Tracer Nanoparticles Research Articles

Microwell Array Based Opto-Electrochemical Detections Revealing Co-Adaptation of Rheological Properties and Oxygen Metabolism in Budding Yeast.

Microdevices composed of microwell arrays integrating nanoelectrodes (OptoElecWell) are developed to achieve dual high-resolution optical and electrochemical detections on single Saccharomyces cerevisiae yeast cells. Each array consists of 1.6×105 microwells measuring 8µm in diameter and 5µm height, with a platinum nanoring electrode for in situ electrochemistry, all integrated on a transparent thin wafer for further high-resolution live-cell imaging. After optimizing the filling rate, 32% of cells are effectively trapped within microwells. This allows to analyse S. cerevisiae metabolism associated with basal respiration while simultaneously measuring optically other cellular parameters. In this study, the impact of glucose concentration on respiration and intracellular rheology is focused. It is found that while the oxygen uptake rate decreases with increasing glucose concentration, diffusion of tracer nanoparticles increases. The OptoElecWell-based respiration methodology provides similar results compared to the commercial gold-standard Seahorse XF analyzer, while using 20 times fewer biological samples, paving the way to achieve single cell metabolomics. In addition, it facilitates an optical route to monitor the contents within single cells. The proposed device, in combination with the dual detection analysis, opens up new avenues for measuring cellular metabolism, and relating it to cellular physiological indicators at single cell level.

A dual signal immunochromatographic strip for the detection of imidaclothiz using a recombinant fluorescent-peptide tracer and gold nanoparticles

Immunochromatographic strips (ICS) attract much attention as practical analytical tools, particularly for point of care testing. However, ICS suffer from insufficient sensitivity, especially for small molecules. Competitive assays developed with analyte peptidomimetics obtained from phage display peptide libraries, usually enable to attain lower detection limits than the widely used chemical haptens, but are rarely used in ICS assay because of the shortcomings of the phage particle. In this work, we used a phage-free fluorescent peptide tracer (C2-15-EmGFP) for ICS, which consists of the emerald green fluorescent protein (EmGFP) fused to a peptidomimetic of imidaclothiz (C2-15). C2-15-EmGFP works as fluorescent donor and colloidal gold nanoparticles (AuNPs) coated with an anti-imidaclohtiz antibody as quencher, which allowed to develop a fluorescence quenching-based ICS (FQICS) for the detection of imidaclothiz in agricultural and environmental samples. The colorimetric and fluorescent signals were determined by both naked eye and imageJ software. Quantitative image analysis showed that the sensitivities obtained using the colorimetric (50% inhibitory concentration (IC50): 9.62 ng mL−1) and fluorescent (50% saturation concentration (SC50): 10.1 ng mL−1) signals were similar. The visual detection by the naked eye showed a sensitivity of 8.00 ng mL−1 with fluorescent readout which was 8-fold lower than that of the colorimetric readout (64.0 ng mL−1). The FQICS performed with excellent recoveries and good correlation with high-performance liquid chromatography in different matrices.

Simultaneous measurements of thin film thickness using total internal reflection fluorescence microscopy and disjoining pressure using Scheludko cell.

This work describes a method for measuring the thin film thickness using total internal reflection fluorescence microscopy, with the use of evanescent wave illumination. The thin liquid film was formed in a hole drilled at the center of a porous plate, which is used for measurement of the disjoining pressure by using the Scheludko cell method. The aim of simultaneous and in situ measurements of thin film thickness and disjoining pressure is to obtain the relationship between them, which is critical for explicitly depicting the thin film profile that determines the interfacial mass and heat fluxes in the thin film region near the triple line. This method can overcome the drawbacks of the optical methods that are insufficient for measuring the thickness of a thin film with curvature. The influence of structural forces formed by tracer nanoparticles seeded in the thin liquid film on the relationship was analyzed. The obtained expression for disjoining pressure vs thin film thickness provides a basis for analyzing the formation, evolution, and stability of the thin liquid film, which is the dominant mechanism of controlling the mesoscopic structure in many transport processes.

Induced-charge electrokinetics in rotating electric fields: A linear asymptotic analysis

Concerning the electroconvective analyte manipulation in microfluidics, we describe the basic physics of fluid flow driven by rotating induced-charge electro-osmosis (ROT-ICEO), which occurs on the planar surface of a single floating electrode in an external rotating electric field. First, based on a linear asymptotic analysis, the dynamic flow stagnation line in ROT-ICEO induced on the bipolar electrode from a rotary Debye screening charge revolves synchronously with the applied rotating fields. A net hydrodynamic torque is then generated that acts on any fluid or particle sample to produce either a synchronous or asynchronous co-field rotation depending on the frequency of the ac signal. Next, from the synergy between the hydrodynamic and electrochemical ion relaxations, an analytical solution of the sample rotation rate subject to ROT-ICEO slipping on an ideally polarizable surface is obtained for different frequency ranges and determined by the transient nature of the rotating electro-osmotic flow oscillating at twice the field frequency. To visualize the flow field in ROT-ICEO, experiments were performed with fluorescent tracer nanoparticles; they exhibited concentric rotational behavior at the polarized phase interface. Formed like the arms of a nebula disk, the four twisted tails of nanoparticles can be arbitrarily directed under voltage-phase rectification. These experimental results are in good agreement with our mathematical simulations using the Debye–Hückel approximation on ROT-ICEO.

Bubble-Free Propulsion of Ultrasmall Tubular Nanojets Powered by Biocatalytic Reactions.

The motion of self-propelled tubular micro- and nanojets has so far been achieved by bubble propulsion, e.g., O2 bubbles formed by catalytic decomposition of H2O2, which renders future biomedical applications inviable. An alternative self-propulsion mechanism for tubular engines on the nanometer scale is still missing. Here, we report the fabrication and characterization of bubble-free propelled tubular nanojets (as small as 220 nm diameter), powered by an enzyme-triggered biocatalytic reaction using urea as fuel. We studied the translational and rotational dynamics of the nanojets as functions of the length and location of the enzymes. Introducing tracer nanoparticles into the system, we demonstrated the presence of an internal flow that extends into the external fluid via the cavity opening, leading to the self-propulsion. One-dimensional nanosize, longitudinal self-propulsion, and biocompatibility make the tubular nanojets promising for future biomedical applications.

Thermo-Osmotic Flow in Thin Films.

We report on the first microscale observation of the velocity field imposed by a nonuniform heat content along the solid-liquid boundary. We determine both radial and vertical velocity components of this thermo-osmotic flow field by tracking single tracer nanoparticles. The measured flow profiles are compared to an approximate analytical theory and to numerical calculations. From the measured slip velocity we deduce the thermo-osmotic coefficient for both bare glass and Pluronic F-127 covered surfaces. The value for Pluronic F-127 agrees well with Soret data for polyethylene glycol, whereas that for glass differs from literature values and indicates the complex boundary layer thermodynamics of glass-water interfaces.

Spacer-induced forward osmosis membrane integrity loss during gypsum scaling

We demonstrated forward osmosis (FO) membrane integrity loss during gypsum scaling with the presence of membrane spacer. The gypsum scalant had preferential accumulation adjacent to membrane spacer where the needle-shape gypsum potentially compromised polyamide thin-film composite FO membrane integrity. However, the loss of FO membrane integrity cannot be sensitively detected by in situ measurements of membrane water and salt (NaCl) permeability coefficients. We, for the first time, employed membrane integrity challenge tests to reveal the impaired FO membrane integrity by fluorescent Rhodamine WT tracer and amine-modified latex nanoparticles, respectively. Challenge tests using Rhodamine WT tracer showed that membrane log removal value decreased to 3.5 after three scaling–cleaning cycles, which corresponded to a pinhole size of 0.06μm2 on the FO membrane. This result was further corroborated by challenge test using latex nanoparticle where the particle size distribution in the permeate became wider and the average particle size increased over the three scaling–cleaning cycles. Both challenge tests were sensitive enough to identify impaired FO membrane integrity. Results reported here have significant implications for achieving better membrane spacer and module design, as well as demanding periodical monitoring of FO membrane integrity in water reuse.

Impact of aggregate formation on the viscosity of protein solutions.

Gaining knowledge on the stability and viscosity of concentrated therapeutic protein solutions is of great relevance to the pharmaceutical industry. In this work, we borrow key concepts from colloid science to rationalize the impact of aggregate formation on the changes in viscosity of a concentrated monoclonal antibody solution. In particular, we monitor the kinetics of aggregate growth under thermal stress by static and dynamic light scattering, and we follow the rise in solution viscosity by measuring the diffusion coefficient of tracer nanoparticles with dynamic light scattering. Moreover, we characterize aggregate morphology in the frame of the fractal geometry. We show that the curves of the increase in viscosity with time monitored at three different protein concentrations collapse on one single master curve when the reaction profiles are normalized based on an effective volume fraction occupied by the aggregates, which depends on the aggregate size, concentration and morphology. Importantly, we find that the viscosity of an aggregate sample is lower than the viscosity of a monomeric sample of a similar occupied volume fraction due to the polydispersity of the aggregate distribution.

Evanescent Wave-Based Particle Tracking Velocimetry for Nanochannel Flows

Understanding fluid flows in 10-1000 nm space, which we call extended nanospace, is important for novel nanofluidic devices in analytical chemistry. This study therefore developed a particle tracking velocimetry for measuring velocity distribution in nanochannel flows, by using the evanescent wave illumination. 64 nm fluorescent nanoparticles were used as flow tracer. The particle position was determined from fluorescent intensity by the evanescent wave field, with a spatial resolution smaller than light wavelengths. The time resolution of 260 μs was achieved to make error by the Brownian diffusion of the tracer small to be neglected. An image processing by multitime particle tracking was established to detect the tracer nanoparticles of weak fluorescent intensity. Though the measurement region was affected by nonuniform particle distribution with the electrostatic interactions, pressure-driven flows of water in a nanochannel of 50 μm width and 410 nm depth were successfully measured. The results of the velocity distribution in the depth-wise direction approximately showed agreement with the fluid dynamics with the bulk liquid properties from the macroscopic view, however, suggested slip velocities even in the hydrophilic channel. We suggest a possibility of appearance of molecular behavior in the fluid near the wall within 10 nm-order scale.

Design of superparamagnetic nanoparticles for magnetic particle imaging (MPI).

Magnetic particle imaging (MPI) is a promising medical imaging technique producing quantitative images of the distribution of tracer materials (superparamagnetic nanoparticles) without interference from the anatomical background of the imaging objects (either phantoms or lab animals). Theoretically, the MPI platform can image with relatively high temporal and spatial resolution and sensitivity. In practice, the quality of the MPI images hinges on both the applied magnetic field and the properties of the tracer nanoparticles. Langevin theory can model the performance of superparamagnetic nanoparticles and predict the crucial influence of nanoparticle core size on the MPI signal. In addition, the core size distribution, anisotropy of the magnetic core and surface modification of the superparamagnetic nanoparticles also determine the spatial resolution and sensitivity of the MPI images. As a result, through rational design of superparamagnetic nanoparticles, the performance of MPI could be effectively optimized. In this review, the performance of superparamagnetic nanoparticles in MPI is investigated. Rational synthesis and modification of superparamagnetic nanoparticles are discussed and summarized. The potential medical application areas for MPI, including cardiovascular system, oncology, stem cell tracking and immune related imaging are also analyzed and forecasted.

One-pot synthesis of silica-coated magnetic plasmonic tracer nanoparticles

We demonstrate a one-pot procedure to synthesize and embed silver nanoparticles inside silica shells together with iron oxide nanoparticles and Raman reporter molecules, followed by fluorophore attachment to the silica, to form a class of tracer nanoparticles suitable for biological and environmental applications.