Article

Physiochemical properties of various polymer substrates and their effects on microchip electrophoresis performance.

Department of Chemistry and Center for BioModular Multi-Scale Systems, Louisiana State University, Baton Rouge, 70803-1804, USA.
Journal of Chromatography (impact factor: 4.53). 05/2006; 1111(2):238-51. DOI:10.1016/j.chroma.2005.08.083 pp.238-51
Source: PubMed

ABSTRACT A suite of polymers were evaluated for their suitability as viable substrate materials for microchip electrophoresis applications, which were fabricated via replication technology. The relevant physiochemical properties investigated included the glass transition temperature (T(g)), UV-vis absorption properties, autofluorescence levels, electroosmotic flow (EOF) and hydrophobicity/hydrophilicity as determined by sessile water contact angle measurements. These physiochemical properties were used as a guide to select the proper substrate material for the intended microchip electrophoretic application. The T(g) of these polymers provided a guide for optimizing embossing parameters to minimize replication errors (REs), which were evaluated from surface profilometer traces. RE values ranged from 0.4 to 13.6% for the polymers polycarbonate (PC) and low-density polyethylene (LDPE), respectively. The absorption spectra and autofluorescence levels of the polymers were also measured at several different wavelengths. In terms of optical clarity (low absorption losses and small autofluorescence levels), poly(methyl methacrylate), PMMA (clear acrylic), provided ideal characteristics with autofluorescence levels comparable to glass at excitation wavelengths that ranged from 488-780 nm. Contact angle measurements showed a maximum (i.e., high degree of hydrophobicity) for polypropylene (PP), with an average contact angle of 104 degrees +/-3 degrees and a minimum exhibited by gray acrylic, G-PMMA, with an average contact angle of 27 degrees +/-2 degrees. The EOF was also measured for thermally assembled chips both before and after treatment with bovine serum albumin (BSA). The electrophoretic separation of a mixture of dye-labeled proteins including; carbonic anhydrase, phosphorylase B, beta-galactosidase, and myosin, was performed on four different polymer microchips using laser-induced fluorescence (LIF) excitation at 632.8 nm. A maximum average resolution of 5.04 for several peak pairs was found with an efficiency of 6.68 x 10(4) plates for myosin obtained using a BSA-treated PETG microchip.

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    Article: Low-pressure, high-temperature thermal bonding of polymeric microfluidic devices and their applications for electrophoretic separation
    Yi Sun, Yien Chian Kwok, Nam-Trung Nguyen
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    ABSTRACT: A new method for thermally bonding poly(methyl methacrylate) (PMMA) substrates has been demonstrated. PMMA substrates are first engraved by CO 2 -laser micromachining to form microchannels. Both channel width and depth can be adjusted by varying the laser power and scanning speed. Channel depths from 50 µm to 1500 µm and widths from 150 µm to 400 µm are attained. CO 2 laser is also used for drilling and dicing of the PMMA parts. Considering the thermal properties of PMMA, a novel thermal bonding process with high temperature and low bonding pressure has been developed for assembling PMMA sheets. A high bonding strength of 2.15 MPa is achieved. Subsequent inspection of the cross sections of several microdevices reveals that the dimensions of the channels are well preserved during the bonding process. Electroosmotic mobility of the ablated channel is measured to be 2.47 × 10 −4 cm 2 V −1 s −1 . The functionality of these thermally bonded microfluidic substrates is demonstrated by performing rapid and high-resolution electrophoretic separations of mixture of fluorescein and carboxyfluorescein as well as double-stranded DNA ladders (X174-Hae III dsDNA digest). The performance of the CO 2 laser ablated and thermally bonded PMMA devices compares favorably with those fabricated by other professional means.
    J. Micromech. Microeng. 01/2006; 16:1681-1688.
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    Yi Sun, M.V.D. Satyanarayan, Nam Trung Nguyen, Yien Chian Kwok
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    ABSTRACT: Recently, polymeric materials have been explored as more versatile alternatives for the fabrication of polymerase chain reaction (PCR) microchips. Poly(methyl methacrylate) (PMMA) is a popular substrate material due to its high mechanical stability, good chemical properties and most importantly, its suitability for cheap and simple CO2 laser ablation. However, it has a low glass transition temperature (Tg) of 105 °C, which is just above the denaturation temperature for PCR, thus the bond integrity is compromised. Polycarbonate (PC) is preferred as a substrate for PCR microchip as it has a higher Tg of 150 °C; but since its thermal properties are not suitable for CO2 laser light, the more expensive excimer laser has to be employed. Here we report a novel hybrid PMMA-PC microchip by bonding a PC cover plate with a PMMA substrate containing microchannel which is fabricated by CO2 laser ablation. This hybrid microchip has improved heat tolerance, such that the bonding integrity is sustained at the denaturation temperature. DNA amplification is found to be more efficiently performed in a PMMA-PC microchip than in a PMMA-PMMA microchip.
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Keywords

absorption spectra
 
autofluorescence levels
 
autofluorescence levels comparable
 
average contact angle
 
bovine serum albumin
 
BSA-treated PETG microchip
 
carbonic anhydrase
 
clear acrylic
 
different wavelengths
 
excitation wavelengths
 
gray acrylic
 
ideal characteristics
 
low absorption losses
 
maximum average resolution
 
microchip electrophoresis applications
 
minimum exhibited
 
optical clarity
 
replication technology
 
small autofluorescence levels
 
viable substrate materials