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.     

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.     

Multi-gas sensing based on photoacoustic spectroscopy using tunable laser diodes

Multi-hydrogenated compounds detection based on photoacoustic (PA) spectroscopy is reported. Three near-infrared semiconductor lasers are used with a resonant PA cell operated in its first longitudinal mode to monitor methane, water vapour and hydrogen chloride in the parts per million range. The design of our cell results from simulations performed in order to optimise its performances. Influence of the buffer gas on the PA signal has also been analysed, both theoretically and experimentally. A reduction of the PA signal of almost one order of magnitude has been observed between N(2) and He, which demonstrates the importance of the buffer gas in PA spectroscopy. Finally, detection limits of 0.5 ppm of CH(4) and 3 ppm of HCl has been achieved experimentally in nitrogen and an H(2)O sensitivity of 0.2 ppm has been estimated.     

Alcohol determination using an acoustic wave sensor

An acoustic wave methodology was developed to quantify alcohols in aqueous solutions. The frequency at minimum impedance of a bare quartz crystal in contact with ethanol solutions was found to be a suitable parameter to quantify ethanol. Ethanol in several Portuguese white wines was analyzed both by the proposed methodology and by the usual areometric method with no statistically significant differences (alpha = 0.05) in precision or accuracy of the results.     

Multienzyme electrochemical array sensor for determination of phenols and pesticides

The screen-printed four-electrode system was used as the amperometric transducer for determination of phenols and pesticides using immobilised tyrosinase, peroxidase, acetylcholinesterase and butyrylcholinesterase. Acetylthiocholine chloride was chosen as substrate for cholinesterases to measure inhibition by pesticides, hydrogen peroxide served as co-substrate for peroxidase to measure phenols. The compatibility of hydrolases and oxidoreductases working in the same array was studied. The detection of p-cresol, catechol and phenol as well as of pesticides including carbaryl, heptenophos and fenitrothion was carried out in flow-through and steady state arrangements. In addition, the effects of heavy metals (Cu²⁺, Cd²⁺, Fe³⁺), fluoride (NaF), benzene and dimethylsulphoxide on cholinesterase activities were evaluated. It was demonstrated that electrodes modified with hydrolases and oxidoreductases can function in the same array.The achieved R.S.D. values obtained for the flow system were below 4% for the same sensor and less than 10% within a group of five sensors. For the steady state system, R.S.D.s were approximately twice higher. One assay was completed in less than 6 min. The limit of detection for catechol using tyrosinase was equal to 0.35 and 1.7 μM in the flow and steady state systems, respectively. On the contrary, lower limits of detection for pesticides were achieved in the steady state system—carbaryl 26 nM, heptenophos 14 nM and fenitrothion 0.58 μM.     

Simultaneous determination of fermented milk aroma compounds by a potentiometric sensor array

The paper reports on the application of an electronic tongue for simultaneous determination of ethanol, acetaldehyde, diacetyl, lactic acid, acetic acid and citric acid content in probiotic fermented milk. The αAstree electronic tongue by Alpha M.O.S. was employed. The sensor array comprised of seven non-specific, cross-sensitive sensors developed especially for food analysis coupled with a reference Ag/AgCl electrode. Samples of plain, strawberry, apple-pear and forest-fruit flavored probiotic fermented milk were analyzed both by standard methods and by the potentiometric sensor array. The results obtained by these methods were used for the development of neural network models for rapid estimation of aroma compounds content in probiotic fermented milk.The highest correlation (0.967) and lowest standard deviation of error for the training (0.585), selection (0.503) and testing (0.571) subset was obtained for the estimation of ethanol content. The lowest correlation (0.669) was obtained for the estimation of acetaldehyde content. The model exhibited poor performance in average error and standard deviations of errors in all subsets which could be explained by low sensitivity of the sensor array to the compound. The obtained results indicate that the potentiometric electronic tongue coupled with artificial neural networks can be applied as a rapid method for the determination of aroma compounds in probiotic fermented milk.     

New improvements in methane detection using a Helmholtz resonant photoacoustic laser sensor: a comparison between near-IR diode lasers and mid-IR quantum cascade lasers

Atmospheric methane was detected by combining a photoacoustic (PA) sensor with several lasers emitting in both the near- and mid-infrared spectral ranges to check the achievable detection limits. The PA spectrometer is based on differential Helmholtz resonance. Near-infrared telecommunication-type laser diodes of increasing power, from Sensors Unlimited Inc. and Anritsu, were first used to scan the 2 nu(3) band of CH(4) near 1.65 microm. The best achieved detection limit is 0.15 ppm of methane at atmospheric pressure and with a 1s integration time. The PA sensor was then operated in conjunction with a quantum cascade laser from Alpes Lasers emitting near 7.9 microm on the nu(4) band of CH(4). The achieved detection limit is then of 3 ppb. The dramatic improvement in the detection limit obtained with the QC laser is due to the stronger optical power as well as to the capability of reaching the fundamental bands of methane lying in the mid-infrared spectral range.     

Potentiometric sensor array for the determination of lysine in feed samples using multivariate calibration methods

A potentiometric sensor array has been developed for the determination of lysine in feed samples. The sensor array consists of a lysine biosensor and seven ion-selective electrodes for NH4+, K+, Na+, Ca2+, Mg2+, Li+, and H+, all based on all-solid-state technology. The potentiometric lysine biosensor comprises a lysine oxidase membrane assembled on an NH4+ electrode. Because the selectivity of the lysine biosensor towards other cation species is not sufficient, there is severe interference with the potentiometric response. This poor selectivity can be circumvented mathematically by analysis of the richer information contained in the multi-sensor data. The sensor array takes advantage of the cross-selectivity of lysine for each electrode, which differs from the other species and quantification of lysine in complex feed sample extracts is accomplished with multivariate calibration methods, such as partial least-squares regression. The results obtained are in a reasonable agreement with those given by the standard method for amino acid analysis.     

A novel detector using a fluorescent sensor array and discrimination of pesticides

A novel, simple, and rapid detector using a fluorescent sensor array for discrimination and quantification of different concentrations (ppb level) of pesticides was proposed in this paper. Employing porphyrin, porphyrin derivatives, and chemically responsive dyes as the sensing elements, the developed sensor array based on a cross-responsive mechanism showed a unique pattern of fluorescence changes upon the reaction that lasted just 10 min. The eigenvalues from raw fluorescence spectra were analyzed via a pattern recognition algorithm, including hierarchical cluster analysis (HCA), principal component analysis (PCA), and back-propagation neural network (BPNN). The results showed that HCA, which were used to assess the feasibility and effectiveness of discrimination of the fluorescent sensor array, revealed a distinct separation between different pesticides. PCA and BPNN were used for automatically predicting the concentration of pesticides, and the recovery was 91.29–109.81 % while the lowest relative standard deviation was up to 3.12 %. It indicates a detector based on the fluorescent sensor array is a rapid and feasible sensing platform for the discrimination and quantitative analysis of pesticides, and also shows the possibilities in the related fields of pesticides identification and detection.     

Identification of catecholamine neurotransmitters using fluorescence sensor array

A nano-based sensor array has been developed for identification and discrimination of catecholamine neurotransmitters based on optical properties of their oxidation products under alkaline conditions. To produce distinct fluorescence response patterns for individual catecholamine, quenching of thioglycolic acid functionalized cadmium telluride (CdTe) quantum dots, by oxidation products, were employed along with the variation of fluorescence spectra of oxidation products. The spectral changes were analyzed with hierarchical cluster analysis (HCA) and principal component analysis (PCA) to identify catecholamine patterns. The proposed sensor could efficiently discriminate the individual catecholamine (i.e., dopamine, norepinephrine, and l-DOPA) and their mixtures in the concentration range of 0.25–30 μmol L⁻¹. Finally, we found that the sensor had capability to identify the various catecholamines in urine sample.     

Detection of odour emissions from a composting facility using a QCM sensor array

Odour emissions from a composting facility were detected by using a quartz crystal microbalance (QCM) sensor array. The array consists of six sensor elements, which were coated with different materials. A series of tests under field conditions showed that considerable sensor frequency changes were detected during the compost-turning period. Using principal component analysis, it was found that more than 90% of the data variance could still be explained by use of two principal components.     

Antibody-free reading of the histone code using a simple chemical sensor array

The histone code refers to the complex network of histone post-translational modifications that control gene expression and are of high interest as drivers of a large number of human diseases. We report here on a mix-and-match toolkit of readily available dyes and calixarene host molecules that can be combined to form dye-displacement sensors that respond to a wide variety of cationic peptides. Using the data from only two or three such simple supramolecular sensors as a chemical sensor array produces fingerprints of data that discriminate robustly among many kinds of histone code elements. "Reads" that are accomplished include the discrimination of unmethylated, mono-, di-, and trimethylated lysines on a single histone tail sequence, identification of different modifications and combinations of modifications on a single histone tail sequence, identification of a single modification type in several different sequence contexts, and identification of isomeric dimethylarginine modifications. Reads that are sometimes troublesome for antibodies are achieved. We also report on the ability of the sensor array to report simultaneously on the concentrations and identities of histone modifications. This sensor array discriminates between post-translationally modified analytes without being limited to partners that contain a single, programmed binding interaction.     

Human skin thermal properties determination using a calorimetric sensor

Journal of Thermal Analysis and Calorimetry - The purpose of the calorimetric sensor developed is to measure the heat flux transmitted by conduction between the human body surface and a thermostat...     

Determination of calcium and total hardness in natural waters using a potentiometric sensor array

The determination of calcium and total hardness in natural waters is carried out with a potentiometric sensor array which consists of a series of ion-selective electrodes (ISEs) for Ca²⁺, Mg²⁺, NH₄⁺, K⁺, Na⁺, Li⁺, and H⁺. The selectivity of the calcium and magnesium ISEs is not fully achieved as other cation species may interfere with the analysis. The proposed sensor array device can overcome this drawback since it can take advantage of the cross-selectivities of cation species towards each ISE. In this approach, the multivariate data generated by the sensor array results in a richer source of analytical information which allows the quantification of calcium and total hardness in the water samples by means of chemometric methods. Results obtained are in reasonable concordance with those given by the standard method based on complexometry.     

Selective spectrophotometric determination of TNT using a dicyclohexylamine-based colorimetric sensor

Because of the extremely heterogeneous distribution of explosives in contaminated soils, on-site colorimetric methods are efficient tools to assess the nature and extent of contamination. To meet the need for rapid and low-cost chemical sensing of explosive traces or residues in soil and post-blast debris, a colorimetric absorption-based sensor for trinitrotoluene (TNT) determination has been developed. The charge-transfer (CT) reagent (dicyclohexylamine, DCHA) is entrapped in a polyvinylchloride (PVC) polymer matrix plasticised with dioctylphtalate (DOP), and moulded into a transparent sensor membrane sliced into test strips capable of sensing TNT showing an absorption maximum at 530 nm when placed in a 1-mm spectrophotometer cell. The sensor gave a linear absorption response to 5-50 mg L⁻¹ TNT solutions in 30% aqueous acetone with limit of detection (LOD): 3 mg L⁻¹. The sensor is only affected by tetryl, but not by RDX, pentaerythritoltetranitrate (PETN), dinitrotoluene (DNT), and picric acid. The proposed method was statistically validated for TNT assay against high performance liquid chromatography (HPLC) using a standard sample of Comp B. The developed sensor was relatively resistant to air and water, was of low-cost and high specificity, gave a rapid and reproducible response, and was suitable for field use of TNT determination in both dry and humid soil and groundwater with a portable colorimeter.     

Construction of an immobilized asparaginase sensor and determination of asparagine and asparaginase in human blood serum

The sensor is based on asparaginase held on an ammonia gas sensor. Asparagine in the range 2.0 X 10^?5?2.3 X 10^?3 M gives a linear calibration graph with response times of 5?2 min. Asparagine can be determined in human serum. Asparaginase (0.01?0.2 U in 0.1 ml of sample) is determined in aqueous solution or serum by adding asparagine to the sample, and measuring the ammonia evolved. Results for both methods agree well with those obtained by the combined Conway—Russell method.