Miniaturized PCR chips for nucleic acid amplification and analysis: latest advances and future trends

Zhang, Chunsun; Xing, Da

The static treatment involves the pre-coating of chip surface, during fabrication of PCR chip or immediately before use, with one of the following substances: SiO 2 (10, 14, 20, 21, 25) , bovine serum albumin (BSA) (11, 17, 25, 37, 53, 61, 73) , polyethylene glycol (PEG) (65, 78, 82) or silanizing agents (for example 3-glycidoxypropyl trimethoxysilane (11) , dichlorodimethylsilane (23, 69) , Sigmacoat Õ (16, 29) or trimethylchlorosilane (33) . The SiO 2 pre-coating is a reproducible and inexpensive standard MEMS process and can be accomplished in a batch fashion. BSA and other agents become popular due to their simplicity but the reproducibility is argued. It is worth noting that diacrylated PEG (DAPEG) can be grafted into PDMS polymer for polyelectrolyte multilayers (PEM) deposition (82) , and that the surface characteristic of PDMS polymer shifts from hydrophobic to hydrophilic after oxygen plasma treatment (44, 83) . The oxygen plasma activation on the surface of PDMS can be performed at the same time with the bonding processes, and thus it is a standard MEMS process with high reproducibility and low costs. Silanization is also a commonly used process to prevent on-chip adsorption of biomolecules, but it is timeconsuming and labor intensive. Moreover, its reproducibility is also problematic. Recently, Legendre et al. developed a rapid (55 min) and simple (one-step) Sigmacoat Õ silanization method on a dry glass surface without extensive rinsing and cleaning steps often associated with other chip coating procedures (29) . This dynamic treatment occurs during the actual operation of PCR chips because the reagents are in the PCR solution. Other widely used dynamic reagents are BSA (10, 11, 13, 16, 20, 21, 28, 31, 50, 51, 53, 57, 59, 60, (62) (63) (64) 70, (74) (75) (76) 78) and polyvinylpyrrolidone (PVP) (17, 21, 44) . Glycerol (10, 78) , formamide (10, 78) , polyethylene glycol (PEG) 8000 (21) , and Tween 20 (21) , have also been studied as dynamic coating agents. It is known that BSA can improve on-chip PCR efficiency because it can compete with DNA polymerase for active adsorption sites on the inner surface. However, it is not yet clear that how components such as (NH 4 ) 2 SO 4 , MgCl 2 and/or KCl in the PCR mixture affect the BSA coating. In addition, when the fluorescence detection technique is applied, possible interactions between BSA and fluorescent probe/dye may be problematic.