Phosphatidylcholine‐Coated Iron Oxide Nanomicelles for In Vivo Prolonged Circulation Time with an Antibiofouling Protein Corona

We report the synthesis of micellar phosphatidylcholine‐coated superparamagnetic iron oxide nanoparticles as a new long circulation contrast agents for magnetic resonance imaging. Oleic acid‐coated Fe₃O₄ nanoparticles were first prepared through thermal degradation and then encapsulated into small clusters with a phosphatidylcholine coating to obtain hydrophilic nanomicelles. A thorough characterization confirmed the chemical nature of the coating and the excellent colloidal stability of these nanomicelles in aqueous media. Magnetization and relaxivity properties proved their suitability as magnetic resonance imaging (MRI) contrast agent and in vitro cell viability data showed low toxicity. Vascular lifetime and elimination kinetics in the liver were assessed by blood relaxometry and by in vivo MRI in rats and compared with “control” particles prepared with a polyethylene glycol derivative. These micellar particles had a lifetime in blood of more than 10 h, much longer than the control nanoparticles (≈2 h), which is remarkable considering that the coating molecule is a small biocompatible zwitterionic phospholipid. The protein corona was characterized after incubation with rat serum at different times by high‐throughput proteomics, showing a higher proportion of bound apolipoproteins and other dysopsonins for the phosphatidylcholine particles. The antibiofouling properties of this corona and its resistance to the adsorption of proteins corroborate the observed enhanced stability and prolonged systemic circulation.     

Rapid crack growth in a thermoelastic solid under mixed-mode thermomechanical loading

A two-dimensional steady-sate analysis of semi-infinite brittlecrack growth at a constant subcritical rate in an unboundedfully-coupled thermoelastic solid under mixed-mode thermomechanicalloading is made. The loading consists of normal and shear tractionsand heat fluxes applied as point sources (line loads in theout-of-plane direction). A related problem is solved exactly in an integral transformspace, and robust asymptotic forms used to reduce the originalproblem to a set of integral equations. The equations are partiallycoupled and exhibit operators of both Cauchy and Abel types,yet can be solved analytically. The temperature change field at a distance from the moving crackedge is then constructed, and its dominant term is found tobe controlled by the imposed heat fluxes. The role of this termis, indeed, enhanced if the heat fluxes serve to render thecrack as a net heat source/sink for the solid, as opposed tobeing a transmitter of heat across its plane. More generally,the influence of the thermoelastic coupling on this field, aswell as other functions, is found to increase with crack speed.     

Surface‐Functionalized Nanoparticles by Olefin Metathesis: A Chemoselective Approach for In Vivo Characterization of Atherosclerosis Plaque

The use of click chemistry reactions for the functionalization of nanoparticles is particularly useful to modify the surface in a well‐defined manner and to enhance the targeting properties, thus facilitating clinical translation. Here it is demonstrated that olefin metathesis can be used for the chemoselective functionalization of iron oxide nanoparticles with three different examples. This approach enables, in one step, the synthesis and functionalization of different water‐stable magnetite‐based particles from oleic acid‐coated counterparts. The surface of the nanoparticles was completely characterized showing how the metathesis approach introduces a large number of hydrophilic molecules on their coating layer. As an example of the possible applications of these new nanocomposites, a focus was taken on atherosclerosis plaques. It is also demonstrated how the in vitro properties of one of the probes, particularly its Ca²⁺‐binding properties, mediate their final in vivo use; that is, the selective accumulation in atherosclerotic plaques. This opens promising new applications to detect possible microcalcifications associated with plaque vulnerability. The accumulation of the new imaging tracers is demonstrated by in vivo magnetic resonance imaging of carotids and aorta in the ApoE^?/? mouse model and the results were confirmed by histology.     

Multi-analyte SPR immunoassays for environmental biosensing of pesticides

Multi-analyte detection of environmentally relevant pesticides is performed by using a two-channelled surface plasmon resonance (SPR) biosensor. The special design of the SPR instrument allows the determination of several analytes (DDT, chlorpyrifos and carbaryl) via different immobilization formats. First, simultaneous pesticide monitoring is possible by flowing chlorpyrifos, carbaryl or DDT samples separately over each channel of the SPR system, wherein their corresponding recognition element was previously immobilized. The second approach is based on the multiple and combined immobilization of several analyte recognition elements on the sensing surface of one individual flow cell. In this format, the analysis time for all three pesticides varied from 40 to 60 min depending on the number of regeneration cycles. In most cases, similar detection limits were attained for the target analyte irrespective of the assay format, with sensitivity values at the nanogram per litre level (18–50 ng L⁻¹). The assay reproducibility was proved through the repeated use of the same sensor surface for over more than 200 assay cycles, whereas the absence of biosensor response to non-related analytes showed the specificity and reliability of the analysis. The SPR instrument, including optics, electronics and microfluidics, is already commercialised by the company SENSIA, SL.     

Dynamic Mach–Zehnder interferometer based on a Michelson configuration and a cube beam splitter system

We developed simultaneous phase-shifting system based on a Mach–Zehnder interferometer and a replicating system integrated by a Michelson configuration and a cube beam splitter. The system is capable to obtain four simultaneous interferograms in a single capture, and the phase shifts are controlled by placing a linear polarizer in each replica obtained. The system retrieves four interferograms with a relative phase shift of π/2 and the optical phase map is calculated using the four-step algorithm. In addition, the configuration presents potential capabilities for generating spiral interference patterns. To show the advantage of the technique, experimental results are presented for static and dynamic samples.

     

Label-free detection of DNA mutations by SPR: application to the early detection of inherited breast cancer

A screening analysis of DNA hybridization and the presence of DNA mutations using an surface plasmon resonance (SPR) biosensor is shown. The influence of lateral and vertical spacers, as well as several hybridization conditions, was studied to optimize the differentiation between fully complementary and mismatched DNA strands. Our results demonstrated that SPR biosensors were able to detect mismatch sequences related to inherited breast cancer, with high specificity and sensitivity. Using PCR synthetic sequences as targets, mutant sequences were clearly discriminated from fully complementary ones, and detection limits below 50 nM were achieved.     

Determination of environmental organic pollutants with a portable optical immunosensor

A portable surface plasmon resonance (SPR) optical biosensor device is described as a direct immunosensing system to determine organic pollutants in natural water samples. Monitoring of organochlorine (DDT), organophosphorus (chlorpyrifos) and carbamate (carbaryl) compounds within the concentration levels stipulated by the European legislation, can be accomplished using this immunosensor. The lowest limit of detection (LOD) was obtained for DDT, at 20 ng L⁻¹, whilst 50 ng L⁻¹ and 0.9 μg L⁻¹, were achieved for chlorpyrifos and carbaryl, respectively. Matrix effects were evaluated for the carbaryl immunoassay in different water types with detection limits within the range of carbaryl standard curves in distilled water (0.9-1.4 μg L⁻¹). The covalent immobilization of the analyte derivative through an alkanethiol self-assembled monolayer (SAM) allowed the reusability of the sensor surface during more than 250 regeneration cycles. The quality of the regeneration was proved over a 1-month period of continuous working. The analysis time for a complete assay cycle, including regeneration, comprises 24 min. Our portable SPR-sensor system is already a market product, commercialized by the company SENSIA, SL. The size and electronic configuration of the device allow its portability and utilization on real contaminated locations.     

Highly sensitive detection of biomolecules with the magneto-optic surface-plasmon-resonance sensor

The characteristics of a novel magneto-optic surface-plasmon-resonance (MOSPR) sensor and its use for the detection of biomolecules are presented. This physical transduction principle is based on the combination of the magneto-optic activity of magnetic materials and a surface-plasmon resonance of metallic layers. Such a combination can produce a sharp enhancement of the magneto-optic effects that strongly depends on the optical properties of the surrounding medium, allowing its use for biosensing applications. Experimental characterizations of the MOSPR sensor have shown an increase in the limit of detection by a factor of 3 in changes of refractive index and in the adsorption of biomolecules compared with standard sensors. Optimization of the metallic layers and the experimental setup could result in an improvement of the limit of detection by as much as 1 order of magnitude.