Diameter-definable tubing-microchips for applications in both continuous-flow and TEC-modulated on-chip qPCRs with reaction signal analyzed between different types of Teflon-polymers: PTFE and FEP

Recently, the tubing microfluidic system has attracted significant research interest because it waives complicated microfabrication machineries and bonding procedures during the manufacture of microchips; however, due to the limited dimensions in the market, the commercially available micro-tubes are generally fixed in diameters and are unmodifiable in radius; this makes it a challenge to obtain a randomly defined channel-dimension for a tubing microsystem. To solve this problem, herein, we proposed a novel and simple method to obtain a tubing-channel with gradually changed diameter. Both the tensile forces and spectrophotometric properties have been analyzed in this study for systemic characterization; as a proof-of-concept, the inner diameter (ID) of a fluorinated ethylene propylene (FEP) tube has been modified from 0.5 mm to 0.3 mm, and the FEP tube has been further applied to both the thermoelectric (TEC)-modulated on-chip polymerase chain reactions (PCRs) and the continuous flow on-chip PCRs. To the best of our knowledge, this is the first time that an FEP tube with so small ID has been applied to on-chip qPCRs. Based on the comparison with polytetrafluoroethylene (PTFE) regarding the fluorescence signal inside the tube, it can be verified that FEP has much better detection sensitivity than PTFE although these two materials are reckoned to be belonging to the same type of polymer family, generally referred to as Teflon.