Bingbing Gao

Patterned Photonic Nitrocellulose for Pseudo-Paper Microfluidics

We report a pseudo-paper microfluidic chip based on patterned photonic nitrocellulose. The photonic nitrocellulose is fabricated using self-assembled monodisperse SiO2 nanoparticles as template. The SiO2 nanoparticles form a photonic crystal having a close-packed hexagonal structure in the microchannels, so the resulting nitrocellulose has a complementary inverse-opal structure. After lamination, a hollow channel is obtained that is partially filled with the photonic nitrocellulose. Owing to the highly ordered photonic structure of the pseudo-paper chip, the flow profile of aqueous solution wicking through the channel is more uniform than conventional paper microfluidic chip. It is also found that the wicking rate of aqueous solution can be easily manipulated by changing the diameter of the self-assembled monodisperse SiO2 nanoparticles, which determines the pore size of the photonic nitrocellulose. The fluorescent enhancement property of the photonic nitrocellulose is used to increase the fluorescent intensity for multiplex detection of two cancer biomarkers. Label-free detection of human immunoglobin G based on the structure color of the photonic nitrocellulose is also demonstrated.

Bottom-up fabrication of paper-based microchips by blade coating of cellulose microfibers on a patterned surface.

We report a method for the bottom-up fabrication of paper-based capillary microchips by the blade coating of cellulose microfibers on a patterned surface. The fabrication process is similar to the paper-making process in which an aqueous suspension of cellulose microfibers is used as the starting material and is blade-coated onto a polypropylene substrate patterned using an inkjet printer. After water evaporation, the cellulose microfibers form a porous, hydrophilic, paperlike pattern that wicks aqueous solution by capillary action. This method enables simple, fast, inexpensive fabrication of paper-based capillary channels with both width and height down to about 10 μm. When this method is used, the capillary microfluidic chip for the colorimetric detection of glucose and total protein is fabricated, and the assay requires only 0.30 μL of sample, which is 240 times smaller than for paper devices fabricated using photolithography.

Patterned Photonic Nitrocellulose for Pseudopaper ELISA

We report an enzyme-link immunosorbent assay (ELISA) based on patterned pseudopaper that is made of photonic nitrocellulose for highly sensitive fluorescence bioanalysis. The pseudopaper is fabricated using self-assembled monodisperse SiO2 nanoparticles that are patterned on a polypropylene substrate as template. The self-assembled nanoparticles have a close-packed hexagonal (opal) structure, so the resulting nitrocellulose has a complementary (inverse opal) photonic structure. Owing to the slow-photon effect of the photonic structure, fluorescence emission for ELISA is enhanced by up to 57-fold without increasing the assay time or complexity. As the detection signal is significantly amplified, a simple smartphone camera suffices to serve as the detector for rapid and on-site analysis. As a demonstration, human IgG is quantitatively analyzed with a detection limit of 3.8 fg/mL, which is lower than that of conventional ELISA and paper-based ELISA. The consumption of sample and reagent is also reduced by 33 times compared with conventional ELISA. Therefore, the pseudopaper ELISA based on patterned photonic nitrocellulose is promising for sensitive, high-throughput bioanalysis.

3D Printing of Bioinspired Liquid Superrepellent Structures

Bioinspired re-entrant structures have been proved to be effective in achieving liquid superrepellence (including anti-penetration, anti-adhesion, and anti-spreading). However, except for a few reports relying on isotropic etching of silicon wafers, most fluorination-dependent surfaces are still unable to repel liquids with extreme low surface energy (i.e., γ < 15 mN m-1 ), especially those fluorinated solvents. Herein, triply re-entrant structures, possessing superrepellence to water (with surface tension γ of 72.8 mN m-1 ) and various organic liquids (γ = 12.0-27.1 mN m-1 ), are fabricated via two-photon polymerization based 3D printing technology. Such structures can be constructed both on rigid and flexible substrates, and the liquid superrepellent properties can be kept even after oxygen plasma treatment. Based on the prepared triply re-entrant structures, micro open capillaries are constructed on them to realize directional liquid spreading, which may be applied in microfluidic platforms and lab-on-a-chip applications. The fabricated arrays can also find potential applications in electronic devices, gas sensors, microchemical/physical reactors, high-throughput biological sensors, and optical displays.

Vertical Paper Analytical Devices Fabricated Using the Principles of Quilling and Kirigami

Here we report the vertical paper analytical devices (vPADs) fabricated using the principles of quilling and kirigami. What differentiates the vPADs from conventional paper microfluidic devices is that the paper substrate used to fabricate the device is placed vertically to the device plane. The fabrication of vPADs with high precision is instrument-free, requiring no photolithography, printing or heating. Two- and three-dimensional vPADs are fabricated for multiplex colorimetric assays of four biochemical indicators and automated enzyme-linked immunosorbent assay of human myoglobin, respectively.

Transpiration-Inspired Fabrication of Opal Capillary with Multiple Heterostructures for Multiplex Aptamer-Based Fluorescent Assays

In this work we report a method for the fabrication of opal capillary with multiple heterostructures for aptamer-based assays. The method is inspired by plant transpiration. During the fabrication, monodisperse SiO2 nanoparticles (NPs) self-assemble in a glass capillary, with the solvent gradually evaporating from the top end of the capillary. By a simple change of the colloid solution that wicks through the capillary, multiple heterostructures can be easily prepared inside the capillary. On the surface of the SiO2 NPs, polydopamine is coated for immobilization of aminomethyl-modified aptamers. The aptamers are used for fluorescent detection of adenosine triphosphate (ATP) and thrombin. Owing to fluorescence enhancement effect of the photonic heterstructures, the fluorescent signal for detection is amplified up to 40-fold. The limit of detection is 32 μM for ATP and 8.1 nM for thrombin. Therefore, we believe this method is promising for the fabrication of analytical capillary devices for point-of-care testing.

Chitin-Based Anisotropic Nanostructures of Butterfly Wings for Regulating Cells Orientation

In recent years, multiple types of substrates have been applied for regulating cell orientation. Among them, surface topography patterns with grooves or ridges have been widely utilizing for cell culturing. However, this construction is still complicated, low cost-effective and exhibits some technological limitations with either “top-down” or “bottom-up” approaches. Here, a simple and green method was developed by utilizing butterfly wings (Morpho menelaus, Papilio ulysses telegonus and Ornithoptera croesus lydius) with natural anisotropic nanostructures to generate cell alignment. A two-step chemical treatment was proposed to achieve more hydrophilic butterfly wings preceding cell culturing. Furthermore, calcein acetoxymethyl ester (Calcein-AM) staining and Methylthiazolyldiphenyl-tetrazolium bromide (MTT) assay results demonstrated the appropriate viability of NIH-3T3 fibroblast cells on those butterfly wings. Moreover, the cells displayed a high degree of alignment in each specimen of these wings. We anticipate that those originating from natural butterfly wings will pose important applications for tissue engineering.

Hepatocyte Aggregate Formation on Chitin-Based Anisotropic Microstructures of Butterfly Wings

Scaffold nanotopography plays the most significant role in the mimicry of the in vivo microenvironment of the hepatocytes. Several attempts have been made to develop methods and substrates suited to growing hepatocytes into aggregates. Functional biomaterials, particularly biodegradable polymers, have been used in several studies aimed to develop improved scaffolds with ordered geometry and nanofibrous architecture for tissue engineering. However, there are still some limitation in their fabrication: it is not cost-efficient, is time-consuming, and exhibits some technological complications. The synthetic scaffolds are usually non-biodegradable and can be non-biocompatible compared to the naturally derived biomaterials. Here, we utilized a simple, cost-effective, and green method with two-step chemical treatment to get more selected hydrophilic butterfly wings from Morpho menelaus, Papilio ulysses telegonus, and Ornithoptera croesus lydius as a chitin-based natural scaffolds to growing hepatocyte aggregates. We established a three-dimensional (3D) in vitro model for culture of HepG2 cells and aggregate formation that maintained the hepatocytes function on these natural anisotropic microstructures. Cells cultured on these substrates show higher viability than those cultured on a two-dimensional (2D) culture plate. Methylthiazolyldiphenyl-tetrazolium bromide (MTT) assay results revealed excellent viability of HepG2 cells on P. u. telegonus wings (fibrous area). The results also demonstrated appropriate cell activity, cell retention, and stable and functional expression in terms of albumin secretion and urea synthesis activity compared to the 2D monolayer culture of hepatocytes on the culture dish surface. With a slightly different degree, the other substrates also shown similar results. We anticipate that these natural anisotropic, biodegradable, and biocompatible substrates can maintain long-term hepatic culture as an in vitro 3D model for potential therapeutic applications and regenerative tissue applications. The model presented here provides a feasible alternative to the synthetic scaffolds and is expected to be more reliable for 3D organotypic liver culture models based on such scaffolds.

Single-Step Fabrication of High-Throughput Surface-Enhanced Raman Scattering Substrates

The combination of surface-enhanced Raman scattering (SERS) with high-throughput screening (HTS) has significant importance for highly sensitive and massive workload assays. Although fabrication of HTS-SERS substrates can be achieved by several methods, the high cost as well as large-equipment dependence limit their applications. Here, we report a simple method to fabricate HTS-SERS substrates within one-step process. The HTS-SERS substrate is fabricated by simply UV-irradiating a fluoroalkylsilane (FAS)-modified liquid-repellent TiO2 surface in AgNO3 solution through a photomask. Owing to the photocatalytic nature of TiO2, the UV irradiation simultaneously triggers the degradation of the attached FAS and the generation of liquid-adhesive Ag nanoparticles (NPs) on exposed area. A HTS-SERS substrate could be directly obtained after UV irradiation. The deposited Ag NPs evidently enhance Raman signals, and the significant difference between the wettability of exposed area and masked area enables fast formation of high-throughput liquid droplet arrays through a simple dragging solution process. The fabrication method is applicable to various substrate materials, to introduce additional functionalities. The photocatalytic activity of TiO2 also allows us to photobleach the residual analyte and Ag NPs after detection to recycle substrate. This single-step method is a highly promising candidate for the fabrication of HTS-SERS substrates.