Search

Fluorescent nanodiamonds (FNDs) with negative nitrogen-vacancy (NV−) defect centers are great probes for biosensing applications, with potential to act as biomarkers for cell differentiation. To explore this concept, uptake of FNDs (≈120 nm) by THP-1 monocytes and monocyte-derived M0-macrophages is studied. The time course analysis of FND uptake by monocytes confirms differing FND-cell interactions and a positive time-dependence. No effect on cell viability, proliferation, and differentiation potential into macrophages is observed, while cells saturated with FNDs, unload the FNDs completely by 25 cell divisions and subsequently take up a second dose effectively. FND uptake variations by THP-1 cells at early exposure-times indicate differing phagocytic capability. The cell fraction that exhibits relatively enhanced FND uptake is associated to a macrophage phenotype which derives from spontaneous monocyte differentiation. In accordance, chemical-differentiation of the THP-1 cells into M0-macrophages triggers increased and homogeneous FND uptake, depleting the fraction of cells that were non-responsive to FNDs. These observations imply that FND uptake allows for distinction between the two cell subtypes based on phagocytic capacity. Overall, FNDs demonstrate effective cell labeling of monocytes and macrophages, and are promising candidates for sensing biological processes that involve cell differentiation.

A compact microfluidic flow cytometer is demonstrated, comprising viscoelastic flow focusing in fused silica capillaries and a fiber optical interface. Viscoelastic flow focusing enables simple device design and operation with a single-inlet/outlet fluidic configuration. Fused silica capillaries with different inner diameters are effortlessly interchanged to eliminate blockage ratio limitations and enable single-train particle focusing for a wide range of particle sizes and geometries. The compact system is mounted on an inverted microscope for easy integration with optical imaging and other optofluidic modalities, such as optical trapping and particle sorting. A real-time cytometric analysis of three channels, forward scattering, side scattering, and fluorescence detection, is performed on LABVIEW. A throughput of 3500 events s(-1) is performed on particles of sizes ranging from 2 to 20 mu m, using capillaries of different inner diameters ranging from 30 to 75 mu m. The outer diameter of all capillaries is identical to the cladding diameter of the applied optical fibers. This enables easy exchange and precise optical alignment of fibers and capillaries on a microfabricated jig. The performance of the microfluidic flow cytometer is benchmarked using polystyrene calibration beads, poly(lactic-co-glycolic acid) particles, erythrocytes, THP-1 leukemic monocytes, and human metaphase chromosomes.

Most tumor-targeted drug delivery systems must overcome a large variety of physiological barriers before reaching the tumor site and diffuse through the tight network of tumor cells. Many studies focus on optimizing the first part, the accumulation of drug carriers at the tumor site, ignoring the penetration efficiency, i.e., a measure of the ability of a drug delivery system to overcome tumor surface adherence and uptake. We used three-dimensional (3D) tumor spheroids in combination with light-sheet fluorescence microscopy in a head-to-head comparison of a variety of commonly used lipid-based nanoparticles, including liposomes, PEGylated liposomes, lipoplexes, and reconstituted high-density lipoproteins (rHDL). Whilst PEGylation of liposomes only had minor effects on the penetration efficiency, we show that lipoplexes are mainly associated with the periphery of tumor spheroids, possibly due to their positive surface charge, leading to fusion with the cells at the spheroid surface or aggregation. Surprisingly, the rHDL showed significantly higher penetration efficiency and high accumulation inside the spheroid. While these findings indeed could be relevant when designing novel drug delivery systems based on lipid-based nanoparticles, we stress that the used platform and the detailed image analysis are a versatile tool for in vitro studies of the penetration efficiency of nanoparticles in tumors. ©