Sylgard 184 silicone elastomer base

The cantilevers were fabricated from a thin film of Polydimethylsiloxane (PDMS). First, a Sylgard 184 Silicone Elastomer base and a curing agent (Dow Corning, Midland, MI, USA) were mixed at a weight ratio of 8:1. We added more curing agent than the typical mixing ratio of 10:1 because stiffer PDMS retained better shapes when cut into small pieces. The PDMS mixture was spin-coated on a glass slide at a speed of 500 rpm at an acceleration of 300 rpm/s for 60 s. It was then cured at 120 °C for 1 h. The fabricated PDMS film with a typical thickness of about 180 μm was cut to cantilevers of length 4 mm and width 300 μm by using a Silver Bullet Cutter (Silver Bullet Cutters, Apple Valley, MN, USA). The cantilevers were attached to the cantilever holders by using a drop of PDMS mixture as a glue.

PDMS polymer was fabricated according to the previous publications. In a typical synthesis, a 10:1:1 (wt:wt:wt) mixture of Sylgard-184 silicone elastomer base (Dow Corning Corp., Midland, MI), silicone elastomer curing agent, and a cyclohexane solution with sSMO NRs or mSMO NRs (about 6.5 mmol) were thoroughly mixed in a glass container. After degassing by ultrasonic treatment, the liquid mixture was aged at 30 °C for 10 h and cured at 90 °C for 1 h in a vacuum oven.

For the fabrication of nano-composites, polydimethylsiloxane (PDMS: Sylgard 184 SILICONE ELASTOMER BASE) was purchased from Dow Corning. 10–15 µm long multi-walled carbon nanotubes (MWCNTs) with 15 nm outer diameter were purchased from Hanwa Nanotech Inc. (CM 250). Silica powders of 3–7 µm and 10–20 nm particle size were purchased from Silbond (Quarzwerke) and Sigma Aldrich, respectively. To ensure effective mixing and dispersion of entangled CNTs and silica particles within the polymer matrix, premixing (Paste mixer, DAEHWA TECH, PDM-lk) were used along with the three-roll milling technique (three-roll mill, Torrey Hills Technologies). A paste was made by mixing varying amounts of CNT/silica and PDMS base elastomer. The elastomer base and curing agent were combined in a 10:1 (w/w) ratio and then mixed with CNT/silica for 1 min to form the CNT/silica paste. Then, the CNT/silica pastes were three-roll milled for several minutes while gradually reducing the gap between the rolls. For the curing process, a hot press (Carver M) was used to press the CNT/silica pastes into the desired thickness at 120 °C for 30 min under a constant pressure of 2 tons. A CNT/silica/PDMS composite thickness of 1 ± 0.05 mm was used for all measurements reported in this paper.

Polydimethylsiloxane (PDMS)/glass microfluidic devices were made using soft lithography by patterning PDMS on a master of SU-83035 (MicroChem Corp, Westborough, MA, USA) with 20-mm-long, 200-μm-wide, and 50-μm-deep channels with volume of 0.2 μl (see Fig. 2). PDMS was made from a 10:1 mixture of Sylgard 184 silicone elastomer base and Sylgard curing agent from Dow Corning. At one end of the channel, a 3-mm hole was punched in the PDMS to obtain an open well used for reagent and sample insertion. At the other end, a 0.35-mm hole was punched for the connection of a PEEK tube (360 μm OD, 150 μm ID, Mengel Engineering) leading to the three-way valve. The patterned PDMS (0.6 mm thickness) was bonded to a glass microscope slide (76 × 26 × 1 mm, VWR) by treatment in a low-pressure plasma etcher (Pico RF, Diner Electronic) for 60 s. The tubing was inserted into the 0.35-mm hole and fixated with uncured PDMS, which was then cured at 80 °C for 20 min.Fig. 2

Schematic drawing of a cross section of the microfluidic PDMS/glass device. A drop of solution (yellow online) is placed over the open well on the left. The other end of the microfluidic channel is connected to a three-way valve through the PEEK tubing (brown online), through which the solution can be drawn

Nanowells were fabricated using SYLGARD 184 silicone elastomer base (PDMS; Dow Corning, Midland, MI, USA) and a curing agent as described previously [17 (link)]. A suspension of 2 × 10⁵ cells in 100 μl of complete culture media was stained with CellTrace Calcein Violet, AM, for live cells and anti-CD19-Alexa Fluor (AF) 488 for 30 minutes on ice (Life Technologies, Carlsbad, CA, USA). Stained cells were washed in PBS and resuspended in 300 μl of culture media. The suspension of cells was loaded into an array of 50-μm nanowells. The cells were allowed to settle via gravity for 5 minutes. Excessive cells were rinsed off with media, and a LifterSlip coverslip (Fisher Scientific, Pittsburgh, PA, USA) was placed on top to prevent evaporation from the nanowells. The arrays were imaged using an automated epifluorescence microscope (Nikon Eclipse Ti; Nikon Instruments, Melville, NY, USA) equipped with a motorized stage, phase contrast, and 405-nm and 488-nm wavelength filter sets using Nikon NIS Elements Advanced Research image capture software.

A silver (I) nitrate particle sample was purchased from Daejung Chemical & Metals (Shiheung-City, Korea). Sodium sulfate powder was purchased from Junsei Chemical (Tokyo, Japan). Phosphate buffered saline (PBS) (pH 7.4, 10 mM) solution used as the electrolyte in this study and triton X-100 solution were obtained from Sigma-Aldrich (St. Louis, MO, USA). Single layer graphene oxide (500 mg/L) dispersed in water was purchased from Graphene Supermarket (Calverton, NY, USA). Sylgard (Dow Corning, Midland, MI, USA) 184 silicone elastomer curing agent and Sylgard 184 silicone elastomer base were acquired from Dow Corning (Midland, MI, USA) for polydimethylsiloxane (PDMS) preparation. All aqueous solutions were prepared using deionized water (DIW) from a Millipore Milli-Q water purifier operating at a resistance of 18 MΩ/cm.

Microfluidic chips were fabricated via ultraviolet photolithography on a silicon wafer. On the patterned wafer, polydimethylsiloxane (PDMS) solution containing SYLGARD 184 silicone elastomer base and curing agent (weight ratio: 10:1, Dow Corning, USA) was cured for 2 h at 80°C. The reservoirs of the PDMS chip were punched with 4- and 1 mm biopsy punches. The punched chips were then sterilized twice at 120°C for 15 min each and dried in an 80°C oven for at least 6 h. After drying, sterile PDMS chips and cover glasses (Paul Marienfeld, Germany) were bonded using an oxygen plasma treatment (Femtoscience, Korea). After plasma treatment, the bonded chips were maintained in an 80°C oven for at least 24 h to recover the hydrophobicity of the microfluidic chip. The samples were then stored at room temperature until experimentation (28 (link)).