3D-printed Laponite/Alginate hydrogel-based suppositories for versatile drug loading and release

Traditional approaches to solid rectal therapies have halted progress, leading to a continual decline in the use of conventional suppositories. Additive manufacturing techniques have been recently explored as a suitable innovative tool for suppository fabrication. However, little advancement has been made in composition materials for 3D-printed suppository (3DPS) manufacturing and still, conventional vehicles are often used for construct fabrication, hindering the growth in the field. As a novelty, this study unveils a ground-breaking Laponite-alginate hydrogel-based 3DPS. Interestingly, this study proposes a novel approach for loading drugs into the 3DPS employing for the first time the post-printing loading. Thus, a passive loading strategy of molecular models is developed, demonstrating the versatility and capacity to load molecules of different charges and molecular sizes within the matrix systems. This novel strategy allows adapting the load of a wide range of drugs into a single ink, which simplifies and speeds up the 3DPS technological development process for drugs with different physico-chemical properties. Additionally, in this research, a displacement strategy of the three-dimensional Laponite matrices is developed in order to enhance the drug release capacity through the 3DPS and their disintegration capacity, resulting in a significant improvement of the drug diffusion through the hydrogel matrix and a rapid disintegration of the 3DPS. Finally, our study demonstrates that the obtained 3DPS have a suitable in vivo behavior, being non-obstructive and allowing the normal motility of the rats intestine.

Ion-induced bias in Ag2S luminescent nanothermometers

Luminescence nanothermometry allows measuring temperature remotely and in a minimally invasive way by using the luminescence signal provided by nanosized materials. This technology has allowed, for example, the determination of intracellular temperature and in vivo monitoring of thermal processes in animal models. However, in the biomedical context, this sensing technology is crippled by the presence of bias (cross-sensitivity) that reduces the reliability of the thermal readout. Bias occurs when the impact of environmental conditions different from temperature also modifies the luminescence of the nanothermometers. Several sources that cause loss of reliability have been identified, mostly related to spectral distortions due to interaction between photons and biological tissues. In this work, we unveil an unexpected source of bias induced by metal ions. Specifically, we demonstrate that the reliability of Ag2S nanothermometers is compromised during the monitoring of photothermal processes produced by iron oxide nanoparticles. The observed bias occurs due to the heat-induced release of iron ions, which interact with the surface of the Ag2S nanothermometers, enhancing their emission. The results herein reported raise a warning to the community working on luminescence nanothermometry, since they reveal that the possible sources of bias in complex biological environments, rich in molecules and ions, are more numerous than previously expected.

3D Optical Coherence Thermometry Using Polymeric Nanogels

In nanothermometry, the use of nanoparticles as thermal probes enables remote and minimally invasive sensing. In the biomedical context, nanothermometry has emerged as a powerful tool where traditional approaches, like infrared thermal sensing and contact thermometers, fall short. Despite the strides of this technology in preclinical settings, nanothermometry is not mature enough to be translated to the bedside. This is due to two major hurdles: the inability to perform 3D thermal imaging and the requirement for tools that are readily available in the clinics. This work simultaneously overcomes both limitations by proposing the technology of optical coherence thermometry (OCTh). This is achieved by combining thermoresponsive polymeric nanogels and optical coherence tomography (OCT)-a 3D imaging technology routinely used in clinical practice. The volume phase transition of the thermoresponsive nanogels causes marked changes in their refractive index, making them temperature-sensitive OCT contrast agents. The ability of OCTh to provide 3D thermal images is demonstrated in tissue phantoms subjected to photothermal processes, and its reliability is corroborated by comparing experimental results with numerical simulations. The results included in this work set credible foundations for the implementation of nanothermometry in the form of OCTh in clinical practice.

Exploring the Origin of the Thermal Sensitivity of Near-Infrared-II Emitting Rare Earth Nanoparticles

Rare-earth doped nanoparticles (RENPs) are attracting increasing interest in materials science due to their optical, magnetic, and chemical properties. RENPs can emit and absorb radiation in the second biological window (NIR-II, 1000-1400 nm) making them ideal optical probes for photoluminescence (PL) in vivo imaging. Their narrow emission bands and long PL lifetimes enable autofluorescence-free multiplexed imaging. Furthermore, the strong temperature dependence of the PL properties of some of these RENPs makes remote thermal imaging possible. This is the case of neodymium and ytterbium co-doped NPs that have been used as thermal reporters for in vivo diagnosis of, for instance, inflammatory processes. However, the lack of knowledge about how the chemical composition and architecture of these NPs influence their thermal sensitivity impedes further optimization. To shed light on this, we have systematically studied their emission intensity, PL decay time curves, absolute PL quantum yield, and thermal sensitivity as a function of the core chemical composition and size, active-shell, and outer-inert-shell thicknesses. The results revealed the crucial contribution of each of these factors in optimizing the NP thermal sensitivity. An optimal active shell thickness of around 2 nm and an outer inert shell of 3.5 nm maximize the PL lifetime and the thermal response of the NPs due to the competition between the temperature-dependent back energy transfer, the surface quenching effects, and the confinement of active ions in a thin layer. These findings pave the way for a rational design of RENPs with optimal thermal sensitivity.

Optomagnetic nanofluids for controlled brain hyperthermia: a critical study

Optomagnetic nanofluids (OMNFs) are colloidal dispersions of nanoparticles (NPs) with combined magnetic and optical properties. They are especially appealing in biomedicine since they can be used as minimally invasive platforms for controlled hyperthermia treatment of otherwise difficultly accessible tumors such as intracranial ones. On the one hand, magnetic NPs act as heating mediators when subjected to alternating magnetic fields or light irradiation. On the other hand, suitably tailored luminescent NPs can provide a precise and remote thermal readout in real time. The combination of heating and thermometric properties allows, in principle, to precisely monitor the increase in the temperature of brain tumors up to the therapeutic level, without causing undesired collateral damage. In this work we demonstrate that this view is an oversimplification since it ignores the presence of relevant interactions between magnetic (γ-Fe₂O₃ nanoflowers) and luminescent nanoparticles (Ag₂S NPs) that result in a detrimental alteration of their physicochemical properties. The magnitude of such interactions depends on the interparticle distance and on the surface properties of nanoparticles. Experiments performed in mouse brains (phantoms and ex vivo) revealed that OMNFs cannot induce relevant heating under alternating magnetic fields and fail to provide reliable temperature reading. In contrast, we demonstrate that the use of luminescent nanofluids (containing only Ag₂S NPs acting as both photothermal agents and nanothermometers) stands out as a better alternative for thermally monitored hyperthermia treatment of brain tumors in small animal models.

SPION nanoparticles for delivery of dopaminergic isoquinoline and benzazepine derivatives

Superparamagnetic iron nanoparticles (SPIONs) have become one of the most useful colloidal systems in nanomedicine. We report here the preparation of new hybrid core@shell systems based on SPION nanoparticles coated with a SiO₂ shell (SPION@SiO₂) and functionalized with carboxyl groups (SPION@SiO₂-COOH). A series of new N-alkylamino- and N-alkylamido-terminated 1-phenyl- tetrahydroisoquinolines (THIQs) and 3-tetrahydrobenzazepines (THBs) derivatives presenting -SMe and -Cl groups, respectively, with potential dopaminergic activity, are synthesized and incorporated to the hybrid system. We include the synthetic details for THIQs and THBs derivatives preparation and investigate the influence of the terminal-functional group as well as the number of carbon atoms linked to THIQ and THB molecules during the coupling to the SPION@SiO₂-COOH. Nuclear magnetic resonance (NMR) and electron ionization mass spectrometry (EI-MS) are used to characterize the synthesized THIQs and THBs. High-angle annular dark-field transmission electron microscopy (HAADF-TEM), energy dispersive X-ray transmission electron microscopy (EDX-TEM), and proton high-resolution magic angle spinning NMR spectroscopy¹H HRMAS-NMR) are used to confirm the presence of THB and THIQ molecules onto the surface of the nanoparticles. The hybrid SPION@SiO₂-THIQ and THB systems show significant activity toward the D₂ receptor, reaching Ki values of about 20 nM, thus having potential application in the treatment of central nervous system (CNS) diseases.

Clickable Albumin Nanoparticles for Pretargeted Drug Delivery toward PD-L1 Overexpressing Tumors in Combination Immunotherapy

We present a simple methodology to design a pretargeted drug delivery system, based on clickable anti-programmed death ligand 1 (anti-PD-L1) antibodies (Abs) and clickable bovine serum albumin (BSA) nanoparticles (NPs). Pretargeted drug delivery is based on the decoupling of a targeting moiety and a drug-delivering vector which can then react in vivo after separate injections. This may be key to achieve active targeting of drug-delivering NPs toward cancerous tissue. In pretargeted approaches, drug-delivering NPs were observed to accumulate in a higher amount in the targeted tissue due to shielding-related enhanced blood circulation and size-related enhanced tissue penetration. In this work, BSA NPs were produced using the solvent precipitation methodology that renders colloidally stable NPs, which were subsequently functionalized with a clickable moiety based on chlorosydnone (Cl-Syd). Those reactive groups are able to specifically react with dibenzocyclooctyne (DBCO) groups in a click-type fashion, reaching second-order reaction rate constants as high as 1.9 M^-1·s^-1, which makes this reaction highly suitable for in vivo applications. The presence of reactive Cl-Syd was demonstrated by reacting the functionalized NPs with a DBCO-modified sulfo-cyanine-5 dye. With this reaction, it was possible to infer the number of reactive moieties per NPs. Finally, and with the aim of demonstrating the suitability of this system to be used in pretargeted strategies, functionalized fluorescent NPs were used to label H358 cells with a clickable anti-PD-L1 Ab, applying the reaction between Cl-Syd and DBCO as corresponding clickable groups. The results of these experiments demonstrate the bio-orthogonality of the system to perform the reaction in vitro, in a period as short as 15 min.

Reliable and Remote Monitoring of Absolute Temperature during Liver Inflammation via Luminescence-Lifetime-Based Nanothermometry

Temperature of tissues and organs is one of the first parameters affected by physiological and pathological processes, such as metabolic activity, acute trauma, or infection-induced inflammation. Therefore, the onset and development of these processes can be detected by monitoring deviations from basal temperature. To accomplish this, minimally invasive, reliable, and accurate measurement of the absolute temperature of internal organs is required. Luminescence nanothermometry is the ideal technology for meeting these requirements. Although this technique has lately undergone remarkable developments, its reliability is being questioned due to spectral distortions caused by biological tissues. In this work, how the use of bright Ag₂ S nanoparticles featuring temperature-dependent fluorescence lifetime enables reliable and accurate measurement of the absolute temperature of the liver in mice subjected to lipopolysaccharide-induced inflammation is demonstrated. Beyond the remarkable thermal sensitivity (≈ 3% °C^-1 around 37 °C) and thermal resolution obtained (smaller than 0.3 °C), the results included in this work set a blueprint for the development of new diagnostic procedures based on the use of intracorporeal temperature as a physiological indicator.

Upconverting Nanoparticles in Aqueous Media: Not a Dead-End Road. Avoiding Degradation by Using Hydrophobic Polymer Shells

The stunning optical properties of upconverting nanoparticles (UCNPs) have inspired promising biomedical technologies. Nevertheless, their transfer to aqueous media is often accompanied by intense luminescence quenching, partial dissolution by water, and even complete degradation by molecules such as phosphates. Currently, these are major issues hampering the translation of UCNPs to the clinic. In this work, a strategy is developed to coat and protect β-NaYF₄ UCNPs against these effects, by growing a hydrophobic polymer shell (HPS) through miniemulsion polymerization of styrene (St), or St and methyl methacrylate mixtures. This allows one to obtain single core@shell UCNPs@HPS with a final diameter of ≈60-70 nm. Stability studies reveal that these HPSs serve as a very effective barrier, impeding polar molecules to affect UCNPs optical properties. Even more, it allows UCNPs to withstand aggressive conditions such as high dilutions (5 µg mL^-1 ), high phosphate concentrations (100 mm), and high temperatures (70 °C). The physicochemical characterizations prove the potential of HPSs to overcome the current limitations of UCNPs. This strategy, which can be applied to other nanomaterials with similar limitations, paves the way toward more stable and reliable UCNPs with applications in life sciences.

Matrix tablets based on a novel poly (magnesium acrylate) hydrogel for the treatment of inflammatory bowel diseases

The objective of this work was to evaluate the potential use of a new polymer (PAMgA) in the development sustained release matrix tablets for the treatment of bowel inflammatory diseases. For this purpose, budesonide, a highly lipophilic compound, was used as model drug. Tablets with two reticulation grades of PAMgA (PAMgA 5 and 40) and with 9 mg of budesonide were developed and characterized. All the studies were carried out using biorelevant media (FaSSGF and FaSSIF). Swelling and erosion of PAMgA tablets was influenced by the reticulation grade of the polymer and the biorelevant media assayed, being water uptake higher for PAMgA 40 tablets in intestinal fluid, whereas PAMgA 5 showed more intense erosion in this biorelevant medium. Budesonide was released slowly from PAMgA tablets, both in gastric and intestinal environment, following Super case II transport kinetics (relaxation-controlled delivery), with a lag time of around 1-2 h. When the dissolution medium was changed sequentially throughout the trial, 75% of the budesonide dose was released in a sustained manner between 4 and 20 h of testing from PAMgA tablets, showing a more controlled budesonide release than Entocort® and Budenofalk® (commercially available sustained release formulations of budesonide). In conclusion, PAMgA polymer allows controlling the release of highly lipophilic drugs as budesonide, being an useful excipient for the development of sustained release matrix tablets.

Oligonucleotide sensor based on magnetic capture and photoligation of upconverting nanoparticles in solid surfaces

In this work, we present a luminescence platform that can be used as point of care system for determining the presence and concentration of specific oligonucleotide sequences. This sensor exhibited a limit of detection as low as 50 fM by means of: (i) the use of single-stranded DNA (ssDNA) functionalized magnetic microparticles that captured and concentrated ssDNA-upconverting nanoparticles (ssDNA-UCNPs) on a solid support, when the target sequence (miR-21-5p DNA-analogue) was in the sample, and (ii) a photoligation reaction that covalently linked the ssDNA-UCNPs and the ssDNA magnetic microparticles, allowing stringent washes. The presented sensor showed a similar limit of detection when the assays were conducted in samples containing total miRNA extracted from human serum, demonstrating its suitability for detecting small specific oligonucleotide sequences under real-like conditions. The strategy of combining UCNPs, magnetic microparticles, and a photoligation reaction provides new insight into low-cost, rapid, and ultra-sensitive detection of oligonucleotide sequences.

Instantaneous In Vivo Imaging of Acute Myocardial Infarct by NIR-II Luminescent Nanodots

Fast and precise localization of ischemic tissues in the myocardium after an acute infarct is required by clinicians as the first step toward accurate and efficient treatment. Nowadays, diagnosis of a heart attack at early times is based on biochemical blood analysis (detection of cardiac enzymes) or by ultrasound-assisted imaging. Alternative approaches are investigated to overcome the limitations of these classical techniques (time-consuming procedures or low spatial resolution). As occurs in many other fields of biomedicine, cardiological preclinical imaging can also benefit from the fast development of nanotechnology. Indeed, bio-functionalized near-infrared-emitting nanoparticles are herein used for in vivo imaging of the heart after an acute myocardial infarct. Taking advantage of the superior acquisition speed of near-infrared fluorescence imaging, and of the efficient selective targeting of the near-infrared-emitting nanoparticles, in vivo images of the infarcted heart are obtained only a few minutes after the acute infarction event. This work opens an avenue toward cost-effective, fast, and accurate in vivo imaging of the ischemic myocardium after an acute infarct.

Ultrafast photochemistry produces superbright short-wave infrared dots for low-dose in vivo imaging

Optical probes operating in the second near-infrared window (NIR-II, 1,000-1,700 nm), where tissues are highly transparent, have expanded the applicability of fluorescence in the biomedical field. NIR-II fluorescence enables deep-tissue imaging with micrometric resolution in animal models, but is limited by the low brightness of NIR-II probes, which prevents imaging at low excitation intensities and fluorophore concentrations. Here, we present a new generation of probes (Ag₂S superdots) derived from chemically synthesized Ag₂S dots, on which a protective shell is grown by femtosecond laser irradiation. This shell reduces the structural defects, causing an 80-fold enhancement of the quantum yield. PEGylated Ag₂S superdots enable deep-tissue in vivo imaging at low excitation intensities (<10 mW cm⁻²) and doses (<0.5 mg kg⁻¹), emerging as unrivaled contrast agents for NIR-II preclinical bioimaging. These results establish an approach for developing superbright NIR-II contrast agents based on the synergy between chemical synthesis and ultrafast laser processing.

Deep tissue imaging has been limited by the low brightness of probes emitting in the second near-infrared window. Here, the authors use femtosecond laser irradiation to grow a protective shell on Ag₂S nanoparticles, achieving 80-fold quantum yield enhancement and imaging with low excitation intensities.

Contribution of resonance energy transfer to the luminescence quenching of upconversion nanoparticles with graphene oxide

Upconversion nanoparticles (UCNP) are increasingly used due to their advantages over conventional fluorophores, and their use as resonance energy transfer (RET) donors has permitted their application as biosensors when they are combined with appropriate RET acceptors such as graphene oxide (GO). However, there is a lack of knowledge about the design and influence that GO composition produces over the quenching of these nanoparticles that in turn will define their performance as sensors. In this work, we have analysed the total quenching efficiency, as well as the actual values corresponding to the RET process between UCNPs and GO sheets with three different chemical compositions. Our findings indicate that excitation and emission absorption by GO sheets are the major contributor to the observed luminescence quenching in these systems. This challenges the general assumption that UCNPs luminescence deactivation by GO is caused by RET. Furthermore, RET efficiency has been theoretically calculated by means of a semiclassical model considering the different nonradiative energy transfer rates from each Er³⁺ ion to the GO thin film. These theoretical results highlight the relevance of the relative positions of the Er³⁺ ions inside the UCNP with respect to the GO sheet in order to explain the RET-induced efficiency measurements.

10-Fold Quantum Yield Improvement of Ag2S Nanoparticles by Fine Compositional Tuning

Ag₂S semiconductor nanoparticles (NPs) are near-infrared luminescent probes with outstanding properties (good biocompatibility, optimum spectral operation range, and easy biofunctionalization) that make them ideal probes for in vivo imaging. Ag₂S NPs have, indeed, made possible amazing challenges including in vivo brain imaging and advanced diagnosis of the cardiovascular system. Despite the continuous redesign of synthesis routes, the emission quantum yield (QY) of Ag₂S NPs is typically below 0.2%. This leads to a low luminescent brightness that avoids their translation into the clinics. In this work, an innovative synthetic methodology that permits a 10-fold increment in the absolute QY from 0.2 up to 2.3% is presented. Such an increment in the QY is accompanied by an enlargement of photoluminescence lifetimes from 184 to 1200 ns. The optimized synthetic route presented here is based on a fine control over both the Ag core and the Ag/S ratio within the NPs. Such control reduces the density of structural defects and decreases the nonradiative pathways. In addition, we demonstrate that the superior performance of the Ag₂S NPs allows for high-contrast in vivo bioimaging.

Controlled Release of Highly Hydrophilic Drugs from Novel Poly(Magnesium Acrylate) Matrix Tablets

The potential of a new poly(magnesium acrylate) hydrogel (PAMgA) as a pharmaceutical excipient for the elaboration of matrix tablets for the extended release of highly hydrophilic drugs was evaluated. The polymer was synthetized with two different crosslinking degrees that were characterized by FTIR and DSC. Their acute oral toxicity was determined in a mouse model, showing no toxicity at doses up to 10 g/kg. Matrix tablets were prepared using metformin hydrochloride as a model drug and the mechanisms involved in drug release (swelling and/or erosion) were investigated using biorrelevant media. This new hydrogel effectively controlled the release of small and highly hydrophilic molecules as metformin, when formulated in matrix tablets for oral administration. The rate of metformin release from PAMgA matrices was mainly controlled by its diffusion through the gel layer (Fickian diffusion). The swelling capacity and the erosion of the matrix tablets influenced the metformin release rate, that was slower at pH 6.8, where polymer swelling is more intensive, than in gastric medium, where matrix erosion is slightly more rapid. The crosslinking degree of the polymer significantly influenced its swelling capacity in acid pH, where swelling is moderate, but not in intestinal fluid, where swelling is more intense.

Control of upconversion luminescence by gold nanoparticle size: from quenching to enhancement

Metallic nanostructures have the potential to modify the anti-Stokes emission of upconverting nanoparticles (UCNPs) by coupling their plasmon resonance with either the excitation or the emission wavelength of the UCNPs. In this regard gold nanoparticles (AuNPs) have often been used in sensors for UCNP luminescence quenching or enhancement, although systematic studies are still needed in order to design optimal UCNP-AuNP based biosensors. Amidst mixed experimental evidence of quenching or enhancement, two key factors arise: the nanoparticle distance and nanoparticle size. In this work, we synthesize AuNPs of different sizes to assess their influence on the luminescence of UCNPs. We find that strong luminescence quenching due to resonance energy transfer is preferentially achieved for small AuNPs, peaking at an optimal size. A further increase in the AuNP size is accompanied by a reduction of luminescence quenching due to an incipient plasmonic enhancement effect. This enhancement counterbalances the luminescence quenching effect at the biggest tested AuNP size. The experimental findings are theoretically validated by studying the decay rate of the UCNP emitters near a gold nanoparticle using both a classical phenomenological model and the finite-difference time-domain method. Results from this study establish general guidelines to consider when designing sensors based on UCNPs-AuNPs as donor-quencher pairs, and suggest the potential of plasmon-induced luminescence enhancement as a sensing strategy.

Development and Characterization of Florfenicol-Loaded BSA Nanoparticles as Controlled Release Carrier

Florfenicol (FLO) is a broad-spectrum fluorinated antibiotic used for the treatment of bacterial diseases such as bovine respiratory disease (BRD) in cattle. FLO is a poorly soluble drug in aqueous solution, and its encapsulation in various nanovehicles has been reported to be less than 30%. In this context, the use of bovine serum albumin (BSA) as a nanocarrier for FLO is an interesting approach. BSA is a biocompatible, biodegradable, nontoxic, and nonimmunogenic natural protein, allowing the vehiculization of hydrophilic and hydrophobic drugs with a well-tolerated administration. The present work focuses on the fabrication and characterization of florfenicol-loaded BSA (FLO-BSA NPs), incorporation efficiency, and in vitro release pattern. FLO-BSA NPs nanoparticles were successfully obtained by a simple, low-cost and in a few steps method. The physicochemical properties of the obtained nanoparticles such as size (~ 120 nm), polydispersity index (0.04), and zeta potential (approximately - 40 mV) suggest a high colloidal stability and suitable characteristics for drug delivery. The drug loading reveals a high incorporation of florfenicol in the nanoparticles, in which 33.6 molecules of FLO are encapsulated per each molecule of BSA. The in vitro release profile exhibits an initial stage characterized by the burst effect and then a prolonged release of FLO from the albumin matrix, which is compatible with the Higuchi model and which follows a Fickian diffusion. The results together suggest a suitable tool for future investigations in drug delivery field in order to use this nanomaterial in food, pharmaceutical, and veterinary industry.

Photochemical Ligation to Ultrasensitive DNA Detection with Upconverting Nanoparticles

In this work, we explore a photochemical ligation reaction to covalently modify oligonucleotide-conjugated upconverting nanoparticles (UCNPs) in the presence of a specific target DNA sequence. The target sequence acts as a hybridization template, bringing together a biotinylated photoactivatable oligonucleotide probe and the oligonucleotide probe that is attached to UCNPs. The illumination of the UCNPs by NIR light to generate UV emission internally or illuminating the photoactivatable probe directly by an external UV light promotes the photochemical ligation reaction, yielding covalently biotin functionalized UCNPs that can be selectively captured in streptavidin-coated microwells. Following this strategy, we developed a DNA sensor with a limit of detection of 1 × 10^-18 mol per well (20 fM). In addition, we demonstrate the possibility to create UCNP patterns on the surface of solid supports upon NIR illumination that are selectively formed under the presence of the target oligonucleotide.

Sensors and bioassays powered by upconverting materials

In recent years, considerable efforts have been done to better understand the peculiar emission properties of upconverting materials due to their widespread applications in different and important technological fields such as upconversion-based photoactivated cancer therapies, photoactivated drug-delivery, magnetic resonance imaging contrast agents, bioimaging. However, one of the most promising applications of upconverting materials concerns the field of sensing, due to their unique emission properties. In fact, the minimal autofluorescence, blinking, photo-bleaching, and high photostability makes them an excellent alternative to organic dyes or quantum dots. This article reviews the state-of-the-art, design, and sensing strategies of upconversion-based sensing platforms, with special attention to upconverting nanoparticles, as well as how the incorporation of these materials into pre-existing diagnostic tests and bioassays have improved their capabilities for the detection of different kinds of analytes.

Oligonucleotide Sensor Based on Selective Capture of Upconversion Nanoparticles Triggered by Target-Induced DNA Interstrand Ligand Reaction

We present a sensor that exploits the phenomenon of upconversion luminescence to detect the presence of specific sequences of small oligonucleotides such as miRNAs among others. The sensor is based on NaYF₄:Yb,Er@SiO₂ nanoparticles functionalized with ssDNA that contain azide groups on the 3' ends. In the presence of a target sequence, interstrand ligation is possible via the click-reaction between one azide of the upconversion probe and a DBCO-ssDNA-biotin probe present in the solution. As a result of this specific and selective process, biotin is covalently attached to the surface of the upconversion nanoparticles. The presence of biotin on the surface of the nanoparticles allows their selective capture on a streptavidin-coated support, giving a luminescent signal proportional to the amount of target strands present in the test samples. With the aim of studying the analytical properties of the sensor, total RNA samples were extracted from healthy mosquitoes and were spiked-in with a specific target sequence at different concentrations. The result of these experiments revealed that the sensor was able to detect 10^-17 moles per well (100 fM) of the target sequence in mixtures containing 100 ng of total RNA per well. A similar limit of detection was found for spiked human serum samples, demonstrating the suitability of the sensor for detecting specific sequences of small oligonucleotides under real conditions. In contrast, in the presence of noncomplementary sequences or sequences having mismatches, the luminescent signal was negligible or conspicuously reduced.

Enhancement of the Upconversion Emission by Visible-to-Near-Infrared Fluorescent Graphene Quantum Dots for miRNA Detection

We developed a sensor for the detection of specific microRNA (miRNA) sequences that was based on graphene quantum dots (GQDs) and ssDNA-UCNP@SiO2. The proposed sensor exploits the interaction between the sp(2) carbon atoms of the GQD, mainly π-π stacking, and the DNA nucleobases anchored on the upconversion nanoparticles (UCNPs). This interaction brings the GQD to the surface of the ssDNA-UCNP@SiO2 system, enhancing the upconversion emission. On the other hand, hybridization of the single-stranded DNA (ssDNA) chains anchored on the nanoparticles with their complementary miRNA sequences blocks the capacity of the UCNPs to interact with the GQD through π-π stacking. That gives as result a reduction of the fluorescent enhancement, which is dependent on the concentration of miRNA sequences. This effect was used to create a sensor for miRNA sequences with a detection limit of 10 fM.

Synthesis of catalytically active gold clusters on the surface of Fe3O4@SiO2 nanoparticles

This work proposes a novel method to obtain catalytically active gold clusters by using the water-soluble 5,10,15,20-Tetrakis(4-trimethyl-ammonio-phenyl)porphyrin under mild conditions instead of using strong reducing agents.

Synthesis, Characterization, and Application in HeLa Cells of an NIR Light Responsive Doxorubicin Delivery System Based on NaYF4:Yb,Tm@SiO2-PEG Nanoparticles

Herein, we present a phototriggered drug delivery system based on light responsive nanoparticles, which is able to release doxorubicin upon NIR light illumination. The proposed system is based on upconversion fluorescence nanoparticles of β-NaYF4:Yb,Tm@SiO2-PEG with a mean diameter of 52±2.5 nm that absorb the NIR light and emit UV light. The UV radiation causes the degradation of photodegradable ortho-nitrobenzyl alcohol derivates, which are attached on one side to the surface of the nanoparticles and on the other to doxorubicin. This degradation triggers the doxorubicin release. This drug delivery system has been tested "in vitro" with HeLa cells. The results of this study demonstrated that this system caused negligible cytotoxicity when they were not illuminated with NIR light. In contrast, under NIR light illumination, the HeLa cell viability was conspicuously reduced. These results demonstrated the suitability of the proposed system to control the release of doxorubicin via an external NIR light stimulus.

Highly Sensitive DNA Sensor Based on Upconversion Nanoparticles and Graphene Oxide

In this work we demonstrate a DNA biosensor based on fluorescence resonance energy transfer (FRET) between NaYF4:Yb,Er nanoparticles and graphene oxide (GO). Monodisperse NaYF4:Yb,Er nanoparticles with a mean diameter of 29.1 ± 2.2 nm were synthesized and coated with a SiO2 shell of 11 nm, which allowed the attachment of single strands of DNA. When these DNA-functionalized NaYF4:Yb,Er@SiO2 nanoparticles were in the proximity of the GO surface, the π-π stacking interaction between the nucleobases of the DNA and the sp(2) carbons of the GO induced a FRET fluorescence quenching due to the overlap of the fluorescence emission of the NaYF4:Yb,Er@SiO2 and the absorption spectrum of GO. By contrast, in the presence of the complementary DNA strands, the hybridization leads to double-stranded DNA that does not interact with the GO surface, and thus the NaYF4:Yb,Er@SiO2 nanoparticles remain unquenched and fluorescent. The high sensitivity and specificity of this sensor introduces a new method for the detection of DNA with a detection limit of 5 pM.

Temperature controlled fluorescence on Au@Ag@PNIPAM-PTEBS microgels: effect of the metal core size on the MEF extension

In this work, we present a novel method to produce thermoresponsive, monodisperse microgels which display temperature-dependent photoluminescence. The system is based on bimetallic cores of Au@Ag encapsulated within thermoresponsive poly(N-isopropylacrylamide) microgels and coated with a photoluminescent polymer (poly[2-(3-thienyl)ethoxy-4-butylsulfonate] (PTEBS) using the Layer-by-Layer technique. The electromagnetic radiation used to excite the PTEBS induces a local electromagnetic field on the surface of the bimetallic cores that enhances the excitation and emission rates of the PTEBS, yielding a metal enhanced fluorescence (MEF). This effect was studied as a function of the bimetallic core size and the separation distance between the PTEBS and the bimetallic cores. Our results permit evaluation of the effect that the metallic core size of colloidal particles exerts on the MEF for the first time, and prove the relevance of the metallic cores to extend the effect far away from the metallic surface.

Synthesis of thermosensitive microgels with a tunable magnetic core

In this work, we describe a new methodology for the preparation of monodisperse and thermosensitive microgels with magnetic core. In order to produce such a material, hydrophobic magnetic Fe(3)O(4) nanoparticles were prepared by two methods: thermal decomposition and coprecipitation. The surface of these nanoparticles was modified by addition of 3-butenoic acid, and after that these nanoparticles were dispersed in water and submitted to free radical polymerization at 70 °C in the presence of N-isopropylacrylamide (NIPAM) and bisacrylamide. The result of this reaction was monodisperse microgels with a magnetic core. By varying the amount of 3-butenoic acid, it was possible to obtain hybrid microgels with different magnetic core sizes and different architectures.

Template-assisted fabrication of magnetically responsive hollow titania capsules

This study reports on the fabrication of magnetically responsive hollow titania capsules by confining the superparamagnetic Fe(3)O(4) nanoparticles within a hollow and porous titania (TiO(2)) shell. The employed protocol involves precipitation of titania shell on the magnetite (Fe(3)O(4)) encapsulated polystyrene beads followed by the calcination of resulting composite particles at elevated temperature. Scanning electron microscopy and transmission electron microscopy reveal the presence of a thick, complete but irregular titania shell on the magnetic polystyrene beads after the templating process. Electron energy loss mapping image analysis has been employed to investigate the spatial distribution of titania and magnetite phases of magnetic hollow titania capsules (MHTCs). Magnetic characterization indicates that both titania-coated magnetic polystyrene beads (TMPBs) and MHTCs are superparamagnetic in nature with the saturated magnetizations of 5.6 and 8.1 emu/g, respectively. X-ray diffraction (XRD) analysis reveals that titania shell of these capsules is composed of photoactive anatase phase. Nitrogen adsorption-desorption analysis has been employed to estimate the specific surface area and the average pore diameter of the fabricated hollow structures. Photocatalytic activity of the fabricated MHTCs for the photodegradation of rhodamine 6G dye has been demonstrated and compared with that of bulk titania nanoparticles.

Investigation of the relationship between hydrogen bonds and macroscopic properties in hybrid core-shell gamma-Fe2O3-P(NIPAM-AAS) microgels

We investigate in a hybrid material the interactions existing between magnetic nanoparticles of gamma-Fe(2)O(3) and the polymer matrix constituted by core-shell poly(N-isopropylacrylamide-sodium acrylate) microgels. These interactions provoke the shifting of the microgel volume phase transition to higher temperatures when the amount of gamma-Fe(2)O(3) increases. The study was performed using different techniques such as incoherent quasi-elastic neutron scattering (IQNS), infrared spectroscopy (FTIR-ATR), and dynamic light scattering (DLS). Below the low critical solution temperature (LCST) of the polymer, the IQNS data confirm that the presence of inorganic nanoparticles affects the PNIPAM chain motions. Thus, in the swollen state both the mean-square displacement of the polymer segments and the diffusive motion of the polymer chains decrease as the iron oxide content increases. The FTIR-ATR study indicates that the reduction of vibrational and diffusional motions of the polymer chains is due to the formation of hydrogen bonds between the amide groups of the polymer matrix and the OH groups of the magnetic nanoparticles. The creation of this hybrid complex would explain the reduction of the swelling capacity with increasing the iron content in the microgels. Furthermore, this interaction could also explain the shift of the polymer LCST to higher temperatures as due to the extra energy required by the system to break the hydrogen bonds prior to the PNIPAM collapse.

Interpenetrated PNIPAM-polythiophene microgels for nitro aromatic compound detection

In this work, we present a facile and reproducible method to obtain thermally responsive, monodisperse, fluorescent microgels with diameters smaller than 700 nm based on poly(N-isopropyl acrylamide) (PNIPAM) interpenetrated with poly(thiophene-ethyl buthyl sulfonate) (PTEBS). Changing the temperature and inducing the microgel volume phase transition, it is possible to modify the photoluminescence (PL) properties of the microgels. Thus, when the temperature was below the low critical solution temperature (LCST) of PNIPAM, the PL intensity was higher than that above the LCST. Time-resolved fluorescence measurements indicate that, in the swollen state, the increment of cross-linking increases the fluorescence decay time of PTEBS. By contrast, in the collapsed state, variations in the decay time were attributed to higher rigidity of the PNIPAM-PTEBS system, which was confirmed by neutron scattering measurements. Moreover, the shift in the wavelength of the fluorescence emission peak observed above the LCST indicates that the collapsed PNIPAM matrix was able to interact with the PTEBS chains hindering the formation of pi-pi interactions. This property is envisaged for developing a picric acid microsensor based on the formation of pi-pi interactions with the pi-conjugated polymer, thus quenching its PL emission. Above the LCST of PNIPAM-PTEBS microgels, the interactions would be broken and the initial PL emission would be recovered. This property could render reusable microsensors for detection of nitro aromatic compounds.

Gels and microgels for nanotechnological applications

In recent years, "smart" materials have been the focus of considerable interest, from both fundamental and applied perspectives. Polymer gels are within this category; they respond to specific environmental stimuli by changing their size. Thus, the internal structure, the refractive index, and the mechanical properties of the polymer network change. They are considered super absorbent materials, as they can absorb solvent up to several hundred times their own weight. They respond rapidly to local environmental variations, an important fact in device miniaturization and microsensor developments. As size changes are accompanied by changes in internal dimensions, microgels have found application as carriers of therapeutic drugs and as diagnostic agents. They have also been used as microreactors, optically active materials, for template synthesis of nanoparticles or fabrication of artificial muscle. In this paper we review a set of application based on the special features associated to this systems. Basic concepts on the physical-chemistry of gel swelling is first described, followed by different applications covering drug delivery, composite materials using polymer gels to modulate optical or magnetic and electrical properties, molecular imprinting, gel-based biosensors and polymer sensors and actuators used in the field of artificial muscles.

Influence of the surfactant chain length on the fluorescence properties of a water-soluble conjugated polymer

In this work, we report the influence of surfactant chain length and surfactant concentration on the photoluminescence (PL) of water-soluble pi-conjugated poly(thienyl ethylene oxide butyl sulfonate) (PTE-BS). We have used alkylammomium surfactants with 8, 9, 10, and 12 carbon atoms per hydrocarbon chain. The surfactant concentration was varied from 0.125 the critical micelle concentration (CMC) up to 2 times the CMC. The results show that at premicellar concentrations all the surfactants promote the polymer aggregation inducing an increase in the interchain charge transfer by pi-pi interactions, which competes with PL emission processes. However, in the premicellar range, the polymer PL emission is sharply affected by the surfactant chain length. Thus, the PL is quenched by the surfactants with the shortest tails, whereas the surfactants with the longest ones provoke an enhancement of the PL emission. This behavior has been associated with the capacity of the surfactants with the longest hydrocarbon chains to accommodate their tails inside the polymer, obstructing the appearance of pi-pi interchain interactions during aggregation and reducing intrachain defects. By contrast, at the CMC, the surfactant chain length does not modify the PL emission, since the excess of surfactant inhibits polymer aggregation, thus enhancing the efficiency of light emissive processes.

Switchable photoluminescence of CdTe nanocrystals by temperature-responsive microgels

In the present study, we report a method for preparing a fluorescent thermosensitive hybrid material based on monodisperse, thermosensitive poly( N-isopropyl acrylamide) (PNIPAM) microgels covered with CdTe nanocrystals of 3.2 nm diameter. The CdTe nanocrystals were covalently immobilized on the surface of PNIPAM microgels. The chemical environment around the CdTe nanocrystals was modified by changing the temperature and inducing the microgel volume-phase transition. This change provoked a steep variation in the nanocrystal photoluminescence (PL) intensity in such a way that when the temperature was under the low critical solution temperature (LCST) of the polymer (36 degrees C) the PL of the nanocrystals was strongly quenched, whereas above the LCST the PL intensity was restored.

Synthesis and characterization of thermosensitive PNIPAM microgels covered with superparamagnetic gamma-Fe2O3 nanoparticles

In the present study we report a facile and reproducible method of preparing magnetic thermosensitive hybrid material based on P(NIPAM) microgels covered with gamma-Fe2O3 nanoparticles of 6-nm size. The iron oxide nanoparticles provided magnetic response to the microgels. In addition, the presence of the magnetic nanoparticles on the microgels altered their swelling behavior and shifted their volume phase transition temperature to higher values. In particular, for inorganic shells with 18% (w/w) of magnetic nanoparticles the volume phase transition of the microgels was shifted from 36 to 40 degrees C. In contrast, for shells consisting of 38% (w/w) magnetic nanoparticles the volume phase transition of the microgels was almost blocked, thus indicating that the microgel thermal response was strongly affected by the presence of the inorganic nanoparticles. The synthesized thermosensitive magnetic microgels are envisaged to be ideal for potential applications as thermosensitive targeted drug delivery systems.

Synthesis and characterization of poly(magnesium acrylate) microgels

In this work, we present the synthesis of a novel poly(magnesium acrylate) microgel, its microstructural characterization, and its application as an enzyme immobilization system. The variation of the monomer concentration employed in the synthesis permitted to tune up the shape of the microgels in such a way that using 1.5 mol L(-1) we produced microgels of average size 40 microm formed by smaller subunits of around 1 microm. This fact confers the microgels a pomegranate-like structure that increases the specific surface of the system. Glucose oxidase (GOx) from Aspergillus niger was immobilized within the microgels with the aim of using them as bioreactors. The microgels were characterized by scanning electron microscopy and by neutron scattering. The incorporation of the enzyme results in an increment in the network mesh size and the appearance of a new correlation length in the neutron scattering pattern. Finally, the enzymatic activity of the microgels with GOx entrapped was studied as a function of the microgel cross-linking content.