Solar-driven photoelectrochemical (PEC) water splitting for hydrogen production promises to solve the impending energy and environmental crisis. The key to increase the efficiency of PEC hydrogen generation is developing high-performance catalysts and photocathodes. 3D p-type silicon (p-Si) arrays are promising architectures due to the high light harvesting and the large interfacial areas. We demonstrate its enhanced PEC performance with a photocurrent density of -37.5 mA/cm² at 0 V (vs. RHE) under simulated 100 mW/cm² (1 Sun) with an AM 1.5 G filter, which is the highest value reported for p-type Si photocathodes. The synergic effects of the excellent light harvesting of Si nanopillar (NP) array core and the good optical transparency , as well as excellent electrocatalytic activity of NiCoSe_x shell boost the production and utilization of photogenerated electrons. The Faradaic efficiency of H₂ and O₂ on p-Si/NiCoSe_x was approximately 100%, which confirmed that the photocurrent during PEC reaction was attributed to hydrogen generation. The completely enclosed core-shell structure isolated the Si NP from air and aqueous electrolyte and minimized the oxidation of silicon, leading to good stability. The design of p-Si/NiCoSe_x core/shell NP arrays offers a new strategy for preparing highly efficient photoelectrochemical solar energy conversion devices.

Tumor metastasis causes the death in most cancer patients. During metastasis, cell migrated from primary tumor was the very first step and study the tumor cell migration and interaction with somatic cells is therefore of great important. Development of in vitro technology that can quantitatively gain migration and cell-cell interaction data is there high desirable. Conventional methods for study tumor migration and cell-cell interaction are plagued by inaccessible to get quantitative data or complication of microfabrication process which brings into additional efforts rather than study the biological question itself. Herein, we developed a 3D printed “LEGO”-like device combined with a quantitative data gaining process which can be used for investigation into tumor cell migration process dynamically at single cell resolution and tumor-stromal interactions with high flexibility.

A Biosensor Combining Molecularly Imprinted Polymers (M-MIPs) and Surface Enhanced Raman Spectroscopy (SERS) to Detect Antibiotics in Food Samples

Yi Sun^,1*, Jon Ashley¹, Kaiyu Wu¹, and Anja Bosen¹.

¹ Department of Micro- and Nanotechnology, Technical University of Denmark, Ørsteds Plads, DK-2800 Kgs. Lyngby, Denmark

* Email: [email protected]; Tel.: +45 45256319

In this study, temperature-responsive magnetic molecularly imprinted polymers (M-MIP) nanoparticles were synthesized for the first time for the extraction of cloxacillin in pork products. By combining the M-MIPs with surface enhanced Raman spectroscopy (SERS), a sensitive biosensor was demonstrated to detect cloxacillian with pico-mole sensitivity.

MIPs are synthetic ligands which can be tailored to bind any analyte of choice¹.  They are of great interest due to their thermal stability, robustness, low cost and comparable binding affinity. They have been used in sample preparation and biosensing as an attractive alternative to natural antibodies to capture targets ranging from small molecules to big proteins.  

In this work, the magnetic nanoparticles with MIP-based receptors were synthesized for efficient and rapid extraction of antibiotic residues in pork samples.  Fe₃O₄ nanoparticles were obtained using the solvothermal synthesis.  The resultant nanoparticles were treated with Tetraethyl orthosilicate (TEOS) to form a SiO₂ layer.  Finally a thin MIP layer was polymerized round the nanoparticles using azobisisobutyronitrile (AIBN) as the initiator, ethylene glycol dimethacrylate (EDGMA) as the cross-linker, N-isopropylmethacryamide (NIPAm), methacrylic acid (MAA) as the monomers and the antibiotic as the template.  By adding the monomer NIPAm, the MIPs become temperature responsive, and can swell at low temperature to release the target. The corresponding magnetic non-imprinted polymer nanoparticles (M-NIP) was prepared using the same method in the absence of the template. An Overview of the synthesis strategy is shown in Fig. 1. The resultant M-MIP nanoparticles were characterized using IR, XRD scanning electron microscopy (SEM) and transmission electron microscopy (TEM) (Fig. 2).  Both binding affinities of the resultant M-MIPs and M-NIPs were tested using UV absorbance (Fig. 3). M-MIPs with 300-400 nm in size and good binding capacities were obtained.

To demonstrate the feasibility of using M-MIPs for sample preparation, the synthesized M-MIPs were mixed with pork blood samples spiked with Chloxacillian. After incubation at room temperature, the M-MIPs were collected using a magnet and washed by acetonitrile. Owing to the thermos-responsive properties of MIPs, Chloxacillian was easily released by cooling the MIPs to 4 degree. The collected Chloxacillian was dropped on a SERS substrate which contained an array of silicon micropillars coated with silver. The corresponding calibration plots showed a detection limit (LOD) of about 50 pmol (Fig. 4). The biosensor combining M-MIPs and SERS would be widely used on site or in the field for rapidly screening food contaminants to ensure food safety.

Fig. 1: Overview of the synthesis of M-MIPs

Fig.2 IR characterization of Fe₃O₄, Fe₃O₄@SiO₂, Fe₃O₄@ SiO₂-MPA and, Fe₃O₄@SiO₂-MIP; XRD of Fe₃O_4.

Fig.3 (A) Binding kinetics and (B) Binding capacity of Cloxacillian MIPs and NIPs.

Fig.4 SERS spectra of cloxacillin in MeOH:acetic acid (9:1) and corresponding calibration plots.

REFERENCES:

1. J. Ashley, M-A. Shahbazi, K. Kant, V. A. Chidambara, A.Wolff, D. D. Bang, Y. Sun, “Molecularly Imprinted Polymers for Sample Preparation and Biosensing in Food analysis: Progress and Perspectives, Biosens. Bioelectron. 2017, 91, 606-615.
2.  

Progress Claims

This article presents a novel method to bond PLA, a 3D-printing material, and PMMA, a popular substrate material for microfluidic applications. With this technique, the tubing connectors can be fabricated by 3D printing and make this PLA/PMMA hybrid microfluidic chip extremely easy to use for experiments. The major challenge of bonding this hybrid chip is the high level surface roughness of PLA substrates with its significant influences on bonding strength [1]. After Ethanol treatment and UV irradiation of this hybrid chip, a post-annealing step was realized to facilitate the bonding. To further analyze the bonding quality leakage test, cross-sectional image by microscope, and pressure bursting test were conducted. The experiment results clearly showed that this method could successfully and rapidly form a strong bond (＞13 bars) between PLA and PMMA substrates.

Background

Nowadays, thermoplastics are used commonly in microfluidic applications. The bonding of PMMA/PLA can offer significant benefits taken advantages from 3D-printing process such as allowing producing incredibly complex products in a short time, while minimizing material waste.

Description of Bonding Procedure

Ethanol solution was distributed uniformly sandwiched between two substrates by spin-coating process (190 rpm, 10 sec). Following the UV irradiation (56 sec), an instantaneous and permanent bonding can be formed between PMMA and PLA. However, the bonding strength is significantly affected by the high level of surface roughness of PLA substrates (range from 4.5 to 6.5μm). It can cause the failure of bonding. To solve this critical issue, we employed a post-annealing strategy (55℃, 30 min) straightforwardly after UV exposure step. Its purpose is help create more contacting points between two bonded substrates because of surface degradation caused by coarsening phenomena [3]. Besides post annealing can help relieve stress and therefore improve the bonding strength. The temperature executed for post-annealing is below the glass transition temperature of PLA (Tg of PLA = 60~65℃), hence there has no significant channel deformation observed. The overall bonding procedure is described in Fig. 1.

After bonding, several experiments were conducted to characterize the bonding quality such as leakage tests, cross-sectional images by microscope, and burst tests.

Experimental Results

1. Comprehensive examination

Following the completion of the bonding experiments, leakage tests and the cross sectional investigation using microscope of bonded chip were conducted, the results of which are presented in Fig. 2. The figure clearly demonstrates the effectiveness of the proposed bonding method for heterogeneous substrates between PMMA/PLA. Figure 2(a) shows the bonded chip, Figure 2(b) shows the enlarged figure of the microchannel, both figures clearly showed that no leakage was observed. Figure 2(c) shows the cross-sectional image of bonded chip.

1. The influence of post-annealing conditions on bonding strength.

Fig.3 illustrates the set up for busting test and Table 1 lists the experiment results of bonding strength. In all of the experiments, the microchannels were fabricated on the PMMA substrates and the cover substrates were PLA. Table 1 clearly shows that the microfluidic chips have sufficient bonding strength above 10 bars.

We demonstrated a fiber integrated optofluidic platform to perform miRNA detection with high sensitivity and specificity based on FRET principle. Recently miRNA has attracted extensive interest as a biomarker, providing important evidence for early disease diagnosis and post treatment. Traditionally, numerous analytical approaches such as northern blotting, micro arrays , and real-time quantitative polymerase chain reaction have been developed for miRNA detection. However, the existing methods have many technical challenges, for example, the concentration of miRNA in vivo is normally at low level, and the short sequence and easy degradation by RNAase makes it difficult for PCR. Therefore, we developed an innovative optofluidic platform that combines the advantage of droplet microfluidics and optofluidic technology, and provides a low-cost, compact and high specificity approach for identification and quantification of miRNA using FRET principle. Single-nucleotide differences within miRNA family can be distinguished by a novel Y-junction design of donor, receptor and miRNA sequence. We performed one step miRNA detection with simple device operation, and our platform achieved target miRNA identification at a low concentration and high specificity.