RESUMO
Electrowetting-on-dielectric (EWOD) technology has been considered as a promising candidate for digital microfluidic (DMF) applications due to its outstanding flexibility and integrability. The dielectric layer with a hydrophobic surface is the key element of an EWOD device, determining its driving voltage, reliability, and lifetime. Hereby, inspired by the ionic-liquid-filled structuring polymer with high capacitance independent on thickness, namely ion gel (IG), we develop a polymer (P)-ion gel-amorphous fluoropolymer, namely, PIGAF, composite film as a replaceable hydrophobic dielectric layer for fabrication of a high-efficiency and stable EWOD-DMF device at relatively low voltage. The results show that the proposed EWOD devices using the PIGAF-based dielectric layer can achieve a large contact angle (θ) change of â¼50° and excellent reversibility with a contact angle hysteresis of ≤5° at a relatively low voltage of 30 Vrms. More importantly, the EWOD actuation voltage did not change obviously with the PIGAF film thickness in the range of several to tens of microns, enabling the thickness of the film to be adjusted according to the demand within a certain range while keeping the actuation voltage low. An EWOD-DMF device can be prepared by simply stacking a PIGAF film onto a PCB board, demonstrating stable droplet actuation (motion) at 30 Vrms and 1 kHz as well as a maximum moving velocity of 69 mm/s at 140 Vrms and 1 kHz. The PIGAF film was highly stable and reliable, maintaining excellent EWOD performance after multiple droplet manipulations (≥50 cycles) or long-term storage of 1 year. The proposed EWOD-DMF device has been demonstrated for digital chemical reactions and biomedical sensing applications.
RESUMO
Fabrication of large-area devices with patternable nanostructures is important for practical applications in optical or electrical devices. In this work, we describe an easy and environment-friendly method for preparing large-area nano-dot (ND) arrays via the electrolytic reaction of a metal oxide film. NDs with various size and morphology can be obtained by adjusting the applied voltage, electrolysis time, and the film thickness of the indium tin oxide (ITO) layer. High-density NDs with size of 50-60 nm can be obtained by electrolysis of a 25-nm-thick ITO film at 150 V for 1.5 min under a water droplet medium, which have been applied for surface-enhanced Raman spectroscopy (SERS) after depositing a thin layer of silver. The SERS substrate with optimized ND structure exhibits sensitive detection of Rhodamine 6G (R6G) with detection limit down to 5 × 10-12 M. The enhancement factors (EFs) of 1.12 × 106 and 6.79 × 105 have been achieved for characterization of 4-methylbenzenethiol (4-MBT) and R6G, respectively. With an additional photolithographic step, multiple areas of ND arrays can be created on one substrate, enabling simultaneous detection of various samples containing different molecules at once experiment. Such a method is quick, easy, patternable, and environment-friendly, being suitable for on-site quick and synchronous determination of various molecules for applications in point-of-care, environmental monitoring, and airport security fields.
RESUMO
Self-healing flexible conductive films have been fabricated, evaluated, and applied. The film is composed of a fragile indium tin oxide (ITO) layer covered with sprayed liquid metal (LM) droplets. Self-healing of electrical conductivity is achieved via spontaneous capillary wicking of LM droplets into cracks/defects of the ITO film. The liquid metal adhering onto the ITO layer can also connect the ITO fragments during bending to keep the overall conductivity of the composite LM/ITO film stable. Stable and reversible electrowetting performance has been achieved with the composite LM/ITO as the conductive film, in either flat or curved states.
