Characteristics and impact of Taq enzyme adsorption on surfaces in microfluidic devices

Abstract

We investigated the adsorption of Taq enzyme, using sessile droplets, on different microfluidic materials. In propagating adsorption materials, the contact angle (CA) of a sessile Taq droplet continually recedes and collapses due to adsorption. Contrastingly, in contained adsorption materials it exhibits an initial reduced CA due to an instantaneous adsorption, however remains timeinvariant. Spectrophotometer analysis on SU8, a propagating adsorption material, reveals a gradual loss of Taq from the droplet onto the surface during droplet collapsing, as opposed to a rapid saturated adsorption in Teflon, a contained adsorption material. AFM micrographs of the adsorbed surfaces suggest a network-like structure in SU8 and distinctly different pillar-like structures in Teflon. With this understanding, we have successfully applied a SU8-Teflon coating to impart a time-invariant contact angle with minimal loss of Taq in surface microfluidic devices.

Inhibitory effect of common microfluidic materials on PCR outcome

“…Jeyachandran et al showed that BSA molecules can be adsorbed to both hydrophobic and hydrophilic surfaces [23] with differing adsorption mechanisms and rates [9]. Prakash et al systematically studied polymerase adsorption on 13 materials [11], but this study did not use actual PCR conditions, and thus the results are not necessarily translatable to PCR compatibility due to the temperature dependence of adsorption. And while a variety of materials have been tested for PCR compatibility [11], our study is the first to investigate a wide range of materials.…”

“…Prakash et al systematically studied polymerase adsorption on 13 materials [11], but this study did not use actual PCR conditions, and thus the results are not necessarily translatable to PCR compatibility due to the temperature dependence of adsorption. And while a variety of materials have been tested for PCR compatibility [11], our study is the first to investigate a wide range of materials. Some solutions that avoid the problem of inhibitory effects of certain materials' in enzymatic reactions, such as PCR, have been reported [21,25].…”

“…BSA is thought to compete with the polymerase for adsorption at the chip walls and, thus, to improve PCR yields [2]. The adsorption mechanism of Taq polymerase [11] and BSA protein [9,23] has been extensively studied. BSA also acts as a polymerase competitor in the inhibitor chelation [24].…”

“…Further, tests like SEM, TEM and XPS must be performed in vacuum, where water is removed from the sample [6][7][8][9]. Although AFM works at ambient temperature, even in liquid the surface is visualized only over a very small area [7,8,[10][11][12]. FTIR is suitable only for micro-samples, allowing the molecular bond and grouping vibrations to be deducted [7,[13][14][15][16].…”

Liquid dielectrophoresis and surface microfluidics

“…Biofouling often results in increased sample stiction to the surface, exhibited by a significant drop in droplet contact angles that adversely affects sample actuation and device performance. 30 In addition to this, biofouling followed by uncontrolled and unrestricted desorption of proteins becomes a source of cross contamination, which limits device reusability. Researchers have developed intricate strategies to address and overcome the problem of biofoul- ing, most of which are based on superficial modifications of surfaces by depositing self-assembled monolayers or other polymeric materials which respond to optical, thermal, chemical ͑pH͒, or electrical signals to control interfacial interactions.…”