Accurate nano-injection system for capillary gas chromatography.

The first version of nano-injection device for capillary gas chromatography (cGC) based on inkjet microchip was developed. The nano-injector could accurately control the injection volume in nano-liter, even pico-liter range. Its configuration and mechanism were discussed in detail. Adopting photolithography and plasma etching technology, we firstly fabricated the inkjet microchip and stuck to a piezoelectric device to eject droplets. Then, a special feedback tube was added to make it function as a nano-injector for cGC, which was an important design to compensate pressure difference between the evaporation chamber of cGC and the sample extrusion chamber of inkjet microchip. The injected volume can be precisely controlled by the number of injected droplets. Excellent precision (RSDs were below 10.0%, n=5) was observed for the injection of ethanol at elevated pressure. Minimum injection volume was about 1.25nL at present. Additionally, good repeatability of the calibration curves for the hydrocarbons ethanolic solution (the RSDs of all components were below 5.30%, n=5) confirmed its feasibility in quantitative analysis regardless of concentration. These results suggested that it can be an accurate nano-injector for cGC.

Property of ionic liquid in electrophoresis and its application in chiral separation on microchips.

The aqueous solution of a kind of room-temperature ionic liquids (RTILs), 1-ethyl-3-methylimidazolium-tetrafluoroborate (1E-3MI-TFB), demonstrated its exclusive electroosmotic property in microchip electrophoresis. It was applied as the working electrolyte for chiral separation in glass microchip electrophoresis. Compared with boric acid buffer, 1E-3MI-TFB aqueous solution exhibited a broader separation window for enantiomers of dipeptides. Then the influences of chiral selector, pH and concentration on efficiency of chiral separation were discussed in detail. The unique mechanism of the generation of EOF was explored in a glass microchannel using 1E-3MI-TFB aqueous solution as working electrolyte. A possible status of 1E-3MI cation in water was suggested at the first time, which facilitated the explanation of EOF and its characteristics in glass microchannel. Additionally, microchip electrophoresis using 1E-3MI-TFB aqueous solution was successfully applied to the chiral separation of complex enantiomers of dipeptides. RTILs aqueous solution, as the electrolyte for the separation of complicated optical isomers, could lead to a revolution in the analytical methods of chiral or conformational analysis for biomolecules.

Steady surface modification of polydimethylsiloxane microchannel and its application in simultaneous analysis of homocysteine and glutathione in human serum.

A novel polydimethylsiloxane (PDMS) surface modification method for microchip electrophoresis has been developed to make a stable and sufficient electroosmotic flow (EOF). Poly(l-glutamic acid) (PGA) which had ionizable carboxyl groups at a high pH-range was immobilized on the surface of microchannel fabricated with PDMS. The surface modification involved surface oxidation by plasma, the silanization of 3-aminopropyldimethylethoxysilane (APDMES) and immobilization of PGA via amide bond. The modified channel was extremely stable against consecutive electric power supply over 5h, and its long-term stability was demonstrated by the efficient separation of four amino acid derivatives reproducibly after a week. Additionally, homocysteine (Hcy), important risk factor of cardiovascular disease, osteoporosis and problems in pregnancy, was successfully measured in human serum in modified PDMS channel with the other thio amino acid simultaneously.

Chiral separation of FITC-labeled amino acids with gel electrochromatography using a polydimethylsiloxane microfluidic device.

A chiral separation model of gel electrochromatography in a polydimethylsiloxane (PDMS) microfluidic device for amino acids (AAs) is presented. Six pairs of fluorescein isothiocyanate (FITC)-labeled dansyl amino acids (Dns-AAs) were separated in a 36-mm effectual separation channel in less than 120 sec, with resolutions all above 0.96. This highly efficient PDMS chiral microfluidic chip was prepared by inserting the mixture solution of monomers, crosslinkers, and radical initiation into the microchannel via syringe. Specifically, allyl-gamma-cyclodextrin (CD) as a chiral selector and crosslinker was bonded in gamma-CD-bonded polyacrylamide (PAA) gel, which was the separation media, and was immobilized in a PDMS microchannel through the stable linkage of 3-(trimethoxysilyl)-propyl methacrylate (Bind-Silane, Sigma, St. Louis, MO, U.S.A.). The preparation not only permitted the prompt chiral separation of AAs, but also extended application of the PDMS microfluidic device by restraining its hydrophobicity through the PAA gel monolithic column. Furthermore, the longevity of the PDMS microfluidic device was prolonged significantly. This can also be a powerful way to develop a rapid and efficient bioanalysis method and portable analytical apparatus.

Development of a gel monolithic column polydimethylsiloxane microfluidic device for rapid electrophoresis separation.

A beta-cyclodextrin (beta-CD)-bonded gel monolithic column polydimethylsiloxane (PDMS) microfluidic device was developed in a simple and feasible way. Before preparation of gel monolithic column in PDMS microchannel, PDMS surface was activated by UV light to create silanol groups, which is an active molecule to covalently bond 3-(trimethoxysilyl)-propyl methacrylate (Bind-Silane) and seal microfluidic device. By the way, Bind-Silane is a bifunctional molecule to link polyacrylamide (PAA) gel and inner wall of PDMS microchannel covalently. Allyl-beta-CD was used not only as a multifunctional crosslinker in PAA gel to control the size of the pores, but also as a chiral selector for the enantioseparation. The stability, transferring heat and optical characteristic of the microfluidic device were examined. The separation capability of the gel monolithic column was confirmed by the successful separation of fluorescein isothiocyanate (FITC)-labeled arginine (Arg), glutamine acid (Glu), tryptophan (Try), cysteine (Cysteine) and phenylalanine (Phe) in the PDMS microfluidic device less than 100 s at 36 mm effective separation length. A maximum of 2.06 x 10(5) theoretical plates was obtained by the potential strength of 490 V/cm. A pair of FITC-labeled dansyl-D,L-threonine (Dns-Thr) was separated absolutely.