A fluorescent magnetic core-shell nanosensor for detection of copper ions in natural waters.

A nanosensor based on magnetic core-shell nanoparticles functionalized with rhodamine derivative, N-(3-carboxy)acryloyl rhodamine B hydrazide (RhBCARB), using (3-aminopropyl)triethoxysilane (APTES) as a linker, has been synthesized for detection of Cu(II) ions in water. The magnetic nanoparticle and the modified rhodamine were fully characterized, showing a strong orange emission sensitive to Cu(II) ions. The sensor shows a linear response from 10 to 90 µg L-1, detection limit of 3 µg L-1 and no interference of Ni(II), Co(II), Cd(II), Zn(II), Pb(II), Hg(II) and Fe(II) ions. The nanosensor performance is similar to those described in the literature, being a viable option for the determination of Cu(II) ions in natural waters. In addition, the magnetic sensor can be easily removed from the reaction medium with the aid of a magnet and its signal recovered in acidic solution, allowing its reuse in subsequent analysis.

Optimizing the Efficiency of a Cytocompatible Carbon-Dots-Based FRET Platform and Its Application as a Riboflavin Sensor in Beverages.

In this work, the Förster resonance energy transfer (FRET) between carbon dots (CDs) as energy donors and riboflavin (RF) as an energy acceptor was optimized and the main parameters that characterize the FRET process were determined. The results were successfully applied in the development of an ultrasensitive ratiometric fluorescent sensor for the selective and sensitive determination of RF in different beverages. Water-soluble CDs with a high quantum yield (54%) were synthesized by a facile and direct microwave-assisted technique. The CDs were characterized by transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), dynamic light scattering (DLS), Zeta potential, and UV-visible and molecular fluorescence spectroscopy. The study of the FRET process at two donor concentrations showed that the energy transfer efficiency decreases as the donor concentration increases, confirming its dependence on the acceptor:donor ratio in nanoparticle-based systems. The results show the importance of optimizing the FRET process conditions to improve the corresponding output signal. The variation in the ratiometric signal with the concentration of RF showed linearity in a concentration range of 0 to 11 µM with R2 = 0.9973 and a detection limit of 0.025 µM. The developed nanosensor showed good selectivity over other possible types of interference. The sensor was then applied for the determination of RF in beverage samples using the standard addition method with recoveries between 96% and 106%. Preliminary cytocompatibility tests carried out with breast cancer cells (MDA-MB-231) revealed the nanosensor to be cytocompatible in its working concentration regime, even after long incubation times with cells. Altogether, the developed RF determination method was found to be fast, low-cost, highly sensitive, and selective and can be extended to other samples of interest in the biological and food sectors. Moreover, thanks to its long-lasting cytocompatibility, the developed platform can also be envisaged for other applications of biological interest, such as intracellular sensing and staining for live cell microscopy.

Fluorescent Amorphous Distyrylnaphthalene-Based Polymers: Synthesis, Characterization and Thin-Film Nanomolar Sensing of Nitroaromatics in Water.

Two new fluorescent segmented conjugated polymers with either 1,4- or 2,6-distyrylnaphthalene chromophores and their model compounds were synthesized and the chemosensing abilities of the polymeric thin films to detect nitroaromatics (NACs) in aqueous media were evaluated. The structural, thermal and optical properties of the polymers were correlated with those displayed by their corresponding model compounds. Changes in the connectivity of naphthylene units caused minor differences in optical properties, morphology and quenching efficiencies. Molecular modeling highlighted the extremely bent character of polymer microstructures that explains their high solubility and amorphous character. Polymeric films are amorphous, strongly fluorescent and showed remarkable quenching efficiencies in the nanomolar range with picric acid (PA) and trinitrotoluene (TNT). Quenching experiments using either different nitroaromatic quenchers, excitation wavelengths, excitation beam path-lengths, or time of exposure of the film to the quenching solution evidenced the dominant role of inner filter effects (IFE) in the polymer response to NACs in the micromolar range. The sensing response towards PA, a quencher that strongly absorbs at the excitation wavelength, has an IFE contribution even at the nanomolar range, while the response towards the non-absorbing TNT depends only on the quenching occurring after diffusion of the analyte into the film.