Comprehensive Analytical Modelling of an Absolute pH Sensor.

In this work, we present a comprehensive analytical model and results for an absolute pH sensor. Our work aims to address critical scientific issues such as: (1) the impact of the oxide degradation (sensing interface deterioration) on the sensor's performance and (2) how to achieve a measurement of the absolute ion activity. The methods described here are based on analytical equations which we have derived and implemented in MATLAB code to execute the numerical experiments. The main results of our work show that the depletion width of the sensors is strongly influenced by the pH and the variations of the same depletion width as a function of the pH is significantly smaller for hafnium dioxide in comparison to silicon dioxide. We propose a method to determine the absolute pH using a dual capacitance system, which can be mapped to unequivocally determine the acidity. We compare the impact of degradation in two materials: SiO2 and HfO2, and we illustrate the acidity determination with the functioning of a dual device with SiO2.

Gold nanoparticles downregulate interleukin-1ß-induced pro-inflammatory responses.

Interleukin 1 beta (IL-1ß)-dependent inflammatory disorders, such as rheumatoid arthritis and psoriasis, pose a serious medical burden worldwide, where patients face a lifetime of illness and treatment. Organogold compounds have been used since the 1930s to treat rheumatic and other IL-1ß-dependent diseases and, though their mechanisms of action are still unclear, there is evidence that gold interferes with the transmission of inflammatory signalling. Here we show for the first time that citrate-stabilized gold nanoparticles, in a size dependent manner, specifically downregulate cellular responses induced by IL-1ß both in vitro and in vivo. Our results indicate that the anti-inflammatory activity of gold nanoparticles is associated with an extracellular interaction with IL-1ß, thus opening potentially novel options for further therapeutic applications.

Nanopatterned submicron pores as a shield for nonspecific binding in surface plasmon resonance-based sensing.

We present a novel approach to tackle the most common drawback of using surface plasmon resonance for analyte screening in complex biological matrices--the nonspecific binding to the sensor chip surface. By using a perforated membrane supported by a polymeric gel structure at the evanescent wave penetration depth, we have fabricated a non-fouling sieve above the sensing region. The sieve shields the evanescent wave from nonspecific interactions which interfere with SPR sensing by minimizing the fouled area of the polymeric gel and preventing the translocation of large particles, e.g. micelles or aggregates. The nanopatterned macropores were fabricated by means of colloidal lithography and plasma enhanced chemical vapor deposition of a polyethylene oxide-like film on top of a polymeric gel matrix commonly used in surface plasmon resonance analysis. The sieve was characterized using surface plasmon resonance imaging, contact angle, atomic force microscopy and scanning electron microscopy. The performance of the sieve was studied using an immunoassay for detection of antibiotic residues in full fat milk and porcine serum. The non-fouling membrane presented pores in the 92-138 nm range organized in a hexagonal crystal lattice with a clearance of about 5% of the total surface. Functionally, the membrane with the nanopatterned macropores showed significant improvements in immunoassay robustness and sensitivity in untreated complex samples. The utilization of the sensor built-in sieve for measurements in complex matrices offers reduction in pre-analytical sample preparation steps and thus shortens the total analysis time.

Universal control of proton concentration using an electrochemically generated acid compatible with miniaturization.

Controlling locally produced acidity in miniaturized spaces is of high importance to manage simultaneous chemical reactions. Here, we present a platform that hosts miniaturized micro-reactors each one enabling electrochemical control of the acidity in ∼nL volumes. We demonstrated the local control of chemical reactions with the deprotection of strong acid labile groups in a region of 150 µm of diameter of upstanding glass using high proton concentrations (∼10-1 M) and the acidity contrasts between the cell region and the outside. We demonstrated accurate control of the proton concentration in aqueous and organic solvents and the control of chemical reactions in organic electrolytes achieved with a sulfonated tetrafluoroethylene-based membrane, which isolates the acid generating electrodes from the reagents in the solution. The quantitative control of the acidity by faradaic currents was demonstrated by the calibration of carboxyfluorescein adjusted with external titrations and with a tautomer transition occurring at pH 4.2. To the best of our knowledge, this platform shows the best control of acidity in the smallest volume reported so far.

Detection of silver nanoparticles inside marine diatom Thalassiosira pseudonana by electron microscopy and focused ion beam.

In the following article an electron/ion microscopy study will be presented which investigates the uptake of silver nanoparticles (AgNPs) by the marine diatom Thalassiosira pseudonana, a primary producer aquatic species. This organism has a characteristic silica exoskeleton that may represent a barrier for the uptake of some chemical pollutants, including nanoparticles (NPs), but that presents a technical challenge when attempting to use electron-microscopy (EM) methods to study NP uptake. Here we present a convenient method to detect the NPs interacting with the diatom cell. It is based on a fixation procedure involving critical point drying which, without prior slicing of the cell, allows its inspection using transmission electron microscopy. Employing a combination of electron and ion microscopy techniques to selectively cut the cell where the NPs were detected, we are able to demonstrate and visualize for the first time the presence of AgNPs inside the cell membrane.

Silica nanoparticle uptake induces survival mechanism in A549 cells by the activation of autophagy but not apoptosis.

We report here an in vitro evaluation of silica nanoparticle uptake by lung epithelial cells (A549), the cytotoxic effect of the particles and we propose autophagy as possible survival strategy. The effect of surface charge, serum proteins and the influence of inhibitors on the uptake of 20 nm monodispersed nanoparticles with various functional groups are discussed. Uptake rate of the particles with various functional groups is demonstrated to be similar in the presence of serum proteins, while the uptake rate ranking is COOH>NH2>OH under serum free conditions. Our results suggest an actin-dependent, macropinocytotic uptake process that was also confirmed by scanning and transmission electron microscopy. In spite of the intensive active uptake, significant cytotoxic effect is detected only at relatively high concentrations (above 250 µg/mL). Blebbing of the cell surface is observed already at 5h of exposure and is shown to be related to autophagy rather than apoptotic cell death. The A549 cells display elevated levels of autophagosomes, however they do not express typical apoptosis markers such as increased amount of active caspase-3 and release of mitochondrial cytochrome C. Based on these results, we propose here an autophagic activity and cross-talk between autophagic and apoptotic pathways as a mechanism allowing the survival of A549 cells under exposure to silica nanoparticles.

Size-dependent toxicity and cell interaction mechanisms of gold nanoparticles on mouse fibroblasts.

Gold nanoparticles (AuNPs) are currently used in several fields including biomedical applications, although no conclusive information on their cytotoxicity is available. For this reason this work has investigated the effects of AuNPs in vitro on Balb/3T3 mouse fibroblasts. Results obtained exposing cells for 72 h to AuNPs 5 and 15 nm citrate stabilized, revealed cytotoxic effects only for AuNPs 5 nm at concentration ≥ 50 µM if measured by colony forming efficiency (CFE). To understand the differences in cytotoxicity observed for the two AuNPs sizes, we investigated the uptake and the intracellular distribution of the nanoparticles. By TEM it was observed that 5 and 15 nm AuNPs are internalized by Balb/3T3 cells and located within intracellular endosomal compartments. Quantification of the uptake by ICP-MS showed that AuNPs internalization enhanced even up to 72 h. Disruption of the actin cytoskeleton was evident, with cell footprints narrow and contracted; effects more remarkable in cells exposed to 5 nm AuNP. The mechanism of NPs cell internalization was investigated using immunocytochemistry and western blot. No significant effect was observed in the expression level of caveolin, while reduction of the expression and degradation of the clathrin heavy chain was observed in cells exposed for 72 h to AuNPs.

Separation and characterization of gold nanoparticle mixtures by flow-field-flow fractionation.

We show that using asymmetric flow-field-flow fractionation and UV-vis detector it is possible to separate, characterize, and quantify the correct number size distribution of gold nanoparticle (AuNP) mixtures of various sizes in the 5-60 nm range for which simple dynamic light scattering measurements give misleading information. The size of the collected nanoparticles fractions can be determined both in solution and in the solid state, and their surface chemistry characterized by NMR. This method will find widespread applications both in the process of "size purification" after the synthesis of AuNP and in the identification and characterization of gold-based nanomaterials in consumer products.

Optical control of energy-level structure of few electrons in AlGaAs/GaAs quantum dots.

Optical control of the lateral quantum confinement and number of electrons confined in nanofabricated GaAs/AlGaAs quantum dots is achieved by illumination with a weak laser beam that is absorbed in the AlGaAs barrier. Precise tuning of energy-level structure and electron population is demonstrated by monitoring the low-lying transitions of the electrons from the lowest quantum-dot energy shells by resonant inelastic light scattering. These findings open the way to the manipulation of single electrons in these quantum dots without the need of external metallic gates.

Evidence of correlation in spin excitations of few-electron quantum dots.

We report inelastic light scattering measurements of spin and charge excitations in nanofabricated AlGaAs/GaAs quantum dots with few electrons. A narrow spin excitation peak is observed and assigned to the intershell triplet-to-singlet monopole mode of dots with four electrons. Configuration-interaction theory provides precise quantitative interpretations that uncover large correlation effects that are comparable to exchange Coulomb interactions.