Weijie Wan

The effects of gold nanoparticles with different sizes on polymerase chain reaction efficiency

We report the effect of 5, 10 and 20 nm gold nanoparticles (AuNPs) on polymerase chain reaction (PCR) efficiency and a proposed mechanism for AuNPs affecting the PCR. It is observed that AuNPs can cause PCR inhibition, the degree of which is affected by the concentration of the AuNPs. AuNPs of larger sizes can cause complete PCR inhibition at a lower particle concentration than those of smaller sizes. Evidence from different experiments suggests that a probable mechanism is through polymerase-AuNP binding. The collected data show that the product yield is modulated by the total surface area of the AuNPs regardless of the size, which further supports the hypothesis.

Integration of nanoparticle cell lysis and microchip PCR for one-step rapid detection of bacteria

This paper describes an integrated microchip system as an efficient and cost-effective solution involving Nanotechnology and Lab-on-a-Chip technology for the rapid detection of bacteria. The system is based on using surface-modified gold nanoparticles for efficient cell lysis followed by microchip PCR without having to remove the nanoparticles from the PCR solution. Poly(quaternary ammonium) modified gold nanoparticles are used to provide a novel and efficient cell lysis method without the need to go through time-consuming, expensive and complicated microfabrication processes as most of current cell lysis methods for Lab-on-a-Chip applications do. It also facilitates the integration of cell lysis and PCR by sharing the same reaction chamber as PCR uses. It is integrated with a prototype microchip PCR system consisting of a physical microchip PCR device and an automated temperature control mechanism. The research work explores solutions for the problem of PCR inhibition caused by gold nanoparticles as well as for the problem of non-specific PCR amplification in the integrated microchip system. It also explores the possibility of greatly reducing PCR cycling time to achieve the same result compared to the protocol for a regular PCR machine. The simplicity of the setup makes it easy to be integrated with other Lab-on-a-Chip functional modules to create customized solutions for target applications.

Study of a novel cell lysis method with titanium dioxide for Lab-on-a-Chip devices

In this paper, a novel method is proposed and demonstrated to be able to lyse gram-negative (E. coli) bacteria cells for Lab-on-a-Chip applications. The proposed method incorporates using titanium dioxide particles as photocatalysts and a miniaturized UV LED array as an excitation light source to perform cell lysis on microchips. The experimental result demonstrates the feasibility of the proposed prototype device. The working device suggests an inexpensive, easy to be fabricated and effective way for microchip cell lysis. The miniaturized UV LED array and the microchip with a reaction chamber can be easily integrated with other functional components to form a customized whole Lab-on-a-Chip system.

Size-dependent PCR inhibitory effect induced by gold nanoparticles

In this work, the effect of gold nanoparticles (AuNPs) with diameters of around 5, 10 and 20 nm on PCR efficiency is evaluated respectively using a real-time PCR machine. Gold nanoparticles show no obvious effect on PCR at low particle concentration. When the concentration is increased, PCR inhibition is observed. At the same particle concentration, gold nanoparticles of different sizes show different inhibitory effects on PCR. It is found that Taq polymerase can interact with AuNPs. The interaction is probably due to the binding of polymerase to AuNPs therefore lowering the concentration of free polymerase. It is also found that bovine serum albumin can interact with gold nanoparticles. It is believed that BSA blocks the surface of AuNPs from forming biding sites for polymerase. It can be used as an additive to reverse the inhibitory effect caused by gold nanoparticles.

Working towards a sample preparation device with carbon nanotubes

Advances in microfabrication have introduced new possibilities for automated, high-throughput biomedical investigations and analyses. Physical effects such as dielectrophoresis and electroporation can be used to manipulate particles in solution to coordinate a sequence of bioanalytical processing steps. Dielectrophoresis is accomplished with non-uniform electric fields that can polarize particles in suspension and exert static or translational forces. Electroporation is accomplished with high-strength electric fields that can create pores on the plasma membranes of cells. Membrane breakdown under high voltage is associated with cell death and a dispersal of cell contents including nucleic acids and protein. This paper presents summaries of multiple experiments in both dielectrophoresis and electroporation. In the electroporation experiments, carbon nanotubes were used to enhance electric field strengths with the goal of reducing the voltage requirements for portable lab-on-a-chip devices with strict power limitations. The concept is to create a sample preparation device which is capable of separating cells into multiple chambers for cell lysis by carbon nanotubes and releasing their DNA for further analysis.

Controlling two-dimensional movement of microparticles over an electrode array surface.

This paper presents an original microchip device that manipulates planar x- and y-positions of dielectric microbeads over an electrode array with dielectrophoresis (DEP) effects. Implemented with a simple single-layer metal process, the microchip device consists of two parallel arrays of triangular-shaped electrodes. The two arrays of electrodes are arranged such that they locked into each other to form interdigitated electrodes. The unique geometry and placement of the electrodes can produce different configurations of DEP waveforms. The different DEP waveforms will, in turn, allow the strength and the locations of the electric field maxima and minima to be manipulated. Our experiments showed that with a quad-pole traveling wave, the microbeads can be moved across the electrode array surface in directions parallel to the fluid flow to establish their x-positions via traveling wave dielectrophoresis (TWD) effect. In addition, the microbeads can be moved in directions perpendicular to the fluid flow to establish their y- positions via activating one or both sets of electrode arrays with DEP waveforms. A line of microbeads can be held indefinitely at the predetermined location or be immediately moved to an arbitrary location on the electrode array. With a functional transportation of particles along two planar axes, the “teeth-like” electrode structure can be easily integrated into a microfluidic system where an accurate position control of particles is required.

The effects of nanoparticles on polymerase chain reaction

The ability of synthesizing nanomaterials marked the beginning of the Nanotechnology era. Due to their extremely small sizes, nanomaterials present unique properties that are not seen in their bulk counterparts. However, understanding how nanomaterials behave in all kinds of biochemical reactions is the key to utilize them in potential applications. In this paper, the effects of gold, titanium dioxide and silver nanoparticles on polymerase chain reaction (PCR) are reported. It is found that they all cause PCR inhibition. Surface interaction between nanoparticles and PCR components such as Taq polymerase should account for the inhibition. PCR inhibition caused by gold nanoparticles can be reversed by adding chemical reagents to block surface of the nanoparticles from interacting with Taq polymerase. Surface modification of nanoparticles has a large impact on PCR. Titanium dioxide nanoparticles modified with different functional groups show different PCR inhibition behavior. It is also found that mixing titanium dioxide nanoparticles with silver nanoparticles at a certain ratio can reduce PCR inhibition caused by both nanoparticles.

Evaluation of antibacterial property induced by surface-modified titanium dioxide nanoparticles

In this paper, we evaluate excellent antibacterial effect induced by poly(quaternary ammonium) functionalized titanium dioxide nanoparticles without external excitations. The idea originates from the excellent antimicrobial property of quaternary ammonium salts. The effects of poly(quaternary ammonium) and polyacrylate sodium functional groups as nanoparticle surfactants are compared to show that poly(quaternary ammonium) functional groups are responsible for the induced antibacterial effect. 99.999% of E. coli can be destructed in 10 minutes by simply mixing bacteria with nanoparticle dispersions. Nanoparticle concentration has an impact on the antibacterial property and is evaluated. The engineered nanoparticles can find enormous applications such as self-cleaning surfaces, waste water treatment, Lab-on-a-Chip devices and many more.

Lysing E. Coli Using Titanium Dioxide Particles for Lab-on-a-Chip Applications

A novel method is proposed and demonstrated to be able to lyse E. Coli bacteria cells for Lab-on-a-Chip applications. The proposed method uses titanium dioxide particles as a photocatalyst and a miniaturized UV LED array as an excitation light source on the microchip level to perform cell lysis. The experimental result demonstrates the feasibility of the proposed novel device. The working device suggests an inexpensive, easy to be fabricated and effective way for microchip cell lysis. The miniaturized UV LED array and the microchip with a reaction chamber can be easily integrated with other functional components to form a customized whole Lab-on-a-Chip system.Copyright