Heat and pressure-resistant room temperature irreversible sealing of hybrid PDMS–thermoplastic microfluidic devices via carbon–nitrogen covalent bonding and its application in a continuous-flow polymerase chain reaction

In this study, we have introduced a facile room-temperature strategy for irreversibly sealing polydimethylsiloxane (PDMS) elastomers to various thermoplastics using (3-aminopropyl)triethoxysilane (APTES) and [2-(3,4-epoxycyclohexyl)ethyl]trimethoxysilane (ECTMS), which can resist heat and pressure after sealing due to the high chemical reactivity of the used chemicals. An irreversible chemical bond was realized at RT within 30 min through the initial activation of PDMS and thermoplastics using oxygen plasma, followed by surface modification using amino- and epoxy-based silane coupling reagents on either side of the substrates and then conformally contacting each other. Surface characterizations were performed using contact angle measurements, fluorescence measurements, X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM) to verify the successful surface modification of PDMS and thermoplastics. The tensile strengths of the bonded devices were 274.5 ± 27 (PDMS–PMMA), 591.7 ± 44 (PDMS–PS), 594.7 ± 25 (PDMS–PC), and 510 ± 47 kPa (PDMS–PET), suggesting the high stability of interfacial bonding. In addition, the results of the leakage test revealed that there was no leakage in the indigenously fabricated hybrid devices, even at high pressures, which is indicative of the robust bond strength between PDMS and thermoplastics obtained through the use of the chemical bonding method. Moreover, for the first time, the heat and pressure-resistant nature of the bonded PDMS–PC microfluidic device was assessed by performing a continuous-flow polymerase chain reaction (CF-PCR), which requires a high temperature and typically generates a high pressure inside the microchannel. The results demonstrated that the microfluidic device endured high heat and pressure during CF-PCR and successfully amplified the 210 bp gene fragment from the Shiga-toxin gene region of Escherichia coli (E. coli) O157:H7 within 30 min.