Fiber Optic Spectrophotometer Research Articles

Ferrozine colorimetry and reverse flow injection analysis (rFIA) based method for the determination of total iron in aqueous solutions at nanomolar concentrations

Iron is one of the most microbiologically and chemically important metals in natural waters. The biogeochemical cycling of iron is significantly influenced by the redox cycling of Fe(II) and Fe(III). Because of the unique chemistry of iron, it is often needed to analyze iron at nano-molar concentrations. This article describes a reverse flow injection analysis (rFIA) based method with ferrozine spectrophotometric detection to quantify total iron concentration in stream water at nanomolar concentrations. The rFIA system has a 0.65 nM detection limit and a linear dynamic range up to 1.40 μM for the total iron analysis. The detection limit was achieved using a 1.0 m long liquid waveguide capillary flow cell, 1.50 m long knotted reaction coil, 87.50 μL injection loop and a miniature fiber optics spectrophotometer. The optimized colorimetric reagent has 1.0 mM ferrozine, 0.1 M ascorbic acid, 1.0 mM citric acid and 0.10 M acetate buffer adjusted to pH 4.0. The best sample flow rate is 2.1 mL min−1 providing a sample throughput of more than 15 samples h−1. The linear dynamic range of the method can be adjusted by changing the volume of the injection loop. The rFIA manifold was assembled exclusively from commercially available components.

G-quadruplex microspheres-based optical RNA biosensor for arthropod-borne virus pathogen detection: A proof-of-concept with dengue serotype 2

Dengue virus (DENV) is a positive-sense single-stranded RNA virus and that the detection of viral RNA itself is highly desirable, which can be achieved by using RNA biosensor diagnostic method. Herein, acrylic micropolymer-based optical RNA biosensor was developed by binding anionic copper(II) phthalocyanine (CPC) planar aromatic ligand to the G-quadruplex DNA probe via end-stacking with π-system of the guanine (G) quartet, and a blue coloration was developed on the G-quadruplex microspheres. Hybridization of G-quadruplex DNA probe with target DENV serotype 2 (DENV2) RNA unfolded the G-quadruplex, and rendering release of the CPC planar optical label, causing discoloration of the G-quadruplex microbiosensor. Optical characterization of the RNA biosensor was performed by means of fiber optic reflectance spectrophotometer at maximum reflectance wavelength of 774 nm. The reflectance response enhancement of the RNA-responsive G-quadruplex-based reflectometric biosensor was linearly proportional to the target oligo DENV2 RNA concentration in the range of 2 zM–2 μM, with a 0.447 zM limit of detection and a rapid response time of 30 min. Heightening in the reflectance signal based on structural transition of G-quadruplex in response to target RNA was successfully implemented in real-time DENV2 detection in non-invasive human fluid samples (i.e. saliva and urine) under informed consent.

Development of an embedded system for real-time milk spoilage monitoring and adulteration detection

In the current work, a fluorescence-based method with a point-of-use colorimetric sensing system was developed to test the quality of the milk in real-time using fluorophores. The fluorescence intensities of fluorophores were optimised to predict the pH of the milk samples using colour sensor device (CSD) and were cross-reference using a fibre optic spectrophotometer (FOS). The developed CSD and FOS measured the pH and adulteration in a linear range of 4–9 pH units and 0–70 mm urea in milk with a quick response time of 30 s and 5 min. The interday variability for pH sensing by the CSD and FOS was evaluated and expressed as a percentage relative standard deviation (%RSD) which was found to be 1.89 for CSD and 4.72 for FOS. The results indicate that CSD and FOS can be suitable tools for spoilage and urea adulteration detection in milk samples.

A simple cost-effective microfluidic platform for rapid synthesis of diverse metal nanoparticles: A novel approach towards fighting SARS-CoV-2

The latest addition to the family of Coronaviruses, SARS-CoV-2, unleashed its wrath across the globe. The outbreak has been so rapid and widespread that even the most developed countries are still struggling with ways to contain the spread of the virus. The virus began spreading from Wuhan in China in December 2019 and has currently affected more than200 countries worldwide. Nanotechnology has huge potential for killing viruses as severe as HIV, herpes, human papilloma virus, and viruses of the respiratory tract, both inside as well as outside the host. Metal-nanoparticles can be employed for biosensing methodology of viruses/bacteria, along with the development of novel drugs and vaccines for COVID-19 and future pandemics. It is thus required for the nanoparticles to be synthesized quickly along with precise control over their size distribution. In this study, we propose a simple microfluidic-reactor-platform for in-situ metal-nanoparticle synthesis to be used against the pandemic for the development of preventive, diagnostic, and antiviral drug therapies. The device has been fabricated using a customized standard photolithography process using a simple and cost-effective setup. The confirmation on standard silver and gold metal nanoparticle formation in the microfluidic reactor platform was analysed using optical fiber spectrophotometer. This novel microfluidic platform provides the advantage of in-situ synthesis, flow parameter control and reduced agglomeration of nanoparticles over the bulk synthesis due to segregation of nucleation and growth stages inside a microchannel. The results are highly reproducible and hence scaling up of the nanoparticle production is possible without involving complex instrumentation.

Reflectance aptasensor based on metal salphen label for rapid and facile determination of insulin

An optical aptasensor-based sensing platform for rapid insulin detection was fabricated. Aminated porous silica microparticles (PSiMPs) were synthesized via a facile mini-emulsion method to provide large surface area for covalent immobilization of insulin-binding DNA aptamer (IGA3) by glutaraldehyde cross-linking protocol. A Nickel-salphen type complex with piperidine side chain [Ni(II)-SP] was synthesized with a simple one-pot reaction, and functionalized as an optical label due to strong π-π interaction between aromatic carbons of G-quadruplex DNA aptamer and planar aromatic groups of Ni(II)-SP to form the immobilized IGA3-Ni(II)-SP complex, i.e. the dye-labeled aptamer, thereby bringing yellow colouration to the immobilized G-quartet plane. Optical characterization of aptasensor towards insulin binding was carried out with a fiber optic reflectance spectrophotometer. The maximum reflectance intensity of the immobilized IGA3-Ni(II)-SP complex at 656 nm decreased upon binding with insulin as aptasensor changed to brownish orange colouration in the background. This allows optical detection of insulin as the colour change of aptasensor is dependent on the insulin concentration. The linear detection range of the aptasensor is obtained from 10 to 50 μIU mL−1 (R2 = 0.9757), which conformed to the normal fasting insulin levels in human with a limit of detection (LOD) at 3.71 μIU mL−1. The aptasensor showed fast response time of 40 min and long shelf life stability of >3 weeks. Insulin detection using healthy human serums with informed consent provided by participants suggests the DNA aptamer biosensor was in good agreement with ELISA standard method using BIOMATIK Human INS (Insulin) ELISA Kit.

Application of single and dual fluorophore-based pH sensors for determination of milk quality and shelf life using a fibre optic spectrophotometer

Milk is a high nutrient value food substance consumed by the entire population in several forms. Spoilage and degradation of milk and its products during transportation, processing and packaging are some of the major losses by dairy industries. The change in milk pH with time is an indicating factor of milk degradation. This research reports a rapid, sensitive and facile fluorescence-based technique to study the time-based milk degradation at room temperature. Fluorescein isothiocyanate (FITC)/ FITC-dextran (FITC-dex) and Tris (2, 2′-bipyridyl) dichloro ruthenium (II) hexahydrate (Ru-bpy) were used to develop solution phase and immobilized phase pH sensors. Immobilized phase sensors constituted of alginate microspheres (5 ± 3 μm) produced using an air driven atomizer. The pH sensor works in a linear range of 3–8 pH units with a quick response time of 30 s. The percentage recovery of the system lay in the range of 89.23%–101.28% for detection of milk pH. Accurate detection was possible during entire shelf life of milk (˜24 h) and Inter-sample and inter-day reproducibility was checked over 10 days duration. The results clearly indicate that both single and dual fluorophore-based assay in solution phase and immobilized phases can predict milk pH with good accuracy.

Fully Automated System for 99Tc Monitoring in Hospital and Urban Residues: A Simple Approach to Waste Management.

99Tc is an artificial beta emitter widely used in nuclear medicine for diagnostic tests. A fully automated and rapid system for 99Tc monitoring is introduced with the aim to improve hospital residues management. This system can also be helpful for controlling urban wastewater. Figures of merit similar to those obtained with liquid scintillation counting were achieved by exploiting a simple, economic, and portable system with spectrophotometric detection. The combination of flow analysis techniques, i.e., lab-on-valve (LOV) and multisyringe flow injection analysis (MSFIA), with a selective resin ((weak base extraction chromatographic (WBEC) resin) enables the analysis to be performed in a short time, achieving high selectivity and sensitivity levels. After elution with NH4OH (3 mol·L-1), 99Tc is derivatized with 1,5-diphenylcarbohydrazide (DPC) and finally detected by a miniaturized fiber optic CCD spectrophotometer at 520 nm, exploiting a long path-length liquid waveguide capillary cell (LWCC) of 100 cm path length. The proposed method was optimized by experimental design, achieving a limit of detection (LOD) of 4 ng of 99Tc (2.5 Bq), a reproducibility of 6%, and a resin durability of 78 injections. The microcolumn allows one to preconcentrate up to 100 mL of sample without deterioration of the analytical signal. The automated system was successfully applied to hospital residues and urban wastewater, and the attained recoveries were between 90% and 110%.

Optical carbon dioxide sensor based on fluorescent capillary array

A novel carbon dioxide (CO2) gas sensor based on capillary array is presented. The capillary array is composed of 51 capillaries and modified by fluorescent dye 8-hydroxy-1,3,6-pyrenetrisulfonic acid trisodium salt (HPTS, PTS−) and tetraoctylammonium cation (TOA+) doped porous ethyl cellulose. A Y-fiber is used to transmit exciting light and fluorescence. A fiber optic pigtail-contained spectrophotometer is used to collect and deal with optical signals. Due to its structural features, each capillary has the two rolling-up layers of inner and outer sensing films, which make the 2cm long capillary array has large sensing area about 12.81cm2 and the fluorescence signal easily be collected. The sensing probe has advantages such as small volume, compact structure and large sensing area. The results demonstrate that the sensor has a linear response in the CO2 volume ratio range from 0 to 10%.

Acrylic microspheres-based optosensor for visual detection of nitrite

A new optosensor for visual quantitation of nitrite (NO2−) ion has been fabricated by physically immobilizing Safranine O (SO) reagent onto a self-adhesive poly(n-butyl acrylate) [poly(nBA)] microspheres matrix, which was synthesized via facile microemulsion UV lithography technique. Evaluation and optimization of the optical NO2− ion sensor was performed with a fiber optic reflectance spectrophotometer. Scanning electron micrograph showed well-shaped and smooth spherical morphology of the poly(nBA) microspheres with a narrow particles size distribution from 0.6μm up to 1.8μm. The uniform size distribution of the acrylic microspheres promoted homogeneity of the immobilized SO reagent molecules on the microspheres’ surfaces, thereby enhanced the sensing response reproducibility (<5% RSD) with a linear range obtained from 10 to 100ppm NO2− ion. The micro-sized acrylic immobilization matrix demonstrated no significant barrier for diffusion of reactant and product, and served as a good solid state ion transport medium for reflectometric nitrite determination in food samples.

Furfural Determination with Disposable Polymer Films and Smartphone-Based Colorimetry for Beer Freshness Assessment.

We have developed disposable color-changing polymeric films for quantification of furfural-a freshness indicator-in beer using a smartphone-based reader. The films are prepared by radical polymerization of 4-vinylaniline, as a furfural-sensitive indicator monomer, 2-hydroxymethyl methacrylate as a comonomer, and ethylene dimethyl methacrylate (EDMA) as a cross-linker. The sensing mechanism is based on the Stenhouse reaction in which aniline and furfural react in acidic media with the generation of a deep red cyanine derivative, absorbing at 537 nm, which is visible to the naked eye. The colorimetric response has been monitored using either a portable fiber-optic spectrophotometer or the built-in camera of a smartphone. Under the optimized conditions, a linear response to furfural in beer was obtained in the 39 to 500 μg L(-1) range, with a detection limit of 12 μg L(-1), thus improving the performance of other well-established colorimetric or chromatographic methods. The novel films are highly selective to furfural, and no cross-reactivity has been observed from other volatile compounds generated during beer aging. A smartphone application (app), developed for Android platforms, measures the RGB color coordinates of the sensing membranes after exposure to the analyte. Following data processing, the signals are converted into concentration values by preloaded calibration curves. The method has been applied to determination of furfural in pale lager beers with different storage times at room temperature. A linear correlation (r > 0.995) between the storage time and the furfural concentration in the samples has been confirmed; our results have been validated by HPLC with diode-array detection.

Liquid–liquid microextraction in sequential injection analysis for the direct spectrophotometric determination of acid number in biodiesel

Sequential injection analysis (SIA) is used here for acid number determination in biodiesel exploiting liquid–liquid microextraction and spectrophotometric detection. Free fatty acids (FFA) from biodiesel are partially extracted to an aqueous bromocresol green (BCG) aliquot placed in between two aliquots of biodiesel without any pretreatment. Microextraction is favored by using holding coils and transmission lines made of Teflon® due to the formation of biodiesel film in the tube walls. Detection was performed in a glass tube coupled to a fiber-optic spectrophotometer and analytical signals were related to the discoloration of the BCG after FFA microextraction. A linear response was observed up to 0.6mg KOH g−1, with detection limit, coefficient of variation, and sampling rate estimated at 0.0074mg KOH g−1, 2.9 % (n=10) and 12h−1, respectively. The procedure is a fast, reliable, and mechanized alternative for acid number determination, which requires only 250μL of sample, 10μg BCG and 500μL of ethanol. A reference procedure based on visual titration was used for comparison and results agreed at the 95% confidence level.

Exploitation of pulsed flows for on-line dispersive liquid–liquid microextraction: Spectrophotometric determination of formaldehyde in milk

Formaldehyde is often added to foods as a preservative, but it is highly toxic to humans, having been identified as a carcinogenic substance. It has also been used for the adulteration of milk in order to diminish the bacteria count and increase the shelf life of the product. Herein, we present a green dispersive liquid–liquid microextraction procedure in a flow-batch system for the determination of formaldehyde in milk. Pulsed flows were exploited for the first time to improve the dispersion of the extractant in the aqueous phase. The Hantzsch reaction was used for the derivatization of formaldehyde and the product was extracted with the ionic liquid (IL) trihexyltetradecylphosphonium chloride with methanol as the disperser. The flow-batch chamber was made of stainless steel with the facility for resistive heating to speed up the derivatization reaction. Spectrophotometric measurements were directly carried out in the organic phase using an optical fiber spectrophotometer. The limit of detection and coefficient of variation were 100μgL−1 and 3.1% (n=10), respectively, with a linear response from 0.5 to 5.0mgL−1, described by the equation A=0.088+0.116CF (mgL−1) in which A is absorbance and CF is formaldehyde concentration in mgL−1. The estimated recoveries of formaldehyde from spiked milk samples ranged from 91% to 106% and the slopes of the analytical curves obtained with reference solutions in water or milk were in agreement, thus indicating the absence of matrix effects. Accuracy was demonstrated by the agreement of the results with those achieved by the reference fluorimetric procedure at the 95% confidence level. The proposed procedure allows for 10 extractions per hour, with minimized reagent consumption (120μL of IL and 3.5μL acetylacetone) and generation of only 6.7mL waste per determination, which contribute to the eco-friendliness of the procedure.

Nile Blue chromoionophore-doped kappa-carrageenan for a novel reflectometric urea biosensor

A new optical urea biosensor based on urease (Urs) physically attached to a pH optode made from Nile Blue (NB) chromoionophore-doped kappa-carrageenan (KC) membrane is described in this paper. The immobilized Urs on the biosensor surface catalyzed the hydrolytic decomposition of urea into ammonium hydroxide, a pH changed to a more basic condition, and resulted in a colour change of the pH sensor membrane from blue to violet, which can be quantified reflectometrically using a fibre optic reflectance spectrophotometer. A linear relationship was perceived between the reflectance intensity of the KC membrane-based biosensor and the urea concentration in the range of 0.001–100mM with the detection limit calculated at 0.001mM. The response time of the urea biosensor was 10min, and no significant discrepancy was noted for the results obtained from the direct analysis of urine samples by both the reflectance catalytic biosensor and the UV–vis spectrophotometric standard method based on the p-dimethylaminobenzaldehyde (DMAB) reagent.

Study on Solubility of Surfactants in Water by Fiber Optic Spectrophotometer

The vegetable oil based emulsifiers represent a remarkable potential in the petroleum industry. In the chemical enhanced oil recovery (EOR) the application of the nonionic surfactants have a growing importance as a biodegradable type additive. The aim of our work is to prepare a simple and rapid instrumental measurement that could be used in the industrial practice and would be suitable to control the water solubility of the surfactants produced for EOR technologies by using of the available AvaSpec fiber optic spectrophotometer. Показано, що емульгатори на основі олій є значним потенціалом у нафтовій промисловості. Застосування нейоногенних поверхнево-активних речовин (ПАР) при видобутку нафти набуває все більшого значення як додатку біодегредабельного типу. Розроблено прості та швидкі методи вимірювання, які можуть бути використані в промисловій практиці і придатні для контролю розчинності у воді ПАР, отриманих для вищевказаного процесу. Контроль здійснюється за допомогою волоконно-оптичного спектрофотометра AvaSpec.

Method for estimating optimal spectral and energy parameters of laser irradiation in photodynamic therapy of biological tissue

We have solved the problem of layer-by-layer laser-light dosimetry in biological tissues and of selecting an individual therapeutic dose in laser therapy. A method is proposed for real-time monitoring of the radiation density in tissue layers in vivo, concentrations of its endogenous (natural) and exogenous (specially administered) chromophores, as well as in-depth distributions of the spectrum of light action on these chromophores. As the background information use is made of the spectrum of diffuse light reflected from a patient's tissue, measured by a fibre-optic spectrophotometer. The measured spectrum is quantitatively analysed by the method of approximating functions for fluxes of light multiply scattered in tissue and by a semi-analytical method for calculating the in-depth distribution of the light flux in a multi-layered medium. We have shown the possibility of employing the developed method for monitoring photosensitizer and oxyhaemoglobin concentrations in tissue, light power absorbed by chromophores in tissue layers at different depths and laser-induced changes in the tissue morphology (vascular volume content and ratios of various forms of haemoglobin) during photodynamic therapy.

Liquid–liquid microextraction in a multicommuted flow system for direct spectrophotometric determination of iodine value in biodiesel

A flow-based procedure was developed for the direct spectrophotometric determination of the iodine value (IV) in biodiesel. The procedure was based on the microextraction/reaction of unsaturated compounds with triiodide ions in an aqueous medium by inserting the reagent solution between the aliquots of biodiesel without any pretreatment. The interaction occurred through the biodiesel film formed on the inner walls of the hydrophobic tube used as the reactor and at the aqueous/biodiesel interfaces. The spectrophotometric detection was based on the discoloration of the I3− reagent in the aqueous phase by using a glass tube coupled to a fiber-optic spectrophotometer as the detection cell. Reference solutions were prepared by dilution of biodiesel samples with previously determined IV in hexane. The analytical response was linear for IV from 13 to 135g I2/100g with a detection limit of 5g I2/100g. A coefficient of variation of 1.7% (n=10) and a sampling rate of 108 determinations per hour were achieved by consuming 224μL of the sample and 200μg of I2 per determination. The slopes of analytical curves obtained with three different biodiesel samples were in agreement (variations in slopes lower than 3.1%), thus indicating an absence of any matrix effects. Results for biodiesel samples from different sources agreed with the volumetric official procedure at the 95% confidence level. The proposed procedure is therefore a simple, fast, and reliable alternative for estimating the iodine value of biodiesel.

Simultaneous high-resolution pH and spectrophotometric recordings of oxygen binding in native blood microvolumes

Oxygen equilibrium curves have been widely used to understand oxygen transport in numerous organisms. A major challenge has been to monitor oxygen binding characteristics and concomitant pH changes as they occur in vivo, in limited sample volumes. Here we report a technique allowing highly resolved and simultaneous monitoring of pH and blood pigment saturation in minute blood volumes. We equipped a gas diffusion chamber with a broad-range fibre-optic spectrophotometer and a micro-pH optode and recorded changes of pigment oxygenation along oxygen partial pressure (PO2) and pH gradients to test the setup. Oxygen binding parameters derived from measurements in only 15 μl of haemolymph from the cephalopod Octopus vulgaris showed low instrumental error (0.93%) and good agreement with published data. Broad-range spectra, each resolving 2048 data points, provided detailed insight into the complex absorbance characteristics of diverse blood types. After consideration of photobleaching and intrinsic fluorescence, pH optodes yielded accurate recordings and resolved a sigmoidal shift of 0.03 pH units in response to changing PO2 from 0 to 21 kPa. Highly resolved continuous recordings along pH gradients conformed to stepwise measurements at low rates of pH changes. In this study we showed that a diffusion chamber upgraded with a broad-range spectrophotometer and an optical pH sensor accurately characterizes oxygen binding with minimal sample consumption and manipulation. We conclude that the modified diffusion chamber is highly suitable for experimental biologists who demand high flexibility, detailed insight into oxygen binding as well as experimental and biological accuracy combined in a single setup.

A novel organic–inorganic hybrid monolithic column prepared in-situ in a microchip and its application for the determination of 2-amino-4-chlorophenol in chlorzoxazone tablets

γ-Alumina nanoparticles (γ-Al2O3) were introduced to the conventional poly(methacrylic acid-co-ethylene glycol dimethacrylate) (MAA-co-EGDMA) monolith to prepare a novel organic-inorganic hybrid monolith, poly(MAA-co-EGDMA)-Al2O3 monolith. The polymerization was induced in-situ with UV irradiation in an ultraviolet transparent polymethyl methacrylate (PMMA) microfluidic chip. The monolith-based solid phase microextraction system was used for the on-line determination of 2-amino-4-chlorophenol (ACP) in chlorzoxazone tablets coupled with an optical fiber spectrophotometer. Several parameters affecting the adsorption/desorption, including sample pH value, sample flow rate, sampling time, eluent flow rate, and eluting time, were investigated in detail. Under the optimized conditions, limit of detection (LOD) and limit of quantification (LOQ) of the method were calculated to be 2.8 and 9.1µgL−1, respectively, with the relative standard deviation (RSD) of 3.1%.

A multicommuted flow system with liquid–liquid microextraction for determination of anionic surfactants in freshwaters

Anionic surfactants are usually determined by the spectrophotometric methylene blue method that is exhaustive, time-consuming and requires large amounts of sample and organic solvent. In this work, a flow system with liquid–liquid microextraction was developed for the environmentally friendly determination of anionic surfactants in natural waters. A CHCl3 aliquot was introduced at the front of the sample zone to form a film of the organic phase in the inner wall of a hydrophobic (PTFE) reactor, followed by sample and reagent aliquots inserted in tandem. Then a second CHCl3 aliquot removed the ion-pair for detection at a glass tube without phase isolation by using a fiber-optic spectrophotometer. A linear response from 0.05 to 2.0 mg L−1, detection limit of 0.02 mg L−1 (99.7% confidence level), coefficient of variation of 1.5% (n = 15, 1.0 mg L−1 SDS) and sampling rate of 18 determinations per hour were achieved. In each determination, only 44 μL of CHCl3 was consumed, which is 2200-fold lower than the amount required in the official procedure. The proposed procedure was successfully applied for determination of anionic surfactants in freshwaters, with results in agreement with those obtained by the official method at the 95% confidence level. The proposal is thus a fast, reliable, inexpensive and greener alternative for determination of anionic surfactants in natural waters, with reduction in the solvent and reagent consumption as well as waste generation.

Sequential Injection Lab-at-Valve Micro-Solvent Extraction Assay of Tetracycline

Sequential injection lab-at-valve (SI-LAV) micro-solvent extraction determination procedure for tetracycline hydrochloride in pharmaceutical analysis is proposed. It is based on the formation of a yellow colored ion associate of a protonated cation of tetracycline (TCLN + ) with anionic form of bromocresol green (BCG), in phthalate buffer pH 4, which could be extracted into dichloromethane. The organic phase is separated from the aqueous phase by means of a conical separating chamber in lab-at-valve unit which placed in one port of the selection valve. An extracted organic layer containing TCLN + -BCG - associate is monitored by a fiber optic spectrophotometer. The procedure leads to micro-volume analysis. This is a green analytical chemistry. The proposed method was applied to the assay of tetracycline hydrochloride in pharmaceutical samples.