluid, as well as porous silicon samples of various porosities saturated with these solutions were measured. The porosity and glucose content in the pores were determined by the gravimetric method. Measurements of the I–V characteristics and photoconductivity of nanocomposites showed that their electrical conductivity appreciably depends on the glucose content in solutions .

Highly Sensitive Closed Loop Enclosed Split Ring Biosensor With High Field Confinement for Aqueous and Blood-Glucose Measurements

This paper presents a highly sensitive closed loop enclosed split ring biosensor operating in microwave frequencies for measuring blood glucose levels in the human body. The proposed microwave glucose biosensor, working on the principle of high field confinement and concentrated energy, has been tested using both in-vitro and in-vivo methods. This principle allows the sensor to concentrate energy at the surface which results in improved accuracy of measurements. For in-vitro measurements, the biosensor has been tested using de-ionized water glucose solutions of different concentrations. The miniaturized micrometer scale biosensor is fabricated over a thin Si-substrate using photolithographic technique. The biosensor has been designed in a way to operate at desired microwave frequencies. Highly confined fields and concentrated energy inside the closed loop line containing the split ring resonators are responsible for the sensitivity enhancement. This new biosensor has obtained a high sensitivity of 82 MHz/mgmL−1 within the clinical diabetic range during in-vivo testing over the human body. In addition, the subjects (undergoing experiments) steady state has been continuously monitored throughout the experiment which helps in improving the accuracy of the results. The proposed biosensor has further obtained a low detection limit of <0.05 wt.% and can be useful for continuous non-invasive blood glucose monitoring.

Structure or Exchange? On the Feasibility of Chemical Exchange Detection with Balanced Steady-State Free Precession in Tissue - An In Vitro Study.

Balanced steady-state free precession imaging has recently been suggested for chemical exchange detection (bSSFPX). The objective of this work is to investigate the contributions of microstructural, chemical shift and chemical exchange effects to the asymmetry of the bSSFP profile at field strengths of 3 T and 9.4 T. To this end, in vitro bSSFPX experiments are performed for a range of repetition times and flip angles in glucose water solutions with different MnCl2 concentrations and tissue homogenates obtained from the brainstem of pig brains. The experimental results are compared to multi-pool Bloch-McConnell simulations. Additionally, the influence of white matter tract geometry is analyzed ex vivo in pig brain hemispheres measured at two different angles with respect to B0 . The detectable bSSFP profile asymmetry in glucose solutions with tissue-like relaxation times and white matter homogenates was consistent with Bloch-McConnell simulations but relatively small. In intact white matter tracts, the asymmetry was dominated by structural effects with a strong dependency on tract orientation relative to B0 . In tracts perpendicular to B0 , the asymmetry was ≈ 3-4 times higher than in the homogenates, thus barely affected by chemical exchange effects. In conclusion, chemical exchange-related bSSFP profile asymmetries are detectable in tissue homogenates, however, the observed asymmetry level is generally low and prone to confounding structural effects rendering in vivo chemical exchange detection with bSSFP challenging in the brain.