Noninvasive determination of blood constituents using an array of modulated laser diodes and a photoacoustic sensor head

Using photoacoustic laser spectroscopy, the noninvasive determination of blood constituents like hemoglobin and glucose is feasible. The aim of our investigations is the development of a sensor which is suitable for continuously noninvasive monitoring of blood glucose concentrations in diabetic patients. For this purpose a photoacoustic sensor head was developed and coupled via an optical fiber bundle to an array of 8 laser diodes emitting at various wavelengths in the near infrared region. Applying a special modulation scheme, the tiny changes of the absorption coefficient of whole blood caused by the variations of blood glucose concentrations could be measured. A resolution of 70 mg/dl was achieved, a value which is already close to the clinical requirements for a continuously working glucose sensor.     

Carbon nanotube enhanced mediator-type biosensor for real-time monitoring of glucose concentrations in fish

We have developed a mediator-type biosensor to rapidly monitor blood glucose concentrations in fish, which are an indicator of stress. Glucose oxidase was used to detect glucose concentrations and ferrocene was used to limit the effect of oxygen. We also improved the sensitivity and durability of the sensor for better performance. Single-walled carbon nanotubes were used to enhance sensor sensitivity. Affixing the carbon nanotubes (30 mg ml^-1) to the working electrode increased the sensor sensitivity to 61.9 mM nA^-1 mm^-2, twice the value for the sensor without single-walled carbon nanotubes. A fabricated mediator-type biosensor sensor was used to perform real-time in vivo measurements. The sensor was implanted into the interstitial fluid of a fish eyeball, and detection was transmitted to a personal computer by a wireless potentiostat. Continuous measurement of the glucose concentration was possible for 78 hours. Stress was artificially applied to the fish during the measurement, and the change of blood glucose concentrations were observed. Our proposed sensor is applicable for effectively monitoring stress in free-swimming fish.     

Novel Helmholtz-based photoacoustic sensor for trace gas detection at ppm level using GaInAsSb/GaAlAsSb DFB lasers

A new and compact photoacoustic sensor for trace gas detection in the 2-2.5 microm atmospheric window is reported. Both the development of antimonide-based DFB lasers with singlemode emission in this spectral range and a novel design of photoacoustic cell adapted to the characteristics of these lasers are discussed. The laser fabrication was made in two steps. The structure was firstly grown by molecular beam epitaxy then a metallic DFB grating was processed. The photoacoustic cell is based on a Helmholtz resonator that was designed in order to fully benefit from the highly divergent emission of the antimonide laser. An optimized modulation scheme based on wavelength modulation of the laser source combined with second harmonic detection has been implemented for efficient suppression of wall noise. Using a 2211 nm laser, sub-ppm detection limit has been demonstrated for ammonia.     

Infrared spectroscopic analysis of human interstitial fluid in vitro and in vivo using FT-IR spectroscopy and pulsed quantum cascade lasers (QCL): Establishing a new approach to non invasive glucose measurement

Interstitial fluid, i.e. the liquid present in the outermost layer of living cells of the skin between the Stratum corneum and the Stratum spinosum, was analyzed by Fourier transform infrared spectroscopy and by infrared spectroscopy using pulsed quantum cascade infrared lasers with photoacoustic detection. IR spectra of simulated interstitial fluid samples and of real samples from volunteers in the 850-1800cm(-1) range revealed that the major components of interstitial fluid are albumin and glucose within the physiological range, with only traces of sodium lactate if at all. The IR absorbance of glucose in interstitial fluid in vivo was probed in healthy volunteers using a setup with quantum cascade lasers and photoacoustic detection previously described. A variation of blood glucose between approx. 80mg/dl and 250mg/dl in the volunteers was obtained using the standard oral glucose tolerance test (OGT). At two IR wavelengths, 1054cm(-1) and 1084cm(-1), a reasonable correlation between the photoacoustic signal from the skin and the blood glucose value as determined by conventional glucose test sticks using blood from the finger tip was obtained. The infrared photoacoustic glucose signal (PAGS) may serve as the key for a non-invasive glucose measurement, since the glucose content in interstitial fluid closely follows blood glucose in the time course and in the level (a delay of some minutes and a level of approx. 80-90% of the glucose level in blood). Interstitial fluid is present in skin layers at a depth of only 15-50μm and is thus within the reach of mid-IR energy in an absorbance measurement. A non-invasive glucose measurement for diabetes patients based on mid-infrared quantum cascade lasers and photoacoustic detection could replace the conventional measurement using enzymatic test stripes and a drop of blood from the finger tip, thus reducing pain and being a cost-efficient alternative for millions of diabetes patients.     

Biosensor system for continuous glucose monitoring in fish

A biosensor system was developed for continuous estimation of blood glucose in fish. Because it is difficult to measure blood components in real-time due to decreased sensor output resulting from blood coagulation and coalescing blood proteins at the sensor placement site, we used the eyeball scleral interstitial fluid (EISF) as the site of sensor implantation. Evaluation of the relationship between EISF and blood glucose concentrations revealed that the blood glucose concentration correlated closely with the EISF glucose concentration (y = 2.2996 + 0.9438x, R = 0.960, n = 112). To take advantage of the close correlation between blood and EISF glucose, we prepared a needle-type enzyme sensor for implantation in the fish sclera using a flexible wire electrode. The sensor provided a rapid response, good linearity, and reproducibility. Continuous glucose monitoring could be carried out by implanting this needle-type glucose sensor onto the eye. The findings indicated that the glucose concentration increased with sensor output current over time, and that changes in the blood glucose were continuously reflected in the EISF. The glucose concentration was estimated based on the one-point or two-point calibration methods. The two-point calibration method yielded the most accurate glucose monitoring (blood glucose range of 70-420 mg dL⁻¹) over 160 min. Sensor-estimated glucose and whole blood glucose values were highly correlated (y = 0.4401 + 0.8656x, R = 0.958).     

Determination of blood glucose parameter from human blood serum by using a quartz crystal microbalance sensor coated with phthalocyanines compounds

Determining the blood glucose level is important for the prevention and treatment of diabetes mellitus. We developed a sensor system using Quartz Crystal Microbalance (QCM) to determine the blood glucose level from human blood serum. This study consists of two experimental stages: artificial glucose/pure water solution tests and human blood serum tests. In the first stage of the study, the QCM sensor with the highest performance was identified using artificial glucose solution concentrations. In the second stage of the study, human blood serum measurements were performed using QCM to determine blood glucose levels. QCM sensors were coated with phthalocyanines (Pcs) by jet spray method. The blood glucose values of 96 volunteers, which ranged from 71 mg/dL to 329 mg/dL, were recorded. As a result of the study, human glucose values were determined with an average error of 3.25%.     

New concept for the non-invasive determination of physiological glucose concentrations using modulated laser diodes

The detection of small absorption differences is one of the basic requirements for the non-invasive determination of blood substrates. As conventional spectrometers are limited in their detection capabilities of small absorption changes, semiconductor lasers are applied for this purpose. By using a special modulation scheme, physiological glucose concentrations could be successfully predicted. The results demonstrate the feasibility of using small and inexpensive laser diodes for the spectroscopic determination of glucose in aqueous solutions as a step towards a portable non-invasive glucose sensor for self- monitoring of diabetic patients.     

New concept for the non-invasive determination of physiological glucose concentrations using modulated laser diodes

The detection of small absorption differences is one of the basic requirements for the non-invasive determination of blood substrates. As conventional spectrometers are limited in their detection capabilities of small absorption changes, semiconductor lasers are applied for this purpose. By using a special modulation scheme, physiological glucose concentrations could be successfully predicted. The results demonstrate the feasibility of using small and inexpensive laser diodes for the spectroscopic determination of glucose in aqueous solutions as a step towards a portable non-invasive glucose sensor for self- monitoring of diabetic patients.     

Near-infrared diode laser wavelength modulation-based photoacoustic spectrometer

An inexpensive resonant photoacoustic spectrometer based on a low-power distributed feedback diode laser and wavelength modulation spectroscopy is developed. This sensor has been applied to the detection of acetylene (C2H2) using a properly designed photoacoustic cell operating on its second longitudinal mode. The minimum detectable limit of about 10 parts-per-million volume (signal to noise ratio=1) is achieved at atmospheric pressure, and the pressure and laser power linear dependence of the photoacoustic signal is also investigated. Moreover, in this paper we also describe some basic theory of gas photoacoustic spectroscopy.     

Dynamics of L-tryptophan in aqueous solution by simultaneous laser induced fluorescence (LIF) and photoacoustic spectroscopy (PAS)

An experimental system for measuring simultaneously photoacoustic (PA) and fluorescence signals is described. The simultaneous measurement of laser induced fluorescence and photoacoustic signals provide a suitable method for the study of different quenching phenomena occurring in fluorescent systems. In this paper we report tryptophan solvation dynamics in water using fluorescence and photoacoustic spectra recorded simultaneously by photoacoustic and fluorescence signals as functions of concentration, indicate that quantum yield is maximum at low concentrations. Also, the energy lost in the fluorescence path of tryptophan, due to different quenching phenomena like self quenching, Resonance energy transfer (RET), solvation relaxation, etc. is clearly seen from the photoacoustic signal intensity which increases as the fluorescence intensity decreases.     

Continuous glucose monitoring in interstitial fluid using glucose oxidase-based sensor compared to established blood glucose measurement in rats

Glucose monitoring is of importance for success of complex therapeutic interventions in diabetic patients. Its impact on treatment and glycemic control is demonstrated in large clinical trials. Up to eight blood glucose measurements per day are recommended. Notwithstanding, a substantial number of diabetic patients cannot or will not monitor their blood glucose appropriately. Considerable progress in control of disturbed metabolism in diabetic patients can be expected by continuous glucose monitoring. The aim of the study was to evaluate the performance of a new amperometric glucose oxidase-based glucose sensor in vitro and in vivo after subcutaneous implantation into rats.For in vitro testing current output of sensors was measured by exposure to increasing and decreasing glucose concentrations up to 472 mg dL⁻¹ over a time period of 7 days. After subcutaneous implantation of sensors into interscapular region of male rats glucose in interstitial fluid was evaluated and compared to glucose in arterial blood up to 7 days. Hyper- and hypoglycaemia were induced by intravenous application of glucose and insulin, respectively. Current of each implanted sensor was converted into glucose concentration using the first blood glucose measurement only.A change of current with glucose of 0.35 nA mg⁻¹ dL⁻¹ indicates high sensitivity of the sensor in vitro. The response time (90% of steady state) was calculated by approximately 60 s. Test strips for blood glucose measurement as reference for sensor readings was found as an appropriate and rapidly available method in rats by comparison with established hexokinase method in an automated lab analyzer with limits of agreement of +32.8 and −25.7 mg dL⁻¹ in Bland-Altman analysis. In normo- and hypoglycaemic range sensor readings in interstitial fluid correlated well with blood glucose measurements whereas hyperglycaemia was not reflected by the sensor completely when blood glucose was changing rapidly.The data given characterize a sensor with high sensitivity, long term stability and short response time. A single calibration of the sensor is required only in measurement periods up to 7 days. The findings demonstrate that the sensor is a highly promising candidate for assessment in humans.     

On-line monitoring of opaque liquids by photoacoustic spectroscopy

A new photoacoustic sensor system for on-line monitoring of highly concentrated and optical opaque liquid samples is presented. The dyeing of textiles is performed with highly concentrated dye solutions with concentrations ranging from 50 mg L(-1) up to 40 g L(-1). For process optimization and control of the wastewater, an on-line monitoring of the dye concentration is needed. Optical transmission measurements allow the determination of the dye concentration in a relatively small range. Samples with concentrations in the upper mg L(-1) and g L(-1) range have to be diluted before the measurement due to their optical opacity. Additionally, light-scattering particles have a strong effect on the transmitted light intensity. By photoacoustic spectroscopy, concentrations in condensed matter can be determined over several orders of magnitude. Furthermore, scattering particles do not generate any photoacoustic signal.     

Electrochemical Biosensor Based on Bienzyme and Carbon Nanotubes Incorporated into an Os‐complex Thin Film for Continuous Glucose Detection in Human Saliva

Saliva opens a door for noninvasive and painless glucose testing since it reflects changes in the body physiology of diabetic individuals as compared to healthy ones. In this paper, a unique, disposable saliva biosensor has been developed for accurate, low cost, and continuous glucose monitoring. The biosensor exhibits linear dependence of the catalytic current upon glucose bulk concentration over the 0.05–1.5 mM range (R=0.998). A detection limit of 0.003 mM can be calculated considering three times the standard deviation of the blank signal divided by the sensitivity of the sensor. The selectivity of the biosensor was evaluated by adding the interferent species of lactate, ascorbic acid and uric acid into in 0.5 mM glucose; the nearly negligible interference current indicates its good selectivity. The operational stability of the biosensor was measured in 1 mM glucose over a 2 h period (RSD=3.27 %). A clinical trial on real‐time noninvasive salivary glucose monitoring was carried out on 30 individuals by measuring subjects’ salivary glucose and blood glucose in parallel. The results show that there is a good correlation of glucose levels in saliva and in blood 2 h after breakfast. Thus, the disposable biosensor would be a potential alternative for continuous glucose detection in human saliva.     

Toward CMOS image sensor based glucose monitoring

Complementary metal oxide semiconductor (CMOS) image sensor is a powerful tool for biosensing applications. In this present study, CMOS image sensor has been exploited for detecting glucose levels by simple photon count variation with high sensitivity. Various concentrations of glucose (100 mg dL(-1) to 1000 mg dL(-1)) were added onto a simple poly-dimethylsiloxane (PDMS) chip and the oxidation of glucose was catalyzed with the aid of an enzymatic reaction. Oxidized glucose produces a brown color with the help of chromogen during enzymatic reaction and the color density varies with the glucose concentration. Photons pass through the PDMS chip with varying color density and hit the sensor surface. Photon count was recognized by CMOS image sensor depending on the color density with respect to the glucose concentration and it was converted into digital form. By correlating the obtained digital results with glucose concentration it is possible to measure a wide range of blood glucose levels with great linearity based on CMOS image sensor and therefore this technique will promote a convenient point-of-care diagnosis.     

Glucose Biosensor Based on Oxygen Electrode Part III: Long-Term Performance of the Glucose Biosensor in Blood Plasma at Body Temperature

Abstract

A potentially implantable glucose biosensor for continuous monitoring of glucose levels in diabetic patients has been developed. The glucose biosensor is based on an amperometric oxygen electrode and Glucose Oxidase immobilized on carbon powder held in a form of a liquid suspension. The enzyme material can be replaced (the sensor recharged) without sensor disassembly. Glucose diffusion membranes from polycarbonate (PC) and from polytetrafluorethylene (PTFE) coated with silastic are used.

Sensors were evaluated continuously operating in phosphate buffer solution and in undiluted blood plasma at body temperature. Calibration curves of the sensors were periodically obtained. The sensors show stable performance during at least 1200 hours of operation without refilling of the enzyme. The PTFE membrane demonstrates high mechanical stability and is little effected by long-term operation in undiluted blood plasma.     

Glucose Biosensor Based on Oxygen Electrode Part IV: In Vivo Evaluation of the Rechargeable Glucose Sensor

Abstract

A glucose monitoring system consisting of a pair of amperometric sensors: a glucose biosensor based on oxygen electrode and an oxygen sensor, two miniature potentiostats, an instrumentation amplifier and a data logger has been developed. The glucose sensor has linear response to the glucose concentration in vitro at 37°C up to 26 mM (480 mg/dL) in the phosphate buffer solution (pH 7.4), and linear range up to 21 mM (380 mg/dL) in undiluted bovine plasma. The system was evaluated in vivo with the sensors subcutaneously implanted in healthy mongrel dogs. During the implantation the system output was continuously recorded. The results of short-term subcutaneous implantation of the integrated system demonstrated good agreement between the glucose concentration measured by the biosensor and that obtained using standard glucose determination methods. The delay-time between the tissue glucose level (measured by the biosensor) and the blood glucose level (obtained by standard methodology) was 3 to 10 minutes. During the chronic implantation the biosensor was refilled in vivo. Rejuvenation of the sensor response after refilling was observed demonstrating the potential of such sensors for long-term implantation.     

Quantitative analysis in medicine using photoacoustic tomography

Photoacoustic imaging, or photoacoustic tomography, is a 2D or 3D optical imaging method based on localized optical absorption of pulsed laser radiation. By a spatially resolved detection of the following thermoelastic expansion, the local distribution of the absorption can be determined. The technique has been proven to have significant potential for the imaging of human and animal organs and single blood vessels, combining high contrast with good spatial resolution. The contrast is based on the specific optical absorption of certain components in the visible and near-infrared spectral range, for most applications of blood. Generally, the images represent the local distribution of blood in a qualitative or semiquantitative way. Although photoacoustic imaging is capable of revealing absolute and spatially resolved concentrations of endogenous (such as oxyhemoglobin and deoxyhemoglobin) or artificial (such as tumor markers) chromophores, only a very limited number of publications have dealt with this demanding task. In this report, the problems involved and possible solutions are reviewed and summarized.     

利用Cu0/多壁碳纳米管纳米复合物修饰玻碳电极快速非酶法检测葡萄糖和果糖(英文)

A nonenzymatic electrochemical sensor for glucose and fructose was fabricated that contained a glassy carbon electrode modified with a copper oxide (CuO)/multiwalled carbon nanotube (MWCNT) nanocomposite. The electrochemical properties of the CuO/MWCNT‐modified glassy carbon electrode were investigated. Two distinguishable anodic peaks were observed around 0.30 and 0.44 V corresponding to the oxidation of glucose and fructose, respectively, at the surface of the modified electrode. The detection limits for glucose and fructose were both 0.04 mmol/L. The sensor was used to simultaneously determine the concentrations of glucose and fructose in hydrolyzed sucrose samples, and to measure glucose in blood serum samples, demonstrating its potential as a nonenzymatic carbohydrate sensor.     

Glucose Biosensor Based on Oxygen Electrode. Part II: Long-Term Operational Stability of the Rechargeable Glucose Biosensor

Abstract

A potentially implantable glucose biosensor for measuring blood or tissue glucose levels in diabetic patients has been developed. The glucose biosensor is based on an amperometric oxygen electrode and immobilized glucose oxidase enzyme, in which the immobilized enzyme can be replaced (the sensor recharged) without surgical removal of the sensor from the patient. Recharging of the sensor is achieved by injecting fresh immobilized enzyme into the sensor using a septum. A special technique for immobilization of the enzyme on Ultra-Low Temperature Isotropic (ULTI) carbon powder held in a liquid suspension has been developed.

In vitro studies of the sensors show stable performance during several recharge cycles over a period of 3 months of continuous operation.

Diffusion membranes which ensure linear dependence of the sensor response on glucose concentration have been developed. These membranes comprise silastic latex-rubber coatings over a microporous polycarbonate membrane. Calibration curves of the amperometric signal show linearity over a wide range of glucose concentrations (up to 16 mM), covering hypoglycemic, normoglycemic and hyperglycemic conditions.

The experimental results confirm the suitability of the sensors for in vitro measurements in undiluted human sera.     

High sensitivity in gas analysis with photoacoustic detection

Introduction of a new type of pressure sensor has been shown to improve orders of magnitude the sensitivity of a photoacoustic measurement system using a black body radiation source. A new pressure sensor was developed to overcome the limitations in the capacitive microphone technology and to obtain ultimate sensitivity in photoacoustic gas detection when using low modulation frequency below 500 Hz. The pressure sensor is a cantilever-type microphone with interferometric measurement of the sensor displacement. By using conventional filter-type photoacoustic setup with the cantilever microphone and a black body radiation source, we obtained a detection limit in the sub-ppb range for methane gas with 100 s measurement time.