Alejandro Lapresta-Fernández

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.

A General Perspective of the Characterization and Quantification of Nanoparticles: Imaging, Spectroscopic, and Separation Techniques

This article gives an overview of the different techniques used to identify, characterize, and quantify engineered nanoparticles (ENPs). The state-of-the-art of the field is summarized, and the different characterization techniques have been grouped according to the information they can provide. In addition, some selected applications are highlighted for each technique. The classification of the techniques has been carried out according to the main physical and chemical properties of the nanoparticles such as morphology, size, polydispersity characteristics, structural information, and elemental composition. Microscopy techniques including optical, electron and X-ray microscopy, and separation techniques with and without hyphenated detection systems are discussed. For each of these groups, a brief description of the techniques, specific features, and concepts, as well as several examples, are described.

Portable light-emitting diode-based photometer with one-shot optochemical sensors for measurement in the field

This report describes the electronics of a portable, low-cost, light-emitting diode (LED)-based photometer dedicated to one-shot optochemical sensors. Optical detection is made through a monolithic photodiode with an on-chip single-supply transimpedance amplifier that reduces some drawbacks such as leakage currents, interferences, and parasitic capacitances. The main instrument characteristics are its high light source stability and thermal correction. The former is obtained by means of the optical feedback from the LED polarization circuit, implementing a pseudo-two light beam scheme from a unique light source with a built-in beam splitter. The feedback loop has also been used to adjust the LED power in several ranges. Moreover, the low-thermal coefficient achieved (-90 ppm/degrees C) is compensated by thermal monitoring and calibration function compensation in the digital processing. The hand-held instrument directly gives the absorbance ratio used as the analytical parameter and the analyte concentration after programming the calibration function in the microcontroller. The application of this photometer for the determination of potassium and nitrate, using one-shot sensors with ionophore-based chemistries is also demonstrated, with a simple analytical methodology that shortens the analysis time, eliminating some calibrating solutions (HCl, NaOH, and buffer). Therefore, this compact instrument is suitable for real-time analyte determination and operation in the field.

Particle tuning and modulation of the magnetic/colour synergy in Fe(II) spin crossover-polymer nanocomposites in a thermochromic sensor array

Thermochromic thin films of the spin crossover (SCO) polymer [Fe(NH2trz)3](BF4) are prepared using a variety of organic polymers as hosts. The formation of different polymeric networks is confirmed macroscopically by the colour changes related to an SCO phenomenon induced by thermal variation, and the results are correlated with electron microscopy and energy dispersive X-ray spectroscopy. Large particles of the SCO material are observed in SCO/polymer hybrid systems with hydrophobic polymers, while more dispersed nano-crystals appear in the hydrophilic matrices, leading to the transformation of the particles into fibrous structures. Subsequently, submicrometer-size SCO fibrous nanoparticles undergo colourimetric spin transitions near room temperature while grains with sizes larger than several microns move their transitions to lower temperatures. The difference in properties between the SCO/polymer hybrid materials is not only due to the differences in the size and shape of the SCO crystals in each polymer but also to the nature of the polymer and solvent interactions. The optical changes obtained for each SCO/polymer hybrid material are related to the microscopic origin of the cooperative interactions tracked by using a photographic digital camera. A linear correlation is obtained (colour values versus temperature) when processing all the colourimetric data by artificial neural networks, thus avoiding the uncertainty inherent in the hysteresis loop.

Evaluation of a reconfigurable portable instrument for copper determination based on luminescent carbon dots

A portable reconfigurable platform for copper (Cu(II)) determination based on luminescent carbon dot (Cdots) quenching is described. The electronic setup consists of a light-emitting diode (LED) as the carbon dot optical exciter and a photodiode as a light-to-current converter integrated in the same instrument. Moreover, the overall analog conditioning is simply performed with one integrated solution, a field-programmable analog array (FPAA), which makes it possible to reconfigure the filter and gain stages in real time. This feature provides adaptability to use the platform as an analytical probe for carbon dots coming from different batches with some variations in luminescence characteristics. The calibration functions obtained that fit a modified Stern-Volmer equation were obtained using luminescence signals from Cdots quenching by Cu(II). The analytical applicability of the reconfigurable portable instrument for Cu(II) using Cdots has been successfully demonstrated in tap water analysis.