Isoelectric Focusing in a Microfluidically Defined Electrophoresis Channel

Electrophoretic Determination of L-Carnosine in Health Supplements Using an Integrated Lab-on-a-Chip Platform with Contactless Conductivity Detection

The health supplement industry is one of the fastest growing industries in the world, but there is a lack of suitable analytical methods for the determination of active compounds in health supplements such as peptides. The present work describes an implementation of contactless conductivity detection on microchip technology as a new strategy for the electrophoretic determination of L-carnosine in complex health supplement formulations without pre-concentration and derivatization steps. The best results were obtained in the case of +1.00 kV applied for 20 s for injection and +2.75 kV applied for 260 s for the separation step. Under the selected conditions, a linear detector response of 5 × 10-6 to 5 × 10-5 M was achieved. L-carnosine retention time was 61 s. The excellent reproducibility of both migration time and detector response confirmed the high precision of the method. The applicability of the method was demonstrated by the determination of L-carnosine in three different samples of health supplements. The recoveries ranged from 91 to 105%. Subsequent analysis of the samples by CE-UV-VIS and HPLC-DAD confirmed the accuracy of the obtained results.

Connector-Free World-to-Chip Interconnection for Microfluidic Devices

In the development of functional lab-on-a-chip (LOC), there is a need to produce a reliable and high pressure connection between capillary tubes and microfluidic devices for carrying fluids. The current technologies still have limitations in achieving ideal interconnection since they are bulky, expensive or complicated. In this paper, a novel connector-free technique using an interference fit mechanism is introduced for world-to-chip interconnection. The proposed technique has considerable potential for replacing current interconnection tools for microfluidic devices due to the advantages including no chemical contamination, easy plugging, enough strength to sustain pressure, high density integration, simple and rapid integration.

Recent developments in microfluidic chip-based separation devices coupled to MS for bioanalysis

In recent years, the development of microfluidic chip separation devices coupled to MS has dramatically increased for high-throughput bioanalysis. In this review, advances in different types of microfluidic chip separation devices, such as electrophoresis- and LC-based microchips, as well as 2D design of microfluidic chip-based separation devices will be discussed. In addition, the utilization of chip-based separation devices coupled to MS for analyzing peptides/proteins, glycans, drug metabolites and biomarkers for various bioanalytical applications will be evaluated.

Recent progress of on-line sample preconcentration techniques in microchip electrophoresis

This review highlights recent developments and applications of on-line sample preconcentration techniques to enhance the detection sensitivity in microchip electrophoresis (MCE); references are mainly from 2008 and later. Among various developed techniques, we focus on the sample preconcentration based on the changes in the migration velocity of analytes in two or three discontinuous solutions system, since they can provide the sensitivity enhancement with relatively easy experimental procedures and short analysis times. The characteristic features of the on-line sample preconcentration applied to microchip electrophoresis (MCE) are presented, categorized on the basis of "field strength-" or "chemically" induced changes in the migration velocity. The preconcentration techniques utilizing field strength-induced changes in the velocity include field-amplified sample stacking, isotachophoresis and transient-isotachophoresis, whereas those based on chemically induced changes in the velocity are sweeping, transient-trapping and dynamic pH junction.

Ion-permeable membrane for on-chip preconcentration and separation of cancer marker proteins

Cancer marker proteins have been electrophoretically concentrated and then separated in a microfluidic device. On-chip preconcentration was achieved using an ion-permeable membrane, consisting of acrylamide, N,N'-methylene-bisacrylamide and 2-(acrylamido)-2-methylpropanesulfonate. This negatively charged membrane was photopolymerized in the microdevice near the injection intersection. Anionic proteins were excluded from the porous membrane based on both size and charge, which concentrated target components in the injection intersection prior to separation by microchip capillary electrophoresis (μ-CE). Bovine serum albumin was used in the initial characterization of the system and showed a 40-fold enrichment in the μ-CE peak with 4 min of preconcentration. Adjustment of buffer pH enabled baseline resolution of two cancer biomarkers, α-fetoprotein (AFP) and heat shock protein 90 (HSP90), while fine control over preconcentration time limited peak broadening. Our optimized preconcentration and μ-CE approach was applied to AFP and HSP90, where enrichment factors of >10-fold were achieved with just 1 min of preconcentration. Overall, the process was simple and rapid, providing a useful tool for improving detection in microscale systems.

Reagent-release capillary array-isoelectric focusing device as a rapid screening device for IEF condition optimization

This report describes the fabrication and characterization of a simple and disposable capillary isoelectric focusing (cIEF) device containing a reagent-release capillary (RRC) array and poly(dimethylsiloxane) (PDMS) platform, which allows rapid (within 10 min) screening of cIEF conditions by introducing a sample solution into plural RRCs by capillary action followed by electric field application. To prepare the RRC, covalent immobilization of poly(dimethylacrylamide) (PDMA) was conducted to suppress electro-osmotic flow (EOF), followed by physical adsorption of the mixture of carrier ampholyte (CA), surfactant, labeling reagent (LR), and other additives to the PDMA surface to construct a two-layer structure inside a square glass capillary. When the sample solution containing proteins was introduced into the RRC, physically adsorbed CA, surfactant, and LR can be dissolved and released into the sample solution. Then, complexation of LR with proteins, mixing with CA and surfactant, and exposure of the PDMA surface spontaneously occurs for the IEF experiments. Here, three different RRCs that immobilize different CAs were prepared, and simultaneous cIEF experiments involving hemoglobin AFSC mixtures for choosing the best CA demonstrated the proof of concept.