Passive UHF RFID Tag for Multispectral Assessment.

This work presents the design, fabrication, and characterization of a passive printed radiofrequency identification tag in the ultra-high-frequency band with multiple optical sensing capabilities. This tag includes five photodiodes to cover a wide spectral range from near-infrared to visible and ultraviolet spectral regions. The tag antenna and circuit connections have been screen-printed on a flexible polymeric substrate. An ultra-low-power microcontroller-based switch has been included to measure the five magnitudes issuing from the optical sensors, providing a spectral fingerprint of the incident electromagnetic radiation from ultraviolet to infrared, without requiring energy from a battery. The normalization procedure has been designed applying illuminants, and the entire system was tested by measuring cards from a colour chart and sensing fruit ripening.

Smartphone-based simultaneous pH and nitrite colorimetric determination for paper microfluidic devices.

In this work, an Android application for measurement of nitrite concentration and pH determination in combination with a low-cost paper-based microfluidic device is presented. The application uses seven sensing areas, containing the corresponding immobilized reagents, to produce selective color changes when a sample solution is placed in the sampling area. Under controlled conditions of light, using the flash of the smartphone as a light source, the image captured with the built-in camera is processed using a customized algorithm for multidetection of the colored sensing areas. The developed image-processing allows reducing the influence of the light source and the positioning of the microfluidic device in the picture. Then, the H (hue) and S (saturation) coordinates of the HSV color space are extracted and related to pH and nitrite concentration, respectively. A complete characterization of the sensing elements has been carried out as well as a full description of the image analysis for detection. The results show good use of a mobile phone as an analytical instrument. For the pH, the resolution obtained is 0.04 units of pH, 0.09 of accuracy, and a mean squared error of 0.167. With regard to nitrite, 0.51% at 4.0 mg L(-1) of resolution and 0.52 mg L(-1) as the limit of detection was achieved.

Highly deformable and strongly magnetic semi-interpenetrating hydrogels based on alginate or cellulose.

The effective implementation of many of the applications of magnetic hydrogels requires the development of innovative systems capable of withstanding a substantial load of magnetic particles to ensure exceptional responsiveness, without compromising their reliability and stability. To address this challenge, double-network hydrogels have emerged as a promising foundation, thanks to their extraordinary mechanical deformability and toughness. Here, we report a semi-interpenetrating polymer networks (SIPNs) approach to create diverse magnetic SIPNs hydrogels based on alginate or cellulose, exhibiting remarkable deformability under certain stresses. Achieving strong responsiveness to magnetic fields is a key objective, and this characteristic is realized by the incorporation of highly magnetic iron microparticles at moderately large concentrations into the polymer network. Remarkably, the SIPNs hydrogels developed in this research accommodate high loadings of magnetic particles without significantly compromising their physical properties. This feature is essential for their use in applications that demand robust responsiveness to applied magnetic fields and overall stability, such as a hydrogel luminescent oxygen sensor controlled by magnetic fields that we designed and tested as proof-of-concept. These findings underscore the potential and versatility of magnetic SIPNs hydrogels based on carbohydrate biopolymers as fundamental components in driving the progress of advanced hydrogels for diverse practical implementations.

Capacitive platform for real-time wireless monitoring of liquid wicking in a paper strip.

Understanding the phenomenon of liquid wicking in porous media is crucial for various applications, including the transportation of fluids in soils, the absorption of liquids in textiles and paper, and the development of new and efficient microfluidic paper-based analytical devices (µPADs). Hence, accurate and real-time monitoring of the liquid wicking process is essential to enable precise flow transport and control in microfluidic devices, thus enhancing their performance and usefulness. However, most existing flow monitoring strategies require external instrumentation, are generally bulky and unsuitable for portable systems. In this work, we present a portable, compact, and cost-effective electronic platform for real-time and wireless flow monitoring of liquid wicking in paper strips. The developed microcontroller-based system enables flow and flow rate monitoring based on the capacitance measurement of a pair of electrodes patterned beneath the paper strip along the liquid path, with an accuracy of 4 fF and a full-scale range of 8 pF. Additionally to the wired transmission of the monitored data to a computer via USB, the liquid wicking process can be followed in real-time via Bluetooth using a custom-developed smartphone application. The performance of the capacitive monitoring platform was evaluated for different aqueous solutions (purified water and 1 M NaCl solution), various paper strip geometries, and several custom-made chemical valves for flow retention (chitosan-, wax-, and sucrose-based barriers). The experimental validation delivered a full-scale relative error of 0.25%, resulting in an absolute capacitance error of ±10 fF. In terms of reproducibility, the maximum uncertainty was below 10 nl s-1 for flow rate determination in this study. Furthermore, the experimental data was compared and validated with numerical analysis through electrical and flow dynamics simulations in porous media, providing crucial information on the wicking process, its physical parameters, and liquid flow dynamics.

Validated stability-indicating HPLC method for paricalcitol in pharmaceutical dosage form according to ICH guidelines: application to stability studies.

A stability-indicating HPLC method with diode array detection for the determination of paricalcitol, a synthetic vitamin D2 analog, was developed. Analytical parameters were studied according to International Conference on Harmonization guidelines. A C18 column (250 x 4.6 mm, 5 microm particle size) maintained at 25 degrees C was used as the stationary phase, and acetonitrile-water (70 + 30, v/v) as the mobile phase. Chromatograms were recorded at 250 nm. In forced degradation studies, the effects of acid, base, oxidation, temperature, and UV light were investigated and showed no interference with the drug peak. The method was found to be linear (r = 0.9989) at concentrations ranging from 0.6 to 10.0 mg/L paricalcitol, precise (repeatability and intermediate precision estimated as RSD less than 3.5%), accurate (recoveries higher than 95%), specific, and robust. The LOD and LOQ were 0.6 and 0.2 mg/L, respectively. The validated method was used for paricalcitol determination in a formal stability study of its pharmaceutical dosage form in preloaded syringes. The stability of a diluted solution of its pharmaceutical form in Viaflo bags was also tested. The results showed that paricalcitol was stable in preloaded syringes during a period of 30 days from preparation in the different storage conditions tested (room temperature without protection from daylight and 4.4 degrees C with protection from daylight). On the contrary, paricalcitol was quickly lost when stored in Viaflo bags by adsorption onto the walls of the container.

Highly stable luminescent europium-doped calcium phosphate nanoparticles for creatinine quantification.

The determination of creatinine levels is essential for the detection of renal and muscular dysfunction. Luminescent nanoparticles are emerging as fast, cheap and highly selective sensors for the detection and quantification of creatinine. Nevertheless, current nanosensors only have a short shelf life due to their poor chemical and colloidal stability, which limits their clinical functionality. In this work, we have developed a highly stable, selective and sensitive nanosensor based on europium-doped, amorphous calcium phosphate nanoparticles (Eu-ACP) for the determination of creatinine by luminescence spectroscopy. The colloidal stability of Eu-ACP nanoparticles in aqueous solutions was optimised to ensure a constant signal after up to 4 months in storage. The luminescence intensity of Eu-ACP decreased linearly with the creatinine concentration over the range of 1-120 µM (R2 = 0.995). This concentration-response relationship was used to determine creatinine levels in real urine samples resulting in good recovery percentages. Significantly, selectivity assays indicated that none of the potential interfering species provoked discernible changes in the luminescence intensity.

Ferrocene-carbohydrate conjugates as electrochemical probes for molecular recognition studies.

We report two methods that have allowed the attachment of glucose, mannose and lactose to one or both of the cyclopentadienyl rings of ferrocene. The resulting ferrocene-carbohydrate conjugates were synthesised by the reaction of thioglycosides with ferrocenemethanol and 1,1'-ferrocenedimethanol in acidic media. A second method based on the regiospecific copper(I)-catalysed cycloaddition of propargyl glycoside, azidomethyl and bis(azidomethyl)ferrocene as well as azidoethyl glycoside and ethynylferrocene was also used and led to the synthesis of 1,2,3-triazole-containing glycoconjugates. The electrochemical behaviour of the synthesised glycoconjugates was investigated. In addition, their binding interactions with beta-cyclodextrin were studied by means of NMR spectroscopy, isothermal titration calorimetry, and cyclic and differential pulse voltammetric experiments. These techniques allowed the determination of the thermodynamic parameters of the complexes, the stability constants for the complexes formed with both the neutral and the oxidised states of the ferrocenyl glycoconjugates, the mode of inclusion and the diffusion coefficients for both the glycoconjugates and the complexes.

Heavy metal concentrations in the general population of Andalusia, South of Spain: a comparison with the population within the area of influence of Aznalcóllar mine spill (SW Spain).

Levels of metalloids (As - urine) and heavy metals (Hg - urine, Cd - whole blood and Zn - serum) were determined by atomic absorption spectrometry in 601 subjects living in the area affected by the Aznalcóllar mine spill (SW, Spain) and compared with those of a representative sample (960 subjects) selected from the Andalusian community (non-affected area), southern Spain. The characteristic parameters of the analytical method including uncertainty were determined for each metal. Potential associations of metal concentration with age, sex and body mass index as well as life-style habits (smoking, alcohol consumption and food habits) were explored. Concentrations of all the metals studied were statistically higher in the population of the affected area with respect to that of the non-affected area in Andalusia, although levels were always lower or similar to the values reported for the general population and below occupational reference limits. In conclusion, there is a lack of evidence that the spill had any incidence on human health in the population living in the affected area. There are few references in scientific literature reporting values from large series of samples, and hence our data could be useful for further studies.

Fluorescence quenching of the europium tetracycline hydrogen peroxide complex by copper (II) and other metal ions.

The europium-tetracycline complex [Eu(Tc)] is known to show only weak fluorescence with an emission maximum at 615 nm. On addition of hydrogen peroxide (HP), the strongly fluorescent [Eu(Tc)(HP)] complex is formed, which displays a 15-fold stronger luminescence intensity. This study describes the decrease in luminescence intensity of the [Eu(Tc)(HP)] complex in aqueous solution in the presence of Cu2+, Fe3+, Ag+, Al3+, Zn2+, Co2+, Ni2+, Mn2+, Ca2+, and Mg2+. Static and dynamic quenching can be induced by Cu2+, and these processes were quantified by means of their quenching constants. Stern-Volmer plots were also derived from lifetime imaging measurements accomplished by the rapid lifetime determination (RLD) technique based on microwell plate assays, and also by the time-correlated single photon counting (TCSPC) technique. According to those data, a time-resolved fluorescent method for copper determination can be proposed that is based on dynamic quenching of the [Eu(Tc)(HP)] complex by Cu2+ ions. The response to copper concentrations is linear up to 1.6 micromol L(-1), providing a detection limit of 0.2 micromol L(-1).

Convenient methods for the synthesis of ferrocene-carbohydrate conjugates.

[structure: see text] We report two methods for the attachment of mono- and disaccharides to one or both of the cyclopentadienyl rings in ferrocene. The first strategy involves the reaction in acidic media of thioglycosides with ferrocenemethanol or 1,1'-ferrocenedimethanol. The second method consists of the regiospecific catalytic cycloaddition of propargyl glycoside and azidomethyl and bis(azidomethyl)ferrocene leading to the 1,2,3-triazole derivatives. The inverse strategy was also explored. The electrochemical behavior of the synthesized ferrocene-containing glycoconjugates was investigated.

Simultaneous determination of codeine and pyridoxine in pharmaceutical preparations by first-derivative spectrofluorimetry.

A method for the simultaneous determination of codeine and pyridoxine was developed, based on the measurement of their native fluorescence signals, by using first-derivative spectrofluorimetry to resolve the mixture. Codeine was measured at lambda(em) = 309 nm, and pyridoxine was measured at lambda(em) = 450 nm. Instrumental parameters were optimized, and the emission spectra were recorded between 275 and 475 nm, at lambda(ex) = 255 nm and excitation and emission slit widths of 2.5 and 10 nm, respectively. Systematic studies on the influence of species usually present along with the analytes (such as caffeine, ascorbic acid, paracetamol, and thiamine) were also performed. The calibration graphs were linear over the ranges of 0.5-7.0 and 0.1-1.0 microg/mL for codeine and pyridoxine, respectively, and the relative standard deviations (n = 10) were about 3%. The method was successfully applied to the determination of codeine and pyridoxine in solutions of synthetic mixtures and in synthetic and semisynthetic pharmaceutical formulations.

Stability of daptomycin 5 mg/mL and heparin sodium 100 units/mL combined in lactated Ringer's injection and stored in polypropylene syringes at 4 and -20°C.

PURPOSE: The stability of an admixture containing reconstituted daptomycin and heparin in lactated Ringer's injection was evaluated. METHODS: Two samples of the admixture of daptomycin 5 mg/mL and heparin sodium 100 USP units/mL diluted in lactated Ringer's injection were prepared and divided into 5-mL portions for storage in syringes at 4 and -20 °C for 14 days. The percentage of the initial concentration of the drugs remaining in the syringes was assessed using a high-performance liquid chromatographic (HPLC) method with diode-array detection previously validated as stability indicating for both drugs. Forced degradation studies were performed independently with each drug diluted in lactated Ringer's injection. One sample from each stored syringe was analyzed in triplicate on days 0, 1, 2, 3, 4, 7, and 14; quality-control samples of each concentration tested were used throughout the analysis. The admixture samples were visually inspected for color, clarity, and the formation of particulate matter. RESULTS: The HPLC analysis indicated no significant reduction (loss of ≤5%) in the concentration of daptomycin and heparin diluted in lactated Ringer's injection stored in syringes refrigerated at 4 °C and frozen at -20 °C. None of the chromatographic peaks observed in samples subjected to forced degradation were detected in any sample during the 14-day study. All of the syringe-stored samples remained clear and colorless on visual inspection for the duration of the study. CONCLUSION: The admixture of daptomycin 5 mg/mL and heparin sodium 100 USP units/mL was stable when stored in polypropylene syringes for up to 14 days at 4 and -20 °C.

Monitoring of degradation of porous silicon photonic crystals using digital photography.

We report the monitoring of porous silicon (pSi) degradation in aqueous solutions using a consumer-grade digital camera. To facilitate optical monitoring, the pSi samples were prepared as one-dimensional photonic crystals (rugate filters) by electrochemical etching of highly doped p-type Si wafers using a periodic etch waveform. Two pSi formulations, representing chemistries relevant for self-reporting drug delivery applications, were tested: freshly etched pSi (fpSi) and fpSi coated with the biodegradable polymer chitosan (pSi-ch). Accelerated degradation of the samples in an ethanol-containing pH 10 aqueous basic buffer was monitored in situ by digital imaging with a consumer-grade digital camera with simultaneous optical reflectance spectrophotometric point measurements. As the nanostructured porous silicon matrix dissolved, a hypsochromic shift in the wavelength of the rugate reflectance peak resulted in visible color changes from red to green. While the H coordinate in the hue, saturation, and value (HSV) color space calculated using the as-acquired photographs was a good monitor of degradation at short times (t < 100 min), it was not a useful monitor of sample degradation at longer times since it was influenced by reflections of the broad spectral output of the lamp as well as from the narrow rugate reflectance band. A monotonic relationship was observed between the wavelength of the rugate reflectance peak and an H parameter value calculated from the average red-green-blue (RGB) values of each image by first independently normalizing each channel (R, G, and B) using their maximum and minimum value over the time course of the degradation process. Spectrophotometric measurements and digital image analysis using this H parameter gave consistent relative stabilities of the samples as fpSi > pSi-ch.

Carbon dots for copper detection with down and upconversion fluorescent properties as excitation sources.

Carbon dots were synthesized by a simple and green strategy for selective and sensitive Cu(2+) ion detection using both down and upconversion fluorescence. These fluorescent nanosensors show low cytotoxicity and are applied for intracellular sensing and imaging of Cu(2+) in biological systems.