Polydimethylsiloxane (PDMS) is one of the materials of choice for the fabrication of microfluidic chips. However, its broad application is constrained by its incompatibility with common organic solvents and the absence of surface anchoring groups for surface functionalization. Current solutions involving bulk-, ex-situ surface-, and in-situ liquid phase modifications are limited and practically demanding. In this work, we present a simple, novel strategy to deposit a metal oxide nano-layer on the inside of bonded PDMS microfluidic channels using atmospheric pressure atomic layer deposition (AP-ALD). Using three important classes of microfluidic experiments, i.e., (i) the production of micron-sized particles, (ii) the cultivation of biological cells, and (iii) the photocatalytic degradation in continuous flow chemistry, we demonstrate that the metal oxide nano-layer offers a higher resistance against organic solvent swelling, higher hydrophilicity, and a higher degree of further functionalization of the wall. We demonstrate the versatility of the approach by not only depositing SiO_x nano-layers, but also TiO_x nano-layers, which in the case of the flow chemistry experiment were further functionalized with gold nanoparticles through the use of AP-ALD. This study demonstrates AP-ALD as a tool to broaden the applicability of PDMS devices.

Endotoxin is a deadly pyrogen, rendering it crucial to monitor with high accuracy and efficiency. However, current endotoxin detection relies on multistep processes that are labor-intensive, time-consuming, and unsustainable. Here, we report an aptamer-based biosensor for the real-time optical detection of endotoxin. The endotoxin sensor exploits the distance-dependent scattering of gold nanoparticles (AuNPs) coupled to a gold nanofilm. This is enabled by the conformational changes of an endotoxin-specific aptamer upon target binding. The sensor can be used in an ensemble mode and single-particle mode under dark-field illumination. In the ensemble mode, the sensor is coupled with a microspectrometer and exhibits high specificity, reliability (i.e., linear concentration to signal profile in logarithmic scale), and reusability for repeated endotoxin measurements. Individual endotoxins can be detected by monitoring the color of single AuNPs via a color camera, achieving single-molecule resolution. This platform can potentially advance endotoxin detection to safeguard medical, food, and pharmaceutical products.

Polymeric ion-exchange membranes (IEMs) are key to many electrochemical processes, but their intrinsic selectivity limitations restrict scale-up possibilities. Nanofluidic IEMs, based on inorganic rigid materials and charged nanopores, offer a promising alternative. We present design criteria for selective nanofluidic membranes. We used commercial anodized aluminium oxide (AAO) membranes with varying pore sizes to measure permselectivity between different KCl concentrations. Our experiments reveal that membranes with 10-nm pores have permselectivities above 90%, comparable to those of polymeric IEMs, up to electrolyte concentrations of 0.15 vs. 0.75 M. To our knowledge, this is the highest reported ion selectivity for nanofluidic IEMs. Conversely, asymmetric AAO membranes featuring a thin selective layer, exhibited low permselectivity. We explored the influence of other parameters through simulations using the space-charge model. Our numerical results indicate that pore size and surface potential are the most sensitive parameters for increasing selectivity. Additionally, pore length has a minimum requirement for good performance although increasing it beyond the μm scale yields no significant result. This study highlights nanofluidic IEMs as a promising alternative to polymeric IEMs and their capability to improve performance of many electrochemical processes, especially those involving low electrolyte concentrations on at least one membrane side.

The interaction of 2,5-dimercapto-1,3,4-thiadiazole (DMTD) with the AA2024-T3 local microstructure (S-phase, secondary phases and matrix) as function of the NaCl concentration is studied. The inhibiting power and the local interaction of DMTD with the metal were studied by in–situ opto-electrochemistry, XPS and Raman spectroscopy. The stability of the inhibiting layers was evaluated by re-exposing the samples to NaCl solutions without inhibitor. The amount of DMTD and its interaction state (chemisorption/physisorption) vary with the local microstructural composition and NaCl concentration. Higher stability of the inhibiting layers is obtained when these are formed in presence of small amounts of NaCl (0.025–0.25 M).

We explore three variants of atomic layer deposition (ALD) to deposit titanium oxide on the soft polymer polydimethylsiloxane (PDMS). We show that the organic solvent resistance of PDMS is increased by two orders of magnitude compared to uncoated PDMS for ALD performed at atmospheric pressure, which results in a unique surface-subsurface coating of PDMS.