Nanoparticle patterning for biomedicine

In Situ Kinetic Observations on Crystal Nucleation and Growth

Nucleation and growth are critical steps in crystallization, which plays an important role in determining crystal structure, size, morphology, and purity. Therefore, understanding the mechanisms of nucleation and growth is crucial to realize the controllable fabrication of crystalline products with desired and reproducible properties. Based on classical models, the initial crystal nucleus is formed by the spontaneous aggregation of ions, atoms, or molecules, and crystal growth is dependent on the monomer's diffusion and the surface reaction. Recently, numerous in situ investigations on crystallization dynamics have uncovered the existence of nonclassical mechanisms. This review provides a summary and highlights the in situ studies of crystal nucleation and growth, with a particular emphasis on the state-of-the-art research progress since the year 2016, and includes technological advances, atomic-scale observations, substrate- and temperature-dependent nucleation and growth, and the progress achieved in the various materials: metals, alloys, metallic compounds, colloids, and proteins. Finally, the forthcoming opportunities and challenges in this fascinating field are discussed.

Effect of Particles of Irregular Size on the Microstructure and Structural Color of Self-Assembled Colloidal Crystals

Self-assembled colloidal crystals can exhibit structural colors, a phenomenon of intense reflection within a range of wavelengths caused by constructive interference. Such diffraction effects are most intense for highly uniform crystals; however, in practice, colloidal crystals may include particles of irregular size, which can reduce the quality of the crystal. Despite its importance in realizing high-quality structural colors, a quantitative relationship between particles of irregular size, crystal quality, and the resultant structural color response remains unclear. This study systematically and quantitatively investigates the effect of adding particles of irregular size on the microstructural quality and structural color reflectivity of colloidal crystals formed by evaporative self-assembly via experiment and simulation. We examine two sizes of irregular particles─those which are 1.9 times larger and 0.4 times smaller than the host crystal. We find that small irregular particles are more detrimental to surface crystal quality and structural color reflectivity than large irregular particles. When incorporated with 10% volume fraction of irregularly sized particles, the reflectivity of crystal films with large (small) irregularly sized particles decreases by 18.4 ± 5.6% (27.5 ± 5.8%), and a measure of surface crystal quality derived from Fourier analysis of scanning electron microscopy images reduces by 40.0 ± 4.5% (48.8 ± 6.0%). By modeling colloidal films incorporated with irregular particles via molecular dynamics simulation and computing the reflection spectra of the modeled crystals via the finite-difference time-domain method, we find that the peak reflectivity of the assembled structures increases monotonically with overall crystallinity, and that overall crystallinity is correlated with the volume fraction of incorporated irregular particles. The quantitative relationships developed in this study can be applied to predict the level of irregularly sized particles that can be tolerated in colloidal films before significant degradation in crystal quality and reflectivity occurs.

Doxorubicin-conjugated D-glucosamine- and folate- bi-functionalised InP/ZnS quantum dots for cancer cells imaging and therapy

Nanoscaled quantum dots (QDs), with unique optical properties have been used for the development of theranostics. Here, InP/ZnS QDs were synthesised and functionalised with folate (QD-FA), D-glucosamine (QD-GA) or both (QD-FA-GA). The bi-functionalised QDs were further conjugated with doxorubicin (QD-FA-GA-DOX). Optimum Indium to fatty acid (In:MA) ratio was 1:3.5. Transmission electron microscopy (TEM) micrographs revealed spherical morphology for the QDs (11 nm). Energy-dispersive spectroscopy (EDS) spectrum confirmed the chemical composition of the QDs. MTT analysis in the OVCAR-3 cells treated with bare QDs, QD-FA, QD-GA, QD-FA-GA and QD-FA-GA-DOX (0.2 mg/mL of QDs) after 24 h indicated low toxicity for the bare QDs and functionalised QDs (about 80-90% cell viability). QD-FA-GA-DOX nanoparticles elicited toxicity in the cells. Cellular uptake of the engineered QDs were investigated in both folate receptor (FR)-positive OVCAR-3 cells and FR-negative A549 cells using fluorescence microscopy and FACS flow cytometry. The FA-functionalised QDs showed significantly higher uptake in the FR-positive OVCAR-3 cells, nonetheless the GA-functionalised QDs resulted in an indiscriminate uptake in both cell lines. In conclusion, our findings indicated that DOX-conjugated FA-armed QDs can be used as theranostics for simultaneous imaging and therapy of cancer.