Xiangchen Che

High Throughput Studies of Cell Migration in 3D Microtissues Fabricated by a Droplet Microfluidic Chip

Arrayed three-dimensional (3D) micro-sized tissues with encapsulated cells (microtissues) have been fabricated by a droplet microfluidic chip. The extracellular matrix (ECM) is a polymerized collagen network. One or multiple breast cancer cells were embedded within the microtissues, which were stored in arrayed microchambers on the same chip without ECM droplet shrinkage over 48 h. The migration trajectory of the cells was recorded by optical microscopy. The migration speed was calculated in the range of 3–6 µm/h. Interestingly, cells in devices filled with a continuous collagen network migrated faster than those where only droplets were arrayed in the chambers. This is likely due to differences in the length scales of the ECM network, as cells embedded in thin collagen slabs also migrate slower than those in thick collagen slabs. In addition to migration, this technical platform can be potentially used to study cancer cell-stromal cell interactions and ECM remodeling in 3D tumor-mimicking environments.

A molecular beacon biosensor based on the nanostructured aluminum oxide surface

A new class of molecular beacon biosensors based on the nanostructured aluminum oxide or anodic aluminum oxide (AAO) surface is reported. In this type of sensor, the AAO surface is used to enhance the fluorescent signals of the fluorophore-labeled hairpin DNA. When a target DNA with a complementary sequence to that of the hairpin DNA is applied on the sensor, the fluorophores are forced to move away from the AAO surface due to the hybridization between the hairpin DNA and the target DNA, resulting in the significant decrease of the fluorescent signals. The observed signal reduction is sufficient to achieve a demonstrated detection limit of 10nM, which could be further improved by optimizing the AAO surface. The control experiments have also demonstrated that the bioassay used in the experiments has excellent specificity and selectivity, indicating the great promise of this type of sensor for diagnostic applications. Since the arrayed AAO micropatterns can be fabricated on a single chip in a cost-effective manner, the arrayed sensors could provide an ideal technical platform for studying fundamental biological process and monitoring disease biomarkers.

Characterization of the silicon nanopillar-surface filled and grafted with nanomaterials

This paper reports the characterization of the silicon nanopillar-surface filled and grafted with nanomaterials. Usually a silicon nanopillar-surface contains nanopillars and air among them. The air is not a good medium to absorb and trap the incoming photons. In order to improve this capability, the air should be replaced with other material. To this end, copper sulfide–gold (CuS–Au) core–shell nanostructures and silver nanoplates are used as two representative substitutes for air among the nanopillars. Experiments find that the reflectance of the nanomaterial-coated nanopillar-surface can be reduced at least 50% compared to that of the bare nanopillar-surface. Different nanomaterial-coated nanopillar-surface can tune the optical reflectance and absorption profile, thereby trapping photons in different wavelength ranges.

Controlled drug loading and release enabled by nanopore thin film and layer-by-layer nanoassembly

Herein a new drug loading and release device based on nanopore thin film and layer-by-layer (LbL) nanoassembly is reported. The nanopore thin film is a layer of anodic aluminum oxide (AAO), which consists of periodically distributed honeycomb-shape nanopores. Using LbL nanoassembly process, the drug (gentamicin sulfate (GS) as the model) can be loaded into the nanopores and the stacked layers on the nanopore thin film surface. This procedure can be monitored optically. As a technical demonstration, the drug release from the device is achieved by immersing it into flowing DI water, which again can be monitored optically. The simple preparation process and bio-compatibility of the device render it as a potential implantable controlled drug release device.

Nanopore thin film enabled optical platform for drug loading and release

In this paper, a drug loading and release device fabricated using nanopore thin film and layer-by-layer (LbL) nanoassembly is reported. The nanopore thin film is a layer of anodic aluminum oxide (AAO), consisting of honeycomb-shape nanopores. Using the LbL nanoassembly process, the drug, using gentamicin sulfate (GS) as the model, can be loaded into the nanopores and the stacked layers on the nanopore thin film surface. The drug release from the device is achieved by immersing it into flowing DI water. Both the loading and release processes can be monitored optically. The effect of the nanopore size/volume on drug loading and release has also been evaluated. Further, the neuron cells have been cultured and can grow normally on the nanopore thin film, verifying its bio-compatibility. The successful fabrication of nanopore thin film device on silicon membrane render it as a potential implantable controlled drug release device.

Rapid detection of theophylline using aptamer-based nanopore thin film sensor

This paper reports, for the first time, an aptamer-based nanopore thin film sensor for detecting theophylline in buffer and complex fluids. Compared to antibody-based detection, aptamer-based detection offers many advantages such as low cost and high stability at elevated temperatures. Experiments found that this type of sensor, without any optimization, can detect theophylline at a concentration as low as 0.2 μΜ, which is comparable to the detection limit of current lab-based equipment such as liquid chromatography (LC). Experiments also found the aptamer-based sensor has good specificity and selectivity. By using some nanopore thin film sensors as the reference sensors to further cancel out the non-specific binding effect, the theophylline in plant extract has been detected successfully.

A Top-Down Fabrication Process for Vertical Hollow Silicon Nanopillars

Hollow silicon nanopillars (HSiNPs) have been fabricated from a single crystal silicon wafer by a series of standard top-down microfabrication processes, specifically by an ambient temperature Bosch process using the nanosphere beads as the mask. The dimensions of the hollow silicon nanopillars can be tuned with an outer diameter in the range of hundreds of nanometers and inner diameter from 70 to 700 nm. The density of the HSiNPs can be as high as 1.3 × 108/cm2 and their heightto-width aspect ratio can be as high as 20. The ratio of the wall thickness to the outer diameter of the HSiNPs can be tuned from 1/3 to 1/16. This process could be adapted or modified to fabricate hollow nanopillars from different semiconductors, oxides, and metals, thereby offering a generic method for fabricating hollow nanopillars.

Correction to: Microtissue size and cell-cell communication modulate cell migration in arrayed 3D collagen gels

The original version of this article unfortunately contained a mistake. One line indicating statistical significance was improperly placed in Fig. 5.

Studies of mechanisms and characteristics of the fluorescence enhancement on anodic aluminum oxide thin film

Anodic aluminum oxide (AAO) thin film recently has been found as a new type of fluorescence enhancement nanomaterial. However, the mechanisms of the AAO thin film for the fluorescence enhancement have not been completely understood. Herein, the studies of its mechanisms are reported. Based on the experimental and modeling results, it has been found that the main contributing factor to the fluorescence enhancement is probably the plasmonic Al nanoparticles (NPs) embedded in the film, while the nanopore size and porosity of AAO thin film have a limited contribution. The characteristics of the enhancement have also been studied. It has been found that the enhancement is highly related to the gap between the fluorophore and the surface of the AAO thin film. Different excitation wavelength also results in different fluorescence enhancement. Using a simple model with a layer of Al NPs uniformly distributed in the thin film, the calculated enhancement factor of electric field and characteristics of the fluorescence enhancement match the experimental results.

Studies of single neuron cell growth on nanoporous surface and under transcranial magnetic stimulation

This paper reports the behaviors of neuron cell N27 growth on nanostructured surface and under transcranial magnetic stimulation (TMS) at single cell level for the first time. First, the growth of neuron cell N27 on anodic aluminum oxide (AAO) nanoporous surface has been studied. It has been found the cells show much preference to grow on the nanostructured surface over the flat coverslip glass surface. Second, the sizes of cells grown on AAO nanoporous surface with TMS and without TMS have been studied. It has been found the sizes of cells with TMS are statistically smaller than those without TMS in the same period of time, indicating the TMS might speed up the cell division. To verify this observation, the growth of single N27 cells inside SU8 microholders with and without TMS has been investigated. It has been found that up to 17% more daughter cells can be divided when the cells are subjected to TMS compared to those without TMS. All these results suggest the TMS can contribute to the growth of N27 cells, benefiting the neuron regeneration.