Plastic chip

Plastic materials have gained importance in microfabrication due to their ease of molding, inexpensiveness, and disposability. Some workers have used these substrates for fabrication of microchips. Pethig et al. [78] and Roberts et al. [79] used laser ablation as a direct method for creating microchannels in plastic chips without the need for fabrication. The methods used an UV excimer laser to bum the microchannels onto the polymer substrate, moving in a predefined, 

Rossier et al. [80] used UV excimer laser photoablation for changing the surface properties of the plastics and drilling. The authors discussed the method for patterning biomolecules on a polymer along with surface coverage of active antibodies and equilibration time. Besides, a method of designing NCE comprising an on-chip injector, column and electrochemical detector was also discussed. Furthermore, the potential of this disposable device was discussed and compared to classical systems. 

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The industrial interest in this area is driven for two reasons The first one is the steady miniaturization of semiconductor devices down to sizes for which the bulk properties of inorganic semiconductors reach their limit and molecular approaches become important. The second is the need for materials for the increasing low-cost consumer market that is dominated by identifier tags, plastic chip cards, and displays for cellular phones that are all driven by small electronic or optoelectronic circuits. The materials for these applications should be cheap, easy to make, and, last but not least, be environment-friendly, combustible, or better yet biodegradable. 

Optical properties of the material are less critical for microchips hyphenated with MS than for devices with on-chip optical detection where low background absorption or fluorescence is mandatory. Thus, completely opaque polymers like glassy carbon or polyimide " can be used as microfabrication substrates. Furthermore, polymer microchips are of great interest because their potentially low manufacturing costs may allow them to be disposable. Methods used for the fabrication of plastic chips include laser ablation and molding methods. 

The PET and aluminum chips require further drying so that they can be electrostatically separated. This is the most expensive part of the entire process. "The aluminum cap is only 1% by weight of the bottle," explains Dittman, "but the equipment to remove it represents about 30% of the investment in the plant. It s out of balance, and we are trying to remove the aluminum more cheaply." The process-which at the CPRR plant can handle about 600 lb per hour, or a potential capacity of about 5 million lb per year—generates clean, well-separated (99.9%) granulated plastic chips that can be sold to a manufacturer who uses the resins. 

The plastic chips are more effective and attractive due to their inexpensiveness with rapid mass productivities. SU-8 has versatile applications in the... 

Yuan, C.-H. Shiea, J. 2001. Sequential electrospray analysis using sharp-tip channels fabricated on a plastic chip. Anal. Chem., 73,1080-1083. 

Ablation using radiations of various wavelengths (IR, visible, UV, or x-ray) has been employed to fabricate plastic chips. For instance, photoablation using pulsed UV lasers (193 nm) has been used to fabricate plastic chips out of polyethylene terephthalate (PET, 100 pm thick) [189,190, 258,758] and polycarbonate (PC, 125 pm thick) [189,258]. Channels as narrow as 30 pm and as deep as 100 pm can be made [258,758]. The cross section of a photoablated PET channel plate laminated with another PET using a thin PE adhesive layer was shown in Figure 2.20 [191]. 

Liquid-phase photopolymerization was used to fabricate plastic chips [218, 219]. To create a microchannel, a UV photomask was used so that the masked channel areas were prevented from polymerization, while the exposed areas were photopo-lymerized. Subsequent suction and flushing removed the unexposed monomer mixtures [218]. 

The thermal conductivity (in W m 1 K-1) of PDMS (0.15) appears to be sufficient, although it is lower than PC (0.16), PET (0.2), glass (0.7-1.0), fused silica (1.38), and silicon (124) [159,246]. Since the channels in the plastic chip are usually narrow (i.e., with high surface-to-volume ratio), the heat dissipation properties of the plastic (e.g., acrylic) channel compared favorably with that of a fused silica capillary (75 pm i.d.) [186]. 

Another way to reduce the fluorescence background, especially from plastic chips, is to modulate the velocity of a fluorescent analyte. The analyte velocity is modulated by periodic variation (in 7-20 Hz) of the separation voltage. Noise rejection is achieved using a lock-in amplifier because only the fluorescent signal but not the background from the chip substrate was modulated. With this method, a decrease in LOD by one order of magnitude has been obtained [685],... 

A Pd film decoupler has also been constructed for amperometric detection of catecholamines. The Pd film has been thermally evaporated onto a plastic chip (without the use of the Cr or Ti adhesion underlayers). Owing to the fast diffusion of H2 on a Pd surface, gas bubbles will not form. Pd is able to absorb H2 produced at the cathode up to a Pd/H ratio of 0.6. This reduces one of the interferences to the EC signal, leading to an improvement of LOD to 0.29 pM dopamine [205,375]. With an optimal decoupler size of 500 pm, up to 6 h of operation was achieved with an electric field of 600 V/cm [375]. 

Conducting carbon polymer ink, which filled a UV-ablated microchannel, was used to construct the integrated microelectrode on a plastic chip. Both chronoamperometry and CV were employed to detect a model compound (fer-rocenecarboxylic acid) down to 3 iM, corresponding to 0.4 fmol within a volume 120 pL [758], In another report, a carbon-paste electrode was constructed by filling a laser-ablated (PET or PC) channel with C ink. The whole structure was then cured at 70°C for 2 h [189]. 

List six polymeric materials commonly used to fabricate plastic chips. (3 marks)... 

Htaoka, Y., Notomi, T., Baba, Y., Integrated microsystem of isothermal amplification of DNA and electrophoresis on a microfabricated plastic chip for detection of specific gene and analysis of genetic materials. Micro Total Analysis Systems Proceedings pTAS 2002 Symposium, 6th Nara, Japan, Nov. 3-7, 2002, 215-216. 

Obtain two small (2-mm) plastic chips from your instructor. 

Place a 50-mL graduated cylinder containing a small magnetic spin-bar on a magnetic stirrer. Add 30 mL of acetone and begin to stir the liquid slowly. Add the plastic chips to the liquid. Stop the stirring and note that the chips will sink to the bottom. 

With slow intermittent stirring, add 3-4 mL of water dropwise. Watch the plastic chips as you add the water see if they rise or stay on the bottom. If they stay on the bottom, keep adding more drops of water until the chips float in the middle of the liquid. At this point, the liquid has the same density as that of the plastic chips. 

Calculate the density of the liquid, and hence the density of the plastic chips (20). Determine the average density of the plastic chips. 

Assume that the plastic chips in your flotation experiment were floating on top of the acetone. Could you still use water as a second liquid to bring the chips to the middle of the liquid Explain. 

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