Microchip-based electrochromatography: designs and applications

Different techniques and methods of electrochromatography on “lab on a chip” devices are reviewed. Described approaches include open-channel microchip electrochromatography relying on C₈, C₁₈ and novel gold nanoparticle (GNP) coating of microchannel wall; packed-channel microchip electrochromatography with new ways of automated loading and unloading of conventional octadecylsilica beads; monolith-based microchip electrochromatography with tailored casting of stationary phase at the specific places of microfluidic network and novel photolitographically fabricated collocated monolithic structures. Specific issues related to the microchip electrochromatography, i.e. importance of high aspect ratio of the microchannels in the open-channel electrochromatography or approaches eliminating the wall effect in the monolith-based electrochromatography, are discussed. Various applications for environmental, pharmacological, genomic and proteomic analysis are described. The operation parameters of reviewed microsystems are summarized in easy-to-read tables.     

Open tubular capillary electrochromatography: A useful microreactor for collagen I glycation and interaction studies with low-density lipoprotein particles

Diabetes, a multifunctional disease and a major cause of morbidity and mortality in the industrialized countries, strongly associates with the development and progression of atherosclerosis. One of the consequences of high level of glucose in the blood circulation is glycation of long-lived proteins, such as collagen I, the most abundant component of the extracellular matrix (ECM) in the arterial wall. Glycation is a long-lasting process that involves the reaction between a carbonyl group of the sugar and an amino group of the protein, usually a lysine residue. This reaction generates an Amadori product that may evolve in advanced glycation end products (AGEs). AGEs, as reactive molecules, can provoke cross-linking of collagen I fibrils. Since binding of low-density lipoproteins (LDLs) to the ECM of the inner layer of the arterial wall, the intima, has been implicated to be involved in the onset of the development of an atherosclerotic plaque, collagen modifications, which can affect the affinity of native and oxidized LDL for collagen I, can promote the entrapment of LDLs in the intima and accelerate the progression of atherosclerosis.In this study, open tubular capillary electrochromatography is proposed as a new microreactor to study in situ glycation of collagen I. The kinetics of glycation was first investigated in a fused silica collagen I-coated capillary. Dimethyl sulphoxide, injected as an electroosmotic flow marker, gave information about the charge of coating. Native and oxidized LDL, and selected peptide fragments from apolipoprotein B-100, the protein covering LDL particles, were injected as marker compounds to clarify the interactions between LDLs and the glycated collagen I coating. The method proposed is simple and inexpensive, since only small amounts of collagen and LDL are required. Atomic force microscopy images complemented our studies, highlighting the difference between unmodified and glycated collagen I surfaces.