Zhiwei Zou

State-of-the-art lab chip sensors for environmental water monitoring

As a result of increased water demand and water pollution, both surface water and groundwater quantity and quality are of major concern worldwide. In particular, the presence of nutrients and heavy metals in water is a serious threat to human health. The initial step for the effective management of surface waters and groundwater requires regular, continuous monitoring of water quality in terms of contaminant distribution and source identification. Because of this, there is a need for screening and monitoring measurements of these compounds at contaminated areas. However, traditional monitoring techniques are typically still based on laboratory analyses of representative field-collected samples; this necessitates considerable effort and expense, and the sample may change before analysis. Furthermore, currently available equipment is so large that it cannot usually be made portable. Alternatively, lab chip and electrochemical sensing-based portable monitoring systems appear well suited to complement standard analytical methods for a number of environmental monitoring applications. In addition, this type of portable system could save tremendous amounts of time, reagent, and sample if it is installed at contaminated sites such as Superfund sites (the USAs worst toxic waste sites) and Resource Conservation and Recovery Act (RCRA) facilities or in rivers and lakes. Accordingly, state-of-the-art monitoring equipment is necessary for accurate assessments of water quality. This article reviews details on our development of these lab-on-a-chip (LOC) sensors.

Highly sensitive rapid, reliable, and automatic cardiovascular disease diagnosis with nanoparticle fluorescence enhancer and mems.

Cardiovascular diseases (CVDs) have been the leading threat to human life. An effective way for sensitive and accurate CVD diagnosis is to measure the biochemical markers released from the damaged myocardial cells in the bloodstream. Here, a multi-analyte, fluorophore mediated, fiber-optic immuno-biosensing system is being developed to simultaneously and rapidly quantify four clinically important cardiac markers, myoglobin, C-reactive protein, cardiac troponin I, and B-type natriuretic peptide. To quantify these markers at a pico-molar level, novel nanoparticle reagents enhancing fluorescence were used and signal enhancement was obtained as high as approximately 230%. Micro-electro-mechanical system (MEMS) was integrated to this system to ensure a reliable and fully-automated sensing performance. A point-of-care, automatic microfluidic sensing system for four cardiac marker quantification was developed with the properties of 3 cm sensor size, 300 microL sample volume, 9-minute assay time, and an average signal-to-noise ratio of 35.

A Polymer Microfluidic Chip With Interdigitated Electrodes Arrays for Simultaneous Dielectrophoretic Manipulation and Impedimetric Detection of Microparticles

This paper presents the design, fabrication, and characterization of a polymer microfluidic biochip with integrated interdigitated electrodes arrays (IDAs) used to simultaneously separate, manipulate, and detect microparticles using dielectrophoresis (DEP) and electrochemical impedance spectroscopy (EIS) methods. The DEP response of silica microspheres has been characterized, and microspheres of different sizes (1.8 and 3.5 in diameter) have been DEP flow separated and individually trapped in different microchambers by IDAs in a single run. Simultaneously, the impedance change caused by microspheres captured on IDAs has been analyzed for quantification. High-throughput polymer microfabrication techniques such as micro injection molding were used in this work, so that the polymer microfluidic chip can be produced in a low-cost, disposable platform. This low-cost microfluidic chip provides a generic platform for developing multifunctional lab-on-a-chip devices that require the ability to handle and sense microparticles.

Potentiometric and voltammetric polymer lab chip sensors for determination of nitrate, pH and Cd(II) in water

Due to their toxicity to humans and animals, heavy metals and nitrate in groundwater are of particular concern. The combination of high toxicity and widespread occurrence has created a pressing need for effective monitoring and measurement of nitrate and heavy metals in soil pore water and groundwater at shallow depths. In this work, a new electrochemical sensing platform with the self-assembly nanobeads-packed (nBP) hetero columns has been developed for the pH and nitrate measurements. In addition, for on-site determination of cadmium (Cd(II)), a bismuth (Bi(III)) based polymer lab chip sensor using the square-wave anodic stripping voltammetry (SWASV) sensing principle has been designed, fabricated and successfully characterized. Factors affecting sensitivity and precision of the sensor, including deposition potential and deposition time, were studied. Miniaturized electrochemical lab chip sensors could be very valuable in environmental monitoring area due to their many benefits, such as greatly reduced sensing cost, sensing system portability, and ease of use.

An On-Site Heavy Metal Analyzer With Polymer Lab-on-a-Chips for Continuous Sampling and Monitoring

An on-site analyzer system for monitoring of heavy metals has been presented. This analyzer can automatically perform long-term continuous water sampling and on-site heavy metals measurement using an array of disposable polymer lab-on-a-chips (lab chip) and a continuous flow sensing method. The system consists of a plastic fluidic motherboard with a microchannels network, microvalves and pump, control circuits, a wireless communication module, a potentiostat, LabVIEW control, and seven disposable heavy metal lab chips. Square wave anodic stripping voltammetry was performed using a microfabricated planar bismuth electrode on the chip for detecting heavy metal (e.g., cadmium, Cd) concentrations. Sensing performance sensitivity was improved with by the continuous flow sensing method propelled by the analyzer. On-site measurement of the Cd concentration change of the soil pore and ground water samples from a lab-scale reactor was automatically performed to evaluate the performance of the analyzer with lab chips.

Electrical characterization of suspended gold nanowire bridges with functionalized self-assembled monolayers using a top-down fabrication method

In this paper, a very simple top-down fabrication method, which is compatible with standard silicon (Si) fabrication processes, is proposed to fabricate new suspended gold nanowire bridges with flexible designs. The electrical characteristics of the nanowire bridges which include the V–I curve, thermoresistive and impedance spectra change before and after nanowire bridges release and resistivity change with different design parameters are measured. The suspended nanowire bridge structures show the reduction of interference from the substrate and a large design flexibility to fit varying application desires. Furthermore, the nanowire bridge has shown a high potential for biomolecular detection by the mechanical, electrical or optical sensing mechanism through the formation of functionalized self-assembled monolayers (SAMs) on the bridge structure.

Development of a portable analyzer with polymer lab-on-a-chip (LOC) for continuous sampling and monitoring of Pb(II).

A new portable analyzer with polymer lab-on-a-chip (LOC) has been designed, fabricated and fully characterized for continuous sampling and monitoring of lead (Pb(II)) in this work. As the working electrodes of the sensor, bismuth (Bi (III)) which allowed the advantage of being more environmentally friendly than traditional mercury drop electrodes was used, while maintaining similar sensitivity and other desirable characteristics. The size of a portable analyzer was 30 cmx23 cmx7 cm, and the weight was around 3 kg. The small size gives the advantage of being portable for field use while not sacrificing portability for accuracy of measurement. Furthermore, the autonomous system developed in coordination with the development of new polymer LOC integrated with electrochemical sensors can provide an innovative way to monitor surface waters in an efficient, cost-effective and sustainable manner.

Automated Fluidic System with a Chaotic Microfluidic Reaction Chamber for Rapid, Multi-Analyte Immunosensing

In this paper, a fully automated fluidic system with a chaotic reaction chamber for rapid and accurate fiber-optic immuno-sensing has been developed and applied for the measurement of cardiac biomarkers. A new microchannel with serpentine bump structures has improved the sensor performance by generating local turbulence near the sensor surface. A full immunoassay with the automated fluidic system has been successfully performed, and the total assay time spent for detecting four cardiac markers was less than 10 minutes.

Simultaneous Dielectrophoretic Separation and Impedimetric Detection of Microbeads using Interdigitated Electrodes Array

This paper presents a polymer microfluidic biochip integrated with interdigitated electrodes arrays (IDAs), which is used for simultaneous separation, accumulation, and detection of microbeads using dielectrophoresis (DEP) and electrical impedance spectroscopy (EIS) methods. The DEP response of silica microspheres has been characterized, and microspheres with different sizes (1.8 mum and 3.5 mum) have been successfully separated and individually trapped in different microchambers with IDAs. Simultaneously, the impedance variation caused by captured microspheres at IDAs has been analyzed.