Optimization of PTFE Coating on PDMS Surfaces for Inhibition of Hydrophobic Molecule Absorption for Increased Optical Detection Sensitivity

Abstract

Polydimethylsiloxane (PDMS) is a polymer widely used for fabrication and prototyping of microfluidic chips. The porous matrix structure of PDMS allows small hydrophobic molecules including some fluorescent dyes to be readily absorbed to PDMS and results in high fluorescent background signals, thereby significantly decreasing the optical detection sensitivity. This makes it challenging to accurately detect the fluorescent signals from samples using PDMS devices. Here, we have utilized polytetrafluoroethylene (PTFE) to inhibit absorption of hydrophobic small molecules on PDMS. Nile red was used to analyze the effectiveness of the inhibition and the absorbed fluorescence intensities for 3% and 6% PTFE coating (7.7 ± 1.0 and 6.6 ± 0.2) was twofold lower compared to 1% and 2% PTFE coating results (17.2 ± 0.5 and 15.4 ± 0.5). When compared to the control (55.3 ± 1.6), it was sevenfold lower in background fluorescent intensity. Furthermore, we validated the optimized PTFE coating condition using a PDMS bioreactor capable of locally stimulating cells during culture to quantitatively analyze the lipid production using Chlamydomonas reinhardtii CC-125. Three percent PTFE coating was selected as the optimal concentration as there was no significant difference between 3% and 6% PTFE coating. Intracellular lipid contents of the cells were successfully stained with Nile Red inside the bioreactor and 3% PTFE coating successfully minimized the background fluorescence noise, allowing strong optical lipid signal to be detected within the PDMS bioreactor comparable to that of off-chip, less than 1% difference.

Surface functionalization of poly(dimethylsiloxane) substrates facilitates culture of pre-implantation mouse embryos by blocking non-selective adsorption

“…However, most embryo culture media contain bovine serum albumin (BSA), which serves as a surface coating for substrates and helps avoid embryo retention on polystyrene or glass substrates. Although ostensibly BSA pretreatment would mitigate any absorption of small molecules by PDMS substrates, observations from Kim et al suggest that BSA is not effective in blocking absorption in PDMS substrates for an extended time [23,27]. Similar findings were reported with a cotreatment of fibrinogen and BSA on a PDMS surface, where fibrinogen adsorption was impeded for about 6 h in favour of diffusion-limited BSA adsorption but was later allowed to coat the surface [28].…”

Organ on a Chip: A Novel in vitro Biomimetic Strategy in Amyotrophic Lateral Sclerosis (ALS) Modeling

“…Hence, these molecules are easily absorbed by the PDMS, which ultimately interferes with light tracking. Of interest is that recently, covering the PDMS with polytetrafluoroethylene (PTFE) has been proposed as a practical solution, which can have a significant contribution to increasing the sensitivity of optical detecting ( 134 ). Another drawback of OOC systems is the formation of bubbles in microfluidic channels, which is considered as a barrier to creating a suitable chip in modeling diseases ( 135 ).…”

Biomimetic <i>in vitro</i> heart platforms for drug development

“…Polytetrafluoroethylene (PTFE) can be used for microfluidic devices due to its thermo-processability, chemical inertness, and [52]. In 2021, Yao et al [53] showed that PTFE could be used to inhibit the absorption of small hydrophobic molecules in PDMS. Another problem is that the reproducibility of OOC manufacturing varies depending on the properties of materials used, hydrophilic and hydrophobic surface treatment, the ECM used, and the storage conditions of the manufactured chip.…”