Silica chips

Deposit and Pattern Photoresist 1 Form Upper Parylene Layer 

Xie et al. [20] reported the fabrication chip for pumps and an electrospray nozzle. The process used to fabricate the electrochemical pump chips with electrospray nozzle is shown in Fig. 2.11. A 1.5 xm layer of Si02 was grown on the surface of a 4 inch silicon wafer by thermal oxidation. The front side oxide layer was patterned and removed with buffered FIF. XeF2 gaseous etching was used to roughen the silicon surface in order to promote the adhesion between subsequent layers and the substrate. The first 4.5 p,m parylene layer was deposited. 

Form the Nozzle Pattern 1st Parylene (4.5 pm) Pattern sacrificial 

5 (xm photoresist layer was patterned as the sacrificial layer, followed by the deposition of a second 4.5 p,m parylene layer. The parylene/photoresist/ parylene sandwich structure formed the electrospray nozzle and channel when the photoresist was subsequently dissolved. A 1500 A sputtered aluminum layer was used as a mask for parylene etching to define the shape of the nozzle. Aluminum was removed by a wet etching process. After SU-8 developing, wafers were left inside the SU-8 developer for 2 days to release the photoresist. A serpentine channel (250 pan x 500 pm x 15 mm) extending from the junction of pump channels to the edge of the chip was patterned in the SU-8 layer. Platinum/titanium lines spaced 200 pm apart were patterned under the channel after the electrode deposition step. 

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Array types There are two main types of arrays (i) oligonucleotide and (ii) cDNA arrays. In the first type short 20-25mers are synthesized on a silica chip... 

Schulze et al. [135] developed fused-silica chips dynamically coated with hydroxypropylmethyl cellulose and utilized them for the separation of aromatic low molecular weight compounds such as serotonin, propranolol, a diol, and tryptophan. The authors used deep UV laser-induced fluorescence detection for these compounds. Schuchert-Shi et al. [136] identified ethanol, glucose, ethyl acetate, and ethyl butyrate, byproducts obtained in enzymatic conversions using hexokinase, glucose oxidase, alcohol dehydrogenase, and esterase. The authors reported that the quantification for ethyl acetate was possible using contactless conductivity detection. Hu et al. [137] described the separation of reaction products of (3-thalassemia in a multiplex primer-extension reaction using NCE. The method developed was used for patient samples and the results coincided with those of a detection kit. 

Microdialysis was achieved in a fused silica chip with in situ photopattemed porous membrane, as shown in Figure 5.13. Phase-separation polymerization of the membrane (7-50 pm thick) was formed between posts. The posts maximize the mechanical strength of the membrane so that it can withstand a pressure drop of 1 bar. Low MW cutoff (MWCO) membrane, which can be formed by using less organic solvent, 2-methoxyethanol, appears to be more transparent (see Figure 5.13). This low MWCO membrane can be used to dialyze away low MW molecules, such as rhodamine 560, but not fluorescently labeled proteins (insulin, BSA, anti-biotin, and lactalbumin). Fligh MWCO membrane, which was formed by more organic solvent, allows diffusion of lactalbumin [347]. 

Pre-concentration of proteins was achieved by a nanoporous membrane formed in a fused silica chip. Subsequent CE separation was conducted to achieve a concentration factor of 130 for BSA and 160 for phosphorylase b [594]. 

In one report, the sample stream was physically focused so that it was within the illumination region of the laser probe beam. In this way, fluorescence detection of DNA was enhanced [329]. In another report, the effective observation volume was reduced by confinement within nanochannels in a fused silica chip. In this way, fluorescent detection of even single molecules was achieved [673]. 

Single nucleotide polymorphism (SNP) analysis of the p53 cDNA from clinical samples was analyzed by CGE separation on a fused silica chip. No... 

In competitive homogeneous immunoassay, separation and quantitation of free and bound labeled antigen (cortisol) were carried out in a fused silica chip. Since the antibody-antigen complex was not detected, an internal standard (fluorescein) was added to aid quantitation. In addition, since most of the total cortisol was bound in the serum, a releasing agent, 8-anilino-l-naphthalenesulfonic acid (ANS), should be added [1006]. In other reports, competitive immunoassay for BSA was demonstrated after performing a CE separation on-chip [105,1005]. 

Competitive immunoassay was also conducted for serum T4 (3,5,3, 5 -tet-raiodo-L-thyroxine) on a fused silica chip. Again a T4-releasing agent (TAPS) was used to release T4 from serum [152]. 

Vortex and centrifuge at 4°C for 10 min. The lower phase containing lipid A is collected, and dried under a stream of nitrogen. To remove residual silica chips and other possible contaminants, the purified sample can be passed through a DEAE-cellulose column. 

In nature, phosphorus is not foimd free but only in combination with oxygen in the form of phosphates. The commonest mineral is phosphorite (tricalcium phosphate) which occurs in Russia, North Africa, parfs of fhe Southern United States and in smaller quantities around the globe. There are many other native phosphates including coprolite and the apatites (fluorapatite, chlorapatite and hydroxyapatite). Industrial preparation involves the heating of calcium phosphate from such mineral deposifs or bone ash wifh silica chippings or sand and coke or anthracite in an electric furnace fo about 1500°C. Phosphorus distils over as a vapour and is condensed under water to produce the white allotrope. This can be further purified and converted into red phosphorus if required, although the bulk is now used in the production of phosphoric acid. 

In CE, the principle detection schemes are spectrometric and electrochemical. Fluorescence is easy to implement (especially off-chip), is extremely sensitive, which is useful since the sample volumes are typically very small, and is well understood. However, some compounds may need to be fluorescently labelled . This can be done prior to, during or after separation. Renzi et al. from Sandia National Laboratories have reported a handheld microanalytical instrument for CE analysis of proteins using laser-induced fluorescence detection ". The fused silica chip is 2 X 2 cm and features on-chip sample introduction, inlet port filters and a 10 cm separation column. Nanomolar concentrations of fluores-camine-labelled proteins were detected. 

As noted earlier in this chapter, a small cell volume is desirable for faithful reproduction of peak shapes and greater sensitivity. Typically, TCD cells have volumes around 140 piL which are very good for packed columns or wide bore capillaries. Their use with narrow capillaries has not become routine, but cells are available with volumes down to 20 and several studies have shown that good chromatograms can be obtained in some cases [18,19]. Make-up gas is usually required when capillary columns are used with TCDs. An extremely small cell has been made by etching a nL volume on a silica chip for a micro-GC instrument. Another manufacturer uses a small volume (5 pL) single-cell TCD in its operation the two gas streams (sample and reference) are passed alternately through the cell at a frequency of 10 times per second [5]. 

DRE Suffield is also investigating the use of CE and CE-Laser Induced Fluorescence (LIF) Detection for ultra-high sensitive analysis under field laboratory conditions. Some specific applications for highly polar, water soluble molecules, such as proteins, peptides and toxins, have been developed. DRE Suffield, in cooperation with the University of Alberta, is also developing miniaturized, silica-chip based CE instrumentation and field portable CE-LIF instruments for detection and identification of biological and chemical warfare agents. 

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