BackgroundUnderstanding the pathogenic role of extracellular vesicles (EVs) in disease and their potential diagnostic and therapeutic utility is extremely reliant on in-depth quantification, measurement and identification of EV sub-populations. Quantification of EVs has presented several challenges, predominantly due to the small size of vesicles such as exosomes and the availability of various technologies to measure nanosized particles, each technology having its own limitations.Materials and MethodsA standardized methodology to measure the concentration of extracellular vesicles (EVs) has been developed and tested. The method is based on measuring the EV concentration as a function of a defined size range. Blood plasma EVs are isolated and purified using size exclusion columns (qEV) and consecutively measured with tunable resistive pulse sensing (TRPS). Six independent research groups measured liposome and EV samples with the aim to evaluate the developed methodology. Each group measured identical samples using up to 5 nanopores with 3 repeat measurements per pore. Descriptive statistics and unsupervised multivariate data analysis with principal component analysis (PCA) were used to evaluate reproducibility across the groups and to explore and visualise possible patterns and outliers in EV and liposome data sets.ResultsPCA revealed good reproducibility within and between laboratories, with few minor outlying samples. Measured mean liposome (not filtered with qEV) and EV (filtered with qEV) concentrations had coefficients of variance of 23.9% and 52.5%, respectively. The increased variance of the EV concentration measurements could be attributed to the use of qEVs and the polydisperse nature of EVs.ConclusionThe results of this study demonstrate the feasibility of this standardized methodology to facilitate comparable and reproducible EV concentration measurements.

Nanopore devices are extremely useful tools for the simple, sensitive, and high-throughput characterization of particles and biomolecules. [ 1 , 2 ] However, the fi xed diameter of conventional pores severely limits the size range of structures that can be effectively analyzed with a given pore. Herein we use a novel resizable elastic nanopore to discriminate between and selectively gate the passage of a mixed suspension of 100, 220, and 400 nm particles and to detect DNA modifi cation of 220 nm particles. Changing the pore size in real time allows 'tuning' of the signal to improve the characterization of closely related particle size distributions and surface-modifi ed particles. Tuning of the pore size to the experimental system at hand holds promise as an easy, robust, and versatile technique for the characterization of nanometer-sized materials and for biological sensing applications.The detection and characterization of individual molecules or small bodies by nano/micropore resistive pulse sensing devices has generated considerable interest for applications such as high-throughput DNA sequencing [ 1 , 3-5 ] and nanoparticle characterization. [ 2 , 6 , 7 ] Microchannel and nanopore instruments detect a modulation in resistance or ionic current caused by the passage of a large molecule or small body through the narrow channel. These devices hold several advantages compared to other commonly employed nanobiotechnological sensing techniques, including single particle or molecule detection, relatively low cost, simplicity in both design and implementation, and the capacity for true, labelfree molecular detection.Microchannel resistive pulse sensing for the characterization of colloidal and cellular suspension size and concentration has been widely accepted and successfully commercialized as

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Physicochemical properties of nanoparticles, such as size, shape, surface charge, density, and porosity play a central role in biological interactions and hence accurate determination of these characteristics is of utmost importance. Here we propose tunable resistive pulse sensing for simultaneous size and surface charge measurements on a particle-by-particle basis, enabling the analysis of a wide spectrum of nanoparticles and their mixtures. Existing methodologies for measuring zeta potential of nanoparticles using resistive pulse sensing are significantly improved by including convection into the theoretical model. The efficacy of this methodology is demonstrated for a range of biological case studies, including measurements of mixed anionic, cationic liposomes, extracellular vesicles in plasma, and in situ time study of DNA immobilisation on the surface of magnetic nanoparticles. The high-resolution single particle size and zeta potential characterisation will provide a better understanding of nano-bio interactions, positively impacting nanomedicine development and their regulatory approval.

-Aptamers are short single-stranded pieces of DNA or RNA capable of binding to analytes with specificity and high affinity. Due to their comparable selectivity, stability and cost, over the last two decades aptamers have started to challenge antibodies in their use on many technology platforms. The binding event often leads to changes in the aptamer's secondary and tertiary structure; monitoring such changes has led to the creation of many new analytical sensors. Here we demonstrate the use of a tunable resistive pulse sensing (TRPS) technology to monitor the interaction between several DNA aptamers and their target -thrombin. We immobilised the aptamers onto the surface of superparamagnetic beads, prior to their incubation with the thrombin protein. The protein binding to the aptamer caused a conformational change resulting in the shielding of the polyanion backbone; this was monitored by a change in the translocation time and pulse frequency of the particles traversing the pore. This signal was sensitive enough to allow the tagless detection of thrombin down to nanomolar levels. We further demonstrate the power of TRPS by performing real time detection and characterisation of the aptamer-target interaction and measuring the association rates of the thrombin protein to the aptamer sequences.

NCL in Merino sheep is a subunit c-storing disease, clinically and pathologically similar to NCL in South Hampshire sheep. We propose that the disease in both breeds represents mutation at the same gene locus in chromosomal region OAR7q13-15.

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