Blister formation in dynamic release mirror structures using femtosecond laser pulses.

Blister formation occurs when a laser pulse interacts with the underside of a polymer film on a glass substrate and is fundamental in Laser-Induced Forward Transfer (LIFT). We present a novel method of controlling blister formation using a thin metal film situated between two thin polymer films. This enables a wide range of laser pulse energies by limiting the laser penetration in the film, which allows us to exploit nonlinear interactions without transmitting high intensities that may destroy a transfer material. We study blisters using a helium ion microscope, which images their interiors, and find that laser energy deposition is primarily in the metal layer and the top polymer layer remains intact. Blister expansion is driven by laser-induced spallation of the gold film. Our work shows that this technique could be a viable platform for contaminant-free LIFT using nonlinear absorption beyond the diffraction limit.

Non-specific adsorption of protein to microfluidic materials.

Non-specific adsorption of proteins to the surfaces of microfluidic channels poses a serious problem in lab-on-a-chip devices involving complex biological fluids. Materials commonly used in the formation of microfluidic channels include CYTOP, silica and SU-8. CYTOP is a transparent fluoropolymer (Poly[perfluoro(4-vinyloxy-1-butene)]) with a low refractive index that approximately matches the refractive index of biologically compatible fluids, and is useful in optical biosensors. Using a microfluidic and fluorescence microscopy set-up, the non-specific adsorption of bovine serum albumin (BSA) labeled with fluorescein isothiocyanate (FITC) to three grades of CYTOP (S, M and A), silica, and SU-8 is investigated. Surface properties such as roughness and wettability are also characterized via an atomic force microscope and a contact angle measurement system. The non-specific adsorption of protein occurs with a highly variable load across these materials. Surprisingly, significantly lower adsorption occurred on SU-8 compared to the other materials, likely due to its hydrophilicity (post-cleaning). Among the 3 grades of CYTOP considered, the lowest adsorption occurred on S-grade. BSA adsorption to silica was higher than on S-grade CYTOP and significantly higher than on SU-8 despite being hydrophilic, due to a fixed positive charge formed within the layer during fabrication, which attracts negatively-charged BSA in buffer.