Structural orderings of anisotropically confined colloids interacting via a quasi-square-well potential.

We implement Brownian dynamics to investigate the static properties of colloidal particles confined anisotropically and interacting via a potential which can be tailored in a repulsive-attractive-respulsive fashion as the interparticle distance increases. A diverse number of structural phases are self-assembled, which were classified according to two aspects, that is, their macroscopic and microscopic patterns. Concerning the microscopic phases we found the quasicrystalline, triangular, square, and mixed orderings, where this latter is a combination of square and triangular cells in a 3×2 proportion, i.e., the so-called (3(3),4(2)) Archimedian lattice. On the macroscopic level the system could self-organize in a compact or perforated single cluster surrounded or not by fringes. All the structural phases are summarized in detailed phases diagrams, which clearly show that the different phases are extended as the confinement potential becomes more anisotropic.

Structural ordering of trapped colloids with competing interactions.

The structure of colloids with competing interactions which are confined in a harmonic external trap potential is analyzed numerically by energy minimization in two spatial dimensions. A wealth of different cluster structures is found to be stable including clusters with a fringed outer rim (reminiscent to an ornamental border), clusters perforated with voids, as well as clusters with a crystalline core and a disordered rim. All cluster structures occur in a two-dimensional parameter space. The structural ordering can therefore be efficiently tuned by changing few parameters only providing access to a controlled fabrication of colloidal clusters.

Structural phases of colloids interacting via a flat-well potential.

Using Langevin dynamics simulations we investigate the self-assembly of colloidal particles in two dimensions interacting via an isotropic potential, which comprises both a hard-core repulsion and an additional softened square-well potential of controllable width α. In dilute concentrations, the particles assemble in small clusters with a well-defined crystalline order. For small values of α the particles form triangular lattices. As α is increased, more particles can be captured by the potential well giving rise to different crystalline symmetries and the structural phase transitions between them. The main structures observed are triangular, square, and a mixture of square and triangular cells forming an Archimedean tiling. In the concentrated regime the particles form a single percolated cluster with essentially the same orderings at the same ranges of α values as observed in the dilute regime, thus showing that cluster boundary effects have a minor influence on the cluster crystal symmetry. By using energy analysis and geometry arguments we discuss how the different observed structures minimize the system energy at different values of α.

Desenvolvimento do radioimunoensaio para determinacao do estriol no fluido salivar. / Development of a radioimmunoassay for estriol determination in salivary fluid

O objetivo deste trabalho foi o de desenvolver um sistema de deteccao sensivel e especifico, necessitando assim, pequenas quantidades de saliva, e pouca ou nenhuma purificacao das amostras, alem de ser o ensaio rapido o suficiente para ser efetuado varias vezes num so dia, e realizavel na maioria dos laboratorios do nosso meio. Utilizaram-se 60 amostras de saliva de gestantes escolhidos ao acaso, em diferentes idades gestacionais colhidas 5 minutos apos estimulo com goma de mascar (Trident). Foram comparados 2 metodos: metodo com extracao e metodo direto. E apresentado um protocolo final de teste com analise dos parametros de sensibilidade, exatidao e precisao. O metodo desenvolvido apresenta caracteristicas que permite o seu uso para a determinacao do estriol no fluido salivar