A low temperature bonding of quartz microfluidic chip for serum lipoproteins analysis

Microfluidic Immunoassay System for Rapid Detection and Semi-Quantitative Determination of a Potential Serum Biomarker Mesothelin

Mesothelin (MSLN) is considered as a potential serological tumor biomarker for early diagnosis of pancreatic cancer. Nevertheless, low sensibility, high reagent consumption, and time costs of traditional detection methods limit their utility in clinical disease diagnoses. Here, we combined the immunoassay technique with microfluidic chips to develop a microfluidic immunoassay system (MIAS) that can be used for rapid semi-quantitative detection of serum MSLN levels. The MIAS was composed of 12 uniform structures, including 12 inlets, 12 reaction chambers, and one outlet allowing measurement of four samples with three repeats, simultaneously. A unique microarray cylinder was located at the end of each reaction chamber where immunoassay was performed to trap microspheres. A feasible interception efficiency (∼80%) was attained, with microspheres filling the reaction column. It has been demonstrated that fluorescence intensity is proportional to the MSLN concentration on the MIAS (R² = 0.95). Subsequently, 16 clinical serum samples collected from Changhai Hospital, Shanghai were selected from eight patients with pancreatic cancers, four with pancreatitis, and four with other digestive system diseases (2 gastric cancer, 1 bile duct stricture, and 1 bile duct stones). MSLN levels for these samples were detected via MIAS. The results showed a significant correlation between MIAS and traditional enzyme-linked immunosorbent assay (ELISA), with the correlation coefficient, 0.93. The detection limit of MSLN fluorescence intensity and concentration was ∼6 a.u. and ∼20 pg/mL, respectively. The entire duration of analysis by MIAS decreased to ∼40 min compared to 2 h by ELISA. Statistical analysis of MIAS data revealed that MSLN was overexpressed in pancreatic cancer than in the others (P value = 0.0014). Moreover, the diagnostic accuracies of MSLN detected by MIAS and CA19-9 detected by ELISA in hospitals were 87.5 and 81.3%, respectively. MSLN is helpful for the early diagnosis of pancreatic cancer and other diseases, and it had a significant ability to discriminate between pancreatic and nonpancreatic cancers (P value = 0.0159). The results from this study show that MIAS has the potential to become a new serological tumor marker detection platform for rapid detection and semi-quantitative determination of MSLN and would have broad applications in early clinical diagnosis.

Surface patterning of bonded microfluidic channels

Microfluidic channels in which multiple chemical and biological processes can be integrated into a single chip have provided a suitable platform for high throughput screening, chemical synthesis, detection, and alike. These microchips generally exhibit a homogeneous surface chemistry, which limits their functionality. Localized surface modification of microchannels can be challenging due to the nonplanar geometries involved. However, chip bonding remains the main hurdle, with many methods involving thermal or plasma treatment that, in most cases, neutralizes the desired chemical functionality. Postbonding modification of microchannels is subject to many limitations, some of which have been recently overcome. Novel techniques include solution-based modification using laminar or capillary flow, while conventional techniques such as photolithography remain popular. Nonetheless, new methods, including localized microplasma treatment, are emerging as effective postbonding alternatives. This Review focuses on postbonding methods for surface patterning of microchannels.

Room temperature UV adhesive bonding of CE devices

A simple low temperature adhesive 'stamp-and-stick' bonding procedure for lab-on-a-chip glass devices has been tested for capillary electrophoresis applications. This technique involves use of a mask aligner to transfer a UV-curable adhesive selectively onto the top CE substrate which is then aligned with and bonded to the bottom CE wafer. The entire bonding process can be carried out at room temperature in less than 30 minutes, involved only user-friendly laboratory operations, and provided a near 100% success rate. CE microchips made in this manner exhibited similar electroosmotic flow and separation characteristics as ones made via conventional high temperature thermal bonding. Equally important, the devices provided stable long-term performance over weeks of use, encompassing hundreds of individual CE runs without structural failure or any apparent change in operating characteristics. Finally, these devices exhibited excellent chip-to-chip reproducibility. Successful adaptation of the stamp-and-stick approach did require the development and testing of new but easily implemented structural features which were incorporated into the chip design and whose nature is described in detail.

Microchip-based capillary electrophoresis for determination of lactate dehydrogenase isoenzymes

This article describes a novel microchip-based capillary electrophoresis and oncolumn enzymatic reaction analysis protocol for lactate dehydrogenase (LDH) isoenzymes with a home-made xenon lamp-induced fluorescence detection system. A microchip integrated with a temperature-control unit is designed and fabricated for low-temperature electrophoretic separation of LDH isoenzymes, optimal enzyme reaction temperature control, and product detection. A four-step operation and temperature control are employed for the determination of LDH activity by on-chip monitoring of the amount of incubation product of NADH during the fixed incubation period and at a fixed temperature. Experiments on the determination of LDH standard sample and serum LDH isoenzymes from a healthy adult donor are carried out. The results are comparable with those obtained by conventional CE. Shorter analysis times and a more stable and lower background baseline can be achieved. The efficient separation of different LDH forms indicates the potential of microfluidic devices for isoenzyme assay.

Numerical analysis of an electrokinetic double-focusing injection technique for microchip CE

The injection techniques in electrophoresis microchips play an important role in the sample-handling process, whose characteristics determine the separation performance achieved, and the shape of a sample plug delivered into the separation channel has a great impact on the high-quality separation performance as well. This paper describes a numerical investigation of different electrokinetic injection techniques to deliver a sample plug within electrophoresis microchips. A novel double-focusing injection system is designed and fabricated, which involves four accessory arm channels in which symmetrical focusing potentials are loaded to form a unique parallel electric field distribution in the intersection of injection channel and separation channel. The parallel electric field effectuates virtual walls to confine the spreading of a sample plug at the intersection and prevents sample leakage into separation channel during the dispensing step. The key features of this technique over other injection techniques are the abilities to generate regular and nondistorted shape of sample plugs and deliver the variable-volume sample plugs by electrokinetic focusing. The detection peak in the proposed injection system is uniform regardless of the position of the detection probe in the separation channel, and the peak resolution is greatly enhanced. Finally, the double-focusing injection technique shows the flexibility in detection position and ensures improved signal sensitivity with good peak resolution due to the delivered high-quality sample plug.