Search Results (34)

Aloin, a kind of active phenolic component, is sourced from Aloe vera. Recently, the determination of aloin has received enormous attention, owing to its positive performance (including anti-tumor, antibacterial, detoxification, liver protection, anti-stomach damage, and skin protection activities) and painful side effects (increased carcinogenicity caused by excessive use of aloin) impacting human health. This investigation was inspired by the good fluorescence properties of carbon dots (CDs); CD-based sensors have aroused a great deal of interest due to their excellent sensitivity and selectivity. Thus, it is of great significance to develop novel CD-based sensors for aloin determination. Herein, N,F-CDs were designed and synthesized through a convenient hydrothermal strategy; the synthesized N,F-CDs possessed good fluorescence performance and a small particle size (near 4.3 nm), which demonstrated the successful preparation of N,F-CDs. The resulting N,F-CDs possessed a large Stokes shift and could emit a highly stable green fluorescence. The fluorescence of the N,F-CDs could be effectively quenched by aloin through the inner filter effect. Furthermore, the synthesis procedure was easy to operate. Finally, the N,F-CD-coated test strips were fabricated and combined with a miniaturized fluorimeter for the fluorescence detection of aloin via the inner filter effect for the first time. The N,F-CD-coated test strips were fabricated and used for the fluorescence sensing of aloin, and the results were compared with a typical ultraviolet (UV) method. The N,F-CD-coated test strips exhibited high recovery (96.9~106.1%) and sensitivity (31.8 nM, n = 3), good selectivity, low sample consumption (1 μL), high speed (5 min), good stability, and anti-interference properties. The results indicate that N,F-CD-coated test strips are applicable for the quantitative determination of aloin in bovine serum, orange juice, and urine samples. Full article

A device was developed to study the evolution of fluorescence spectra as a function of time. A previously designed fluorimeter based on the diode array mini-spectrometer CM12880MA was used. The control and measurement were carried out by programming a SAM21D microcontroller. Considerations regarding the optimization of acquisition speed, memory, and computer interface have been analyzed and optimized. As a result, a very versatile device with great adaptability, reduced dimensions, portability, and a low budget (under EUR 500) has been built. The sensitivity, controlled by the integration time of the photodiodes, can be adjusted between 10 µs and 20 s, thus allowing sampling times ranging from 10 ms to more than 10 h. Under these conditions, chemical rate constants from 20 s⁻¹ to 10⁻⁸ s⁻¹ can be experimentally determined. It has a very wide operating range for the kinetic rate constant determination, over six orders of magnitude. As proof of the system performance, the oxidation reaction of Thiamine in a basic medium to form fluorescent Thiochrome has been employed. The evolution of the emission spectrum has been followed, and the decomposition rate constant has been measured at 2.1 × 10⁻³ s⁻¹, a value which matches those values reported in the literature for this system. A Thiochrome calibration curve has also been performed, obtaining a detection limit of 13 nM, consistent with literature data. Additionally, the stability of Thiochrome has been tested, being the photo-decomposition rate constants 1.8 × 10⁻⁴ s⁻¹ and 3.0 × 10⁻⁷ s⁻¹, in the presence and absence of UV light (365 nm), respectively. Finally, experiments have been designed to obtain, in a single measurement, the values of both rate constants: the formation of Thiochrome from Thiamine and its photo-decomposition under UV light to a non-fluorescent product. The rate constant values obtained are in good agreement with those previously obtained through independent experiments under the same experimental conditions. These results show that, under these conditions, Thiochrome can be considered an unstable intermediate in a chemical reaction with successive stages. Full article

The aim of this study was to analyze the association between circulating amino acids and central and peripheral body temperature in subjects with and without fibromyalgia syndrome (FMS). A total of 47 patients with FMS and 59 healthy subjects were included in the study. The concentration of amino acids was determined in serum samples using a fluorimeter coupled with a high-performance liquid chromatography system. An infrared thermography camera was used to estimate peripheral hand temperatures. The core temperature of the body was estimated using an infrared thermometer, which was applied to the axillary and tympanic areas. Correlations between several thermographic variables of the hands and tryptophan, methionine, 3-methylhistidine, histidine, glutamic acid, and tyrosine were identified exclusively within the FMS group. In contrast, correlations between aminoadipic acid and serine and thermographic variables were observed only in the healthy control group. The concentrations of asparagine and lysine correlated with thermographic variables in both groups. The essential amino acid leucine was found to correlate with axillary temperature in FMS patients. However, it should be noted that the observed associations between aminoadipic acid and tryptophan blood concentrations and axillary temperature were limited to the control group. Several correlations were identified between circulating amino acids and different body temperatures in both healthy controls and patients with FMS. However, the correlation pattern differs significantly between FMS patients and healthy controls. These findings suggest the possibility of a change in the function of several amino acids in the thermoregulatory process in patients with FMS. Full article

The development of a novel strategy for the measurement of SARS-CoV-2 IgG antibodies is of vital significance for COVID-19 diagnosis and effect of vaccination evaluation. In this investigation, an SiO₂@Au@CDs nanoparticle (NP)-based lateral flow immunoassay (LFIA) strip was fabricated and coupled with a miniaturized fluorimeter. The morphology features and particle sizes of the SiO₂@Au@CDs NPs were characterized carefully, and the results indicated that the materials possess monodisperse, uniform, and spherical structures. Finally, this system was employed for SARS-CoV-2 IgG antibody test. In this work, the strategy for the SARS-CoV-2 IgG antibody test possesses several merits, such as speed (less than 15 min), high sensitivity (1.2 × 10⁻⁷ mg/mL), broad linearity range (7.4 × 10⁻⁷~7.4 × 10⁻⁴ mg/mL), accurate results, high selectivity, good stability, and low cost. Additionally, future trends in LFAs using quantum dot-based diagnostics are envisioned. Full article

Environmental screening is essential due to the increased occurrence of harmful substances in the environment. Open Meter Duo (OMD) is an open-source field photo/fluorimeter that uses an RGB diode that imitates a color according to the selected wavelength and uses a UV LED from the security kit diode as an excitation light source. The prepared PCB shield with a 3D-printed aperture was connected to Arduino UNO R4 WiFi. This system was used for the fluorescent detection of cholinesterase activity with the indoxyl acetate method. Carbofuran—a toxic pesticide—and donepezil—a drug used to treat Alzheimer’s disease—were tested as model inhibitors of cholinesterase activity. The limit of detection of indoxyl acetate was 11.6 μmol/L, and the IC50 values of the inhibitors were evaluated. This system is optimized for wireless use in field analysis with added cloud support and power source. The time of analysis was 5 min for the fluorimetric assay and 20 min for the optional photometric assay. The time of field operation was approximately 4 h of continuous measurement. This system is ready to be used as a cheap and easy control platform for portable use in drug control and point-of-care testing. Full article

There is a growing need for portable, highly sensitive measuring equipment to analyze samples in situ and in real time. For these reasons, it is becoming increasingly important to research new experimental equipment to carry out this work with advanced, robust and low-cost devices. In this framework, a flexible, portable and low-cost fluorimeter (under EUR 500), based on a C12880 MA MEMS micro-spectrometer with an Arduino compatible breakout board, has been developed for the trace analysis of biological substances. The proposed system can employ two selectable excitation sources for flexibility, one in the visible region at 405 nm (incorporated in the board) and an external LED at 365 nm in the UV region. This additional excitation source can be easily interchanged, varying the LED type for investigating any fluorophore compound of interest. The measurement process is micro-controlled, which allows the precise control of the spectrometer sensitivity by adjusting the integration time of each experiment separately. Data acquisition is easy, reliable and interfaced with a spreadsheet for fast spectra visualization and calculations. For testing the performance of the new device in fluorescence measurements, different fluorophore molecules which can be commonly found in biological samples, such as Fluorescein, Riboflavin, Quinine, Rhodamine b and Ru (II)-bipyridyl, have been employed. A high sensitivity and low quantitation limits (in the ppb range) have been found in all cases for the investigated chemicals. The portable device is also suitable for the study of other interesting phenomena, such as fluorescence quenching induced by chemical agents (such as halide anions or even auto-quenching). In this sense, an application for the quantification of chloride anions in aqueous solutions has been performed obtaining a LOD value of 18 ppm. The obtained results for all chemicals investigated with the proposed fluorimeter are always very similar in quantification figures, or even better than the data reported in literature, when using commercial laboratory equipment. Full article

The age estimation of biological traces is one of the holy grails in forensic investigations. We developed a method for the age estimation of semen stains using fluorescence spectroscopy in conjunction with a stoichiometric ageing model. The model describes the degradation and generation rate of proteins and fluorescent oxidation products (FOX) over time. The previously used fluorimeter is a large benchtop device and requires system optimization for forensic applications. In situ applications have the advantage that measurements can be performed directly at the crime scene, without additional sampling or storage steps. Therefore, a portable fiber-based fluorimeter was developed, consisting of two optimized light-emitting diodes (LEDs) and two spectrometers to allow the fluorescence protein and FOX measurements. The handheld fiber can be used without touching the traces, avoiding the destruction or contamination of the trace. In this study, we have measured the ageing kinetics of semen stains over time using both our portable fluorimeter and a laboratory benchtop fluorimeter and compared their accuracies for the age estimation of semen stains. Successful age estimation was possible up to 11 days, with a mean absolute error of 1.0 days and 0.9 days for the portable and the benchtop fluorimeters, respectively. These results demonstrate the potential of using the portable fluorimeter for in situ applications. Full article

Loop-mediated isothermal amplification (LAMP) is the most popular technology for point-of-care testing applications due its rapid, sensitive and specific detection with simple instrumentation compared to PCR-based methods. Many systems for reading the results of LAMP amplifications exist, including real-time fluorescence detection using fluorophore-labelled probes attached to oligonucleotide sequences complementary to the target nucleic acid. This methodology allows the simultaneous detection of multiple targets (multiplexing) in one LAMP assay. A method for multiplexing LAMP is the amplification by release of quenching (DARQ) technique by using a 5′-quencher modified LAMP primer annealed to 3′-fluorophore-labelled acting as detection oligonucleotide. The main application of multiplex LAMP is the rapid and accurate diagnosis of infectious diseases, allowing differentiation of co-infecting pathogens in a single reaction. Schistosomiasis, caused among other species by Schistosoma mansoni and strongyloidiasis, caused by Strongyloides stercoralis, are the most common helminth-parasite infections worldwide with overlapping distribution areas and high possibility of coinfections in the human population. It would be of great interest to develop a duplex LAMP to detect both pathogens in the same reaction. In this study, we investigate the use of our two previously developed and well-stablished LAMP assays for S. mansoni and Strongyloides spp. DNA detection in a new duplex real-time eight-primer system based on a modified DARQ probe method that can be performed in a portable isothermal fluorimeter with minimal laboratory resources. We also applied a strategy to stabilize the duplexed DARQ-LAMP mixtures at room temperature for use as ready-to-use formats facilitating analysis in field settings as point-of-care diagnostics for schistosomiasis and strongyloidiasis. Full article

Background: The present study was devoted to the search for possible associations between various adipokines/cytokines associated with the secretory activity of visceral adipocytes, elevated blood levels of LDL-C and abdominal obesity in people under 45 years. Methods: A population sample of Novosibirsk residents (n = 1415) was divided into deciles based on the levels of LDL-C. The study included 158 people, 87 men and 71 women, who had serum LDL-C levels of ≥4.2 mmol/L. Abdominal obesity was found in 50% of people (54% men, 45% women). By multiplex analysis using the human metabolic hormone V3 panel and the human adipokine magnetic bead panel, levels of adipokines and inflammatory markers were determined on a Luminex MAGPIX flow fluorimeter. Results: According to multivariate regression analysis (binary logistic regression), the most significant biomolecules, regardless of other factors, associated with the presence of AO against the background of hyper-LDL-C in young people were leptin (direct association) and lipocalin-2 (reverse association), leptin in young men (direct association), and leptin and TNF-alpha in women (direct association). Conclusions: Thus, in young people under 45 years with the presence of two important, potentially atherogenic risk factors—hyper-LDL-C and abdominal obesity—a complex of adipokines and metabolic hormones were associated with the presence of these diseases. Full article

A novel portable low-cost Arduino-controlled photo- and fluorimeter for on-site measurements has been developed. The device uses LEDs as a light source and a phototransistor as a light sensor. The circuit is based on the discharge of a capacitor with the photocurrent from the phototransistor. Validation experiments for absorbance measurements were performed by measuring protein concentration using the Bradford method and measuring phosphate ions in water using a commercial test kit. The emission light of the excited fluorescent dyes rhodamine 6G and calcofluor white was measured to validate the usability of the device as a fluorescence photometer. In all validation experiments, similar correlation coefficients and limit of detection could be achieved with the portable photo- and fluorimeter and a laboratory spectrometer and fluorimeter. Real sample analysis was performed, measuring phosphate concentration in freshwater and concentration of green fluorescent protein, extracted from Escherichia coli. Full article

Lichens often grow in microhabitats where they absorb more light than they can use for fixing carbon, and this excess energy can cause the formation of harmful reactive oxygen species (ROS). Lichen mycobionts can reduce ROS formation by synthesizing light-screening pigments such as melanins in the upper cortex, while the photobionts can dissipate excess energy radiationlessly using non-photochemical quenching (NPQ). An inherent problem with using fluorimetry techniques to compare NPQ in pale and melanised thalli is that NPQ is normally measured through a variously pigmented upper cortex. Here we used a dissection technique to remove the lower cortices and medullas of Lobaria pulmonaria and Crocodia aurata and then measure NPQ from the underside of the thallus. Results confirmed that NPQ can be satisfactorily assessed with a standard fluorimeter by taking measurement from above using intact thalli. However, photobionts from the bottom of the photobiont layer tend to have slightly lower rates of PSII activity and lower NPQ than those at the top, i.e., display mild “shade” characteristics. Analysis of pale and melanised thalli of other species indicates that NPQ in melanised thalli can be higher, similar or lower than pale thalli, probably depending on the light history of the microhabitat and presence of other tolerance mechanisms. Full article

Due to the gradual increase in the concentration of algae, in general, in continental surface water reservoirs, it is necessary to incorporate advanced technologies in drinking water treatment plants with a view to reduce/eliminate the algae present. This degradation of the algal mass will additionally lead to the destruction of the toxins that could be released into the aqueous medium during the course of potabilisation. In this work, degradation assays of Microcystis sp. in surface water by oxidation processes with ozone have been studied. Ozonation experiments have been carried out in a homogeneous regime (mixture of an aqueous solution with dissolved ozone and surface water) and heterogeneous regime (continuous bubbling of a gaseous current with ozone in surface water). Different aqueous matrices were used for the assays (distilled water, Guadiana river as it passes through Badajoz (Spain), Villar del Rey reservoir (Spain) and a stream that circulates through the campus of the University of Extremadura in Badajoz (Spain)), which were doped with different amounts of a culture of Microcystis sp., provided by the University of Coimbra (Portugal), to achieve the desired initial load of algal mass. The original aqueous matrices were filtered through 0.45 micrometer filters (Millipore). An ozonizer (Sander, model 300.5) was used, capable of generating from pure oxygen a mass flow rate of 6 g/h with an ozone concentration in the gas phase of 1.6% by volume. In the case of the experiments in a heterogeneous regime, the reactor was a cylindrical column 20 cm high and 8 cm in diameter, fitted with a microporous diffuser. To determine the content of algal mass present in the initial sample and in those treated by ozonation, a portable fluorimeter (Aquafluor, Turner) was used, which allows to measure the content of chlorophyll in vivo between 0.3 and 300 µg/L. Ozone analysis in the aqueous phase was performed by the Karman Indigo method and in the gas phase by iodometry. Experiments carried out in homogeneous regime show that in only 5 minutes the chlorophyll content is reduced by 50% for all types of aqueous matrices and for different initial contents of algal mass between 15 and 50 µg/L. For a time of 30 minutes, the conversion is between 80 and 90%, except for the Guadiana river matrix, which is between 70 and 80%. In the case of the heterogeneous regime, ozonation experiments have been carried out by varying the ozone concentration between 4.5 × 10⁻⁵ and 5.4 × 10⁻⁴ mol/L. It is observed that this variable has a strong positive influence on the degradation of the algae. Thus, for a time of 30 minutes, the degradation is total with the four matrices for the ozone concentration of 5.4 × 10⁻⁴ mol/L, while for the concentration of 4.5 × 10⁻⁵ mol/L the degradation is between 80 and 90%. A kinetic study has been carried out in both types of ozonation regime. In the case of the homogeneous regime, the model includes both the self-decomposition of ozone in water and the direct reaction of ozone with the algae, and in the case of the heterogeneous regime, the mass transfer of ozone from the gas to the liquid phase is also incorporated. The resolution of the model with the MATLAB software leads to a value of the kinetic degradation constant of the alga between 9 × 10⁻⁴ (Villar del Rey reservoir) and 1.4 × 10⁻³ (distilled water) L/(µg chlorophyll min). Full article

The fluorescence emission by aged organic binders used in painting is a well-known phenomenon. Several literature studies were devoted to its investigation, both on pure binders and on their mixtures with some pigments. Nevertheless, a systematic study about the real possibility of exploiting such a phenomenon for the non-invasive identification of binders in ancient paintings is still lacking. In the present work, a prototype portable fluorimeter was used to analyze a significant number of model painting samples containing different binders (drying oils, egg yolk, milk, animal glue, and gum Arabic) mixed with various pigments having different hues. The model samples were naturally aged in a period ranging from fifteen to one year. The effects on the spectral pattern due to the different binders, the recipes used to prepare them, and the pigments mixed with them were examined. The fluorescence spectra were corrected for the absorption of the emitted radiation due to the pigments. Finally, the corrected spectra were treated by principal component analysis to determine if the possibility of distinguishing at least the most fluorescent and common binders, i.e., drying oils and egg, existed. It was shown that, even if the technique cannot be effectively applied in the case of mixed or superimposed binders, it allows to put forward at least a preliminary hypothesis when pure binders are used. Full article

The study investigated the inhibitory activity of protocetraric and salazinic acids against SARS-CoV-2 3CL^pro. The kinetic parameters were determined by microtiter plate-reading fluorimeter using a fluorogenic substrate. The cytotoxic activity was tested on murine Sertoli TM4 cells. In silico analysis was performed to ascertain the nature of the binding with the 3CL^pro. The compounds are slow-binding inactivators of 3CL^pro with a K_i of 3.95 μM and 3.77 μM for protocetraric and salazinic acid, respectively, and inhibitory efficiency k_inact/K_i at about 3 × 10⁻⁵ s⁻¹µM⁻¹. The mechanism of inhibition shows that both compounds act as competitive inhibitors with the formation of a stable covalent adduct. The viability assay on epithelial cells revealed that none of them shows cytotoxicity up to 80 μM, which is well below the K_i values. By molecular modelling, we predicted that the catalytic Cys145 makes a nucleophilic attack on the carbonyl carbon of the cyclic ester common to both inhibitors, forming a stably acyl-enzyme complex. The computational and kinetic analyses confirm the formation of a stable acyl-enzyme complex with 3CL^pro. The results obtained enrich the knowledge of the already numerous biological activities exhibited by lichen secondary metabolites, paving the way for developing promising scaffolds for the design of cysteine enzyme inhibitors. Full article

Until recently, the classic approach to mineral exploration studies was to bring the field samples/drill cores collected during field studies to the laboratory, followed by laborious analysis procedures to generate the analytical data. This is very expensive, time-consuming, and difficult for exploring vast areas. However, rapid technological advances in field-portable analytical instruments, such as portable visible and near-infrared spectrophotometers, gamma-ray spectrometer, pXRF, pXRD, pLIBS, and µRaman spectrometer, have changed this scenario completely and increased their on-site applications in mineral exploration studies. LED fluorimeter is a potential portable tool in the hydrogeochemical prospecting studies of uranium. These instruments are currently providing direct, rapid, on-site, real-time, non-destructive, cost-effective identification, and determination of target elements, indicator minerals and pathfinder elements in rock, ore, soil, sediment, and water samples. These portable analytical instruments are currently helping to obtain accurate chemical and mineralogical information directly in the field with minimal or no sample preparation and providing decision-making support during fieldwork, as well as during drilling operations in several successful mineral exploration programs. In this article, the developments in these portable devices, and their contributions in the platinum group elements (PGE), rare earth elements (REE), gold, base metals, and lithium exploration studies both on land and on the ocean bed, have been summarized with examples. Full article