Electrochemistry-based sensors offer sensitivity, selectivity and low cost for the detection of selected DNA sequences or mutated genes associated with human disease. DNA-based electrochemical sensors exploit a range of different chemistries, but all take advantage of nanoscale interactions between the target in solution, the recognition layer and a solid electrode surface. Numerous approaches to electrochemical detection have been developed, including direct electrochemistry of DNA, electrochemistry at polymer-modified electrodes, electrochemistry of DNA-specific redox reporters, electrochemical amplifications with nanoparticles, and electrochemical devices based on DNA-mediated charge transport chemistry.

/pdf/electrochemical-dna-sensors-4ft4krws65.pdf

Electrochemical DNA sensors

http://cau.ac.kr/~jjang14/BioMEMS/Lazcka_BSBE_Pathogen_Detection_Review_2006.pdf

Pathogen detection: a perspective of traditional methods and biosensors.

The suitability of electrowetting-on-dielectric (EWD) microfluidics for true lab-on-a-chip applications is discussed. The wide diversity in biomedical applications can be parsed into manageable components and assembled into architecture that requires the advantages of being programmable, reconfigurable, and reusable. This capability opens the possibility of handling all of the protocols that a given laboratory application or a class of applications would require. And, it provides a path toward realizing the true lab-on-a-chip. However, this capability can only be realized with a complete set of elemental fluidic components that support all of the required fluidic operations. Architectural choices are described along with the realization of various biomedical fluidic functions implemented in on-chip electrowetting operations. The current status of this EWD toolkit is discussed. However, the question remains: which applications can be performed on a digital microfluidic platform? And, are there other advantages offered by electrowetting technology, such as the programming of different fluidic functions on a common platform (reconfigurability)? To understand the opportunities and limitations of EWD microfluidics, this paper looks at the development of lab-on-chip applications in a hierarchical approach. Diverse applications in biotechnology, for example, will serve as the basis for the requirements for electrowetting devices. These applications drive a set of biomedical fluidic functions required to perform an application, such as cell lysing, molecular separation, or analysis. In turn, each fluidic function encompasses a set of elemental operations, such as transport, mixing, or dispensing. These elemental operations are performed on an elemental set of components, such as electrode arrays, separation columns, or reservoirs. Examples of the incorporation of these principles in complex biomedical applications are described.

/pdf/digital-microfluidics-is-a-true-lab-on-a-chip-possible-2w1y39xegp.pdf

Digital microfluidics: is a true lab-on-a-chip possible?

This Review summarizes methods for constructing systems and structures at micron or submicron scales that have applications in microbiology. These tools make it possible to manipulate individual cells and their immediate extracellular environments and have the capability to transform the study of microbial physiology and behaviour. Because of their simplicity, low cost and use in microfabrication, we focus on the application of soft lithographic techniques to the study of microorganisms, and describe several key areas in microbiology in which the development of new microfabricated materials and tools can have a crucial role.

/pdf/microfabrication-meets-microbiology-3fk5svoxk6.pdf

Microfabrication meets microbiology

PCR microfluidic devices for DNA amplification

Nucleic acid purification using microfabricated silicon structures

A miniaturized, fully automated, PCR-based detection system has been developed for the rapid detection of bacterial pathogens. Monolithic DNA purification/real-time PCR silicon chips were fabricated and tested for their ability to purify and detect the pathogeneic bacterium Listeria monocytogenes. Using silica-coated microstructures, nucleic acids could be selectively bound, washed and eluted for subsequent real-time PCR. These microstructures were included in an integrated detection microchip containing two distinct regions, one for DNA purification and one for real-time PCR. Using an automated detection platform with integrated microprocessor, pumps, valves, thermocycler and fluorescence detection modules, microchips were used to purify and detect bacterial DNA by real-time PCR amplification using SYBR Green fluorescent dye. Between 104 and 107 L. monocytogenes cells could be detected using this system with an average turnaround time of 45 min.

Real-time PCR detection of Listeria monocytogenes using an integrated microfluidics platform

A microfabricated flow cytometer has been developed that is capable of detecting nearly all of the microparticles in an aqueous suspension. Current design allows for integrated coupling between an optical fiber-based detection system and the particle stream via hydrodynamic focusing. By adjusting the relative flow-rates at the auxiliary inputs of the focusing manifold, the particle stream can be steered out-of-plane relative to the illuminating laser, and similarly the particle stream can be squeezed or expanded. The microfabricated device was constructed in polydimethylsiloxane with cross-sectional microfluidic dimensions of 125 µm × 125 µm. Using the present device and method, fluorescent microparticles in aqueous solution were counted at an absolute counting efficiency of 91 ± 4%. The coefficient of variation of the fluorescence pulse-heights for far-red fluorescent microparticles was 15%. The device exhibited a linear response to fluorescence intensity calibration microparticles as shown by comparison with a commercial cytometer instrument.

/pdf/hydrodynamic-optical-alignment-for-microflow-cytometry-3slti58wme.pdf

Hydrodynamic optical alignment for microflow cytometry

Low-power electrolysis-based microfluidic pumps utilizing the principle of hydraulics, integrated with microfluidic channels in polydimethylsiloxane (PDMS) substrates, are presented. The electro-hydraulic pumps (EHPs), consisting of electrolytic, hydraulic and fluidic chambers, were investigated using two types of electrodes: stainless steel for larger volumes and annealed gold electrodes for smaller-scale devices. Using a hydraulic fluid chamber and a thin flexible PDMS membrane, this novel prototype successfully separates the reagent fluid from the electrolytic fluid, which is particularly important for biological and chemical applications. The hydraulic advantage of the EHP device arises from the precise control of flow rate by changing the electrolytic pressure generated, independent of the volume of the reagent chamber, mimicking the function of a hydraulic press. Since the reservoirs are pre-filled with reagents and sealed prior to testing, external fluid coupling is minimized. The stainless steel electrode EHPs were manufactured with varying chamber volume ratios (1 : 1 to 1 : 3) as a proof-of-concept, and exhibited flow rates of 1.25 to 30 µl/min with electrolysis-based actuation at 2.5 to 10 VDC. The miniaturized gold electrode EHPs were manufactured with 3 mm diameters and 1 : 1 chamber volume ratios, and produced flow rates of 1.24 to 7.00 µl/min at 2.5 to 10 VAC, with a higher maximum sustained pressure of 343 KPa, suggesting greater device robustness using methods compatible with microfabrication. The proposed technology is low-cost, low-power and disposable, with a high level of reproducibility, allowing for ease of fabrication and integration into existing microfluidic lab-on-a-chip and analysis systems.

Low-power microfluidic electro-hydraulic pump (EHP)

A portable, fully-automated, microchip including a DNA purification region fluidly integrated with a PCR-based detection region is used to detect specific DNA sequences for the rapid detection of bacterial pathogens. Using an automated detection system with integrated microprocessor, pumps, valves, thermocycler and fluorescence detection modules, the microchip is able to purify and detect bacterial DNA by real-time PCR amplification using fluorescent dye. The fully automated detection system is completely portable, making the system ideal for the detection of bacterial pathogens in the field or other point-of-care environments.

Scott J. Stelick

Papers

Nucleic acid purification using microfabricated silicon structures

Real-time PCR detection of Listeria monocytogenes using an integrated microfluidics platform

Hydrodynamic optical alignment for microflow cytometry

Low-power microfluidic electro-hydraulic pump (EHP)

Real-Time Pcr Detection of Microorganisms Using an Integrated Microfluidics Platform