Generation of Size-controlled Poly (ethylene Glycol) Diacrylate Droplets <em>via </em>Semi-3-Dimensional Flow Focusing Microfluidic Devices

Uniform and size-controllable poly (ethylene glycol) diacrylate (PEGDA) droplets could be produced via the flow focusing process in a microfluidic device. ...

Tsinghua University

Label-free biosensing based on optical waveguide spectroscopy of silica nanotube (SNT) arrays is realized with high sensitivity. The SNT arrays fabricated using a porous anodic alumina (PAA) template assisted by surface sol-gel (SSG) method showed a high value of 552 reciprocal refractive index unit as the sensing figure of merit by exchanging the sensing environment with water and ethanol. A standard biotin-streptavidin affinity model was tested using the SNT arrays which support a TM1 mode and the fundamental response of the system was investigated. Results show that the response of the SNT arrays for adsorption of streptavidin is higher than the one using substrate without removing the PAA template due to the larger surface area and the stronger electromagnetic field. The limit of detection (LOD) of the SNT arrays for detection of streptavidin was estimated as 93 pM, with the detection time of 40 min. Additionally, the Fresnel calculations suggested higher potential sensitivity of the current system compared to that of the conventional SPR sensors. Thus, the SNT arrays may be used as a versatile platform for high-sensitive label-free optical biosensing due to the high performance and the large potential of the surface functionality.

Optical waveguide sensor based on silica nanotube arrays for label-free biosensing.

A green-light emitting germanium nanocrystal-based biosensor to monitor lysosomal pH changes is developed. The Ge nanocrystals are synthesized in an aqueous solution with a significantly enhanced photoluminescence quantum yield of 26%. This synthesis involves a facile solution based route which avoided the use of toxic or environmentally unfriendly agents. Importantly, the photoluminescence intensity of the synthesized Ge nanocrystals is particularly sensitive to changes in pH between 5 and 6. When incubated with cultured cells, the nanocrystals are internalized and subsequently translocated via the lysosomal pathway, and the Ge nanocrystals' fluorescence are greatly enhanced, even when the lysosomal pH is only slightly increased. These results reveal that the Ge nanocrystals possess high pH sensitivity compared to a commercially available dye, LysoSensor Green DND-189. The fluorescent properties of the Ge nanocrystals are demonstrated to be dependent on both the crystal form and their surface chemistry. The superior fluorescence properties and bioapplicability of the Ge nanocrystals makes them a promising intracellular bioimaging probe for monitoring various pH-sensitive processes in cells. 

Facile Synthesis of pH-sensitive Germanium Nanocrystals with High Quantum Yield for Intracellular Acidic Compartment Imaging.

Isolation and amplification procedures are indispensable for traditional single-molecule detection methods applied in low-abundance biomolecule analysis. Here, we describe a method for ultrasensitive detection of DNA through encoding a single target molecule with a single-countable nanometer-sized substitute (gold nanorod, AuNR) and enrichment of the substitute AuNRs into a limited region followed by accurate microscopic enumeration. The enrichment and the bright distinct color allow the AuNRs to be efficiently counted from as few as 1-2 to tens of thousands in 3 μL of test solution, which demonstrates the ability of rapid digital concentration readout of the target DNA. On this basis, a detection limit of 6.5 aM was achieved for DNA associated with human papillomavirus (HPV). Notably, our method requires neither complicated isolation and amplification procedures nor extremely expensive instruments and consumables.

Digital Concentration Readout of DNA by Absolute Quantification of Optically Countable Gold Nanorods.

Arrays of ordered nanorods are of special interest in many fields. However, it remains challenging to obtain such arrays on conducting substrates in a facile manner. In this article, we report the fabrication of highly ordered and vertically standing nanorod arrays of both metals and semiconductors on Au films and indium tin oxide glass substrates without an additional layering. In this approach, following the simple hydrophilic treatment of an anodic aluminum oxide (AAO) membrane and conducting substrates, the AAO membrane was transferred onto the modified substrates with excellent adhesion. Subsequently, nanorod arrays of various materials were electrodeposited on the conducting substrates directly. This method avoids any expensive and tedious lithographic and ion milling process, which provides a simple yet robust route to the fabrication of arrays of 1D materials with high aspect ratio on conducting substrates, which shall pave the way for many practical applications in a range of fields.

Hydrophilicity Reinforced Adhesion of Anodic Alumina Oxide Template Films to Conducting Substrates for Facile Fabrication of Highly Ordered Nanorod Arrays.

A new analytical method has been developed to detect three kinds of DNA simultaneously based on magnetic beads and color-encoded plasmonic nanocrystals. Magnetic beads modified with capture DNA are employed to collect the specific target DNA, and color-encoded plasmonic nanocrystals are applied to signal the target through DNA hybridization. As a proof of concept, three types of representative metal nanocrystals of gold nanoparticle (AuNP), gold nanorod (AuNR), and gold/silver nanoparticle (Au/AgNP) were employed to signal three dissimilar virus-related protective antigen genes, Ebola virus (EV), Variola virus (VV), and Bacillus anthracis (BA), respectively. Detection limits of 0.5-3 fM were obtained showing the high sensitivity for DNA detection. The microscopic discrimination of the encoded nanoparticles allows simple, rapid, accurate, and cost-effective detection of multiple DNA molecules, indicative of the potential in practical applications. Graphical abstract Development of a novel digital triplex DNA assay based on single-countable color-encoded plasmonic nanocrystals.

Digital triplex DNA assay based on plasmonic nanocrystals.

The development of highly sensitive and rapid methods for detecting DNA is of critical importance. Here, we describe a strategy for the digital detection of target DNA at the femto-molar level. Individual DNA molecules were encoded with a single gold nanorod (AuNR), separated and enriched by magnetic immune-separation. The coding gold nanorods were then de-hybridized and dispersed into a gold nanosphere (AuNS) solution at a certain concentration, and both gold nanoparticles were immobilized on glass slides for dark-field microscopic imaging. Using an in-house Matlab program, the concentration of the target DNA was calculated based on the ratio of the coding gold nanorods to gold nanospheres. By combining the coding of individual biomolecules with a single gold nanorod and the use of gold nanospheres as an internal standard, a method for the rapid and accurate digital detection of target DNA to the femto-molar level was developed.

Microscopic Differentiation of Plasmonic Nanoparticles for the Ratiometric Read-out of Target DNA.

A highly sensitive homogeneous method for DNA detection has been developed. The system relies on two kinds of gold nanorod (AuNR) probes with complementary DNA sequences to the target DNA. In the presence of the target DNA, two kinds of AuNR probes are assembling into dimers or small aggregates. The target-induced AuNR aggregate has higher scattering intensity than that of a single AuNR because of the plasmonic coupling effect. Dark field microscopy was utilized to image the single particle and measure its scattering intensity. We wrote our own Matlab code and used it to extract the scattering signal of all particles. Difference in distribution of scattering intensity between the single AuNR and its aggregate provides a quantitative basis for the detection of target DNA. A linear dynamic range spanning from 0.1pM to 1nM and a detection limit of ~ 30fM were achieved for the detection of DNA in serum sample.

Scattering measurement of single particle for highly sensitive homogeneous detection of DNA in serum.

In this paper, we present a stable silver-based surface plasmon resonance (SPR) sensor using a self-assembled monolayer (SAM) as a protection layer and investigated its efficiency in water and 0.01 M phosphate buffered saline (PBS). By simulation, silver-based SPR sensor has a better performance in field enhancement and penetration depth than that of a gold-based SPR sensor, which are 5 and 1.4 times, respectively. To overcome the instability of the bare silver film and investigate the efficiency of the protected layer, the SAM of 11-mercapto-1-undecanol (MUD) was used as a protection layer. Stability experiment results show that the protected silver film exhibited excellent stability either in pure water or 0.01 M PBS buffer. The sensitivity of the silver-based SPR sensor was calculated to be 127.26 deg/RIU (refractive index unit), measured with different concentrations of NaCl solutions. Further, a very high refractive resolution for the silver-based SPR sensor was found to be 2.207 × 10 RIU, which reaches the theoretical limit in the wavelength of 632.8 nm for a SPR sensor reported in the literature. Using a mixed SAM of 16-mercaptohexadecanoic acid (MHDA) and a MUD layer with a ratio of 1:10, this immunosensor for the rabbit immunoglobulin G (IgG) molecule with a limit of detection as low as 22.516 ng/mL was achieved.

A Sensitive and Stable Surface Plasmon Resonance Sensor Based on Monolayer Protected Silver Film.

In this work, we developed a robust and ultrasensitive bio-sensor based on the target-aptamer recognition strategy and microscopic enumeration of gold nanoparticles (AuNPs) using dark field microscopy (DFM). The aptasensor with a core-shell structure consisting of a magnetic bead (MB), aptamer and AuNPs was fabricated by complementary hybridization of the DNA probe on the AuNPs surface to the aptamer coupled to the MB. Upon addition of the target molecule, the strong interaction between the aptamer and the target molecule, thrombin, results in the release of the AuNPs from the MB. The quantities of thrombin is therefore linearly correlated to the number of the released AuNPs, which can be digitally counted using DFM. To demonstrate the feasible use of the aptasensor for target detection, thrombin was evaluated as the model target. The limit of detection was determined to be 2.54 fM with dynamic range of 6 fM-100 fM. When the concentration of thrombin exceeded 100 fM, the counted number of AuNPs didn't correlate linearly to molecules of thrombin anymore, as the nanoparticles aggregated partly due to high concentration. However, the color of the solution changes to purple and the concentration of free AuNPs can be conveniently quantified by UV-Vis spectroscopy for up to 100 nM. It is noteworthy that our aptasensor is very easy to operate and requires neither complex isolation and amplification processes nor expensive instruments and consumables. Furthermore, this strategy can be easily generalized to other targets by replacing the corresponding aptamers and show great potential for the detection of biomarkers in clinical samples.

Shuqing Sun

Graduate School at Shenzhen

Tsinghua University

Generation of Size-controlled Poly (ethylene Glycol) Diacrylate Droplets via Semi-3-Dimensional Flow Focusing Microfluidic Devices

Shuqing Sun

.css-o250i3{font-size:18px;font-family:Open Sans,sans-serif;line-height:21.6px;}Graduate School at Shenzhen

Tsinghua University

Generation of Size-controlled Poly (ethylene Glycol) Diacrylate Droplets via Semi-3-Dimensional Flow Focusing Microfluidic Devices

Graduate School at Shenzhen