Ring Electrode Geometry for Microfluidic Electrochemistry.

We developed a ring electrode sensor for down-stream electrochemical sensing of microfluidic ELISA assay. The sensor is designed to easily integrate into the flow environment. Noble metal inks on Low Temperature Co-fired Ceramic provide straight forward fabrication at the mesoscale yielding robust sensors with very low sensing volumes. Two different sensor geometries were modeled. The best design was fabricated and tested in both static and flowing solutions. The sensor exhibits both macroelectrode and microelectrode behavior depending on fluid flow rate. Sensors of this type may be ideal for applications where electrochemical detection is desired in a flowing solution since the ring electrode has low propensity for bubble trapping.

Multiplexed and fully automated detection of metabolic biomarkers using microdialysis probe.

We report here, the design and development of an automated near real-time continuous detection system for lactate, glutamate, pyruvate and glucose using microdialysis probe. The system developed can automatically push perfusate through microdialysis probe (20, 100 and 1000 kDa MWCO cutoff probe) at low to medium flow rate of 0.5-2 µL/min with almost 100% fluid recovery. The microdialysate collected from the probe is analyzed automatically for these four metabolite biomarkers. It operates in a continuous mode with measurements of all four biomarkers once every 20 min. The dynamic range for these different markers covers the entire clinical range of traumatic brain injury. The prototype shows a low variation of ~ 7-10% across the entire clinical range for all the biomarkers with fairly good accuracy of ~95%. The instrument canrun continuously for 24 h without user intervention. With a long tubing of 1 m to and from the microdialysis probe and associated dead volume, the total lag time for actual event at the probe site versusreported concentration is roughly 1 h.

Capabilities of Next-Generation Patch Pump: Improved Precision, Instant Occlusion Detection, and Dual-Hormone Therapy.

Insulin pumps allow patients to attain better blood glucose control with more lifestyle flexibility. Their size and cost, however, limit their usefulness. Current CSII pumps are bulky, intrusive, and expensive. SFC Fluidics is addressing these problems by developing a new type of wearable patch pump based on the patented electro-chemiosmotic (ECO) microfluidic pumping technology. This nonmechanical pumping technology allows accurate and precise delivery of very small amounts of insulin and/or other drugs, including concentrated insulin. The pump engine is small and can be made inexpensively from injection molded parts, allowing its use in a disposable or semidisposable pod format. In addition, a single ECO pump engine can be used to deliver two drugs through independent pathways. Other features of SFC Fluidics' pod include latching safety valves that prevent accidental overdosing of insulin due to pressure changes and an instantaneous occlusion sensor that can immediately detect delivery failure at the first missed dose. These features allow for the development of a series of patch pumps that will offer users the benefit of CSII therapy in a more discreet and reliable patch pump form.

Evaluation of disposable microfluidic chip design for automated and fast Immunoassays.

We report here, the design and development of a disposable immunoassay chip for protein biomarker detection within ∼1 h. The unique design allows for real-time dynamic calibration of immunoassay for multiple biomarker detections on the chip. The limit of detection achieved for this test chip is 10 pg/ml for IL6, and 50 pg/ml for GFAP with a detection time of 1 h. The prototype instrument used for flowing the reagents through the chip can be easily assembled from off-the-shelf components with the final chemiluminescent detection carried out in a commercial plate reader. Optimization of different aspects of chip design, fabrication, and assay development is discussed in detail.

Development of Fully Automated Low-Cost Immunoassay System for Research Applications.

Enzyme-linked immunosorbent assay (ELISA) automation for routine operation in a small research environment would be very attractive. A portable fully automated low-cost immunoassay system was designed, developed, and evaluated with several protein analytes. It features disposable capillary columns as the reaction sites and uses real-time calibration for improved accuracy. It reduces the overall assay time to less than 75 min with the ability of easy adaptation of new testing targets. The running cost is extremely low due to the nature of automation, as well as reduced material requirements. Details about system configuration, components selection, disposable fabrication, system assembly, and operation are reported. The performance of the system was initially established with a rabbit immunoglobulin G (IgG) assay, and an example of assay adaptation with an interleukin 6 (IL6) assay is shown. This system is ideal for research use, but could work for broader testing applications with further optimization.

Electrical characterization of protein molecules by a solid-state nanopore.

The authors measured ionic current blockages caused by protein translocation through voltage-biased silicon nitride nanopores in ionic solution. By calculating the mean amplitude, time duration, and the integral of current blockages, they estimated the relative charge and size of protein molecules at a single molecule level. The authors measured the change in protein charge of bovine serum albumin (BSA) protein induced by pH variation. They also confirmed that BSA molecules indeed traverse nanopores using an improved chemiluminescent analysis. They demonstrated that a larger protein fibrinogen could be distinguished from BSA by a solid-state nanopore measurement.

Detecting single stranded DNA with a solid state nanopore.

Voltage biased solid-state nanopores are used to detect and characterize individual single stranded DNA molecules of fixed micrometer length by operating a nanopore detector at pH values greater than approximately 11.6. The distribution of observed molecular event durations and blockade currents shows that a significant fraction of the events obey a rule of constant event charge deficit (ecd) indicating that they correspond to molecules translocating through the nanopore in a distribution of folded and unfolded configurations. A surprisingly large component is unfolded. The result is an important milestone in developing solid-state nanopores for single molecule sequencing applications.