Organic electrochemical transistors are integrated in flexible microfluidic systems. A novel label‐free DNA sensor is developed based on the devices with single‐stranded DNA probes immobilized on gate electrodes. These devices successfully detect complementary DNA targets at low concentrations using a pulse‐enhanced hybridization technique in microfluidic channels. Organic electrochemical transistors are excellent candidates for flexible, highly sensitive, and low‐cost biosensors.

The transport of water vapor through a Nafion membrane includes absorption of water at one membrane/gas diffusion layer interface, water transport in the membrane, and desorption of water at another interface. Based on the structure of the membrane, a model for the water transport through the membrane is presented. It was assumed that the mass-transfer coefficients for the absorption and desorption of water and the water diffusion coefficient were dependent on the volume fraction of water ͑ f V ͒ in the membrane. These parameters were determined from steady-state water transport flux through the membranes at different water activity gradients. The results show that the mass-transfer coefficient for the absorption of water ͑k a = 3.53 ϫ 10 −5 fv m/s, 353 K͒ is much lower than that for the desorption of water ͑k d = 1.42 ϫ 10 −4 fv m/s, 353 K͒. The parameters k a and k d describe the nonequilibrium water uptake of the membrane on operating conditions. Using these obtained parameters, the simulation results agree well with experimental data under many different conditions, including thickness of the membrane, water vapor/liquid water, temperature, and flow rate.

We present a nonlinear hybridization chain reaction (HCR) system in which a trigger DNA initiates self-sustained assembly of quenched double-stranded substrates into fluorescent dendritic nanostructures. During the process, an increasing number of originally sequestered trigger sequences labeled with fluorescent reporters are freed up from quenched substrates, leading to chain-branching growth of the assembled DNA dendrimers and an exponential increase in the fluorescence intensity. The triggered assembly behavior was examined by PAGE analysis, and the morphologies of the grown dendrimers were verified by AFM imaging. The exponential kinetics of the fluorescence accumulation was also confirmed by time-dependent fluorescence spectroscopy. This method adopts a simple sequence design strategy, the concept of which could be adapted to program assembly systems with higher-order growth kinetics.